Christine Petr

FREE ADMISSION TO MUSEUMS AND MONUMENTS: AN EXPLORATION OF SOME PERCEPTIONS OF THE AUDIENCES. Final draft, to be published in International Journal

This paper considers the theme of the audiences' perceptions of free admission in national French museums and monuments. The results show that, from an individual perspective, perceptions of free admission are linked to perceptions of price, of money and of payment, hence complementing perceptions expressed in a collective perspective (a symbolic, political measure, causing either adhesion or rejection). These perspectives are generally put forward by both advocates and opponents of the measure in their discussions. This different vision of free admission has managerial implications for managers of museums and monuments.

FREE ADMISSION TO MUSEUMS AND MONUMENTS: AN EXPLORATION OF SOME PERCEPTIONS OF THE AUDIENCES.

The concept of exemption from payment is not restricted to museums and monuments, and has in fact been a key issue in discussions between philosophers (notably quarrels opposing Socrates and the Sophists on the value of the reflections of philosophers), and in novels (the gratuitous murders in Les caves du Vatican by Gide, or Othello by Shakespeare). The transport sector (urban transport systems in several French towns such as Compiègne, Issoudun and Châteauroux), the general public press sector (METRO, 20 minutes, SPORT), the scientific press (PLoS Biology and PLoS Medicine), computer systems and the software sector (Linux, GNU's, Openoffice, Mozilla), the music sector (peer-to-peer exchange of musical files) today all face non financial exchanges. A founding principle of museums and monuments, free admission belongs to their original ideology. It constitutes the symbol of democracy and the collective ownership of culture, as well as portraying those places as public centres of education. When museums and monuments progressively started to appeal to the market in the 1980s, free admission became the issue of passionate recurrent discussions. As stated by [START_REF] Gombault | Current practices in free admission to museums: an international perspective[END_REF], little by little, it gave way to various fee schemes which included targeted measures of reduction and exoneration, then progressively, in the past ten years, according to institutions, to true pricing strategies. Today, in an almost consensual market oriented patrimonial world, the issue of free admission is in the news again. The movement which began in the United Kingdom is spreading to all of Europe. In France, its installation has evolved in several stages: in 1996, at the Minister of Culture's instigation, the Louvre's entrance fee was waived on the first Sunday of each month during a two year experimental period. Considered as a success, in 1998, the measure was established on a permanent basis. In 2000, the measure was extended to all national museums and monuments. Numerous towns adopted the measure in municipal museums, especially Paris in 2002. However, even if advocates of free admission welcome this move because of its conformity to the original ideology of a collective heritage, justifying the scheme's success on increased attendance figures, quantitative studies demonstrate that it is a kind of short-term "honeymoon effect" and that in the middle or long term, free admission has no effect on attendance (Bailey et al., 1997b[START_REF] Bailey | Charging for admission to museums and galleries: a framework for analysing the impact on access[END_REF][START_REF] Dickenson | The economics of museum admission charges[END_REF][START_REF] Hare | Why do people go to museums? The effect of prices and hours on museum utilization[END_REF][START_REF] O'hagan | National museums: to charge or not to charge ?[END_REF]. Furthermore, there is another question which those studies do not answer and that, paradoxically, cultural managers rarely deal with as they take the answer for granted: "what does the audience think of free admission? Is this ideal of culture also supported by the audience?" as Claude Fourteau, in charge of public relations in the Louvre museum at the time of the introduction of free admission, and a pioneer of this reflection, would ask evoking the Louvre and especially free Sundays. Faced by the absence of theoretical research and the scarcity of institutional studies on the subject of perceptions of free admission by the audiences, the Département des Etudes, de la Prospective et des Statistiques (DEPS) of the French Ministère de la Culture et de la Communication financed research into this field of enquiry: in the French context, what perceptions of free admission to museums and monuments do the audiences have and how are these perceptions1 linked with individual's perceptions, their organised visit and patterns of behaviour in museums and monuments?

Results of the study have been published [START_REF] Gombault | La gratuité des musées et des monuments côté publics Représentations, projets d'usage et comportements des publics[END_REF]. The results of this exploratory study have been formulated as three metapropositions and twenty-seven propositions that can be considered as hypothesis. These are related to free entrance perceptions, and the effects of free entrance on behaviour and on the experience of the visit.

In this paper, we have chosen to investigate more thoroughly only a part of the results, those focusing on the perceptions the free admission visitors have from an individual perspective, i.e. those related to the perceptions of free entrance as a price. The first part of the paper presents the framework of the research : the scarcity of literature on the perceptions of exemption from payment in general, and, more specifically, of free admission in museums and monuments, has led us to adopt a multiangulation exploratory methodology. The second part shows some of the results of this research: the audiences' perception of free admission when considered from an individual perspective.

AN EXPLORATION OF THE PERCEPTIONS OF MUSEUM AND MONUMENT

AUDIENCES.

A lack of research on the perceptions of exemption from payment

The consumer research literature on the issue of exemption from payment is very scarce.

Despite extensive research on promotional tools, research on free trial offer [START_REF] Scott | The effects of trial and incentives on repeat purchase behavior[END_REF] or free gift [START_REF] Raghubir | Free gift with purchase: promoting or discounting the brand ?[END_REF]) used as a promotional tool is rare compared to research based on coupons or price discounts [START_REF] Chandon | A benefit congruency framework of sales promotion effectiveness[END_REF]. Some recent research on non-price promotions show that these tools have different effects on sales from monetary ones and it concludes that these promotional tools could have a more long term impact on sales, and could also serve as a loyalty development tool. Promotions offering two for the price of one products have a positive effect on the offer perceived value, whereas price reductions (Diamond, 2002 ;[START_REF] Smith | The impact of price and extra product promotions on store preference[END_REF] or EDLP strategies [START_REF] Darke | Effects of pricing and promotion on consumer perceptions : it depends on how you frame it[END_REF]) have a negative one. It has also a positive effect on brand knowledge [START_REF] Palazon-Vidal | Sales promotions effects on consumer-based brand equity[END_REF] and on preferences [START_REF] Liao | The effects of nonmonetary sales promotions on consumer preferences: the contingent role of product category[END_REF]. However, these works did not take into account how these promotional tools are perceived by customers. In social marketing [START_REF] Kotler | Social Marketing : Strategies for Changing Public Behavior[END_REF][START_REF] Andreasen | Social Marketing in the 21th century[END_REF], free price has already been a subject of research, especially non-monetary components of free price (see for example, [START_REF] Fox | Time as a component of price in social marketing[END_REF]. But, in the field of services, little research has been developed on that subject [START_REF] Gorn | The impact of free and exaggerated prices on perceived quality of services[END_REF], and finally the issue of permanent free offer seems to have been neglected in marketing. However, in a committed essay entitled Pour la gratuité, Jean-Louis Sagot-Duvauroux (1995) evokes interesting albeit non-scientific elements concerning individual and collective perceptions of exemption from payment. He makes a list of the most significant objections made to exemption from payment ("it is costly", "it devalues"…) and shows how those typically fit in the referential framework of the market trade value characterising our society. In the context of museums and monuments, a review of the literature on free admission results almost exclusively in studies on planned visits and patterns of behaviours. The impact of free admission on attendance constitutes the focal, obstinately recurrent theme of the literature. Multiple studies are contradictory: free admission can have a positive impact on attendance [START_REF] Spalding | The great debate: museum charges[END_REF], no impact or even a negative one (O 'Hare, 1975;[START_REF] O'hagan | National museums: to charge or not to charge ?[END_REF]. Some authors prefer to express uncertainty in this regard [START_REF] Bailey | Charging for admission to museums and galleries: a framework for analysing the impact on access[END_REF] or establish that changes in fees have generally only a short-term impact [START_REF] Dickenson | The economics of museum admission charges[END_REF][START_REF] Bagdali | Il museo come azienda. Management e organizzazione al servizio della cultura[END_REF]. The perceptions that the audience has of free admission seem excluded from those studies.

