Relocation of the Foreshocks and Aftershocks of the 2021 Ms 6.4 Yangbi Earthquake Sequence, Yunnan, China

Abstract

An Ms 6.4 earthquake occurred in Yangbi, Yunnan, China on May 21, 2021, which has obvious foreshock activity and abundant aftershocks. Based on the seismic observation data recorded by the Yunnan Seismic Network three days before and seven days after the mainshock, a double-difference location method was used to relocate 2 133 earthquakes of the Yangbi sequence. Aftershocks are mostly distributed to the southeast of the mainshock in a unilateral rupture pattern. This sequence exhibits a SE-trending linear alignment with a length of about 25 km, and most of the focal depth is above 12 km. Integrated with the seismic distribution and focal mechanism results, we infer that the strike of the seismogenic fault is about 140°, and dipping to the SW. The fault structure revealed by the seismic sequence is complex, with the NW segment exhibiting a steep dip and relatively simple structure of strike-slip rupture and the SE segment consisting of several branching ruptures. The Yangbi Earthquake is a typical foreshock-mainshock-aftershock sequence, and the mainshock is likely triggered by the largest foreshock. This earthquake occurred in the boundary between high- and low-velocity anomalous zone, where is susceptible to generate large earthquakes.

Keywords

Yangbi Earthquake / Weixi-Qiaohou-Weishan fault / earthquake sequence / double-difference relocation / earthquakes

References

Bai D H, Unsworth M J, Meju M A, . Crustal Deformation of the Eastern Tibetan Plateau Revealed by Magnetotelluric Imaging. Nature Geoscience, 2010, 3(5): 358-362.

Bai Z M, Wang C Y. Tomography Research of the Zhefang-Binchuan and Menglian-Malong Wide-Angle Seismic Profiles in Yunnan Province. Chinese Journal of Geophysics, 2004, 47(2): 257-267. in Chinese with English Abstract)

Bao X W, Sun X X, Xu M J, . Two Crustal Low-Velocity Channels beneath SE Tibet Revealed by Joint Inversion of Rayleigh Wave Dispersion and Receiver Functions. Earth and Planetary Science Letters, 2015, 415: 16-24.

Beroza G C, Ellsworth W L. Properties of the Seismic Nucleation Phase. Tectonophysics, 1996, 261(1): 209-227. 2/3

Chang Z F, Chang H, Li J L, . The Characteristic of Active Normal Faulting of the Southern Segment of Weixi-Qiaohou Fault. Journal of Seismological Research, 2016, 39(4): 579-586. (in Chinese with English Abstract)

Chang Z F, Chang H, Zang Y, . Recent Active Features of Weixi-Qiaohou Fault and Its Relationship with the Honghe Fault. Journal of Geomechanics, 2016, 22(3): 517-530. (in Chinese with English Abstract)

Chen J H, Liu Q Y, Li S C, . Seismotectonic Study by Relocation of the Wench Uan M _S 8.0 Earthquake Sequence. Chinese Journal of Geophysics, 2009, 52(2): 390-397. (in Chinese with English Abstract)

Chen S W, Wang B S, Tian X F, . Crustal Structure from yunxian-Ninglang Wide-Angle Seismic Reflection and Refraction Profile in Northwestern Yunnan, China. Seismology and Geology, 2016, 38(1): 91-106. (in Chinese with English Abstract)

Chen Y, Liu J, Ge H. Pattern Characteristics of Foreshock Sequences. Pure and Applied Geophysics, 1999, 155(2–4): 395-408.

Chen Y, Liu J, Ge H. Pattern Characteristics of Foreshock Sequences. Pure and Applied Geophysics, 1999, 155(2): 395-408. 3/4

Davis G H, Bump A P, García P E, . Conjugate Riedel Deformation Band Shear Zones. Journal of Structural Geology, 2000, 22(2): 169-190.

Dodge D A, Beroza G C, Ellsworth W L. Detailed Observations of California Foreshock Sequences: Implications for the Earthquake Initiation Process. Journal of Geophysical Research: Solid Earth, 1996, 101(B10): 22371-22392.

Fang L H, Wu J P, Su J R, . Relocation of Mainshock and Aftershock Sequence of the M _s 7.0 Sichuan Jiuzhaigou Earthquake. Chinese Science Bulletin, 2018, 63(7): 649-662. in Chinese with English Abstract)

Fang L H, Wu J P, Wang W L, . Aftershock Observation and Analysis of the 2013 Ms 7.0 Lushan Earthquake. Seismological Research Letters, 2015, 86(4): 1135-1142.

