Change in Rayleigh wave phase velocity due to decrease of P-wave velocity before an earthquake

Abstract

20per cent decrease of P-wave velocity has often been noted by many workers before an earthquake. Change in Rayleigh wave phase velocity due to such a decrease is studied so as to note the possibility of using the phase velocity change as one of the methods to predict earthquake. For this purpose theoretical phase velocity and its change due to the decrease of P-wave velocity have been obtained for a two-layered crustal model over a homogeneous mantle. 20 per cent decrease of P-wave velocity in the first layer gives a decrease of phase velocity by 4 per cent over a wide range of period with a maximum decrease of 4.8 per cent. While 20 per cent decrease of P-wave velocity in the both first and second layers of the crust gives a phase velocity decrease of 5 per cent over a wide range of period with a maximum decrease of 7.0 per cent.