Relocations of nearly 1,500 earthquakes that occurred between 1950 and 1965 in the area extending from 30° to 75°E and 20° to 45°N delineate the major seismically active tectonic zones in this region. The northern boundary of the Arabian plate is marked by a nearly continuous line of epicenters along the Zagros-Taurus mountains and the Levant fracture zone. The entire series of elongated foothills of the Zagros is a region in which the crustal rocks are contracted by folding, faulting, or a combination of both. The seismic and geological evidence can be explained most simply by a relative northeast motion for the Arabian plate with respect to Eurasia; this motion produces the compressional features along the Zagros thrust zone. In Persia, the Zagros thrust zone separates the presently more continuous seismic regime of the southwest from the episodic seismic regime of the median area. In the Caucasus, a deviation between the alignment of epicenters and geological trends may indicate current changes in the tectonic regime. In the Hindu Kush region, the seismic zone appears as a contorted slab-like structure with a width of 20 to 30 km and consists of a clear east-west alignment of epicenters with focal depths of about 200 km. This zone is connected to another broader zone with a trend of N45°E and focal depths of about 100 km. The trend of the deeper seismic zone does not correspond to that of any surface features, although the shallower seismic zone has the general trend of the Hindu Kush mountains. The focal depths in other areas are generally less than 50 km, with occasional exceptions in front of the Zagros-Taurus thrust zone, the tectonic zones of the Elburz and Caucasus mountains, and the western shore of the Caspian Sea.