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The use of speleothems to better constrain long return period seismic hazard in Lebanon period seismic hazard in Lebanon

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Corinne Lacave
Corinne Lacave
Corinne Lacave
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Benjamin Sadier at Université Savoie Mont Blanc
Benjamin Sadier
Jean-Jacques Delannoy at EDYTEM laboratoy
Jean-Jacques Delannoy
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Carole Nehme at Université de Rouen Normandie
Carole Nehme
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Abstract and Figures

In the framework of the LIBRIS project (Contribution to seismic risk assessment in Lebanon), a work package is devoted to the use of broken or unbroken speleothems (stalagmites and stalactites) to better characterize the local seismic hazard. This kind of study is particularly interesting in the long return period range, where historical information is far from being sufficient. The proposed approach is based on a previous study by Lacave et al. (2004). Two pilot caves, located north of Beirut, along or close to a major fault, were first selected. Then, in situ measurements of speleothems were done using a 3D laser scan. The data were processed to obtain a detailed sampling of the broken and unbroken speleothem population (number, precise shape). These data are finally used to compute, in a statistical approach, the probability of exceeding, or non exceeding, of a certain level of seismic acceleration in the study area.
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The use of speleothems to better constrain long return
period seismic hazard in Lebanon
period seismic hazard in Lebanon
C. Lacave
Résonance Ingénieurs-Conseils SA, Carouge (GE), Switzerland
B. Sadier & J.-J. Delannoy
Laboratoire EDYTEM, Le Bourget-du-Lac, France
C. Nehme
St Joseph University, Beirut, Lebanon - Laboratoire EDYTEM, Le Bourget-du-Lac, France
J.-J. Egozcue
U. Politécnica de Cataluña, Barcelona, Spain
SUMMARY:
In the framework of the LIBRIS project (Contribution to seismic risk assessment in Lebanon), a work package is
devoted to the use of broken or unbroken speleothems (stalagmites and stalactites) to better characterize the local
seismic hazard. This kind of study is particularly interesting in the long return period range, where historical
information is far from being sufficient. The proposed approach is based on a previous study by Lacave et al.
(2004). Two pilot caves, located north of Beirut, along or close to a major fault, were first selected. Then, in situ
measurements of speleothems were done using a 3D laser scan. The data were processed to obtain a detailed
sampling of the broken and unbroken speleothem population (number, precise shape). These data are finally used
to compute, in a statistical approach, the probability of exceeding, or non exceeding, of a certain level of seismic
acceleration in the study area.
Keywords: speleothems, maximum acceleration, seismic hazard, long return period
1. INTRODUCTION
In the framework of the LIBRIS project (Contribution to the study of seismic risk in Lebanon), a
work-package is devoted to the use of information derived from the study of broken or unbroken
speleothems (stalactites and stalagmites), in order to better characterize the seismic hazard in a given
region. This kind of study potentially contributes to the determination of long return period hazard, not
covered by historical seismicity. A critical review of many studies conducted in the field of speleo-
seismicity can be found in Becker et al. (2006).
Another similar field of research is also investigated by Anderson et al. (2011), with the same goal,
using precariously balanced rocks or other fragile geological features. Indeed, probabilistic seismic
hazard analysis (PSHA) is not very reliable at low probabilities where no instrumental verification is
possible. Anderson et al. (2011) conclude that to gain confidence in PSHA it is important to use fragile
geological features (precariously balanced rocks or speleothems, for example) to test hazard curves at
low probabilities, whenever data are available.
2. METHODOLOGY
The proposed approach is based on a previous study by Lacave et al. (2004). The mechanical
behaviour of speleothems was studied by means of static bending tests performed on pieces of broken
stalactites, giving indications of their mean bending resistance as well as on its variability. This study
made it possible to determine fragility curves for different classes of speleothems, by means of Monte
Carlo type simulations, accounting for dynamic amplification and bending resistance heterogeneity, in
each speleothem. Finally, an original statistical approach, valid for incomplete and imprecise data, was
developed. This approach allowed to estimate the probability that at least one relatively strong
earthquake has occurred in the past.
