INTERSEISMIC SLIP RATES AND SHALLOW CREEP ALONG THE NORTHWESTERN SEGMENT OF THE XIANSHUIHE FAULT FROM INSAR DATA

doi:10.3969/j.issn.0253-4967.2023.05.003

Abstract

Abstract:

Located in the eastern boundary of the Qinghai-Tibetan plateau, the Xianshuihe fault zone is one of the most active left-lateral strike-slip faults in Chinese mainland. As the southern boundary of the Bayanhar block, the Xianshuihe Fault accommodates the southeastward transport of material toward southeastern Asia. Earthquakes have occurred frequently along this fault, especially in the northwestern segment. More than 20 earthquakes with M_W>6.0 have ruptured since 1700. The most recent M_W>7 earthquake was the Luhuo earthquake in 1973, and the most recent M_W>6 earthquake was the M_W6.6 Luding earthquake in 2022. As one of the most active faults in mainland China, the present slip pattern of the Xianshuihe Fault, especially the shallow creep characteristics along its northwestern segment, has attracted much attention.

The primary goal of determining slip rates of active faults using geodetic data is to quantify the seismic potential of the faults. Illuminating the long-term slip rate and shallow creep distribution of faults is the basis for calculating the seismic moment rate and evaluating the seismic potential. Due to the backwardness of early measurement methods, the seismic deformation along the Xianshuihe Fault was previously based on geologic, cross-fault short baseline and leveling surveys. With the application of GPS in tectonic geodesy, more and more GPS stations are installed near active faults, which provide accurate constraints on the long-term slip rates of the fault. Subsequently, the appearance of InSAR technology has brought a beneficial supplement to GPS, providing high spatial resolution surface velocity maps, which have been widely used to measure deep and shallow creep along active faults. It is the key to accurately characterize the fault slip behavior and evaluate the seismic potential.

In this study, 119 Sentinel-1 satellite descent data from December 2014 to December 2021 were processed to obtain the average line-of-sight(LOS)velocity field of the northwestern segment of the Xianshuihe Fault based on the small baseline InSAR method. Then the elastic screw dislocation model was used to fit the fault normal InSAR LOS velocity profiles to estimate the long-term slip rates and shallow creep rates. Combined with the viscoelastic earthquake cycle model, the effects of the earthquake recurrence period, and rheology of the lower crust and upper mantle on slip rate estimation in Luhuo segment are analyzed. The main results are as follows:

(1)The average InSAR LOS velocity field is in the northwestern segment of the Xianshuihe Fault during 2014—2021 has been obtained with a large range and high spatial resolution. The velocity field results show an obvious velocity gradient across the surface trace of the Xianshuihe Fault, which is consistent with the left-lateral strike-slip characteristics of the Xianshuihe Fault.

(2)To investigate the slip rate variation along the northwestern segment of the Xianshuihe Fault, we used the two-dimensional elastic screw dislocation model to fit the 14 fault-normal velocity profiles selected along the northwestern segment of the Xianshuihe Fault and estimated the long-term slip rates and shallow creep rates using the Markov Chain Monte Carlo(MCMC)method. The results show that the overall slip rates of the NW segment of the Xianshuihe Fault range from 7.2mm/a to 11.0mm/a, and gradually decrease from west to east. The shallow creep rate ranges from 0.3mm/a to 3.1mm/a. The high creep rate appears mainly at Xialatuo and the segment from Daowu to Songlinkou. The shallow creep rates in other places are close to zero, implying that the fault is completely locked.

