The Deqin-Zhongdian-Daju (DQ-ZD-DJ) fault zone, located in the southeastern Tibetan Plateau, is an active intraplate fault capable of generating moderate-to-large earthquakes, yet its present-day slip behavior remains poorly constrained. In this study, we re-examined this problem through a detailed seismological investigation of the 2013 Mw 5.6 Deqin earthquake sequence. We constructed a high-resolution aftershock catalog spanning ~80\u202fdays following the mainshock, yielding >3 times more detections than previously reported. Relocated seismicity delineates a V-shaped, half-graben–like fault architecture composed of (1) a northeast-dipping segment of the major DQ-ZD-DJ fault that hosts the mainshock and (2) a previously hidden conjugate splay fault intersecting the master fault at depths of ~10–12\u202fkm. Aftershocks on both sub-faults are dominated by normal-faulting mechanisms. We further performed focal mechanism-based stress inversion for the Deqin source region and resolved a near-vertical maximum principal stress, indicating an extensional stress regime. This stress pattern is consistent with that derived from the 2024 Mw 4.8 Zhongdian sequence and with the broader DQ-ZD regional stress field obtained from a focal mechanism dataset of much higher diversity, suggesting a coherent stress loading across the fault system. Quantitative estimates of strike- and dip-slip partitioning derived from aftershock focal mechanisms for both the Deqin and Zhongdian sequences align closely with regional geodetic constraints, independently confirming dominant oblique-normal faulting at present. Considering the long-term strike-slip fault motion revealed by geomorphic records, the aforementioned seismological and geodetic evidence for present-day extensional deformation reflects a tectonic reorganization from Late Quaternary to current interseismic timescales.
", "doi": "10.1016/j.tecto.2026.231219", "issn": "0040-1951", "publisher": "Elsevier", "publication": "Tectonophysics", "publication_date": "2026-06-05", "volume": "932", "pages": "231219" }, { "id": "authors:djzy8-1mf91", "collection": "authors", "collection_id": "djzy8-1mf91", "cite_using_url": "https://authors.library.caltech.edu/records/djzy8-1mf91", "type": "article", "title": "Source Complexity and Faulting Heterogeneity of the 2024 Mw\u00a04.8 Zhongdian Earthquake, Yunnan, China", "author": [ { "family_name": "Wang", "given_name": "Zhenyu", "orcid": "0000-0002-1555-5346" }, { "family_name": "Ren", "given_name": "Chunmei", "orcid": "0009-0007-3165-0304" }, { "family_name": "Wang", "given_name": "Longtan", "orcid": "0000-0003-3630-2927" }, { "family_name": "Chang", "given_name": "Lijun", "orcid": "0009-0004-1467-3254" }, { "family_name": "Zhou", "given_name": "Yijian", "orcid": "0000-0002-7205-1769", "clpid": "Zhou-Yijian" } ], "abstract": "Earthquakes in stable continental regions occur less frequently than those at plate boundaries, and their seismic hazards remain poorly understood. In this study, we analyze the source complexity of the Mw 4.8 Zhongdian earthquake in southeastern Tibet, which occurred in an area where no major faults were previously mapped. Notably, the focal mechanism solutions differ significantly between the different approaches: whereas the centroid moment tensor (CMT) indicates oblique-normal faulting, the first-motion (FM) solution suggests purely dip-slip faulting. This discrepancy points to a complex rupture process involving multiple slip modes. Using multi-point-source inversion, we identify two near-simultaneous subevents. The first aligns with the FM dip-slip mechanism, and the second is dominated by strike-slip motion; together, they are consistent with the overall CMT solution. However, source spectral ratio analysis and displacement records show no distinct temporal separation between the subevents. On the other hand, structural complexities are revealed by relocated aftershocks and spatially diverse focal mechanisms, which enable the observed rupture behavior. We further compare the stress fields across multiple scales and find no significant differences in principal stress orientations between the Zhongdian source region and the broader western Chuandian block. Nevertheless, the two subevent areas display contrasting faulting styles, highlighting the influence of localized strain or deformation heterogeneity. These findings suggest that the moderate-size Zhongdian earthquake was governed by both complex fault geometry and heterogeneous faulting behavior.