A first field trip was conducted in February / March 2010, allowing the choice of two pilot caves. A
second field trip, conducted in October 2010, was devoted to in situ 3D laser measurements. The
processing of the acquired data makes it possible to precisely sample the broken and unbroken
speleothems populations (number and precise shape), in both pilot caves. These data constitutes the
basis for the statistical computation of the probability of having reached, or not attained, a certain level
of seismic acceleration in the studied region.
Beyrouth
Figure 1. Lebanon seismicity between 2006 and 2008.
3. PILOT CAVES
Criteria for the choice of the two pilot caves were as follows:
– Location in a seismic area (after the historical and instrumental seismic maps for Lebanon, as the
one shown on Figure 1, for example).
– Caves containing rather slender speleothems (long and thin). There should be an important number
of speleothems, if possible broken and unbroken ones. The use of soda-straws is not possible as it
is impossible to distinguish a broken from an unbroken soda-straw.
– If broken speleothems are present, one must try and estimate their original size (by means of
broken pieces on the floor, shape indices, etc.).
– Study areas with speleothem populations should be at shallow depth, so that the ground
acceleration can be considered as approximately being the same as the surface rock acceleration.
Based on these criteria, colleagues from the ALES (Lebanese association for speleological studies)
and St Joseph University (Beirut, Lebanon) prepared a list of potentially interesting caves for the
project. These caves were visited during the first field trip, in order to choose interesting pilot caves.
It must be noted here that it is very important, in all visited cave, to account for many different
elements that may cause speleothems rupture, other than earthquakes. Examples of these can be:
– quarry blasting,
– bombardments,
– human activity (pilfering, vandalism, etc.).
During the cave visits, these potential human causes of braking were seriously considered, in order to
select as pilot caves the ones that present the least potential of human origin of breaking. The two
selected pilot caves are the caves of Jeita (Nahr El Kalb) and Kanaan (Antelias), both located near the
coast, North of Beirut, on - or in the prolongation of - a major fault, as shown on the schematic map on
Figure 2. The characteristics of both caves are described hereafter.
Jeita
Kanaan
Figure 2. Location of the two selected pilot caves, both situated on – or in the prolongation of – a major fault
(from the simplified geologic map of Lebanon, Dubertret, 1955).
3.1. Jeita cave
Jeita cave is one of the major caves in Lebanon, due to its development (more that 10 km) as well as to
the vastness of its volumes and the richness of its speleothems population. It is located on the hillside
of the narrow Nahr El Kalb valley, North of Beirut, along a major fault (Figure 2).
Figure 3. Left: results of the dating of a stalagmite in Jeita cave, conducted by Nader et al. (2007). A clear
rupture can be observed at about -4000 years. Right: broken speleothems in the cave of Kanaan. On the bottom
picture, breakings along the two middle columns could be due to drawing off phenomena at their basement.
This cave constitutes an exceptional paleo-environmental recording, as evidenced by the dating
conducted by Nader et al. (2007), on a stalagmite sampled in the cave (Figure 3), with ages of the
beginning of the speleothem formation as about 12000 years before present days. During the first field
trip, part of Jeita cave was visited, especially a lateral gallery located above the touristic area, as well
as another lateral gallery, located further than the touristic section. Many broken speleothems
(especially long stalactites) were observed in the gallery located above the touristic section. This
gallery was then selected as investigation site for the following of the project.
3.2. Kanaan cave
The cave of Kanaan is located in the quarry of Antelias; its entrance is formed by a rather vast porch
opened in the quarry wall. Kanaan is characterized by a rich speleothem population, associated with
many interesting indices allowing the reconstitution of the karstic history and evolution of the cave
(Nehme et al., 2009).
Concerning the LIBRIS project, the cave of Kanaan constitutes a very interesting study area thanks to
its important speleothem population, of large dimensions, broken as well as unbroken (Figure 3).
