活断層・古地震研究報告，No. 4, p. 243-264, 2004
Rupture geometry and multi-segment rupture of the November 2001 earthquake in the Kunlun fault system, northern Tibet, China
Bihong Fu1, Yasuo Awata2, Jianguo Du3 and Wengui He4
1, 2Active Fault Research Center, GSJ/AIST ([email protected], [email protected]) 3Institute of Earthquake Science, CEA ([email protected]) 4Lanzhou Institute of Seismology, CEA ([email protected])
Abstract: We document the spatial distribution and geometry of surface rupture zone produced by the
2001 Mw 7.8 Kunlun earthquake, based on high-resolution satellite images combined with the field measurements. Our results show that the 2001 surface rupture zone can be divided into five segments according to the geometry of surface rupture. They are the Sun Lake, Buka Daban-Hongshui River, Kusai Lake, Hubei Peak and Kunlun Pass segments from west to east. These segments, varying from 55 to 130 km in length, are separated by step-overs or bends. The Sun Lake segment extends about 65 km with a strike of N45º-75ºW (between 90º05'E-90º50'E) along the previously unrecognized West Sun Lake fault. A gap about 30 km long exists between the Sun Lake and Buka Daban Peak where no obvious surface ruptures can be observed either from the satellite images or the field observations. The Buka Daban-Hongshui River, Kusai Lake, Hubei Peak and Kunlun Pass segments run about 365 km striking N75º-85ºW along the southern slope of the Kunlun Mountains (between 91º07'E-94º58'E). This segmentation of the 2001 surface rupture zone is well correlated with the pattern of slip distribution measured in the field; that is, the abrupt changes of slip distribution occur at segment boundaries. Detailed mapping suggest that these five first-order segments can be divided into over 20 second-order segments with the length of 10-30 km, linked by small-scale step-overs or bends. We re-measure the total rupture length produced by the 2001 Kunlun earthquake based on the high precision mapping. It shows that the total length is about 430 km (excluding the 30 km long gap), which is the longest among the intraplate earthquakes ever reported worldwide. On the basis of rupture geometry and segmentation, and slip distribution along the surface rupture zone, we suggest a multiple bilateral rupture propagation model. Our model shows that the faulting process of the 2001 Kunlun earthquake is quite complex, which consists of multiple westward and eastward rupture propagations, and interaction of these bilateral rupture processes. It is much more complex than the simple unilateral rupture process suggested by previous studies.
Keywords: satellite imagery; surface rupture; geometric feature; multi-segment earthquake; step-over and bend; strike-slip faulting; bilateral propagation; great intraplate earthquake; India-Eurasia collision; northern Tibet.
1. Introduction fault of the Kunlun fault system, northern Tibet (Fig. 1; Lin et al., 2002). Immediately after the earthquake, Most large earthquakes in historical time ruptured only several multidisciplinary research teams from China a part of long active faults (Ambraseys, 1970; Barka and Seismological Bureau (CSB), and Institute of Kadinsky-Cade, 1988; Stein et al., 1997). Surface Geomechanics, Chinese Academy of Geological Sciences, ruptures often terminate at geometric or structural and Shizuoka University (Japan) conducted field changes in the fault zone (Allen, 1968; Barka and investigations on deformational characteristics of surface Kadinsky-Cade, 1988). Changes in fault strength, rupture zone and engineering damage. The preliminary geometry, and slip distribution may result in rupture results show that the Kunlun earthquake produced a long segmentation (e.g., Ward, 1997; Zhang et al., 1999; Awata surface rupture zone with a length of ~350 km (CSB, et al., 2001). This segmentation is manifested by 2002; 2003; Dang and Wang, 2002; Xu et al., 2002) or consistent spatial and temporal rupture behavior that may ~400 km (Lin et al., 2002; Fu and Lin, 2003). The typical be used to forecast the timing and magnitude of future lateral slip is 3 to 7 m (Xu et al., 2002; Fu et al., 2003; events (e.g., Schwartz and Coppersmith, 1984; Van der 2004a), and the largest one is up to 16.3 m (Lin et al., Woerd et al., 1998). 2002). Field investigations also indicate that the surface The Kunlun earthquake, of moment magnitude (M w) 7.8, rupture zone is composed of distinct shear faults, occurred on 14 November 2001 along the Kusai Lake extensional cracks, mole tracks, and pull-apart sag ponds.
