RESEARCH Segmentation and Termination of the Surface Rupture Zone Produced by the 1932 Ms 7.6 Changma Earthquake

RESEARCH

Segmentation and termination of the surface rupture zone produced by the 1932 Ms 7.6 Changma earthquake: New insights into the slip partitioning of the eastern Altyn Tagh fault system

Jiaxin Du1,2,†, Bihong Fu1,*,†, Qiang Guo1,†, Pilong Shi1,†, Guoliang Xue1,†, and Huan Xu1,† 1CAS KEY LAB OF DIGITAL EARTH SCIENCE, AEROSPACE INFORMATION RESEARCH INSTITUTE, CHINESE ACADEMY OF SCIENCES, BEIJING 100094, CHINA 2UNIVERSITY OF CHINESE ACADEMY OF SCIENCES, BEIJING 100049, CHINA

ABSTRACT

The 1932 Ms 7.6 earthquake struck the active Changma fault in the NE Tibetan Plateau, and produced a distinct surface rupture along the fault zone. However, the segmentation and termination of the surface rupture zone are still unclear. In this paper, the active tectonic analyses of multiple satellite images complemented by field investigations present the 120-km-long surface rupture zone, which can be divided into five discrete first-order segments, ranging from 14.4 to 39.56 km in length, linked by step-overs. Our results also indicate that the 1932 rupture zone could jump across step-overs 0.3–4.5 km long and 2.2–5.4 km wide in map view, but was terminated by a 6.3-km-wide restraining step-over at the eastern end. The left-lateral slip rates along the mid-eastern and easternmost segments of the Changma fault are 3.43 ± 0.5 mm/yr and 4.49 ± 0.5 mm/yr since 7–9 ka, respectively. The proposed tectonic models suggest that the slip rates on the Changma fault are similar to the slip rate on the eastern segment of the Altyn Tagh fault system near the junction point with the Changma fault. These results imply that the Changma fault plays a leading role in the slip partitioning of the easternmost segment of the Altyn Tagh fault system.

LITHOSPHERE; v. 12; no. 1; p. 19–39 | Published online 12 December 2019 https://doi .org /10 .1130 /L1113 .1

INTRODUCTION 2013; Cheng et al., 2015) (Fig. 1). The 1932 found the extensional tracks, coseismic scarps, Ms 7.6 Changma earthquake produced a N70°W and bulges developed within the surface rup- The Cenozoic tectonic deformation result- striking coseismic surface rupture zone along ture zone (Hou et al., 1986; Lanzhou Institute ing from continuous India–Asia collision has the Changma fault (CMF) (Hou et al., 1986; of Seismology, National Bureau of Seismol- built the remarkable topography in the Tibetan Peltzer et al., 1988) (Figs. 1 and 2). Numerous ogy, 1992). The 14C dating age of upper and Plateau (Molnar and Tapponnier, 1975; Harri- publications have documented the surface rup- lower terraces, estimated to be 12,000–15,000 son et al., 1992; Clark and Royden, 2000; Yin ture zone with complex left-lateral en-echelon yr B.P. and 7000–9000 yr B.P., together with the and Harrison, 2000; Tapponnier et al., 2001). patterns, showing the channels, gullies, and streams of 20–40 m left-lateral offsets, yielded The Altyn Tagh fault (ATF) system and the Qil- scarps of 2.1–3.3 m up to 5.5 m coseismic off- an average Holocene left-lateral slip rate of ian Shan fault (QLSF) belt are two major fault sets along the CMF (Hou et al., 1986; Kang, 3.3–4.3 mm/r along strike of the CMF (Lan- zones associated with the crustal thickening and 1986; Peltzer et al., 1988; Luo et al., 2013; Lan- zhou Institute of Seismology, National Bureau shortening in the NE Tibetan Plateau (Meyer et zhou Institute of Seismology, National Bureau of of Seismology, 1992). Other studies proposed al., 1998; Yin et al., 2002; Cowgill et al., 2003; Seismology, 1992). However, the segmentation, that the surface rupture zone was composed of Royden et al., 2008; Yin, 2010). The NNW to propagation, and termination of the coseismic four reverse S-shaped segments, based on the NEE–trending CMF (between 39°50′N, 96°33′E surface rupture along the CMF remain unclear, geometric features and structural deformations and 39°31′N, 97°46′E) is one of the major active limiting a better understanding of the role the along the CMF (Zheng, 2009; Luo et al., 2013). left-lateral strike-slip faults linking the ATF sys- CMF plays in the tectonic transformation in the Their results indicated that the left-lateral slip tem in the west and the QLSF belt in the east NE Tibetan Plateau. rates of beheaded stream channels and thrust (Peltzer et al., 1988; Zheng, 2009; Zheng et al., On the basis of the spatial distribution rates of fault scarps were 1.17 ± 0.07 mm/yr and and continuities, a previous study carried out 0.14 ± 0.02 mm/yr, respectively, on the aban- by the Lanzhou Institute of Seismology, SSB don alluvial fan along the western CMF (Zheng, *Corresponding author. (1992) divided the CMF surface rupture zone 2009; Zheng et al., 2013). The left-lateral slip †Emails: Du: [email protected]; Fu: [email protected]; Guo: [email protected]; Shi: [email protected]; Xue: into three discrete segments, each extend- rates of offset stream channels increased gradu- [email protected]; Xu: [email protected] ing 40–50 km in length. Their field work also ally from 1.33 ± 0.39 mm/yr to 3.68 ± 0.41 mm/

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/12/1/19/4952161/19.pdf by guest on 25 September 2021 JIAXIN DU ET AL. | New insights into the slip partitioning of the eastern Altyn Tagh fault system RESEARCH

90°E 95°E 100°E N

Dec. 14, 2002 Fig.2 Yumen 40°N Dunhuang Ms 5.9 Dec. 25, 1932 Subei Hexi ATF Ms 7.6 NQFB Feb. 11, 1954 Ms 7.3 CMF Zhangye Corridor

Aug. 28, 2009 Apr. 17, 2003Hala Lake Ms 6.2 Qaidam Ms 6.4 May. 4, 2004 HYF Basin Nov. 10, 2008 Ms 5.4 Ms 6.3 May. 21, 1962 Qinghai Lake Xining Nov. 14, 2001 Golmud Ms 6.8 Apr. 19, 1963 Mw 7.8 Ms 7 Jan. 7, 1932 50°N Ms 7.5 EKF 40°N 35°N Huashixia Tibetan Maqin 30°N Legend EQ Mag. Plateau Luqu 5<=M<6 NormalNormal fault fault India 20°N Apr. 13, 2010 Reverse faultfault or or 6<=M<7 thrust faultfault Ms 6.9 Mar. 17, 1947 0 200 km 10°N Strike-slip fault fault 7<=M Ms 7.7 80°N 90°N 100°N 0 500km

Figure 1. Topographic map based on the Shuttle Radar Topography Mission (SRTM) data showing the active faults and location of the Changma Fault in the NE Tibetan Plateau. ATF—Altyn Tagh Fault; CMF—Changma Fault; EKF—East Kunlun Fault; HYF—Haiyuan Fault; NQFB—North Qilian Fault Belt. Major active faults are adopted from Meyer et al. (1998) and Yin et al. (2008a). Moment magnitudes of earthquake events were derived from National Centers for Environmental Information (NCEI) and He et al. (2004); Taylor and Yin (2009).

yr from west to east, implying that the structural Oglesby, 2006; Wesnousky, 2006; Elliott et al., in the northeastern Tibetan Plateau (Tappon- deformations along the CMF have absorbed the 2009). In order to study the segmentation and nier and Molnar, 1977; Peltzer and Tapponnier, slip of the ATF system (Luo et al., 2013). termination of the surface rupture zone, more 1988) (Figs. 1 and 2A). The NWW-trending The previously mentioned studies focused detailed analyses of discontinuities developed fault propagated through numerous streams on the geologic and geomorphic features of within the surface rupture zone are needed. and rivers, such as the Shule, Daheigou, Anmen, the surface rupture zone. But the discontinui- These results can provide significant implica- Shiyou, Ya’er, and Xishuixia rivers, from west ties developed along the surface rupture zone tions for the role the CMF plays in the tectonic to east (Fig. 2A). The Quaternary alluvial fans, are important for understanding the segmen- transition of the ATF system. stream channels, and ridges appear to have dis- tation of the surface rupture zone (Segall and In this paper, we first interpret the segmenta- placements varying from 3 to 400 m (Peltzer Pollard, 1980; DePolo et al., 1991; Zhang et tion and geometric and geomorphic features of et al., 1988; Lanzhou Institute of Seismology, al., 1991, 1999; Fu et al., 2005). These discon- the CMF rupture zone in detail based on high- National Bureau of Seismology, 1992) (Fig. 2B). tinuities are mainly characterized by complex resolution satellite images and field observations. The structural deformation of warping rivers, step-overs and bends with great impacts on Then, CMF slip rates will be estimated using age gullies, and surface ruptures as well as bulges the initiation, propagation, and termination of dating data and slip displacements. Finally, we and scarps correspond well to long-term hori- coseismic ruptures (Barka and Kadinsky-Cade, explore the reasons for the termination of the zontal and vertical motion on the CMF since 1988; Wesnousky, 1988; Harris and Day, 1993; 1932 Changma co-seimic surface rupture zone, the late Quaternary (Lanzhou Institute of Seis- Zhang et al., 1999; Duan and Oglesby, 2005, and propose a new tectonic model to explain mology, National Bureau of Seismology, 1992). 2006; Lozos et al., 2011; Elliott et al., 2018). the role the CMF played in the slip partitioning Moreover, the recurrence interval for large earth- Numerical geological models agree with the of the ATF system. quakes with magnitude 7–7.5 along the CMF field observations that large earthquakes could was roughly estimated to be 1000–2620 years easily propagate through step-overs with widths GEOLOGICAL SETTING during the Holocene (Hou et al., 1986; Kang, of <4 km, but could be arrested by those ones 1986; Peltzer et al., 1988; Luo et al., 2016). with widths of >5 km (Crone and Haller, 1991; The left-lateral strike-slip CMF with a south- In the western end of the CMF, the 1600 Zhang et al., 1991; Lettis et al., 2002; Duan and westward dip of thrust faulting was observed km-long ATF system started left-lateral motion

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 20

96°40'E 97°0'E 97°20'E 97°40'E A !Changma N ! Lujiawan

Dec. 25, 1932 Dec. 14, 2002 Ms 7.6 Ms 5.9 1 Daheigou ! River Chouliugou Anm en River 2 Choushuiliugou 39°40'N ! ! Shule River ! Sangequan 3 Shiyou River Moshiju 4 Baiyang River EQ Mag. Honggou ! Ya’e r River 5<=M<6 Xishuixia 0 10km 6<=M 5

96°40'E 97°0'E 97°20'E 97°40'E B ! Changma N ! Lujiawan LJW-CLG Segment

Shule River Shule RiverDHGR Segment 1 Daheigou SGQ-MSJ Segment ! River CSLG-SYR Segment An men Chouliugou 2

River 39°40'N ! River ! Choushuiliugou ! Fig.3 3 Sangequan Moshiju 4 Fig.10 Shiyou BaiyangBaiyang River SYR-XSX Segment Fig.4 Fig.6 Honggou 0 10km ! Ya’e r River Fig.8 Xishuixia 5

Quaternary Jurassic Devonian Presinian E E E D D D E E E D D D Gabbro River alluvium conglomerate sandstone griotte Granite

B B B B __ _ _ _ ( ( ( ( ( Triassic Quaternary Silurian B B B B ( ( ( Aplitic dyke _ sandstone sandstone Plagiogranite _ Diorite Thrust fault diluvium B B B B ______

! ! ! ! ! ! ! ! Tertiary Permian Ordovician ! ! ! ! ! ! ! Olivinite K K K K Alum iron Belt Strike-slip fault ! ! ! ! ! ! ! ! sandstone glutenite limestone K K K K Cretaceous Carboniferous Cambrian Quartzite Ultra-basic rocks Surface Rupture sand-mudstone shale limestone

Figure 2. (A) First-order segmentation of surface rupture zone related to the 1932 Ms7.6 earthquake along the CMF between 96°33′ and 97°46′E as shown in Landsat TM mosaic image. The active faults shown on this map were modified from Hetzel et al. (2004) and Yin et al. (2008a). (B) Spatial distribution of surface rupture zone along the CMF (geological information partially modified from geological map of Gansu Bureau of Geological and Mineral Resources, 1969, 1972). LJW-CLG segment—Lujiawan-Chouliugou segment; DHGR segment—Daheigou River segment; SGQ-MSJ segment—Sangequan-Moshiju segment; CSLG-SYR segment—Choushuiliugou-Shiyou River segment; SYR-XSX segment—Shiyou River-Xishuixia segment. The 1932 Changma earthquake and 2002 Yumen earthquake events shown on the map were obtained from National Centers for Environmental Information (NCEI).

