Source parameters of earthquakes in northeast India from spectra of Rayleigh waves

Abstract

A quantitative description of eight earthquakes in northeast India, in terms of seismic moment, dislocation, apparent stress and apparent average strain is sought. The analysis is based on the theory of radiation pattern of surface waves from buried seismic sources proposed by Ben-Menahem and Harkrider (1964). Further, it makes use of the amplitude spectra of digitally recorded Rayleigh waves at the Central Seismological Observatory in Erlangen (GRF), F.R. Germany. The amplitude spectra of Rayleigh waves are corrected for instrument response, path propagation effects and effects of the radiation pattern. Published results on attenuation and focal mechanism solutions are utilized to arrive at reasonable estimates of the quantities under investigation. Comparison of the calculated values is also made with the estimates based on body-wave spectra.It is concluded that the earthquakes in northeast India are of low moment type. The faulting process is supposed to be non-homogeneous, which results in low estimates of seismic source parameters and a characteristic source time function (Upadhyay and Duda, 1980). Comparison of source parameter values with known estimates for intraplate earthquake is made. For equal-magnitude earthquakes, intraplate earthquakes are characterized by higher seismic moment. Two of the earthquakes (Ms = 6.3) considered here are compared with the Koyna earthquake of Dec. 10, 1967. Emphasis is laid on development of theoretical models to account for the strain build-up rates in inter- and intraplate earthquakes.