In a study made in the Louvre museum, [START_REF] Gottesdiener | Les dimanches gratuits du musée du Louvre. enquête qualitative[END_REF] shows that paying may be a barrier to entry, but that entry is never entirely free as non-monetary costs remained (the crowds, the noise, other visitors' behaviour preventing the calm atmosphere judged necessary for the visit, and the lack of fluidity in the circulation). They also conclude that perceptions of free entry are diverse and complex: some interviewees are favourable because it reduces financial, social, cultural barriers; some are defavourable because they think that it creates annoyances and less commited behaviours. These very interesting results, the only ones on perceptions of free entry in museums, produced in a very specific context, should be deepened in other venues.

Yet some papers on pricing can be used to try to shed light on our field of enquiry.

First of all, in museums and monuments, the "true" price, from the visitor's point of view, does not merely consist of the amount of money that he/she must pay to enter (Mc Lean, 1997), but contains other financial elements (spending associated to the visit) and non-financial elements (time, length or difficulty of the journey, possible disappointment, incomprehension or disapproval from others, and other psychological and sociological barriers) [START_REF] Fines | The Marketing of Ideas and Social Issues[END_REF]. In other words, the perceived price does not result from the confrontation of the sole financial sacrifices to the associated benefits gained from the visit and from places [START_REF] Zeithaml | Consumers perceptions of price quality and value: a means-end model and synthesis of evidence[END_REF]. It also takes into account associated non-financial sacrifices. Therefore, when entry is free of charge, some costs remain, even if the measure has a liberating effect, as the visitor no longer feels obliged to make his visit profitable by staying in the museum or monument for a long time [START_REF] Book | The Audience for the Performing Arts[END_REF]Hendon, Shanahan, and MacDonald, 1980). Otherwise, it has been shown that the associated costs of cultural visits would, in most cases, double the ticket price, because free admission fosters peripheral consumption [START_REF] Gombault | Current practices in free admission to museums: an international perspective[END_REF].

Another field of research considers the role of price on visit intentions. It appears that the first impediment to the visit is not price, but cultural distance. "The price or fee does not hamper museum attendance. Demand comes first from a minority of people over-equipped in human capital. That means that the key question is above everything else the education that one has received" [START_REF] Gottesdiener | Freins et motivations à la visite des musées d'art[END_REF]. The price is taken into account in the visit decision only when the potential visitor is interested in this visit beforehand [START_REF] Walshe | Pricing in the Arts[END_REF][START_REF] Blamires | What price entertainment ?[END_REF][START_REF] Kotler | Museum Strategy and Marketing[END_REF]Bailey et al., 1997aBailey et al., , 1997b)).

As for exemption from payment in general, no significant research exists on the perceptions of free admission in museums or monuments by the visiting public. Only a few institutional studies are available, sometimes made by researchers [START_REF] Gottesdiener | Les dimanches gratuits du musée du Louvre. enquête qualitative[END_REF][START_REF] Ducros | Pour un marketing de l'altruisme : une application aux musées d'art contemporain[END_REF]. This theoretical quasi-vacancy on the subject of perceptions of free admission by the audiences is highly significant: debates on free admission, so important in the "world" of museums and monuments, relies on hypotheses of institutional actors on the audiences' perceptions.

A multiangulation research strategy

The aim of the research is to describe and understand perceptions that the general publicvisitors and non-visitors -have of free admission to museums and monuments, and to tackle their relations with perceptions of museums and monuments, planned visits and patterns of behaviour. The expected contribution of the study was to generate a theory or theoretical knowledge from empirical data by inductive reiterated reasoning. To serve this exploratory goal, the research has used a strategy of multiangulation of the data production and the data analysis, warranting validity and reliability of the albeit limited results.

Multiangulation consists in comparing empirical data and multiple theoretical streams to produce knowledge [START_REF] Weick | Theory construction as disciplined imagination[END_REF][START_REF] Lewis | Metatriangulation: building theory from multiple paradigms[END_REF][START_REF] Gombault | Crossing frontiers in quantitative and qualitative research methods[END_REF]. As a methodology, it could be defined as the consistent use of multiple tactics or methods to produce knowledge. Multiangulation of data, data collection, analysis techniques, respondent convergence, researchers, theories, and paradigms are the tactics frequently used. However, in order to make sense and to be defined as a research strategy and not only as a simple confirmation tool, multiangulation must be applied in a coherent manner. In this research, all multiangulation tactics were implemented (except respondent convergence) in order to match the research question, as presented in the table below.

< Insert Table 1 >

The main data collection technique has been individual interviews, and, in order to deepen the results of the main collection mode, other data collection techniques (focus groups, observations and visit interviews, survey) have had only a secondary role. Focus groups results are very similar to those of individual interviews, collecting further information on publics' profiles. Observation enables the gathering of information on free entrance perceptions and effects in real settings, and surveys permit the collection of additional information on museums and monuments perceptions, on free entrance perceptions related to visitor profiles (see the interviewees' profiles and the main results of the survey in table 2).

< Insert table 2 >

Verbatims from the interviews were retranscribed and analyzed by thematic content analysis.

From these interviews' analysis, a dictionary of empirical themes was defined. With themes and sub-themes, it recreates the analysis the researchers had of public perceptions and interpretations of free entrance to museums and monuments. Then, an analysis by theoretical inference (induction and iteration) was made from this dictionary of empirical themes. This led to the discovery of theoretical themes that we listed in a dictionary of theoretical themes.

It produced an inventory of concepts and theories that may contribute to the interpretation and comprehension of empirical themes. It is organised as a tree diagram, allowing the reader to return to the original empirical theme from which it was inferred. The main structure of the dictionary of theoretical themes comes from individual in-depth interviews and has been completed with the theoretical analysis of the three complementary phases of the research : themes have been reinforced, invalidated, and adjusted, and additional ones have appeared.

