A possible seismic gap and high earthquake hazard in the North China Basin

An Yin1,2*, Xiangjiang Yu2,3, Z.-K. Shen2, and Jing Liu-Zeng4 1Structural Geology Group, China University of Geosciences (Beijing), Beijing 100083, China 2Department of Earth, Planetary, and Space Sciences, University of California–Los Angeles, Los Angeles, California 90095-1567, USA 3School of Earth and Space Sciences, Peking University, Beijing 100871, China 4Institute of Geology, China Earthquake Administration, Beijing 100027, China

ABSTRACT indicated by a southward increase in eastward In this study we use combined historical records and results of early paleo-earthquake studies GPS velocities across the North China Basin to show that a 160 km seismic gap has existed along the northeast-striking right-slip Tangshan- (Fig. 2A) may have driven current right-slip Hejian-Cixian fault (China) over more than 8400 yr. The seismic gap is centered in Tianjin, a motion along northeast-striking faults via book- city in the North China Basin with a population of 11 million and located ~100 km from Bei- shelf faulting (Fig. 2B). jing, which has a population of 22 million. Current data indicate that the recurrence interval of major earthquakes along the Tangshan-Hejian-Cixian fault is 6700–10,800 yr. This implies SPATIOTEMPORAL PATTERNS OF that a large earthquake with an estimated magnitude of ~M 7.5 is either overdue or will occur SEISMIC RUPTURE within the next 2000–3000 yr along the inferred seismic gap if it is ruptured by a single event. Because of a general lack of surface ruptures Alternatively, the seismic gap may be explained by aseismic creeping, strain transfer between for most major historical earthquakes in the adjacent faults, or much longer recurrence times than the current knowledge indicates. North China Basin (Xu et al., 2002), we plot the distributions of subsurface rupture length INTRODUCTION and Wentworth (1997) proposed a model that along the Sanhe-Laishui and Tangshan-Hejian- Intracontinental earthquakes have caused the converts seismic intensity to seismic magnitude Cixian faults using the scaling relationship of most fatalities in human history (Dubar et al., based on recorded intensity observed at single Wells and Coppersmith (1994) (Fig. 3). The plot 1992), yet their controlling mechanisms remain locations; their method is ideal for regions such incorporates uncertainties of locating and esti- poorly understood (e.g., Obermeier et al., 1991; as the western United States with sparse inten- mating the magnitude of historical earthquakes Stein et al., 2012). This issue is well illustrated sity data, which is not the case for north China. (see the Data Repository). Assuming symmetric by the North China Basin, in which there were In addition, the model depends on local geol- rupture, which was the case for the A.D. 1976 24 devastating earthquakes with M ≥ 6 in the ogy that would require additional calibration if Tangshan earthquake (Butler et al., 1979), the past millennium, along buried faults below thick applied to north China. For these reasons, we plot reveals a 160 km seismic gap centered at (300–1200 m) Quaternary sediments with no or chose to use the empirical relationship of Min et Tianjin that has not ruptured in the past 1000 little surface expression (Xu et al., 1996). For al. (1995) rather than the Bakun and Wentworth yr (Fig. 3). This gap can be projected onto the example, the active faults responsible for the (1997) model. The uncertainties of locating pre- seismically active section of the Sanhe-Laishui 1966 M 7.2 Xingtai and 1976 M 7.8 Tangshan instrumentation earthquakes in the North China fault, dominated by the A.D. 1679 M 8 Sanhe earthquakes were not known until after the earth- Basin are 20–100 km (Min et al., 1995) (see the earthquake rupture. The duration of the Tianjin quake disasters (e.g., Xu et al., 1996). Despite GSA Data Repository1). seismic gap may extend to ~4000 yr ago, based this challenge, north China is an ideal place to Nearly all of the M ≥ 6 earthquakes in the on the known written records of historical earth- examine spatiotemporal patterns of major his- past millennium occurred along the northeast- quakes in the region (Chen et al., 2004, 2010). torical earthquakes along slow-moving (<2–3 striking Sanhe-Laishui and Tangshan-Hejian- However, the large uncertainty (>100 km) in mm/yr) faults, because the region has more than Cixian faults in the northern North China Basin. locating ancient earthquakes and estimating 4000 yr of written records of preinstrumentation The Sanhe-Laishui fault in the mountainous their magnitudes prior to A.D. 1000 (Min et al., seismic events (Min et al., 1995). In this study regions has well-expressed morphology (Xu et 1995) makes the usefulness of this inference we show that a 160-km-long seismic gap has al., 2002), whereas the Tangshan-Hejian-Cixian questionable. This prompts us to examine the existed along the right-slip Tangshan-Hejian- fault is buried below Quaternary sediments (Xu paleo-earthquake activities in the Tianjin area Cixian fault zone (Fig. 1B) in the past 1000 yr et al., 1996), recognizable only through seismic- along the Tangshan-Hejian-Cixian fault zone. and possibly over the past 8400 yr. reflection profiling (e.g., Xu et al., 2002), exam- In Tianjin the northeast-striking North Tian- ining clustering of small earthquakes (e.g., Shen jin and South Tianjin faults are linked by the REGIONAL BACKGROUND et al., 2000), drill-core surveys (e.g., Chen et al., northwest-striking Haihe fault (Fig. 4A) (Chen Among estimated M ≥ 6 historical earth- 2004), and trenching (e.g., Guo et al., 2011). et al., 2010). The Haihe fault extends ~40 km quakes since 2300 B.C. across north China (Fig. Because GPS data show no detectable fault southeastward with left-slip kinematics (Chen 1A), those that occurred in the past 1000 yr are motion across the Tangshan-Hejian-Cixian fault et al., 2004). A drill-core study shows that the the best located (Fig. 1B) (Min et al., 1995). within the uncertainties of data (1–2 mm/yr) base of the youngest marine layer (MB1) in Estimating preinstrumentation earthquake mag- (Fig. 2), the current slip rate of the Tangshan- the region is nearly flat (~13± 2 m below the nitudes in this study is based on an empirical Hejian-Cixian fault must be slower than 1–2 surface), whereas the older marine marker beds relationship that converts the maximum seis- mm/yr. A broad east-trending left-slip shear (MB2, MB3, and MB4) have variable thick- mic intensity to seismic magnitude in the North nesses and basal-contact depths (Fig. 4B). This China Basin. The relationship was tested against 1GSA Data Repository item 2015023, historical observation has been used to suggest that the last instrumentally recorded events with a magnitude earthquake locations, and uncertainties of locating them major earthquake in Tianjin occurred between and estimating their magnitudes, is available online at uncertainty of ±0.5 (Min et al., 1995). Bakun www​.geosociety​.org​/pubs​/ft2015.htm, or on request deposition of MB1 and MB2, dated as 8415 ± 14 from [email protected] or Documents Secretary, 115 C yr B.P. and 36–39 ka (optically stimu- *E-mail: [email protected] GSA, P.O. Box 9140, Boulder, CO 80301, USA. lated luminescence ages), respectively (Chen et

GEOLOGY, January 2015; v. 43; no. 1; p. 19–22; Data Repository item 2015023 | doi:10.1130/G35986.1 | Published online 14 November 2014 ©GEOLOGY 2014 Geological | Volume Society 43 | ofNumber America. 1 For| www.gsapubs.org permission to copy, contact [email protected]. 19 al., 2004). This interpretation implies that the Tianjin seismic gap may not have ruptured for at Hetao rift zone least 8400 yr, assuming that the observed rela- A Sanhe-Laishui fault tionship applies to the entire section of the 160 Beijing km seismic gap. We note that the 1624 Luanxian earthquake 40°N (M 6.5) was followed by the 1976 Tang- Tianjin shan earthquake (M 7.8) ~50 km to the south, Zhang-Bo seismic zone whereas the 1830 Cixian earthquake (M 7.5) Tangshan- was followed by the 1966 Xingtai earthquake Heijian- 38°N (M 7.2) ~100 km to the north. These four earth- Cixian fault quakes are the largest seismic events along the Tangshan-Hejian-Cixian fault zone in the past 1976 M 7.8 400 yr and their progressive migration toward Tangshan EQ the Tianjin seismic gap may be interpreted in 1967 M 6.5 36°N two ways: (1) the pattern is accidental in a ran- Qinling fault zone Hejian EQ dom process (Swafford and Stein, 2007), and (2) the pattern was controlled by a deterministic stress-transfer mechanism generated by sequen- tial seismic events along the fault zone (Stein et 34°N al., 1997). 1966 M 7.2 Xingtai EQ