Interesting is to note that the broken stalactites shown on Figure 3 are broken since several hundreds
of years, as shown by the re-growths at their extremities. This makes it possible to consider that the
breaking occurred prior to the quarry exploitation.
4. SPELEOTHEM POPULATION MEASUREMENTS
4.1. In situ measurements
Data acquisition was extracted from high resolution digital terrain models recorded by 3D laser
sampling. The field trip conducted in October 2010 made it possible to acquire in situ data by means
of a Leica HDS 6000 Lidar (Figure 4), on a dome of 360° by 310°.
Figure 4. Setting and details of the high speed and high resolution 3D laser scanner, used for the sampling of the
speleothems populations.
This equipment is able to measure from up to a distance of 70 m and register about 500000 points per
second with a maximum resolution of 1 mm at a distance of 10 m, which corresponds to an angular
step of 127 m between each measure. However, the precision in the positioning of each point is given
to be 2 mm, in x, y and z directions, up to a distance of 25 m. Details on the validation of this in situ
measurement technique is given in the publication by Sadier et al. (2011).
In the cave of Jeita, for example, 49 scanner locations were necessary to cover the whole study area,
with a point density chosen as a function of the distance between the scanner and the ceilings where
the stalactites are located. A heavy data processing is then applied in order to restore and combine the
measurement scenes between them, with a precision of 3 mm. Horizontality and orientation were
obtained by geo-referencing with an electronic compass and a compensator integrated in the scanner.
4.2. Data processing
Details on the restoration procedure used in order to be able to proceed to the speleothems
measurements are given in the publication by Sadier et al. (2011). After this heavy processing, in the
case of the cave of Jeita, 37 scenes were selected, on which the total number of measured points was
kept. The represents scenes constituted of 75 to 175 millions of points. Finally, the global cloud of
points is made of more than 3.3 milliards of points. In becomes then possible to conduct direct
measurements on the pictures (Figure 5), as one easily navigates through the 3D numerical model.
Figure 5. Extract of a solid picture from the 3D numerical model on which one can directly measure the
speleothems size (right). The left picture is a photo of the same area directly taken on the field with a camera
(from Sadier et al., 2011).
5. VULNERABILITY ANALYSIS
A study previously conducted by Lacave et al. (2004) allowed developing a model of speleothem
behaviour under seismic solicitation. This approach also included the account for uncertainties linked
to the shape of the speleothem, to the heterogeneity of its internal structure, to possible dynamic
amplification effects, etc. The conducted modelling made it possible to establish fragility curves for
speleothems (Figure 6), associated to four vulnerability classes ranging from "highly vulnerable" to
"not vulnerable", respectively. A stalactite, about 80 cm long, with a diameter ranging between 2 and
2.5 cm belongs to the vulnerability class 1, whereas a stalactite of 50 cm in length and with a diameter
of 1 to 2 cm belongs to the vulnerability class 2, for example. Fragility curves shown on Figure 6 show
that, for example, with an acceleration of 3 m/s2, there is about 30 % probability to break a stalactite of
class 2, whereas there is about 90 % probability to break a stalactite of class 1.
0.061 m
Figure 6. Fragility curves (probability of breaking as a function of acceleration) for four stalactite classes (from
Lacave et al., 2004).
After the speleothem's geometry has been measured precisely, it is possible to proceed to a
classification of the whole speleothems population, broken and unbroken, into the four vulnerability
classes. Then, an original statistical approach, valid for incomplete and imprecise data, developed by
J.-J. Egozcue (Lacave et al., 2004), is applied to the whole dataset. This procedure accounts for the
uncertainty of the classification of each speleothem in one or another vulnerability class. It also
accounts for the uncertainty on the fact that the speleothem has, or not, been actually broken, and if
yes, potentially by a non seismic cause. Finally, this approach allows an estimation of the probability
that a certain level of acceleration was reached, or not attained, during a certain period of time, in the
studied region. This result, for several caves, combined with the results of other paleo-seismicity
studies in the considered region, makes it possible to better determine long return period seismic
hazard in Lebanon.
