HR: 11:35h
AN: T42B-06    [Abstracts]
TI: Deciphering the Paleoseismic History of the Yammouneh Fault (Lebanon)
AU: Sursock, A
EM: asursock@cnrs.edu.lb
AF: National Council for Scientific Research, P.O.Box 11-8281 Riad el-Solh, Beirut, 1107-2260, Lebanon
AU: * Le Beon, M
EM: lebeon@ipgp.jussieu.fr
AF: IPGP, Equipe de Tectonique, 4 Place Jussieu Box 89, Paris cedex 05, 75252, France
AU: Klinger, Y
EM: klinger@ipgp.jussieu.fr
AF: IPGP, Equipe de Tectonique, 4 Place Jussieu Box 89, Paris cedex 05, 75252, France
AU: Daeron, M
EM: daeron@gps.caltech.edu
AF: Caltech, MC 100-23, Pasadena, CA 91125, United States
AU: Tapponnier, P
EM: tappon@ipgp.jussieu.fr
AF: IPGP, Equipe de Tectonique, 4 Place Jussieu Box 89, Paris cedex 05, 75252, France
AU: Elias, A
EM: elias@ipgp.jussieu.fr
AF: National Council for Scientific Research, P.O.Box 11-8281 Riad el-Solh, Beirut, 1107-2260, Lebanon
AU: Jomaa, R
EM: geophys@cnrs.edu.lb
AF: National Council for Scientific Research, P.O.Box 11-8281 Riad el-Solh, Beirut, 1107-2260, Lebanon
AB: North of the Hula basin, the main branch of the 1000 km-long Dead Sea transform veers eastwards, forming a 160 km-long restraining bend responsible for the uplift of Mount Lebanon. The corresponding transpression is partitioned between the offshore Mount Lebanon Thrust and the Yammouneh fault, whose Late-Pleistocene- Holocene slip rate has been estimated to be 5.1 +/- 1.3 mm/yr from offset alluvial fans. Paleoseismic trenches in the Yammouneh basin have shown that the fault produces large earthquakes (M > 7) with a recurrence time of 1127 +/- 135 years, and that the last such event occurred in AD 1202. The new study we present here is from a trench in the Jbab el-Homr basin, 20 km north of Yammouneh. The chief goal is to compare the succession of events at both sites, to obtain evidence for simultaneous or asynchronous earthquake rupture, a key question to assess seismic hazard in Lebanon. The 4 m-deep trench reveals a succession of very thin palustrine and lacustrine layers, ruptured by 10 to 12 earthquakes. Given the dearth of radiocarbon dates, we rely for now on regional paleoclimatic variations to infer a tentative stratigraphic chronology. We identify cycles that might correspond to a solar cycle of 1500 years, but the most striking features are yearly varves that likely formed when a permanent lake flooded the basin. This episode may be correlated with the Early Holocene Climatic Optimum, from 9.8 to 6.8 ka B.P., a particularly humid period recorded by various proxies in the Middle-East, during which the Yammouneh lake level was also high. Based on such a correlation, 9 earthquakes would have occurred at Jbab el-Homr in the last 9.8 ka, providing a recurrence interval of about 1100 years, in keeping with paleoseismic results at Yammouneh. Sedimentological and chemical analyses are in progress to try to date at least a few of these earthquakes.
DE: 3344 Paleoclimatology (0473, 4900)
DE: 8036 Paleoseismology (7221)
DE: 8111 Continental tectonics: strike-slip and transform
SC: Tectonophysics [T]
MN: 2007 Fall Meeting