", "doi": "10.1785/0220250259", "issn": "0895-0695", "publisher": "Seismological Society of America", "publication": "Seismological Research Letters", "publication_date": "2026-03", "series_number": "2A", "volume": "97", "issue": "2A", "pages": "679-697" }, { "id": "authors:377je-3wb69", "collection": "authors", "collection_id": "377je-3wb69", "cite_using_url": "https://authors.library.caltech.edu/records/377je-3wb69", "type": "article", "title": "P-Wave First-Motion Polarity Determination Using Order Statistics and Entropy Theory (POSE) With Applications to Southeastern Tibetan Plateau", "author": [ { "family_name": "Wang", "given_name": "Longtan", "orcid": "0000-0003-3630-2927" }, { "family_name": "Zhou", "given_name": "Yijian", "orcid": "0000-0002-7205-1769", "clpid": "Zhou-Yijian" }, { "family_name": "Meng", "given_name": "Haoran", "orcid": "0000-0002-1951-2319" }, { "family_name": "Pei", "given_name": "Weilai" }, { "family_name": "Zhou", "given_name": "Shiyong", "orcid": "0000-0002-0006-806X" } ], "abstract": "The Focal Mechanism Solutions (FMSs) of small earthquakes provide valuable insights into crustal structure and stress conditions, while its reliability is limited by the accuracy of first-motion polarity determination, which remains challenging. In this study, we develop an FMS determination workflow based on a rule-based Polarity picker using Order Statistics and Entropy theory (POSE). The performance of POSE is compared with two representative deep learning-based approaches (CNN, Ross et al., 2018, https://doi.org/10.1029/2017jb015251; APP, L. Zhang et al., 2023, https://doi.org/10.1785/0220220247) in two tectonically diverse regions: Southern California and Southeastern Tibetan Plateau. In Southern California, we evaluate the polarity picking accuracy using manual labels as reference. All methods achieve comparable picking accuracy, while POSE and APP identify twice as many polarities previously labeled as “unknown,” indicating higher picking sensitivity. Moreover, POSE exhibits superior stability against noise levels and picking uncertainties. We then compute FMS from the polarities derived by each method. In Southern California, all algorithms produced similar number of FMSs with a comparable ratio of high-quality solutions. In more tectonically complex Southeastern Tibet, POSE yields approximately twice as many FMSs as APP and ∼40% more than CNN. Analysis of POSE-derived FMS catalog reveals fine-scale variations in faulting style and stress orientation along the Xianshuihe-Xiaojiang Fault Zone that are not resolved in previous FMS studies but consistent with GPS-constrained regional strain fields. These results highlight the effectiveness and cross-regional generalizability of POSE, demonstrating its potential to enhance the resolution and reliability of stress field characterization from small-magnitude earthquake data sets.
", "doi": "10.1029/2025jb032118", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research: Solid Earth", "publication_date": "2026-01", "series_number": "1", "volume": "131", "issue": "1", "pages": "e2025JB032118" }, { "id": "authors:j83zb-21e74", "collection": "authors", "collection_id": "j83zb-21e74", "cite_using_url": "https://authors.library.caltech.edu/records/j83zb-21e74", "type": "article", "title": "Rheological and tectonic implications of eastern Tibet: Insights from early aftershock sequences driven by afterslip following three 2021\u20132022 moderate-large events", "author": [ { "family_name": "Liu", "given_name": "Xiaoge" }, { "family_name": "Xu", "given_name": "Wenbin" }, { "family_name": "Frank", "given_name": "William B." }, { "family_name": "Zhou", "given_name": "Yijian", "orcid": "0000-0002-7205-1769", "clpid": "Zhou-Yijian" }, { "family_name": "Zhao", "given_name": "Guoqiang" }, { "family_name": "Fang", "given_name": "Lihua" }, { "family_name": "Huang", "given_name": "Hui" }, { "family_name": "He", "given_name": "Lijia" }, { "family_name": "Gan", "given_name": "Weijun" } ], "abstract": "Early aftershock sequences and afterslip provide key insights into crust rheology and the triggering mechanisms of seismicity sequences. Three recent moderate-large strike-slip earthquakes in eastern Tibet, including the 2021 Yangbi Mw 6.1, the 2021 Maduo Mw 7.4, and the 2022 Menyuan Mw 6.4 events, provide an ideal opportunity to investigate the driving processes of aftershocks and the regional crustal rheology. In this study, we inverted for the early afterslip and statistically analyzed the spatiotemporal evolution of these three aftershock sequences. Our results reveal a significant spatial complementarity between the relocated aftershocks, coseismic slip and early afterslip, suggesting aftershocks were triggered by afterslip driven by the coseismic stress changes. The depth of the aftershock sequences consistently shallows over time, which we interpret as a transient response of the brittle-ductile transition zone to early postseismic relaxation. For the first time, we quantify the depth-dependent variations of aftershock-derived rheological and frictional parameters along these three strike-slip faults in eastern Tibet. The recurrence times derived from early aftershocks are generally shorter than those estimated from geodetic or geological data, demonstrating that fault loading rates are not constant