喜马拉雅东构造结主要断裂的地震矩亏损与危险性评估

doi:10.3969/j.issn.0253-4967.2020.01.003

摘要/Abstract

摘要：

喜马拉雅东构造结是研究青藏高原构造演化的关键地区, 地震活动频繁。文中基于地震矩平衡理论, 利用GPS资料与历史地震目录分析东构造结地区的地震矩亏损, 继而评估该区未来的地震活动。结果表明: 研究区总体的地震矩累积率高于青藏高原的平均水平, 近200a内的累积总量达(1.15±0.03)×10²²N·m, 明显高于地震矩的释放总量(5.50±2.54)×10²¹N·m。而地震矩亏损量最高的主前缘断裂不丹段具备发生M_W8.1以上地震的可能, 那加山断裂及嘉黎断裂通麦段则不排除未来发生震级大于M_W7.5与M_W7.3地震的可能, 其余断层发生强震(M_W7.1以上)的概率相对较低。而对于米什米断层与主前缘断层东段, 虽然察隅M_S8.6地震发生于此, 但这2条断层未来的地震危险性仍不容忽视, 且无论察隅地震发生于哪条断层, 其复发周期均为660~1 030a。

关键词: GPS, 滑动速率, 地震矩亏损, 地震复发周期, 东构造结

Abstract:

The Eastern Himalayan Syntaxis(EHS)is a critical region for studying the tectonic evolution of Tibetan plateau, which was affected by the intense seismic activities. We use the theory of moment balance, GPS velocities and historical earthquake records to analyze the moment deficits in the EHS, assess the future seismicity and further to predict the recurrence interval of the 1950 Chayu M_S8.6 earthquake.
We first collected multiple sets of GPS velocity fields and combined them to reduce the systematic bias. Then a micro-blocks model, constrained by GPS velocities, was built by TDEFNODE software to simultaneously invert the fault elastic strain parameters and rigid motion parameters based on the grid research and simulated annealing methods. The long-term slip rates on the faults were further estimated by the differential motions between the neighboring blocks. The results show that the nearly NS dextral strike-slip faults, Naga Fault and Sagaing Fault, slip with the average rates of ~10.6 and ~16.6mm/a, which are consistent with the lateral extrusion in the Tibetan plateau. However, the Main Frontal Thrust shows a distinguished sinistral strike-slip feature(6~10mm/a), possibly caused by the NNE pushing from the Indian plate to the Eurasian plate. On the other hand, because the EHS is located in frontal area of the collision between Indian and Eurasian plate, most faults show thrusting feature. The most obvious one is the Mishimi Fault, slipping with the rate of 23.3mm/a, implying that the convergence rate of the Indo-European plates is largely absorbed by this fault. The moment accumulation rate in the EHS is higher than the average rate in the Tibetan plateau and the total moment accumulation is(1.15±0.03)×10²² N·m in the last 200a. About 59.7% and 21.6% of the moment accumulation rate concentrate on the Main Frontal Thrust and Mishimi Fault.
Second, we selected the earthquake records occurring on the upper crust since 1800AD to analyze the moment release in the EHS based on the data from the International Seismological Centre, United States Geological Survey, and catalogue of historical strong earthquakes in China and some other previous studies. In addition, the Global Centroid Moment Tensor Project and linear regression method were adopted to estimate the relationship between body wave magnitude(m_b), surface wave magnitude(M_S), local magnitude(M_L)and the moment(M₀). Then we further estimated the total fault moment release in the EHS, (5.50±2.54)×10²¹N·m, which is significantly lower than the total moment accumulation. About 79.2% of the moment release occurs on the Mishimi Fault, this is because the 1950 M_S8.6 Chayu earthquake is assumed to have ruptured on this fault.
Finally, the present-day moment deficits on the faults in the EHS were calculated by the differences between the moment accumulation and release, which represent the possibility to produce earthquakes on the upper crust faults in the future. The largest moment deficit was found on the Main Frontal Thrust near Bhutan, which is able to rupture with M_W8.1+. Similarly, earthquakes with M_W7.5+ and M_W7.3+ have the potentials to occur on the Naga Fault and the Jiali Fault near Tongmai. However, the future earthquake scales may be less than M_W7.1 on the remaining faults. Moderate minor earthquakes are the main activity in the area near the Yarlung Zangbo Suture zone and the southern Sagaing Fault. Although the Chayu M_S8.6 earthquake occurred near the Mishimi Fault and the eastern MFT, the earthquake risk on those two faults cannot be ignored. Meanwhile, no matter which fault produced the Chayu earthquake, its recurrence will likely be 660a to 1 030a.

