Co-seismic deformation during the M_w 7.3 Aqaba earthquake (1995) from ERS-SAR interferometry

The M_w 7.3 1995 Aqaba earthquake is the largest instrumental earthquake along the Dead Sea Fault. We complement previous seismological studies by analyzing co‐seismic ground displacement from differential interferometry computed from ERS images spanning 3 different areas. They are compared with a synthetic model derived from seismological study. Only far‐field deformation related to the main sub‐event could be revealed because the near‐field area lies within the gulf. The interferometric data imply a 56 km long and 10 km wide fault segment, connecting the Elat Deep to the Aragonese Deep, which strikes N195°E and dips 65° to the west, with 2.1 m left‐lateral slip and a 15.5° rake indicating a slight normal component. The geodetic moment compares well with the seismic momen

Co-Registration of Optically Sensed Images and Correlation (COSI-Corr): an Operational Methodology for Ground Deformation Measurements

Recent methodological progress, Co-Registration of Optically Sensed Images and Correlation, outlined here, makes it possible to measure horizontal ground deformation from optical images on an operational basis, using the COSI-Corr software package. In particular, its sub-pixel capabilities allow for accurate mapping of surface ruptures and measurement of co-seismic offsets. We retrieved the fault rupture of the 2005 Mw 7.6 Kashmir earthquake from ASTER images, and we also present a dense mapping of the 1992 Mw 7.3 Landers earthquake of California, from the mosaicking of 30 pairs of aerial images

Inference of Multiple Earthquake-Cycle Relaxation Timescales from Irregular Geodetic Sampling of Interseismic Deformation

Characterizing surface deformation throughout a full earthquake cycle is a challenge due to the lack of high‐resolution geodetic observations of duration comparable to that of characteristic earthquake recurrence intervals (250–10,000 years). Here we approach this problem by comparing long‐term geologic slip rates with geodetically derived fault slip rates by sampling only a short fraction (0.001%–0.1%) of a complete earthquake cycle along 15 continental strike‐slip faults. Geodetic observations provide snapshots of surface deformation from different times through the earthquake cycle. The timing of the last earthquake on many of these faults is poorly known, and may vary greatly from fault to fault. Assuming that the underlying mechanics of the seismic cycle are similar for all faults, geodetic observations from different faults may be interpreted as samples over a significantly larger fraction of the earthquake cycle than could be obtained from the geodetic record along any one fault alone. As an ensemble, we find that geologically and geodetically inferred slip rates agree well with a linear relation of 0.94±0.09. To simultaneously explain both the ensemble agreement between geologic and geodetic slip‐rate estimates with observations of rapid postseismic deformation, we consider the predictions from simple two‐layer earthquake‐cycle models with both Maxwell and Burgers viscoelastic rheologies. We find that a two‐layer Burgers model, with two relaxation timescales, is consistent with observations of deformation throughout the earthquake cycle, whereas the widely used two‐layer Maxwell model with a single relaxation timescale, is not, suggesting that the earthquake cycle is effectively characterized by a largely stress‐recoverable rapid postseismic stage and a much more slowly varying interseismic stage.Earth and Planetary Science

Off-fault Damage Patterns Due to Supershear Ruptures with Application to the 2001 Mw 8.1 Kokoxili (Kunlun) Tibet Earthquake

