GPS Observations and Modelling of Crustal Deformation in Gulf of Aqaba

Abstract

The Dead Sea Transform fault (DST) is one of the most prominent tectonic features in the eastern Mediterranean region, located between the Arabian plate and the Sinai sub-plate. Several aspects of this fault system have been thoroughly studied. However, its present-day kinematics along its southern end in Gulf of Aqaba remains poorly understood. This dissertation focusses on crustal motions near Gulf of Aqaba by using geodetic observations and analytical models of crustal deformation. Here we present a crustal motion velocity field for this region based on three GPS surveys conducted between 2015 and 2019 at 30 campaign sites, complemented by 12 permanent stations operating in Gulf of Aqaba. A new pole of rotation for the Sinai sub-plate was constrained based on five selected stations on the Sinai Peninsula. This Euler pole predicts slip rates of ~ 4.5 mm/yr on the fault system in the gulf. Furthermore, our results show that interseismic models of crustal deformation do not provide a reasonable constraint on fault locking depths due to limited near-fault measurements.

Despite this, our results show a coherent left-lateral residual motion across the fault system in Gulf of Aqaba that could not be resolved by conventional strain accumulation models. We tested whether postseismic viscoelastic relaxation of the lower crust and upper mantle following the Nuweiba Earthquake (MW 7.2, 1995) can explain this residual signal. We found that modelled postseismic velocities match the direction of residual velocities in the NE and SW quadrants relative to the Aragonese fault, which ruptured during the Nuweiba Earthquake. However, our forward models of postseismic deformation could not reproduce the overall magnitudes of the residual velocity field, underestimating eastward residuals in the quadrants NE and SW and overshooting northward misfits in the quadrants SE and NE relative to the fault trace.

Estimates of the current geodetic moment accumulated on the fault system in the gulf indicate that impending earthquakes could potentially reach MW 7.0. Our results further suggest recurrence times of ~840 yr and ~1160 yr for large earthquakes (MW 7.2) on the Eilat and Dahab fault segments in the gulf, respectively. We anticipate our results to be a starting point for future geodetic studies incorporating more GPS stations on both sides of the gulf and implementing more sophisticated models of crustal deformation considering three-dimensional rheological variations and precise finite-fault models.