基于密集台阵的川滇块体西边界乔后段震源参数与应力场研究

利用大量的中小地震数据开展震源参数与应力场研究，能够帮助我们认识区域的地震活动特征，刻画地下精细断裂带结构，认识区域构造应力场特征以及孕震环境，为防震减灾工作提供重要科学依据。川滇块体周边和内部构造断裂众多，地震活动频发。前人利用发生在川滇块体附近的中小地震，开展了大量震源参数与应力场研究，在川滇块体及边界断裂带区域取得了丰硕的研究成果。近几年蓬勃发展的密集台阵观测方式为深入研究更为精细的震源参数、断裂带结构以及应力场特征等提供了可能。前人在川滇块体区域开展了多期次的密集台阵观测研究，但主要集中于块体东边界的活动断裂带，而对块体西边界的关注度相对较低。
本文基于本人所在课题组于2021年1月中旬至5月初期间在川滇块体西边界乔后段布设的密集台阵观测数据，开展了精细的地震震源参数与应力场研究。本文首先利用绝对和相对定位法获得了12779个地震事件的精确位置。在此基础上，利用拾取的P波初动极性与测量的S/P振幅比资料反演得到了441个地震的震源机制解。然后，根据地震定位结果与震源机制解联合分析了断裂带的精细几何结构特征。最后，根据反演得到的震源机制解，开展应力场反演，获得了区域整体以及0.1°× 0.1°子区域的构造应力场分布特征。本文研究结果显示，研究区域附近地震事件分布整体上较为散乱，部分区域有呈簇状分布特征，震源机制类型以走滑型机制、正断型机制为主。维西-乔后断裂西侧存在一条右旋正断层，倾角近45°，记录到的地震深度在7 km至9 km左右，走向北北西-南南东（NNW-SSE）；该右旋正断层西侧存在一条左旋走滑断层，走向北北东-南南西（NNE-SSW），断层倾角近65°，记录到的地震深度在6 km至8 km左右。龙蟠-乔后断裂附近存在尺度较小的左旋走滑断层，倾角近80°。应力场反演结果表明，研究区域整体上最大和最小主压应力方向近水平，其中最大主压应力轴方向为北北西-南南东（NNW-SSE）向，走向约167°，最小主压应力轴方向为南西西-北东东（SWW-NEE）向，走向约78°。多数子区域的最大和最小主压应力与区域整体结果相近，R 值偏低，表现为双轴挤压的应力特征，以走滑型应力为主。部分子区域上的最大主压应力呈近垂直状态，应力场显示为正断型应力特征。研究区域应力特征整体上与川滇块体向SE方向楔入的构造应力一致，局部区域应力场的变化特征受到区域内精细断裂带结构的影响。

Using a large number of small and medium-sized earthquake data to conduct research on source parameters and stress fields can help us understand the characteristics of regional seismic activity, depict the fine subsurface fault structures, understand the regional tectonic stress characteristics and seismogenic environment, and provide important scientific basis for earthquake prevention and disaster reduction. There are many tectonic faults around and within the Sichuan-Yunnan block, with frequent seismic activity. Previous researchers have conducted a large number of studies on source parameters and stress fields using small and medium-sized earthquakes that occurred near the Sichuan-Yunnan block, and have achieved many research results in the Sichuan-Yunnan block and boundary fault zone areas. The dense array observation method that has developed rapidly in recent years has made it possible to further study more precise source parameters, fault zone structure, and stress field characteristics. Previous researchers have conducted multiple dense array observation studies in the Sichuan-Yunnan block area, but they mainly focused on the active fault zones on the eastern boundary of the block, while the attention paid to the western boundary of the block is relatively low.