This final dictionary of theoretical themes represents the theoretical framework of the whole research and allows the formulation of 27 theoretical propositions. These have been reconsidered, discussed and reduced to three metapropositions that can be considered as hypothesis. Following the " analytical generalisation " [START_REF] Yin | Case study research : design and methods[END_REF] or " generative modelization " [START_REF] Gergen | Realities and relationships. Soundings in social construction[END_REF], results have been extended, not to populations or others fields, but to theoretical propositions.

PERCEPTIONS OF FREE ADMISSION TO MUSEUMS AND MONUMENTS FROM AN INDIVIDUAL PERSPECTIVE Exemption from payment: a price

Free admission is at first considered by interviewees as a price strategy and results in the visitor making calculations, relying on internal or external reference prices to assess visit value. The importance of other monetary costs, and, moreover, of non-monetary costs of the visit are underlined.

The price of the visit: a global price. Although people say that they do not take price into account, during interviews, they often talk about this. Likewise, even if they say they do not calculate, they often compare and use reference prices. Admission price is notably related to the number of people taking part in the visit. Reference is then frequently made to family budgets ("Numerous families would go much more often. For instance, even if that (admission price) does not cost more than 3 or 4 euros, if there is a family of five…" extract from a focus group of regular visitors).

Price is also linked to the intensity of the practice, to the visitor involvement in the practice, to the experienced pleasure and to the time that one can spare to visit. Admission price is also compared to the price of other leisure activities (cinema, theatre, sports, dining in restaurants, meetings with friends). Admission cost is then very diversely assessed according to individuals and according to chosen references. Admission price is also compared to the budget that one can or wants to spare for cultural or other leisure activities ("This is a question of resources. Some prefer to buy a bottle of Coca-cola rather than to buy an entry to a museum," extract from a visit interview).

These empirical results lead to the following conclusion: perceptions of free admission in museums and monuments by the audience are linked to perceptions of the price of the visit.

The price of the museum or monument visit, as perceived by the visitor, is of the same kind as traditional market perceptions of price exposed in marketing literature [START_REF] Murphy | Classifying products strategically[END_REF][START_REF] Zeithaml | Consumers perceptions of price quality and value: a means-end model and synthesis of evidence[END_REF]. Evocations of free admission, associated to the price of the visit, cause the audience to make calculations, to rely on internal or external reference prices to assess visit value (Biswas, Wilson, and Licata, 1991). They use external reference prices (displayed local price, other museum and monument prices, other leisure activity prices, notably cinema ticket prices) and internal reference prices (remembered prices, prices considered as "fair") to judge free admission or the high cost of the admission price.

Monetary costs and non-monetary costs associated to the visit. Answering the following question-"When you are planning a visit to a museum or a monument, what expenditures do you consider?"-74.14% of the interviewees stated that they consider the admission fee; 37.41% of the interviewees the transport costs (petrol, motorway tolls, train tickets… -22% for respondents living in Paris, 40.6% for people living in others regions either in a town or in a rural area -Chi2=12.261, dof=2, signif.=0.002); 21.55% the hotel cost (14% for respondents living in Paris, 24.3% for people living in another town and 21.6% for people living in a rural area -Chi2=4.584, dof=2, signif.=0.101); 9.48% the meal or coffee costs; 5.69% the post cards and gadgets costs; 13.1% declare not to know. 1.21% call upon other costs (catalogue, exhibition, guided visit), and 0.69% declare not to consider costs. The costs mentioned do not change with different attendance profiles. Consequently, linked to admission price, are the above mentioned costs of transport, hotels when needed, and subsidiary costs such as refreshments, the purchase of post cards… These results could differ according to the museum or the monument considered.

Financing the costs of museums and monuments and their free admission is also a theme which is often present in these interviews. Those costs are seen as monetary indirect costs linked to free visit: visitors consider that they do not pay at the time of the visit but that they pay indirectly, notably by taxes. This perception of a global price for the visit is interpreted by some audiences as if free admission does not exist ("The free visit does not exist", extract from an individual interview). In the survey, 58% of interviewees agree with the statement that "freeness does not exist" 2 .

Psychological and physical barriers related to paying, crowds, an oppressive atmosphere in the museum or monument, fatigue generated by the visit, organisational and time constraints, 2 Only 51% of the regular visitors agree, 54.5% of the occasional visitors but 61.1% of the non-visitors -Chi2=20.695, dof=10, signif.=0.023. This statement is not related to the region of living. and difficulty accessing information, are, like many non-monetary costs associated with museums and monuments visits, expressed in the interviews. The perception of those costs is perhaps heightened in the context of free admission because of the annoyances it is considered to create (too many people, degrading conditions of visit, the requirement to queue or to organise visit times when free admission is periodical). This perception can also be put forward in so far as free admission suppresses the admission fee and its absence then underlines other costs, notably non-monetary ones, ("There are too many people, this is unbearable. You see nothing, you are jammed, you are elbow-to-elbow. It would be better to buy a beautiful book of art," extract from an individual interview). Lastly, the perception of non-monetary costs may be attenuated when free admission is considered as a means to shorten the duration of the visit, to create a pleasant environment, or, furthermore, to minimise perceived risk or disappointment.

Interviewees who have experienced free admission visits declare that the experience is pleasant. Despite the fact that before the visit non-monetary costs are more apparent, during and after the visit, satisfaction regarding the free admission measure is effective. Moreover, interviewees in the qualitative studies declare that free admission allows them to "try out" museums and monuments. It allows an apprenticeship, and they will come back either on a free admission day (non-monetary costs are less salient for people who have experienced free admission) or on a paying day. Of the people that have experienced free admission (80% of the respondents in the quantitative survey 3 ), 67% declare that they are ready to come back on a free admission day in the future. But when visitors have not experienced free admission, they are only 52% to envisage a visiting project.

Thus, in the context of museums and monuments, empirical results show the importance of the non-monetary aspects of price (qualified by Mc Lean (1997) as "non-monetary price"), and already underlined by [START_REF] Bailey | Charging for admission to museums and galleries: a framework for analysing the impact on access[END_REF] and [START_REF] Fines | The Marketing of Ideas and Social Issues[END_REF]. Lastly, empirical results confirm conclusions made by [START_REF] Prottas | The cost of free services: organization impediments of access to public services[END_REF], who shows that non-monetary components of price are more important when service is free. This supports the idea that for many price is not the overriding factor: by suppressing certain monetary costs free admission brings other costs to the fore, and the decision to visit weighs heavily on these costs.

Free admission is associated with payment

For audiences, free admission is associated with the action of paying or not paying for admission. This action structures the exchange relationship [START_REF] Crump | Money as a ritual system[END_REF]. Perceptions of free admission refer to perceptions of money. It abolishes the admission visa provided by the act of paying, but also the distance established by the payment. Free admission has a negative effect on the commitment of the attendant in the visit and could have either a negative or positive effect or even no effect at all on the visit value.