243 Bihong Fu, Yasuo Awata, Jianguo Du, Wengui He
The width of surface rupture zone ranges from several the surface rupture zone to obtain detailed deformational meters to 1000 m, generally from 5 m to 50 m (Fu et al., and geometric features of the surface rupture zone. 2003, 2004a). This earthquake also triggered avalanches of snow and glacial ice and caused slight damage to the 3. Late Quaternary activity and seismicity of the base of the Qinghai-Tibet railway and road between Kunlun fault system Golmud and Lhasa. Ground shaking collapsed temporary The Tibetan Plateau is one of the most imposing housing for workers on the railway (Fu et al., 2003). topographic features on the earth surface (Fig. 1a), having Up to now, there is no detailed report on the geometry a mean elevation of ~4500 m, which was resulted from of surface rupture zone. The surface rupture occurred on India-Eurasia collision (Molnar and Tapponnier, 1975; the Kunlun Mountains with an elevation over 4500 m, 1978; Peltzer et al., 1989). The E-W to WNW-ESE where detailed field mapping of the surface rupture is striking Kunlun fault system, extending about 1600 km difficult. Thus, it is difficult to document the entire between 86 geometry of surface rupture zone from the field mapping. ºE to 105ºE, is one of the largest strike-slip In this study, we shall document geometric and faults in the northern Tibet, China (Molnar and geomorphic features of the 2001 Kunlun surface rupture Tapponnier, 1975; Van der Woerd et al., 1998; SBPQ, zone based on detailed analysis of high-resolution satellite 1999). As a major strike-slip fault, it plays an important images combined with the data obtained from the field role in the eastward extrusion of Tibet plateau investigations. We shall also discuss rupture segmentation accommodate to northeastward shortening caused by the and rupture processes related to the 2001 seismic event. India-Eurasia convergence (Avouac and Tapponnier, 1993; Tapponnier et al., 2001). The main trace of the 2. Data and methods Kunlun fault system may be roughly divided into six principal faults, each 150-270 km long, on basis of the Satellite remote sensing technique has been geometry of fault trace and structural assemblage (Fig. demonstrated as a powerful tool for mapping coseismic 1b; Van der Woerd et al., 1998). The left-lateral strike-slip deformational features caused by large earthquakes (e.g., faulting of the Kunlun fault may have initiated since the Fu and Lin, 2003; Wright et al., 2004). Satellite remote early Pliocene or early Pleistocene (Kidd and Molnar, sensing data acquired by the American Landsat Thematic 1988; Fu and Awata, 2004). Analyses of satellite images, Mapper (TM) and Enhanced Thematic Mapper (ETM), cosmogenic surface dating and radiocarbon dating and the French Systeme Probatoire de 1’ Observation de 1a trench surveys suggested that the Kunlun fault is an active Terre (SPOT) High Resolution Visible (HRV) sensor, and left-lateral strike-slip fault with an average slip rate of the Japanese Advanced Spaceborne Thermal Emission 10-20 mm/yr in the Quaternary (Kidd and Molnar, 1988); and Reflection Radiometer (ASTER) currently provide or 11.5 ± 2 mm/yr in the past 40 kyr (Zhao, 1996; Van der important sources for earth surface mapping. Landsat Woerd et al., 1998; 2000). TM/ETM have 15 to 30 m ground resolution, whereas Three large earthquakes (M > 7.0) including the 14 ground resolutions of SPOT HRV Panchromatic (PAN) November 2001 Mw 7.8 Kunlun earthquake occurred and ASTER data in Visible and Near Infrared (VNIR) along the Kunlun fault system during the last 100 years. region are 10 m and 