Nature of P-wave signals from Hindukush earthquakes

Abstract

Several causes for complexity of P-wave signals from earthquakes in the Hindukush focal region and recorded at Gauribidanur seismic array in southern India, have been investigated. Visual inspection of the records of these earthquakes revealed that most of the events occurring at shallow depths had complex signatures as compared to the deeper events. A positive correlation of complexity with magnitude is found. Spectral ratio measurements have demonstrated that complex signals are richer in low frequency energy. A number of theoretical seismograms for short period P-waves were computed and the analysis reveals that within certain constraints, complexity increases with focal fault area and decreases with focal depth. The structure of the fault rock in the source region, the source functions itself, and the ray-scattering in the crust-upper mantle near the source are the main responsibilities for the complexity of the Hindukush earthquake records at GBA since the transmission of the ray-tubes for all events studied is practically identical, with the exception of the very first near source part. © 1994.