Key words: GPS, fault slip rates, moments deficit, earthquake recurrence period, Eastern Himalayan Syntaxis

中图分类号:

P315.2

田镇, 杨志强, 王师迪. 喜马拉雅东构造结主要断裂的地震矩亏损与危险性评估[J]. 地震地质, 2020, 42(1): 33-49.

TIAN Zhen, YANG Zhi-qiang, WANG Shi-di. MOMENT DEFICITS ON THE MAJOR FAULTS AND EARTHQUAKE HAZARD ASSESSMENT IN THE EASTERN HIMALAYAN SYNTAXIS[J]. SEISMOLOGY AND GEOLOGY, 2020, 42(1): 33-49.

图/表 8

图1 a 东构造结地区的构造背景与历史地震(M≥4); b 6级以上地震的次数及其释放的地震矩(M0) 数据 I: 来自USGS、 ISC; 数据 Ⅱ: 来自国家地震局震害防御司(1995); 数据 Ⅲ: 来自其它文献资料(见2.1节)。黑色实线为主要断裂带在地表的展布(Gupta et al., 2015)。 MFT 喜马拉雅主前缘断层; YZS 雅鲁藏布江缝合带;JLF 嘉黎断裂; MTF 墨脱断裂; MSMT 米什米断裂; NGF 那加山断裂; SF 实皆断裂

Fig. 1 a Tectonic setting and seismicity of the Eastern Himalayan Syntaxis(M≥4); b The number and the moment(M0)time series of the earthquakes(M>6).

图2 GPS速度场分布(欧亚基准, 误差椭圆代表90%置信区间) 不同颜色的箭头代表不同来源的速度场资料: 紫色来自唐方头等(2010); 蓝色来自Devachandra等(2014); 红色来自Gupta等(2015); 绿色来自Zheng等(2017)。速度场的比例一致。白色实线代表研究区内主要断裂的展布,黑色实线代表微块体模型的边界

Fig. 2 GPS velocities in the study area(relative to the stable Eurasia, error ellipses represent the 90% confidence level).

图3 融合后的速度场分布(欧亚基准)与断层现今的走向运动速率(a); 微块体模型的残差分布与断层的倾向运动速率(误差椭圆代表90%置信区间)(b); 残差统计直方图(c)

Fig. 3 Combined GPS velocities(relative to the stable Eurasia)and strike-slip rates on the major faults(a);Residuals of the micro-block model and the dip-slip rates(error ellipses represent the 90%confidence level)(b);Histogram of residuals(c).

图 4 反演残差 χ2与闭锁深度的关系图

Fig. 4 The relation between residuals and locking depths.

图 5 东构造结地区的地震矩累积速率(单位: N·m/a)

Fig. 5 Moment accumulation rate in the Eastern Himalayan Syntaxis(unit: N·m/a).

图 6 矩心矩张量分布(a)及体波震级mb(b)、面波震级MS(c)与地震矩M0的线性关系

Fig. 6 Centroid moment tensor from GCMT in the study area(a), the linear relation between scalar moment and the body-wave(b), and the surface-wave magnitude(c).

图 7 研究区自1800AD以来的地震矩累积量(a)与释放量(b)(单位:N·m) b 大括号标出段表示察隅MS8.6地震的潜在发震断层

Fig. 7 Moment accumulation(a)and release(b)since 1800AD in the study area(unit:N·m).

图 8 研究区自1800AD以来的地震矩亏损量(单位: N·m)

Fig. 8 Estimated regional moment deficit since 1800AD(unit: N·m).

