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Spatial and temporal variations in t s /t p at Monticello Reservoir, South Carolina
Author(s) -
Rastogi B. K.,
Talwani Pradeep
Publication year - 1980
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl007i010p00781
Subject(s) - induced seismicity , geology , radius , seismology , magnitude (astronomy) , spatial variability , physics , statistics , astronomy , computer science , computer security , mathematics
Following its impoundment in December 1977, induced seismicity was observed at Monticello reservoir in South Carolina. This shallow (< 2 km), low level (M L < 3.0) activity is still continuing and is confined to the immediate vicinity of the reservoir (in an area of about 5 × 10 km²). Spatial and temporal variations in t s /t p ratios were examined in detail for the period July‐September 1978. We observed two periods of precursory decrease of 6‐12% in t s /t p for M L 2.7 and 2.3 events on August 27 and September 15, 1978, respectively. A precursor time of about 15 days was observed for each of these events. During the anomalous periods, stations within about 8 km of the epicentral area (S‐P ∼ 1 sec) were associated with low ratio values, while the distant stations were associated with normal ratio values ( ∼ 1.75) suggesting that the size of the anomalous zone associated with 2.0 < M L < 3.0 earthquakes is about 4 km in radius.