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 21

during early Paleocene to Middle Eocene observed to correlate well with surface faults in out at Beta Analytic Radiocarbon Dating Labo- (50–49 Ma) (Yin et al., 2002, 2008a). A total the NE Tibetan Plateau (Taylor and Yin, 2009). ratory, United States. The OSL testing works left-lateral displacement of ~470 km occurred Several large earthquakes occurred during and for quartz samples were completed at the OSL on its western segment (Cowgill et al., 2003), after the 20th century on these active faults, Research Laboratory of Geology and Geophys- dropping to ~280 km toward the east (Yin and including the 1932 Ms 7.6 Changma earth- ics, Chinese Academy of Science. The age

Harrison, 2000). The slip rate on the eastern quake, the 1954 Ms 7¼ Shandan earthquake dating data from the lower terraces T1 deter- segment of ATF system (between 84° to 97°E) (Tapponnier and Molnar, 1977; Deng, 1984), mined the youngest age of the offset (Cowgill, is highly debated. Some studies constrained and the 2002 Ms 5.9 Yumen earthquake (He et 2007). Combined with the estimates of dis- an average slip rate of 17.8–26.9 mm/yr by al., 2004) (Fig. 1). placements, the maximum Quaternary slip using geomorphic features of offsets and 14C rates of the CMF were yielded (Cowgill, 2007). dating of organic material from individual DATA AND METHODS The results of OSL data and 14C dating data cobbles (Mériaux et al., 2004, 2005). These are represented in Tables 1 and 2, respectively. estimates were higher than other slip rates of In this study, multiple sources of satellite 10–12 mm/yr yielded by both geological and remote sensing data obtained by the Landsat RESULTS geodetic methods (Bendick et al., 2000; Wal- Thematic Mapper/Enhanced Thematic Map- lace et al., 2004; Cowgill, 2007; Zhang et al., per (TM/ETM+), Satellite pour l’observation The interpretation of satellite images 2007; Elliott et al., 2008; Gold et al., 2011). de la terre (SPOT), Worldview, Quickbird as showed a 120-km-long surface rupture zone Since the slip rates of secular variations cannot well as Geoeye, were used to interpret remark- along strike of the CMF from Lujiawan be determined by transient processes related to able geometric and geomorphic features of the (39°51′35″N, 96°33′10″E) to Xishuixia the earthquake cycle, it is more appropriate to surface rupture zone along the CMF. The spatial (39°31′9″N, 97°46′14″E) (Fig. 2A). The 1932 obtain short-term slip rates using reconstruc- resolution of these images ranges from 0.5 m to earthquake broke it into five reverse S-shaped tion of lower and upper terraces (Cowgill, 2007; 30 m. In addition, the Digital Elevation Model first-order segments, according to the geo- Gold et al., 2009; Hetzel, 2013). Toward the (DEM) obtained from the Shuttle Radar Topog- metric features of discontinuities (Fig. 2B). east, the slip rate of the ATF system decreased raphy Mission, the Global DEM generated from From west to east, these include the Lujiawan- down to 2 mm/yr near 97°E (Xu et al., 2005; Advanced Spaceborne Thermal Emission and Chouliugou (LJW-CLG), Daheigou River Cowgill, 2007; Zhang et al., 2007; Gold et al., Reflection Radiometer (ASTER GDEM), and (DHGR), Sangequan-Moshiju (SGQ-MSJ), 2011). The unsolved problem is whether slip the DEM data obtained from the unmanned Choushuiliugou-Shiyou River (CSLG-SYR) on the ATF system is mainly transferred into aerial vehicle (UAV) have spatial resolutions and Shiyou River-Xishuixia (SYR-XSX) seg- crustal shortening in the QLSF belt (Burchfiel of 90 m, 30 m and 4 cm, respectively, which ments, respectively, as shown in Figure 2B. et al., 1989; Yin and Harrison, 2000; Yin et enable us to precisely document the displace- These 14.4–39.6-km-long first-order segments al., 2002), or whether some of the deformation ments of terraces riser, channels, and streams are separated from one another by 0.3–4.5-km- is primarily absorbed by strike-slip faulting along the fault trace. long and 2.2–5.4-km-wide step-overs. Each accommodated with crustal eastward extru- Based on the geologic and geomorphic first-order segment can be further divided sion (Xu et al., 2005). analyses of these multiple remote sensing into second-order segments of 2.5–18.8 km in The QLSF belt, located in the eastern portion data complemented by a geologic map with length, linked by step-overs or bends of less of the ATF system, extends ~600-km long and a scale of 1:200,000 (Gansu Bureau of Geol- than 2 km in width (Figs. 3 and 4). 350-km wide (Burchfiel et al., 1989; Yin and ogy and Mineral Resources, 1965–1979), we Harrison, 2000; Cowgill et al., 2004; Hetzel et mapped the geometric and kinematic features Segmentation of CMF Surface Rupture al., 2004; Zuza et al., 2018). Intracontinental of the surface rupture zone in different scales. Zone orogenesis and active structures in the QLSF Particularly, we documented the step-overs belt initiated after the early Cenozoic (Yin and with different sizes along the rupture zone in Lujiawan-Chouliugou Segment Harrison, 2000; Zuza et al., 2018). Approxi- detail. In order to estimate the age of these The LJW-CLG segment (between 96°33′ and mately 200 km of NS-trending shortening displaced geomorphic surfaces, fourteen 14C 96°54′E), the westernmost part of the surface occurred across the QLSF belt associated with dating samples and five Optically Stimulated rupture zone, extends ~39.56 km as shown in crustal shortening of the NE Tibetan Plateau Luminescence (OSL) samples were collected Figure 3A. It can be further divided into three

(Zhang et al., 2007; Zuza et al., 2018). Most from clay and loess of lower terraces T1. The second-order segments, from west to east, each seismic events of magnitudes larger than 5 were 14C dating of the charcoal samples was carried 10.2–16.2 km long with strike of N30°-70°W

TABLE 1. OPTICALLY STIMULATED LUMINESCENCE (OSL) DATING RESULTS OF LOESS SAMPLES COLLECTED ALONG THE CHANGMA FAULT Sample Latitude Longitude Locality Depth* Material† U Th K Water content Cosmic ray Dose rate De Optical age number (°) (°) (m) dated (ppm) (ppm) (%) (%) (Gy/ka) (Gy/ka) (Gy) (ka) SGQ01W 39.6389 97.3278 Choushuiliugou 0.7 Quartz 2.38 10.4 1.77 13 0.31 3.00 ± 0.15 28.19 ± 2.75 9.4 ± 1.0 SGQ02W 39.6389 97.3278 Choushuiliugou 0.2 Quartz 2.11 10.9 1.94 17 0.31 3.01 ± 0.16 21.21 ± 3.08 7.0 ± 1.1 SGQ03E 39.6389 97.3278 Choushuiliugou 0.9 Quartz 2.62 10.7 2.02 16 0.31 3.19 ± 0.17 29.40 ± 3.51 9.2 ± 1.2 XSX04E 39.5141 97.7345 Xishuixia 1.8 Quartz 2.51 11.5 2.22 12 0.32 3.53 ± 0.18 26.89 ± 1.44 7.6 ± 0.6 XSX05E 39.5141 97.7345 Xishuixia 1.1 Quartz 2.27 10.6 2.09 19 0.32 3.10 ± 0.17 19.20 ± 1.68 6.2 ± 0.6 *Depth below the surface where the samples were collected. †Testing for quartz samples using Single-aliquot Regenerative-dose Protocol was performed at the OSL Research Laboratory of Geology and Geophysics, Chinese Academy of Science.

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 22

TABLE 2. 14C DATING RESULTS ALONG THE CHANGMA FAULT Sample Laboratory Latitude Longitude Locality Depth* Material Variables: Radiocarbon Calendar age§ (cal yr BP) number number (°) (°) (m) dated 13C/12C (‰) age† (2σ) (95%) C1E Beta-448132 39.5141 97.7345 Xishuixia 1.5 Charcoal -22.6 6140 ± 30 7160–6945 C2W Beta-448137 39.5141 97.7345 Xishuixia 2.1 Charcoal -24.7 2560 ± 30 2750–2705 C3W Beta-448138 39.5141 97.7345 Xishuixia 1.86 Charcoal -24.2 2390 ± 30 2490–2345 C4W Beta-448139 39.5141 97.7345 Xishuixia 1.42 Charcoal -21.3 2030 ± 30 2055–1920 C5E Beta-448133 39.5141 97.7345 Xishuixia 1.9 Charcoal -21.8 2870 ± 30 3070–2920 C6W Beta-448140 39.5141 97.7345 Xishuixia 1.98 Charcoal -24.2 3000 ± 30 3320–3305 C7W Beta-448141 39.5141 97.7345 Xishuixia 3 Charcoal -26.2 5700 ± 30 6555–6410 C9E Beta-448135 39.5141 97.7345 Xishuixia 0.5 Charcoal -22.4 2970 ± 30 3215–3060 C10E Beta-448136 39.5141 97.7345 Xishuixia 0.7 Charcoal -21 2800 ± 30 2965–2845 XXXC2A Beta-448130 39.5141 97.7345 Xishuixia 1.5 Charcoal -22.7 6050 ± 30 6975–6830 XXXC4A Beta-448131 39.5141 97.7345 Xishuixia 0.7 Charcoal -24.2 1200 ± 30 1230–1210 SGQC1E Beta-448142 39.6389 97.3278 Choushuiliugou 0.5 Charcoal -23.4 6610 ± 30 7570–7435 SGQC3E Beta-448143 39.6389 97.3278 Choushuiliugou 0.5 Charcoal -23.1 2690 ± 30 2850–2750 HYZC4N Beta-448144 39.6389 97.3278 Choushuiliugou 0.7 Charcoal -24.8 6720 ± 30 7615–7565 *Depth below the surface where the samples were collected. †Accelerator mass spectrometry measurement was completed by Beta Analytic Radiocarbon Dating Laboratory, USA. §Calendar ages were calibrated at the 2σ confidence level using IntCal13 and Marine13 radiocarbon age calibration curves 0–50,000 years cal BP (Reimer et al., 2013).