参考文献 59

[1]	陈培善, 白彤霞, 李保昆. 2003. b 值和地震复发周期[J]. 地球物理学报, 46(4): 510—519.
	CHEN Pei-shan, BAI Tong-xia, LI Bao-kun.2003. b-value and earthquake occurrence period[J]. Chinese Journal of Geophysics, 46(4): 510—519(in Chinese).
[2]	陈运泰, 刘瑞丰. 2018. 矩震级及其计算[J]. 地震地磁观测与研究, 39(2): 1—9.
	CHEN Yun-tai, LIU Rui-feng.2018. Moment magnitude and its calculation[J]. Seismological and Geomagnetic Observation and Research, 39(2): 1—9(in Chinese).
[3]	程成, 白玲, 丁林, 等. 2017. 利用接收函数方法研究喜马拉雅东构造结地区地壳结构[J]. 地球物理学报, 60(8): 2969—2979.
	CHENG Cheng, BAI Ling, DING Lin, et al.2017. Crustal structure of Eastern Himalayan Syntaxis revealed by receiver function method[J]. Chinese Journal of Geophysics, 60(8): 2969—2979(in Chinese).
[4]	邓起东, 张培震, 冉勇康, 等. 2003. 中国活动构造与地震活动[J].地学前缘, 10(S1): 66—73.
	DENG Qi-dong, ZHANG Pei-zheng, RAN Yong-kang, et al.2003. Active tectonics and earthquake activities in China[J]. Earth Science Frontiers, 10(Sl): 66—73(in Chinese).
[5]	国家地震局震害防御司. 1995. 中国历史强震目录(公元前23世纪—公元1911年)[M]. 北京: 地震出版社.
	Department of Earthquake Disaster Prevention, State Seismological Bureau. 1995. The Catalogue of Chinese Historical Strong Earthquakes(23th Century BC—1911AD)[M]. Seismological Press, Beijing(in Chinese).
[6]	康国发, 高国明, 白春华, 等. 2013. 喜马拉雅东构造结周边地区地壳磁异常分布特征研究[J]. 地球物理学报, 56(11): 3877—3886.
	KANG Guo-fa, GAO Guo-ming, BAI Chun-hua, et al.2013. Study on distribution features of crustal magnetic anomalies around eastern Himalayan syntaxis[J]. Chinese Journal of Geophysics, 56(11): 3877—3886(in Chinese).
[7]	李煜航, 郝明, 季灵运, 等. 2014. 青藏高原东缘中南部主要活动断裂滑动速率及其地震矩亏损[J]. 地球物理学报, 57(4): 1062—1078.
	LI Yu-hang, HAO Ming, JI Ling-yun, et al.2014. Fault slip rate and seismic moment deficit on major active faults in mid and south part of the eastern margin of Tibet plateau[J]. Chinese Journal of Geophysics, 57(4): 1062—1078(in Chinese).
[8]	刘代芹, Liu M, 王海涛, 等. 2016. 天山地震带境内外主要断层滑动速率和地震矩亏损分布特征研究[J]. 地球物理学报, 59(5): 1647—1660.
	LIU Dai-qin, Liu M, WANG Hai-tao, et al.2016. Slip rates and seismic moment deficits on major faults in the Tianshan region[J]. Chinese Journal of Geophysics, 59(5): 1647—1660(in Chinese).
[9]	马晓静, 高祥林. 2011. 横跨喜马拉雅造山带的构造运动转换与变形分配[J]. 地球物理学报, 54(6): 1528—1535.
	MA Xiao-jing, GAO Xiang-lin.2011. Transformation of tectonic movement and deformation partitioning across the Himalayan orogenic belt[J]. Chinese Journal of Geophysics, 54(6): 1528—1535(in Chinese).
[10]	史海霞, 孟令媛, 张雪梅, 等. 2018. 汶川地震前的b值变化[J]. 地球物理学报, 61(5): 1874—1882.
	SHI Hai-xia, MENG Ling-yuan, ZHANG Xue-mei, et al.2018. Decrease in b-value prior to the Wenchuan earthquake[J]. Chinese Journal of Geophysics, 61(5): 1874—1882(in Chinese).
[11]	宋键, 唐方头, 邓志辉, 等. 2011. 喜马拉雅东构造结周边地区主要断裂现今运动特征与数值模拟研究[J]. 地球物理学报, 54(6): 1536—1548.
	SONG Jian, TANG Fang-tou, DENG Zhi-hui, et al.2011. Study on current movement characteristics and numerical simulation of the main faults around Eastern Himalayan Syntaxis[J]. Chinese Journal of Geophysics, 54(6): 1536—1548(in Chinese).
[12]	唐方头, 宋键, 曹忠权, 等. 2010. 最新GPS数据揭示的东构造结周边主要断裂带的运动特征[J]. 地球物理学报, 53(9): 2119—2128.
