Relocation of Iran Earthquakes Using the National Seismic Networks

Iran is one of the most seismically active intra-continental regions. The collision between the Arabian plates and the Eurasian plate results in significant seismicity beneath the Zagros Mountains. In the north, earthquakes occur throughout the crust along the Alboz fold belt. Two nation-wide seismic networks (Iranian Seismic Telemetry Network and Iran National Seismic Networks) have been installed in recent years. Most ISTN stations are equipped with short period seismometers while INSN employs broadband ones. In total, 97 stations routinely report arrivals of events in the country and surrounding regions. Most travel-time data are at local and regional distances so that it is possible to obtain more accurate locations of earthquakes. We combined the catalogues from ISTN and INSN and relocated more than 26,000 events using about 150,000 P-wave arrivals and 70,000 S-wave arrivals and 1D P- and S-wave velocity models. This dataset contains ten times more data than the one we previously used, and therefore improves the resolution of 3D tomography. We then employed 3D travel-time tomography to invert the crust and upper most mantle seismic structure and to improve the accuracy of earthquake location. The result reveals a clear high velocity boundary along the Zagros suture. The high velocity anomaly beneath the Caspian Sea suggests an oceanic crust. The most remarkable low velocity zone is the Lesser Caucasus, where many quaternary volcanoes are located. The central Iranian microplate appears as a low velocity zone.