Geophysical investigations of the western Ohio-Indiana region: Annual report, October l986-September 1987

Technical Report · Mon Feb 01 04:00:00 EST 1988

OSTI ID:6935663

Schwartz, S Y; Christensen, D H; Lay, T; Cohee, B P

Earthquake activity in the Western Ohio--Indiana region has been monitored with a precision seismograph network consisting of nine staions located in west-central Ohio and four stations located in Indiana. One local and eleven near-regional earthquakes have been recorded during this report period. The local event had a duration magnitude of 0.7 and was not large enough to be felt. Its location is very close to the larger (m/sub b/ = 4.5) 12 July 1986 St. Marys, Ohio earthquake. Many of the regional events were felt with magnitudes ranging from m/sub bLg/ = 2.7--4.9. The two largest of these events (27 March 1987 in northeastern Tennessee, m/sub b/Lg = 4.2, and 10 June 1987 in southeastern Illinois, m/sub b/Lg = 4.9) had minor damage reported in each case. P/sub n/ travel time residuals, computed for all well-recorded regional events since deployment of the Anna Seismic Network, display a strong azimuthal dependence with positive residuals (slow observed arrival times) obtained from events with northeasterly through southerly back azimuths and negative residuals (fast observed arrival times) from events with westerly back azimuths. This pattern has large residuals, but is similar to the azimuthal dependence displayed in the teleseismic P-wave residuals, supporting an interpretation that shallow structural heterogeneity is responsible for the P/sub n/ residual pattern. 10 refs., 10 figs., 4 tabs.

• Research Organization: Michigan Univ., Ann Arbor (USA). Dept. of Geological Sciences
• OSTI ID: 6935663
• Report Number(s): NUREG/CR-3145-Vol.6; ON: TI88010123
• Country of Publication: United States
• Language: English

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