A study of the seismic waves SKS and SKKS

Abstract

Arrival times, amplitudes, and periods of the seismic phases SKS and SKKS have been investigated for shallow, intermediate, and deep earthquakes recorded at Pasadena and Huancayo, Peru. New observed time-distance curves are constructed for depths of <60, 100, 200, and 600 kilometers. Travel times for the core have been calculated from shallow-shock time data. Slight modification of wave velocity just inside the core and of travel times within the core are suggested. Calculated travel times of SKS, SKKS, and SKKKS are in good agreement with observations. Energy parameters determined from observed amplitude/period ratios are found in only fair agreement with those calculated from theory. Observed energies are too large for most of the phase components and depths considered. The horizontal components of SKKS over the whole distance range, and of SKS at Δ ≦ 100° for all depths, yield observed energies less than those predicted by theory. Both discrepancies are at least qualitatively explained by a proposed nonspherical distribution of shear strain about the fault source, and by abnormal absorption in the outer 700 kilometers of the core. Anomalous observed energies, as functions of epicentral location, are also accounted for by the proposed nonspherical distribution of energy.