(Fig. 3B). At the western part of the LJW-CLG Sangequan-Moshiju Segment field photo in Fig. 8A). East of the Shiyou River, segment, numerous offset stream channels were To the east of Daheigou River, the 14.4 km- a 2.3 ± 0.1–km-long and 5.4 ± 0.1–km-wide found around the Xiaokouzi site (Fig. 3). To the long SGQ-MSJ segment (between 97°8′ and right-stepping step-over is found between the eastern part of the LJW-CLG segment, the left- 97°13′E) is composed of three second-order CSLG-SYR and SYR-XSX segments (Fig. lateral offset of a small gully was measured to be segments, each 2.7–6.1 km long as shown in 2; Table 3). 6 ± 0.4 m at Chouliugou (see field photo in Fig. Figure 6. In the western part of the SGQ-MSJ 3A). Eastward to the Shule River, the Quickbird segment, the Quickbird images clearly show that Shiyou River-Xishuixia Segment image shows that the LJW-CLG and DHGR seg- the discrete ruptures are linked by small bends Continuously eastward to the Shiyou River, ments are linked by a 4.5 ± 0.1 km-long and with widths of 100–300 m (Figs. 7A and 7B). the 34.9-km-long SYR-XSX segment (between 3.4 ± 0.1 km-wide left-stepping step-over (Fig. The Quickbird image and our measurements 97°25′ and 97°46′E) can be further divided into 2; Table 3). indicate that the gullies were left-laterally dis- four second-order segments, varying from 6 to placed by 15 m across the rupture zone (Figs. 7A 11.5 km long (Fig. 10A). Detailed interpreta- Daheigou River Segment and 7C, see field photo in Fig. 7A). Surface tion of the SPOT6 image shows that hundreds Located northeast of Shule River, the ruptures were observed along the fault trace (see of meters–wide step-overs developed at the N45°-80°W-striking DHGR segment (between field photo in Fig. 7B). In the central part of boundaries among the second-order segments 96°58′ and 97°7′E) runs ~17.1 km long (Fig. the SGQ-MSJ segment, a series of left-stepping from Ya’er to Baiyang rivers (Fig. 10B). To the 4A). The rupture zone can be further divided step-overs were found among the second-order easternmost portion of the SYR-XSX segment, into three discontinuous second-order segments segments (Fig. 6B). Toward the easternmost a gully across the rupture zone was left-later- ranging from 2.4 to 8.6 km long (Fig. 4B). In portion of the SGQ-MSJ segment, detailed ally displaced 6.2 ± 0.5 m, as measured in the the western part of the DHGR segment, the interpretation and field mapping show that the field (see location of field photo in Fig. 10A). Quickbird images show that a series of left- rupture was separated from another segment by Both our interpretation of the satellite images stepping en-echelon fissures striking N70°W a 0.81 ± 0.1–km-long and 2.5 ± 0.1–km-wide and field observations showed the coseismic are linked by small step-overs or bends (Figs. left-stepping step-over around the Anmen River left-stepping surface ruptures along the east- 4B and 5A). In the central part of the DHGR (Fig. 2; Table 3). ern segment of the CMF (see field photo in Fig. segment, a 18-m-long and 462-m-wide right- 10A). The geomorphic analyses of high-reso- stepping step-over developed between two Choushuiliugou-Shiyou River Segment lution images obtained by the UAV show that

distinctive second-order segments (1 and 2), as East of the Anmen River, the 15.6-km- terraces riser T1 in front of the ridges match well indicated in the satellite images (Figs. 4 and long CSLG-SYR segment (between 97°17′E after restoring a 35 ± 2.6 m offset (Figs. 11A– 5B). Near the Xiaoheigou site, the left-laterally and 97°25′E) consists of three second-order 11C). The loess and clay samples of terraces 14 displaced gully has an offset of 9 ± 0.6 m across segments (Fig. 8). Our interpretation of the high- T1 were collected for OSL and C age dating the rupture (see location of field photo in Fig. resolution Geoeye image shows that the terraces (Tables 1 and 2; Figs. 11D–11G, see location of

4A). In the easternmost portion of the DHGR riser T1 has a left-lateral offset of 31 ± 2.3 m samples collected in Fig. 11A). The 6–28 m left- segment, the surface rupture zone is arranged on the western part of the CSLG-SYR segment lateral displacements of gullies along the CMF in a left-stepping en-echelon pattern as shown (Fig. 9). The OSL and 14C age dating samples were measured from DEM obtained by UAV

on the Quickbird image (Fig. 5C). Eastward were collected at the terraces T1 (Tables 1 and (Figs. 12 and 13). In the easternmost part of the to Daheigou River, a 0.32 ± 0.1 km-long and 2; see location of samples collected in Fig. 9). SYR-XSX segment, a large right-stepping step- 2.2 ± 0.1 km-wide right-stepping step-over has Eastward, the ruptures appear as left-stepping over with a length of 3.5 ± 0.1 km and a width developed between the DHGR and SGQ-MSJ en-echelon arrangements at the boundaries of 6.3 ± 0.1 km arrested the surface rupture near segments (Fig. 2; Table 3). among the second-order segments (Fig. 8, see Xishuixia River (97°46′E) (Fig. 2; Table 3).

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 23

96°40'0"E 96°50'0"E A N

( Lujiawan 39°50'0"N

( Xiaokouzi

Fig.12A Chelugou ( 0 5 km (

( Figure 3. (A) Spatial distribu- Chouliugou tion of the surface rupture zone along the LJW-CLG segment mapped from SPOT6 mosaic image. The location of field photo in Figure 12A is shown. 96°40'0"E 96°50'0"E B (B) Image interpretation of active tectonic map displaying d3 d1 a1 N the geometry of second-order a2 segmentations along the LJW- a1 River CLG segment. ( LJW-CLG SegSegment Xiaochangma 1 Lujiawan a2 d2 39°50'0"N a1 d3 d3 d2 d2 d2 d2 d2 d2 d3 d2 2 d2

Quaternary d2 a2 d2 alluviumⅡ a2 Quaternary a1 a1 alluviumⅠ Xiaokouzi ( ( ( ( d3 ( ( Quaternary d2 ( d3( ( diluviumⅢ d3 d3 d2 d2 ( ( ( ( ( Quaternary ( d2( ( diluviumⅡ d2 d3

( ( ( ( ( Quaternary ( ( ( d2 d1 diluviumⅠ d3 Cretaceous Chelugou d3 d3 ( d2 sand-mudstone 0 5 km Permian 3 glutenite 3520 d2 Carboniferous shale Ordovician River ( limestone Thrust fault Chouliugou Cambrian Stream channel Strike-slip fault limestone Boundary of first and Ultra-basic rocks Surface Rupture second-order segment

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 24

A 97°0'0"E N

Fig.5A

Fig.5B Toudaogou (

Erdaogou ( Fig.12B Fig.5C ( 39°40'0"N ( Xiaoheigou 0 2 km

Figure 4. (A) Spatial distribution of the surface rupture zone along the DHGR segment interpreted from SPOT6 mosaic image. The location of field photo in Fig- ure 12B is shown. (B) Image interpretation of active tectonic map showing the geom- Bd2 97°0'0"E etry of second-order segmentations along d3 N the DHGR segment. d2 d2 d2 d1 DHGR Segment d2 d1 d3 Daheigou River d1

d2 Toudaogou d3 ( d2 2717 1 d2 d2 d2 d2 d3 Erdaogou ( d3 d3 d3 2 d2

( ( ( ( ( Quaternary ( d3( ( Ⅲ diluvium d2 ( ( ( ( ( Quaternary ( d2( ( Ⅱ 39°40'0"N diluvium ( 3

( ( ( ( ( Quaternary ( d1( ( diluviumⅠ Xiaoheigou d1 Ultra-basic rocks ! ! ! ! ! ! ! ! Triassic ! ! ! ! ! ! ! E E E ! ! ! ! ! ! ! ! sandstone E E E Granite Cretaceous Thrust fault sand-mudstone 0 2 km Permian Strike-slip fault River glutenite Surface rupture Ordovician Boundary of first and limestone Stream channel second-order segment

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 25

TABLE 3. STEP-OVERS ALONG THE CHANGMA FAULT B.P. (Figs. 9E and 9F). We used these results Step-over name Latitude Longitude Width Error Length Error Type together with the 27 ± 2.3 m offset to estimate (°) (°) (km) (km) (km) (km) the left-lateral slip rate as 2.87 ± 0.4 mm/yr, Shule River step-over 39.7054 96.9392 3.4 0.3 4.5 0.3 Releasing step-over 3.86 ± 0.7 mm/yr, and 3.56 ± 0.3 mm/yr, for Daheigou River step-over 39.6452 97.1283 2.2 0.2 0.32 0.02 Restraining step-over samples SGQ01W, SGQ02W, and HYZC4N, Anmen River step-over 39.6315 97.2842 2.5 0.2 0.81 0.1 Releasing step-over respectively (Fig. 9G). Hence, on the CSLG- Shiyou River step-over 39.5573 97.4326 5.4 0.4 2.3 0.2 Restraining step-over SYR segment, the average left-lateral slip rate Xishuixia River step-over 39.4866 97.7672 6.3 0.5 3.5 0.3 Restraining step-over of lower terrace riser T1 was calculated as 3.43 ± 0.5 mm/yr, which may be the maximum slip rate of the offset (Cowgill, 2007). This slip rate Late Quaternary Slip Rate of CMF (Luo et al., 2013; Lanzhou Institute of Seismol- is slightly smaller than the 3.68 ± 0.41 mm/yr ogy, National Bureau of Seismology, 1992), the result, which was estimated by using the 16 ± 1

In this study, the maximum Quaternary slip long-term displacements should be 27 ± 2.3 m m offset lower terrace riser T1 and age dating rates on the CSLG-SYR and SYR-XSX seg- and 31 ± 2.6 m on these two segments, respec- of 3270 ± 95 yr B.P. (Luo et al., 2013). How- ments were estimated using the offsets of lower tively. The abandonment age of a lower terrace ever, the field observations and dating results

terraces riser T1 and age dating data (Cowgill, can be regarded as the youngest age of displace- showed that the deposits of lower terrace T1 2007). The calculation formula is: ment and the estimates of slip rate constrains should have started around 9.4 ± 1.0 ka rather the maximum displacement rate (Cowgill, 2007; than being younger than 3 ka (Fig. 9D). Thus, Slip rate = Offset/age . (1) Zhang et al., 2008). multiple slip rates were used in this work to In the CSLG-SYR segment, the loess determine the average slip rate of terrace riser

The reconstructed terraces riser T1 had 31 deposit ages (9.4 ± 1.0 ka and 7.0 ± 1.1 ka) of T1, which can provide better upper boundaries

m and 35 m left-lateral displacements on the terraces T1 were obtained from OSL samples for the slip rates of this segment. CSLG-SYR and SYR-XSX segments as shown SGQ01W and SGQ02W (Figs. 9C and 9D). In the SYR-XSX segment, the OSL dating 14 in Figures 9 and 11. Considering the 4-m coseis- Meanwhile, the C sample HYZC4N gave the age of terraces T1 loess samples XSX05E and

mic offsets caused by the 1932 earthquake event dating results of terraces T1 as 7615–7565 yr XSX04E were 6.2 ± 0.6 ka and 7.6 ± 0.6 ka,

A 97°1'0"E N B 97°2'0"E 97°3'0"E N 39°42'30"N

Bend

Step-over

0 200 m

C 97°7'0"E N 318±10 m 462±10 m

Step-over 39°41'0"N

39°39'30"N

0 200 m 0 400m

Figure 5. Interpretation of Quickbird mosaic images showing the detailed geometric features of DHGR segment. (A) Ruptures appearing as left-stepping en-echelon pattern in the western part of DHGR segment. (B) Ruptures displaying as right-stepping en-echelon pattern in the middle part of DHGR segment. (C) Ruptures appearing as right-stepping en-echelon pattern in the eastern part of DHGR segment.

