Abstrakt
We analyze the location of earthquakes in near regional networks using complete seismic records. The method is based on the source scanning algorithm (SSA) of Kao and Shan (2004), but similarly to Grigoli et al. (2013), seismograms are substituted by a P-wave picker trace.
The picker traces in a network are repeatedly stacked using grid of trial source positions, and hypocenter is identified with the point providing the best stack (the largest brightness). The first innovation of this paper is a new picker, measuring the ratio of the summed absolute values of seismogram in the right and left part of a moving time window, the RPA/LPA picker.
The brightness maps based on this picker are clearer than those based on the STA/LTA picker. The second innovation is a simple theoretical model of the brightness maps.
It makes it easy to identify how individual stations contribute to form the brightness spot. It is shown on synthetic tests that the performance of the method depends on focal mechanism, progressively improving from normal to reverse and strike-slip events.
The method is successfully applied to four events of different mechanisms and depths, recorded at different ranges of epicentral distance by either broad-band sensors or accelerographs. The events have been located close to previously published epicenters.
The brightness maps provide an estimate of the relative uncertainty of the (non-linear) location problem. The uncertainty estimate is also applicable without measured arrival times, "without earthquakes", thus useful when designing or upgrading seismic networks for better location performance.