Array measurements of higher mode Rayleigh wave dispersion: an approach utilizing source parameters

Abstract

Summary. The array stacking method (Nolet 1975) is extended to include information from the source mechanism by adding a ‘seismogram’ constructed from theoretical phase and amplitude excitations. If the location of the everit is favourable, the effective size of the array can be significantly increased in this way, which is desirable for better resolution of higher mode dispersion. By putting the origin at the earthquake location in the stacking method it is possible to utilize the phase of the array stack as well as the amplitude as a criterion of phase velocity across the array. Also, using events close to the array of stations should minimize adverse effects of propagation across tectonic boundaries. Synthetic seismograms of multimode surface waves were processed in order to find out the expected errors in the staclung method. In the presence of noise or interference between modes, it is shown that the errors in phase velocity from the phase criterion are relatively independent of the errors in the phase velocity from the peak amplitude criterion. The array stacking method is applied to an array composed of western US WWSSN stations recording two events in southern Mexico. This array lies within the western North America Cordilleran Belt, a large region characterized by low seismic wave velocity and a high level of tectonic activity. The fundamental mode and five higher mode Rayleigh wave dispersion curves for this region are derived from stacking the data. These have low velocity compared with average continental structure, but agree with dispersion curves computed from published average western US structures.