汶川MW7.9地震周边地区布格重力异常与岩石圈垂向构造应力场

地震 ›› 2018, Vol. 38 ›› Issue (2): 28-36.

汶川M_W7.9地震周边地区布格重力异常与岩石圈垂向构造应力场

付广裕¹, 金红林¹, 王灼华¹, 佘雅文²

1.中国地震局地震预测重点实验室, 中国地震局地震预测研究所, 北京 100036;
2.中国地震局地球物理研究所, 北京 100081

收稿日期:2017-11-08 发布日期:2019-08-15
作者简介:付广裕(1973-),男,湖北广水人,博士,研究员,主要从事地震位错理论与地壳重力均衡研究。
基金资助:
国家自然科学基金(41574071); 中国地震局地震预测研究所基本科研业务费专项(2016IES0201和2016IES010204); 新疆精河6.6级地震深入科学研究项目

Bouguer Gravity Anomaly and Isostasy around the 2008 Wenchuan M_W7.9 Earthquake

FU Guang-yu¹, JIN Hong-lin¹, WANG Zhuo-hua¹, SHE Ya-wen²

1.Key Laboratory of Earthquake Prediction, Institute of Earthquake Science, CEA, Beijing 100036, China;
2.Institute of Geophysics, CEA, Beijing 100081, China

Received:2017-11-08 Published:2019-08-15

摘要/Abstract

摘要： 前人研究给出, 龙门山断裂带中南段地壳均衡异常显著, 具有发生7级以上大地震的深部动力背景。 2016年6月, 我们围绕该均衡异常显著区域开展重力/GNSS加密观测, 提高了该地区布格重力异常和地壳均衡异常场的空间分辨率。依据上述观测结果与前期同类观测数据, 反演了汶川M_W7.9地震周边地区地壳密度构造。结果显示, 龙门山断裂带是地壳密度变化的高梯度带, 其东侧地壳较薄, 但其西部明显变厚, 上、中、下地壳变化趋势均呈现上述特征; 研究区东侧的莫霍面深度为35~40 km, 西侧为60~65 km。此外, 利用重力/GNSS联合观测数据计算了汶川M_W7.9地震震中区周边地区岩石圈承载的垂向构造应力场, 结果表明, 汶川M_W7.9地震震中区北部、宁强、峨眉山周边地区蓄积了-30 MPa至-40 MPa的负向构造应力, 龙门山断裂带中南段蓄积了约40 MPa的正向构造应力, 区域最大垂向构造应力分布在龙门山断裂带中南段, 临近芦山M_W6.6地震。统计结果表明, 地震多发生在垂向构造应力高梯度带附近, 或垂向构造应力的高值区域。

关键词: 汶川M_W7.9地震, 地壳均衡, 布格重力异常, 密度构造, 岩石圈垂向构造应力

Abstract: Previous isostatic study shows that the crust around the middle and south segments of the Longmenshan fault zone is in great isostatic imbalance, which indicates an M≥7.0 earthquake in the future. We conducted a gravity and hybrid GNSS observation campaign in June of 2016 around the above great imbalance area, and improved spatial resolution of the gravity anomalies. We inversed the density structures around the Wenchuan M_W7.9 earthquake using the above and previous observation data. Our results show that the Longmenshan fault zone is the high gradient belt of crustal density change. The crust east of which is relatively thinner than that in the west. As a whole the upper, middle and lower crusts show the same characteristics. Moho depths in the eastern parts of the study area are 35~40 km. but those in the western parts are 60~65 km. Besides, we calculated the vertical tectonic stress of the lithosphere of the study area using gravity and GNSS data. We found that the crusts store up vertical tectonic stress of -30~-40 MPa around Lingqiang, Emei Mountain, and the area north to Wenhcuan M_W7.9 earthquake. However, the crust stores up vertical tectonic stress of 40 MPa around the middle and south segments of the Longmenshan fault zone. The maximum of vertical stress locates near the epicenter of the 2013 Lushan M_W6.6 earthquake. Statistical results show that the earthquakes often occur near the high gradient zones of vertical tectonic stress.

Key words: Bouguer gravity anomaly, Isostasy, Density structure, Vertical tectonic stress of the lithosphere, The 2008 Wenchuan M_W7.9 earthquake

中图分类号:

P315.7

付广裕, 金红林, 王灼华, 佘雅文. 汶川M_W7.9地震周边地区布格重力异常与岩石圈垂向构造应力场[J]. 地震, 2018, 38(2): 28-36.

