Mustapha Meghraoui

Evidence for 830 years of seismic quiescence from palaeoseismology, archaeoseismology, and historical seismicity along the Dead Sea fault in Syria

An edited version of this paper was published in Earth and Planetary Science Letters by Elsevier Science. Elsevier Science retains the copyright to this paper (Copyright 2003). See also: http:\\dx.doi.org\10.1016\S0012-821X(03)00144-4; http://atlas.geo.cornell.edu/deadsea/publications/Meghraoui2003_EPSL.htm

Coastal uplift and thrust faulting associated with the Mw = 6.8 Zemmouri (Algeria) earthquake of 21 May, 2003

[1] A shoreline uplift marked by a continuous white band visible at rocky headlands occurred during the 21 May 2003 earthquake (Mw 6.8) in northern Algeria. We measured the amount of coastal uplift on a white band (emerged algae) and harbors quays between Boumerdes and Dellys. Most of measured points were collected using tape and differential GPS on rocky headlands with σ ± 0.15 m error bar (tidal prism). Leveling lines running parallel and orthogonal to the coast also provide the precise amount of uplift in the epicentral area. The uplift distribution shows an average 0.55 m along the shoreline with a maximum 0.75 m east of Boumerdes and a minimum close to 0 near Cap Djinet. The active deformation related to a thrust fault is modeled along the ∼55 km coastline. The dislocation model predicts surface slip on a N 54°E trending reverse fault, dipping 50° SE in agreement with CMT solution and coastal uplift. The faulting characteristics imply a fault geometry with possible sea bottom ruptures between 5 to 10 km offshore.

Earthquake‐induced flooding and paleoseismicity of the El Asnam, Algeria, fault‐related fold

Late Quaternary activity of the El Asnam thrust fault (responsible for the October 10, 1980, MS = 7.3 earthquake and 36-km coseismic faulting) is explored through diverse paleoseismological field methods. We trenched through the main and secondary 1980 coseismic scarps, made an analysis of earthquake-induced flood deposits, conducted a geomorphic study of leveling profiles and offset geological units across thrust and normal scarps, and considered the geomorphology of the active fold. Twenty-five radiocarbon ages from colluvial and alluvial deposits, along with conventional (fossils and artefacts) dating of geological units, show the timing of successive net vertical displacements on the thrust-related fold and bending-moment faults. Previous work showed that eight pre-1980 earthquakes occurred in clusters during the late Holocene. Cumulative net vertical slip that amounts to 3 times the 1980 displacement is observed on multiple thrust fault scarps and offsets of geological units on bending-moment faults. Maximum cumulative vertical displacements, which are visible in different zones along the fault segments, can reach 10 to 25 times the 1980 coseismic displacements. The late Quaternary uplift rate on the El Asnam fault is 0.6 mm/yr, and taking into account slip variation along the fault, this rate may range between 0.25 – 1.6 mm/yr, from which we obtain a shortening rate of 0.17 – 1.2 mm/yr. Because the Tell Atlas mountains exhibit comparable seismogenic fault-related folds with parallel and sequential structures of active faults, a total average shortening rate of 2.05 mm/yr during the late Quaternary represents part of the convergence accommodated along the Africa-Eurasia plate boundary.

Late Quaternary earthquake-related soft-sediment deformation along the Belgian portion of the Feldbiss Fault, Lower Rhine Graben system

Abstract Trench investigations along the Bree fault scarp in Belgium, in the framework of a first paleoseismological experience in the area of the Lower Rhine Graben system, have not only demonstrated the existence of seismogenic faults almost extending to the present ground surface, but also exposed several types of soft-sediment deformation affecting sandy sediments and soils of inferred late Weichselian to Holocene age. The observed features include asymmetric folding, small-scale normal faulting, possible sand intrusions, and small water escape or load structures. Establishing a seismic origin for the individual features is not always possible based on their sedimentary characteristics only, particularly due to the potential confusion with periglacial phenomena, but their abundance, the close association of different deformational styles, and their vicinity to a known active fault, all seem to be compatible with an earthquake-induced scenario. The features are to some extent comparable to those generated during the recent MS 5.3 Roermond earthquake at the opposite side of the Roer Valley Graben. Stratigraphical and mutual geometrical relationships suggest the occurrence of at least three distinct deformational events since probably 30,000 years, and one event before that time. Since nothing is yet known about their regional distribution, however, estimating the associated paleomagnitudes from these soft-sediment deformations is premature.

The use of geophysical prospecting for imaging active faults in the Roer Graben, Belgium

As part of a paleoseismological investigation along the Bree fault scarp (western border of the Roer Graben), various geophysical methods [electrical profiling, electromagnetic (EM) profiling, refraction seismic tests, electrical tomography, ground‐penetrating radar (GPR), and high‐resolution reflection seismic profiles] were used to locate and image an active fault zone in a depth range between a few decimeters to a few tens of meters. These geophysical investigations, in parallel with geomorphological and geological analyses, helped in the decision to locate trench excavations exposing the fault surfaces. The results could then be checked with the observations in four trenches excavated across the scarp. Geophysical methods pointed out anomalies at all sites of the fault position. The contrast of physical properties (electrical resistivity and permittivity, seismic velocity) observed between the two fault blocks is a result of a differences in the lithology of the juxtaposed soil layers and of a change ...

