12:00 PM - 12:15 PM
[SSS04-12] Radiated energy catalog for Taiwan: Physical insight into ground-motion generation of a complex tectonic region
★Invited Papers
Keywords:Radiated Energy, Seismic Attenuation, Earthquake Catalog
The amount of energy radiated ER by an earthquake is a measure of the potential for damage to man-made structures. Although Taiwan at a whole is seismically active with many cities in high-hazard zones, no ER catalog exists while catalogs for moment magnitude MW (and thus seismic moment M0) and local magnitude ML are compiled for decades. This circumstance can be traced to the inherent complexity of energy computation. Contrary to ML, which is calibrated against some standard and MW (M0), which is computed at very low frequencies of the seismic spectrum, ER is directly calculated over the entire waveform spectrum. Therefore, many factors must be taken into account.
For our ER computation, we combine several data archives to account for the computational complexity of ER by including seismic radiation patterns from moment tensors, ray paths calculated in a 3D velocity model and a 3D density model. The waveforms of the Broadband Array in Taiwan for Seismology (BATS) form the basis of the spectral integration which includes a correction for seismic noise. Although we can account for many factors of the ER computation, one factor requires special attention: seismic attenuation (Q). Q-models exist for the shallow part onshore Taiwan, but no Q-structure model is currently available which is comparable to the existing velocity models and covers the subduction zone east of Taiwan.
To assess the influence of Q on ER estimates, we perform several iterations of energy estimations and derive a Q-model based on the energy estimates. Despite representing only an apparent Q because of the mix of QP, QS and Qcoda, this Q-model not only guarantees consistent ER estimates, even from a theoretical perspective, but it also reveals the sensitivity of ER on Q, as our Q-model reveals structures such as the subducting slab of the Phillipine Sea Plate. Local variations of our energy-based Q-model are in agreement with previous studies on Q.
With all parts for the ER estimation available we can provide a consistent ER catalog also suitable for routine processing. The catalog reflects various tectonic regions and we can identify different earthquake processes from their energy signature alone, e.g. the increased seismicity episode in 2021 offshore Taiwan in the Okinawa graben and various hightened seismic activities with several major events in the Longitudinal Valley on the east coast of Taiwan.
For our ER computation, we combine several data archives to account for the computational complexity of ER by including seismic radiation patterns from moment tensors, ray paths calculated in a 3D velocity model and a 3D density model. The waveforms of the Broadband Array in Taiwan for Seismology (BATS) form the basis of the spectral integration which includes a correction for seismic noise. Although we can account for many factors of the ER computation, one factor requires special attention: seismic attenuation (Q). Q-models exist for the shallow part onshore Taiwan, but no Q-structure model is currently available which is comparable to the existing velocity models and covers the subduction zone east of Taiwan.
To assess the influence of Q on ER estimates, we perform several iterations of energy estimations and derive a Q-model based on the energy estimates. Despite representing only an apparent Q because of the mix of QP, QS and Qcoda, this Q-model not only guarantees consistent ER estimates, even from a theoretical perspective, but it also reveals the sensitivity of ER on Q, as our Q-model reveals structures such as the subducting slab of the Phillipine Sea Plate. Local variations of our energy-based Q-model are in agreement with previous studies on Q.
With all parts for the ER estimation available we can provide a consistent ER catalog also suitable for routine processing. The catalog reflects various tectonic regions and we can identify different earthquake processes from their energy signature alone, e.g. the increased seismicity episode in 2021 offshore Taiwan in the Okinawa graben and various hightened seismic activities with several major events in the Longitudinal Valley on the east coast of Taiwan.