Stress mapping, focal mechanism display and stress tensor inversion in Qeshm Island, Southern Iran

Knowing about the stress field is essential to have insight into the seismotectonics and to understand the geodynamics of any study area. Stress tensor inversion is used for obtaining more precise stress information from cluster of earthquakes. Moreover, it is shown that the proper display of earthquake focal mechanism can help to get a better understanding of the seismotectonics of the region. In this study, the maximum horizontal stress directions in Qeshm Island, southern Iran, are extracted by using single earthquake focal mechanism. The Island is very important regarding its oil and gas reservoirs, still being explored, and planned industrial and business developments. Following previous studies in the region, there is an ambiguity in the main stress orientation in the area arising from the cross-cutting directions of the earthquake focal mechanism P axes. The stress tensor inversion of the focal mechanisms related to the 2005 earthquake aftershock sequence in Qeshm Island helped to resolve the observed ambiguity and revealed the correct maximum horizontal stress direction. The stress field is then mapped by implementing a new data visualization method. According to a circular color scale, this method is based on attributing RGB specific values to each rectangular grid cells. For a correct illustration of the directions with a color scale, the opposite directions (SHmax) should be of the same color, which necessitates introducing a new color wheel. The obtained anomaly in the stress direction coincides with the geological features and also InSAR results in the study area. These findings reveal the different stress field of the central parts of the Island, which is uplifted during the 2005 earthquake. Finally, it is proved that the 2005 earthquake and its aftershock sequence perturb the stress field in Qeshm Island.