Real-time Moment Tensor Inversion and Centroid Location for Large Events from Local and Regional Displacement Records

We will present here an algorithm to determine the moment tensor and centroid location for large earthquakes employing local and regional real-time displacement records from GPS or GPS/seismic data. The algorithm extracts the coseismic offset from the displacement waveforms and uses the information to invert for the moment tensor. The Green's functions for a layered Earth are obtained numerically from open source code EDGRN. To determine the centroid multiple inversions are performed simultaneously with different centroid coordinates (inversion nodes), the node with the smallest misfit is then assigned the centroid location. We will show results for two example earthquakes in simulated real-time mode using recorded 1 Hz GPS displacements: the 2003 Mw 8.3 Tokachi-Oki and the 2010 Mw 7.2 El Mayor-Cucapah events. We demonstrate that it is feasible with this methodology to obtain accurate source parameters (magnitude, fault plane geometry and style of faulting) within the first 2-3 minutes after rupture initiation, making this methodology amenable for early detection purposes and rapid source modeling.