EARTHQUAKES IN CONTINENTAL INTERIORS: A GLOBAL STUDY

Plate boundaries often coincide with the densely-populated margins of continents, and relatively large earthquakes occur at these boundaries. Much attention has been paid to seismic hazard assessment and earthquake preparedness in continental areas located along or near these boundaries. In contrast, a relatively small number of earthquakes, accounting for approximately 0.5% of the total global moment release (Johnston and Kanter, 1990), are not directly related to plate boundaries and are therefore termed intraplate earthquakes. Though limited in number, their consequences can be disastrous, as is illustrated by a very recent example, the Mw=7.7 earthquake of 26 January 2001 in Bhuj, India. As a result of this earthquake at least 20,000 lives were lost, more than 200,000 people were injured and nearly 400,000 houses destroyed (Rajendran et al. 2001). Whereas plate boundary earthquakes are well understood, the mechanisms that cause intraplate earthquakes are subject to considerable debate. In this paper we discuss some common features of intraplate earthquakes, and summarize hypotheses for the mechanisms that trigger these events. We conclude by describing new global datasets that may hold the key to understanding intraplate seismicity.