Active faulting and paleoseismology along the Bree fault, lower Rhine graben, Belgium

Paleoseismic analysis of the 10-km-long Bree fault scarp in the lower Rhine graben yields numerous lines of evidence of earthquake activity in the Holocene and late Pleistocene. This active normal fault, a part of the Feldbiss fault system, dips 70°NE and is expressed at the surface by a prominent NW-SE trending 7 to 20 m high scarp, formed since the deposition of the Maas River main terrace <700 kyr. B.P. Trenches and geophysical prospecting show that the fault, which is known to have ∼100 m of vertical offset since the late Pliocene, breaks late Pleistocene and Holocene deposits. Ground-penetrating radar, seismic refraction, and electric tomography suggest that at shallow depth the amount of displacement is larger than the youngest vertical offset visible in the trenches and corresponds to cumulative fault displacements. The analysis of 36 leveling profiles across the scarp indicates that its height can be classified into three groups, likely corresponding to different events. A morphologic dating gives approximate ages of 2±1.5 kyr B.P., 14±5 kyr B.P., and 41±6 kyr B.P. for the past three surface-faulting earthquakes. Analysis of faulted stratigraphy and earthquake-induced deformation structures exposed in trenches suggests the occurrence of three large earthquakes during the past 45×l03 years and yields 0.07 mm/yr of relative vertical deformation rate. The most recent seismic event occurred between A.D. 610 and 890. The first identification of an active fault with surface ruptures in the lower Rhine graben area emphasizes that large earthquake sources exist within intraplate Europe and that at least some of these events are preserved in the geologic record.

Coseismic displacements along the Serghaya Fault: an active branch of the Dead Sea Fault System in Syria and Lebanon

Examination of the Serghaya fault, a branch of the Dead Sea Fault System in western Syria and eastern Lebanon, documents Late Quaternary and Recent left-lateral fault movements including the probable remnant of a historic coseismic surface rupture. Carbon-14 dating and the presence of fault-scarp free faces in soft, late Pleistocene lake deposits suggest coseismic slip during the past two or three centuries, possibly corresponding with one of the well-documented earthquakes of 1705 or 1759. With an estimated Holocene slip rate of 1–2 mm a−1, the Serghaya Fault accommodates a significant part of the active deformation along the Arabian–African plate boundary. These results suggest that multiple active fault branches are involved in the transfer of strain through the ‘Lebanese’ restraining bend.

Onset of aseismic creep on major strike-slip faults

Time series analysis of spaceborne synthetic aperture radar (SAR) data, GPS measurements, and field observations reveal that the central section of the Izmit (Turkey) fault that slipped with a supershear rupture velocity in the A.D. 1999, M w 7.4, Izmit earthquake began creeping aseismically following the earthquake. Rapid initial postseismic afterslip decayed logarithmically with time and appears to have reached a steady rate comparable to the pre-earthquake full fault-crossing rate, suggesting that it may continue for decades and possibly until late in the earthquake cycle. If confirmed by future monitoring, these observations identify postseismic afterslip as a mechanism for initiating creep behavior along strike-slip faults. Long-term afterslip and/or creep has significant implications for earthquake cycle models, recurrence intervals of large earthquakes, and accordingly, seismic hazard estimation along mature strike-slip faults, in particular for Istanbul which is believed to lie adjacent to a seismic gap along the North Anatolian fault in the Sea of Marmara.

Fault fragment control in the 1997 Umbria‐Marche, central Italy, Earthquake Sequence

The Umbria-Marche region in central Italy experienced a sequence of shallow earthquakes in late 1997, including three mainshocks on September 26th (Ms 5.5 and 5.9) and October 14th (Ms 5.5). This seismic sequence illustrates the relationships between small-scale active faults and moderate-magnitude earthquakes. We suggest that a small-scale active fault corresponds to a “fault fragment” and that it refers to the fault area required for producing a coseismic deformation at the ground surface. The seismic activity and related three mainshocks occurred along three fault fragments which total ∼25 km in length and show a listric geometry at depth. Fault fragments are laterally controlled by pre-existing transverse fold-and-thrust structures and may constitute a major component of the seismic strain release in active continental regions.

Stress transfer among en echelon and opposing thrusts and tear faults: Triggering caused by the 2003 Mw = 6.9 Zemmouri, Algeria, earthquake

Stress transfer among en echelon and opposing thrusts and tear faults: Triggering caused by the 2003 M w = 6.9 Zemmouri, Algeria, earthquake [1] The essential features of stress interaction among earthquakes on en echelon thrusts and tear faults were investigated, first through idealized examples and then by study of thrust faulting in Algeria. We calculated coseismic stress changes caused by the 2003 M w = 6.9 Zemmouri earthquake, finding that a large majority of the Zemmouri afterslip sites were brought several bars closer to Coulomb failure by the coseismic stresses, while the majority of aftershock nodal planes were brought closer to failure by an average of ∼2 bars. Further, we calculated that the shallow portions of the adjacent Thenia tear fault, which sustained ∼0.25 m slip, were brought >2 bars closer to failure. We calculated that the Coulomb stress increased by 1.5 bars on the deeper portions of the adjacent Boumerdes thrust, which lies just 10–20 km from the city of Algiers; both the Boumerdes and Thenia faults were illuminated by aftershocks. Over the next 6 years, the entire south dipping thrust system extending 80 km to the southwest experienced an increased rate of seismicity. The stress also increased by 0.4 bar on the east Sahel thrust fault west of the Zemmouri rupture. Algiers suffered large damaging earthquakes in A.D. 1365 and 1716 and is today home to 3 million people. If these shocks occurred on the east Sahel fault and if it has a ∼2 mm/yr tectonic loading rate, then enough loading has accumulated to produce a M w = 6.6–6.9 shock today. Thus, these potentially lethal faults need better understanding of their slip rate and earthquake history. among en echelon and opposing thrusts and tear faults: Triggering caused by the 2003 M w = 6.9 Zemmouri, Algeria, earthquake,