We extend a model of a two-dimensional self-healing slip pulse, propagating dynamically in steady state with slip-weakening failure criterion, to the supershear regime in order to study the off-fault stressing induced by such a slip pulse and investigate features unique to the supershear range. Specifically, we show that there exists a nonattenuating stress field behind the Mach front that radiates high stresses arbitrarily far from the fault (practically this would be limited to distances comparable to the depth of the seismogenic zone), thus being capable of creating fresh damage or inducing Coulomb failure in known structures at large distances away from the main fault. We allow for both strike-slip and dip-slip failure induced by such a slip pulse. We show that off-fault damage is controlled by the speed of the slip-pulse, scaled stress drop, and principal stress orientation of the prestress field. We apply this model to study damage features induced during the 2001 Kokoxili (Kunlun) event in Tibet, for which it has been suggested that much of the rupture was supershear. We argue that an interval of simultaneous induced normal faulting is more likely due to a slip partitioning mechanism suggested previously than to the special features of supershear rupture. However, those features do provide an explanation for otherwise anomalous ground cracking at several kilometers from the main fault. We also make some estimates of fracture energy which, for a given net slip and dynamic stress drop, is lower than for a sub-Rayleigh slip pulse because part of the energy fed by the far-field stress is radiated back along the Mach fronts.Earth and Planetary SciencesEngineering and Applied Science

Roughness of fault surfaces over nine decades of length scales

International audienc

Millennial Recurrence of Large Earthquakes on the Haiyuan Fault near Songshan, Gansu Province, China

International audienceThe Haiyuan fault is a major active left-lateral fault along the northeast edge of the Tibet-Qinghai Plateau. Studying this fault is important in understanding current deformation of the plateau and the mechanics of continental deformation in general. Previous studies have mostly focused on the slip rate of the fault. Paleo-seismic investigations on the fault are sparse, and have been targeted mostly at the stretch of the fault that ruptured in the 1920 M ϳ8.6 earthquake in Ningxia Province. To investigate the millennial seismic history of the western Haiyuan fault, we opened two trenches in a small pull-apart basin near Songshan, in Gansu Province. The excavation exposes sedimentary layers of alternating colors: dark brown silty to clayey deposit and light yellowish brown layers of coarser-grained sandy deposit. The main fault zone is readily recognizable by the disruption and tilting of the layers. Six paleoseismic events are identified and named SS1 through SS6, from youngest to oldest. Charcoal is abundant, yet generally tiny in the shallowest parts of the trench exposures. Thirteen samples were dated to constrain the ages of paleoseismic events. All six events have occurred during the past 3500–3900 years. The horizontal offsets associated with these events are poorly known. However, events SS3 to SS6 appear to be large ones, judging from comparison of vertical separations and widths of fault zones. The youngest event SS1 instead seems to be a minor one, probably the 1990 M w 5.8 earthquake. Thus, four large events in 3500–3900 years would imply a recurrence interval of about 1000 years. Three events SS2 to SS4 prior to 1990 occurred sometime during 1440–1640 A.D., shortly after 890–1000 A.D. and 0–410 A.D., respectively. We tentatively associate them with the 1514 A.D., 1092 A.D., and 143 or 374 A.D. historical earthquakes. Taking 10 ‫ע‬ 2 m of slip for large events (SS3 and SS4), comparable to the 1920 M Ͼ8 Haiyuan earthquake, their occurrence times would be consistent with the long-term 12 ‫ע‬ 4 mm/yr estimate of Lasserre et al. (1999). However, a more realistic evaluation of slip rate and its possible change with time requires a more rigorous determination of coseismic slip amounts of past earthquakes

Bathymetry and uplift rate of the Gulf of Aqaba, Dead Sea Fault.

peer reviewedInitially described in the late 50"s, the Dead Sea Fault system connects at its southern end to the Red Sea extensive system, through a succession of left-stepping faults. In this region, the left-lateral differential displacement of the Arabian plate with respect to the Sinai micro-plate along the Dead Sea fault results in the formation of a depression corresponding to the Gulf Aqaba. We acquired new bathymetric data in the areas of the Gulf of Aqaba and Strait of Tiran during two marine campaigns (June 2018, September 2019) in order to investigate the location of the active faults, which structure and control the morphology of the area. The high-resolution datasets (10-m posting) allow us to present a new fault map of the gulf and to discuss the seismic potential of the main active faults.We also investigated the eastern margin of the Gulf of Aqaba and Tiran island to assess the vertical uplift rate. To do so, we computed high-resolution topographic data and we processed new series of U-Th analyses on corals from the uplifted marine terraces.Combining our results with previous studies, we determined the local and the regional uplift in the area of the Gulf of Aqaba and Strait of Tiran.Eventually, we discussed the tectonic evolution of the gulf since the last major change of the tectonic regime and we propose a revised tectonic evolution model of the area