	TANG Fang-tou, SONG Jian, CAO Zhong-quan, et al.2010. The movement characters of main faults around Eastern Himalayan Syntaxis revealed by the latest GPS data[J]. Chinese Journal of Geophysics, 53(9): 2119—2128(in Chinese).
[13]	谢超, 杨晓平, 黄雄南, 等. 2016. 东喜马拉雅构造结墨脱断裂晚第四纪活动地质证据的发现[J]. 地震地质, 38(4): 1095—1106. doi: 10.3969/j.issn.0253-4967.2016.04.023.
	XIE Chao, YANG Xiao-ping, HUANG Xiong-nan, et al.2016. Geological evidences of late Quaternary activity of Motuo Fault in Eastern Himalayan Syntaxis[J]. Seismology and Geology, 38(4): 1095—1106(in Chinese).
[14]	尹凤玲, 韩立波, 蒋长胜, 等. 2018. 2017年米林6.9级地震与1950年察隅8.6地震的关系及2次地震对周边活动断层的影响[J]. 地球物理学报, 61(8): 3185—3197.
	YIN Feng-ling, HAN Li-bo, JIANG Chang-sheng, et al.2018. Interaction between the 2017 M6.9 Mainling earthquake and the 1950 M8.6 Zayu earthquake and their impacts on surrounding major active faults[J]. Chinese Journal of Geophysics, 61(8): 3185—3197(in Chinese).
[15]	占伟, 武艳强, 梁洪宝, 等. 2015. GPS观测结果反映的尼泊尔MW7.8地震孕震特征[J]. 地球物理学报, 58(5): 1818—1826.
	ZHAN Wei, WU Yan-qiang, LIANG Hong-bao, et al.2015. Characteristics of the seismogenic model for the 2015 Nepal MW7.8 earthquake derived from GPS data[J]. Chinese Journal of Geophysics, 58(5): 1818—1826(in Chinese).
[16]	Ader T, Avouac J P, Liu-Zeng J, et al.2012. Convergence rate across the Nepal Himalaya and interseismic coupling on the Main Himalayan Thrust: Implications for seismic hazard[J]. Journal of Geophysical Research: Solid Earth, 117(B4): 1—11.
[17]	Ambraseys N N, Douglas J.2004. Magnitude calibration of north Indian earthquakes[J]. Geophysical Journal International, 159(1): 165—206.
[18]	Bai L, Li G, Khan N G, et al.2017. Focal depths and mechanisms of shallow earthquakes in the Himalayan-Tibetan region[J]. Gondwana Research, 41:390—399.
[19]	Bettinelli P, Avouac J P, Flouzat M, et al.2006. Plate motion of India and interseismic strain in the Nepal Himalaya from GPS and DORIS measurements[J]. Journal of Geodesy, 80(8-11): 567—589.
[20]	Bilham R, Larson K, Freymueller J.1997. GPS measurements of present-day convergence across the Nepal Himalaya[J]. Nature, 386(6620): 61—64.
[21]	Bird P, Kagan Y Y.2004. Plate-tectonic analysis of shallow seismicity: Apparent boundary width, beta, corner magnitude, coupled lithosphere thickness, and coupling in seven tectonic settings[J]. Bulletin of the Seismological Society of America, 94(6): 2380—2399.
[22]	Bonilla M G, Mark R K, Lienkaemper J J.1984. Statistical relations among earthquake magnitude, surface rupture length, and surface fault displacement[J]. Bulletin of the Seismological Society of America, 74(6): 2379—2411.
[23]	Chandra U.1978. Seismicity, earthquake mechanisms and tectonics along the Himalayan mountain range and vicinity[J]. Physics of the Earth and Planetary Interiors, 16(2): 109—131.
[24]	Chen W, Molnar P.1977. Seismic moments of major earthquakes and the average rate of slip in central Asia[J]. Journal of Geophysical Research, 82(20): 2945—2969.
[25]	Chen W P, Molnar P.1990. Source parameters of earthquakes and intraplate deformation beneath the Shillong Plateau and the Northern Indoburman Ranges[J]. Journal of Geophysical Research: Solid Earth, 95(B8): 12527—12552.