6. CONCLUSION
In the framework of the LIBRIS project, two pilot caves were selected north of Beirut, located on, or
in line with, a major fault. A 3D laser scanning field campaign made it possible to measure all
speleothems in a selected area in both caves. The processing of the acquired data allows a detailed
sampling of the broken and unbroken speleothem population (number and precise shape
measurements), in both caves. These data are the basis of the statistical approach to compute the
probability of having reached or not exceeded a certain level of acceleration in the considered region.
This will finally contribute to a better determination of long return seismic hazard in Lebanon.
AKCNOWLEDGEMENT
The LIBRIS project is financed by the ANR (French national agency for research) and the IRD (French institute
of research for development). All the work conducted here would not have been possible without the active
collaboration of the members of the St Joseph University, Beirut, Lebanon and of the ALES (Lebanese
association for speleological studies); we would like to warmly acknowledge all of them here.
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Engineering. Zürich, Switzerland.
Becker A., C.A. Davenport, U. Eichenberger, E. Gilli, P.-Y. Jeannin and C. Lacave (2006). Speleoseismology: A
critical perspective. Journal of Seismology, vol. 10, pp. 371–388. DOI 10.1007/s10950-006-9017-z.
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morphologies externes de spéléothèmes pour une étude paléo-sismologique du Liban. Cahier de géographie
et de géologie - collection EDYTEM, n°12, Université de Savoie, (Images et modèles 3D en milieu
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... Plusieurs travaux sont actuellement menés à une échelle fine sur les objets karstiques. Ils concernent aussi bien des questions associant préhistoire et géo-morphologie qui s'appuient systématiquement sur des relevés 3D comme à la grotte Chauvet-Pont d'Arc Sadier et al., 2012), à la grotte des Deux Ouvertures (Delannoy et al., 2012 c), à la grotte aux Points, à la grotte des Fraux (Burens et al., 2011), à la grotte des Gorges (Cailhol et Jaillet, 2012) ou en Australie à Nawarla Gabarnamang . Les travaux traitent des salles et galeries comme à Foussoubie ou Midroï Sadier, 2013) ou d'identification d'objets de plus petites dimensions comme les stalagmites (Hajri et al., 2009 ou les stalactites (Chakroun et al., 2009 ;Hajri et al., 2011 ;Perrette et Jaillet, 2010 ;Sadier et al., 2011 ;Lacave et al., sous presse). ...
... Ils concernent aussi bien des questions associant préhistoire et géo-morphologie qui s'appuient systématiquement sur des relevés 3D comme à la grotte Chauvet-Pont d'Arc Sadier et al., 2012), à la grotte des Deux Ouvertures (Delannoy et al., 2012 c), à la grotte aux Points, à la grotte des Fraux (Burens et al., 2011), à la grotte des Gorges (Cailhol et Jaillet, 2012) ou en Australie à Nawarla Gabarnamang . Les travaux traitent des salles et galeries comme à Foussoubie ou Midroï Sadier, 2013) ou d'identification d'objets de plus petites dimensions comme les stalagmites (Hajri et al., 2009 ou les stalactites (Chakroun et al., 2009 ;Hajri et al., 2011 ;Perrette et Jaillet, 2010 ;Sadier et al., 2011 ;Lacave et al., sous presse). Certains de ces travaux sont présentés dans le présent chapitre ou dans le cadre des activités de la plateforme CTI3D. ...
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... Finally, the correlation between field observations and quantitative modeling is disputed. Some authors state that high accelerations are needed to break speleothems and that only thin and long concretions can be damaged following seismic shaking due to "reasonably" strong earthquake (3 m s −2 < PGA < 10 m s −2 ) (e.g., Cadorin et al., 2001;Lacave et al., 2000Lacave et al., , 2004Lacave et al., , 2012. Nevertheless, field evidence cannot be neglected and suggests that empirical mechanical relations are possibly lacking for considering some significant parameters and conditions (Delaby, 2001). ...