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 26

respectively (Figs. 11D and 11E). The age of previously, the long-term average slip rate is DISCUSSION 14C loess sample C1E was estimated as 7.05 4.49 ± 0.5 mm/yr on the SYR-XSX segment ± 0.11 ka (Figs. 11F and 11G). The C9E sample (Fig. 11H). A previous study constrained the The Segmentation, Length, and Slip was not used for age dating since it was col- slip rates of offset ridges as 4.6 ± 1.4–5.5 ± 2.2 Displacements of Surface Ruptures lected from the clay above the loess and could mm/yr on the eastern section of CMF since Related to the Changma Earthquake not represent the age of loess itself (Fig. 11G). the last glacial retreat (~10 ka) (Peltzer et al., The left-lateral slip rates for samples XSX05E, 1988). However, these rates were proven to be The segment geometry, length, and slip dis- XSX04E, and C1E were calculated to be 5 ± 0.6 quite high, as the ridge displacements must have placements of surface ruptures are critical for mm/yr, 4.08 ± 0.5 mm/yr, and 4.40 ± 0.4 mm/ accumulated before the last glacial retreat (Luo the study of earthquakes (Eberhart-Phillips et al., yr, respectively, combined with these age dat- et al., 2013). Hence, the maximum slip rate on 2003; Fu et al., 2005). The surface rupture zones ing results and the 31 ± 2.6 m left-lateral offset the eastern section of CMF was 4.49 ± 0.5 mm/ caused by historically large earthquakes with

of terrace risers T1 (Fig. 11H). As discussed yr or at least not more than 5 mm/yr. magnitudes >7 appear to have multi-segment

A ( N Hongkengzi Fig.7A Fig.7B

( ( Sangequan Dahuitiaogou Moshiju

( 39°38'0"N

0 2 km 97°10'0"E

d1 d4 d4 B d3 ( N Hongkengzi d2 d1 d4 d2 d3 d3 d3 d3 d3 Daheigou River d3 d4 Anmen d3 d2 d3 d2 d3 River d2 d1 d2 d1 d3 d3 d1 d1 d2 d3 d1 d1 d2 ( 1 2 Sangequan ( Dahuitiaogou d4 3 d1 Moshiju 39°38'0"N

( 39°38'0"N 2916 SGQ-MSJ Segment 0 2 km 97°10'0"E

( ( ( ( ( Quaternary Quaternary Permian Cambrian ( d4( ( Thrust fault Stream channel diluviumⅣ alluvium glutenite limestone

( ( ( ! ! ! ! ! ! ! ! ( ( Quaternary Tertiary Carboniferous Presinian ( d3( ( ! ! ! ! ! ! ! Strike-slip fault River diluviumⅢ ! ! ! ! ! ! ! ! sandstone shale griotte

( ( ( ( ( Quaternary Cretaceous Silurian ( d2( ( Plagiogranite Surface Rupture diluviumⅡ sandstone sandstone

( ( ( Boundary of first and ( ( Quaternary Triassic Ordovician ( d1( ( Ultra-basic rocks diluvium Ⅰ sandstone limestone second-order segment

Figure 6. (A) Spatial distribution of the surface rupture zone along the SGQ-MSJ segment interpreted from SPOT6 mosaic image. (B) Image interpretation of active tectonic map displaying the geometry of second-order segmentations along the SGQ-MSJ segment.

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 27

A N

39°38'30"N Fig.12C

Fig.7C Bend

Bend

39°38'0"N 97°8'0"E

0 400 m 97°9'0"E

B 97°10'0"E N C N

6.9±0.5m Fig.12D 15±1.1m Bend

0 400 m 0 20 m 39°38'0"N

Figure 7. (A) Interpretation of Quickbird mosaic image showing the bend developed in the west of SGQ-MSJ segment. Location of field photo in Figure 12C is shown. (B) A bend developed between two discrete second-order segments along the SGQ-MSJ segment. Loca- tion of field photo in Figure 12D is shown. (C) Field measures and image interpretation showing offset gullies near the Dahuitiaogou site.

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 28

A 97°20'0"E N

Fig.9

( Chouliushuigou

Fig.12E ( Hongyaozi

( Dabaozigou ( Xiaobaozigou

39°35'0"N 0 3 km

Quaternary a1 alluvium Ⅰ 97°20'0"E B N Quaternary a2 alluvium Ⅱ

! ! ! ! ! ! Tertiary ! ! ! ! ! !

! ! ! ! ! ! a2 sandstone Cretaceous CSLG-SYR Segment sand-mudstone a2 CSLG Seg Triassic a2 sand-mudstone a1 ( Permian Chouliushuigou glutenite 1 Carboniferous shale Silurian HYZ Seg sandstone Hongyaozi ( Ordovician Hongyaozigou River limestone Cambrian limestone Presinian SGQ-MSJ Segment 2 griotte a2 Ultra-basic rocks a2 a2 a2 XBZ Seg ( Strike-slip fault Dabaozigou a2 a2 ( Surface Rupture 3 Xiaobaozigou a2 a2 Thrust fault a1 a1 River 39°35'0"N Stream channel 0 3 km a1 Boundary of first and Shiyou River second-order segment Figure 8. (A) Spatial distribution of the surface rupture zone along the CSLG-SYR segment mapped from SPOT6 mosaic image. Location of field photo in Figure 12E is shown. (B) Image interpretation of active tectonic map showing the geometry of second-order segmentations along the CSLG-SYR segment.

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 29

97°19'45"E 97°20'0"E A N C 0 D SGQ02W SGQ02W (7.0±1.1)ka

Depth (m) SGQ01W SGQ01W (9.4±1.0)ka

0 25 cm 1

39°38'15"N E 0 F

HYZC4N Depth (m) 1 HYZC4N 0 100 m 7615-7565 yr B.P. 0 50 cm B 97°19'45"E 97°20'0"E N SGQ01W G T2 SGQ02W HYZC4N Average slip rate of T 31±2.3 m 1 T2 3.43±0.5 mm/yr

2.87±0.4 mm/yr T2 T 3.56±0.3 mm/yr 2 39°38'15"N T1 T

1 (m) Left lateral offset

3.86±0.7 mm/yr

T1 T0 T2 0 100 m T2 Age (ka)

Clay Loess Gravel Surface rupture Stream T0 T1 T2 SGQ01W Sample Active fault

Figure 9. (A) Geoeye-1 mosaic image showing the geometric and geomorphic features along the CSLG-SYR segment around the Choushuili-

ugou site. (B) 31 ± 2.3 m left-lateral offset of terrace risers T1 measured by image interpretation on the western part of CSLG-SYR segment. The real offset should be 27 ± 2.3 m omitted 4 m coseismic offset caused by the 1932 earthquake (Luo et al., 2013; Lanzhou Institute of

Seismology, National Bureau of Seismology, 1992). The location of samples collected from T1 is shown on the map. T0—river bed; T1—lower

terraces; T2—upper terraces. (C) Photograph showing the location of samples collected for OSL age dating. (D) Profile sketch displaying strata features and the OSL dating age of samples. (E) Photograph showing the location of sample collected for 14C age dating. (F) Profile 14 sketch displaying strata features and C dating age of sample. (G) The slip rates of T1 around Choushuiliugou site.

patterns (Lettis et al., 2002; Fu et al., 2005). in length from 14.4 to 39.6 km. The first-order zone (Figs. 7 and 12). The changes in the size The 1932 Ms 7.6 Changma earthquake nucle- rupture segments could be subdivided into of these offsets might also record the propa- ated around the Xiaokouzi site and propagated several second-order segments linked by left- gation and stress mechanisms of coseismic a bilateral rupture to the east and west (Lan- lateral releasing step-overs and bends (Figs. 5, ruptures (Zhang et al., 1991). Particularly, the zhou Institute of Seismology, National Bureau 7, and 12). Field observations also showed an longest continuous ruptures on the easternmost of Seismology, 1992) (Fig. 2A). The coseismic increase in the scale of the rupture from west segment are associated with pure left-lateral surface rupture caused by the 1932 earthquake to east (Fig. 12). Moreover, our interpretation strike slip faulting, whereas the western part has been well preserved over the past nearly 90 of satellite images and field investigations of the CMF is characterized by strike-slip and years. The surface rupture zone can be divided showed that gullies or channels have a 6–15 m reverse faulting components (Peltzer et al., into five discrete first-order segments varying coseismic offset within the Changma rupture 1988) (Figs. 2 and 10).

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 30

97°30'0"E 97°40'0"E N A Erdaogou Honggou ! ! Fig.12F ! Fig.11 Banjiegou Fig.12H Xibanjiegou ! Xiaojiangou ! Daquankou !

0 5 km Fig.12G 39°30'0"N

a1 a1 97°30'0"E a2 97°40'0"E B a1 Erdaogou N

a1 a1 !

Baiyang Honggou Baiyang ! Ya’er River a1 a1 ! a1 Shiyou River 1 Banjiegou a1 Xibanjiegou Xishuixia ! Xiaojiangou River ! a2 2 a1 Daquankou ! 3 SYR-XSX Segment 4 0 5 km 4029 3885 39°30'0"N

( ( ( Quaternary! ! ! ! ! ! ! ! Ordovician Presinian ( ( Tertiary ( a2( ( ! ! ! ! ! ! ! limestone Thrust fault Normal fault Stream channel alluvium Ⅱ! ! ! ! ! ! ! ! sandstone griotte

( ( ( Quaternary Boundary of first and ( ( Cretaceous Cambrian ( ( ( Strike-slip fault Surface Rupture River a1 alluvium Ⅰ sand-mudstone limestone second-order segment

Figure 10. (A) Spatial distribution of the surface rupture zone along the SYR-XSX segment mapped from SPOT6 mosaic image. Locations of field photos in Fig- ures 12F–12H are shown. (B) Image interpretation of active tectonic map showing the geometry of second-order segmentations along the SYR-XSX segment.

