Fault orientations in the upper crust beneath an intraplate active zone in northern Egypt

A K Abdel-Fattah,W Farid,M F Abdelwahed,M Fnais,A El-Nekhely

doi:10.5047/eps.2012.12.005

Abstract

The present study aims to demarcate the active fault orientation in the upper crust of Dahshour Seismic Zone (DSZ) in Northern Egypt, and its relation to the regional tectonics. High-resolution earthquake relocations and focal mechanism solutions were determined using the double-difference location method and the forward modelling of the amplitude spectrum constrained with P-wave polarities, respectively. Up to 244 earthquakes were relocated by measuring differential travel times between events, as obtained from cross-correlation waveform analysis. The relocated hypocenters exhibited a seismogenic crust of 6-km thickness (most hypocenters have a focal depth of 18 to 24 km). Incorporation of hypocentral distributions and focal mechanisms depicts distinct fault planes trending to the NW and ENE to EW, randomly distributed in the whole dislocation zone. The reactivation of these pre-existing faults is attributed to the northern Red Sea-Gulf of Suez rifts and the closure of the Neotethys, respectively; implying a potential impact of the regional tectonic process on the deformation acting in the upper crust of the local seismogenic zones of northern Egypt.

Highlights

It is generally recognised that the study of intraplate earthquakes is a difficult task because their seismogenic faults may have minor features, strain rates are low, and large size earthquakes are infrequent (Dunn and Chapman, 2006)
Focal mechanisms that computed for small- to moderate-sized earthquakes recorded by the Egyptian National Seismic Network (ENSN) indicate a dominant tension stress along the northeastern African corner, which changes to a dominant compression towards the Mediterranean Sea along the transition zone between the continental-oceanic crust
The earthquakes were recorded by the ENSN operated by the National Research Institute of Astronomy and Geophysics (NRIAG)

Summary

Introduction

It is generally recognised that the study of intraplate earthquakes is a difficult task because their seismogenic faults may have minor features, strain rates are low, and large size earthquakes are infrequent (Dunn and Chapman, 2006). The present study aims to demarcate the active fault orientation in the upper crust of Dahshour Seismic Zone (DSZ) in Northern Egypt, and its relation to the regional tectonics.

Results

Conclusion