Rapid identification of earthquake rupture plane using Source-Scanning Algorithm

Accurate identification of an earthquake's rupture plane is critical in many aspects, ranging from scientific, such as seismology and plate tectonics, to societal, such as emergency rescue planning. We modify the recently developed Source-Scanning Algorithm (SSA) to rapidly image the rupture pattern of an earthquake using waveform data recorded at local and regional distances. The method calculates the brightness function of a grid point by summing the observed amplitudes of the P wave envelopes at the corresponding predicted arrival times at all stations. The composite image, consisting of brightness functions of all grid points within a prescribed source volume and time interval, illuminates the locations on the rupture plane where significant seismic energy is emitted. Synthetic tests indicate that the proposed method is robust even under the presence of hypocentral mislocation and origin time errors. Application of this method to the 2003 San Simeon and 2004 Parkfield earthquakes (both occurred in central California) clearly identifies the NW-SE-striking planes as the actual rupture planes, a conclusion consistent with all available evidences. Limited azimuthal distribution of seismic stations will not severely affect the identification result, making this method ideal for offshore earthquake studies. Because the proposed method is able to identify the rupture plane using seismic waveform data only, it is perfectly suited for near-real-time operation and may enable routine report of earthquake rupture planes by local seismic networks in the future.