Quantifying rupture characteristics of microearthquakes in the parkfield area using a high-resolution borehole network
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Published version
Date
2023-02-06
Authors
Pennington, Colin N.
Wu, Qimin
Chen, Xiaowei
Abercrombie, Rachel
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Published version
OA Version
Citation
C.N. Pennington, Q. Wu, X. Chen, R.E. Abercrombie. 2023. "Quantifying rupture characteristics of microearthquakes in the Parkfield Area using a high-resolution borehole network" Geophysical Journal International, Volume 233, Issue 3, pp.1772-1785. https://doi.org/10.1093/gji/ggad023
Abstract
[It is well known that large earthquakes often exhibit significant rupture complexity such as well separated subevents. With improved recording and data processing techniques, small earthquakes have been found to exhibit rupture complexity as well. Studying these small earthquakes offers the opportunity to better understand the possible causes of rupture complexities. Specifically, if they are random or are related to fault properties. We examine microearthquakes (M < 3) in the Parkfield, California, area that are recorded by a high-resolution borehole network. We quantify earthquake complexity by the deviation of source time functions and source spectra from simple circular (omega-square) source models. We establish thresholds to declare complexity, and find that it can be detected in earthquakes larger than magnitude 2, with the best resolution above M2.5. Comparison between the two approaches reveals good agreement (>90 per cent), implying both methods are characterizing the same source complexity. For the two methods, 60–80 per cent (M 2.6–3) of the resolved events are complex depending on the method. The complex events we observe tend to cluster in areas of previously identified structural complexity; a larger fraction of the earthquakes exhibit complexity in the days following the M_w 6 2004 Parkfield earthquake. Ignoring the complexity of these small events can introduce artefacts or add uncertainty to stress drop measurements. Focusing only on simple events however could lead to systematic bias, scaling artefacts and the lack of measurements of stress in structurally complex regions.]
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© The Author(s) 2023. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.