DETERMINATION OF ATTAINABLE BOUNDARIES OF THE REGION OF PERMISSIBLE VELOCITY PROFILES IN THE τ METHOD

Abstract

In the present article we shall focus on a method of obtaining the attainable boundaries of the region containing the admissible velocity profiles from estimates of the function τ(p) and some logical assumptions regarding the behavior of the time-distance plot. This method is best suited to the processing of large banks of travel-time data for body waves generated by earthquakes. Calculations with the new algorithm give more accurate boundaries of the region of admissible profiles, which are identical with the boundaries obtained from Molchan's model; but the new algorithm requires considerably less computational time than Molchan's simplex method. The algorithm was evaluated by a FORTRAN program and tested on various modeling cases. One approach to processing the measurements is presented below. In addition to determining the boundaries of the region of admissible velocity profiles, the programs can be used to construct a family of velocity profiles that fit the initial geophysical data with the desired degree of error and that mark out the region that has been constructed. This method was applied to the analysis of data obtained by the Special Regional Geophysical Field Parts of the Neftegeofizika Corporation in 1978 on a submeridional profile crossing the Siberian craton. The result provides the information that is needed in order to construct a preliminary velocity model of the lithosphere of the Siberian craton to a depth of 160 km.