Payment: an admission "visa" in museums and monuments. Paying to enter museums and monuments is associated with power: being able to spare financial means that allow entering places (being able to save for this activity), being independent (not feeling like a debtor), being able to acquire culture ("To pay or not to pay, this is to have the power or not to have it," extract from an individual interview). Those perceptions refer to the significance of money such as power (influence, control, domination, superiority) and freedom (having control over one's destiny, not being dependent upon others).

Payment appears also in the interviews as a financial, socio-cultural, motivational way of selecting visitors. Free admission is then described as a means to raise a psychological and social barrier. In the survey, 71.4% of interviewees stated that free entry allows them to visit when they have the desire to do it. It is supposed to encourage the practice by the members of the public that do not normally visit museums and monuments. Indeed, one can think that paying to acquire cultural goods is like a socialisation process: people learn to attend museums and monuments and to pay for that. "Cultural capital" and competence developed by the "regular visitor" give sense to payment [START_REF] Bourdieu | La distinction: critique sociale du jugement[END_REF]. With free admission, a social barrier is raised for those who have not learned though the experience of visiting museums and monuments.

Lastly, for some visitors, paying gives the right to use the place but may also give visitors a feeling of empowerment. (" It is true that people who pay go everywhere. That really struck me in Versailles; there are some places where we are requested not to go, a large number of people pass without permission in the restricted areas, they feel that because they have paid, they deserve this for their money," extract from an individual interview). Payment represents the visitor's contribution to the upkeep of the heritage, it is an individual contribution but also a symbolic manifestation of a collective protecting action of safeguarding the heritage. In the survey, 99.5% of the interviewees agree with the proposition that museums and monuments represent a heritage that must be maintained 4 . Moreover it's the main perception for 49.4% 5 . This is correlated (0.200) to the perception that a symbolic entrance fee should be paid.

86.3% of the respondents agree with that proposition and it's the main perception for 67% 6 .

Those perceptions fit in the paradigm of social exchange [START_REF] Homans | Social Behavior, its Elementary Forms[END_REF]. By paying, visitors make a contribution in order to receive what they expect is a fair retribution as described by [START_REF] Walster | Equity and social justice[END_REF]. By paying an entrance fee for museums and monuments, the visitor obtains the power to have access to them while respecting economic rules and social codes. By paying, the visitor is integrated in a social group, which distinguishes him from the members of the public who do not go to museums and monuments. Those are then excluded, not only economically, but also socially and culturally.

From those considerations we can deduce that payment may be considered by visitors as an "admission visa" to museums and monuments. 28.1% of the interviewees 7 agree with the proposition that a fee should always be paid to enter museums and monuments and it's the main perception of 6% 8 . Should visitors therefore be allowed into museums and monuments free of charge? This first reading of the results clarifies some fundamentals of the discussion engaged between actors. 4 100% of the regular visitors agree, 99.5% of the occasional visitors and 96% of the non-visitors -Chi2=28.356, dof=8, signif.=0.000. This is not related to the region of living. 5 56.7% of the regular visitors agree, 45.3% of the occasional visitors and 36.7% of the non-visitors -Chi2=35.133, dof=8, signif.=0.000. This is not related to the region of living. 6 This is not related to attendance profiles, but it's the main perception for 73.7% of the respondents living in Paris, 65.7% of the people living in another town and 69.7% of the people living in a rural area -Chi2=14.387, dof=6, signif.=0.026. 7 This is not related to attendance profiles or region of living.

For some, free admission is seen in a favourable light (a visa obtained by paying is then perceived as negative discrimination) while for others, it is seen in an unfavourable manner (the visa is then perceived as positive discrimination).

Payment: a distance between museums and monuments and their audiences.

According to whether it is periodical or permanent, perceptions of the effects of free admission highlight the distance that payment may establish. Permanent free admission seems to bring museums and monuments and their visitors together: one is free to enter when one wants, to spend the time that one desires. Museums and monuments are then a part of the visitor's daily and private life. Perceptions of periodical free admission create a temporal distance: to benefit from it, people must plan the visit. It then seems more difficult to gain proximity to museums and monuments by taking advantage of free admission, ("We wished to go the day when museums are free, the first Sunday of each month, but we never seemed to be able to do this… because we forgot…or…each time we had something else to do," extract from individual interview). 62.6% of the interviewees9 agree with the proposition that entry should always be free (it's the main perception of 21.5%10 ).

Lastly, permanently paying to enter museums and monuments suppresses this temporal distance but introduces a financial one: the visitor must accept to spend, to lose a monetary sum.

A distance between museums and monuments and their audience appears. A visitor must compare his feelings, his desires (emotions, knowledge, social recognition) that may be fulfilled by visiting museums and monuments with the money that he has had to save for their realisation [START_REF] Simmel | La philosophie de l'argent[END_REF]. In a process of objectivation, admission paying leads a visitor to see a distance between himself and the cultural object. Let us note that, if the visitor does not perceive any distance between himself and the museum or the monument (in other words, if he considers that it belongs to himself), paying or not will have no meaning for him.

Payment: a commitment by the visitor in the action of visiting. The interviews show that paying is a symbol of the visitor's commitment in the action of visiting. Paying is described as a visible sign of the step accomplished by the visitor to open himself up to culture and knowledge. Some see in this manifestation of commitment a means for the visitor to arrange absolutely, officially, the visit ("Otherwise, it is a rip-off," extract from an individual interview), while others see it as a constraint ("[the heritage] belongs to everybody. It would be logical that everybody could benefit from it for free. But, on the other hand, it has to be maintained in proper conditions. Then, should it be covered by public taxes? Yes, no doubt, but a participation should also be paid. I think that for the building maintenance, they must pay a little, to participate in the upkeep of their heritage," extract from an individual interview). Free admission suppresses this commitment. The visitor is thus less constrained.

Finally, let us note that in the survey, 43.18% of people declare to be in favour of weekly free admission; 23.66% in favour of permanent free admission; 23.49% in favour of monthly free admission and 6.56% against free admission. These results are not related to involvement in museums and monuments, attendance profiles or region of living (non significant Khi2 tests). But a positive attitude toward free admission is related to the free admission experience (Khi-deux=13.44, ddl=3): people who have experienced free admission are more in favour of permanent admission.

Paying for admission makes the visitor an actor of the museums and monuments visit. For several people, it seems that payment makes the visitor conscious of what he is doing (he makes budgetary choices, and renounces other visiting activities); it creates responsibility awareness. According to this meaning, payment should be understood as a way to more easily arrange the visit. On the contrary, free admission seems to encourage spontaneous behaviour, which is freer and less committed.

