抄録
The November 9, 1968, south central Illinois earthquake generated fundamental and higher mode Love and Rayleigh waves, which were recorded widely by stations in North America and Canada. After applying the necessary corrections, the reduced observed Love wave amplitude versus distance data were fitted by a function in which the amplitudes decrease exponentially with epicentral distance, yielding average fundamental mode values for the coefficient of anelastic attenuation γ as a function of period in the period range of 5 to 50 sec. For paths to the west of the Rocky Mountains, γ=1.2×10-3km-1 at a period of 5 sec, decreases to 0.8×10-3km-1 at a period of 7 sec and then remains approximately constant through a period of 12 sec. In the period range 15 to 50 sec, γ=0.4×10-3km-1. For paths to the north and northeast, γ=0.6×10-3km-1 in the period range of 5 to 8 sec and γ=0.19×10-3km-1 at a period of 15 sec remaining nearly constant through a period of 40 sec. A comparison of the theoretical Love wave spectral values with the observed data yielded a focal depth of approximately 20 km and a seismic moment of (2+0.8)×1024 dyne-cm, for the 1968 event. The Love wave radiation pattern is consistent with the focal mechanism solution of STAUDER and NUTTLI (1970).
