Real-time Finite Fault Rupture Detector (FinDer) for large earthquakes.

SUMMARY To provide rapid estimates of fault rupture extent during large earthquakes, we have developed the Finite Fault Rupture Detecto r algorithm, 'FinDer'. FinDer uses image recognition techniques to detect automatically surface-projected fault ruptures in real-time (assuming a line source) by estimating their current centroid position, length L, and strike θ. The approach is based on a rapid high-frequency near/far-source classification of ground motion amplitudes in a dense seismic network (station spacing <50 km), and comparison with a set of pre-calculated templates using 'Matching by Correlation'. To increase computational efficiency, we perform the correlation in the wavenumber domain. FinDer keeps track of the current dimensions of a rupture in progress. Errors in L are typically on the same order as station spacing in the network. The continuously updated estimates of source geometries as provided by FinDer make predicted shaking intensities more accurate and thus more useful for earthquake early warning, ShakeMaps, and related products. The applicability of the algorithm is demonstrated for several recorded and simulated earthquakes with different focal mechanisms, including the 2009 Mw 6.3 L'Aquila (Italy), the 1999 Mw 7.6 ChiChi (Taiwan) and the Mw 7.8 ShakeOut scenario earthquake on the southern San Andreas Fault (California). [ABSTRACT FROM AUTHOR]