The southeastern Illinois earthquake of 10 June 1987: The later aftershocks
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Abstract
The 10 June 1987 southeastern Illinois earthquake (mbLg = 5.2) was the seventh in a series of moderate magnitude (≧ 4.5) MMI VII shocks to occur in the Wabash Valley seismic zone of southeastern Illinois and southwestern Indiana since 1891. Located about 200 km east of St. Louis, Missouri, the shock caused minor damage in the epicentral area, had a contiguous felt area of about 433,000 km2, and had a total felt area over 1 million km2. Within 47 hours after the main shock, a cooperative effort between the U.S. Geological Survey and Memphis State University installed a 15-station aftershock monitoring network (later expanded to 21 instruments) that recorded more than 100 aftershocks in the following 4-day period. Results from the 56 aftershocks that were well located indicate a compact, cylindrically shaped aftershock volume about 1.7 km long, 0.8 km wide, and with a vertical distribution between about 9 and 12 km in depth. Composite focal mechanism solutions of the aftershocks suggest that the predominant mode of faulting is reverse slip, but some strike-slip type motion occurred similar to the mechanism for the main shock as determined from teleseismic data. The maximum principal compressive stress (P axes) is oriented easterly to east-southeasterly and is subhorizontal in plunge. These results, combined with historical observations and the recent discovery of earthquake-induced liquefaction features in the area, imply that the seismic potential of the zone may be greater than generally perceived.
Study Area
Publication type | Article |
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Publication Subtype | Journal Article |
Title | The southeastern Illinois earthquake of 10 June 1987: The later aftershocks |
Series title | Bulletin of the Seismological Society of America |
DOI | 10.1785/BSSA0810020423 |
Volume | 81 |
Issue | 2 |
Year Published | 1991 |
Language | English |
Publisher | Seismological Society of America |
Description | 23 p. |
First page | 423 |
Last page | 445 |
Country | United States |
State | Illinois |
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