STUDY OF THE VERTICAL SCATTERING PROPERTIES OF THE LITHOSPHERE BASED ON THE INVERSION OF P- AND S-WAVE PULSE BROADENING DATA

Abstract

The vertical distribution of the scattering properties of the lithosphere can be found using Bocharov's formula which describes the broadening of an incoherent pulse with distance as it propagates in a scattering medium with scattering varying along the raypath. For a piecewise constant scattering distribution, Bocharov’s formula yields a linear equation for every raypath that relates the scattering of the blocks traversed by the raypath to a parameter that defines the pulse width. This set of equations can be solved by least squares to find scattering distribution in a certain lithospheric volume. Records of P and S waves from local earthquakes with focal depths of up to 140 km made at six Kamchatkan stations were measured to determine the onset-to-peak delay times (400-600 measurements). These data were inverted for each station to find scattering for a layer-on-half-space model. The results did not differ much between the stations and yielded the following distribution: scattering was 0.02 1/km (P waves) and 0.008 1/km (S waves) in the upper layer 30-50 km thick and 5-10 times as low in the lower layer ((30…50)-140 km). The exact scattering of the lower layer was not evaluated.