Earthquakes related to active salt doming near Kulyab, Tadjikistan, USSR

Abstract

In the region near Kulyab, Tadjikistan, hundreds of shallow earthquakes with magnitudes greater than 2½ have been reported in Soviet yearly catalogs since 1964. This area appears as a well‐defined cluster of activity, distant from the line of epicenters that defines the Gissar‐Kokshal seismic zone, to the north of the Pamir ranges. The geology of this region is dominated by the presence of numerous salt domes, surrounded by Neogene and Quaternary continental deposits. The spatial relationship between these earthquakes and the salt domes suggests that the two phenomena may be related. Moderate earthquakes (M > 5) occurred in 1972 and 1973, and intensities of surface shaking greater than MM=6 were reported from earthquakes in 1937, 1952, 1969, 1972, 1973 and 1978. The earthquake on 2 April 1973 and its aftershocks were located in a region where no salt domes have been mapped at the surface. However, a buried salt diapir has been mapped at depth by geophysical means. These earthquakes may result from active salt diapirism at depth. The mechanism for producing this seismicity could be either the active fracturing of the cap rock by the rising diapir, or the concentration of tectonic stresses in the thinned section above and adjacent to the diapir. The salt‐related earthquakes may produce lower frequency radiation than other events of the same size.