Previous work on historical earthquake 7.4–7.5 using the regression equations, rupture in a restraining step-over than in a releasing events showed the regression relationship length, and coseismic offset. The estimate of step-over, even though the releasing step-over between the rupture length on magnitude and moment magnitude fits the regression relation- is wider than the restraining step-over (Harris slip displacements on magnitude (Wells and ship. These results provide valuable insights for et al., 1991; Harris and Day, 1993; Oglesby, Coppersmith, 1994). Based on the regression evaluating and predicting the possibility of large 2005). Further studies also discovered that the equations proposed by Wells and Coppersmith earthquakes on strike-slip faults. stress heterogeneity accumulated in a releas- (1994), earthquakes with moment magnitudes ing step-over could enable a rupture to jump >7.4 can produce surface ruptures of >100 km The Influence of Step-Overs on Rupture across the step-over, whereas the stress pattern in length and generate average coseismic slip Propagation and Termination of a restraining step-over is more efficient at displacements of offset >3.3 m. The regression arresting a rupture (Duan and Oglesby, 2006; equations (Wells and Coppersmith, 1994) are: Previous workers have suggested that a Wesnousky, 2006). step-over plays a key role in determining In this work, our results show that there M 50..8116*log SRL (2) coseismic rupture dynamics (Wesnousky, 2006; are five first-order segments along the CMF, Oglesby, 2008). On the one hand, numerous which are linked by step-overs of different and studies indicated that a step-over with width sizes (Fig. 14A). Some of these step-overs, >4 km could effectively stop coseismic rup- such as the Shule River step-over (3.4 ± 0.3 M 69..3082* log AD , (3) ture (Segall and Pollard, 1980; Sibson, 1985; km wide), the Daheigou River step-over (2.2 Wesnousky, 1988, 2006; Harris and Day, 1993; ± 0.2 km wide), and the Anmen River step-over where M = moment magnitude, SRL = surface Sieh et al., 1993; Lettis et al., 2002; Oglesby, (2.5 ± 0.2 km wide), are <4 km wide, while rupture length, and AD = average displacement. 2008). In addition, the ability of a rupture to the Shiyou River step-over has a width of 5.4 The field investigations for this work identi- jump across step-overs decreases exponentially ± 0.4 km (Figs. 14B–14E). These results imply fied the 120-km Changma surface rupture zone as the width of step-overs increases (Bruce and that the 1932 Changma earthquake could rup- with an average coseismic offset of 3–4 m. Dieterich, 2007). On the other hand, some stud- ture through step-overs >5 km wide. However, These observations were also consistent with ies proposed that the restraining and releasing the rupture propagation was arrested by the previous results (Luo et al., 2013; Lanzhou step-overs have different impacts on the conti- 3.5 ± 0.3–km-long and 6.3 ± 0.5–km-wide Institute of Seismology, National Bureau of nuity of coseismic surface ruptures (Harris and Xishuixia River step-over at the easternmost Seismology, 1992). The moment magnitude of Day, 1993; Oglesby, 2005; Wesnousky, 2006). end of the rupture (Fig. 14F). Geomorphic the 1932 Changma earthquake was calculated as Rupture propagation is much more difficult interpretations showed that the Xishuixia

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 31

A N

XSX04E

XSX05E 3500 C1E, C9E 3450 3500

Fig.13A

3400

3400 3450 Fig.13C 3450 3450 3500

3480 3550 3480 3500

3490 0 200m N B

H I J L K T F G 0 T T1 E 0 T1 D T2 T2 B A T T2 Figure 11. (A) The UAV image showing the 1 T T1 1 T2 T1 T1 T2 T1 T geomorphic features of surface rupture T 1 T2 2 T T T0 2 zone along the eastern SYR-XSX segment T T H’ T 1 T T T 0 T 1 2 and the location of samples collected 0 C T 1 2 2 J’ K’ 2 I’ from the terraces T1. (B) Image interpre- T2 G’ I1 T T1 0 200m tation showed the 35 ± 2.6 m left-lateral 2 E’ F’F1 T0 B’ C1 D’ offset of terrace risers T on the eastern A1 A’ 1 A2 SYR-XSX segment. The real offset should N be 31 ± 2.6 m omitted 4 m coseismic offset caused by 1932 earthquake (Luo et C al., 2013; Lanzhou Institute of Seismol- ogy, National Bureau of Seismology, H I J L 1992). T0—river bed; T1—lower terraces; G KTT F 0 0 T2—upper terraces. (C) Reconstructed T1 TT TT1 1 E 0 0 TT1 1 showing a 35 ± 2.6 m horizontal offset D TT2 2 TT2 2 B occurred along the eastern SYR-XSX seg- A TT TT2 2 T 1 1 TT1 1 1 TT2 2 T1 ment after being restored. (D) Photograph TT1 1 TT1 1 TT2 2 TT1 1 TT TT 1 1 of samples collected from the Xishuixia TT2 2 2 2 TT 35±2.6 m TT TT0 0 2 2 TT TTH’ TT 1 1 site for OSL age dating. (E) Profile sketch TT TT 0 0 TT 1 1 2 2 TT0 0 1 1 2 2 2 2 K’ displaying strata features and OSL dating C TT2 2 J’ I’ 14 TT2 2 I1 data. (F) Photograph of C samples col- TT TT1 1 G’ 2 2 F1 0 200m lected from the Xishuixia site. (G) Profile TT0 0 D’ E’ F’ A’ B’ C1 14 A1 A2 sketch displaying strata features and C dating data of samples. (H) The slip rates

of T1 around Xishuixia site. D E H 0

Average slip rate of T1 XSX05E XSX05E 4.49±0.5 mm/yr

Depth (m) (6.2±0.6)ka

1 4.40±0.4 mm/yr

4.08±0.5 mm/yr Left lateral offset (m) Left lateral offset 0 25cm XSX04E XSX04E (7.6±0.6)ka 5.00±0.6 mm/yr

F 0 G Age (ka) C9E C9E 3215–3060 yr B.P. T0 T2 Loess A Depth (m) Trunk river

1 T1 Clay Gravel A’ Upstream C1E C1E 7160–6945 yr B.P. A1 Tributary XSX04E Sample Surface rupture 0 50cm 3500 Contours Stream

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 32

A E B E

6±0.4 m 9±0.6 m

C E D S

15±1.1 m Surface rupture

E E F E

6.2±0.5 m

Surface rupture

G W H S

Surface rupture Surface rupture

Active fault Gully 6 m Displacement

Figure 12. Photographs showing left-lateral offsets and surface ruptures observed along the CMF. (A) The offset channel at Chouliugou (see location in Fig. 3A). (B) The displaced gully west of Xiaoheigou (see location in Fig. 4A). (C) The offset gully developed at west of Sangequan (see location in Fig. 7A). (D) Surface ruptures at the east of Sangequan (see location in Fig. 7B). (E) Surface ruptures at the east of Choushuiliugou (see location in Fig. 8A). (F) The offset channel located west of Xibanjiegou (see location in Fig. 10A). (G) Coseismic surface ruptures developed west of Baiyang River (see location in Fig. 10A). (H) Coseismic surface ruptures located near the Xihshuixia River (see location in Fig. 10A). Red solid line—fault trace; white dotted line—indication of offset; black line—channel or gully; white arrow—indication of surface rupture.

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 33

A N B N

3490 T0 T T 2 T T1 0 1 T2

3510 T1 T1

28±2.1m 3500 28±2.1m T T1 T1 1 T1 T2

0 20m 0 20m

C N D N

3450

T1 T1

T T T2 0 T2 0

T1 T T0 1 T1

3470 16±1.2m

16±1.2m 3460

T0 T0

T1 T1 0 10m 0 10m

3500 16m Surface rupture Gully T0 T1 T2 Elevation Displacement

Figure 13. (A) The UAV image displaying the geologic and geomorphic features along the eastern part of SYR-XSX segment. (B) Interpre- tation of topographic data derived from the UAV image and field observations, which both showed the 28 ± 1.0 m offset near Xishuixia River. (C) The UAV image displaying the geologic and geomorphic features west of the site shown in A. (D) The topographic data derived

from the UAV image showing the 16 ± 2.0 m offset. T0—river bed; T1—lower terraces; T2—upper terraces.

River step-over is a restraining step-over with Implications for the Tectonic Transition et al., 2016; Zuza et al., 2016; Yu et al., 2017). a mountain peak as high as ~4927 m. It sug- between the CMF and the ATF System For example, Xu et al. (2005) indicated that the gests that both the large size and restraining significant fall of slip rates occurred at three mechanism of the Xishuixia River step-over Numerous studies indicated that slip rates junction points, including the Subei (SB), Shiba- contributed to the termination of the 1932 decreased from 11 mm/yr to 4.8 mm/yr, then ocheng (SBC), and Changma (CM) junctions coseismic rupture. down to 0–2 mm/yr along the ATF system (Fig. 16). These junction points linked the ATF Previously discussed results show that a rup- (between 84° to 98°E) (Xu et al., 2005; Cowgill, system and those adjacent faults west of the ture caused by an earthquake with a magnitude 2007; Zhang et al., 2007; Cowgill et al., 2009; QLSF belt, including Danghe Nanshan fault, >7 could propagate through a step-over with a Gold et al., 2009, 2011; Hetzel, 2013) (Fig. 15). Yema River-Daxue Shan fault, and CMF (Het- width >5 km, implying that the assumption that Most of these argue that the tectonic deforma- zel et al., 2002; Darby et al., 2005; Zheng, 2009; rupture propagation can be effectively stopped tion of thrust or strike-slip faults developed in Zhang et al., 2014; Cheng et al., 2015, 2016) by step-overs with widths >4 km needs to be the Qaidam Basin and QLSF belt is the main (Figs. 15 and 16). Structural analysis showed reconsidered. Therefore, this point must be reason for slip decrease (Burchfiel et al., 1989; that the ATF system and its adjacent thrust and taken into account for the prediction and assess- Yin and Harrison, 2000; Xu et al., 2005; Yin strike-slip faults, the Sanweishan and Nanjie- ment of future earthquake risks. et al., 2008b; Cheng et al., 2015; Cunningham shan faults, formed an asymmetric half-flower

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 34

A 96°40'E 97°0' E 97°20'E 97°40'E N

Shule River step-over Fig.14B Daheigou River step-over Fig.14C Anmen River Fig.14D step-over Fig.14E Shiyou River step-over

39°40'N Fig.14F Xishuixia River step-over LJW-CLG Segment DHGR SGQ-MSJ Elevation Segment Segment (m) CSLG-SYR 5573 0 20 km Segment SYR-XSX Segment 1131

96°55'E 97°0'E N 97°26'E 97°30'E B Daheigou River E CSLG-SYR N Shule River

Shiyou River DHGR step-over

Toudaogou Shiyou River 5.4±0.4 km 39°33'N

3.4±0.3 km 39°42'N 4.5±0.3 km LJW-CLG Shule River step-over Erdaogou SYR-XSX 2.3±0.2 km 0 1km 0 1km

97°8'E 97°10'E C Daheigou N F 97°44'E 97°48'E N Xishuixia River 39°32'N CMF DHGR Daheigou River step-over 39°39'N

River 2.2±0.2 km 4927m 6.3±0.5 km

Sangequan SGQ-MSJ Xishuixia River 3.5±0.3 km step-over 39°28'N 0.32±0.02 km 39°28'N 0 1km 0 2km

97°18'E N D Anmen Thrust fault

Active fault River CSLG-SYR Choushuiliugou Surface Rupture

2.5±0.2 km Anmen River

Moshiju step-over 39°38'N Assumed Rupture

SGQ-MSJ River

0 1km 0.81±0.1 km Discontinued zone

Figure 14. (A) ASTER GDEM map showing step-overs among these first-order segments of surface rupture along the CMF. (B) Quickbird2 image displaying the left-stepping releasing Shule River step-over. (C) The right-stepping restraining Daheigou River step-over as shown in the Quickbird2 image. (D) SPOT6 image represents the left-stepping releasing Anmen River step-over. (E) Worldview2 image showing a large pressure Shiyou River step-over. (F) SPOT6 image showing the large right-stepping restraining Xishuixia River step-over around the eastern end of the CMF.

