U.S. Geological Survey Sponsored by National Nuclear Security Administration

Middle Eastern countries have a very high level of seismic activity. For this reason, there are a large number of seismic networks in operation, and data from these networks have provided details of the crustal structure of the region. One such network, the Tehran Telemetry Seismic Network (TTSN), consists of twelve stations and is located around the city of Tehran. Nearly two years of local data are available from this array, and these data yield estimates of crustal thickness based on receiver function analysis. These results consistently show a crustal thickness of 44 – 50 km. This value is about 12 km thicker than has been measured in eastern Turkey, and 9 km greater than the global average for stable platform regions. The 45 km crustal thickness near Tehran is almost exactly the same as the 46 – 48 km thickness reported from receiver function analysis from the central Zagros mountains. The apparent uniformity of the crustal thickness implies that mountain building has only recently started in the region, and the crust beneath the Zagros mountains has not been appreciably thickened by compression. Despite the platform-like crustal structure, we find evidence that the upper mantle Pn velocity is lower than the typical value of 8.1 km/s. The relocated earthquakes of Engdahl et al. (2004) show a consistent pattern of longer (by several seconds) Pn travel times compared with the predictions of the global seismic velocity model ak135. The Pn velocity observations are confirmed by a new tomographic model that shows variation in seismic velocities in the uppermost mantle across the Middle East. The zone of low upper mantle velocity coincides with the region of high seismic activity, which indicates that the mantle anomaly is related to active tectonic processes