Based on the observation data of the dense array deployed in the Qiaohou section of the western boundary of the Sichuan-Yunnan block during the period from mid January to early May 2021 by my research team, this article has conducted a detailed study of seismic source parameters and stress fields. In this article, we first obtained the precise locations of 12779 earthquakes using absolute and relative location methods; On this basis, the focal mechanisms of 441 earthquakes were obtained by inversion using the picked up P-wave polarity and measured S/P amplitude ratio data; Then, based on the earthquakes location and focal mechanisms, the fine geometric structure characteristics of the fault zone are analyzed jointly; Finally, based on the focal mechanisms, carring out stress field inversion, the structural stress field distribution characteristics of the regional overall and the 0.1 ° × 0.1 ° subregion have been obtained. The results of this article show that the distribution of earthquakes around the study area is generally scattered, and some regions have a cluster distribution feature. The focal mechanisms in the study area are mainly strike-slip and normal fault mechanisms. There is a right-lateral normal fault on the west side of the Weixi-Qiaohou fault zone, with a dip angle of nearly 45 °, the recorded seismic depth is about 7 km to 9 km, with a strike of NNW-SSE. There is a left-lateral strike-slip fault on the west side of the right-lateral normal fault. The left-lateral strike-slip fault has a dip angle of nearly 65 °, with a strike of NNE-SSW, and the recorded seismic depth is about 6 km to 8 km. There are some small scale left-lateral strike-slip faults near the Longpan-Qiaohou fault zone, with a dip angle of nearly 80 °. The inversion results of the stress field indicate that the directions of the maximum and minimum principal compressive stress axises in the study area as a whole are nearly horizontal, with the maximum principal compressive stress axis in the NNW-SSE direction, approximately 167 °, and the minimum principal compressive stress axis in the SWW-NEE direction, approximately 78 °. The maximum and minimum principal compressive stresses in most subregions are similar to the overall results of the region, with a low R value, showing a stress characteristic of biaxial compression, and generally dominated by strike-slip stress. The maximum principal compressive stress axis in the subregion is in a nearly vertical state, and the stress field shows a normal fault type stress characteristic. The stress characteristics of the study area are generally consistent with the tectonic stress of the Sichuan-Yunnan block wedged in the SE direction, and the variation characteristics of the local regional stress field are affected by the fine fault zone structure in the subregion.

[1] REID H F. The mechanics of the earthquake[M]. Carnegie institution of washington, 1910.
[2] 骆佳骥, 崔效锋, 胡幸平, et al. 川滇地区活动块体划分与现代构造应力场分区研究综述[J]. 地震研究, 2012, 35(03): 309-317.
[3] 邓起东, 张培震, 冉勇康, et al. 中国活动构造基本特征[J]. 中国科学(D 辑:地球科学), 2002, 12: 1020-1030.
[4] 阚荣举, 张四昌, 晏凤桐, et al. 我国西南地区现代构造应力场与现代构造活动特征的探讨[J]. 地球物理学报, 1977, 02: 96-109.
[5] 李玶, 汪良谋. 云南川西地区地震地质基本特征的探讨[J]. 地质科学, 1975, 04:308-326.
[6] 徐锡伟, 闻学泽, 郑荣章, et al. 川滇地区活动块体最新构造变动样式及其动力来源[J]. 中国科学(D 辑:地球科学), 2003, S1: 151-162.
[7] 张培震, 王敏, 甘卫军, et al. GPS 观测的活动断裂滑动速率及其对现今大陆动力作用的制约[J]. 地学前缘, 2003, S1: 81-92.
[8] 常祖峰, 常昊, 臧阳, et al. 维西—乔后断裂新活动特征及其与红河断裂的关系[J]. 地质力学学报, 2016, 22(03): 517-530.
[9] FENG J, YAO H, WANG W. Imaging mantle transition zone discontinuities insouthwest China from dense array ambient noise interferometry[J]. EarthquakeScience, 2018, 31(5-6): 301-310.
[10] LIN F-C, LI D, CLAYTON R W, et al. High-resolution 3D shallow crustal structurein Long Beach, California: Application of ambient noise tomography on a denseseismic array[J]. geophysics, 2013, 78(4): 45-56.
[11] SHARE P-E, ALLAM A A, BEN-ZION Y, et al. Structural Properties of the SanJacinto Fault Zone at Blackburn Saddle from Seismic Data of a Dense LinearArray[J]. Pure and Applied Geophysics, 2018, 176(3): 1169-1191.
[12] YANG H, LI Z, PENG Z, et al. Low-velocity zones along the San Jacinto Fault, Southern California, from body waves recorded in dense linear arrays[J]. Journal ofGeophysical Research: Solid Earth, 2014, 119(12): 8976-8990.