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 35

To explore the role the CMF played in the Geologic rates Geodetic rates 30 slip partitioning of the ATF system, a three- Xu et al., 2005 GPS Cowgill, 2007 Bendick et al., 2000 dimensional tectonic model related to tectonic Cowgill et al., 2009 Wallace, 2004 Zhang et al., 2007 deformation of the ATF system and its adjacent Gold et al., 2009 25 Gold et al., 2011 InSAR faults in the western part of QLSF belt was pro- Elliott et al., 2008 posed (Fig. 17). Currently, these active faults present thrust faulting with rates less than 1 20 mm/yr in the west QLSF belt (Zheng, 2009). Toward the east, their motions change to strike- slip faulting with average slip rates of 1–3 mm/ 15 yr (Hetzel et al., 2004; Zheng, 2009). In particu- lar, both this study and other previous studies

Slip rate (mm/yr) (Luo et al., 2013; Zheng et al., 2013) indicate 10 that the CMF shows a change from dominant thrust (0.14 ± 0.02 mm/yr) and strike-slip faulting (1.17 ± 0.07 mm/yr) to pure left-lateral slip 5 faulting (3–4 mm/yr) toward the east. In addition, it is noticeable that the left-lateral slip rate is 4.49 ± 0.5 mm/yr along the eastern segment 0 of the CMF, which is similar to the slip rate of DHNSF YMR-DXSF CMF ~4.8 mm/yr on the ATF system around the CMF junction (Fig. 17). This means that the major 82 84 86 88 90 92 94 96 98 100 slip of the ATF system may transfer into the Longitude (°) CMF. These results imply that the CMF plays a major role in slip partitioning of the ATF system Figure 15. Distribution of slip rates along the ATF system. The abrupt reductions of slip rates occurred at three junction points with active faults in the west of Qilianshan fault (QLSF) belt such as the as compared with other active faults. In addi- DHNSF—Danghe Nanshan Fault; YMR-DXSF—Yema River-Daxue Shan Fault; CMF—Changma Fault. tion, we infer that a 3–4 mm/yr slip of the ATF system may have been absorbed by the CMF through the transformation from thrust to strike structure dominated by non-strain partitioned to the north of Tibetan Plateau and southern slip faulting. Therefore, we believe that the slip left-lateral transpression that affected the defor- Gobi Alashan proposed that both the reverse on the eastern ATF system has been partially mation of the northeast Tibetan Plateau foreland and strike-slip faults in this area have absorbed transferred into the CMF, accommodated with (Cunningham et al., 2016). The oblique-extru- the slip on the ATF system accommodated with slip partitioning and the NNE–SSW compression deformation model for the Hexi Corridor the crustal shortening (Yu et al., 2016, 2017). sional stress (Fig. 17).

A 94°30'E 95°0'E N B 96°0'E N C 96°30'E N Dang Dangshi

River River 50° ATF 40°0'N 7.4° ATF 31.1° Subei ATF

Shibaocheng 40°0'N 39°30'N Changma Shule DHNSF CMF River YMR-DXSF 39°30'N 39°30'N

0 20km Active fault Strike-slip fault Thrust fault River

Figure 16. Active tectonic map documented by the SRTM shaded relief topographic maps showing the tectonic features around the junction points linking the ATF system and its adjacent faults in the QLSF belt (After Meyer et al., 1998; Xu et al., 2005). ATF—Altyn Tagh fault; CMF—Changma fault; DHNSF—Danghe Nanshan fault; YMR-DXSF—Yema River-Daxue Shan fault.

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 36

SGL H 4.6 SB H 11 ~ 10 DHNSF V 0.86 ATF

YMR-DXSFH 1.4~2.8 HYZ H 3.9 ~ 4.8 V 0.4~1 SBC

Dahaleben V 0.14 YM CM

H 1~2 H 1.17~1.3 H 1 ~ 2.2 Dang River H 3.1 Hexi V 0.4

NQLSF River Corridor

H 1 CMF SLNSF H 3.7

Shule TLF HSF

YMF

River HLL V 2.1 H 4.7 H 1.6 × ×

Figure 17. Proposed three-dimensional tectonic models showing the tectonic deformation related to the ATF system and CMF zone in the NE Tibetan Plateau. Fault traces are based on Meyer et al. (1998), Yin et al. (2008a), and Cheng et al. (2015). The slip rates along the ATF system experienced abrupt reduction at the junction points (SB, SBC, and CM) (Meyer et al., 1998; Xu et al., 2005) linking the ATF system and adjacent faults developed in the QLSF belt. These findings suggest that the CMF plays the dominant role in the slip partitioning of the ATF system. The model also indicates that the stress mechanism within the CMF converted from thrust-dominated to pure left-slip–dominated faulting toward the east. The CMF and the ATF system are shown in thick red lines. Other active faults within NE Tibetan Plateau are represented by thinner red lines. Red arrows along the fault traces are used to indicate the directions of fault motions. Black bold arrows outside the model represent the NNE–SSW-trending compression. Black numbers indicate slip rates (mm/ yr) of faults obtained from Hetzel et al. (2002), Xu et al. (2005), Zhang et al. (2007), Elliott et al. (2008), Zheng (2009), and Luo et al. (2013). H and V represent horizontal and vertical slip rates (mm/yr), respectively. ATF—Altyn Tagh fault; CMF—Changma fault; DHNSF—Danghe Nanshan fault; YMR-DXSF—Yema River-Daxue Shan fault; HSF—Hei Shan fault; NQLSF—North Qilian Shan fault; QLSF—Qilian Shan fault; SLNSF—Shule Nanshan fault; TLF—Tuolai fault; YMF—Yumen fault. CM—Changma; DH—Dunhuang; HLL—Hala Lake; HYZ—Hongyazi; SB—Subei; SBC—Shibaocheng; SGL—Sugan Lake; YM—Yumen.

CONCLUSIONS with lengths of 14.4–39.56 km. The rupture mainly absorbed by the CMF, suggesting that could propagate through 0.3–4.5-km-long and the CMF plays a leading role in the slip parti- In this study, the geometric and geomor- 2.2–5.4-km-wide step-overs, but was terminated tioning of the eastern segment of the ATF system. phic features, segmentation, and termination of by a 6.3-km-wide restraining step-over with high the 1932 Changma earthquake surface rupture relief in the easternmost portion of the CMF. ACKNOWLEDGMENTS zone were well documented, which provides (2) Left-lateral slip rates of 3.43 ± 0.5 mm/yr This research was supported by the Strategic Priority new insights into the tectonic transition in the and 4.49 ± 0.5 mm/yr since the Holocene were Research Program of the Chinese Academy of Sciences (XDA 20070202) and National Natural Science Foundation of China NE Tibetan Plateau as follows. calculated in the mid-east and easternmost seg- (No. 41761144071), as well as by the research project of China (1) The surface rupture zone produced by ments of the CMF. Active Fault Survey-The South-North Seismic Zone from the Institute of Geology, China Earthquake Administration for the the 1932 Changma earthquake can be divided (3) A new tectonic model proposed that a Changma Active Fault Mapping (201408023). We sincerely into five discontinuous first order segments slip of 3–4 mm/yr on the ATF system has been appreciate the editor and reviewers for their constructive

