水平方向不均質媒質におけるラブ波の伝搬様式

Abstract

Propagation of Love waves across a symmetrical mountain root structure with a high dip angle is investigated by use of the finite difference method. The structure is modelled by a set of steps of the Moho discontinuity, and has crustal thicknesses of 35 and 87.5km at the thinnest and thickest portions over a distance of 250km, respectively. The dip angle of the Moho discontinuity is about 20°. The important and interesting results obtained are as follows:(1) The phase velocities for the downdip propagation are higher than those for the updip propagation in the period range 18-37s. They are inverse in the period range 38-46s.(2) The phase velocities for the downdip propagation oscillate several times in the period range 18-46s, while the phase velocities for the updip propagation increase monotonously with increasing period in the period range 22-46s.(3) At the periods of 18, 26 and 38s, the phase velocities for the downdip propagation accord with those for the updip propagation.(4) The average phase velocity dispersion curve across the mountain root structure shows the middle one between the dispersion curves for the downdip and updip propagations.(5) The average dispersion curve across the mountain root structure does not show the middle one between two typical dispersion curves for the thinnest (S-structure) and thickest (D-structure) crustal structures.(6) The average dispersion curve is close to that for the D-structure at short periods and approaches that for the S-structure at long periods.