15 m, respectively. Pre-earthquake The 18 November 1997 Manyi earthquake with Mw 7.6 (during 1998 to 2000) and post-earthquake (from late broke the western-most 170-km-long Manyi fault between November, 2001 to May, 2002) satellite remote sensing 86º30’E and 88º30’E (Fig. 1b). Maximum left-lateral data covering the western part of the Kunlun fault system displacement is ~7 m for the Manyi earthquake as are used in this study. The rupture zone can not be revealed by synthetic aperture radar (SAR) interferometry distinguished clearly from post-earthquake satellite (Peltzer et al., 1999). The 1937 Ms 7.5 Tuosuo Lake images obtained after June 2002 because the surface earthquake produced rupture zone about 300-km-long rupture zone was eroded by summer snow and ice between 96ºE and 99ºE on the Tuosuo Lake fault with a meltwaters. In addition, to analyze geometry of the 2001 maximum left-lateral offset of 6-7 m (Jia et al., 1988; Fig. surface rupture in detail we use post-earthquake 1b). No historical record of earthquakes had been reported American IKONOS data with 1 m resolution for post- along the Kusai Lake and Xidatan-Dongdatan faults earthquake period for some key regions. although there are geomorphic features associated with These multi-source satellite remote sensing data were seismic activities (Kidd and Molnar, 1988; Van der Woerd geometrically corrected and processed using ER-Mapper. et al., 1998; 2000). Based on the trenching survey, it has Image mosaic, contrast stretch and band composition been inferred that recurrence interval of great earthquakes were used to enhance imagery feature of the surface in the Xidatan-Dongdatan fault is 850 ± 200 yr with a rupture zone. Above-mentioned satellite remote sensing characteristic slip of 10 ± 2 m (Zhao, 1996; Van der data provide an excellent view of the 2001 Kunlun Woerd et al., 1998; 2000; 2002). earthquake surface rupture. Satellite images at different scales (1/5,000 to 4. Geometry and segmentation of the 2001 surface 1/100,000) are used to interpret the geometric and rupture zone geomorphic features of the 2001 rupture zone. Moreover, we carried out the field investigation several times along In the satellite image, the trace of Kusai Lake and
244 Rupture geometry and multi-segment rupture of the November 2001 earthquake in the Kunlun fault system, northern Tibet, China
Kunlun Pass faults exhibit striking lineaments (Fig. 2a). tail pattern occurred on the moraine deposits on the The 2001 surface rupture zone distributes mostly along southeast of the Buka Daban Peak (Figs. 6b and 7a). The the pre-existing Kusai Lake and Kunlun Pass faults. We IKONOS image exhibits the left-stepping geometry of can divide the surface rupture zone into five first-order major rupture zone, and the stream across the rupture segments according to their geometric and structural zone is displaced left-laterally (Fig. 7b). Northeastward, features (Fig. 2b). They are the Sun Lake, Buka Daban- the rupture bends into N80ºW (Fig. 6b). The Buka Daban- Hongshui River, Kusai Lake, Hubei Peak, and Kunlaun Hongshui River segment is further divided into 5 to 6 Pass segments from west to east, respectively. These first second-order segments, each 20-30 km long, order segments, each 55 to 130 km long, are linked by 5 interconnected by small-scale bends or step-overs (Fig. to 30 km long and 1 to 10 km wide step-overs or bends 6b). These small bends or step-overs, 1-3 km long and (Figs. 3, 6, 8a, 9, 10a, 12, 13). The detailed geometry of several hundreds meters wide, appear as the pressure- each segment is summarized as follows. ridges on satellite image (Fig. 6a).