[13] YAO H. Building the community velocity model in the Sichuan-Yunnan region, China: Strategies and progresses[J]. Science China Earth Sciences, 2020, 63(9):1425-1428.
[14] 王松, 张振勋, 房立华. 西昌流动地震台阵微震观测[J]. 四川地震, 2015, 03: 5-8.
[15] 姚远, 杨周胜, 姜金钟, et al. 云南小江断裂带中段的微震活动性——PALM 自动检测方法在密集台阵中的应用[J]. 北京大学学报(自然科学版), 2022, 58(05): 829-838.
[16] KARASöZEN E, KARASöZEN B. Earthquake location methods[J]. GEM -International Journal on Geomathematics, 2020, 11(1): 1-28.
[17] GEIGER L. Probability Method for the Determination of Earthquake Epicenters fromArrival Time Only[J]. Bull St Louis Univ, 1912, 8(1): 60-71.
[18] KISSLING E, ELLSWORTH W L, EBERHART-PHILLIPS D, et al. Initial referencemodels in local earthquake tomography[J]. Journal of Geophysical Research: SolidEarth, 1994, 99(B10): 19635-19646.
[19] DOUGLAS A. Joint epicentre determination[J]. Nature, 1967, 215: 47-48.
[20] JORDAN T, SVERDRUP K A. Teleseismic location techniques and their applicationto earthquake clusters in the South-central Pacific[J]. Bulletin of the SeismologicalSociety of America, 1981, 71(4): 1105-1130.
[21] DEWEY J W. Seismicity and Tectonics of Western Venezula[J]. Bulletin of theSeismological Society of America, 1972, 62(6): 1711-1751.
[22] GOT J L, FRéCHET J, KLEIN F W. Deep fault plane geometry inferred frommultiplet relative relocation beneath the south flank of Kilauea[J]. Journal ofGeophysical Research, 1994, 99(B8): 15375-15386.
[23] WALDHAUSER F, ELLSWORTH W L. A Double-Difference Earthquake LocationAlgorithm: Method and Application to the Northern Hayward Fault, California[J]. Bulletin of the Seismological Society of America, 2000, 90(6): 1353-1368.
[24] TRUGMAN D T, SHEARER P M. GrowClust: A Hierarchical Clustering Algorithmfor Relative Earthquake Relocation, with Application to the Spanish Springs andSheldon, Nevada, Earthquake Sequences[J]. Seismological Research Letters, 2017, 88(2A): 379-391.
[25] 陈运泰, 刘瑞丰. 用 P 波初动资料确定地震震源机制教程(三)[J]. 地震地磁观测与研究, 2021, 42(5): 1-11.
[26] 许忠淮, 阎明, 赵仲和. 由多个小地震推断的华北地区构造应力场的方向[J]. 地震学报, 1983, 03: 268-279.
[27] REASENBERG P, OPPENHEIMER D. FPFIT, FPPLOT and FPPAGE: Fortrancomputer programs for calculating ana displaying earthquake fault-plane solutions[J]. USGeolSurvOpen-File Rept, 1985, 85: 1-109.
[28] HARDEBECK J L, SHEARER P M. A New Method for Determining First-MotionFocal Mechanisms[J]. Bulletin of the Seismological Society of America, 2002, 92(6):2264-2276.
[29] 俞春泉, 陶开, 崔效锋, et al. 用格点尝试法求解 P 波初动震源机制解及解的质量评价[J]. 地球物理学报, 2009, 52(05): 1402-1411.
[30] KISSLINGER C. Evalution of S to P amplitude ratios for determining focalmechanisms from regional network observations[J]. bull Seismol Soc Am, 1980, 70(4): 999-1014.
[31] NAKAMURA M. Determination of focal mechanism solution using initial motionpolarity of P and S waves[J]. Physics of the Earth and Planetary Interiors, 2002, 130:17-29.
[32] NAKAMURA A, HORIUCHI S, HASEGAWA A. Joint Focal MechanismDetermination with Source-Region Station Corrections Using Short-Period Body- Wave Amplitude Data[J]. Bulletin of the Seismological Society of America, 1999, 89(2): 373-383.
[33] 吴大铭, 王培德, 陈运泰. 用 SH 波和 P 波振幅比确定震源机制解[J]. 地震学报, 1989, 03: 275-281.