Gao T Y, Ding Z F, Wang X C, . Joint Inversion of Receiver Functions, Reyleigh Wave Dispersion and ZH Ratio for Crustal Structure in Southeast Tibetan Plateau and Its Implications for Dynamics. Chinese Journal of Geophysics, 2021, 64(6): 1885-1906. (in Chinese with English Abstract)

He C C, Li X R, Wang J, . Seism-Tectonic Background, Deep Rheological Structure and Triggering Mechanism of Diqing Earthquake (Ms 5.9), Yunnan. Earth Science, 2015, 40(10): 1653-1666. (in Chinese with English Abstract)

Hu J F, Su Y J, Zhu X G, . S-Wave Velocity and Poisson’s Ratio Structure of Crust in Yunnan and Its Implication. Science in China Series D: Earth Sciences, 2005, 33(8): 714-722. (in Chinese)

Hua Y, Zhao D, Toyokuni G, . Tomography of the Source Zone of the Great 2011 Tohoku Earthquake. Nature Communications, 2020, 11(1): 1163

Huang X L, Wu Z H, Jiang Y, . Seismic Intensity Distribution and Seismogenic Structure Analysis of the March 3, 2013 Eryuan Ms5.5 Earthquake in Dali, Yunnan Province. Geological Bulletin of China, 2015, 34 1 135-145. (in Chinese with English Abstract)

Institute of Geology China Earthquake Administration Yunnan Earthquake Administration Active Faults in the Northwest Yunnan Region, 1990, Beijing: Seismological Press, 1-321

Jones L M, Wang B Q, Xu S X, . The Foreshock Sequence of the February 4, 1975, Haicheng Earthquake (M = 7.3). Journal of Geophysical Research: Solid Earth, 1982, 87(B6): 4575-4584.

Katz Y, Weinberger R, Aydin A. Geometry and Kinematic Evolution of Riedel Shear Structures, Capitol Reef National Park, Utah. Journal of Structural Geology, 2004, 26(3): 491-501.

Korenaga M, Matsumoto S, Iio Y, . Three Dimensional Velocity Structure around Aftershock Area of the 2004 Mid Niigata Prefecture Earthquake (M 6.8) by the Double-Difference Tomography. Earth, Planets and Space, 2005, 57(5): 429-433.

Lanza F, Chamberlain C J, Jacobs K, . Crustal Fault Connectivity of the Mw 7.8 2016 Kaiköura Earthquake Constrained by Aftershock Relocations. Geophysical Research Letters, 2019, 46(12): 6487-6496.

Laske G, Masters G, Ma Z, . Update on CRUST1.0-A 1-Degree Global Model of Earth’s Crust, 2013, Vienna: EGU General Assembly 2013, 2658

Li Y Q, Wang D, Xu S H, . Thrust and Conjugate Strike-Slip Faults in the 17 June 2018 M _JMA 6.1 (Mw 5.5) Osaka, Japan, Earthquake Sequence. Seismological Research Letters, 2019, 90(6): 2132-2141.

Liu Y, Yao H J, Zhang H J, . The Community Velocity Model V. 1.0 of Southwest China, Constructed from Joint Body- and Surface-Wave Travel-Time Tomography. Seismological Research Letters, 2021, 92(5): 2972-2987.

Momeni S M, Tatar M. Mainshocks/Aftershocks Study of the August 2012 Earthquake Doublet on Ahar-Varzaghan Complex Fault System (NW Iran). Physics of the Earth and Planetary Interiors, 2018, 283: 67-81.

Qin W B, Zhang S X, Li M K, . Distribution of Intra-Crustal Low Velocity Zones beneath Yunnan from Seismic Ambient Noise Tomography. Journal of Earth Science, 2018, 29(6): 1409-1418.

Ren J J, Zhang S M, Hou Z H, . Study of Late Quaternary Slip Rate in the Mid-Segment of the Tongdian-Weishan Fault. Seismology and Geology, 2007, 29(4): 756-764. (in Chinese with English Abstract)

Ross Z E, Cochran E S, Trugman D T, . 3D Fault Architecture Controls the Dynamism of Earthquake Swarms. Science, 2020, 368(6497): 1357-1361.

Sun J, Xu C F, Jiang Z, . The Electrical Structure of the Crust and Upper Mantle in the West Part of Yunnan Province and Its Relation to Crustal Tectonics. Seismology and Geology, 1989, 11(1): 35-45. (in Chinese with English Abstract)

Tang P, Chang Z F. Study on the Activity of the Weishan Basin Section of the Wixi-Qiaoghou Fault. Geological review, 2013, 59: 108-109. (in Chinese)

The Earthquake Disaster Prevention Department of China Earthquake Administration Catalogue of Chinese Historical Strong Earthquakes, 1999, Beijing: China Science and Technology Press (in Chinese)

The Earthquake Disaster Prevention Department of China Earthquake Administration Catalogue of Chinese Present Earthquakes, 1999, Beijing: China Science and Technology Press (in Chinese)

Toyokuni G, Zhao D P, Chen K H. Tomography of the Source Zone of the 2016 South Taiwan Earthquake. Geophysical Journal International, 2016, 207(1): 635-643.

Waldhauser F, Ellsworth W L. A Double-Difference Earthquake Location Algorithm: Method and Application to the Northern Hayward Fault, California. Bulletin of the Seismological Society of America, 2000, 90(6): 1353-1368.

