Seismic source characterization using a neighbourhood algorithm

The full characterization of a seismic source requires the specification of the hypocentre location and the source mechanism. The non-linear inversion is accomplished in two stages using the Neighbourhood Algorithm (NA), a di rect search method in parameter space which is able to preferentially sampl e those regions with least data misfit; there are just two control paramete rs and no differentiation is employed. The first step is hypocentre locatio n using a 4-D search space and a focussed search strategy. The second step is waveform inversion of the early part of P and S wavetrains to refine sou rce depth and extract the source mechanism. With a moment tensor representa tion, this second stage explores an 8-D parameter space. For both the hypoc entre and source mechanism inversion the NA method provides rapid and effec tive results with information from just a few stations, as illustrated with an event in southern Xinjiang.