Payment is also considered as a principle: it is not so much the amount paid that seems important but the action of paying. For some, it appears that there is a dissonance between museums and monuments perceptions and paying an arbitrarily fixed price. Gift is then at the issue, as a voluntary contribution, notably to mark his commitment or to contribute to the upkeep of the heritage. In the United Kingdom, many museums and galleries offering free entry propose to visitors to make a donation instead of paying an entrance fee. This is a good solution which enables the visitor to underline his commitment to the venue or visit.

Nevertheless, since admission charges were scrapped in December 2001 in UK museums and galleries, the MORI report [START_REF] Martin | The Impact of Free Entry to Museums[END_REF] has shown that only 21% of visitors say that they donate more when visiting.

In spite of the ambiguity in the interviews about the theme of gift, audiences seem to want to occult the market character of price and of paying a price to give it a collective social meaning. The payment form then seems very related to the commitment of the visitor in the visit.

Payment: an interpellation of the museums and monuments value and of what they give to their audiences. For visitors, the term "value" is polysemic: related to offer characteristics, to admission price... Indeed, in the interviews, it is a question of:

-collective heritage, culture and knowledge that museums and monuments represent, -the ability of those places to propose a high quality "offer" (famous artworks, pleasant places and associated services), -social relationships when visiting with others (family, friends), -the ability of those places to give rise to admiration, astonishment, surprise, pleasure (on that issue, we note also the expression of a "counter-value" related to worry or embarassment), -the ability of those places to generate curiosity and to stimulate desire of newness or of knowledge.

The relationship between paying for admission and value is widely discussed according to individuals and according to context: the risk of being downgraded by standardisation and induced costs, ("There is an idea, that what is free is necessarily of poor quality." extract from an individual interview), or its possible upgrading with the creation of social ties and liberty during the visit, ("One is not obliged to see it through," extract from an individual interview). In the quantitative survey, 83.39% of the respondents disagree with the statement "Free admission depreciates the museums and monuments visit". Lastly, the value of the visit and admission fee may be disconnected ("To pay or not to pay, that does not change anything," extract from an individual interview). The quantitative survey shows that visitors think that paying or not does not change their patterns of behaviour. They are neutral regarding the statement " When I pay to enter, I am expecting more services than when it's free" (the mean is 3.33 on a scale of 1 to 6) or "Knowing that it's free pleases me" (mean = 3.85). They agree with the statement "Whether I pay or not, I do not change my patterns of behaviour (mean = 4.49)" 11 .

Those results bring an empirical validation, in the museums and monuments context, to research on the perceived value concept [START_REF] Zeithaml | Consumers perceptions of price quality and value: a means-end model and synthesis of evidence[END_REF], considered as a compromise between what is given and what is received, weighted by personal features.

In conclusion, we establish that paying for admission is embodied in the process of the creation of a relationship between museums and monuments and their audiences. Paying may so "desacralize" or "marchandise" museums and monuments, as underlined by several interviewees.

SYNTHESIS OF THE RESULTS AND MANAGERIAL IMPLICATIONS

Perceptions of free admission in museums and monuments that audiences express when they adopt an individual perspective can be summarised as propositions, that can be considered as hypothesis:

• Free admission is seen as a price: it is considered as a removal of a financial cost and can modify the perception of non-financial costs related to the visit; free admission is never defined as totally free: free admission does not suppress certain financial costs and efforts; in this sense, the visit is never free.

• Free admission abolishes the admission "visa" in museums and monuments that comes with the payment to enter, hence confirming the importance of payment as a mode of approval and participation.

11 All these statements are not related to attendance profiles and to region of living.

• Free admission abolishes the distance that paying establishes between museums and monuments and their visitors.

• Free admission abolishes the monetary distance existing between museums and monuments and their visitors.

• Free admission questions the widely discussed concept of value in museums and monuments, and of what they offer to their audiences: the risk of being downgraded by standardisation and induced costs, but also its possible development with the creation of social ties and liberty during the visit, or the disconnection between the value of the visit and the admission fee.

To understand the different behaviour that can be generated by free admission, it is then necessary to take into account the context of free admission and its meanings for the audience that may benefit from it. From a managerial point of view, those results strongly question the pricing policy of museums and monuments. Indeed, if, from a collective perspective, free admission is perceived as a symbolic measure creating adhesion or rejection, from an individual perspective, the visitor puts it in a market trade framework. It is perceived as related to fees and prices. The pricing of the admission must then be related to the proposed offer: visitors want to know "what they are paying for". Moreover when admission is free, attendants seem to concentrate far more on non-monetary costs, despite the fact that they express a surprisingly positive feeling. Museums and monuments should take better care, during the free admission days, of crowds and flows management. Quality perception could also be improved at low costs by offering self-service information services (audio-guides, interactive web terminal…). It should be noticed however that most visitors feel abandoned when no human guide services are proposed and these low cost solutions are not a panacea.

Otherwise, discriminatory fees (free admission on the occasion of a special event, on a recurrent basis or related to individual characteristics) must be known and understood by the audience. It is important to clarify pricing objectives as a means of achieving missions and financing museums and monuments. This research could also be deepened by considering the different types of free admission perceptions (regular or periodical; restricted to specific categories of visitors or for everyone; for the entire museum or restricted to some exhibitions). For example, regular and periodical free admissions seem to be perceived differently. These two kinds of free admission may be subject to framing effects [START_REF] Kahneman | Prospect theory: an analysis of decision under risk[END_REF].

Our results also put forward the fact that fee measures are not the primary focus of attendants.

In managerial terms, if we examine the arrangements being considered by professionals, their job is to construct the experience to be had by proposing peripheral services capable of producing emotional, ludic and aesthetic reactions in response to a cultural object, and so engage their visitors. Non-visitors speak of "having restaurants, discotheques [… making them] more like places for discussion and exchange", putting in music or lighting.

Respondents are looking for "shows". For increasing attendance, this suggests the experience should be organised for individuals within a theatricalised staging of their visit (Bourgeon et al., 2006). More generally, those results raise the issue of the identity of museums and monuments: are they to be viewed as places of culture? places of leisure? market places? places "apart"?

Even if the research process is valid and reliable, our work shows some limitations. Results have been obtained during a unique period (synchronic approach) and in a limited number of venues. A diachronic study would permit the checking of the reliability of observations over time. It would also be interesting to obtain results on diverse types of offers (more or less famous sites, with various positioning, …). From a conceptual point of view, the methodology permits, in an inductive way, the identification of several dimensions which structure the perceptions the public has of free entrance in museums and monuments. It would be helpful to further study each of these dimensions and to conceive measurement tools useful to implement them, taking into account the publics' diversity in a typology. Moreover, our results question free pricing practices of all organisations (profit or non-profit making) as the promotional use of free products, and incite further research on the influence of free pricing on perceptions of price (its monetary and non-monetary dimensions), reference price formation and willingness to pay.

