Simultaneous Determination of Focal Mechanism and Moment Distribution for Rapid Responses to Large Earthquakes

Rapidly determining seismic source characteristics, particularly the moment tensor and finite-fault inversion, is critical for providing timely and detailed information for rapid responses to large earthquakes. We proposed an automatic method to improve the efficiency of these inversions, which was limited previously by using far-field data in moment tensor inversions and manual operation in finite-fault inversions. Using near-field data, we simultaneously determined the moment tensor solution and the horizontal moment distribution. It can recover the source mechanism and identify moment-concentrated regions based solely on preliminary location and magnitude results. In addition, by solving the horizontal moment distribution, this approach can handle ruptures on complex fault systems, including curved, branched, parallel, and conjugated faults. The effectiveness of this method was validated through numerical tests and applications to the 2008 Wenchuan and 2016 Kaikōura earthquakes. By utilizing real-time near-field data, this method can identify meizoseismal areas within minutes after an earthquake, providing valuable insights for intensity distribution and disaster assessment.