Higher-degree moment tensor inversion using far-field broad-band recordings: Theory and evaluation of the method with application to the 1994 Bolivia deep earthquake

Abstract

We present a method to estimate parameters of the extended earthquake source using higher-degree moment tensors at 27 centroid locations. We show that a Taylor series expansion of Green's functions around a single centroid is not accurate enough when working with seismic wave periods and wavelengths in the range of the rupture duration and spatial extent of the fault, respectively. Introducing a grid of 27 centroid locations on the fault and using higher-degree moment tensors we are able to model adequately body and surface waves with periods and wavelengths smaller than the rupture duration and fault dimensions. Under simplifying assumptions an iterative inversion scheme is coded to estimate parameters of planar, Haskell-type faults. Realistic inversion examples for deep and shallow earthquakes show that uni- and bidirectional rupture models, rupture direction, fault and auxiliary plane and kinematic source dimensions and times can be constrained with teleseismic body and/or surface waves. The application to the deep Bolivia event indicates a subhorizontal fault plane. Unidirectional rupture to the north is slightly preferred. The rupture duration of 25 s and fault dimensions of 47 x 25 km agree well with the estimates for the main pulse moment release given in other studies.