Pn velocities beneath Iran

In active tectonic areas like Iran, where the coverage of seismograph stations is inadequate but earthquakes occur frequently, uppermost mantle body wave velocities are conventionally determined by using a single station and an array of earthquake sources. This method fails when earthquakes are mislocated or source areas have varied structures. An extension of the traditional surface wave two-station method is developed for body waves and shown to be independent of mislocation errors. It thus gives accurate estimates of body wave velocities along two station paths with greatly reduced errors.Uppermost mantle P wave (P_n) velocities are determined along several paths in Iran using this method and show zones of low-velocity corresponding to zones of high attenuation and Quaternary volcanic activity in the country. A remarkably high P_n velocity of 8.30 km/s is found for the Zagros area of western Iran more typical of shield like structures than that of tectonic areas.