CONCLUSION

Those conclusions lead us to say that free admission, regarded as the freedom to enter a museum or a monument or as an absence of an admission fee, does not only have the symbolic power lent to it by museum and monument managers. From an individual perspective, perceptions of free admission are linked to perceptions of price and money, and are in line with the market trade framework [START_REF] Sagot-Duvauroux | Pour la gratuité[END_REF]. Like money, exemption from payment fits into an ideology, or even morals which also bring the individual to consider free admission from a collective perspective. When considering free admission for oneself or free admission for others as a collective entity, as a kind of price or as an audience policy for everyone, then exemption from payment becomes equivocal.

Table 1 -Multiangulation tactics used in the research

Definition of multiangulation tactics

How it has been implemented in the research Data multiangulation, or sampling criteria has several dimensions • Time: enables to check the degree of stability of observations over time (diachronic reliability), the stability in the same time frame (synchronic reliability) and the evolution of the process under study.

A synchronic approach only: most of the data was collected in 2003.

• Space: seeks to identify different contexts and natural environments in order to highlight similarities and divergences in the observed results.

The data were collected… • throughout different regions in France distinguishing between the "Paris" region and outside Paris "province region" and between rural and urban zones • a two-site test: a monument and a museum, with different admission configurations (payable, periodically free, exceptionally free).

• Combinations of different analysis levels

Two main levels of analysis:

-Perceptions, planned visits and patterns of behaviours of audiences in France. • perceptions of free admission and perceptions of museums and monuments • planned visits • patterns of behaviour -Visitors' profiles according to attendance • regular visitors (more than 2 visits in the current year) • occasional visitors (at least 1 visit during the last 5 years and no more than 2 visits during the last year) The perceptions of free admission, planned visits and the public's behaviour during visits were compared.

The perceptions of free admission in museums and monuments were also confronted with the public's perceptions of museums and monuments Respondent convergence: refers to the decision the researcher made to present his preliminary conclusions to the original informants so as to get their reaction and to reorient his own interpretation if necessary. The informants' comments generate new data.

Not used. This tactic would have been too time-consuming and heavy to be made operational.

Researchers multiangulation:

implies that several researchers participate in the investigation. They compare their observations, their interpretations. Collected data is validated by the group on a permanent basis.

Used.

A team of five researchers, based on theoretical and methodological skills.

Researchers were triangulated at each research step (from data collection to analysis).

Theoretical multiangulation:

anticipates that the analysis of the data will be done through their comparison with different theories.

Existing theories about free admission, price, museums/monuments, and cultural consumer behaviour, were multiangulated in the literature review. Then, in addition to these theories, other theories from different fields (psycho-sociology, psychoanalysis, sociology) about money, culture, museums and monuments were compared and mobilised (when relevant) to explain the data. Paradigm multiangulation: implies that the research as a whole or the data collection and/or their analysis will be done through different paradigms.

The research was conducted according to 3 epistemological frameworks both for used methods and developed theories. Main epistemological framework: interpretative Complementary epistemological frameworks: positivist and semiotic or "Museums in Spring"

Measurement scale of free entry perceptions

A measurement scale of 7 items captures 67% of the variance. A principal component analysis results in three factors related to free entrance perceptions: no limit to behaviour, disillusion, inequity.

Measurement scale of experience of free visit perceptions

A measurement scale of 8 items captures 65.8% of the variance. A principal component analysis results in three factors related to perceptions of the experience of free visits: a pleasant environment, feelings of individual advantage, and embarrassment.

Measurement scale of involvement in free entry

A measurement scale of 4 items captures 62% of the variance. Involvement in free entry can be considered as a one-dimensional concept.

Costs related to the visit 74.14% of the interviewees stated that they take into consideration the admission fee, 21.55% the hotel cost, 37.41% the transport costs (petrol, motorway tolls, train ticket…), 9.48% the meal or coffee costs, 5.69% the post cards and gadgets costs, 13.1% declare not to know.

Cost, value and act of payment perceptions

Three measurement scales (of visit cost perception, of free entry value perception, of the act of payment perception) have also been developed but should be further tested.

Motives for visit

The motives cited are firstly fame, then the type of site (museum or monument), the organisation of an event and finally the price. Constraints for visit The constraints cited are firstly the lack of time, then family duties, crowds, the lack of desire and finally the lack of interest.

  • non-visitors (no visit during the last 5 years) All studied individuals were persons living in France (foreign tourists have not been surveyed). • 36 observations on-site (observation of visitors' behaviour with biases inherent to each technique an interview in the middle of visit) • a quantitative survey based on 580 questionnaires (311 regular visitors, 219 occasional visitors and 50 non-visitors) Multi-interpretation analysis: verifies if every actor assesses the situation in the same way and/or if people interject in the same way during the succession of events taking place.

	Multiangulation of data	Main data collection technique
	collection techniques: refers to the	52 individual interviews (20 regular visitors, 19 occasional visitors
	combination of different	and 13 non-visitors)
	techniques of data collection in order to obtain various forms of	Complementary data collection techniques • 4 focus groups interviews (two groups of regular visitors, one
	expression and views, and to	group of occasional visitors and one group of non visitors)
	minimize the weaknesses and

Perceptions are defined as cognitive products generated by exemption from payment, results of the interaction between the consumer and his environment, that may be used in the short term or stored in memory to be used in the long term[START_REF] Denis | Image et cognition[END_REF]. Perceptions give sense to the environment of the consumer and can be considered as behaviours' organisers.

90% of the regular visitors, 71.7% of the occasional visitors and 54% of the non-visitors -Chi2=50.141, dof=2, signif.=0.000 ; 81% of the respondents living in Paris, 85.1% of the people living in another town and 72.5% of the people living in rural area -Chi2=11.707, dof=2, signif.=0.003.

This is not related to attendance profiles, but people living in Paris are more in agreement with paying for entry : this is the main perception of 12.1% of them, 5.5% of the people living in other towns and 4.5% of the people living in rural areas.

This is not related to attendance profiles or region of living.

Again, this is not related to attendance profiles, but people living in Paris agree less with the idea of free entry: this is the main perception of only 12.1% of them, 25.8% of the people living in other towns and 21.7% of the people living in rural areas.

Regular visitors (53.6%), occasional visitors (37.7), non-visitors (8.7) Working (53.3),retired (17.3) Living in and around Paris (17.2), in other French towns (47.6), in rural areas (35.2) Women (60.3), men (39.7) Under 18 years old (1.21), between 18 and 25 (26.72), 26 and 35 (14.83), 36 and 45 (17.41), 46 and 55 (18.97), 56 and 65 (10.86), 66 and more (10) With no diploma (2.1), under baccalaureat (18.2), baccalaureat and BA (40. 3), MBA and more (39.7) Earning less than 18,000 euros per year for the household (26.3), between 18,000 and 42,000 euros (28.3), between 42,000 and 66,000 (10.2), more than 66,000 euros (5.4), non-responses (29.8)

Perceptions of museums and monuments

Are sites that should be open access for all people (97% agree with this proposition and it's the main perception of 35.5%). Represent a heritage that must be maintained (99.5% agree with this proposition and it's the main perception of 49.4%). Can be considered as a form of leisure (82% agree with that proposition and it's the main perception of 8.3%). Are not considered, as people are not concerned or interested (20% agree with this proposition and it's the main perception of 4.2%). Five measurement scales (of perceptions of museums; of perceptions of monuments, of perceptions of of the experience of visiting museums, of perceptions of of the experience of visiting monuments, and of involvement in museums and monuments) have also been developed.

