Selection and Modification of Ground Motion Prediction Equations for Makran Subduction Zone, Southeast Iran

Abstract

The Iranian Plateau is considered mostly as a shallow crustal area, except the Makran region in southeast Iran where subduction events can occur. Because of the tectonic characteristics of the Makran subduction zone, different categories of ground motion prediction equations (GMPEs) are required for seismic hazard assessment, including GMPEs for shallow crustal events and subduction zone earthquakes (both in-slab and interface events). To show the applicability of candidate GMPEs, a selected dataset consisting of 314 records from 80 earthquakes is used for statistical analyses and modification of the candidate GMPEs. The earthquakes in the studied area are classified into two groups: shallow (events with focal depth less than 40 km; including 67 events and 210 records) and in-slab (events with focal depth more than 40 km; 13 events and 104 records). There are no recorded instrumental data in the region for the interface earthquakes. About ten GMPEs (developed based on local, regional, and global data) for shallow earthquakes are initial candidates for selection and modification in the studied region. In addition, four relationships are used in the statistical analyses for in-slab events. Different statistical analyses have been applied to show the performance of GMPEs and their applicability for the region. The results show that the modification term applied in the GMPEs improved the applicability of the relations significantly. The results are very important for the assessment of seismic hazard in the Makran region and other neighborhood countries, i.e., Oman and United Arab Emirates. Finally, a new model for vertical-to-horizontal spectral ratio has been proposed for the studied region that helps us to obtain vertical design spectra from horizontal spectra and their predominant scenarios resulting from seismic hazard analyses.