4.1 The Sun Lake Segment 4.3 The Kusai Lake Segment The Sun Lake segment extends ~65 km between the To the east of the Hongshui River, the rupture zone is Kushuiwan Lake (90º05’E) and east bank of the Sun Lake called the Kusai Lake segment (Fig. 2b). There is a large (90º50’E, Fig. 3). This segment can be further divided step-over, ~10 km long and 1 km wide, between the Buka into four second-order segments, each 10 to 20 km long Daban-Hongshui River and Kusai Lake segments (Figs. (Fig. 3b). It is the westernmost part of the 2001 November 6b and 8a). The IKONOS image clearly shows that the rupture zone (Zhao et al., 2002) and strikes N40º-75ºW ruptures consist of third-order segments, each several (Fig. 3). Typical lateral offset is 1 to 3 m as observed in hundreds meters long, which are linked by small step- the field (Zhao et al., 2002). At the westernmost overs or bends (Fig. 8b). The pressure ridges are formed termination of the Sun Lake segment, some N70º-75ºW in these small-scale bends or step-overs (Fig. 8b). The striking fissures and a N10ºW extending pressure ridge Kusai Lake segment extends 55 km between 92º15’E and occurred in the frozen surface of the Kushuiwan Lake (Fig. 92º48’E. This segment also can be further divided into 4a). On the east bank of the Kushuiwan Lake, two five second-order segments by small-scale step-overs or distinctive surface ruptures appear right-stepping pattern bends (Fig. 9b). There are large-scale half-graben and (Fig. 4a). The ruptures show a right-stepping en echelon pressure ridges, several kilometers long and several arrangement in the central part of the Sun Lake segment. hundreds meters wide, linking these second-order Eastward to the south of Peace Island, rupture zone splays segments (Fig. 9b). A segment boundary is just located on into two distinctive ruptures (Fig. 3b). The southern the northeast of Kusai Lake (Fig. 9b), where the ruptures branch runs about 3 km striking N45ºW, and northern display a complex geometry, appearing flat-lying Y-shape branch continuously extends towards the Sun Lake with a pattern (Fig. 10a). In the field, a striking rupture zone strike of N65ºW (Figs. 4b and 5a). Large-scale IKONOS passes through northeast of the Kusai Lake (Fig. 10b). image shows that the third-order rupture segments (a, b, c, d, e, f, and g in Fig. 5a), each several hundreds meters to 2 4.4 The Hubei Peak Segment km long, display a typical right-stepping en echelon The Hubei Peak segment distributes to the south of the pattern (Fig. 5a). In the field, the striking rupture zone Kunlun range, where several ice-capped high peaks stand occurs on the late Quaternary alluvial fans (Fig. 5b). over 5500 m. The length of this segment is about 70 km Farther east to the west of the Sun Lake, three major with a strike of N75º-85ºW between 92º48’E and 93º40’E ruptures developed in the frozen surface of the Sun Lake, (Fig. 9b). The rupture zone cut the pre-Quaternary which display as a tail pattern (Figs. 3b and 4b). These basement rocks and Quaternary fluvial fans (Fig. 9b). ruptures terminate on the eastern bank of the Sun Lake Again, the Hubei Peak segment is divided into 5 to 6 near 90º50’E (Fig. 3b). There is an about 30 km long gap second-order segments, each 10 to 30 km long (Fig. 9b). between the Sun Lake and Buka Daban-Hongshui River The small step-overs and bends, 1-3 km long and several segments, which display a left-stepping pattern (Figs. 2b hundreds meters wide, link those second-order segments and 3b). No obvious surface ruptures can be observed (Fig. 11). To the east of this segment, the rupture zone from the satellite images or field investigations. It may be consists of several sub-parallel ruptures with several a large unbroken barrier between the Sun Lake and Buka hundreds meters separation (Fig. 9b), where the widest Daban-Honshui River rupture segments, where the step- surface deformation zone was observed in the field (Lin et over shows a large pull-apart basin (Fig. 3). al., 2002; Xu et al., 2002). To the east of 93º30’E, the rupture zone splays