Earth and Planetary Physics BREVIA 2: 84–85, 2018 SOLID EARTH: SEISMOLOGY doi: 10.26464/epp2018009 An M6.9 earthquake at Mainling, Tibet on Nov.18, 2017 XueMei Zhang1, GuangBao Du1, Jie Liu1*, ZhiGao Yang1, LiYe Zou1, and XiYan Wu2 1China Earthquake Networks Center, Beijing 100045, China; 2Institute of Geology, Chinese Earthquake Administration, Beijing 100029, China Keywords: Mainling M6.9 earthquake; focal mechanism; aftershock Citation: Zhang X. M., Du G. B., Liu J., Yang Z. G., Zou L. Y., and Wu X. Y. (2018). An M6.9 earthquake at Mainling, Tibet on Nov.18, 2017. Earth Planet. Phys., 2, 84–85. http://doi.org/10.26464/epp2018009 At 06:34 (CST) on Nov.18, 2017, an M6.9 earthquake occurred in 93°E 94°E 95°E 96°E 97°E 31°N P! the Mainling County, Nyingchi Region of Xizang Autonomous Re- Banbar Lhorong Lhari-Zayu Fault P! gion, China. The epicenter is located at 95.02°E, 29.75°N and the ± P! Lhari focal depth is about 10 km (Figure 1). The epicenter is about 100 !(!(!( !((!!(!(!( !( !( !( !( km from the Mainling County. The average elevation within 5 km Boxoi !(!(!(P! !( Gongbogyamda !( 30°N is about 3100 m. This earthquake has caused widespread concern !( P! !( Bome !( P! among members of government, research institutions, and public ^_!( #P! Nyingchi !( media. !( Lhari-Zayu Fault P!Medog P! By 16:00 of Nov.19, seven aftershocks (M>3.0) were recorded, in- P! Yarlung-Zangbo Fault Yarlung-Zangbo FaultMainling !( P! !( !( Nang !( 29°N cluding one M5.0–5.9 earthquake, two M4.0–4.9 earthquakes, and !( !( !( (! !( !( four M3.0–3.9 earthquakes (Table 1, Figure 2). The aftershock se- !( quence presents spatial variation with NW-SE striking in various Maniweng Fault !(!( !( shallower depths above 10 km. !( 010 20 40 60 80 km ^_ Epicenter Fault # Station Based on the seismic data from 26 stations of the China Seismic !( 3.0-3.9 !( 4.0-4.9 !( 5.0-5.9 !( 6.0-6.9 !( >7.0 Network, applying the W phase method (Kanamori and Rivera, Figure 1. The epicenter position of the M6.9 earthquake of Nov.18, 2008) we determined the focal mechanism of the earthquake. The 2017 and the distribution of previous earthquakes in this region (from result is as follows: the moment magnitude Mw is about 6.5; nod- 2012). al plane 1 has a strike of 127°/dip 39°/rake 92°, nodal plane 2 has strike 304°/dip 51°/rake 88°. The centroid depth from waveform fitting is 17 km; it is preliminarily inferred that this was mainly a Lhari Fault, and Mainling Fault are Holocene faults. The Zanda- thrusting event (Figure 2). Lazi-Qiongduojiang Fault is a Late Pleistocene fault. It is conjec- tured that the NWW-trending Tamu-Banbar Fault is the seismo- Since 1950, 89 earthquakes (Figure 3) above M5.0 have occurred genic fault of this earthquake, which is presently a belt of dense within 300 km from the epicenter of the M6.9 earthquake of Main- small earthquakes, and is a south branch of the Lhari Fault ling, Tibet, including 13 M6.0–6.9 earthquakes but no M7.0–7.9 (Figure 4). earthquake; however, the largest previous event was the Zayu M8.5 earthquake of Aug.15, 1950 about 220 km from the present earthquake. Acknowledgments The present earthquake took place in the eastern syntaxis region The seismic data were provided by China Seismic Network. We are of Namjagbarwa, which is an intense seismic belt caused by con- grateful to the workgroup on earthquake