... Evidence of falls and collapses, moreover, shows that the cave underwent several sudden deformation events (probably of different origin) during its development. Nevertheless, for the Galleria della Devas- tazione branch earthquake-induced damages are difficult to be invoked as the main cause of its present-day configuration, since the strength of the seismic events would have to have been far greater to break such large concretions (e.g., Cadorin et al., 2001;Lacave et al., 2000Lacave et al., , 2004Lacave et al., , 2012. A strong influence, instead, could have been exerted by gravitational processes that possibly caused the floor to sink (Fig. 3e), probably as a consequence of the collapse of a deeper karst network. ...
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A speleoseismological study has been conducted in the Cavallone Cave, located in the easternmost carbonate sector of the Central Apennines (Maiella Massif), in a seismically active region interposed between the post-orogenic extensional domain, to the west, and the contractional one, to the east. The occurrence of active “silent normal faults”, to the west, close to blind thrusts, to the east, raises critical questions about the seismic hazard for this transitional zone. Large collapses of cave ceilings, fractures, broken speleothems with new re-growing stalagmites on their top, preferential orientation of fallen stalagmites and the absence of thin and long concretions have been observed in many portions of the karst conduit. This may indicate that the cave suffered sudden deformation events likely linked to the occurrence of past strong earthquakes. Radiocarbon dating and, above all, the robust correspondence with other coeval on-fault and off-fault geological data collected in surrounding areas outside the cave, provide important constraints for the individuation of a mid-Holocene paleoearthquake around 4.6–4.8 kyr BP. On the basis of the available paleoseismological data, possible seismogenic sources can be identified with the Sulmona normal fault and other active normal fault segments along its southern prosecution, which recorded synchronous strong paleoevents. Although the correlation between speleotectonic observations and quantitative modeling is disputed, studies on possible effects of earthquake on karstic landforms and features, when corroborated by independent data collected outside caves, can provide a useful contribution in discovering past earthquakes.
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  • Apr 2024
  • J ARCHAEOL METHOD TH
The cave of Saint-Marcel is known for its extensive network (64 km of galleries) and its history of human occupation (Middle Palaeolithic and Neolithic) in the entrance area. Close observation of the main network reveals areas with high concentrations of broken speleothems, which are usually attributed to the first tourist visits of the nineteenth century. However, archaeo-geomorphological mapping of the broken speleothems, many of which are lying on the floor and sealed by stalagmite regrowth or crust, indicates intentional organisation of the underground space into speleothem supply zones and zones in which the speleothems were used to build structures. Age estimates of the stalagmite seals on these human-made structures suggest that the structures were a result of human activity that occurred between the end of the Upper Palaeolithic and the European Mesolithic. These age estimates radically change the way we look at the broken speleothems in the cave of Saint-Marcel and the structures associated with them. They bring to light the engagement of past human communities with the deep underground environment, at more than 1.5 km from the cave entrance, which can only be accessed by crossing obstacles (pits) that, today, are considered as difficult to be crossed. Our findings and ongoing research stress the unequivocal archaeological significance of the cave.
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Defining a Mid-Holocene earthquake through speleoseismological and independent data: constraints for the outer Central Apennines (Italy) seismotectonic framework
Article
Full-text available
  • Jun 2016
  • SED
A speleoseismological study has been conducted in the Cavallone Cave, located in the easternmost carbonate sector of the Central Apennines (Maiella Massif), in a seismically active region interposed between the post-orogenic extensional domain, to the west, and the compressional one, to the east. The occurrence of active ''silent normal faults'', to the west, close to blind thrust, to the east, raises critical questions about the identification of the true seismogenic sources for this transitional zone. Large ceiling collapses, fractures, broken speleothems with new re-growing stalagmites on their top, preferential orientation of fallen stalagmites and absence of thin and long concretions have been observed in many portions of the conduit and may indicate that the cave suffered of sudden and catastrophic events likely linked to the occurrence of past strong earthquakes. Although controversies exist about the correlation between speleotectonic observations and quantitative modeling, speleotectonic studies, when corroborated by independent data collected outside caves, can play a fundamental role in discovering past earthquakes. Radiocarbon dating and, above all, the surprisingly correspondence with other coeval paleoseismological and geological data collected in surrounding areas outside the cave, provide important constraints for the individuation of a Mid-Holocene paleoearthquake around 4770 ± 30 yr BP and for the identification of the Sulmona normal fault as the most likely causative structure.