into two branches: the northern one 4.2 The Buka Daban -Hongshui River Segment extends along the pre-existing Xidatan-Dongtatan fault of The trace of the Buka Daban-Hongshui River segment the Kunlun fault system, and it terminates near 93º40’E, runs 110 km between the southeast Buka Daban Peak whereas the southern branch continuously runs eastward (91º07’E) and Hongshui River (92º18’E) with a strike of (Fig. 9b). These two splaying ruptures appear as a left N75º-80ºW (Fig. 6). In the westernmost part of this step-over, which forms a boundary between the Hubei segment, the rupture zone trends N45ºE and three left- Peak and Kunlun Pass segments (Figs. 12 and 13). stepping en-echelon arranging ruptures display a horse-
245 Bihong Fu, Yasuo Awata, Jianguo Du, Wengui He
4.5 The Kunlun Pass Segment few kilometers long. Similarly, the surface rupture The trace of the Kunlun Pass segment runs mostly segments with different scales might be products of along the pre-existing Kunlun Pass fault, extending more rupture events or sub-events with different scales (e.g., than 130 km in length between 93º35’E and 94º58’E (Fig. DePolo et al., 1991; Awata et al., 2001). 13). This segment can be also separated into 6 to 7 Our mapping also exhibits that step-overs or bends with second-order segments, 10-30 km long (Fig. 13 b). The different scales exist at segment boundaries (Figs. 3b, 4, surface rupture starts at south of 5933 m high peak, 5a, 6b, 8, 9b, 10a, 11, 12 and 13b). These step-overs and passes through the north of the Kunlun Pass, and bends are very important features that control the process continues to farther east. On the southern slope of Yuzhu of rupture initiation, propagation and termination (e.g., Peak, the rupture zone runs across the modern glaciers Segall and Pollard, 1980; King and Nabelek, 1985; Zhang (Fig. 13). Detailed geometry of the eastern part of the et al., 1999). They not only reflect structural and Kunlun Pass segment can be clearly observed in the large- geomorphic changes of fault geometry on the surface, but scale post-earthquake SPOT image (Fig. 14a). Near the also represent variations of mechanical fault movement at easternmost end of this segment, the rupture zone splays depth (e.g., Schwartz and Coppersmith, 1984; Ward, 1997; into two major zones at point B, which display a flat-lying Sugiyama et al., 2002). Formation mechanism of step- Y-shape pattern as shown on the SPOT image (Fig. 14a). over and bend and their geomorphic features had been The northern one extends straightly eastward, and noted by a number of previous studies (e.g., King, 1986; terminates near 94º55’E (point C in Fig. 14a). The Dooley and McClay, 1997; McClay and Bonora, 2001). At southern one bends southeastward and appears as a horse- these segment boundaries, the slip distribution along the tail pattern (Fig. 14a). Finally, the surface rupture zone rupture zone shows an abrupt change (Fig. 15b). Thus, disappears near 94º58’E (point E in Fig. 14a). At the multi-segment geometry pattern of the surface rupture easternmost end of the Kunlun Pass segment, the ruptures zone might record the processes of fault nucleation, slip, consist of the right-stepping cracks with a strike of N60º- linkage and propagation (Schultz, 1999; Aydin and 65ºE as observed in the field (Fig. 14b). Kalafat, 2002). Comparing the analysis of geometry of the surface 5. Discussion rupture zone and pattern of slip distribution with the seismic data, we suggest a model to explain the faulting 5.1 Linkage among segment geometry, slip processes or rupture propagation during the 2001 distribution and rupture process November earthquake (Fig. 15c). As indicated by seismic It is a timely topic how to link the relations among waveform inversion, the 2001 M 7.8 Kunlun earthquake segment geometry, surface displacements, and rupture w may consist of three major sub-events (Lin et al., 2003; propagation process of the long seismogenic faults (e.g., Xu and Chen, 2004). Our model shows that the 2001 Schultz, 1999; Phillips et al., 2003). Our results show that