[26]	Chousianitis K, Ganas A, Evangelidis C P.2015. Strain and rotation rate patterns of mainland Greece from continuous GPS data and comparison between seismic and geodetic moment release[J]. Journal of Geophysical Research: Solid Earth, 120(5): 3909—3931.
[27]	D’Agostino N.2014. Complete seismic release of tectonic strain and earthquake recurrence in the Apennines(Italy)[J]. Geophysical Research Letters, 41(4): 1155—1162.
[28]	Devachandra M, Kundu B, Catherine J, et al.2014. Global Positioning System(GPS)measurements of crustal deformation across the frontal eastern Himalayan syntaxis and seismic-hazard assessment[J]. Bulletin of the Seismological Society of America, 104(3): 1518—1524.
[29]	Elliott J R, Jolivet R, González P J, et al.2016. Himalayan megathrust geometry and relation to topography revealed by the Gorkha earthquake[J]. Nature Geoscience, 9(2): 174—180.
[30]	Feldl N, Bilham R.2006. Great Himalayan earthquakes and the Tibetan plateau[J]. Nature, 444(7116): 165—170.
[31]	Ge W P, Molnar P, Shen Z K, et al.2015. Present-day crustal thinning in the southern and northern Tibetan plateau revealed by GPS measurements[J]. Geophysical Research Letters, 42(13): 5227—5235.
[32]	Gan W, Zhang P, Shen Z K, et al.2007. Present-day crustal motion within the Tibetan plateau inferred from GPS measurements[J]. Journal of Geophysical Research, 112(B8): B08416.
[33]	Gupta T D, Riguzzi F, Dasgupta S, et al.2015. Kinematics and strain rates of the Eastern Himalayan Syntaxis from new GPS campaigns in Northeast India[J]. Tectonophysics, 655:15—26.
[34]	Gutenberg B, Richter C F.1944. Frequency of earthquakes in California[J]. Bulletin of the Seismological Society of America, 34(4): 185—188.
[35]	Hanks T C, Kanamori H.1979. A moment magnitude scale[J]. Journal of Geophysical Research, 84(B5): 2348—2350.
[36]	Harrison M T, Ryerson F J, Le Fort P.1997. A Late Miocene-Pliocene origin for the Central Himalayan inverted metamorphism[J]. Earth and Planetary Science Letters, 146(1-2): E1—E7.
[37]	Holt W E, Ni J F, Wallace T C.1991. The active tectonics of the eastem Himalayan syntaxis and surrounding region[J]. Journal of Geophysical Research: Solid Earth, 96(B9): 14595—14632.
[38]	Jenny S, Goes S, Giardini D, et al.2004. Earthquake recurrence parameters from seismic and geodetic strain rates in the eastern Mediterranean[J]. Geophysical Journal International, 157(3): 1331—1347.
[39]	Krishna M R, Sanu T D.2000. Seismotectonics and rates of active crustal deformation in the Burmese arc and adjacent regions[J]. Journal of Geodynamics, 30(4): 401—421.
[40]	Kreemer C, Blewitt G, Klein E C.2014. A geodetic plate motion and Global Strain Rate Model[J]. Geochemistry, Geophysics, Geosystems, 15(10): 3849—3889.
[41]	Larson M, Freymueller T.1999. Kinematics of the India-Eurasia collision zone from GPS measurements[J]. Journal of Geophysical Research: Solid Earth, 104(B1): 1077—1093.
[42]	Liang S, Gan W, Shen C, et al.2013. Three-dimensional velocity field of present-day crustal motion of the Tibetan plateau derived from GPS measurements[J]. Journal of Geophysical Research: Solid Earth, 118(10): 5722—5732.
