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Some seismological and geometric features of intraplate earthquakes

Publication Date
DOI: 10.1016/0040-1951(91)90383-4
  • Earth Science
  • Mathematics
  • Physics


Abstract To understand the nature and cause of intraplate earthquakes we carried out a systematic search for common features associated with them. Various geological, geophysical and seismic data were analyzed and geometric and seismic parameters were compared for 29 intraplate events ( M ⩾ 4.5) occurring worldwide. The results suggest that intraplate earthquakes occur by the reactivation of pre-existing zones of weakness in a compressional stress regime which is generally oriented parallel to the absolute direction of plate motion. Two styles of faulting were observed. For type A earthquakes, observed in the eastern United States, eastern China, western Europe and West Africa, deformation occurs by strike-slip motion on steeply dipping faults. Type B events are usually associated with thrust or normal faulting and were observed in eastern Canada, Fennoscandia, Australia and peninsular India. Focal depths did not explain the differences between type A and type B earthquakes; rather, the differences are due to the perturbation of a regional stress field by a local stress field. The regional stress field for type A events is primarily due to ridge push forces. The method of stress perturbation varied from region to region. The earthquakes in the type B category were further divided into three subcategories: type B 1 (occurring in eastern Canada and Fennoscandia), type B 2 (occurring in Australia, peninsular India and central Brazil) and type B 3 (occurring in the Gulf Coast of the U.S.). The inferred causes of the perturbing stresses are deglaciation, intracontinental resistive forces resulting from the collision of plates and the deposition of a large thickness of sediments, respectively. Type A events were found to be associated with intersecting faults and generally supported the intersection model of Talwani (1988) and had analogs in plate boundary events.

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