The 1995 November 22,M_w7.2 Gulf of Elat earthquake cycle revisited

Abstract

S U M M A R YThe 1995 November 22, M w = 7.2 Nuweiba earthquake occurred along one of the left-stepping segments of the Dead Sea Transform (DST) in the Gulf of Elat (Aqaba). It was the largest earthquake along the DST in at least 160 yr. The main shock was preceded by earthquake swarms north and south of its NE-striking rupture since the early 1980s, and was followed by about 6 months of intense aftershock activity, concentrated mainly northwest and southeast of the main rupture. In this study we re-analyse ERS-1 and ERS-2 InSAR data for the period spanning the main shock and 5 post-seismic years. Because the entire rupture was under the Gulf water, surface observations related to the earthquake are limited to distances greater than 5 km away from the rupture zone. Coseismic interferograms were produced for the earthquake +1 week, +4 months and +6 months. Non-linear inversions were carried out for fault geometry and linear inversions were made for slip distribution using an ascending-descending 2-frame data set. The moment calculated from our best-fitting model is in agreement with the seismological moment, but trade-offs exist among several fault parameters. The present model upgrades previous InSAR models of the Nuweiba earthquake, and differs from recent teleseismic waveform inversion results mainly in terms of slip magnitude and distribution.The moment released by post-seismic deformation in the period of 6 months to 2 yr after the Nuweiba earthquake is about 15 per cent of the coseismic moment release. Our models suggest that this deformation can be represented by slip along the lower part of the coseismic rupture. Localised deformation along the Gulf shores NW of the main rupture in the first 6 months after the earthquake is correlated with surface displacements along active Gulfparallel normal faults and possibly with shallow M > 3.9, D < 6 km aftershocks. The geodetic moment calculated by modelling this deformation is more than an order of magnitude larger than expected for a single M ∼ 4 aftershock, but could be a result of a sequence of aftershocks and/or aseismic slip. The major aftershocks and the slip along Gulf-parallel normal faulting NW of the main rupture are associated with positive Coulomb stress changes induced by the main event.

Subsurface faults detection based on magnetic anomalies investigation: A field example at Taba protectorate, South Sinai

“…In the study area, in order to distinguish the near surface structure (b 150 m) (El-Refaei, 1992;Taha et al, 2004;Baer et al, 2008), filters of the vertical derivatives, Butterworth high-pass, analytic signal amplitude, and total horizontal derivative of the tilt derivative were used. Whereas, apparent susceptibility and Butterworth low-pass filters were carried out to recognize the deep-seated structure (N150 m).…”

“…(B) Geological map of the study area. (Dames and Moore, 1983;ElRefaei, 1992;Egyptian Geological Survey, 2002;Taha et al, 2004;Baer et al, 2008).…”

“…1). This boundary is connecting Zagros-Taurus zone of continental collision with the seafloor spreading in the Red Sea (El-Sayed and Wahlstrom, 1996;Baer et al, 2008). The Gulf of Aqaba-Dead Sea transform fault was initiated in the pre-Miocene as a pure left lateral strike slip fault with little extensional components across the rift and in post-Miocene it displayed some components of oblique extension (Eyal et al, 1981;Garfunkel, 1981).…”

“…These fracture systems are inherited by activations on earlier ductile fault patterns that were formed in late Precambrian tectonics in Arabian-Nubian Shield (Bosworth and Mc Clay, 2001). Dames and Moore, 1983;El-Refaei, 1992;Egyptian Geological Survey, 2002;Taha et al, 2004;Baer et al, 2008). (B) Geological map of the study area.…”

“…The Gulf of Aqaba-Dead Sea transform fault was initiated in the pre-Miocene as a pure left lateral strike slip fault with little extensional components across the rift and in post-Miocene it displayed some components of oblique extension (Eyal et al, 1981;Garfunkel, 1981). The predominance of tilted blocks on normal faults and the associated large-scale uplifting indicate divergent wrenching tectonics associated with rifting of the gulf (Baer et al, 2008).…”