Surface-wave generation by the south central Illinois earthquake of November 9, 1968

Abstract

Surface-wave studies of the November 9, 1968 Illinois earthquake substantiate the body-wave determined focal mechanism solution of Stauder and Nuttli (1970) and yield the source spectrum, together with Rayleigh- and Love-wave anelastic attenuation coefficients. By using narrow-band filtering techniques, fundamental-mode Rayleigh data in the 5-to-70-sec period range, first higher Rayleigh-mode data in the 7-to-14-sec period range and Love-wave fundamental-mode data in the 7-to-60-sec period range are analyzed. For a 20-km focal depth, the seismic moment is 9 × 1023 dyne-cm, within a factor of 1.5 for 95 per cent confidence. The anelastic attenuation coefficients determined for Rayleigh waves are about twice as large as those determined by Mitchell (1973a) and indicate anomalous surface-wave transmission properties in northern Canada. Synthetic records of ground velocity are generated to compare the earthquake model with maximum observed ground velocities.