71 research outputs found
On the Testing of Ground--Motion Prediction Equations against Small--Magnitude Data
Ground-motion prediction equations (GMPE) are essential in probabilistic
seismic hazard studies for estimating the ground motions generated by the
seismic sources. In low seismicity regions, only weak motions are available in
the lifetime of accelerometric networks, and the equations selected for the
probabilistic studies are usually models established from foreign data.
Although most ground-motion prediction equations have been developed for
magnitudes 5 and above, the minimum magnitude often used in probabilistic
studies in low seismicity regions is smaller. Desaggregations have shown that,
at return periods of engineering interest, magnitudes lower than 5 can be
contributing to the hazard. This paper presents the testing of several GMPEs
selected in current international and national probabilistic projects against
weak motions recorded in France (191 recordings with source-site distances up
to 300km, 3.8\leqMw\leq4.5). The method is based on the loglikelihood value
proposed by Scherbaum et al. (2009). The best fitting models (approximately
2.5\leqLLH\leq3.5) over the whole frequency range are the Cauzzi and Faccioli
(2008), Akkar and Bommer (2010) and Abrahamson and Silva (2008) models. No
significant regional variation of ground motions is highlighted, and the
magnitude scaling could be predominant in the control of ground-motion
amplitudes. Furthermore, we take advantage of a rich Japanese dataset to run
tests on randomly selected low-magnitude subsets, and check that a dataset of
~190 observations, same size as the French dataset, is large enough to obtain
stable LLH estimates. Additionally we perform the tests against larger
magnitudes (5-7) from the Japanese dataset. The ranking of models is partially
modified, indicating a magnitude scaling effect for some of the models, and
showing that extrapolating testing results obtained from low magnitude ranges
to higher magnitude ranges is not straightforward
Toward a ground-motion logic tree for probabilistic seismic hazard assessment in Europe
The Seismic Hazard Harmonization in Europe (SHARE) project, which began in June 2009, aims at establishing new standards for probabilistic seismic hazard assessment in the Euro-Mediterranean region. In this context, a logic tree for ground-motion prediction in Europe has been constructed. Ground-motion prediction equations (GMPEs) and weights have been determined so that the logic tree captures epistemic uncertainty in ground-motion prediction for six different tectonic regimes in Europe. Here we present the strategy that we adopted to build such a logic tree. This strategy has the particularity of combining two complementary and independent approaches: expert judgment and data testing. A set of six experts was asked to weight pre-selected GMPEs while the ability of these GMPEs to predict available data was evaluated with the method of Scherbaum et al. (Bull Seismol Soc Am 99:3234-3247, 2009). Results of both approaches were taken into account to commonly select the smallest set of GMPEs to capture the uncertainty in ground-motion prediction in Europe. For stable continental regions, two models, both from eastern North America, have been selected for shields, and three GMPEs from active shallow crustal regions have been added for continental crust. For subduction zones, four models, all non-European, have been chosen. Finally, for active shallow crustal regions, we selected four models, each of them from a different host region but only two of them were kept for long periods. In most cases, a common agreement has been also reached for the weights. In case of divergence, a sensitivity analysis of the weights on the seismic hazard has been conducted, showing that once the GMPEs have been selected, the associated set of weights has a smaller influence on the hazar
Ătudes de taphonomie archĂ©ologique en milieu pĂ©riglaciaire actuel : le Projet Gavarnie
