Magnitude scales regression for Egyptian seismological network
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ORIGINAL PAPER
Magnitude scales regression for Egyptian seismological network H. E. Abdel Hafiez
Received: 15 August 2014 / Accepted: 20 January 2015 # Saudi Society for Geosciences 2015
Abstract After Cairo Earthquake in 1992 (Ms 5.9), the government established the Egyptian National Seismological Network (ENSN) organized by the National Research Institute of Astronomy and Geophysics (NRIAG) start to work since 1997; NRIAG has a real monitoring of the seismological activity in and around different parts of Egypt. A selected 5000 events from the ENSN annual bulletin in the period 2004–2013 with calculated local magnitude (ML) based on Richter regular formula was used in this study; a duration magnitude was calculated for these events and regressed with ML. Another aim of this study is to develop a regression relation of the calculated body wave magnitude (Mb) to the unified moment magnitude (Mw) which is the base for homogenization of earthquake catalogue needed for seismic hazard studies. Standard least square regression usually fails to give reliable results when both regressed variables have measurement errors; orthogonal standard regression (OSR) is the most reliable tool used for conversion of observed Mb values with the moment magnitude Mw. The accuracy of the resulting relations from regression have been checked with another 20 events of the data and shows the advantage of using OSR method to get regressed relation to homogenize any catalogue containing various magnitudes with measurement errors, by their regression with a Mw. The proposed procedure also remains valid in case the magnitudes have measurement errors different from unity.
Keywords Earthquake catalogue . Magnitude conversion . Regression relations
H. E. Abdel Hafiez (*) National Research Institute of Astronomy and Geophysics (NRIAG), Helwan, Egypt e-mail: [email protected]
Introduction Egypt is located near a zone of plate boundaries; in the eastern side, the Red Sea Rift which is a zone of plate separation along which sea floor spreading separates the African plate and Arabian plates apart; from the northeastern part, the Gulf of Aqaba–Dead Sea transform fault, which is a major left-lateral strike slip fault, that accommodates the motion between the Africa, Arabian, and Eurasian plates; and from the north Egypt is bounded by the subduction zone where the African plate subducts beneath the Eurasian plate at the Cyprean and Hellenic Arcs. Relative motions along these boundaries are the reason for tectonic deformation within Egypt (Abu El Enean 1997) (Fig. 1). Magnitude is one of the important factors for the homogenization of earthquake catalogue which is essential for further hazard assessment studies, and because earthquake magnitude scales generally lack consistency due to differences in the recording instruments, so conversion of different observed magnitude types to the unified magnitude value is being essential. Egyptian National Seismological Network (ENSN) consists of 65 different seismological stations (Fig. 2), and the Nationa
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