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Evaluation of Deep, Widespread Seismicity with Long Beach Dense Array

Lei Yang, Xin Liu, Weiqiang Zhu, & Gregory C. Beroza

Published August 15, 2019, SCEC Contribution #9858, 2019 SCEC Annual Meeting Poster #071

Earthquake monitoring in urban settings is challenging due to high levels of cultural noise, yet it’s important because comprehensive and precise earthquake locations provide essential constraints on the location and geometry of active faults. Dense array measurements, such as the Long Beach dense nodal deployment (which included several thousand geophones with ~100 m spacing), facilitate extracting weak signals from noisy data. Using the Long Beach array, Inbal et al. (2015; 2016) located widespread seismicity at depths greater than 20 km, which is much deeper than the widely accepted seismogenic depth limit beneath the western Los Angeles. In this research, we use Long Beach dense array to explore whether these deep earthquakes are real. We first analyze the recorded data, both with and without randomizing the traces recorded at different locations. Then we perform back-projection to locate the events. The back-projection imaging results without trace-randomization do show widespread events below 20 km. However, with the data from randomized traces, we locate the events with a similar distribution, which suggests that these data may not require widespread sources at depth. To suppress the strong cultural noise, we are working to apply the deep-learning-based DeepDenoiser algorithm to these data. Preliminaty results indicate that after denoising, the number of the detected events is greatly reduced.

Yang, L., Liu, X., Zhu, W., & Beroza, G. C. (2019, 08). Evaluation of Deep, Widespread Seismicity with Long Beach Dense Array. Poster Presentation at 2019 SCEC Annual Meeting.

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