DISCUSSION AND CONCLUSIONS Tanlu fault zone The available data suggest that the 160 km 32°N Tianjin seismic gap may have not been rup- tured by M ≥ 6 earthquakes in more than 8400 110°E 114°E 118°E 122°E yr. Whether this apparently long-lasting seis- mic gap represents a seismic threat depends on our knowledge of the characteristic time of M 112°E 114°E 116°E 118°E 120°E the earthquake cycle on the Tangshan-Hejian- 4.0 Yan Shan 3.0 Cixian fault (Swafford and Stein, 2007). For 1 B 10 9 2.0 example, if the duration of the earthquake cycle 1.0 is much longer than the currently known dura- 40°N Beijing Tangshan 6 tion of the seismic gap, then our observation Bohai 8 23 would not be able to differentiate whether the SL fault 5 22 13 Bay 20 gap was already filled by rupture events before 7 Tianjin 21 our time constraints (i.e., prior to 8400 yr). 3 Hejian 24 Trenching of the Tangshan-Hejian-Cixian fault 2 (1) A.D. 1057 S. Beijing Earthquake (M 6.8) zone north of the Tianjin gap revealed that the 19 return times of major earthquakes were between (2) A.D. 1068 Hejian Earthquake I (M 6.5) 12 (3) A.D. 1144 Hejian Earthquake II (M 6.0) 38°N Tianjin Gap 6700 and 10,800 yr in the past 75,000 yr (Guo et Taihang (4) A.D. 1314 Shexian Earthquake (M 6.0) al., 2011). If the Tianjin section shares the same 15 (5) A.D. 1536 Tongxian Earthquake (M 6.0) 17 temporal evolution of major earthquakes, it (6) A.D. 1624 Luanxian Earthquake (M 7.0) Shan 14 16 (7) A.D. 1658 Laishui Earthquake (M 6.0) would imply that the seismic gap is either ~1700 THC fault (8) A.D. 1665 W. Tongxian Earthquake (M6.5) 4 18 yr overdue for a major earthquake, as suggested (9) A.D. 1679 Sanhe Earthquake (M 8.0) North China (10) A.D. 1730 W. Beijing Earthquake (M 6.5) by the shortest return time, or that the next major Basin (11) A.D. 1830 Cixian Earthquake (M 7.5) event will occur within ~2400 yr, as required by (12) A.D. 1882 Shenxian Earthquake (M 6.0) Cixian the longest return time. The magnitude of this (13) A.D. 1945 Luanhe Earthquake (M 6.3) (14) A.D. 1966-1 Xingtai Earthquake (M 6.8) potential earthquake is estimated to be ~M 7.5, 36°N 11 (15) A.D. 1966-2 Xingtai Earthquake (M 6.7) assuming a rupture length of 160 km, a rupture North China (16) A.D. 1966-3 Xingtai Earthquake (M 7.2) 10 (17) A.D. 1966-4 Xingtai Earthquake (M 6.2) depth of 20 km, a shear modulus of 3 × 10 Pa, Basin (18) A.D. 1966-5 Xingtai Earthquake (M 6.0) a slip rate of 1 mm/yr constrained by the GPS (19) A.D. 1967 Hejian Earthquake (M 6.5) data, and a slip accumulation period of 8000 yr. Earthquakes in written records. Size (20) A.D. 1976-1 Tangshan Earthquake (M 7.8) of circles represents uncertainty (21) A.D. 1976-2 Changli Earthquake (M 6.2) The accumulated seismic energy at the Instrumentally recorded events. Size (22) A.D. 1976-3 Luanxian Earthquake (M 7.4) Tianjin gap could alternatively be explained 050100 km of circles represents uncertainty (23) A.D. 1976-4 Ninghe Earthquake (M 6.9) by energy release via multiple smaller earth- (24) A.D. 1977 Tanggu Earthquake (M 6.2) quakes, aseismic creeping over a wide zone Figure 1. A: Preinstrumentation historical earthquakes (EQ) with M ≥ 6 across north China (i.e., outside the region investigated by drill- (after Min et al., 1995) and focal mechanisms of the A.D. 1966 Xingtai, 1967 Heijian, and 1976 core surveying shown in Figure 4), strain trans- Tangshan earthquakes (from Xu et al., 1996). B: M ≥ 6 earthquakes from A.D. 1000 to the pres- fer between adjacent faults (Liu et al., 2011), ent in the North China Basin against a background of microseismicities between 2009 and 2013. Preinstrumentation data are from Min et al. (1995); instrumentally located major earth- or much longer recurrence intervals than cur- quakes are from both the China Earthquake Administration and the U.S. Geological Survey. rent knowledge indicates. The strain-transfer THC—Tangshan-Hejian-Cixian fault; SL—Sanhe-Lushui fault. For earthquakes that occurred mechanism explains well the projection of the in the same year, they are labelled sequentially, such as 1966-1, 1966-2, 1976-1, and 1976-2.

