Determination of a local earthquake magnitude scale for the Sultanate of Oman

Abstract

Determination of earthquake magnitude is of great importance for quantitative seismological hazard studies. Since no local magnitude scale has been developed for the seismic network of the Sultanate of Oman, the present work is aiming towards developing the first local magnitude scale for earthquakes that occur in and around the Sultanate of Oman. Currently, the Earthquake Monitoring Center (EMC) in Oman uses the Southern California formula for ML calculations; the calculated values of local magnitudes are not comparable to the average magnitude calculated by the international centers (e.g., ISC and NEIC). In many cases, they show clear underestimation in magnitude for the local and regional distance events compared with magnitude values published by the international centers. A database of 424 simulated Wood–Anderson horizontal amplitudes of 55 events recorded by 9 very broadband stations, available since 2011, is built. All of the available events are located in northern Oman region. The attenuation function together with the magnitudes and the station corrections are determined using a multistep inversion process based on the application of the genetic algorithm. The computation provided the values of the empirical coefficients for geometrical spreading (n) and anelastic attenuation coefficient (k) to be 0.95 and 0.001, respectively. Station corrections for the used nine stations are calculated and found to be in the range of ±0.2 magnitude units. Great improvement regarding the local magnitude calculation is achieved as demonstrated by the better correlation with the provided ISC/NEIC magnitude values.