Timing and characteristics of co-seismic surface ruptures in the Yadong rift, southern Tibet

IF 2.6 2区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Journal of Structural Geology Pub Date : 2024-09-19 DOI:10.1016/j.jsg.2024.105264
Shiguang Wang , Marie-Luce Chevalier , Paul Tapponnier , Haibing Li , Wenjun Zheng , Xulong Wang , Kang Li , Xiwei Xu
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Abstract

The Yadong-Gulu rift (YGR) is the most prominent and seismically active of the seven main ∼ NS-trending rifts in southern Tibet. Although the morphology of the southern YGR clearly indicates it has witnessed large earthquakes in the past, and despite its significant late Quaternary throw rates of ∼1 mm/yr, no large historical or instrumental earthquakes have been reported, including in the southernmost Pagri half-graben, in contrast to the northern part of the rift which is highly seismically active. Here, geomorphic characteristics helped us constrain the timing of a paleoearthquake that produced surface ruptures along the Pagri half-graben, used to document its past activity and evaluate its seismic hazard. We demonstrate that the co-seismic surface ruptures extend for ∼65 km along the Yadong normal fault, with a maximum vertical displacement ranging from 2 to 4.0 ± 0.1 m. Based on empirical relationships between magnitude, surface rupture length, and fault displacement, we suggest that this event may correspond to a Mw6.9–7.2 earthquake. Combined with previous studies, our radiocarbon (14C) and Optically Stimulated Luminescence (OSL) ages from three pits within the earthquake wedge across the surface ruptures constrain the paleoearthquake timing at 3470-2056 years BP. We suggest that the southern YGR currently has a high regional seismic hazard for a Mw6.8–7.1 earthquake, considering the significant throw rates and long timespan since the last strong event. Furthermore, we suggest that such different seismic activity and throw/extension rates between the southern and northern YGR may be explained by different upper crustal rheology behavior and mid-crustal structure.
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西藏南部亚东断裂共震地表破裂的时间和特征
亚东-古鲁断裂(YGR)是西藏南部七条主要 ∼ NS 走向断裂中最突出、地震最活跃的断裂。尽管亚东-古鲁断裂南部的形态清楚地表明其在过去曾发生过大地震,尽管其第四纪晚期的抛掷率高达 1 毫米/年,但与地震活动频繁的断裂北部形成鲜明对比的是,包括最南端的帕格里半断裂在内,尚未有大型历史地震或仪器地震的报道。在这里,地貌特征帮助我们确定了一次古地震的时间,该地震沿帕格里半堑沟产生了地表断裂,用于记录其过去的活动并评估其地震危害。根据震级、地表破裂长度和断层位移之间的经验关系,我们认为这次地震可能是一次 Mw6.9-7.2 地震。结合之前的研究,我们从地表断裂处地震楔内的三个坑中采集的放射性碳(14C)和光激发发光(OSL)年龄将古地震时间限定在公元前 3470-2056 年。我们认为,考虑到显著的抛掷率和距上一次强震发生的时间较长,YGR 南部目前发生 Mw6.8-7.1 地震的区域地震危险性较高。此外,我们认为 YGR 南部和北部之间不同的地震活动性和抛掷/拉伸率可能是由不同的上地壳流变行为和中地壳结构造成的。
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来源期刊
Journal of Structural Geology
Journal of Structural Geology 地学-地球科学综合
CiteScore
6.00
自引率
19.40%
发文量
192
审稿时长
15.7 weeks
期刊介绍: The Journal of Structural Geology publishes process-oriented investigations about structural geology using appropriate combinations of analog and digital field data, seismic reflection data, satellite-derived data, geometric analysis, kinematic analysis, laboratory experiments, computer visualizations, and analogue or numerical modelling on all scales. Contributions are encouraged to draw perspectives from rheology, rock mechanics, geophysics,metamorphism, sedimentology, petroleum geology, economic geology, geodynamics, planetary geology, tectonics and neotectonics to provide a more powerful understanding of deformation processes and systems. Given the visual nature of the discipline, supplementary materials that portray the data and analysis in 3-D or quasi 3-D manners, including the use of videos, and/or graphical abstracts can significantly strengthen the impact of contributions.
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