Three-dimensional P-wave tomography in the Central Alborz, Iran

We obtained the 3D crustal velocity structure of the Central Alborz region in northern Iran using local earthquake tomography . We used P-wave arrival-time data recorded by stations from three national observatories consisting of the Iranian Seismological Center, the International Institute of Earthquake Engineering and Seismology , and the Tehran Disaster Management and Mitigation Organization along with data from a temporary network. The P-wave arrival-times from local earthquakes have been used to produce a 3D tomographic velocity model of the Central Alborz using the inversion code SIMULPS. The low-velocity sedimentary layer in the upper crust is up to ~4 km thick. Our results show a mid-crustal interface at ~15 ± 2.5 km depth. This interface shows a pronounced uplift at a relatively aseismic part of the Mosha fault that might have the potential to produce an earthquake with magnitude Mw ~ 6–6.5. Independent gravity modeling was carried out, which confirms the location of the anomaly at the relatively aseismic part of the Mosha fault. A small uplift of the mid-crustal interface beneath the junction of the Mosha and North Tehran faults close to the city of Tehran might indicate a similar anomaly. Various resolution and synthetic tests (e.g., checkerboard, Resolution Matrix Diagonal, and data uncertainties) were performed and support the reliability of the resolved anomalies.