(3)According to historical earthquake records, the recurrence interval of the Luhuo segment is set to be 150 years, 200 years, and 400 years, and the viscosity of the lower crust and upper mantle is set to be 5.0×10¹⁸Pa·s, 1.0×10¹⁹Pa·s, and 5.0×10¹⁹Pa·s. The slip rate of the Luhuo segment is estimated to be (7.91±0.3)~(9.85±0.4)mm/a using the MCMC method, which is slightly lower than the (10.14±0.5)mm/a obtained by the pure elastic model. In addition, when the earthquake recurrence interval is 150 years and the viscosity of the lower crust and upper mantle is 5.0×10¹⁹Pa·s, we simulate the fault-normal velocity at 5 years, 20 years, 75 years, and 125 years after the 1973 Luhuo earthquake, and find that in any period of the seismic cycle, the estimation of fault slip rate will be biased to some extent if the viscoelastic contribution of the lower crust and upper mantle is ignored.

Key words: Xianshuihe Fault, inter-seismic slip rate, shallow creep, viscoelastic earthquake cycle model

摘要：

作为中国大陆最为活跃的断裂带之一, 鲜水河断裂现今的滑动模式, 尤其是北西段的浅部蠕滑特征长期以来备受关注。文中首先利用Sentinel-1卫星降轨数据, 基于小基线集时序分析(SBAS)方法获取鲜水河断裂带北西段2014—2021年的地表视线向(LOS向)平均速度场; 再采用弹性螺旋位错模型拟合InSAR跨断层剖面速度, 估计断层的长期滑动速率和浅部蠕滑速率; 最后结合黏弹性地震周期模型分析炉霍段地震的复发周期、下地壳和上地幔流变对滑动速率估计的影响。InSAR处理结果显示, 断层两侧LOS向速度场呈现出明显的速度差异。使用弹性螺旋位错模型估计得到的鲜水河断裂北西段的断层滑动速率为7.2~11.0mm/a, 自西向东逐渐减小。断裂带浅部蠕滑速率为0.3~3.1mm/a, 蠕滑主要集中在虾拉沱和道孚—松林口之间。基于历史地震的复发周期及青藏高原东缘下地壳和上地幔黏滞系数的研究, 文中采用黏弹性地震周期模型反演得到炉霍段的滑动速率为(7.91±0.3)~(9.85±0.4)mm/a, 略低于纯弹性螺旋位错模型的结果((10.14±0.5)mm/a)。

关键词: 鲜水河断裂带, 震间滑动速率, 浅部蠕滑, 黏弹性地震周期模型

CHEN Yi, ZHAO Bin, XIONG Wei, WANG Wei, YU Peng-fei, YU Jian-sheng, WANG Dong-zhen, CHEN Wei, QIAO Xue-jun. INTERSEISMIC SLIP RATES AND SHALLOW CREEP ALONG THE NORTHWESTERN SEGMENT OF THE XIANSHUIHE FAULT FROM INSAR DATA[J]. SEISMOLOGY AND GEOLOGY, 2023, 45(5): 1074-1091.

陈毅, 赵斌, 熊维, 王伟, 余鹏飞, 余建胜, 王东振, 陈威, 乔学军. InSAR数据约束的鲜水河断裂带北西段震间滑动速率及浅部蠕滑特征[J]. 地震地质, 2023, 45(5): 1074-1091.

Figures/Tables 11

Fig. 1 Tectonic setting of the Xianshuihe fault zone.

Fig. 2 Spatio-temporal baseline plots of descending track T135.

Fig. 3 Line-of-sight velocities across the Xianshuihe fault zone(a), standard deviation(b).

Fig. 4 Fault-parallel velocities along the Xianshuihe fault zone.

Fig. 5 A schematic of the screw dislocation model.

Fig. 6 Comparied observed fault-parallel velocities to modeled velocities.

Table 1 Slip rate of Luhuo segment, Xianshuihe Fault

地震复发周期/a	黏滞系数/Pa·s	滑动速率/mm·a^-1	闭锁深度/km	WRMS/mm·a^-1
150	5.0×10¹⁸	8.99±0.4	4.73±0.8	0.7886
150	1.0×10¹⁹	9.13±0.4	6.96±1.0	0.7883
150	5.0×10¹⁹	9.85±0.4	8.52±1.2	0.7881
200	5.0×10¹⁸	7.91±0.3	4.67±0.7	0.7889
200	1.0×10¹⁹	8.22±0.3	7.35±1.0	0.7920
200	5.0×10¹⁹	9.56±0.4	9.07±1.2	0.7906
400	5.0×10¹⁸	5.21±0.2	4.43±0.5	0.7984
400	1.0×10¹⁹	5.64±0.2	8.03±1.0	0.7997
400	5.0×10¹⁹	8.26±0.4	11.17±1.1	0.8022

Fig. 7 Best-fit profile of Luhuo.

