Precursors to the Garm Earthquake of March 1969

The average P residual increased by 0.4 s 1.2 yr before the ML = 5.7 Garm earthquake of March 22, 1969. This is interpreted to indicate a decrease in the P velocity by approximately 10–20% in the local crust. The P wave precursor time is slightly shorter than that indicated by a preferred alignment of the compression axes and by a decrease in local seismicity (Nersesov et al., 1973). Barsukov (1972) reported a decrease of apparent resistivity 0.6 yr before the same event. All precursor observations were obtained within a radius of 25 km of the epicenter and outside the 6 by 10 km aftershock zone. The precursor volume must have exceeded the source dimensions by a factor of 5. 1 Supplementary data are available with the entire article on microfiche. Order from American Geophysical Union, 1909 K Street, N.W., Washington, D.C. 20006. Document J75-009; $1.00. Payment must accompany order.