Un programme dâarchĂ©ologie expĂ©rimentale a Ă©tĂ© initiĂ© en milieu pĂ©riglaciaire actuel. Le site sĂ©lectionnĂ© est localisĂ© dans les PyrĂ©nĂ©es centrales, sur le versant sud du Massif du Taillon, secteur de Gavarnie. Les expĂ©riences entreprises traitent des points suivants : (1) vitesse de dĂ©placement des vestiges et Ă©volution des structures anthropiques â amas de taille â par solifluxion et par reptation sur talus gravitaire ; (2) fragmentation des ossements et altĂ©ration des Ă©tats de surface ; (3) vitesse dâacquisition dâune orientation prĂ©fĂ©rentielle des vestiges lithiques dĂ©placĂ©s par solifluxion ou reptation. AprĂšs un an de fonctionnement, certains paramĂštres contrĂŽlant la nature et la vitesse des modifications peuvent ĂȘtre identifiĂ©s. Pour les ossements, le caractĂšre frais ou sec dĂ©termine les dĂ©placements, tandis que le caractĂšre brĂ»lĂ© / non brĂ»lĂ© apparaĂźt prĂ©Ă©minent par rapport Ă leur fragmentation. Dans le cas des vestiges lithiques dĂ©posĂ©s sur coulĂ©e de solifluxion, les dĂ©placements diffĂšrent selon la disposition initiale des objets â en amas ou dispersĂ©s â. Ces premiers rĂ©sultats permettent de rĂ©examiner la validitĂ© des prĂ©cĂ©dentes expĂ©riences de taphonomie archĂ©ologique en contexte pĂ©riglaciaire.A set of long-term experiments have been initiated in an active periglacial environment. The experimental site is located on the south slope of the Taillon Mountain, near Gavarnie, Spain. Experiments address the following points: 1) the rate of displacement of archaeological particles and the disturbance of archaeological features on solifluction sheets and by creep on rockfall screes; 2) the fragmentation of bones and their surface alteration, with emphasis on cutmark disappearance; 3) the rate of linear fabric acquisition of knapped flint displaced by solifluction or creep. After one year, disturbances are observed. Considering bones, factors responsible for the changes noted are 1) green versus dry nature of items with regard to displacements 2) burnt versus unburnt status in respect of alteration. For lithic assemblage, we observe that initial artifact distribution â in regimented intervals or replicating knapping spot â controls the rate of displacement. This last point is crucial to the application of experimental data to archaeological sites. Previous experiments can be discussed in light of these preliminary results
Etudes de taphonomie archéologique en milieu périglaciaire actuel : le projet Gavarnie.
A set of long-term experiments have been initiated in active periglacial environment. The experimental site is located on the south slope of Taillon Mountain, near Gavarnie, Spain. Experiments address the following points: 1) rate of displacement of archaeological particles and disturbance of archaeological features on solifluction sheet and by creep on rockfall screes; 2) fragmentation of bones and their surface alteration, with emphasis on cutmarks disappearance; 3) the rate of linear fabric acquisition of knapped flint displaced by solifluction or creep. After one year, disturbances are observed. Considering bones, factors responsible for the changes noted are 1) green versus dry nature of items with regard to displacements 2) burnt versus unburnt status in respect of alteration. For lithic assemblage, we observe that initial setting of artifacts - in regimented intervals or replicating knapping spot - controls the rate of displacement. This last point is crucial in the application of experimental data to the application of experimental data to archaeological sites. Previous experiments can be discussed in light of these preliminary results.Un programme d'archĂ©ologie expĂ©rimentale a Ă©tĂ© entrepris en milieu pĂ©riglaciaire actuel. Le site sĂ©lectionnĂ© est localisĂ© dans les PyrĂ©nĂ©es centrales, sur le versant sud du Massif du Taillon, secteur de Gavarnie. Les expĂ©riences entreprises traitent des points suivants : 1) vitesse de dĂ©placement des vestiges et Ă©volution des structures anthropiques - amas de taille - par solifluxion et par reptation sur talus gravitaire ; 2) fragmentation des ossements et altĂ©ration des Ă©tats