Fig. 8 Deep and shallow creep rates along the Xianshuihe Fault.

Fig. 9 Calculated velocity profiles across the Luhuo segment of the Xianshuihe Fault at different times after the last earthquake.

Fig. 10 Comparison of observed surface velocities to calculated velocities across Luhuo segment of Xianshuihe Fault at 8 years after the Luhuo earthquake with different Maxwell relaxation times.

References 42

[1]	杜方, 闻学泽, 张培震. 2010. 鲜水河断裂带炉霍段的震后滑动与形变[J]. 地球物理学报, 53(10): 2355—2366.
	DU Fang, WEN Xue-ze, ZHANG Pei-zhen. 2010. Post-seismic slip and deformation on the Luhuo segment of the Xianshuihe fault zone[J]. Chinese Journal of Geophysics, 53(10): 2355—2366. (in Chinese)
[2]	李建中. 1986. 鲜水河断裂带现今构造形变[J]. 地壳形变与地震, (3): 181—192.
	LI Jian-zhong. 1986. Recent structural deformation in the Xianshuihe fault zone[J]. Crustal Deformation and Earthquake, (3): 181—192. (in Chinese)
[3]	刘本培. 1985. 鲜水河断裂带的地震形变与断层蠕动[J]. 四川地震, (2): 10—15, 40.
	LIU Ben-pei. 1985. Seismic deformation and creep of the Xianshuihe fault zone[J]. Earthquake Research in Sichuan, (2): 10—15, 40. (in Chinese)
[4]	孙凯, 孟国杰, 洪顺英, 等. 2021. 联合InSAR和GPS研究鲜水河断裂带炉霍—道孚段震间运动特征[J]. 地球物理学报, 64(7): 2278—2296.
	SUN Kai, MENG Guo-jie, HONG Shun-ying, et al. 2021. Interseismic movement along the Luhuo-Daofu section of the Xianshuihe Fault from InSAR and GPS observations[J]. Chinese Journal of Geophysics, 64(7): 2278—2296. (in Chinese)
[5]	闻学泽. 1990. 鲜水河断裂带未来三十年内地震复发的条件概率[J]. 中国地震, 6(4): 8—16.
	WEN Xue-ze. 1990. Conditional probabilities for the recurrence of earthquakes on the Xianshuihe fault zone within the coming three decades[J]. Earthquake Research in China, 6(4): 8—16. (in Chinese)
[6]	杨见兵. 2020. 鲜水河断裂西北段地震周期过程滑动分布的时空演化及机理研究[D]. 武汉: 中国地震局地震研究所:26—28.
	YANG Jian-bing. 2020. Study on the spatial-temporal sliding distribution and evolution mechanism model along the northwestern Xianshuihe Fault[D]. Institute of Seismology, China Earthquake Administration, Wuhan: 26—28. (in Chinese)
[7]	张晁军, 曹建玲, 石耀霖. 2008. 从震后形变探讨青藏高原下地壳黏滞系数[J]. 中国科学(D辑), 38(10): 1250—1257.
	ZHANG Chao-jun, CAO Jian-ling, SHI Yao-lin. 2008. Study on the viscosity of the lower crust of the Tibetan plateau from post-earthquake deformation[J]. Science in China(Ser D), 38(10): 1250—1257. (in Chinese)
[8]	Allen C R, Luo Z L, Qian H, et al. 1991. Field study of a highly active fault zone: The Xianshuihe Fault of southwestern China[J]. Geological Society of America Bulletin, 103(9): 1178—1199. DOI URL
[9]	Avouac J P. 2015. From geodetic imaging of seismic and aseismic fault slip to dynamic modeling of the seismic cycle[J]. Annual Review of Earth and Planetary Sciences, 43(1): 233—271. DOI URL
[10]	Bai M K, Chevalier M L, Pan J W, et al. 2018. Southeastward increase of the late Quaternary slip-rate of the Xianshuihe Fault, eastern Tibet: Geodynamic and seismic hazard implications[J]. Earth and Planetary Science Letters, 485: 19—31. DOI URL
[11]	Biggs J, Wright T, Lu Z, et al. 2007. Multi-interferogram method for measuring interseismic deformation: Denali Fault, Alaska[J]. Geophysical Journal International, 170(3): 1165—1179. DOI URL
