Development a local magnitude scale for South Egypt

A local magnitude (ML) scale for the southern Egypt region was developed using 3435 maximum amplitudes of 343 high-quality records of earthquakes recorded by the Egyptian National Seismic Network (ENSN). The analysis is started by the relocation of the recorded earthquakes, and then instrument responses were deconvolved from the recording and simulated on a standard Wood-Anderson torsion seismograph. Zero-to-peak amplitude of Sg or Lg waves in the two horizontal components is measured on each simulated Wood-Anderson seismograph. Events that were recorded by at least four stations and located at hypocentral distances between 10 and 1000 km and with a magnitude range of 1-4.5 are selected for preforming the analysis. The maximum recorded hypocentral depth was 40 km. The normalized amplitude decay shows two transition distances at 90 km, and 175 km yielding three segments. The trilinear regression model was adopted to retrieve three formulae that describe the local magnitude as follows: M-L = log (A) + 1.4223*log(R) 0.0014*(R) +0.301 for R < 90. M-L = log (A) +1.3786*log(R) 0.0014*(R) +0.379 for 90 < R < 175. M-L = log (A) +3.1369*log(R) 0.0014*(R) 3.57 for R > 175. Where A is the ground displacement amplitude (mm) on the horizontal component, R is the hypocentral distance (km). The station corrections were also determined for 49 different geological sites using the regression model and producing values ranging between 0.4 and 0.7. The residual of magnitude values are reduced by 46% when using station corrections. The newly derived scale for South Egypt is well correlated with scales determined for South California and those for other intraplate areas, such as the Ethiopian Plateau and central US.