Tracking Earthquake Sequences in Real Time: Application of Seismicity-Scanning based on Navigated Automatic Phase-Picking (S-SNAP) to the 2019 Ridgecrest, California Sequence

Abstract:

Recent improvements in seismic data processing techniques have enhanced our ability to detail the evolution of major earthquake sequences in space and time. However, tracking aftershock sequences automatically is still very challenging due to the highly clustered events in both space and time.

A recently developed algorithm, Seismicity-scanning based on Navigated Automatic Phase-picking (S-SNAP), has demonstrated to be an excellent tool in producing high-quality earthquake catalogs for injection-induced seismicity monitoring (Tan et al., 2019). The S-SNAP workflow comprises four processes: source-scanning, phase-picking, location and magnitude determination, which takes advantage of both waveform- and phase-based methods and combines different criteria to effectively identify real events and eliminate artefacts. In this study, we modify the original S-SNAP workflow to make it capable of delineating the spatiotemporal distribution of major earthquake sequences in real time.

We apply the modified S-SNAP to the 2019 Ridgecrest, southern California earthquake sequence (1 July to 16 July). Compared with the reviewed catalog reported by Southern California Seismic Network (SCSN), events in the S-SNAP catalog have epicentral differences of <2 km in both longitude and latitude and depth differences of <5 km. With additional visual inspection, we estimate the false detection rate of S-SNAP to be lower than 0.3%.

Compared with a customized real-time earthquake information system for Southern California, TriNet, our S-SNAP-based approach produces more events and achieves a higher recall rate. In addition, we found a seismicity rate anomaly and several phase-association errors in the TriNet catalog, which would stay in the SCSN official catalog for a long time (e.g. a year, depending on their review process). Other researches based on the SCSN catalog may suffer from these problems and their results could get biased. We conclude that S-SNAP can deliver an earthquake catalog with consistently high quality and correct phase associations, a unique merit beneficial to both routine network operations and earthquake review process.