[34] HARDEBECK J H, SHEARER P M. Using S/P Amplitude Ratios to Constrain theFocal Mechanisms of Small Earthquakes[J]. Bulletin of the Seismological Society ofAmerica, 2003, 93(6): 2434-2444.
[35] SNOKE J A, MUNSEY J W, TEAGUE A G, et al. A Program for Focal MechanismDetermination by Combined Use of Polarity and SV-P Amplitude Ratio Data[J]. Earthquake Notes, 1984, 55: 3-15.
[36] 刘杰, 郑斯华, 康英, et al. 利用 P 波和 S 波的初动和振幅比计算中小地震的震源机制解[J]. 地震, 2004, 01: 19-26.
[37] ZHAO L S, HELMBERGER D V. Source Estimation from Broadband RegionalSeismograms[J]. Bulletin of the Seismological Society of America, 1994, 84(1): 91- 104.
[38] ZHU L P, HELMBERGER D V. Advancement in Source Estimation TechniquesUsing Broadband Regional Seismograms[J]. Bulletin of the Seismological Society ofAmerica, 1996, 86(5): 1634-1641.
[39] BEN-ZION Y, ZHU L. Parametrization of general seismic potency and momenttensors for source inversion of seismic waveform data[J]. Geophysical JournalInternational, 2013, 194(2): 839-843.
[40] SONG F, TOKSöZ M N. Full-waveform based complete moment tensor inversion andsource parameter estimation from downhole microseismic data for hydrofracturemonitoring.[J]. geophysics, 2011, 76: 103-116.
[41] LI J, ZHANG H, SADI KULELI H, et al. Focal mechanism determination using high￾frequency waveform matching and its application to small magnitude inducedearthquakes[J]. Geophysical Journal International, 2011, 184(3): 1261-1274.
[42] 许忠淮, 汪素云, 黄雨蕊, et al. 由多个小震推断的青甘和川滇地区地壳应力场的方向特征[J]. 地球物理学报, 1987, 05: 476-486.
[43] WALLANCE R E. Geometry of shearing stress and relation to faulting[J]. Geol, 1951, 59(2): 118-130.
[44] BOTT M H P. The mechanics of oblique faulting[J]. Geol, 1959, 96: 109-117.
[45] MICHAEL A J. Determination of stress from slip data: faults and folds[J]. Journal ofGeophysical Research, 1984, 89: 11517-11526.
[46] HARDEBECK J L, MICHAEL A J. Damped regional-scale stress inversions:Methodology and examples for southern California and the Coalinga aftershocksequence[J]. Journal of Geophysical Research: Solid Earth, 2006, 111(B11310):doi:10.1029/2005JB004144.
[47] 虎雄林, 张建国, 李朝才, et al. 云南红河断裂带中小地震重定位及其与地质构造的关系[J]. 地震研究, 2006, 04: 349-354.
[48] 房立华, 吴建平, 王未来, et al. 云南鲁甸 M_S6.5 地震余震重定位及其发震构造[J]. 地震地质, 2014, 36(04): 1173-1185.
[49] 张广伟. 云南地区地震的重新定位及 b 值研究[J]. 中国地震, 2016, 32(01): 54-62.
[50] 雷兴林, 王志伟, 马胜利, et al. 关于 2021 年 5 月滇西漾濞 M_S6.4 地震序列特征及成因的初步研究[J]. 地震学报, 2021, 43(03): 261-286.
[51] 谢富仁, 祝景忠, 粱海庆, et al. 中国西南地区现代构造应力场基本特征[J]. 地震学报, 1993, 04: 408-418.
[52] ANGELIER J. Tectonic analysis of fault slip data sets[J]. Journal of GeophysicalResearch, 1984, 89(B7): 5835-5848.
[53] 陈天长, 堀内茂木, 郑斯华. 利用 P 波初动和短周期 P,S 波振幅测定川滇地区地震震源机制解和应力场[J]. 地震学报, 2001, 04: 436-440.
[54] 吴建平, 明跃红, 王椿镛. 云南地区中小地震震源机制及构造应力场研究[J]. 地震学报, 2004, 05: 457-465.