emergency data tinent-continent collision at the east end of Himalayan Mountains. products and services. The National Natural Science Foundation of The epicenter was located on the northeastern extension of China (Grants 41774069 and 41274062) sponsored this study. Datuo Cameroonf Fault, near to the Lhari Fault, Mainling Fault, and Zanda-Lazi-Qiongduojiang Fault. The Datuo Cameroonf Fault, References Kanamori H, Rivera L. (2008). Source inversion of W phase: Speeding of seismic Correspondence to: J. Liu, [email protected] tsunami warning. Geophys. J. Int., 175(1), 222–238. Received 18 NOV 2017; Accepted 21 NOV 2017. https://doi.org/10.1111/gji.2008.175.issue-1 Accepted article online 24 NOV 2017. Xu X, Han Z, Yang X, et al. (2016). Seismotectonic Map in China and Its Adjacent Regions (in Chinese). Beijing: Seismogical Press. Copyright © 2018 by Earth and Planetary Physics. Earth and Planetary Physics doi: 10.26464/epp2018009 85 Table 1. Earthquakes greater than M3.0 between initial event on Nov. 18 and 16: 00 of Nov.19 No. Time (CST) Latitude (°N) Longitude (°E) Depth (km) Magnitude Location 1 2017-11-18 06:34:19.0 29.75 95.02 10 6.9 Mainling, Tibet 2 2017-11-18 06:37:58.2 29.77 95.11 6 4.0 Mainling, Tibet 3 2017-11-18 08:31:58.7 29.88 94.92 6 5.0 Mainling, Tibet 4 2017-11-18 09:11:50.6 29.89 94.99 5 3.1 Mainling, Tibet 5 2017-11-18 10:13:38.1 29.80 95.10 7 3.3 Mainling, Tibet 6 2017-11-18 11:36:04.2 29.93 94.99 6 4.3 Mainling, Tibet 7 2017-11-18 13:59:44.5 29.90 95.00 6 3.0 Mainling, Tibet 8 2017-11-19 05:24:48.9 29.91 94.99 5 3.1 Mainling, Tibet 94 °E 96 °E 93°E 94°E 95°E 96°E 97°E Riwoqe 31°N Banbar-LhorongNujiang Fault River Nujiang Fault Lhari-Zayu Fault Banbar Lhorong Lhari Fault Nyang River 30°N 30°N Baxoi Lhari-Zayu Fault Gongbogyamda Bome Tamu-Banbar Fault Lhari Fault Zayu Fault Lhari Fault MainlingDatuo Fault Cameroon Fault Mainling Medog Yarlung-Zangbo Suture BeltLilung Fault 29°N Nang Yalung-Zangbo RiverMedog Fault Tamu-Banbar Fault Yarlung-Zangbo Fault Yalung-Zangbo River Zanda-Lazi-Qiongduojiang Fault Yarlung-Zangbo Fault Apalong Fault STDS MBT Lilung Fault Maniweng Fault M6.9 Earthquake 0 25 50 75 100 km 4.0-4.9 Quaternary 5.0-5.9 Holocene fault 6.0-6.9 Later Pleistocene fault Linear tectonic 7.0-7.9 Early-middle Pleistocene fault River Road ı8.0 N Mainshock Fault -9000 -3000 0 30006000 Strike-slip Normal Thrust Altitude (m) Figure 4. Regional seismic structure map of the M6.9 earthquake of Figure 2. The M6.9 earthquake of Nov.18, 2017, its aftershocks up to Nov.18, 2017. (Refer from Xu X et al., 2016). STDS: Southern Tibet 16: 00 of Nov.19, and focal mechanism solution. Detachment System, MBT: Main Boundary Thrust. 93°E 94°E 95°E 96°E 97°E (! 31°N P! Banbar P! ± P! Lhorong (! Lhari Lhari-Zayu Fault ((!! (! (! (! (! (! (! (! P! Gongbogyamda(! (! (((!!! Boxoi 30°N P! ! Bome (! ( P! (! (! ^_ (! #P! Nyingchi (! Lhari-Zayu Fault (! P! Medog P! ((((((((((((((!!!!!!!!!!!!! P! Yarlung-Zangbo Fault (! (! Yarlung-Zangbo Fault (! P! Mainling Nang (! 29°N (! (((!!! (! (((((((!!!!!(((((((((((!!!!!!!!!! (! (! Maniweng(! (! Fault (! Zayu M8.5 (! (! (! 0 20 40 60 80 km ^_ Epicenter Fault # Station !( 5.0-5.9!( 6.0-6.9 !( 7.0-7.9 !( >8.0 Figure 3. Distribution of previous M≥5.0 earthquakes (since 1950) surrounding the M6.9 earthquake. Zhang X M et al.: 2017 M6.9 earthquake at Mainling, Tibet .