[12]	Bürgmann R, Dresen G. 2008. Rheology of the lower crust and upper mantle: Evidence from rock mechanics, geodesy, and field observations[J]. Annual Review of Earth and Planetary Sciences, 36(1): 531—567. DOI URL
[13]	Bürgmann R, Rosen P A, Fielding E J. 2000. Synthetic aperture radar interferometry to measure earth's surface topography and its deformation[J]. Annual Review of Earth and Planetary Sciences, 28(1): 169—209. DOI URL
[14]	Chen C W, Zebker H A. 2000. Network approaches to two-dimensional phase unwrapping: Intractability and two new algorithms[J]. Journal of the Optical Society of America A, 17(3): 401—414. DOI URL
[15]	Dixon T, Decaix J, Farina F, et al. 2002. Seismic cycle and rheological effects on estimation of present-day slip rates for the Agua Blanca and San Miguel-Vallecitos faults, northern Baja California, Mexico[J]. Journal of Geophysical Research: Solid Earth, 107(B10): ETG5-1—ETG5-23.
[16]	Elliott J R, Walters R J, Wright T J. 2016. The role of space-based observation in understanding and responding to active tectonics and earthquakes[J]. Nature Communications, 7(1): 13844. DOI
[17]	Goldstein R M, Werner C L. 1998. Radar interferogram filtering for geophysical applications[J]. Geophysical Research Letters, 25(21): 4035—4038. DOI URL
[18]	Harris R A. 2017. Large earthquakes and creeping faults[J]. Reviews of Geophysics, 55(1): 169—198. DOI URL
[19]	Hussain E, Wright T J, Walters R J, et al. 2016. Geodetic observations of postseismic creep in the decade after the 1999 Izmit earthquake, Turkey: Implications for a shallow slip deficit[J]. Journal of Geophysical Research: Solid Earth, 121(4): 2980—3001. DOI URL
[20]	Ji L Y, Zhang W T, Liu C J, et al. 2020. Characterizing interseismic deformation of the Xianshuihe Fault, eastern Tibetan plateau, using Sentinel-1 SAR images[J]. Advances in Space Research, 66(2): 378—394. DOI URL
[21]	Jolivet R, Agram P S, Lin N Y, et al. 2014. Improving InSAR geodesy using Global Atmospheric Models[J]. Journal of Geophysical Research: Solid Earth, 119(3): 2324—2341. DOI URL
[22]	Jolivet R, Lasserre C, Doin M P, et al. 2013. Spatio-temporal evolution of aseismic slip along the Haiyuan Fault, China: Implications for fault frictional properties[J]. Earth and Planetary Science Letters, 377: 23—33.
[23]	Kaneko Y, Fialko Y, Sandwell D T, et al. 2013. Interseismic deformation and creep along the central section of the North Anatolian Fault(Turkey): InSAR observations and implications for rate-and-state friction properties[J]. Journal of Geophysical Research: Solid Earth, 118(1): 316—331. DOI URL
[24]	Li Y X, Bürgmann R. 2021. Partial coupling and earthquake potential along the Xianshuihe Fault, China[J]. Journal of Geophysical Research: Solid Earth, 126(7): e2020JB021406.
[25]	Lindsey E O, Fialko Y. 2016. Geodetic constraints on frictional properties and earthquake hazard in the Imperial Valley, Southern California[J]. Journal of Geophysical Research: Solid Earth, 121(2): 1097—1113. DOI URL
[26]	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. DOI URL
