Real-time characterization and application of finite fault rupture parameters: A case study of the May 12, 2008 Wenchuan, Sichuan, <italic>M</italic>_S 8.0 earthquake

Finite source geometric, kinematic, and dynamic parameters of large earthquakes (M > 6) are difficult to retrieve in real-time, yet they are essential for understanding complex rupture processes and accurately assessing disaster risk. The Finite-Fault Rupture Detector (FinDer) algorithm rapidly estimates key line source parameters—centroid, length, and strike—from the spatial distribution of near-source high-frequency seismic records. Using the 12 May 2008 Wenchuan MS 8.0 earthquake as a case study, we reevaluate FinDer′s real-time performance and, on the basis of its output, propose a method for simultaneously deriving effective rupture direction and rupture velocity. We further test the usefulness of these parameters for Earthquake Early Warning (EEW). The results show that FinDer continuously updates the line source parameters during rupture and converges to a stable solution approximately 100 s after origin time: rupture length 290 km, magnitude MFD 8.0, strike 50°, epicenter 103.25°E/31.09°N, centroid 104.51°E/32.08°N, predominant rupture direction 49°, and apparent rupture velocity 2.8 km·s−1. This velocity represents the effective near-surface energy-propagation speed and explains the ~20 s pseudo-supershear phase observed in the early rupture. The time history of rupture direction clearly reveals a dominant southeastward propagation between 20 s and 30 s, followed by northeastward propagation after 30 s. EEW scenario analyses indicate that accounting for rupture directivity improves Peak Ground Acceleration (PGA) predictions at some stations and yields, on average, an additional ~4 s of warning time for stations located in high-intensity areas.