Magnitude scales regression for Egyptian seismological network

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 (M (L)) based on Richter regular formula was used in this study; a duration magnitude was calculated for these events and regressed with M (L). Another aim of this study is to develop a regression relation of the calculated body wave magnitude (M (b)) to the unified moment magnitude (M (w)) 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 M (b) values with the moment magnitude M (w.) 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.