FU Guang-yu, JIN Hong-lin, WANG Zhuo-hua, SHE Ya-wen. Bouguer Gravity Anomaly and Isostasy around the 2008 Wenchuan M_W7.9 Earthquake[J]. EARTHQUAKE, 2018, 38(2): 28-36.

参考文献

[1] 许志琴, 李化启, 侯立玮, 等. 青藏高原东缘龙门山—锦屏造山带的崛起: 大型拆离断层和挤出机制[J], 地质通报, 2007, 26 (10): 1262-1276.
[2] Gan W, Zhang P, Shen Z, et al. Present-day crustal motion within the Tibetan Plateau inferred from GNSS measurements[J]. J. Geophys. Res., 2007, 112(B8): B08416.
[3] Zhang Z, Wang Y, Chen Y, et al. Crustal structure across Longmenshan fault belt from passive source seismic profiling[J]. Geophys. Res. Lett., 2009, 36: L17310.
[4] 邓起东, 陈社发, 赵小麟. 龙门山及其邻区的构造和地震活动及动力学[J]. 地震地质, 1994, 16(4): 389-403.
[5] 中国重大科学工程“中国地壳运动观测网络”项目组. GNSS测定的2008年汶川M_S8.0级地震的同震位移场[J]. 中国科学D辑: 地球科学, 2008, 38(10): 1195-1206.
[6] 许才军, 刘洋, 温扬茂. 利用GNSS资料反演汶川M_W7.9级地震滑动分布[J]. 测绘学报, 2009, 38(3): 195-201.
[7] Xu C, Liu Y, Wen Y, et al. Coseismic slip distribution of the 2008 M_W7.9 Wenchuan earthquake from joint inversion of GNSS and InSAR data[J]. Bull. Seism. Soc. Am., 2010, 100(5B): 2736-2749.
[8] 宁津生, 王正涛. 面向信息化时代的测绘科学技术新进展[J]. 测绘科学, 2010, 35(5): 5-10.
[9] Zhang Y, Teng J, Wang Q, et al. Density structure and isostatic state of the crust in the Longmenshan and adjacent areas[J]. Tectonophysics, 2014, 619: 51-57.
[10] 杨光亮, 申重阳, 吴桂桔, 等. 金川—芦山—犍为剖面重力异常和地壳密度结构特征[J]. 地球物理学报, 2015, 58(7): 2424-2435.
[11] Fu G Y, Gao S H, Freymueller J T, et al. Bouguer gravity anomaly and isostasy at western Sichuan Basin revealed by new gravity surveys [J]. J. Geophys. Res., 2014, 119: 3925-3938.
[12] Fu G Y, Zhang G Q. Significant isostatic imbalance near the seismic gap between the M8.0 Wenchuan and the M7.0 Lushan earthquakes[J]. Chin. Sci. Bull., 2014, 59(34): 4774-4780.
[13] 刘冬至, 李辉, 刘绍府. 流动重力资料的处理系统LGADJ(见: 地震预报方法实用化研究文集形变、重力、应变专辑)[M]. 北京: 地震出版社, 1991.
[14] 郭俊义. 地球物理学基础[M]. 北京: 测绘出版社, 2001.
[15] Förste C, Bruinsma S, Abrikosov O, et al. EIGEN-6C4-The latest combined global gravity field model including GOCE data up to degree and order 1949 of GFZ Potsdam and GRGS Toulouse[J]. paper presented at EGU General Assembly Conference Abstracts, 2014.
[16] 高尚华, 佘雅文, 付广裕. 利用重力/GNSS联合观测数据计算地壳垂向构造应力的新方法[J]. 地球物理学报, 2016, 59(6): 2006-2013.
[17] 佘雅文, 付广裕, 王灼华, 等. 重力与地形数据揭示的巴颜喀拉块体东边界垂向构造应力场[J]. 地球物理学报, 2017, 60(6): 2480-2492.
[18] 张永谦, 王谦身, 滕吉文. 川西藏东地区的地壳均衡异常及其与地震分布的关系[J]. 地球物理学报, 2010, 53(11): 2631-2638.