THE ISOSTATIC GRAVITY ANOMALIES AND SEISMIC ACTIVITY IN THE HIMALAYAN REGION

In accordance with the earthquake data from 1950—1975, the diagram of seismic activity in the eastern and mid parts of the Himalaya is plotted by using Earthquake Summation Method, and is compared quantitatively with the isostatic gravity anomalies of the region. The result indicates that seismic activity of the area increases (decreases) with isostatic anomalies descent (ascent). Large negative isostatic anomalies is often related to high seismic activity. Stronger seismic activity is usually found in the area where horizontal gradient of isostatic anomalies vary largely. The energy released by earthquake in the northwest part of Burma is as twice large as that in the central part of the Himalayan region. With the tectonics of the region, the possible causes for sei-mic activity and isostatic anomalies are studied.