de surface ; 3) vitesse d'acquisition d'une orientation prĂ©fĂ©rentielle des vestiges lithiques dĂ©placĂ©s par solifluxion ou reptation. AprĂšs un an de fonctionnement, certains paramĂštres contrĂŽlant la nature et la vitesse des modifications peuvent ĂȘtre identifiĂ©s. Pour les ossements, le caractĂšre frais ou sec dĂ©termine les dĂ©placements, tandis que le caractĂšre brĂ»lĂ© / non brĂ»lĂ© apparaĂźt prĂ©Ă©minent par rapport Ă leur fragmentation. Dans le cas des vestiges lithiques dĂ©posĂ©s sur coulĂ©es de solifluxion, les dĂ©placements diffĂšrent selon la disposition initiale des objets - en amas ou dispersĂ©s -. Ces premiers rĂ©sultats permettent de rĂ©examiner la validitĂ© des prĂ©cĂ©dentes expĂ©riences de taphonomie archĂ©ologique en contexte pĂ©riglaciaire
The European Fault-Source Model 2020 (EFSM20): geologic input data for the European Seismic Hazard Model 2020
Earthquake hazard analyses rely on seismogenic source models. These are designed in various fashions, such as point sources or area sources, but the most effective is the three-dimensional representation of geological faults. We here refer to such models as fault sources. This study presents the European Fault-Source Model 2020 (EFSM20), which was one of the primary input datasets of the recently released European Seismic Hazard Model 2020. The EFSM20 compilation was entirely based on reusable data from existing active fault regional compilations that were first blended and harmonized and then augmented by a set of derived parameters. These additional parameters were devised to enable users to formulate earthquake rate forecasts based on a seismic-moment balancing approach. EFSM20 considers two main categories of seismogenic faults: crustal faults and subduction systems, which include the subduction interface and intraslab faults. The compiled dataset covers an area from the Mid-Atlantic Ridge to the Caucasus and from northern Africa to Iceland. It includes 1248 crustal faults spanning a total length of âŒ95â100âkm and four subduction systems, namely the Gibraltar, Calabrian, Hellenic, and Cyprus arcs, for a total length of âŒ2120âkm. The model focuses on an area encompassing a buffer of 300âkm around all European countries (except for Overseas Countries and Territories) and a maximum of 300âkm depth for the subducting slabs. All the parameters required to develop a seismic source model for earthquake hazard analysis were determined for crustal faults and subduction systems. A statistical distribution of relevant seismotectonic parameters, such as faulting mechanisms, slip rates, moment rates, and prospective maximum magnitudes, is presented and discussed to address unsettled points in view of future updates and improvements. The dataset, identified by the DOI https://doi.org/10.13127/efsm20 (Basili et al., 2022), is distributed as machine-readable files using open standards (Open Geospatial Consortium).</p
Analyse des incertitudes dans une estimation probabiliste de l'aléa sismique, exemple de la France
This thesis proposes a new methodology that allows to pinpoint the key parameters that control probabilistic seismic hazard assessment (PSHA) and at the same time to quantify the impact of these parameters uncertainties on hazard estimates. Cornell-McGuire's method is used here. First, uncertainties on magnitude and location determinations are modeled and quantified : resulting variability on hazard estimates ranges between 5% and 25% (=COV), depending on the site and the return period. An impact study is then performed, in order to determine the hierarchy between the impacts on hazard of the choices of four other parameters : intensity-magnitude correlation, minimum and maximum magnitudes, the truncation of the attenuation relationship. The results at 34 Hz (PGA) indicate that the maximum magnitude is the less influent parameter (from 100 to 10000 years) ; whereas the intensity-magnitude correlation and the truncation of ground motion predictions (>2Ÿ) are the controlling parameters at all return periods (up to 30% decrease each at 10000 