Paleoseismic History of the Dead Sea Fault Zone

International audienceThe aim of this entry is to describe the DSF as a transform plate boundary pointing out the rate of activedeformation, fault segmentation, and geometrical complexities as a control of earthquake ruptures. Thedistribution of large historical earthquakes from a revisited seismicity catalogue using detailedmacroseismic maps allows the correlation between the location of past earthquakes and fault segments.The recent results of paleoearthquake investigations (paleoseismic and archeoseismic) with a recurrenceinterval of large events and long-term slip rate are presented and discussed along with the identification ofseismic gaps along the fault. Finally, the implications for the seismic hazard assessment are also discussed

Blind Thrusting, Surface Folding and the Development of Geological Structure in the Mw 6.3 2015 Pishan (China) Earthquake

The relationship between individual earthquakes and the longer-term growth of topography and of geological structures is not fully understood, but is key to our ability to make use of topographic and geological datasets in the contexts of seismic hazard and wider-scale tectonics. Here we investigate those relationships at an active fold-and-thrust belt in the southwest Tarim Basin, Central Asia. We use seismic waveforms and interferometric synthetic aperture radar (InSAR) to determine the fault parameters and slip distribution of the 2015 Mw 6.3 Pishan earthquake - a blind, reverse-faulting event dipping towards the Tibetan Plateau. Our earthquake mechanism and location correspond closely to a fault mapped independently by seismic reflection, indicating that the earthquake was on a pre-existing ramp fault over a depth range of ˜9–13 km. However, the geometry of folding in the overlying fluvial terraces cannot be fully explained by repeated coseismic slip in events such as the 2015 earthquake nor by the early postseismic motion shown in our interferograms; a key role in growth of the topography must be played by other mechanisms. The earthquake occurred at the Tarim-Tibet boundary, with the unusually low dip of 21° . We use our source models from Pishan and a 2012 event to argue that the Tarim Basin crust deforms only by brittle failure on faults whose effective coefficient of friction is ≤0.05±0.025. In contrast, most of the Tibetan crust undergoes ductile deformation, with a viscosity of order 10²⁰–10²² Pa s. This contrast in rheologies provides an explanation for the low dip of the earthquake fault plane

5000 yr of paleoseismicity along the southern Dead Sea fault

International audienceS U M M A R Y The 1000-km-long left-lateral Dead Sea fault is a major tectonic structure of the oriental Mediterranean basin, bounding the Arabian Plate to the west. The fault is located in a region with an exceptionally long and rich historical record, allowing to document historical seismicity catalogues with unprecedented level of details. However, if the earthquake time series is well documented, location and lateral extent of past earthquakes remain often difficult to establish, if only based on historical testimonies. We excavated a palaeoseismic trench in a site located in a kilometre-size extensional jog, south of the Dead Sea, in the Wadi Araba. Based on the stratigraphy exposed in the trench, we present evidence for nine earthquakes that produced surface ruptures during a time period spanning 5000 yr. Abundance of datable material allows us to tie the five most recent events to historical earthquakes with little ambiguities, and to constrain the possible location of these historical earthquakes. The events identified at our site are the 1458 C.E., 1212 C.E., 1068 C.E., one event during the 8th century crisis, and the 363 C.E. earthquake. Four other events are also identified, which correlation with historical events remains more speculative. The magnitude of earthquakes is difficult to assess based on evidence at one site only. The deformation observed in the excavation, however, allows discriminating between two classes of events that produced vertical deformation with one order of amplitude difference, suggesting that we could distinguish earthquakes that started/stopped at our site from earthquakes that potentially ruptured most of the Wadi Araba fault. The time distribution of earthquakes during the past 5000 yr is uneven. The early period shows little activity with return interval of ∼500 yr or longer. It is followed by a ∼1500-yr-long period with more frequent events, about every 200 yr. Then, for the past ∼550 yr, the fault has switched back to a quieter mode with no significant earthquake along the entire southern part of the Dead Sea fault, between the Dead Sea and the Gulf of Aqaba. We computed the Coefficient of Variation for our site and three other sites along the Dead Sea fault, south of Lebanon, to compare time distribution of earthquakes at different locations along the fault. With one exception at a site located next to Lake Tiberias, the three other sites are consistent to show some temporal clustering at the scale of few thousands years

