Éditeur(s) : HAL CCSD
Résumé : Spatial variability of ground motion may be explained by local soil conditions; it is the so-called "site effects". Site effects are responsible for increasing duration and important amplification of strong ground motion during earthquakes and must be considered as a key parameter in local seismic hazard assessment. French West Indies are prone to strong site effects because of a particular geology, characterized by soft soil deposits and strong alteration of volcanic deposits. In this framework, and considering that French West Indies are considered as a high seismicity level zone in the French building code, part of seismic hazard mitigation policy consists in technical studies to perform identification and mapping of zones characterized by homogeneous seismic response and quantification of associated ground motion. It is the aim of seismic microzonations. In this presentation, we will expose the methodology used on the scale of municipalities for mapping homogeneous seismic areas, based on a study of geological and geotechnical conditions and some geophysical testings. Then, a study of vulnerability of buildings allows to estimate the probability of damage on various sectors for a scenario of risk corresponding to the seismic microzonation.
19ème Conférence Géologique de la Caraïbe
Le Gosier, Guadeloupe, France

hal-00614300
https://hal-brgm.archives-ouvertes.fr/hal-00614300

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Tarim and Junggar basins in central Asia are capped by a thick pile of conglomerates, called the Xiyu Formation, that are commonly linked to a change in climate and/or accelerated uplift near the Plio-Pleistocene boundary. In order to better understand their origin and significance, we carried out a combined structural and magnetostratigraphic study in the Quilitage syncline (southern Tianshan), where the base of the Xiyu conglomerates is observed at both sides of the syncline. A balanced cross-section shows that, even at a local-scale, the base of the Xiyu conglomerates cannot be regarded as a single continuous stratigraphic layer. On the southern flank of the Quilitage syncline, we collected 172 samples collected for magnetostratigraphic dating identify 17 polarity chrons that date the new section from 5.2 to ~ 1.7 Ma and constrain the base of the Xiyu conglomerate here at ~ 1.7 Ma. This is 4.2 Ma younger than the age of the Xiyu previously found on the northern limb of the same syncline. Together with other magnetostratigraphic studies carried out around the Tianshan, our study unambiguously demonstrates that the onset of deposition of the Xiyu conglomerates is diachronous, and that the conglomerates are systematically younger toward the basin. Consequently, the Xiyu Formation should not be considered as a chronostratigraphic marker related to any particular tectonic or climatic event, but is instead a prograding gravel wedge that has prograded over the underthrusting forelands. A synthesis of chronologic and structural results yields progradation rates over the last 10 Ma on the order of ~ 2.0 mm/yr and ~ 3.9 mm/yr south and north of the Tianshan Mountains respectively. These rates are comparable to the shortening rate across the Tianshan range, suggesting that underthrusting is the main factor governing the progradation rate of the Xiyu Formation.
ISSN: 0012-821X

insu-00414151
https://hal-insu.archives-ouvertes.fr/insu-00414151
https://hal-insu.archives-ouvertes.fr/insu-00414151/document
https://hal-insu.archives-ouvertes.fr/insu-00414151/file/Charreau-EPSL-2009.pdf
DOI : 10.1016/j.epsl.2009.07.035