| 云南景谷M_S6.6地震对南汀河断裂带地震危险性的影响 |
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| 引用本文： | 孙浩越,江国焰,何宏林,徐锡伟,魏占玉,高伟.云南景谷M_S6.6地震对南汀河断裂带地震危险性的影响[J].地球物理学报,2015,58(11):4197-4206. |
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| 作者姓名： | 孙浩越 江国焰 何宏林 徐锡伟 魏占玉 高伟 |
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| 作者单位： | 中国地震局地质研究所活动构造与火山重点实验室, 北京 100029 |
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| 基金项目： | 国家公益性重大专项"中国地震活动断层探察--南北地震带南段"(201108001),中国地震局地质研究所基本科研业务专项(IGCEA1403),国家自然科学基金(41404012)和中国博士后科学基金(2014M560102)共同资助. |
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| 摘 要： | 南汀河断裂带是滇西南块体内部的一条左旋走滑断裂带,几乎横切整个块体,总长度达380km,是块体内NE向断裂中最长的一条,也是次级块体的边界断裂.南汀河断裂带晚第四纪活动性非常强烈,但仅南段在1941年记录到一次约7级的地震,其余段落还没有5级以上地震的记录,目前可能正处于应力积累和孕震阶段.2014年10月7日发生的景谷MS6.6地震位于断裂带南东约94km,其地震烈度等震线长轴与余震皆呈北西展布,指向南汀河断裂带.为了解景谷地震对周边构造特别是南汀河断裂带的影响,本文通过数值模拟方法计算了地震触发的同震静态库仑应力变化.利用两种同震滑动分布模型计算获得的结果显示,景谷地震对震中附近的断裂,如澜沧江断裂和景谷断裂影响较大,局部应力增加可达90kPa;对较远的断裂,如南汀河断裂带、龙陵—澜沧断裂带和无量山断裂带的影响较小,应力变化值均小于10kPa.通过设置不同断层参数进一步计算,南汀河断裂带北段两支断裂断层面上的静态库仑应力扰动呈半圆形分布,应力增加的最大值位于24.15°N附近的地表,沿断层的走向和深度都逐渐减小.其中西支断裂上应力变化最大值为0.89kPa,东支断裂上为1.18kPa.此外,在南汀河断裂带北段的古地震研究结果显示,该断裂段全新世以来发生过产生地表破裂的大地震,震级应当不低于7级.放射性碳测年将该次古地震事件的发震时间限定在900—1480AD,离逝时间为535—1115年.结合古地震事件的离逝时间和断裂带的滑动速率,本文计算得到南汀河断裂带北段已经积累的水平滑动量为2.8+1.5/-1.0m,进一步利用滑动量与震级的经验公式可估算出该断裂段目前积累的滑动量如果完全释放将会产生一个7.5+0.1/-0.2级的地震.虽然景谷地震在南汀河断裂带上触发的静态库仑应力变化值表明,该地震可能不会引起南汀河断裂带地震危险性的突变,但仍起到一定的加速作用.再考虑到断裂带北段目前已经积累了约7.5级地震所需的能量,该断裂段在未来具有较高的地震危险性.
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| 关 键 词： | 南汀河断裂带 景谷地震 静态库仑应力 滇西南块体 地震危险性 |
| 收稿时间： | 2014-12-22 |
The influence of the 2014 Jinggu MS6.6 earthquake on the seismic risk of the Nantinghe fault zone in Yunnan Province,China |
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| SUN Hao-Yue,JIANG Guo-Yan,HE Hong-Lin,XU Xi-Wei,WEI Zhan-Yu,GAO Wei.The influence of the 2014 Jinggu MS6.6 earthquake on the seismic risk of the Nantinghe fault zone in Yunnan Province,China[J].Chinese Journal of Geophysics,2015,58(11):4197-4206. |
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| Authors: | SUN Hao-Yue JIANG Guo-Yan HE Hong-Lin XU Xi-Wei WEI Zhan-Yu GAO Wei |
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| Institution: | Key Laboratory of Active Tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing 100029, China |
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| Abstract: | The Nantinghe fault zone (NFZ), dividing the southwest Yunnan block (SYB) into two sub-blocks, is the longest one of NE striking left-lateral strike-slip faults in the SYB with a total length of ~380 km. Although it is very active in late Quaternary, only a M~7 earthquake occurred on its southern segment in 1941 and since then there has been no earthquake of M>5 recorded on the other segments of the NFZ. Therefore, the NFZ might be in the stage of stress accumulation for a large earthquake. The 2014 Jinggu MS 6.6 earthquake, whose aftershocks and longitudinal axis of the seismic intensity zones strike in northwest and point to the NFZ, is ~94 km southeast away from the NFZ. This study attempts to reveal its influence on the static Coulomb stress on surrounding faults, especially the NFZ, and to analyze the seismic risk of the NFZ.#br# To solve the problems above, this work combined the paleoseismological trenching and calculation of numerical simulation. The paleoseismological trench excavation revealed the paleoearthquake history in Holocene as well as the status of the NFZ. On the other hand, utilizing the coseismic slip distribution models of the Jinggu earthquake, the static Coulomb stress perturbations on surrounding faults, especially the NFZ, were calculated. Integrating these studies, the seismic potential of the NFZ was further analyzed.#br# Through the paleoseismological trench on the northern segment of the NFZ, we determined a paleoearthquake that generated surface ruptures in Holocene with a magnitude no less than 7. Using radiocarbon dating, the age of this event is constrained to be between 900 AD and 1480 AD, indicating an elapsed time of 535-1115 years. Utilizing two coseismic slip distribution models, our results show that the static Coulomb stress perturbations triggered by the Jinggu earthquake on neighboring faults, such as the Lancangjiang fault and Jinggu fault, are obviously positive, up to ~90 kPa. While on farther faults, such as the NFZ, Longling-Lancang fault zone, and Wuliangshan fault zone, the increased values are less than 10 kPa. The distribution of the stress perturbation on the fault plane of the NFZ, further computed using different fault parameters, illustrates that the maximum change of stress occurs near the surface at 24.15°N and decreases along the strike and depth. The maximum change of static Coulomb stress on the west branch of the NFZ is 0.89 kPa and the value on the east branch is 1.18 kPa.#br# Combining the slip rate and elapsed time since the latest paleoseismic event, it is estimated that the slip accumulated on the northern segment of the NFZ could be 2.8＋1.5/-1.0 m. Further using the empirical scaling laws between magnitude and displacement, an earthquake with magnitude of 7.5+0.1/-0.2 would be generated by the accumulated slip. Although the change of static Coulomb stress triggered by the Jinggu earthquake indicates that the earthquake does not necessarily produce a sudden acceleration on the seismic risk of the NFZ, under the consideration of that the northern segment of the NFZ has accumulated seismic energy equivalent to M≈7.5, it is suggested that this fault segment will probably be in a high seismic risk with positive stress perturbation from the Jinggu earthquake. |
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| Keywords: | Nantinghe fault zone Jinggu earthquake Static Coulomb stress Southwest Yunnan block Seismic risk |
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