Fluvial styles during fold growth: An example from the eastern segment of the Qiulitage and Yakeng folds, southern Tian Shan, China

International audienceGeomorphological evidence provides significant information on the processes that govern lateral propagation of a growing active anticline. Within actively developing fold-and-thrust belts evidence can be recorded in Quaternary landforms and the drainage network. In the Kuqa fold-and-thrust belt (KFTB), located in the southern foothills of the Tian Shan mountains, we investigate the topographic and fluvial geomorphic records of the eastern part of the Qiulitage and of the Yakeng anticlines. In this study, using a morphometric approach, including the analysis of anomalies in the spatial patterns of river channels, topographic profiles along anticline crests, and the geometry of wind gaps, we speculate on the lateral propagation of these folds. We extract the drainage network related to the growth of the Yakeng and Qiulitage folds from the beginning onset of the folding (5.5 Ma ago) to its acceleration in the Late Quaternary. We examine 15 rivers and their catchments crossing the eastern segment of Qiulitage and the Yakeng anticlines.Our results demonstrate how the ridges along the eastern segment of Qiulitage and Yakeng folds feature (1) an anticline ridge with decreasing relief from the topographic crest to the plunging ends of the ridges, (2) alternating wind gaps and water gaps from west to east, (3) a drainage system closely controlled by folding and differential uplift, (4) a decrease in drainage basin maturity towards the east only, and (5) fluvial features that provide age constraints. We then document the evolution of the drainage network and provide insights on the growth history of the eastern Kuqa fold-and-thrust belt from its nucleation to its growth acceleration. The connections between the topography and the drainage allow us to present an integrated model that could explain their lateral and vertical fold growth along the two folds along their leading edges

Croissance du pli de Qiulitagh au front sud de la chaîne plissée de Kuqa, Tian Shan, Chine

International audienc

Croissance du pli de Qiulitagh au front sud de la chaîne plissée de Kuqa, Tian Shan, Chine

International audienc

The 20 years technical and socio-economic Evian experience conciliating groundwater quality preservation, collective responsibility for environment protection and local development, and its transposition to other Danone water resources in the world.

National audienc

Editorial: Active Fold-and-Thrust Belts: From Present-Day Deformation to Structural Architecture and Modelling

(IF 3.66; Q1)International audienc

Editorial: Active Fold-and-Thrust Belts: From Present-Day Deformation to Structural Architecture and Modelling

(IF 3.66; Q1)International audienc

Structure and Deformation History of the Rapidly Growing Tainan Anticline at the Deformation Front of the Taiwan Mountain Belt

International audienceThis study aims at further documenting the mechanisms of shortening at the front of fold-and-thrust belts. We focus on an actively growing anticline located at the deformation front of the Taiwan fold-and-thrust belt. Based on a multidisciplinary approach combining mainly subsurface data and geodetic techniques, we show that the Tainan anticline is a pure-shear fault-bend fold growing above a 38-45° west dipping back thrust, the Houchiali fault, rooted on a 3.8-km-deep detachment. The cumulative shortening is estimated at 2-3 km since 310 ± 50 ka, including 30-50% of horizontal compaction shortening. The significance of the fold is little in terms of total shortening at the scale of the mountain piedmont, yet the Holocene shortening rate of 10.3 ± 1.0 mm/a accounts for 25% of the present-day shortening rate across the piedmont. Earthquake scaling relationships applied to the Houchiali fault predict Mw 6 earthquakes that would occur a lot more frequently than indicated from historical earthquake catalogs. Hence, the aseismic slip behavior observed from geodetic measurements since two decades is a representative behavior of the fault at least at the scale of a few centuries. Our results bear out the dominance of pure-shear folding at the front of fold-and-thrust belts and support horizontal compaction as a significant shortening mechanism. In contrast, the back thrust wedge structure and the aseismic slip are peculiar characteristics that likely arise from the combination of low friction and high-pore pressure related to the thick mudstone formation hosting the wedge and of high syntectonic sedimentation rates