Tariffs and free entrance perceptions

Entrance should always be free (62.6% agree with this proposition and it's the main perception of 21.5%). A symbolic entrance fee should be paid (86.3% agree with this proposition and it's the main perception of 67%). A price should always be paid (28.1% agree with this proposition and it's the main perception of 6%). Price is not important (5% agree with this proposition and it's the main perception of 3%).

Attitudes toward diverse free entrance formats

43% are in favour of weekly free entry. 23.6% are in favour of permanent free entry. 23.5% are in favour of monthly free entry. 6.5% are against free entry.

Experience of free entrance

80% have experienced free entry. 48% have visited a permanent free site. 39% experienced periodic free entry events such as "Heritage days"


INTRODUCTION

The Trièves is a depression area within the French alpine foreland, located at about 40km south of Grenoble. This 300km 2 large area is covered by a thick Quaternary clay layer (up to 200 m), which was deposited in a glacially dammed lake during the Würm period [START_REF] Monjuvent | La transfluence Durance-Isère. Essais de synthèse du Quaternaire du bassin du Drac[END_REF]. After the glacier melting, rivers have deeply incised the geological formations triggering numerous landslides. The two studied adjacent landslides Avignonet and Harmalière are situated along the west shore of the lake Monteynard (Fig. 1). The clay layers have covered a paleo-topography made of Jurassic limestones and overlying compacted old alluvial layers located along paleo-valleys of the river Drac. This results in an irregular surface of the base of the clay deposits.

In March 1981 the Harmalière landslide was triggered after a heavy rainfall provoking the melting of the snow cover [START_REF] Moulin | Le glissement de Harmalière sur la commune de Sinard[END_REF]. This slide, which affected a surface of about 450,000 m 2 and created a head scarp of 30 m high, evolved into quick mudflow, which reached the lake. No such dramatic effects were observed for the Avignonet landslide but significant signs of instability were noticed during housing development [START_REF] Lorier | Glissement du Mas d'Avignonet, commune d'Avignonet[END_REF], triggering geotechnical and geodetic investigation campaigns. Slide velocity measurements at the surface and in boreholes pointed out that the maximum slide activity is located at the slide toe and is linked to a shallow active rupture surface at about 13 m depth. These geodetic data are consistent with geomorphic observations (scarps, fissures, swampy

The influence of bedrock topography on the dynamics of two clayey landslides in the Trièves (French Alps) U. Kniess, D. Jongmans, E. Pathier, S. Schwartz

LGIT, Université Joseph Fourier, Grenoble Cedex 9, France

G. Bièvre

LGIT, Université Joseph Fourier, Grenoble Cedex 9, France CETE de Lyon, Laboratoire Régional d'Autun, Autun cedex, France

T. Villemin

LGCA, Université de Savoie, Chambéry, France ABSTRACT: The two large adjacent landslides of Avignonet and Harmalière, affecting thick clayey quaternary deposits, are located in the Trièves area (French Alps). Remote techniques (Lidar) and GPS measurements were used to characterize the two landslides. Results show major differences between the dynamics of the two landslides, both in morphology, displacement rate magnitudes and motion directions. Seismic noise measurements (H/V technique) were performed to map the clay layer thickness. Combined with Lidar derived DEM, these data yielded the paleo-topography of the seismic substratum made of compact alluvial layers and Mesozoic bedrock. The difference in dynamics between the two landslides is likely to result from the presence of a ridge of compact formations at the Avignonet landslide toe, preventing an eastward deep active sliding to develop and explaining the observed shallow slip surfaces. To the South, this buttress disappears at the Harmalière toe, favoring a deep sliding in a Southeastern direction with a fast regression of the headscarp, which evolves into a mudslide at its base. areas, bulges), which show an increase of the landslide activity downstream.

In order to understand the differences in the geometrical and dynamical characteristics of these two landslides, which occur on identical slopes made of the same geological, we performed a combined analysis of morphological, geodetic, geological and geophysical data.

LANDSLIDE DYNAMICS

Morphological and geodetic data

Three datasets are available to analyze the landslide dynamics of the two landslides: GPS measurements, aerial photographs and Lidar. GPS measurements have been performed biannually since 1995 by RTM (Restauration des Terrains en Montagne) at 25 points on the Avignonet landslide, relatively to several reference points located on nearby stable bedrock. No GPS measurements are available for the Harmalière landslide, owing to the quick surface evolution. The coordinate accuracy is better than 10 mm, allowing mm/y average velocities to be derived over the past 11 years.

Aerial photographs are available from IGN (Institut Géographique National, France) since 1948 with a periodicity of 8 years and a scale of about 1:30,000 (except in 1970, when the scale was 1:15,000). For this work, all photos were orthorectified, using the IGN DEM with a resolution of 50 m and ground control points measured with differential GPS.

A Lidar (LIght Detection And Ranging) laser scan, covering the Avignonet and Harmalière landslides (Fig. 1), was performed in November 2006 with the handheld airborne mapping system Heli-map® [START_REF] Vallet | Development and Experiences with A Fully-Digital Handheld Mapping System Operated From A Helicopter[END_REF]). The resolution is about 30 cm with an accuracy of 10 cm in vertical and horizontal directions. The point cloud was filtered and interpolated to a 2m raster grid with the software SCOP++®, in order to derive the bare earth model excluding trees and houses (Fig. 2a). Shaded representations with different light angles were used for interpretation.

Interpretation

Several indicators were used to highlight the difference in dynamics between the Avignonet and Harmalière landslides: the general orientation of the landslide, the elevation profile, the surface velocity, the headscarp evolution and the surface roughness. While the Avignonet landslide moves eastward, down the general hill slope, the Harmalière slide runs out to SE (Fig. 2b). The elevation profile through Harmalière (Fig. 2c) is mainly concave, with a classical accumulation zone in the upper part and a sedimentation zone at the toe. On the contrary, the profile at Avignonet exhibits a global convex shape, owing to the presence of the rigid alluvial layers and the bedrock in the lower part.