Kunlun seismic event has a complex multiple rupture the surface rupture zone, produced by the 2001 M w 7.8 process (Fig. 15c). In our model, the rupture started near Kunlun earthquake, has a multi-segment pattern as 90º30’E, which is consistent with the epicenter location described in the section 4 (Fig. 15a). The surface rupture reported by the USGS (Fig. 15b), and it propagated zone is geometrically segmented at a variety of scales bilaterally eastward and westward. Westward rupture (Figs. 2b, 3b, 6b, 9b, and 13b). It can be divided into five terminated on the Kushuiwan Lake near 90º05’E (Fig. first-order segments, individual segment length varying 15c). The seismic moment of first sub-event is equal to an 55 km to 130 km. These first-order segments are M 6.9 shock as revealed by seismological data (Antolik separated by the step-overs 5-30 km long and 1-10 km w et al., 2004). Eastward rupture passed through the Sun wide or bends (Fig. 15a). Meanwhile, these first-order Lake, and then jumped onto the main trace of the Kusai surface rupture segments are subdivided into over 20 Lake fault at 91º07’E in the southeast of the Buka Daban second-order segments of 10 to 30 km long by smaller Peak (Figs. 7a and 15c). The second sub-event occurred step-overs or bends (Figs. 3, 6, 9 and 13). Moreover, even near 92º15’E, which is similar with location of Harvard smaller-scale third-order segments, each several hundreds Moment Centriod (Bufe, 2004). The second sub-event is a meters to 3 km long, can be identified either from high- major rupture event, which is equal to an M 7.8 event resolution satellite images (Figs. 5a, 7b and 8b) or field w (Antolik et al., 2004). The rupture from the second sub- observations (Fu et al., 2003). A number of studies have event continuously propagated eastward and passed demonstrated that faults are geometrically and through the Kusai Lake and south slope of the Kunlun mechanically segmented at variety of scales (e.g., Allen, Range. It triggered the third sub-event near 93º00’E (Fig. 1968; Allen et al., 1991; Wallace, 1970; 1990). For 15c), which is the same with the location of third sub- example, the number of segments identified for the San event suggested by Xu and Chen (2004). The seismic Andreas fault ranges from 4 to 984 (Allen, 1968; Wallace, moment of third sub-event is equal to an M 6.7 event 1970). As explained by Schwartz and Sibson (1989), w (Antolik et al., 2004). Then, it continuously propagated segments may represent the repeated coseismic rupture eastward along the Kunlun Pass fault, but the fracture during a single event on a long fault with tens to hundreds energy gradually dropped. Finally, it terminated near of kilometers, or they may represent a part of a rupture 94º58’E (Fig. 15c). Temporally, the second and third sub- associated with an individual faulting event and only a events occurred 52 and 56 seconds, respectively, after the
246 Rupture geometry and multi-segment rupture of the November 2001 earthquake in the Kunlun fault system, northern Tibet, China
first sub-event as revealed by seismological data (Xu and 6. Conclusions Chen, 2004). However, our model is different from the unilateral rupture process inferred from the inversion of Based on the detailed analyses of satellite images and seismic data (Lin et al., 2003; Antolik et al., 2004). Our field observations, we can conclude as follows: model suggests that rupture caused by the second sub- (1) The 2001 November surface rupture zone can be event also propagated westward. At the east of the Buka divided into five first-order segments according to the Daban Peak, the rupture propagated southwestward, and geometry of surface rupture zone. These first-order terminated near 91º07’E (Figs. 3b and 15c). It can segments, each 55 to 130 km long, are linked by large reasonably explain the complex geometry pattern of step-overs and bends. These first-order segments are surface rupture zone in the southeast of the Buka Daban further divided into over 20 second-order segments, each peak (Fig. 7). It should be noted