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 37

suggestions on the content and many points of this paper. Deng, Q.D., 1984, Research overview of the movement mech- Geology, v. 26, no. 4, p. 688–697, https://doi .org/10.3969 We are grateful for discussions with Professor P. Tapponnier anism, the slip rate and earthquake repeatability of sev- /j.issn.0253-4967.2004.04.014 (in Chinese). that improved the manuscript. We would like to thank driv- eral active faults in China: Recent Developments in World Hetzel, R., 2013, Active faulting, mountain growth, and ero- ers Cao, Guan, and Chen for support during field work. We Seismology, no. 3, p. 5–8, 32 (in Chinese). sion at the margins of the Tibetan Plateau constrained by also acknowledge the technical support of Unmanned Aerial DePolo, C.M., Clark, D.G., Slemmons, D.B., and Ramelli, A.R., in situ-produced cosmogenic nuclides: Tectonophysics, Vehicle (UAV) data provided by the Beijing Esky Tec Ltd. The 1991, Historical surface faulting in the Basin and Range v. 582, p. 1–24, https://doi.org /10.1016 /j.tecto .2012.10.027. 14C and OSL age dating data were measured by Lab Beta province, western North America: implications for fault Hetzel, R., Niedermann, S., Tao, M.X., Kubik, P.W., Ivy Ochs, and the OSL Lab of the Institute of Geology and Geophysics, segmentation: Journal of Structural Geology, v. 13, no. 2, S., Gao, B., and Strecker, M.R., 2002, Low slip rates and Chinese Academy of Sciences. p. 123–136, https://doi .org /10 .1016 /0191 -8141 (91)90061 -M. long-term preservation of geomorphic features in Cen- Duan, B., and Oglesby, D.D., 2005, Multicycle dynamics of tral Asia: Nature, v. 417, no. 6887, p. 428–432, https://doi nonplanar strike-slip faults: Journal of Geophysical Re- .org/10.1038/417428a. REFERENCES CITED search, v. 110, no. B3, B03304, https://doi.org/10.1029 Hetzel, R., Tao, M., Stokes, S., Niedermann, S., Ivy-Ochs, S., Barka, A.A., and Kadinsky-Cade, K., 1988, Strike-slip fault /2004JB003298. Gao, B., Strecker, M.R., and Kubik, P.W., 2004, Late Pleis- geometry in Turkey and its influence on earthquake ac- Duan, B., and Oglesby, D.D., 2006, Hetrogeneous fault tocene/Holocene slip rate of the Zhangye thrust (Qilian tivity: Tectonics, v. 7, no. 3, p. 663–684, https://doi.org/10 stresses from previous earthquakes and the effect on Shan, China) and implications for the active growth of .1029/TC007i003p00663. dynamics of parallel strike-slip faults: Journal of Geo- the northeastern Tibetan Plateau: Tectonics, v. 23, no. 6, Bendick, R., Bilham, R., Freymueller, J.T., Larson, K., and Yin, physical Research, v. 111, B05309, https://doi .org /10 .1029 https://doi.org/10.1029/2004TC001653. G.H., 2000, Geodetic evidence for a low slip rate in the /2005JB004138. Hou, Z.Q., Wang, H.L., and Kang, L.X., 1986, Age of fault- Altyn Tagh fault system: Nature, v. 404, no. 6773, p. 69–72, Eberhart-Phillips, D., Haeussler, P.J., Freymueller, J.T., Frankel, scarps and earthquake recurrence intervals on Changma https://doi.org/10.1038/35003555. A.D., Rubin, C.M., Craw, P., Ratchkovski, N.A., Anderson, fault [in Chinese]: Northwestern Seismological Journal, Bruce, E.S., and Dieterich, J.H., 2007, Probabilities for jumping G., Carver, G.A., Crone, A.J., Dawson, T.E., Fletcher, H., v. 8, no. 1, p. 102–108. fault segment stepovers: Geophysical Research Letters, Hansen, R., Harp, E.L., Harris, R.A., Hill, D.P., Hreinsdót- Kang, L.X., 1986, Fault motion, slip rate and paleoseimicity v. 34, no. 1, L01307, https://doi .org /10 .1029 /2006gl027980. tir, S., Jibson, R.W., Jones, L.M., Kayen, R., Keefer, D.K., on the east segment of the Changma fracture zone since Burchfiel, B.C., Quidong, D., Molnar, P., Royden, L., Yipeng, Larsen, C.F., Moran, S.C., Personius, S.F., Plafker, G., Sher- the later times of the late Pleistocene [in Chinese]: Jour- W., Peizhen, Z., and Weiqi, Z., 1989, Intracrustal detach- rod, B., Sieh, K., Sitar, N., and Wallace, W.K., 2003, The nal of Seismological Research, v. 9, no. 3, p. 343–350. ment within zones of continental deformation: Geology, 2002 Denali Fault Earthquake, Alaska: A large magnitude, Lanzhou Institute of Seismology, National Bureau of Seis- v. 17, no. 8, p. 748–752, https://doi.org/10.1130/0091-7613 slip-partitioned event: Science, v. 300, no. 5622, p. 1113– mology, 1992, Changma Active Fault System: Beijing, (1989)017<0448:IDWZOC>2.3.CO;2. 1118, https://doi.org/10.1126/science.1082703. Seismological Press, 207 p. (in Chinese). Cheng, F., Jolivet, M., Dupont-Nivet, G., Wang, L., Yu, X., and Elliott, A.J., Dolan, J.F., and Oglesby, D.D., 2009, Evidence Lettis, W., Bachhuber, J., Witter, R., Brankman, C., Randolph, Guo, Z., 2015, Lateral extrusion along the Altyn Tagh from coseismic slip gradients for dynamic control on C.E., Barka, A., Page, W.D., and Kaya, A., 2002, Influence Fault, Qilian Shan (NE Tibet): Insight from a 3D crustal rupture propagation and arrest through stepovers: Jour- of releasing step-overs on surface fault rupture and fault budget: Terra Nova, v. 27, no. 6, p. 416–425, https://doi nal of Geophysical Research, v. 114, B02312, https://doi segmentation: Examples from the 17 August 1999 Izmit .org/10.1111/ter.12173. .org/10.1029/2008JB005969. earthquake on the North Anatolian fault, Turkey: Bulle- Cheng, F., Jolivet, M., Fu, S., Zhang, C., Zhang, Q., and Guo, Elliott, A.J., Oskin, M.E., Liu-zeng, J., and Shao, Y.X., 2018, Per- tin of the Seismological Society of America, v. 92, no. 1, Z., 2016, Large-scale displacement along the Altyn Tagh sistent rupture terminations at a restraining bend from p. 19–42, https://doi.org/10.1785/0120000808. Fault (North Tibet) since its Eocene initiation: Insight slip rates on the eastern Altyn Tagh Fault: Tectonophysics, Lozos, J.C., Oglesby, D.D., Duan, B., and Wesnousky, S.G., from detrital zircon U–Pb geochronology and subsur- v. 733, p. 57–72, https://doi .org /10 .1016 /j .tecto .2018 .01 .004. 2011, The effects of double fault bends on rupture propa- face data: Tectonophysics, v. 677–678, p. 261–279, https:// Elliott, J.R., Biggs, J., Parsons, B., and Wright, T.J., 2008, gation: A geometrical parameter study: Bulletin of the doi.org/10.1016/j.tecto.2016.04.023. InSAR slip rate determination on the Altyn Tagh Fault, Seismological Society of America, v. 101, no. 1, p. 385– Clark, M.K., and Royden, L.H., 2000, Topographic ooze: Build- northern Tibet, in the presence of topographically cor- 398, https://doi.org/10.1785/0120100029. ing the eastern margin of Tibet by lower crustal flow: related atmospheric delays: Geophysical Research Let- Luo, H., He, W.G., Wang, D.W., Yuan, D.Y., and Shao, Y.X., Geology, v. 28, no. 8, p. 703–706, https://doi .org/10.1130 ters, v. 35, no. 12, https://doi.org/10.1029/2008GL033659. 2013, Study of the slip rate of CMF in Qilian Mountains /0091-7613(2000)28<703:TOBTEM>2.0.CO;2. Fu, B.H., Awata, Y., Du, J.G., Ninomiya, Y., and He, W.G., 2005, since late Pleistocene: Seismology and Geology, v. 35, Cowgill, E., 2007, Impact of riser reconstructions on estima- Complex geometry and segmentation of the surface rup- no. 4, p. 765–777, https://doi .org /10 .3969 /j .issn .0253 -4967 tion of secular variation in rates of strike slip faulting: ture associated with the 14 November 2001 great Kun- .2013.04.007 (in Chinese). Revisiting the Cherchen River site along the Altyn Tagh lun earthquake, northern Tibet, China: Tectonophysics, Luo, H., He, W.G., Yuan, D.Y., Shao, Y.X., and Wang, Q.M., Fault, NW China: Earth and Planetary Science Letters, v. 407, no. 1-2, p. 43–63, https://doi.org/10.1016/j.tecto 2016, New insight on paleoearthquake activity along v. 254, no. 3–4, p. 239–255, https://doi.org/10.1016/j.epsl .2005.07.002. Changma fault zone: China Earthquake Engineering .2006.09.015. Gansu Bureau of Geological and Mineral Resources, 1969, Journal, v. 38, no. 4, p. 632–638, https://doi.org/10.3969 Cowgill, E., Yin, A., Harrison, T.M., and Xiao-Feng, W., 2003, Geological map of the Yumen City area: Beijing, Geologi- /j.issn.1000-0844.2016.04.0632 (in Chinese). Reconstruction of the Altyn Tagh fault based on U-Pb cal Press, 1 sheet, scale 1:200,000 (in Chinese). Mériaux, A.S., Ryerson, F.J., Tapponnier, P., Woerd, J.V.D., geochronology: Role of back thrusts, mantle sutures, and Gansu Bureau of Geological and Mineral Resources, 1972, Finkel, R.C., Xu, X.W., Xu, Z.Q., and Caffee, M.W., 2004, heterogeneous crustal strength in forming the Tibetan Geological map of the Changma area: Beijing, Geologi- Rapid slip along the central Altyn Tagh Fault: Morpho- Plateau: Journal of Geophysical Research, Solid Earth, cal Press, 1 sheet, scale 1:200,000 (in Chinese). chronologic evidence from Cherchen He and Sulamu v. 108, no. B7, https://doi.org/10.1029/2002jb002080. Gold, R.D., Cowgill, E., Arrowsmith, J.R., Gosse, J., Chen, Tagh: Journal of Geophysical Research, v. 109, B606401, Cowgill, E., Arrowsmith, J.R., An, Y., Wang, X., and Chen, Z., X., and Wang, X.F., 2009, Riser diachroneity, lateral ero- https://doi.org/10.1029/2003JB002558. 2004, The Akato Tagh bend along the Altyn Tagh fault, sion, and uncertainty in rates of strike‐slip faulting: A Mériaux, A.S., Tapponnier, P., Ryerson, F.J., Xu, X.W., King, northwest Tibet 2: Active deformation and the impor- case study from Tuzidun along the Altyn Tagh Fault, NW G., Woerd, J.V.D., Finkel, R.C., Li, H.B., Caffee, M.W., and tance of transpression and strain hardening within the China: Journal of Geophysical Research, v. 114, B04401, Xu, Z.Q., 2005, The Aksay segment of the northern Altyn Altyn Tagh system: Geological Society of America Bul- https://doi.org/10.1029/2008JB005913. Tagh fault: Tectonic geomorphology, landscape evolu- letin, v. 116, no. 11–12, p. 1443–1464, https://doi.org/10 Gold, R.D., Cowgill, E., Arrowsmith, J.R., Chen, X.H., and tion, and Holocene slip rate: Journal of Geophysical Re- .1130/B25360.1. Wang, X.F., 2011, Faulted terrace risers place new con- search, Solid Earth, v. 110, p. 229–246, https://doi.org/10 Cowgill, E., Gold, R.D., Xuanhua, C., Xiao-Feng, W., Arrow- straints on the late Quaternary slip rate for the central .1029/2004JB003210. smith, J.R., and Southon, J., 2009, Low Quaternary slip Altyn Tagh Fault, northwest Tibet: Geological Society of Meyer, B., Tapponnier, P., Bourjot, L., Metivier, F., Gaudemer, rate reconciles geodetic and geologic rates along the America Bulletin, v. 123, no. 5-6, p. 958–978, https://doi Y., Peltzer, G., Shunmin, G., and Zhitai, C., 1998, Crustal Altyn Tagh fault, northwestern Tibet: Geology, v. 37, no. 7, .org/10.1130/B30207.1. thickening in Gansu-Qinghai, lithospheric mantle sub- p. 647–650, https://doi.org/10.1130/G25623A.1. Harris, R.A., and Day, S.M., 1993, Dynamics of fault interac- duction, and oblique, strike-slip controlled growth of the Crone, A.J., and Haller, K.M., 1991, Segmentation and the tion—Parallel strike-slip faults: Journal of Geophysical Tibet plateau: Geophysical Journal International, v. 135, coseismic behavior of Basin and Range normal faults: ex- Research, Solid Earth, v. 98, p. 4461–4472, https://doi.org no. 1, p. 1–47, https://doi.org/10.1046/j.1365-246X.1998 amples from east-central Idaho and southwestern Mon- /10.1029/92JB02272. .00567.x. tana, U.S.A: Journal of Structural Geology, v. 13, no. 2, Harris, R.A., Archuleta, R.J., and Day, S.M., 1991, Fault steps Molnar, P., and Tapponnier, P., 1975, Cenozoic tectonics of p. 151–164, https://doi .org /10 .1016 /0191 -8141 (91)90063 -O. and the dynamic rupture process: 2-D numerical simu- Asia: Effects of a continental collision: Features of recent Cunningham, D., Zhang, J., and Li, Y., 2016, Late Cenozoic lations of a spontaneously propagating shear fracture: continental tectonics in Asia can be interpreted as results transpressional mountain building directly north of the Geophysical Research Letters, v. 18, no. 5, p. 893–896, of the India-Eurasia collision: Science, v. 189, no. 4201, Altyn Tagh Fault in the Sanweishan and Nanjieshan, https://doi.org/10.1029/91GL01061. p. 419–426, https://doi.org/10.1126/science.189.4201.419. North Tibetan Foreland, China: Tectonophysics, v. 687, Harrison, T.M., Copeland, P., Kidd, W.S., and Yin, A., 1992, Oglesby, D.D., 2005, The dynamics of strike-slip step-overs p. 111–128, https://doi.org/10.1016/j.tecto.2016.09.010. Raising Tibet: Science, v. 255, no. 5052, p. 1663–1670, with linking dip-slip faults: Bulletin of the Seismological Darby, B.J., Ritts, B.D., Yue, Y.J., and Meng, Q.R., 2005, Did https://doi.org/10.1126/science.255.5052.1663. Society of America, v. 95, no. 5, p. 1604–1622, https://doi the Altyn Tagh fault extend beyond the Tibetan Plateau?: He, W.G., Zheng, W.J., and Zhao, G.K., 2004, Study on the .org/10.1785/0120050058. Earth and Planetary Science Letters, v. 240, no. 2, p. 425– seismogenic structure of the Yumen, Gansu Province Ms Oglesby, D.D., 2008, Rupture termination and jump on par- 435, https://doi.org/10.1016/j.epsl.2005.09.011. 5.9 earthquake of December 14, 2002: Seismology and allel offset faults: Bulletin of the Seismological Society

