Calibration of IASPEI Standard Broad-band Magnitude mB for Iranian Plateau Earthquakes

Located in Alp-Himalayan belt and an active tectonic plate, Iran is annually struck by major earthquakes. Since shallow earthquakes cause considerable loss of lives and property in this region, using any method to decrease the time of magnitude estimation of great earthquakes is very important for making a prompt decision about what to do. To achieve this aim, mB was computed as a rapid estimator for ۳۸ earthquakes with magnitudes greater than ۶ occurred in Iran and adjacent areas (۲۴°-۴۴°N, ۴۲°-۶۶°E) from ۱۹۹۰ to ۲۰۱۸. The magnitudes that estimated by using the calibration function by Saul & Bormann (۲۰۰۷) have a standard error of ۰.۴۹ from Mw (in this study). Therefore, mB’s calibration function was modified. As a result, the magnitudes obtained are approximately equal to those of reported Mw (a standard error of ۰.۱۸). The calibration function acquired in this study for Iran’s earthquakes is lower than the mB’s global calibration function obtained by Saul & Bormann (۲۰۰۷). Their difference is nearly one unit at short distances, which can be related to the earthquakes located in subduction zones and plates boundaries used by Saul & Bormann (۲۰۰۷) that systemically have lower stress drops than intraplate earthquakes considered here. Thus it is needed to develop improved region-specific calibration functions for mB. However, the difference became smaller at distances greater than ۲۰°. Consequently, this method and new calibration function can be employed to estimate magnitudes as early as possible across Iran plateau.

Keywords:

MB , Mw , Earthquake Magnitude , calibration , Iran Plateau