Towards a Near-Real-Time Earthquake Detection of the MAGIC Project Containing Distributed Acoustic Sensing System and Broadband Seismometer Array

Fiber seismology, which applies distributed acoustic sensing (DAS) technology, has been an emerging field in geoscience in recent years. This technique utilizes the phase changes of Rayleigh scattering of laser light measured within the optical fiber to obtain strain parallel to the direction of laser light propagation. With spatial intervals of several meters, just a few kilometers of optical fiber can generate a data volume comparable to that recorded by thousands of traditional seismometers, providing higher resolution in both spatial and temporal domains. When combined with a seismometer array, the data collected by DAS can benefit earthquake detection. The MAGIC (Multidimensional Active fault of Geo-Inclusive observatory Chihshang) project is dedicated to monitoring microseismicity on the creeping segment of the Chihshang Fault in Taiwan. This project integrates geochemical and geophysical observations to investigate the earthquake generation process, with DAS playing a crucial role. The project involved drilling eight wells, ranging in depth from 40 to 230 meters. Eight downhole and surface fibers, totaling approximately 2.8 kilometers of optic fiber, were deployed and connected to an interrogator unit (AP Sensing N5225B DAS) to enable 3D monitoring since March 2024. In addition to DAS data, five broadband seismometer stations from the Chihshang Seismic Network (CSN) and nine stations of the Broadband Array in Taiwan for Seismology (BATS) have been combined to create a local broadband seismometer array in the study area since November 2021. With real-time data retrieval, this broadband seismometer array successfully compiled the complete earthquake catalog of the 2022 MW 6.9 Chihshang earthquake sequence using a deep learning framework (SeisBlue). This study presents a new DAS data processing workflow to facilitate near-real-time DAS data streaming for integration with SeisBlue for future earthquake detection.