years). An increase in the minimum magnitude contributing to the hazard, from 3.5 to 4.5, can also produce non-negligible impacts at small return periods (up to 20% decrease of hazard results at 475 years). Finally, the overall variability on hazard estimates due to the combined choices of the four parameters can reach up to 30% (COV, at 34Hz). For lower frequencies (2Ÿ) jouent un rĂŽle clef quelle que soit la pĂ©riode de retour considĂ©rĂ©e (diminution de l'alĂ©a jusqu'Ă 30% Ă 10000 ans). Une augmentation de la magnitude minimale contribuant Ă l'alĂ©a, de 3.5 Ă 4.5, peut Ă©galement produire des impacts non nĂ©gligeables Ă courtes pĂ©riodes de retour (diminution des valeurs d'alĂ©a jusqu'Ă 20% Ă 475 ans). Enfin, la variabilitĂ© totale des estimations d'alĂ©a, due aux choix combinĂ©s des quatre paramĂštres, peut atteindre 30% (COV, Ă 34 Hz). Pour des frĂ©quences plus faibles (<5Hz), la variabilitĂ© totale augmente et la magnitude maximale devient un paramĂštre important. Ainsi, la variabilitĂ© des estimations due aux incertitudes de catalogue et aux choix de ces quatre paramĂštres doit ĂȘtre prise en compte dans toute Ă©tude d'estimation de l'alĂ©a sismique probabiliste en France. Cette variabilitĂ© pourra ĂȘtre rĂ©duite en Ă©laborant une corrĂ©lation intensitĂ©-magnitude plus appropriĂ©e, et en recherchant une maniĂšre plus rĂ©aliste de prendre en compte la dispersion du mouvement du sol
Séisme de Rambervillers du 22 février 2003. Sainte-HélÚne. Fort endommagement sur mur en moellons bruts
The magnitude 5.4 Ml earthquake that occurred west of Saint-DiĂ©-des-Vosges (48.34°N; 6.66°E) on Saturday 22 February 2003 at 21:41 hrs was followed by numerous aftershocks, including one of magnitude 3.4 Ml less than a quarter of an hour later (21:54 hrs), one of magnitude 3.1 Ml the next morning (5:54 hrs) and a total of six of magnitude Ml > 3. This earthquake did not cause any casualties or significant damage, except for a few chimney falls, cracks in the walls and the weakening of buildings. It was felt very widely outside the Vosges and the Rhine Ditch, as far as Lyon and Paris. The last major earthquake known in the region had reached the magnitude of 4.8 Ml in 1984 (Haessler and Hoang, 1985). In the commune of Sainte-HĂ©lĂšne, 80% of the buildings are of vulnerability A (rubble, dry stones) and 20% of vulnerability B (masonry, agglo). Fine or superficial cracks were found in large numbers on load-bearing and non-load-bearing structures. 70 damage reports were received from old houses and 10 from houses less than 30 years old. One wall of the façade of the municipal workshop was largely dissociated from the other parts of the structure (degree 3). Wide cracks were also found in large numbers throughout the municipality. This photo was taken during the on-site mission of the Macro-seismic Intervention Group from 26 February to 3 March 2003. The group was made up of members from BCSF-RENASS, BRGM and IRSN. It shows a rubble-stone type wall which showed a failure (degree 4 indication on the EMS98 measurement scale)Le seÌisme de magnitude 5.4 Ml qui sâest produit aÌ lâouest de Saint-DieÌ-des-Vosges (48.34°N ; 6.66°E) le samedi 22 feÌvrier 2003 aÌ 21H41 a eÌteÌ suivi de nombreuses reÌpliques, dont l'une de magnitude 3.4 Ml moins dâun quart dâheure apreÌs (21H54), une de magnitude 3.1 Ml le lendemain matin (5H54) et au total six de magnitude Ml > 3. Ce seÌisme nâa pas causeÌ de victime ni de deÌgĂąts importants, hormis quelques chutes de chemineÌes, des fissures dans les murs et la fragilisation dâeÌdifices. Il a eÌteÌ ressenti treÌs largement en dehors des Vosges et du FosseÌ RheÌnan, jusquâaÌ Lyon et Paris. Le dernier seÌisme important connu dans la reÌgion avait atteint la magnitude de 4.8 Ml en 1984 (Haessler et Hoang, 1985). Dans la commune de Sainte-HĂ©lĂšne, 80% des baÌtiments sont de vulneÌrabiliteÌ A (moellons, pierres seÌches) et 20% de vulneÌrabiliteÌ B (maçonnerie, agglo). Des fissures fines ou superficielles ont eÌteÌ retrouveÌes en grand nombre sur les structures porteuses et non porteuses. 70 deÌclarations de deÌgaÌts sont issues des maisons anciennes et 10 de maisons de moins de 30 ans. Un mur de la façade de l'atelier municipal s'est largement deÌsolidariseÌ des autres parties de la structure (degreÌ 3). Des fissures larges ont eÌteÌ eÌgalement releveÌes en grand nombre sur la commune. Cette photo a Ă©tĂ© prise lors de la mission sur place du Groupe d'intervention macrosismique du 26 fĂ©vrier au 3 mars 2003. Le groupe Ă©tait composĂ© de membres du BCSF-RENASS, du BRGM et de l'IRSN. Elle montre un mur de type moellon qui a montreÌ une deÌfaillance (indication de degreÌ 4 sur l'Ă©chelle de mesure EMS98
