An Earthquake Catalogue (2200 B.C. to 2013) for Seismotectonic and Seismic Hazard Assessment Studies in Egypt

Abstract

The instrumental earthquake catalogues show the overall seismicity of the Earth. However, examining and inspecting the historical records plus the instrumental recorded events is necessary to understand long-term seismicity. Moreover, regional seismic and focal mechanism solutions catalogues provide critical information for different seismological investigations, including seismic hazard assessments and seismotectonic studies. The present work aims at preparing new and up-to-date unified and Poissonian earthquake catalogue for Egypt including the focal mechanism solutions data, so that the earthquake information can be reached from a single source. A catalogue for earthquakes that occurred in Egypt and its vicinity during the period 2200 B.C. - 2013 was compiled for achieving a unified magnitude scale. Data were obtained from different sources, local, regional and international (e.g., the regional catalogue of Ambraseys et al., 1994; the International Seismological Center and the Annual Bulletin of the Egyptian National Seismic Network). The initial compilation spanning a region from 21° to 38°N and from 22° to 38°E, and includes all the events having an assigned magnitude of 3.0 and above for international sources and any magnitude for local sources on any magnitude scale. Earthquake magnitudes are reported in different scales and come from a variety of sources. The initial compiled catalogue comprised a total of 64613 earthquakes (historical and instrumental events). In addition, a focal mechanism solutions database was collected. This database contains 688 fault-plane solutions gathered from different published and unpublished sources, covering the time period from 1940 until the end of 2013. For establishing a common magnitude, namely an equivalent moment magnitude, two new relationships correlating surface-wave and body-wave magnitudes with moment magnitude were derived. After this process, the catalogue was cut off below moment magnitude 3.0, because these magnitudes are not significant for seismic hazard studies. All non-Poissonian (dependent) events were removed using the approach proposed by Gardner and Knopoff (1974). A total of 16642 events represent the final Poissonian catalogue including main shocks with a moment magnitude above or equal to 3.0. Finally, the degree of completeness for the entire catalogue was checked for the different magnitude values. In addition, separately from the Eastern Mediterranean region, the completeness for the Egyptian territory sub-catalogue was also checked. The results derived in each case have been interpreted in the framework of the establishment and development of the international and national networks.