Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Re-evaluating seismic hazard along the southern Longmen Shan, China: Insights from the 1970 Dayi and 2013 Lushan earthquakes Zhigang Li a,b,⁎ , Jing Liu-Zeng a , Rafael Almeida c , Judith Hubbard c , Chuang Sun b , Guixi Yi d a State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China b School of Earth Sciences and Engineering, Sun Yat-Sen University, Guangzhou 510275, China c Earth Observatory of Singapore, Nanyang Technological University, Nanyang 639798, Singapore d Sichuan Earthquake Administration, Chengdu 610041, China ARTICLE INFO Keywords: Longmen Shan Wenchuan earthquake Seismogenic structure Seismic moment Gutenberg-Richter law Seismic hazard ABSTRACT Competing hypotheses have been proposed to explain the seismic hazard (i.e. whether earthquakes with M ≥ 7 occur) of the southern Longmen Shan (LMS). This region did not rupture during the 2008 M w 7.9 Wenchuan earthquake, but later generated the 2013 M w 6.6 Lushan earthquake. Currently, the maximum possible earth- quake magnitude, its average recurrence interval, and the seismogenic structure of the southern LMS, remain poorly documented. This study aims to re-evaluate seismogenic structures and seismic hazard along the southern LMS. We first describe the sub-surface structural geometry, as well as the total slip and Quaternary activity of the Range Front blind thrust (RFBT), using high-resolution seismic reflection profiles, borehole data, and intensity- derived macroscopic epicenters. This thrust, which generated the 1970 M s 6.2 Dayi and 2013 M w 6.6 Lushan earthquakes, extends for > 250 km along the LMS range front. Integrating new evidence of active faulting and folding and previous quantitative horizontal shortening rate results, we estimate that the Quaternary slip rate of the RFBT is nearly 1 mm/yr, with a minimum total slip of 5 km since 8–5 Ma. Furthermore, we calculate the accumulation rate of seismic moment, 8.04 ( ± 2.09) × 10 17 N·m/yr, for the main active thrusts on the southern LMS, to compare with the moment release rate for earthquakes in the region. When we combine this with the Gutenberg–Richter distribution obtained from historical and instrumental catalogs, we estimate that the po- tential maximum moment magnitude of an earthquake in the southern LMS is 7.7. Finally, we conclude that the entire southern LMS is capable of generating much larger earthquakes (M w 7.3–7.7) than seen recently, with an average frequency of once every 1000–1400 years. Therefore, our findings confirm that there is potential for large earthquakes in the southern LMS, especially on the RFBT, which extends beneath the densely populated Chengdu Plain. 1. Introduction The overall tectonic architecture of the Longmen Shan (LMS; Fig. 1) is basically understood (summarized by Yin, 2010). However, due to incomplete historical records and limited previous studies, we still lack a detailed understanding of its seismotectonic setting, despite its im- portance for estimating the present-day seismic hazard posed by the LMS to densely populated areas within the Chengdu Plain (CDP; Fig. 1). The historical seismicity of the LMS is documented in the Chinese earthquake catalog. This catalog contains earthquakes of M ≥ 6.0 that occurred in the pre-instrumental period since 2300 BCE for which there are written records (likely some are missing; Division of Earthquake Monitoring and Prediction, C.S.B, 1995) and instrumentally recorded earthquakes of M s ≥ 4.7 between 1912 and 1990 (Division of Earthquake Monitoring and Prediction, C.S.B, 1999). Earthquakes from this catalog with M s ≤ 5.7 that occurred between 1970 and 2015 have been relocated using a double difference method similar to that de- scribed by Chen et al. (2013) to obtain more accurate epicentral loca- tions. Catalogs of historical seismicity show that between the 14th century and 1970, the LMS has experienced five reverse- and oblique- slip earthquakes of magnitude M ≥ 6: the 1327 M > 6 Tianquan earthquake, the 1657 M 6.5 Wenchuan earthquake, the 1941 M 6.2 Kangting earthquake, the 1958 M 6.2 Chaping earthquake, and the 1970 M 6.2 Dayi earthquake (Division of Earthquake Monitoring and Prediction, C.S.B, 1995, 1999). There is no historical record of any earthquake larger than M = 7 in the LMS in the last 500 years (Liu- Zeng et al., 2009; Wang et al., 2011; Chen and Hsu, 2013). Prior to 2008, the lack of large-magnitude historical earthquakes, combined http://dx.doi.org/10.1016/j.tecto.2017.09.001 Received 31 March 2017; Received in revised form 30 August 2017; Accepted 1 September 2017 ⁎ Corresponding author at: School of Earth Sciences and Engineering, Sun Yat-Sen University, No. 135, Xingang Xi Road, Guangzhou, 510275, China. E-mail address: lizhigang@mail.sysu.edu.cn (Z. Li). Tectonophysics 717 (2017) 519–530 Available online 05 September 2017 0040-1951/ © 2017 Elsevier B.V. All rights reserved. MARK