Fault-plane Solution of the Koyna (India) Earthquake

THE peninsular shield of India has long been regarded as a stable region. The area had not been subject to orogenic deformation since the Pre-Cambrian, although a vast area (5 × 10⁵ square km) was flooded by basalts during Late Cretaceous to the Eocene—the Deccan Trap. Several years ago, a small dam was built across the Koyna river, some 200 km south-east of Bombay (Fig. 1). The dam reservoir filled in stages, beginning with the monsoon of 1962, and reached a capacity of 2 × 10⁹ m³ and a maximum depth of about 70 m¹.