Following its impoundment in December 1977, induced seismicity was observed at Monticello reservoir in South Carolina. This shallow (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 ts/tp ratios were examined in detail for the period July-September 1978. We observed two periods of precursory decrease of 6--12% in ts/tp for ML 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 2.0L<3.0 earthquakes is about 4 km in radius.