20 www.gsapubs.org | Volume 43 | Number 1 | GEOLOGY 112oN 116oN SL Figure 2. A: Global positioning system ve- o 250 km B 40 N locities derived from 10 yr of campaign oc- ZB SL cupations of the Crustal Movement Obser- vation Network of China from 1999 to 2009. 500 km 0 10 mm/yr km (Data observed after that could have been affected by the 2011 Tohoku earthquake sequence and thus are not included.) The THC 250 km THC velocities are referenced to the stable Eur- asia plate, and the error ellipses represent 36oN the 70% confidence level. THC—Tangshan- Hejian-Cixian fault zone; SL—Sanhe-Lushui 0 km fault; TL—Tanlu fault. B: The eastward ve- QL TL locities increase southward, suggesting dis- A TL o 116 N tributed east-west–trending left-slip shear. This shear may be the cause for right-slip faulting along the northeast-striking faults in north China (Shen et al., 2000). QL—Qinling fault zone; ZB—Zhang-Bo fault zone. C: To avoid the effect of left-slip shear along the east-trending Zhang-Bo and Qinling zones, the fault-parallel and fault-perpendicular ve- locity components plotted are from the cen- tral region of the North China Basin (shown in box in A). The THC fault zone is located C approximately along the 0 km line in the box.

Sanhe-Laishui Fault 8.0 A.D. 1679 7.5 9 A.D. 1730 7.0 A.D. A.D. 1057 1658 A.D. 1665 1 117.10 oN 117.20 oN 6.5 A 8 7 A.D North Moment Magnitude 6.0 10 1536 Tianjin Fault 5 Ziya He A Haihe (NTF) 0 100 km 200 Km Fault (HF) Beijing 39.15oN HP1 39.15oN 024 km G2 THC Fault A.D. 1966-3 DG10 Tianjin Train 8.0 A.D. 1976-1 Station 11 Tianjin Gap 20 A.D. South 7.5 (160 km) 1976-2 G12 A.D. 1830 Tianjin A.D. 1068 22 Hai He 16 Fault 7.0 A.D. 1144 G16 A.D. 1966-2 39.10oN 39.10oN 2 3 A.D. 117.10 oN 117.20 oN A.D. 1967-1 15 23 6.5 1976-3 A.D. 14 1624 meter G16 G12 DC10 G2 HP1 Moment Magnitude 17 12 A.D. 6 6.0 A.D. 1966-4 1977 24 0 MB1 18 19 A.D. 1966-5 A.D. 1967 MB2 B 0 200 km 400 km 600 km 50 MB3 Cixian Hejian Tianjin Tangshan ? MB4 ? HF NTF Figure 3. A: Distribution of subsurface rupture length along 100 2 km B the Sanhe-Laishui fault, north China. Only the location un- certainties are considered in this plot as the A.D. 1679 Sanhe earthquake dominates this fault segment. Circled numbers cor- Figure 4. A: Simplified active fault map of the Tianjin area (north respond to those shown in Figure 1B. B: Distribution of maxi- China) modified from Chen et al. (2004). B: Simplified stratigraphic mum subsurface rupture length corresponding to maximum sections revealed by a series of drill cores (shown as black dots in- estimated earthquake magnitudes along the Tangshan-Hejian- side black circles; drill-core numbers are labeled in red) across the Cixian (THC) faults. Gray and red boxes associated with blue Tangshan-Hejian-Cixian fault zone in the Tianjin area. Data are from and red circled numbers, respectively, represent historical and Chen et al. (2004). instrumentally recorded seismic events, and circled numbers correspond to those shown in Figure 1B. For earthquakes that occurred in the same year, they are labelled sequentially, such as 1966-1, 1966-2, 1976-1, and 1976-2 (same as those labelled in Figure 1B). Regions with black horizontal lines indicate location uncertainties of historical earthquakes.

