Seismogenesis in the stable continental interiors: an appraisal based on two examples from India

Abstract

Characteristics of two recent moderate earthquakes from India (1993 Killari, M w 6.1 and 1997 Jabalpur, M w 5.8) are presented in this paper to illustrate the influence of geologic and tectonic setting on the nature of seismicity in stable continental regions (SCRs). The Killari event, which occurred in the middle of a cratonic region of low background seismicity, long recurrence interval and poorly developed neotectonic features, may be qualified as a common type of SCR event. This earthquake is also characterized by a shallow focal depth and a long sequence of aftershocks. In contrast, the Jabalpur earthquake shows a spatial association with a well-defined tectonic structure with significant background seismicity. A remarkable feature of this earthquake is its deep focus, not commonly observed in SCR seismicity. This event was associated with fewer aftershocks unlike most other SCR earthquakes. Analogous events are found in other shield regions as well. Based on their general characteristics, a broad classification of moderate SCR earthquakes is attempted here. Two broad groups have been identified in this study: (1) a set of deep focus earthquakes that are related to intracratonic paleorifts, and (2) shallow-focus earthquakes associated with discrete faults in the less deformed Precambrian terrains. A synthesis of earthquake data from different geologic environments will improve our understanding of the seismogenesis in the shield regions.