Estimating Rupture Dimensions of Three Major Earthquakes in Sichuan, China, for Early Warning and Rapid Loss Estimates

Abstract

Large earthquakes, such as Wenchuan in 2008, Mw 7.9, Sichuan, China, provide an opportunity for earthquake early warning (EEW), as many heavily shaken areas are far (∼50 km) from the epicenter and warning times could be sufficient (≥5 s) to take preventive action. On the other hand, earthquakes with magnitudes larger than ∼M 6.5 are challenging for EEW because source dimensions need to be defined to adequately estimate shaking. Finite-fault rupture detector (FinDer) is an approach to identify fault rupture extents from real-time seismic records. In this study, we playback local and regional onscale strong-motion waveforms of the 2008 Mw 7.9 Wenchuan, 2013 Mw 6.6 Lushan, and 2017 Mw 6.5 Jiuzhaigou earthquakes to study the performance of FinDer for the current layout of the China Strong Motion Network. Overall, the FinDer line-source models agree well with the observed spatial distribution of aftershocks and models determined from waveform inversion. However, because FinDer models are constructed to characterize seismic ground motions (as needed for EEW) instead of source parameters, the rupture length can be overestimated for events radiating high levels of high-frequency motions. If the strong-motion data used had been available in real time, 50%–80% of sites experiencing intensity modified Mercalli intensity IV–VII (light to very strong) and 30% experiencing VIII–IX (severe to violent) could have been issued a warning with 10 and 5 s, respectively, before the arrival of the S wave. We also show that loss estimates based on the FinDer line source are more accurate compared to point-source models. For the Wenchuan earthquake, for example, they predict a four to six times larger number of fatalities and injured, which is consistent with official reports. These losses could be provided 1/2∼3 hr faster than if they were based on more complex inversion rupture models.

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

“…The FinDer line-source model characterizes the entire fault rupture including those segments with no surface exposure. Compared with the results of Li et al (2020a), who tested FinDer with a larger trigger threshold (20 cm/s 2 ), the length of the line-source model is underestimated by about 50 km (corresponding to 0.1 magnitude units). This difference is caused by sparse station density around the Wenchuan earthquake as discussed in Li et al (2020b).…”

“…In most installations, FinDer adopts the GMPEs developed by Cua and Heaton (2009) that were derived from strong-motion records in California (M 2-M 7.3) and the Next Generation Attenuation (NGA) strong-motion dataset (M 2-M 8). Real-time and offline tests of FinDer in the U.S. West Coast, Switzerland, Italy, Japan, and China (Böse et al, 2012(Böse et al, , 2015(Böse et al, , 2018Li et al, 2020a) have confirmed that the templates are globally applicable to crustal earthquakes. In previous work (Li et al, 2020a), we compared the GMPE of Cua and Heaton (2009) with the regional relationship used in the fifth-generation hazard zoning map in southwestern China, as well as with PGA values, that were observed during the 2008 M S 8.0 Wenchuan, 2013 M S 7.0 Lushan and 2017 M S 7.0 Jiuzhaigou earthquakes.…”

“…Real-time and offline tests of FinDer in the U.S. West Coast, Switzerland, Italy, Japan, and China (Böse et al, 2012(Böse et al, , 2015(Böse et al, , 2018Li et al, 2020a) have confirmed that the templates are globally applicable to crustal earthquakes. In previous work (Li et al, 2020a), we compared the GMPE of Cua and Heaton (2009) with the regional relationship used in the fifth-generation hazard zoning map in southwestern China, as well as with PGA values, that were observed during the 2008 M S 8.0 Wenchuan, 2013 M S 7.0 Lushan and 2017 M S 7.0 Jiuzhaigou earthquakes. We found that the GMPEs and PGA values are in good agreement, so we use the same templates based on Cua and Heaton (2009) here in this study.…”

“…length, strike, rupture direction, rupture velocity etc. ), and is expected to significantly improve both EEW and rapid loss estimates in China (Li et al, 2020a).…”

“…For larger events (M ≥ 5.5) M FD is computed from empirical rupture length-magnitude relationships (typically Wells and Coppersmith, 1994) using the length of the FinDer determined line-source. FinDer line-source models were introduced to characterize the temporal-spatial distribution of high-frequency ground-motions (PGA) rather than to provide an accurate source characterization (Li et al, 2020a). These high-frequency ground-motions are of primary concern in practice and therefore are critically important to real-time seismology.…”