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Published July 2023 | Supplemental Material + Published
Journal Article Open

Time-domain source parameter estimation of M_w 3–7 earthquakes in Japan from a large database of moment-rate functions


Time-domain analyses of seismic waveforms have revealed diverse source complexity in large earthquakes (M_w > 7). However, source characteristics of small earthquakes have been studied by assuming a simple rupture pattern on the frequency domain. This study utilizes high-quality seismic network data from Japan to systematically address the source complexities and radiated energies of M_w 3–7 earthquakes on the time domain. We first determine the apparent moment-rate functions (AMRFs) of the earthquakes using the empirical Green's functions. Some of the AMRFs show multiple peaks, suggesting complex ruptures at multiple patches. We then estimate the radiated energies (E_R) of 1736 events having more than ten reliable AMRFs. The scaled energy (e_R = E_R/M₀) does not strongly depend on the seismic moment (M₀), focal mechanisms, or depth. The median value of e_R is 3.7 × 10⁻⁵, which is comparable to those of previous studies; however, e_R varies by approximately one order of magnitude among earthquakes. We measure the source complexity based on the radiated energy enhancement factor (REEF). The values of REEF differ among earthquakes, implying diverse source complexity. The values of REEF do not show strong scale dependence for M_w 3–7 earthquakes, suggesting that the source diversity of smaller earthquakes is similar to that of larger earthquakes at their representative spatial scales. Applying a simple spectral model (e.g. the ω²-source model) to complex ruptures may produce substantial estimation errors in source parameters.

Additional Information

© The Author(s) 2023. Published by Oxford University Press on behalf of The Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) We are deeply grateful to the Editor (Sidao Ni) and the two reviewers, Rachel Abercrombie and Chen Ji, for their constructive comments. We thank Heidi Houston for her comments on the manuscript and Hisahiko Kubo for providing information about machine-learning algorithms. The figures were created using GMT (Wessel & Smith 1998). This research was supported by JSPS KAKENHI (grant numbers JP 20K14569). DATA AVAILABILITY. This study used hypocentres and S-wave arrival time data reported in the JMA unified catalogue. The seismograms were collected and stored by the JMA, national universities and NIED (http://www.hinet.bosai.go.jp/?LANG = en). The seismograms used in this study were collected and stored by the JMA, national universities and the National Research Institute for Earth Science and Disaster Resilience (NIED Hi-net: https://doi.org/10.17598/NIED.0003, NIED KiK-net: https://doi.org/10.17598/NIED.0004). The waveform data can be obtained from the NIED Hi-net website (http://www.hinet.bosai.go.jp/?LANG = en). The authors declare that they have no competing interests.

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August 22, 2023
August 22, 2023