The 1976 Great Tangshan earthquake (
We introduce an algorithm for declustering earthquake catalogs based on the nearest‐neighbor analysis of seismicity. The algorithm discriminates between background and clustered events by random thinning that removes events according to a space‐varying threshold. The threshold is estimated using randomized‐reshuffled catalogs that are stationary, have independent space and time components, and preserve the space distribution of the original catalog. Analysis of catalog produced by the Epidemic Type Aftershock Sequence model demonstrates that the algorithm correctly classifies over 80% of background and clustered events, correctly reconstructs the stationary and space‐dependent background intensity, and shows high stability with respect to random realizations (over 75% of events have the same estimated type in over 90% of random realizations). The declustering algorithm is applied to the global Northern California Earthquake Data Center catalog with magnitudes
- NSF-PAR ID:
- 10373658
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 125
- Issue:
- 4
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract M s 7.8) in North China was the deadliest earthquake in the past century. Understandably, a sequence of moderate (M ≥ 4.5) earthquakes in recent years in the Tangshan region, including theM s 5.1 earthquake on July 12, 2020, raised much social concern and scientific debate about the seismic risk near Tangshan and in North China, a region of active intraplate seismicity. Are these recent events aftershocks of the 1976 Great Tangshan earthquake or are they background earthquakes? Here, we separated clustered events (i.e., aftershocks) from background earthquakes in Tangshan and the entire North China using the nearest‐neighbor (NN) method, and estimated the duration of the 1976 Tangshan aftershock sequence by fitting the decay of seismicity with respect to the background seismicity. Our results suggest that the recent moderate earthquakes are likely aftershocks. This is consistent with their occurrences in places of increased Coulomb failure stress due to the 1976 Great Tangshan earthquake. The estimated aftershock duration is around 65–100 years for the 1976 Great Tangshan earthquake. The background seismicity in North China, obtained by removing aftershocks identified by the NN method, is relatively stationary in space but varies in time, decreasing slightly in recent years. Major active tectonic zones, including the Shanxi Rift and the Zhangjiakou‐Penglai fault system, show correlation between relatively high background seismicity, high geodetic strain rates, and large historic earthquakes. Such correlation, however, is poor within the North China Plain, highlighting the complexity of intraplate earthquakes. -
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