thumbnail

Foreshock occurrence rates before large earthquakes worldwide

Pure and Applied Geophysics

By:

Links

  • The Publications Warehouse does not have links to digital versions of this publication at this time

Abstract

Global rates of foreshock occurrence involving shallow M ??? 6 and M ??? 7 mainshocks and M ??? 5 foreshocks were measured, using earthquakes listed in the Harvard CMT catalog for the period 1978-1996. These rates are similar to rates ones measured in previous worldwide and regional studies when they are normalized for the ranges of magnitude difference they each span. The observed worldwide rates were compared to a generic model of earthquake clustering, which is based on patterns of small and moderate aftershocks in California, and were found to exceed the California model by a factor of approximately 2. Significant differences in foreshock rate were found among subsets of earthquakes defined by their focal mechanism and tectonic region, with the rate before thrust events higher and the rate before strike-slip events lower than the worldwide average. Among the thrust events a large majority, composed of events located in shallow subduction zones, registered a high foreshock rate, while a minority, located in continental thrust belts, measured a low rate. These differences may explain why previous surveys have revealed low foreshock rates among thrust events in California (especially southern California), while the worldwide observations suggest the opposite: California, lacking an active subduction zone in most of its territory, and including a region of mountain-building thrusts in the south, reflects the low rate apparently typical for continental thrusts, while the worldwide observations, dominated by shallow subduction zone events, are foreshock-rich.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Foreshock occurrence rates before large earthquakes worldwide
Series title:
Pure and Applied Geophysics
Volume
155
Issue:
2-4
Year Published:
1999
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
355
Last page:
379
Number of Pages:
25