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

• Published in: Geophysical research letters Vol. 45; no. 15; pp. 7496 - 7503
• Main Authors: Jan, Jyh Cherng, Huang, Hsin‐Hua, Wu, Yih‐Min, Chen, Chien‐Chih, Lin, Cheng‐Horng
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16-08-2018
• Subjects: Amplification; Attenuation; Data; Data transmission; Decay; Direction; Directivity; Distance; Early warning systems; Earthquake damage; Earthquakes; Emergencies; Emergency communications systems; Emergency management; Emergency preparedness; Emergency response; Feasibility studies; finite source effect; Geological hazards; Ground motion; Hazards; Information management; Interpolation; low‐cost seismic network; Methods; near‐real‐time determination; peak ground motions; Regression analysis; Risk assessment; Rupture; rupture directivity; Rupturing; Seismic activity; Seismic hazard; Shaking; Slope; Warning systems; Taiwan
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL078262

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 ML ≥ 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.
Plain Language Summary
When earthquake rupture propagates in a preferential direction, the ground motions in that direction can be greatly amplified and cause serious earthquake‐related damage. The timely knowledge of the rupture direction and possible amplified ground shaking areas is therefore crucial to risk assessment and emergency management. Such information has usually been obtained a few tens of minutes or longer after an earthquake occurs in the past. With short‐distance ground motion data from a dense seismic network and real‐time data streaming system in Taiwan, we propose a method that can shorten the reporting time to within 17 s after the origin time of the earthquake. This method measures the directional decay of peak ground motions with distance and determines the rupture direction where the ground motions decay least. The difference between the maximum and minimum decaying slopes is used to indicate the strength of directivity amplification and shows a prevalence of strong directivity effect for ML ≥ 6.0 earthquakes in Taiwan. Such rapid directivity information is therefore useful for earthquake early warning systems to provide more accurate shaking alerts for distant areas where strong shaking has yet to arrive.
Key Points
Near‐real‐time directivity information can be obtained within 17 s using near‐field ground motion data variations
The method could provide a basis to incorporate directivity information in earthquake early warning systems for more accurate shaking alerts
A prevalence of strong directivity effect is revealed for ML ≥ 6.0 earthquakes in Taiwan