Completion of the Stress Database in Makran with an Insight into the Focal Mechanisms of Earthquakes in the Region

There are many applications for stress field information today. Reservoir identification and management, the stability of mines, tunnels, boreholes and landfills, calibration of geomechanical-numerical models, four-dimensional hydrothermomechanical simulations and seismic hazard assessment using fault slip and failure potential analysis are examples of these applications. Considering the current projects in earthquake risk analysis in the study area with the approach of landslide rate and distributed deformation studies, the importance of using the stress database in an improved and comprehensive manner has been increased. Due to the many applications that exist today for stress field information, as well as current projects in related fields that are closely related to the subject of tectonic crustal stress, the use of an updated database of stress information has become increasingly important. This study has attempted to complete the study area's stress databases as much as possible using various data sources. One of the sources that provide extensive information in this field for free is the World Stress Map Project. In this study, an attempt has been made to add the existing knowledge about the stress field in the Makran region, including data on the focal mechanism of earthquakes and their inversion, etc., to the current database available in the World Stress Map Project. Data on the focal mechanism of earthquakes in the study area have been obtained from various sources. It can be seen that WSM databases in Makran, especially in the central parts, do not contain much information and the available information is not of high quality. Since most World Stress Map database records consist of single focal mechanisms of earthquakes, focal mechanisms extracted from international research centers can be added to this database. In calculating the stress direction of a single focal mechanism, the relationship between the type of focal mechanism and the axis corresponding to the maximum stress direction must be considered. As we know, the principal stress directions are different for various fault mechanisms. In the present study, the information obtained from single focal mechanisms has been compared with the stress inversion results. The current stress database is the most complete one in the area regarding the available data and the ground for improving the relevant studies is provided. According to the present study results, the stress field in the Makran region has significant spatial changes. These changes indicate opposite stress directions in Eastern, Central and Western Makran. In this study, it was shown that single focal mechanism data obtained from the ISC database and other sources are suitable for adding data to the World Stress Map. Also, comparing the results of stress inversion using the focal mechanism of earthquakes in the study area with the results of the present study showed that the individual focal mechanism data of earthquakes generally have a relatively good agreement with the actual directions of stress in the region and can be used as a preliminary estimate of these directions. In this study, using GPS velocity vectors and tectonic plate motion vectors, surface locking was observed in central Makran. However, according to the evidence in the northern parts of central Makran, the deformation continues at great depths aseismically. Also, comparing the results with the geological structures in the area showed good agreement. Depth separation of the focal mechanism of earthquakes showed that the stress data calculated in this study are mainly related to the upper 40 km. Further investigations in this area by installing and operating temporary seismic networks and enhancing permanent facilities are encouraged.