The slide velocity values measured by GPS at the surface of the Avignonet landslide (Fig. 2c) vary from 0-2 cm/year at the top to more than 13 cm/year in the most active parts at the toe. The aerial photos show no major activity in Avignonet for the last 60 years, with no significant evolution of the headscarp. This is in agreement with the smooth topography shown by the Lidar DEM (Fig. 2c) in the upper part of Avignonet, which suggests the absence of fast recent movements. In Harmalière no GPS measurements are available but the aerial photos study yields an average velocity of several meters per year for the landslide body. The headscarp at Harmalière, which was created during the catastrophic event of March 1981 has regressed regularly, through several distinct events, at a mean rate of about 10 m/year [START_REF] Moulin | Le glissement de Harmalière sur la commune de Sinard[END_REF]). This evolution is traceable in the aerial photos and was dated by field observations (Moulin & Roberts 2004). Since 2001, the headscarp regression has started to affect the southern limit of the Avignonet landslide. This southward motion of the crest between the two landslides is also evinced by GPS measurements (Fig. 2a). The surface roughness observed in the Lidar DEM is an indicator for the landslide activity. It is much stronger and small-scale in the Harmalière landslide than in the Avignonet one. Only some areas in the lower part and in the South of Avignonet exhibit small-scale roughness. This is consistent with the location of exposed bare soil surfaces in the most recent aerial photos, which correlate to a higher landslide activity.

BEDROCK TOPOGRAPHY

Method

Seismic noise measurements were conducted for determining the thickness of the clay layer overlying the seismic bedrock. The single station method (also called the H/V technique) was used at 78 locations (Fig. 4). It consists in calculating the horizontal to vertical spectral ratios (H/V) of seismic noise records and the resonance frequency of the soft layer generally appears as a peak on the H/V curve [START_REF] Bard | Microtremor measurements: a tool for site effect estimation?[END_REF]. In cases with a high seismic impedance contrast between the soft layer and the bedrock, this H/V peak results in a change in the ellipticity of the fundamental mode of the Rayleigh waves [START_REF] Bonnefoy-Claudet | H/V ratio: a tool for site effects evaluation. Results from 1-D noise simulation[END_REF]. For a single homogeneous soft layer overlying the bedrock, the resonance frequency is given by f 0 = Vs/4H where Vs is the soft layer shear-wave velocity and H is the layer thickness. A low resonance frequency then corresponds to a thick soil layer and vice-versa. In the investigated area, the measured H/V curves exhibit peaks in a frequency range between 0.58 Hz and 3.63 Hz (see Fig. 3 for the H/V curves and Fig. 4 for measurement location).

In order to interpret the resonance frequency values measured on the H/V curves, we computed the fundamental ellipticity curves of Rayleigh waves and the corresponding theoretical resonance frequency values below each station. The dynamic characteristics (compressional wave velocity Vp, shear wave velocity Vs and density) within the different layers (moraine, clay, alluvium and bedrock) were obtained from a previous seismic study (Jongmans et al., in press). This computation was calibrated using the geotechnical cross-section P01 (Fig. 4), along which several boreholes were made and a detailed H/V profile was conducted. Theoretical and experimental values of the resonance frequency f 0 along this profile show a very good agreement, corroborating the determined velocity values in the layers. Sensitivity tests have shown that the main parameter controlling f 0 is the clay thickness. On the contrary, no change in the f 0 value has been found when passing the landslide headscarp. These results support the use of resonance frequency measurements for determining the clay thickness. The H/V deduced geometry for the seismic bedrock top was compared to a section previously established from a long refraction profile [START_REF] Blanchet | Etude géomécanique de glissements de terrain dans les argiles glaciolacustres de la vallée du Drac[END_REF]) and depicting the top of the Jurassic bedrock. A general good agreement is observed between the two sections, the slight observed differences probably resulting from the presence of alluvial layers in-between the clays and the Jurassic limestones.

The thickness data obtained over the whole area were then subtracted from the Lidar DEM and were spatially interpolated (krigging with an exponential variogram model correction) to produce a topographical map depicting the bottom of the varved clays (Fig. 4).

Paleo-topography analysis

The map of Figure 4 reveals that the paleotopography upon which clays were deposited was very irregular, with elevation variations more than 150 m. The major feature is the presence of a depression striking N-S, which is bordered to the East by a ridge culminating at an elevation of about 640 m. These results are consistent with existing geo-Figure 3. Spectral ratios (H/V) of ambient vibration measurements measured at the two points (HV21, HV1T1) shown in Figure 4. logical data [START_REF] Blanchet | Etude géomécanique de glissements de terrain dans les argiles glaciolacustres de la vallée du Drac[END_REF][START_REF] Lorier | Glissement du Mas d'Avignonet, commune d'Avignonet[END_REF], which pointed out the westward increase of the clay thickness. This depression is probably a paleo-valley of the river Drac as suggested by alluvial outcrops along the lake. The NS ridge corresponds to the presence of carbonate bedrock covered with compact alluvial layers and sporadically outcropping along the lakeshore. To the South, this ridge abruptly disappears (Figure 4). In the same figure are superimposed the headscarps of the landslides of Avignonet and Harmalière. Below the Avignonet slide, the ridge of compact layers continuously extends perpendicularly to the global slide motion and could act as a buttress. On the contrary, the Harmalière landslide clearly developed over the lower elevation zone (Figure 4) and its motion can be explained by the orientation of the Drac paleo-valley which changes from NS to NW-SE in the South.

DISCUSSION / CONCLUSIONS

The presence of a buttress of hard formations (compact alluvial layers and bedrock) along the western shore of the lake was pointed out both by seismic data and geological observations. It probably prevents the development of a deep active slip surface at Avignonet. This geometry explains the higher displacement rates observed at the landslide toe, the clayey material being expelled over the rigid formations. This buttress disappears to the South, resulting from the presence of a paleo-valley of the river Drac shown by seismic data and alluvial layer outcrops. This paleo-valley, which allowed the deposit of thick clay layers, probably controlled the initiation and the unexpected Southeastward motion of the l'Harmalière landslide. The material eroded at the top is moving downward and feeds a funnel shaped track zone through which the material sediments and flows to the lake with a regular slope.

Figure 1 .

 1 Figure 1. Geological map with the location of the Avignonet and Harmalière landslides and the area investigated by Lidar (Fig. 2).

Figure 2

 2 Figure 2. a) Shaded Lidar DEM with displacement vectors measured by GPS. b) Sketch of Fig.2a with the interpretation of the headscarps of the two landslides and location of the two profiles A' and BB'. c) elevation profiles of the two landslides.

Figure 4 .

 4 Figure 4. Paleo-topography of the bottom of the clay layer below the Avignonet and Harmalière landslides and locations of seismic noise measurements .

ACKNOWLEDGMENTS

This work was financially supported by European, regional and national funds coming from the Mountain Risks project (Marie Curie program), the Conseil Général de l'Isère (PGRN), the ECOUPREF project (ANR), the Cluster Environnment (Région Rhône-Alpes) and VOR (Vulnérabilité des Ouvrages aux Risques).