[27]	Papadimitriou E, Wen X Z, Karakostas V, et al. 2004. Earthquake triggering along the Xianshuihe fault zone of Western Sichuan, China[J]. Pure and Applied Geophysics, 161(8): 1683—1707. DOI URL
[28]	Qiao X, Zhou Y. 2021. Geodetic imaging of shallow creep along the Xianshuihe Fault and its frictional properties[J]. Earth and Planetary Science Letters, 567: 117001. DOI URL
[29]	Sandwell D, Mellors R, Tong X P, et al. 2011. Open radar interferometry software for mapping surface deformation[J]. Eos, Transactions American Geophysical Union, 92(28): 234—234. DOI URL
[30]	Savage J C. 1983. A dislocation model of strain accumulation and release at a subduction zone[J]. Journal of Geophysical Research: Solid Earth, 88(B6): 4984—4996.
[31]	Savage J C, Burford R O. 1973. Geodetic determination of relative plate motion in central California[J]. Journal of Geophysical Research, 78(5): 832—845. DOI URL
[32]	Savage J C, Prescott W H. 1978. Asthenosphere readjustment and the earthquake cycle[J]. Journal of Geophysical Research: Solid Earth, 83(B7): 3369—3376.
[33]	Segall P. 2002. Integrating geologic and geodetic estimates of slip rate on the San Andreas Fault System[J]. International Geology Review, 44(1): 62—82. DOI URL
[34]	Shen Z K, Lü J N, Wang M, et al. 2005. Contemporary crustal deformation around the southeast borderland of the Tibetan plateau[J]. Journal of Geophysical Research: Solid Earth, 110(B11): e2004JB003421.
[35]	Wang H, Wright T J, Biggs J. 2009. Interseismic slip rate of the northwestern Xianshuihe Fault from InSAR data[J]. Geophysical Research Letters, 36(3): L03302.
[36]	Wang M, Shen Z K. 2020. Present-day crustal deformation of continental China derived from GPS and its tectonic implications[J]. Journal of Geophysical Research: Solid Earth, 125(2): e2019JB018774.
[37]	Wang M, Shen Z K, Wang Y Z, et al. 2021. Postseismic deformation of the 2008 Wenchuan earthquake illuminates lithospheric rheological structure and dynamics of eastern Tibet[J]. Journal of Geophysical Research: Solid Earth, 126(9): e2021JB022399.
[38]	Zhang J, Wen X Z, Cao J L, et al. 2018. Surface creep and slip-behavior segmentation along the northwestern Xianshuihe fault zone of southwestern China determined from decades of fault-crossing short-baseline and short-level surveys[J]. Tectonophysics, 722: 356—372. DOI URL
[39]	Zhang L, Cao D Y, Zhang J F, et al. 2018. Interseismic fault movement of Xianshuihe fault zone based on across-fault deformation data and InSAR[J]. Pure and Applied Geophysics, 176(2): 649—667. DOI
[40]	Zhang P Z. 2013. A review on active tectonics and deep crustal processes of the Western Sichuan region, eastern margin of the Tibetan plateau[J]. Tectonophysics, 584: 7—22. DOI URL
[41]	Zhang Y J, Fattahi H, Amelung F. 2019. Small baseline InSAR time series analysis: Unwrapping error correction and noise reduction[J]. Computers & Geosciences, 133: 104331. DOI URL
[42]	Zhao B, Bürgmann R, Wang D Z, et al. 2017. Dominant controls of down-dip afterslip and viscous relaxation on the postseismic displacements following the M_W7.9 Gorkha, Nepal earthquake[J]. Journal of Geophysical Research: Solid Earth, 122(10): 1—26. DOI URL