[55] 曹颖, 吴小平, 沈娅宏, et al. 由震源机制解资料研究川滇地区构造应力场[J]. 地震研究, 2013, 36(02): 165-172.
[56] 郭祥云, 陈学忠, 王生文, et al. 川滇地区中小地震震源机制解及构造应力场的研究[J]. 地震工程学报, 2014, 36(03): 599-607.
[57] 裴玮来, 杨周胜, 周仕勇. 云南小江地区小震震源机制及构造应力场研究[J]. 北京大学学报(自然科学版), 2022, 58(04): 602-608.
[58] 李君, 王勤彩, 崔子健, et al. 川滇菱形块体东边界及邻区震源机制解与构造应力场空间分布特征[J]. 地震地质, 2019, 41(06): 1395-1412.
[59] 钱晓东 , 秦嘉政, 刘丽芳. 云南地 区现代构造应 力场研究 [J]. 地震地 质, 2011, 33(01): 91-106.
[60] ZHAO L, LUO Y, LIU T Y, et al. Earthquake Focal Mechanisms in Yunnan and theirInference on the Regional Stress Field[J]. Bulletin of the Seismological Society ofAmerica, 2013, 103(4): 2498-2507.
[61] XU Z, HUANG Z, WANG L, et al. Crustal stress field in Yunnan: implication forcrust-mantle coupling[J]. Earthquake Science, 2016, 29(2): 105-115.
[62] TIAN J, LUO Y, ZHAO L. Regional stress field in Yunnan revealed by the focalmechanisms of moderate and small earthquakes[J]. Earth and Planetary Physics, 2019, 3(3): 243-252.
[63] 盛书中, 胡晓辉, 王晓山, et al. 云南及邻区地壳应力场研究[J]. 地球物理学报, 2022, 65(09): 3252-3267.
[64] 孔 维林 , 黄 禄渊 , 姚 瑞, et al. 川滇地区应力场研究进展 [J]. 地球物理学进展 , 2021, 36(5): 1853-1864.
[65] LEVENBERG K. A Method for the Solution of Certain Problems in Least Squares[J]. Quarterly of Applied Mathematics, 1944, 2: 164-168.
[66] SHEARER P M. Introduction to Seismology, Second edition[M]. United States ofAmerica by Cambridge University Press, New York, 2009.
[67] 许忠淮, 李世愚. 地震学百科知识（二）—震源物理（上）[J]. 国际地震动态, 2013, 2: 23-31.
[68] ZHU W, BEROZA G. PhaseNet: a deep-neural-network-based seismic arrival-timepicking method[J]. Geophysical Journal International, 2019, 216(1): 261-273.
[69] ZHANG M, ELLSWORTH W L, BEROZA G C. Rapid Earthquake Association andLocation[J]. Seismological Research Letters, 2019, 90(6): 2276-2284.
[70] WANG R, SCHMANDT B, ZHANG M, et al. Injection ‐ induced earthquakes oncomplex fault zones of the Raton Basin illuminated by machine ‐ learning phasepicker and dense nodal array[J]. Geophysical Research Letters, 2020, 47(14):e2020GL088168.
[71] ZHANG M, LIU M, FENG T, et al. LOC-FLOW: An End-to-End Machine Learning- Based High-Precision Earthquake Location Workflow[J]. Seismological ResearchLetters, 2022, 93(5): 2426-2438.
[72] HUTTON L K, BOORE D M. THE ML SCALE IN SOUTHERN CALIFORNIA[J]. Bulletin of the Seismological Society of America,, 1987, 77(6): 2074-2094.
[73] YU C, ZHENG Y, SHANG X. Crazyseismic: A MATLAB GUI ‐ Based SoftwarePackage for Passive Seismic Data Preprocessing[J]. Seismological Research Letters, 2017, 88(2A): 410-415.
[74] ZOBACK M L. First- and Second-Order Patterns of Stress in the Lithosphere: TheWorld Stress Map Project[J]. Journal of Geophysical Research, 1992, 97(B8): 703- 728.
[75] HEIDBACH O, TINGAY M, BARTH A, et al. Global crustal stress pattern based onthe World Stress Map database release 2008[J]. Tectonophysics, 2010, 482(1-4): 3- 15.