throughout the seismic cycle. This spatiotemporal comparison between aftershocks, coseismic slip and afterslip allows for the discrimination of different aftershock driving mechanisms. The framework presented here is generalized to other similar tectonic settings, providing a method to identify the dominant aftershock driving mechanism and to constrain the rheological properties, frictional parameters and recurrence times of regular earthquakes.", "doi": "10.1016/j.jag.2025.104770", "issn": "1569-8432", "publisher": "Elsevier", "publication": "International Journal of Applied Earth Observation and Geoinformation", "publication_date": "2025-09", "volume": "143", "pages": "104770" }, { "id": "authors:kf80b-dp514", "collection": "authors", "collection_id": "kf80b-dp514", "cite_using_url": "https://authors.library.caltech.edu/records/kf80b-dp514", "type": "article", "title": "AI-PAL: Self-Supervised AI Phase Picking via Rule-Based Algorithm for Generalized Earthquake Detection", "author": [ { "family_name": "Zhou", "given_name": "Yijian", "orcid": "0000-0002-7205-1769", "clpid": "Zhou-Yijian" }, { "family_name": "Ding", "given_name": "Hongyang", "orcid": "0009-0006-6274-8059" }, { "family_name": "Ghosh", "given_name": "Abhijit", "orcid": "0000-0002-0557-2839" }, { "family_name": "Ge", "given_name": "Zengxi", "orcid": "0000-0003-4161-8635" } ], "abstract": "Delineating fault structures through microseismicity is crucial for earthquake hazard assessment, yet constructing high\u2010resolution catalogs over extended periods remains challenging. This study introduces AI\u2010PAL, a novel deep learning\u2010driven workflow that employs a Self\u2010Attention RNN (SAR) model trained with detections from PAL, an established rule\u2010based algorithm (Zhou, Yue, et al., 2021, https://doi.org/10.1785/0220210111), for generalized earthquake detection. PAL utilizes short\u2010term\u2010average over long\u2010term\u2010average algorithm for event detection, ensuring consistent performance across different datasets. AI\u2010PAL leverages these rule\u2010based picks as training labels, enabling self\u2010supervised learning of the SAR model across arbitrary regions, thereby enhancing PAL's detection capabilities. We applied SAR\u2010PAL to two distinct regions that are featured by recent large earthquakes: (a) the preseismic period of the Ridgecrest\u2010Coso region (2008–2019), and (b) the pre\u2010to\u2010postseismic period of the East Anatolian Fault Zone (EAFZ, 2020–2023/04). Our results demonstrate that SAR\u2010PAL offers slightly higher detection completeness than the quake template matching matched filter catalog, while boosts over 100 times faster processing and a superior temporal stability, avoiding detection gaps during background periods. Compared to PhaseNet and GaMMA, two widely recognized phase picker and associator, SAR\u2010PAL proved more scalable, achieving ∼2.5 times more event detections in the EAFZ case, along with a ∼7 times higher phase association rate. We further experimented training PhaseNet and SAR with PAL detections and routine catalogs, and found that no other combinations matched the detection performance of SAR\u2010PAL. The enhanced catalogs built by SAR\u2010PAL reveals geometrical complexities of the Ridgecrest faults and the Erkenek\u2010Pütürge segment of EAFZ, offering insights into their contrasting roles during the large earthquake.
", "doi": "10.1029/2025jb031294", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research: Solid Earth", "publication_date": "2025-04", "series_number": "4", "volume": "130", "issue": "4", "pages": "e2025JB031294" }, { "id": "authors:a03vp-sg606", "collection": "authors", "collection_id": "a03vp-sg606", "cite_using_url": "https://authors.library.caltech.edu/records/a03vp-sg606", "type": "article", "title": "Abundant Quasi-Repeating Earthquakes Occurring Within Repeater Sequences on the Erkenek\u2010P\u00fct\u00fcrge Fault (SE Turkey)", "author": [ { "family_name": "Zhou", "given_name": "Yijian", "orcid": "0000-0002-7205-1769", "clpid": "Zhou-Yijian" }, { "family_name": "Ghosh", "given_name": "Abhijit", "orcid": "0000-0002-0557-2839" } ], "abstract": "Repeaters are known as earthquakes that rupture the same asperity in similar manners. However, the complexity of repeater asperities is poorly investigated. In this study, we developed a new strategy to systematically detect quasi-repeaters that rupture the same asperities in different ways. It begins by identifying repeaters using waveform cross-correlation (CC) ≥0.9 and CC-measured Δ(S-P) times ≤0.01 s. We then adopt a much lower CC threshold to detect quasi-repeaters, classifying repeater sequences as simple (lacking quasi-repeaters) or complex (including quasi-repeaters). Applying this workflow to the Erkenek-Pütürge fault in Turkey, we detected 43 repeater sequences during 2020–2023/04. Notably, 30 sequences (∼70%) are complex. The repeater magnitudes show weak correlation with their recurrence interval, with only complex sequences following the 2023 Mw 7.8 mainshock an exception. Moreover, ∼74% sequences have the first two events following the mainshocks exhibiting decreasing magnitude. These results suggest that slip rate and asperity complexity may be key factors in such modulation.
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