GEOLOGY | Volume 43 | Number 1 | www.gsapubs.org 21 Tianjin seismic gap onto the seismically active Seismology and Geology, v. 32, p. 138–149 Stein, R.S., Barka, A.A., and Dieterich, J.H., 1997, section of the Sanhe-Laishui fault in the past (in Chinese with English abstract). Progressive failure on the North Anatolian fault 1000 yr (Figs. 1B and 3), but validation of this Dubar, P.A., Lockridge, P.A., and Whiteside, L.S., since 1939 by earthquake stress triggering: Geo- 1992, Catalog of significant earthquakes 2150 physical Journal International, v. 128, p. 594– model requires further analysis of their geo- B.C.–1991 A.D. including quantitative casual- 604, doi:10.1111/j.1365-246X.1997​.tb05321.x. metric and kinematic links. ties and damage: Boulder, Colorado, National Stein, S., Geller, R.J., and Liu, M., 2012, Why earth- Geophysical Data Center Technical Report quake hazard maps often fail and what to do ACKNOWLEDGMENTS SE-49, 332 p. about it: Tectonophysics, v. 562, p. 1–25, Comments by Mian Liu, Seth Stein, and two anony- Guo, H., Jiang, W.L., and Xie, X.S., 2011, Late Qua- doi:10.1016/j.tecto.2012.06.047. mous reviewers greatly improved the early drafts of the ternary strong earthquakes on the seismogenic Swafford, L., and Stein, S., 2007, Limitations of the manuscript. We greatly appreciate the regional GPS fault of the 1976 Ms 7.8 Tangshan earthquake, short earthquake record for seismicity and seis- velocity data provided by Min Wang. Yin’s research Hebei, as revealed by drilling and trench- mic hazard studies, in Stein, S., and Mazzotti, on seismic hazards of north China was supported by ing: Science in China, v. 54, p. 1696–1715, S., eds., Continental intraplate earthquakes: the China University of Geosciences (Beijing) and the doi:10.1007/s11430-011-4218-x. Science, hazard, and policy issues: Geologi- SinoProbe Project administered by the Chinese Acad- Liu, M., Stein, S., and Wang, H., 2011, 2000 years cal Society of America Special Paper 425, emy of Geological Sciences. Yu’s work was supported of migrating earthquakes in north China: How p. 49–58, doi:10.1130/2007.2425(04). by China Scholarship Council grant 201206010118. earthquakes in midcontinents differ from those Wells, D.L., and Coppersmith, K.J., 1994, New at plate boundaries: Lithosphere, v. 3, p. 128– empirical relationships among magnitude, rup- 132, doi:10.1130/L129.1. ture length, rupture width, rupture area, and REFERENCES CITED Min, Z.Q., Wu, G., Jiang, Z.X., Liu, C.S., and Yang, surface displacement: Seismological Society Bakun, W.H., and Wentworth, C.M., 1997, Estimat- Y.L., 1995, Catalog of Chinese historic strong of America Bulletin, v. 84, p. 974–1002. ing earthquake location and magnitude from earthquakes from BC 2300 to AD 1911: Bei- Xu, J., Niu, L., Wang, C., and Han, Z., 1996, Tang- seismic intensity data: Seismological Society jing, Seismological Publishing House, 514 p. shan-Hejian-Cixian newly generated seismotec- of America Bulletin, v. 87, p. 1502–1521. Obermeier, S.F., Bleuer, N.R., Munson, C.A., Mun- tonic zone: Seismology and Geology, v. 18, Butler, R., Stewart, G.S., and Kanamori, H., 1979, The son, P.J., Martin, W.S., McWilliams, K.M., p. 193–198. July 27, 1976 Tangshan, China earthquake—A Tabaczynski, D.A., Odum, J.K., Rubin, M., Xu, X.W., Wu, W.M., Zhang, X.K., Ma, S.L., Ma, complex sequence of intraplate events: Seis- and Eggert, D.L., 1991, Evidence of strong W.T., Yu, G.H., Gu, M.L., and Jiang, W.L., mological Society of America Bulletin, v. 69, earthquake shaking in the lower Wabash Valley 2002, Active tectonics and seismicity in the p. 207–220. from prehistoric liquefaction features: Science, capital city of Beijing and the surrounding Chen, Y.K., Ren, F., Zhang, C.F., and Shao, Y.X., v. 251, p. 1061–1063, doi:10.1126​/science​.251​ regions: Beijing, Science Press, 379 p. 2004, Characteristics of late Quaternary activ- .4997.1061. ity of the Haihe buried fault in Tianjin munici- Shen, Z.K., Zhao, C., Yin, A., Li, Y., Jackson, D.D., pality: Seismology and Geology, v. 26, p. 111– Fang, P., and Dong, D., 2000, Contemporary Manuscript received 16 June 2014 121 (in Chinese with English abstract). crustal deformation in East Asia constrained by Revised manuscript received 6 October 2014 Chen, Y.K., Liu, F., Yuan, D., Li, W.D., Yang, X.Y., global positioning system measurements: Jour- Manuscript accepted 8 October 2014 and Gao, W.P., 2010, Seismic-risk quantita- nal of Geophysical Research, v. 105, p. 5721– tive evaluation on blind faults in Tianjin area: 5734, doi:10.1029/1999JB900391. Printed in USA

22 www.gsapubs.org | Volume 43 | Number 1 | GEOLOGY