that a 30 km long rupture 10 to 30 km long, by smaller step-overs and bends. gap exists between the Sun Lake and Buka Daban- (2) Rupture propagation process associated with the Hongshui River segments (Fig. 3b). It probably is an 2001 Kunlun earthquake is quite complex. It suggested unbroken barrier (Aki, 1984). that multi-segment geometry of the 2001 Kunlun rupture zone is a product of the multiple westward and eastward rupture propagation, and interaction of these bilateral 5.2 Length of the surface rupture rupture propagation, which is consistent with rupture It remains a debate about the length of the 2001 Kunlun process of three major sub-events suggested by surface rupture zone. For example, Xu et al. (2002) seismological research. reported a ~350 km long rupture zone extending between (3) High precision measurement shows that total length 91º07’E-94º48’E. The high-precision mapping of satellite of surface rupture zone is ~430 km, which is the longest images clearly indicate that the five first-order rupture one among the intraplate earthquakes ever reported segments are 65 km, 110 km, 55 km, 70 km and 130 km worldwide. for the Sun Lake, Buka Daban-Hongshui River, Kusai In general, the analyses of the 2001 surface rupture Lake, Hubei Peak and Kunlun Pass segments, respectively zone provide new insights into the complex multi-segment (Figs. 3b, 6b, 9b and 13b). Thus, the total length of the geometry and multiple bilateral rupture propagation surface rupture zone should be ~430 km (excluding a 30 associated with a great intraplate earthquake along a long km long gap). This spatial distribution of surface rupture strike-slip fault. zone has also been confirmed by the field observations (Figs. 5b, 10b and 14b; Zhao et al., 2002; Fu et al., 2004a), Acknowledgements and it is also consistent with the distribution of aftershocks (Fig. 15a). The previous reported longest This study benefited from discussion with A. Lin, K. surface rupture zone is 375 km long, which was produced Kano, E. Tsukuda, Y. Sugiyama, X. Lei, M. Saito and H. by 1905 M 8.2 Bulnay, Mongolia, earthquake (Yeats et Sekiguchi. We thank K. Satake for his constructive al., 1997). The surface rupture zone produced by the 2001 comments and careful review, which are helpful to Mw 7.8 Kunlun earthquake is, therefore, the longest improve this manuscript. ASTER data were provided by rupture zone produced by a single intraplate earthquake the Earth Remote Sensing Data Analysis Center ever reported worldwide. (ERSDAC), Japan. We also used the DEM data released by USGS Shuttle Radar Topography Mission (SRTM) 5.3 Implications for future earthquakes along the Project in Fig. 1a. Especially, we are grateful to Kunlun fault Seismological Bureau of Xinjiang for the permission to The previous studies have demonstrated that the use one photograph (Fig. 5b). B. Fu would like to segment boundaries linking the fault segments are acknowledge the support from Postdoctoral Fellowship (P unstable features and earthquake can easily occur near 03510) of Japan Society for the Promotion of Science the segment boundary (e.g., King and Nabelek, 1985; Fu (JSPS). et al., 2004b). Therefore, it should be noted that the 2001 Kunlun earthquake did not rupture the Xidatan- References Dongdatan segment of the Kunlun fault system (Figs. 13b Aki, K. (1984) Asperities, barriers, characteristic and 15a). It is a “seismic gap” between the 1937 Ms 7.5 earthquakes and strong motion prediction. J. 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caused by the Ms 8.1 earthquake west of the Kunlun 93, 2477-2492. Pass, China. Geol. Bull. China, 21, 105-108. (in McClay, K., and Bonora, M. (2001) Analog models of Chinese with English abstract). restraining stopovers in strike-slip fault systems. DePolo, C.M., Clark, D.G., Slemmons, D.B., and Ramelli, AAPG Bull., 85, 233-260. A.R. (1991) Historical surface faulting in the Basin Molnar, P., and Tapponnier, P. (1975) Cenozoic tectonics and Range Province, western North America: of Asia: Effects of continental collision. Science, implications for fault segmentation. J. Struct. Geol., 189, 419-426. 13, 123-136. Molnar, P., and Tapponnier, P. (1978) Active tectonics of Dooley, T., and McClay, K. (1997) Analog modeling of Tibet. J. Geophys. Res., 83, 5361-5375. pull-apart basins. AAPG Bull., 81, 1804-1826. Phillips, D.E., Haeussler, P.J., Freymueller, J.T., and other Fu, B., and Lin, A. (2003) Spatial distribution of the 26 authors (2003) The 2002 Denali fault earthquake,
