Real-Time Characterization of Finite Rupture and Its Implication for Earthquake Early Warning: Application of FinDer to Existing and Planned Stations in Southwest China

Earthquake early warning (EEW) not only improves resilience against the risk of earthquake disasters, but also provides new insights into seismological processes. The Finite-Fault Rupture Detector (FinDer) is an efficient algorithm to retrieve line-source models of an ongoing earthquake from seismic real-time data. In this study, we test the performance of FinDer in the Sichuan-Yunnan region (98.5 degrees E-106.0 degrees E, 22.0 degrees N-34.0 degrees N) of China for two datasets: the first consists of seismic broadband and strong-motion records of 58 earthquakes with 5.0 <= M-S <= 8.0; the second comprises additional waveform simulations at sites where new stations will be deployed in the near future. We utilize observed waveforms to optimize the simulation approach to generate ground-motion time series. For both datasets the resulting FinDer line-source models agree well with the reported epicenters, focal mechanisms, and finite-source models, while they are computed faster compared to what traditional methods can achieve. Based on these outputs, we determine a theoretical relation that can predict for which magnitudes and station densities FinDer is expected to trigger, assuming that at least three neighboring stations must have recorded accelerations of 4.6 cm/s(2) or more. We find that FinDer likely triggers and sends out a report, if the average distance between the epicenter and the three closest stations, D-epi, is equal or smaller than log(10) (M-a + b) + c, where a = 1.91, b = 5.93, and c = 2.34 for M = M-W >= 4.8, and c = 2.49 for M = M-S >= 5.0, respectively. If the data used in this study had been available in real-time, 40-70% of sites experiencing seismic intensities of V-VIII (on both Chinese and MMI scales) and 20% experiencing IX-X could have been issued a warning 5-10 s before the S-wave arrives. Our offline tests provide a useful reference for the planned installation of FinDer in the nationwide EEW system of Chinese mainland.