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The Contribution of Palaeoseismology to Seismic Hazard Assessment in Site Evaluation for Nuclear Installations
Technical Report
Full-text available
  • Jun 2015
In the framework of site evaluation/re-evaluation procedures for nuclear power plants and other nuclear installations, this publication aims at encouraging and supporting Member States, especially from newcomer countries, to include paleoseismic investigations into the geologic database. In fact, paleoseismology is not just a crucial discipline for Fault Displacement Hazard Assessment (FDHA) but also an indispensable tool for Seismic Hazard Assessment (SHA), as recommended in the reference IAEA Safety Guide (IAEA SSG-9 [1]). Within this scope, this document provides an updated review of the state of the art of paleoseismology, integrated with practical recommendations addressed to Member States, aiming to emphasize the value of earthquake geology studies for nuclear safety.
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Reconstitution spéléogénique de la grotte de Kanaan (Antélias, Liban). Contribution à la morphogenèse du nahr Antelias
Article
Full-text available
  • Sep 2009
This article is devoted to the speleogenic study of Kanaan cave (Mgharet) (Metn, Lebanon) located on the left bank of the Nahr Antelias’ lower valley, at the north-east of Beirut. The variety of morphologies and present fillings in this cavity allows to trace accurately its speleogenic evolution and, beyond, the geomorphologic evolution of the Mount Lebanon’s western edge intersected by a series of small coastal rivers, such as Nahr Beirut, Antelias and El Kelb. At this prospect is highlighted the approach used in Mgharet Kanaan and the speleogenic study which has been taken from a geomorphological mapping of this endokarst. Geomorphological and geological implications issued from the speleogenic study are developed at the end of this study. It is also an expression of work currently undertaken on certain Lebanese cavities in order to reveal the richness of palaeogeographic and palaeoenvironmental informations contained therein. This work is in close scientific cooperation between the “Association Libanaise d’Etudes Spéléologiques” – ALES, the Department of Geography of St. Joseph University, USJ - Beirut and the EDYTEM Laboratory, Savoie University – France. The map hereunder inserted is the first underground geomorphologic mapping in Lebanon. Other publications will soon give evidence of the current researches in the abyss (Houet) Qattîne Azar and the Jeita cave.
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ETUDE PETROGRAPHIQUE ET GEOCHIMIQUE D'UNE STALAGMITE DE LA GROTTE DE JEITA (LIBAN)
Article
Full-text available
  • Jan 2007
The JeG-stm-1 stalagmite (Jeita, central Lebanon) shows petrographic variations tuned with different rates of growth and stable isotope composition. These may reflect regional variations (e.g. climatic and/or environmental changes) that were probably accentuated by local changes - on shorter periods of time. Three distinct growth periods of the investigated stalagmite are proposed: 1) from 12 to 10ka BP, calcite precipitation close to isotopic equilibrium conditions - δ18O as well as δ13C values deplete along a parallel pattern; 2) from 10 to 6ka BP, humid and hot conditions
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Speleoseismology: A critical perspective
Article
Full-text available
  • Jul 2006
Speleoseismology is the investigation of earthquake records in caves. Traces can be seen in broken speleothems, growth anomalies in speleothems, cave sediment deformation structures, displacements along fractures and bedding plane slip, incasion (rock fall) and co-seismic fault displacements. Where earthquake origins can be proven, these traces constitute important archives of local and even regional earthquake activity. However, other processes that can generate the same or very similar deformation features have to be excluded before cave damage can be interpreted as earthquake induced. Most sensitive and therefore most valuable for the tracing of strong earthquake shocks in caves are long and slender speleothems, such as soda straws, and deposits of well-bedded, water-saturated silty sand infillings, particularly in caves close to the earth's surface. Less easily proven is a co-seismic origin of an incasion and other forms of cave damage. The loads and creep movements of sediment and ice fillings in caves can cause severe damage to speleothems which have been frequently misinterpreted as evidence of earthquakes. For the dating of events in geological archives, it is important to demonstrate that such events happened at approximately the same time, i.e. within the error bars of the dating methods. A robust earthquake explanation for cave damage can only be achieved by the adoption of appropriate methods of direct dating of deformation events in cave archives combined with correlation of events in other geological archives outside caves, such as the deformation of lake and flood-plain deposits, locations of rock falls and active fault displacements.