Séisme de Rambervillers du 22 février 2003. Sainte-HélÚne. Endommagement de l'église
The 5.4 Ml earthquake that occurred west of Saint-DiĂ©-des-Vosges (48.34°N ; 6.66°E) on Saturday, February 22, 2003 at 21H41 was followed by many aftershocks, including one of magnitude 3.4 Ml less than a quarter of an hour later (21H54), one of magnitude 3.1 Ml the next morning (5H54) and a total of six of magnitude Ml > 3. The earthquake did not cause any casualties or major damage, except for a few falls of chimneys, cracks in the walls and the weakening of buildings. It was felt very widely outside the Vosges and the Rhine Ditch, as far as Lyon and Paris. The last known major earthquake in the region reached 4.8 Ml in 1984 (Haessler and Hoang, 1985). This photo was taken during the Macroseismic Response Group's on-site mission from February 26 to March 3, 2003. The group was composed of members of BCSF-RENASS, BRGM and IRSN. It shows the cracking of the church bell tower and the plateau effect on the roof. The slenderness ratio is an important element in shock resistance. The church of St Helena, like some churches in the epicentral region, has experienced a large crack in its bell tower. We can highlight here a weakness of its design in the opening on a false duplicator. It has also undergone a "spin effect" or "plateau effect" with rotation around the axis of the bell tower.Le seÌisme de magnitude 5.4 Ml qui sâest produit aÌ lâouest de Saint-DieÌ-des-Vosges (48.34°N ; 6.66°E) le samedi 22 feÌvrier 2003 aÌ 21H41 a eÌteÌ suivi de nombreuses reÌpliques, dont l'une de magnitude 3.4 Ml moins dâun quart dâheure apreÌs (21H54), une de magnitude 3.1 Ml le lendemain matin (5H54) et au total six de magnitude Ml > 3. Ce seÌisme nâa pas causeÌ de victime ni de deÌgĂąts importants, hormis quelques chutes de chemineÌes, des fissures dans les murs et la fragilisation dâeÌdifices. Il a eÌteÌ ressenti treÌs largement en dehors des Vosges et du FosseÌ RheÌnan, jusquâaÌ Lyon et Paris. Le dernier seÌisme important connu dans la reÌgion avait atteint la magnitude de 4.8 Ml en 1984 (Haessler et Hoang, 1985). Cette photo a Ă©tĂ© prise lors de la mission sur place du Groupe d'intervention macrosismique du 26 fĂ©vrier au 3 mars 2003. Le groupe Ă©tait composĂ© de membres du BCSF-RENASS, du BRGM et de l'IRSN. Elle montre la fissuration du clocher de l'Ă©glise et l'effet de plateau sur la toiture. Le rapport Ă l'Ă©lancement est un Ă©lĂ©ment important dans la rĂ©sistance Ă la secousse. L'Ă©glise de Sainte-HĂ©lĂšne, comme quleques Ă©glises de la rĂ©gion Ă©picentrale, a connu une fissuration large de son clocher. On peut souligner ici une faiblesse de sa conception dans l'ouverture sur un faux doubleau. Celle-ci a subi par ailleurs "un effet de vrille" ou "effet de plateau" avec rotation autour de l'axe du clocher
SĂ©isme Ă la Martinique. 29 novembre 2007. Fonds Saint Denis. Fissuration du clocher
