Near-Real-Time Estimates on Earthquake Rupture Directivity Using Near-Field Ground Motion Data From a Dense Low-Cost Seismic Network

Rupture directivity of earthquakes could amplify ground shaking and cause serious earthquake hazards. Its timely information is therefore of great importance for early shaking alerts and emergency responses. To this end, we test the feasibility of using near-field (<25 km) ground motion data from a dense low-cost seismic network in Taiwan to constrain directivity information and provide warning for far-field areas. The method is simple and robust, based on the real-time shaking map interpolation and directional attenuation regression analysis. Applications to 16 moderate- to large-magnitude earthquakes in Taiwan and California show that the directivity can be stably obtained within 17 s and agrees well with previous studies when available. An indicator of the strength of directivity amplification is also defined and reveals a prevalence of strong directivity effect for M_L ≥ 6.0 earthquakes in Taiwan. Such near-real-time directivity information can therefore be useful in earthquake early warning systems for providing more accurate ground shaking alerts.