Pn velocity and other seismic studies from the data of recent southeast Missouri earthquakes

Abstract

Five earthquakes occurred in the southeastern Missouri seismic region during the first seven months of 1962. The largest of these took place on 2 February 1962, and was located near New Madrid. The felt area of this shock covered 35,000 square miles; the maximum intensity was Intensity V in the Modified Mercalli scale. The magnitude is estimated to have been 4 1/2 to 4¾. P_n arrival times from thirty-five stations in the distance range 200 km to 1000 km fit a composite travel time curve for all five earthquakes given by This contrasts with interval velocities of 8.3 km/sec to 8.5 km/sec obtained by Herrin and Taggart for this region from the Gnome data. S_n and P and S crustal velocities are also studied. Pulse-like Rayleigh and Love waves were also recorded, each indicating a group velocity maximum at a period of about 6 seconds. The amplitudes of each of these wave types vary strongly, and in an inverse relation, with azimuth about the source. Group velocities correlate with the sedimentary and upper crustal structure along the path.