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Relevés lasergrammétriques et calibration sur calcite de morphologies externes de spéléothèmes pour une étude paléo-sismologique du Liban
Article
  • Jan 2011
Cet article présente les travaux de recherche engagés par le laboratoire Edytem dans le cadre du programme ANR Libris sur la paléo-sismicité du Liban. L'originalité de cette étude est la mesure sur un modèle numérique 3D d'indices paléo-sismiques dans l'endokarst et plus particulièrement dans la morphologie des spéléothèmes. Nous présentons ici la validité de la mesure au Lidar terrestre de tels objets en mettant en place un protocole expérimental spécifique à la calcite rencontrée dans le milieu souterrain. Une évaluation du bruit et des erreurs de mesure sur calcite est proposée. Cependant si la position des objets mesurés n 'est pas satisfaisante, la méthode reste valide pour des mesures géométriques des repousses de stalactites.
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What can be concluded about seismic history from broken and unbroken speleothems?
Article
  • May 2004
  • J EARTHQ ENG
Is it really plausible that earthquakes break speleothems? May unbroken speleothems prove that no strong earthquake has ever occurred during a certain period of time? The mechanical behaviour of speleothems has been investigated through static bending tests performed on stalactites and soda straws. These tests give an indication not only of the mean tensile resistance, but also—more importantly—of its variation. In fact, it is this variation that makes it difficult to estimate the acceleration necessary to break an individual speleothem. That is why a statistical approach is mandatory. The potentially most vulnerable unbroken as well as broken stalactites were measured in a pilot cave (Milandre, Switzerland). Four classes of stalactites were denned, according to their shapes. For each of these classes, a vulnerability curve (probability of breaking as a function of peak ground acceleration) was obtained by means of a Monte Carlo simulation. Dynamic amplification as well as heterogeneity of bending resistance within each speleothem were taken into account. Finally, an original statistical approach, valid for incomplete and imprecise data, was developed. This approach allowed to estimate the probability that at least one moderate earthquake has occurred in the past.
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Benefits of the use of precariously balanced rocks and other fragile geological features for testing the predictions of probabilistic seismic hazard analysis
  • Jan 2011
  • J G Anderson
  • J N Brune
  • M Purvance
  • G Biasi
  • R Anooshehpoor
Anderson J.G., J.N. Brune, M. Purvance, G. Biasi and R. Anooshehpoor (2011). Benefits of the use of precariously balanced rocks and other fragile geological features for testing the predictions of probabilistic seismic hazard analysis. 11 th International Conference on Applications of Statistics and Probability in Civil Engineering. Zürich, Switzerland.
Carte géologique du Liban au 1/200000 avec notice explicative. République Libanaise
  • Jan 1955
  • L Dubertret
Dubertret L. (1955). Carte géologique du Liban au 1/200000 avec notice explicative. République Libanaise, Ministère des Travaux Publics, Beyrouth, 74 p.