Three dimensional surface displacement of the Sichuan earthquake (Mw 7.9, China) from Synthetic Aperture Radar

International audienceThe Sichuan earthquake, Mw 7.9, struck the Longmen Shan range front, in the western Sichuan province, China, on 12 May 2008. It severely affected an area where little historical seismicity and little or no significant active shortening were reported before the earthquake (e.g. Gu et al., 1989; Chen et al., 1994; Gan et al., 2007). The Longmen Shan thrust system bounds the eastern margin of the Tibetan plateau and is considered as a transpressive zone since Triassic time that was reactivated during the India-Asia collision (e.g., Tapponnier and Molnar, 1977, Chen andWilson 1996; Arne et al., 1997, Godard et al., 2009). However, contrasting geological evidences of sparse thrusting and marked dextral strike-slip faulting during the Quaternary along with high topography (Burchfiel et al., 1995; Densmore et al., 2007) have led to models of dynamically driven and sustained topography (Royden et al., 1997) limiting the role of earthquakes in relief building and leaving the mechanism of long term strain distribution in this area as an open question. Here we combine C and L band Synthetic Aperture Radar (SAR) offsets data from ascending and descending paths to retrieve the three dimensional surface displacement distribution all along the earthquake ruptures of the Sichuan earthquake. For the first time on this earthquake we present near field 3D co-seismic surface displacement, which is an important datum for constraining modelled fault geometry at depth. Our results complement other Interferometric Synthetic Aperture Radar (InSAR) and field analyses in indicating that crustal shortening is one of the main drivers for topography building in the Longmen Shan (Liu-Zeng, 2009; Shen et al., 2009; Hubbard and Shaw, 2009). Moreover, our results put into evidence a small but significant amount of displacement in the range front that we interpret as due to slip at depth on a blind structure. We verify this hypothesis by inverting the data against a simple elastic dislocation model.We discuss this result and its implications for understanding strain partitioning during the Sichuan earthquake

Serial ruptures of the San Andreas fault, Carrizo Plain, California, revealed by three-dimensional excavations

It is poorly known if fault slip repeats regularly through many earthquake cycles. Well‐documented measurements of successive slips rarely span more than three earthquake cycles. In this paper, we present evidence of six sequential offsets across the San Andreas fault at a site in the Carrizo Plain, using stream channels as piercing lines. We opened a latticework of trenches across the offset channels on both sides of the fault to expose their subsurface stratigraphy. We can correlate the channels across the fault on the basis of their elevations, shapes, stratigraphy, and ages. The three‐dimensional excavations allow us to locate accurately the offset channel pairs and to determine the amounts of motion for each pair. We find that the dextral slips associated with the six events in the last millennium are, from oldest to youngest, ≥ 5.4 ± 0.6, 8.0 ± 0.5, 1.4 ± 0.5, 5.2 ± 0.6, 7.6 ± 0.4 and 7.9 ± 0.1 m. In this series, three and possibly four of the six offset values are between 7 and 8 m. The common occurrence of 7–8 m offsets suggests remarkably regular, but not strictly uniform, slip behavior. Age constraints for these events at our site, combined with previous paleoseismic investigations within a few kilometers, allow a construction of offset history and a preliminary evaluation of slip‐ and time‐predictable models. The average slip rate over the span of the past five events (between A.D. 1210 and A.D. 1857.) has been 34 mm/yr, not resolvably different from the previously determined late Holocene slip rate and the modern geodetic strain accumulation rate. We find that the slip‐predictable model is a better fit than the time‐predictable model. In general, earthquake slip is positively correlated with the time interval preceding the event. Smaller offsets coincide with shorter prior intervals and larger offset with longer prior intervals