[43]	Loveless J P, Meade B J.2011. Partitioning of localized and diffuse deformation in the Tibetan plateau from joint inversions of geologic and geodetic observations[J]. Earth and Planetary Science Letters, 303(1-2): 11—24.
[44]	McCaffrey R, Qamar A I, King R W, et al.2007. Fault locking, block rotation and crustal deformation in the Pacific Northwest[J]. Geophysical Journal International, 169(3): 1315—1340.
[45]	Meade B J.2007. Present-day kinematics at the India-Asia collision zone[J]. Geology, 35(1): 81—84.
[46]	Meade B J, Hager B H.2005. Spatial localization of moment deficits in southern California[J]. Journal of Geophysical Research: Solid Earth, 110(4): 1—6.
[47]	Molnar P, Pandey M R.1989. Rupture zones of great earthquakes in the Himalayan region[J]. Journal of Earth System Science, 98(1): 61—70.
[48]	North-East Institute of Science and Technology.2013. Earthquake catalogue in and around north eastern region of India(including historical earthquakes)[R]. Jorhat, India.
[49]	Royden L H, Burchfiel B C, Van Der Hilst R D.2008. The geological evolution of the Tibetan plateau[J]. Science, 321(5892): 1054—1058.
[50]	Singh C, Singh A, Chadha R K.2009. Fractal and b-value mapping in eastern Himalaya and southern Tibet[J]. Bulletin of the Seismological Society of America, 99(6): 3529—3533.
[51]	Stevens V L, Avouac J P.2015. Interseismic coupling on the main Himalayan thrust[J]. Geophysical Research Letters, 42(14): 5828—5837.
[52]	Tapponnier P, Peltzer G, Le Dain A Y, et al.1982. Propagating extrusion tectonics in Asia: New insights from simple experiments with plasticine[J]. Geology, 10(12): 611—616.
[53]	Tian Z, Yang Z, Bendick R, et al.2019. Present-day distribution of deformation around the southern Tibetan plateau revealed by geodetic and seismic observations[J]. Journal of Asian Earth Sciences, 171:321—333.
[54]	Vernant P, Bilham R, Szeliga W, et al.2014. Clockwise rotation of the Brahmaputra Valley relative to India: Tectonic convergence in the eastern Himalaya, Naga Hills, and Shillong Plateau[J]. Journal of Geophysical Research: Solid Earth, 119(8): 6558—6571.
[55]	Wang H, Liu M, Cao J.2011. Slip rates and seismic moment deficits on major active faults in mainland China[J]. Journal of Geophysical Research: Solid Earth, 116(2): 1—17.
[56]	Wang H, Liu M, Shen X, et al.2010. Balance of seismic moment in the Songpan-Ganze region, eastern Tibet: Implications for the 2008 great Wenchuan earthquake[J]. Tectonophysics, 491(1-4): 154—164.
[57]	Wang Y, Wang M, Shen Z K.2017. Block-like versus distributed crustal deformation around the northeastern Tibetan plateau[J]. Journal of Asian Earth Sciences, 140:31—47.
[58]	Wells D L, Coppersmith K J.1994. New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement[J]. Bulletin of the Seismological Society of America, 84(4): 974—1002.
[59]	Zheng G, Wang H, Wright T J, et al.2017. Crustal deformation in the India-Eurasia collision zone from 25 years of GPS measurements[J]. Journal of Geophysical Research: Solid Earth, 122(11): 9290—9312.