Wang C Y, Mooney W D, Wang X L, . A Study on 3-D Velocity Structure of Crust and Upper Mantle in Sichuan-Yunnan Region, China. Acta Seismologica Sinica, 2002, 24(1): 1-17. in Chinese with English Abstract)

Wang D, Hutko A R. Relative Relocations of the North Korean Nuclear Tests from 2006 to 2017 Using the Hi-Net Array in Japan. Geophysical Research Letters, 2018, 45(15): 7481-7487.

Wang K, Chen Q F, Sun S, . Predicting the 1975 Haicheng Earthquake. Bulletin of the Seismological Society of America, 2006, 96(3): 757-795.

Wang M, Shen Z K. Present-Day Crustal Deformation of Continental China Derived from GPS and Its Tectonic Implications. Journal of Geophysical Research: Solid Earth, 2020, 125(2): e2019JB018774

Wang Z, Kao H. The Significance of Tomographic Edge Zones for Large Earthquakes in Taiwan. Journal of Geophysical Research: Solid Earth, 2019, 124 11 11822-11839.

Wang Z, Wang J, Yang X Q. The Role of Fluids in the 2008 Ms 8.0 Wenchuan Earthquake, China. Journal of Geophysical Research: Solid Earth, 2021, 126(2): e2020JB019959

Wessel P, Smith W H F. New, Improved Version of Generic Mapping Tools Released. Eos, Transactions American Geophysical Union, 1998, 79 47 579

Wu K, Dong Y P, Duan J X, . Cenozoic Uplift of the Central Yunnan Fragment, Southwestern China, Revealed by Apatite (U-Th)/ He Dating. Journal of Earth Science, 2020, 31 4 735-742.

Wu P, Gao Y, Chen A G, . Preliminary Study on the Anisotropy of the Upper Crust in the Sanjiang Area, Southeastern Margin of the Tibetan Plateau. Chinese Journal of Geophysics, 2020, 63(3): 1104-1116. (in Chinese with English Abstract)

Xie Z J, Zheng Y, Yao H J, . Preliminary Analysis on the Source Properties and Seismogenic Structure of the 2017 M _s7.0 Jiuzhaigou Earthquake. Science China Earth Sciences, 2018, 61(3): 339-352.

Xu F K, Liu Z F, Zhang Z Q, . Double Difference Relocation and Focal Mechanisms of the Jinggu Ms 6.6 Earthquake Sequences in Yunnan Province in 2014. Earth Science, 2015, 40(10): 1741-1754. (in Chinese with English Abstract)

Xu Y, Koper K D, Burlacu R, . A New Uniform Moment Tensor Catalog for Yunnan, China, from January 2000 through December 2014. Seismological Research Letters, 2020, 91(2A): 891-900.

Xu Y, Yang X T, Liu J H. Tomographic Study of Crustal Velocity Structures in the Yunnan Region Southwest China. Chinese Journal of Geophysics, 2013, 56(6): 1904-1914. (in Chinese with English Abstract)

Yang T, Wu J P, Fang L H, . 3-D Crustal p-Wave Velocity Structure in Western Yunnan Area and Its Tectonic Implications. Seismology and Geology, 2014, 36(2): 392-404. (in Chinese with English Abstract)

Yang Z G, Liu J, Zhang X M, . A Preliminary Report of the Yangbi, Yunnan, M _S6.4 Earthquake of May 21, 2021. Earth and Planetary Physics, 2021, 5(4): 1-3.

Yano T E, Matsubara M. Effect of Newly Refined Hypocenter Locations on the Seismic Activity Recorded during the 2016 Kumamoto Earthquake Sequence. Earth, Planets and Space, 2017, 69 74

Yi G X, Long F, Liang M J, . Focal Mechanism Solutions and Seismogenic Structure of the 17 June 2019 M _S6.0 Sichuan Changning Earthquake Sequence. Chinese Journal of Geophysics, 2019, 62(9): 3432-3447. (in Chinese with English Abstract)

Yu X W, Chen Y T, Zhang H. Relocation of Earthquakes in Beijing-Tianjin-Tangshan Region with Double-Difference Tomography Technique. Acta Seismologica Sinica, 2010, 32(3): 257-269. (in Chinese with English Abstract)

Zhang G W, Lei J S, Liang S S, . Relocations and Focal Mechanism Solutions of the 3 August 2014 Ludian, Yunnan M _s6.5 Earthquake Sequence. Chinese Journal of Geophysics, 2014, 57(9): 3018-3027. (in Chinese with English Abstract)

Zhang T J, Jin M P, Liu Z F, . Distribution and Significance of Crustal Thickness and Poisson’s Ratio in Northwestern Yunnan. Journal of Seismological Research, 2020, 43(1): 10-18. (in Chinese with English Abstract)

Zhang Z Q, Gao Y. Crustal Thicknesses and Poisson’s Ratios beneath the Chuxiong-Simao Basin in the Southeast Margin of the Tibetan Plateau. Earth and Planetary Physics, 2019, 3(1): 69-84.

Zhao B, Gao Y, Huang Z B, . Double Difference Relocation, Focal Mechanism and Stress Inversion of Lushan M _S7.0 Earthquake Sequence. Chinese Journal of Geophysics, 2013, 56(10): 3385-3395. (in Chinese with English Abstract)