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 38

of America, v. 98, no. 1, p. 440–447, https://doi.org/10 Wells, D.L., and Coppersmith, K.J., 1994, New empirical re- and the southern Gobi Alashan, China: Tectonophysics, .1785/0120070163. lationships among magnitude, rupture length, rupture v. 721, p. 28–44, https://doi .org /10 .1016 /j .tecto .2017 .09 .014. Peltzer, G., and Tapponnier, P., 1988, Formation and evolu- width, rupture area, and surface displacement: Bulletin Zhang, H.P., Zhang, P.Z., Zheng, D.W., Zheng, W.J., Chen, Z.W., tion of strike-slip faults, rifts, and basins during the In- of the Seismological Society of America, v. 84, no. 4, and Wang, W.T., 2014, Transforming the Miocene Altyn dia-Asia collision—An experimental approach: Journal p. 974–1002. Tagh fault slip into shortening of the north-western Qil- of Geophysical Research-Solid Earth and Planets, v. 93, Wesnousky, S.G., 1988, Seismological and structural evolu- ian Shan: Insights from the drainage basin geometry: p. 15085–15117, https://doi .org /10 .1029 /JB093iB12p15085. tion of strike-slip faults: Nature, v. 335, no. 6188, p. 340– Terra Nova, v. 26, no. 3, p. 216–221, https://doi.org/10 Peltzer, G., Tapponnier, P., Gaudemer, Y., Meyer, B., Guo, S.M., 343, https://doi.org/10.1038/335340a0. .1111/ter.12089. Yin, K., Chen, Z.T., and Dai, H.G., 1988, Offsets of late Wesnousky, S.G., 2006, Predicting the endpoints of earth- Zhang, P.Z., Slemmons, D.B., and Mao, F.Y., 1991, Geomet- quaternary morphology, rate of slip, and occurrence of quake ruptures: Nature, v. 444, no. 7117, p. 358–360, ric pattern, rupture termination and fault segmentation large earthquakes on the Chang Ma fault (Gansu, China): https://doi.org/10.1038/nature05275. of the Dixie Valley active normal fault system, Nevada, Journal of Geophysical Research, v. 93, p. 7793–7812, Xu, X.W., Tapponnier, P., Van Der Woerd, J., Ryerson, F.J., U.S.A: Journal of Structural Geology, v. 13, no. 2, p. 165– https://doi.org/10.1029/JB093iB07p07793. Wang, F., Zheng, R.Z., Chen, W.B., Ma, W.T., Yu, G.H., 176, https://doi.org/10.1016/0191-8141(91)90064-P. Reimer, P.J., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G., Chen, G.H., and Mériaux, A.S., 2005, Late quaternary Zhang, P.Z., Mao, F.Y., and Slemmons, D.B., 1999, Rupture ter- Bronk Ramsey, C., Buck, C.E., Cheng, H., Edwards, R.L., sinistral slip rate along the ATF and its structural transfor- minations and size of segment boundaries from historical Friedrich, M., and Grootes, P.M., 2013, IntCal13 and Ma- mation model: Science in China, Series D, Earth Sciences, earthquake ruptures in the Basin and Range Province: rine13 radiocarbon age calibration curves 0–50,000 years v. 48, no. 3, p. 384–397, https://doi.org/10.1360/02yd0436. Tectonophysics, v. 308, no. 1-2, p. 37–52, https://doi.org cal BP: Radiocarbon, v. 55, p. 1869–1887, https://doi .org Yin, A., 2010, Cenozoic tectonic evolution of Asia: A prelimi- /10.2458/azu_js_rc.55.16947. nary synthesis: Tectonophysics, v. 488, p. 293–325, https:// /10.1016/S0040-1951(99)00089-X. Royden, L.H., Burchfiel, B.C., and van der Hilst, R.D., 2008, doi.org/10.1016/j.tecto.2009.06.002. Zhang, P.Z., Molnar, P., and Xu, X.W., 2007, Late Quaternary The geological evolution of the Tibetan Plateau: Sci- Yin, A., and Harrison, T.M., 2000, Geologic evolution of the and present-day rates of slip along the Altyn Tagh Fault, ence, v. 321, no. 5892, p. 1054–1058, https://doi.org/10 Himalayan-Tibetan orogen: Annual Review of Earth and northern margin of the Tibetan Plateau: Tectonics, v. 26, .1126/science.1155371. Planetary Sciences, v. 28, no. 1, p. 211–280, https://doi .org no. 5, https://doi.org/10.1029/2006TC002014. Segall, P., and Pollard, D.D., 1980, Mechanics of discontinuous /10.1146/annurev.earth.28.1.211. Zhang, P.Z., Li, C.Y., and Mao, F.Y., 2008, Strath terrace forma- fault: Journal of Geophysical Research, v. 85, p. 4337– Yin, A., Rumelhart, P.E., Butler, R., Cowgill, E., Harrison, T.M., tion and striking-slip faulting: Seismology and Geology, 4350, https://doi.org/10.1029/JB085iB08p04337. Foster, D.A., Ingersoll, R.V., Zhang, Q., Zhou, X.Q., and v. 30, no. 1, p. 44–57, https://doi.org/10.3969/j.issn.0253 Sibson, R.H., 1985, A note on fault reactivation: Journal of Wang, X.F., 2002, Tectonic history of the Altyn Tagh fault -4967.2008.01.004 (in Chinese). Structural Geology, v. 7, no. 6, p. 751–754, https://doi.org system in northern Tibet inferred from Cenozoic sedi- Zheng, W.J., 2009, Geometric pattern and active tectonics of /10.1016/0191-8141(85)90150-6. mentation: Geological Society of America Bulletin, v. 114, the Hexi Corridor and its adjacent regions [Ph.D.]: Geo- Sieh, K., Jones, L., Hauksson, E., Hudnut, K., Eberhart-Phillips, no. 10, p. 1257–1295, https://doi.org/10.1130/0016-7606 logical institute of China Seismological Bureau, 220 p. (in D., Heaton, T., Hough, S., Hutton, K., Kanamori, H., Lilje, (2002)114<1257:THOTAT>2.0.CO;2. Chinese). A., Lindvall, S., Mcgill, S.F., Mori, J., Rubin, C., Spotila, Yin, A., Dang, Y.Q., Wang, L.C., Jiang, W.M., Zhou, S.P., Chen, Zheng, W.J., Zhang, P.Z., He, W.G., Yuan, D.Y., Shao, Y.X., J.A., Stock, J., Thio, H.K., Treiman, J., Wernicke, B., and X.H., Gehrels, G.E., and McRivette, M.W., 2008a, Ceno- Zheng, D.W., Peng, G.W., and Min, W., 2013, Transfor- Zachariasen, J., 1993, Near-field investigations of the zoic tectonic evolution of Qaidam basin and its surround- mation of displacement between strike-slip and crustal landers earthquake sequence, April to July 1992: Sci- ing regions (Part 1): The southern Qilian Shan-Nan Shan shortening in the northern margin of the Tibetan Plateau: ence, v. 260, no. 5105, p. 171–176, https://doi .org/10.1126 thrust belt and northern Qaidam basin: Geological Soci- Evidence from decadal GPS measurements and late Qua- /science.260.5105.171. ety of America Bulletin, v. 120, no. 7-8, p. 813–846, https:// ternary slip rates on faults: Tectonophysics, v. 584, no. 1, Tapponnier, P., and Molnar, P., 1977, Active faulting and doi.org/10.1130/B26180.1. p. 267–280, https://doi.org/10.1016/j.tecto.2012.01.006. tectonics in China: Journal of Geophysical Research, Yin, A., Dang, Y.Q., Zhang, M., Chen, X.H., and McRivette, Zuza, A.V., Cheng, X.G., and Yin, A., 2016, Testing models v. 82, no. 20, p. 2905–2930, https://doi.org/10.1029 M.W., 2008b, Cenozoic tectonic evolution of the Qaidam of Tibetan Plateau formation with Cenozoic shortening /JB082i020p02905. basin and its surrounding regions (Part 3): Structural estimates across the Qilian Shan-Nan Shan thrust belt: Tapponnier, P., Zhiqin, X., Roger, F., Meyer, B., Arnaud, N., Wit- geology, sedimentation, and regional tectonic recon- Geosphere, v. 12, no. 2, p. 501–532, https://doi.org/10 tlinger, G., and Jingsui, Y., 2001, Oblique stepwise rise struction: Geological Society of America Bulletin, v. 120, .1130/GES01254.1. and growth of the Tibet Plateau: Science, v. 294, no. 5547, no. 7-8, p. 847–876, https://doi.org/10.1130/B26232.1. Zuza, A.V., Chen, W., Reith, R.C., Yin, A., and Liu, W., 2018, p. 1671–1677, https://doi.org/10.1126/science.105978. Yu, J., Zheng, W., Kirby, E., Zhang, P., Lei, Q., Ge, W., Wang, W., Taylor, M., and Yin, A., 2009, Active structures of the Himala- Li, X., and Zhang, N., 2016, Kinematics of late Quaternary Tectonic evolution of the Qilian Shan: An early Paleozoic yan-Tibetan orogen and their relationships to earthquake slip along the Yabrai fault: Implications for Cenozoic tec- orogen reactivated in the Cenozoic: Geological Society distribution, contemporary strain field, and Cenozoic vol- tonics across the Gobi Alashan block, China: Lithosphere, of America Bulletin, v. 130, no. 5/6, p. 881–925, https:// canism: Geosphere, v. 5, no. 3, p. 199–214, https://doi .org v. 8, no. 3, p. 199–218, https://doi.org/10.1130/L509.1. doi.org/10.1130/B31721.1. /10.1130/GES00217.1. Yu, J.-X., Zheng, W.-J., Zhang, P.-Z., Lei, Q.-Y., Wang, X.-L., Wallace, K., Yin, G., and Bilham, R., 2004, Inescapable slow Wang, W.-T., Li, X.-N., and Zhang, N., 2017, Late Quater- MANUSCRIPT RECEIVED 11 JUNE 2019 slip on the Altyn Tagh Fault: Geophysical Research Let- nary strike-slip along the Taohuala Shan-Ayouqi fault REVISED MANUSCRIPT RECEIVED 28 SEPTEMBER 2019 ters, v. 31, no. 9, https://doi.org/10.1029/2004GL019724. zone and its tectonic implications in the Hexi Corridor MANUSCRIPT ACCEPTED 14 NOVEMBER 2019

Geological Society of America | LITHOSPHERE | Volume 12 | Number 1 | www.gsapubs.org 39

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/12/1/19/4952161/19.pdf by guest on 25 September 2021