The 1995 November 22, Mw 7.2 Gulf of Elat earthquake cycle revisited

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SUMMARY

The 1995 November 22, Mw= 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 Gulf-parallel 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.

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