| 汶川地震前后b值的时空变化及构造意义 |
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| 引用本文： | 刘雁冰,裴顺平.汶川地震前后b值的时空变化及构造意义[J].地球物理学报,2017,60(6):2104-2112. |
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| 作者姓名： | 刘雁冰 裴顺平 |
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| 作者单位： | 1. 中国科学院青藏高原研究所, 大陆碰撞与高原隆升重点实验室, 北京 100085;2. 中国科学院大学, 北京 100049 |
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| 基金项目： | 地震行业科研专项项目（201408019），国家自然科学基金（41674090，41374091），中国科学院先导专项（XDB03010702）和深地资源勘查开采重点专项（2016YFC0600303）联合资助. |
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| 摘 要： | 地震b值与地应力具有密切的关系,即高应力对应低b值,研究汶川地震区b值的时空变化可以获得地震前后的应力演化过程.本文通过震源位置和速度模型联合反演的方法和双差定位法对龙门山地区汶川地震(M_s8.0)前后的地震进行了重定位工作,在此基础上精确计算了汶川地震前后不同时间段内b值大小的变化趋势及b值空间分布.结果显示:(1)b值在深度上存在明显的分层性,15 km以上b值较高,15 km以下b值较低,反映上部岩石为脆性,下部岩石为韧性的特征;(2)区域平均b值在汶川地震之后出现下降,而后有所恢复并逐渐增加,芦山地震后又降低,反映了龙门山断裂带的同震变化和震后愈合过程;(3)分时段b值空间分布结果显示,在芦山地震之后,汶川地震破裂区b值下降,即应力增加,这意味着汶川芦山地震之间的空段存在韧性变形,且芦山地震的发生促进了汶川地震破裂区的愈合;(4)映秀附近彭灌杂岩区在震前呈现低b值异常,反映该区域存在较大的差应力,可能是震后最大位错发生在该区域的根本原因.
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| 关 键 词： | 汶川地震 芦山地震 b值 差应力 脆韧性 |
| 收稿时间： | 2016-06-08 |
Temporal and spatial variation of b-value before and after Wenchuan earthquake and its tectonic implication |
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| LIU Yan-Bing,PEI Shun-Ping.Temporal and spatial variation of b-value before and after Wenchuan earthquake and its tectonic implication[J].Chinese Journal of Geophysics,2017,60(6):2104-2112. |
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| Authors: | LIU Yan-Bing PEI Shun-Ping |
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| Institution: | 1. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China;2. University of Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | Seismic b-value shows close relationship with stress, with high stress corresponding to low b-values. Research on temporal and spatial variation of b-value in Longmenshan area will provide useful information to understand stress evolution of Wenchuan earthquake. In this paper, we relocated the earthquakes in Longmen Shan region before and after the Wenchuan earthquake (MS8.0) by both joint inversion of hypocenter location and velocity structure and the double difference earthquake location method, and then calculated temporal variation of the b-value in entire region and its spatial distribution in different time periods before and after Wenchuan earthquake. The results show: (1) The b-values show a significant boundary at depth of ~15 km, above which the b-value is much higher than that blow 15 km. This boundary indicates the division between brittle and ductile layers in the upper crust. (2) Temporal variation of average b-value shows clear decrease after the Wenchuan Earthquake, and then gradually increases till Lushan earthquake, however decreases again after the Lushan Earthquake. This variation trend represents not only the co-seismic change but also healing process of the Longmenshan fault. (3) Spatial variation of b-value shows increase (i.e. decreased stress) in Wenchuan rupture zone after Lushan earthquake that reveals possible ductile deformation in the gap between the Lushan and the Wenchuan earthquake and the Lushan earthquake promoted the healing of the rupture zone of the Wenchuan earthquake. (4) The significant low b-value anomaly in the Pengguan complex rock area near Yingxiu before Wenchuan earthquake suggests high differential stress in this region and therefore maximum dislocation occurred here after the Wenchuan Earthquake. |
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| Keywords: | Wenchuan Earthquake Lushan Earthquake b-value Differential stress Brittle and ductile behavior |
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