Cracking of the bell tower of the church of Saint-Denis following the earthquake of November 29, 2007, on the masonry part as well as on the structure (concrete beam above the vault). Cracks were also found inside the bell tower. The damage is level 2.This picture was taken during the field mission that took place from December 5 to 11 following the earthquake of November 29, 2007 in Martinique. This earthquake was of magnitude 7.4 (MW), its epicenter being located in the north of the island, at sea. Fonds Saint Denis is located 25km from the epicenter and the intensity of the tremors felt is V on the European intensitĂ©Ì EMS-98 scale. Martinique is, with Guadeloupe, classified in seismicity zone III (decree n°2007-1467 of October 12, 2007) which is the highest level of seismic hazard for the French territory. From the point of view of intensities, with a maximum intensity of VI-VII, the earthquake of November 29, 2007 is the most important one felt in Martinique since the earthquake of June 8, 1999 (intensity VII). Macro-seismic intensity reached (in order of distance from the epicenter) VI-VII in the communes of Sainte-Marie, La TrinitĂ©, Fort-de-France, Le François, Trois Ilets, Le Marin and Sainte-Anne. The analysis of this earthquake mobilized many people, research laboratories and technical centers. The French Central Seismological Office has prepared a report based on the data processed by the Volcanological and Seismological Observatory of Martinique of the IPGP. The macro-seismic data were collected thanks to the survey forms distributed to the town halls and gendarmerie services by the SIDPC of the prefectures of Martinique and Guadeloupe, thanks to the testimonies filed on the BCSF website and thanks to the information collected during the BCSF field survey that took place from December 5 to 11, 2007. The BCSF's mission is to collect data on the earthquakes felt in France, to gather useful information and to facilitate its dissemination to the actors concerned by the seismic risk or conducting studies or research requiring the use of these observations. It is a member of the Transversal Seismicity Action of the RĂ©sif research infrastructure (French Seismological and Geodetic Network).Fissuration du clocher de l'Ă©glise de Saint-Denis suite au sĂ©isme du 29 novembre 2007, sur la partie maçonnĂ©e ainsi que sur la structure (poutre bĂ©ton au-dessus de la voĂ»te). Des fissures ont Ă©galement Ă©tĂ© constatĂ©es Ă lâintĂ©rieur du clocher. Les dommages sont de niveau 2.Cette photo a Ă©tĂ© prise lors de la mission de terrain qui s'est dĂ©roulĂ©e du 5 au 11 dĂ©cembre suite au sĂ©isme du 29 novembre 2007 Ă la Martinique. Ce sĂ©isme Ă©tait de magnitude 7.4 (MW), son Ă©picentre se situant au nord de lâĂźle, en mer. Fonds Saint Denis se situe Ă 25km de lâĂ©picentre et lâintensitĂ© des secousses ressenties est de V sur lâĂ©chelle dâintensitĂ©Ì europĂ©enne EMS-98. La Martinique est, avec la Guadeloupe, classĂ©e en zone de sismicitĂ© III (dĂ©cret n°2007-1467 du 12 octobre 2007) qui est le niveau d'alĂ©a sismique le plus Ă©levĂ© pour le territoire français. Du point de vue des intensitĂ©s, avec une intensitĂ© maximale de VI-VII, le sĂ©isme du 29 novembre 2007 est le plus important ressenti en Martinique depuis le sĂ©isme du 8 juin 1999 (intensitĂ© VII). LâintensitĂ© macrosismique a atteint (par ordre de distance aÌ l'Ă©picentre) VI-VII dans les communes de Sainte-Marie, La TrinitĂ©, Fort-de-France, Le François, Trois Ilets, le Marin et Sainte-Anne. Lâanalyse de ce sĂ©isme a mobilisĂ© de nombreuses personnes, laboratoires de recherche et centres techniques. Le Bureau Central Sismologique Français a Ă©laborĂ© un rapport qui sâest appuyĂ© sur les donnĂ©es traitĂ©es par lâObservatoire Volcanologique et Sismologique de Martinique de lâIPGP. Les donnĂ©es macrosismiques ont Ă©tĂ© collectĂ©es grĂące aux formulaires dâenquĂȘte distribuĂ©s auprĂšs des mairies et des services de gendarmerie par le SIDPC des prĂ©fectures de Martinique et de Guadeloupe, grĂące aux tĂ©moignages dĂ©posĂ©s sur le site Internet du BCSF et grĂące aux informations recueillies lors de lâenquĂȘte BCSF sur le terrain qui s'est dĂ©roulĂ©e du 5 au 11 dĂ©cembre 2007. Le BCSF a pour mission de collecter les donnĂ©es sur les sĂ©ismes ressentis en France, de rassembler les informations utiles et de faciliter leur diffusion vers les acteurs concernĂ©s par le risque sismique ou menant des Ă©tudes ou recherches nĂ©cessitant lâusage de ces observations. Il est membre de lâAction transverse sismicitĂ© de lâinfrastructure de recherche RĂ©sif (RĂ©seau sismologique et gĂ©odĂ©sique français)
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