surface rupture zone associated with the 2001 Ms 8.1 Alaska: A large magnitude, slip-partitioned event. Central Kunlun earthquake, northern Tibet, revealed Science, 300, 1113-1118. by satellite remote sensing data. Int. J. Remote Sens., Peltzer, G., Tapponnier, P., and Armijo, R. (1989) 24, 2191-2198. Magnitude of late Quaternary left-lateral Fu, B., Awata, Y., Kano, K., Lin, A., Tsukuda, E. (2003) displacements along the north edge of Tibet. Science, Coseimsic surface deformation and engineering 246, 1285-1289. damage associated with the large strike-slip faulting: Peltzer, G., Grampe, F., King, G. (1999) Evidence of
Lessons from the 2001 Mw 7.8 Central Kunlun nonlinear elasticity of the crust from the Mw 7.6 earthquake. Ann. Report on Active Fault and Manyi earthquake. Science, 286, 272-276. Paleoearthq. Res., 3, 191-209. Schultz, R.A. (1999) Understanding the process of
248 Rupture geometry and multi-segment rupture of the November 2001 earthquake in the Kunlun fault system, northern Tibet, China
faulting: selected challenges and opportunities at the M. W., Zhao, G., and Xu, Z. (2002) Uniform edge of the 21st century. J. Struct. Geol., 21, postglacial slip- rate along the central 600 km of the 985-993. Kunlun fault (Tibet), from 26Al, 10Be, and 14C dating Schwartz, D.P., and Sibson, R.H. (1989) Fault of riser offsets, and climatic origin of the regional segmentation and controls of rupture initiation and morphology. Geophys. J. Int., 148, 356-388. termination. U.S. Geological Survey Open File Wallace, R.E. (1970) Earthquake recurrence intervals on Report 89-315, 447p. the San Andreas fault. Bull. Seismol. Soc. Am., 81, Schwartz, D.P., and Coppersmith, K.J. (1984) Fault 2875-2890. behavior and characteristic earthquakes: examples Wallace, R.E. (1990) Geomorphic expression. In: Wallace, from the Wasatch and San Andreas fault zones. J. R.E. (Eds.), The San Andreas Fault System, Geophys. Res., 89, 5681-5698. California, U.S. Geological Survey Professional Segall, P., and Pollard, D.D. (1980) Mechanics of Paper 1515, pp.15-58. discontinuous faults. J. Geophys. Res., 85, Ward, S.N. (1997) Dogtails versus rainbows: synthetic 4337-4350. earthquake rupture models as an aid in interpreting Seismological Bureau of Qinghai Province and the geological data. Bull. Seismol. Soc. Am., 87, Institute of Crustal Dynamics, China Seismological 1422-1441. Bureau (SBQP) (1999) Eastern Kunlun Active Fault Wright, T.J., Parsons, B.E., and Lu, Z. (2004) Toward Zone. Seismological Press, Beijing, 186 p. (in mapping surface deformation in three dimensions Chinese with English abstract). using InSAR. Geophys. Res. Lett., 31, L01607. Stein, R.S., Barka, A.A., and Dietrich, H.J. (1997) Xu, L., and Chen, Y. (2004) Temporal and spatial rupture Progressive failure on the North Anatolian fault process of the great Kunlun earthquake of November since 1939 by earthquake stress triggering. Geophys. 14, 2001 from the Gdsn long period waveform data. J. Int., 128, 594-604. Science in China (Ser.D), 34, 256-264 (in Chinese). Sugiyama, Y., Sekiguchi, H., and Awata, Y. (2002) Xu, X., Chen, W., Yu, G., Ma, W., Dai, H., Zhang, Z., Correlation analysis between active fault parameters Chen, Y., He, W., Wang, Z. and Dang, G. (2002) and heterogeneous source characteristics. In: Study Characteristic features of the surface ruptures of the
on the Master Model for Strong Ground Motion Huh Sai Hu (Kunlunshan) earthquake (Ms 8.1), Prediction toward Earthquake Disaster Mitigation, northern Tibetan Plateau, China. Seismology and pp.37-42 (in Japanese with English abstract). Geology, 24, 1-13 (in Chinese with English abstract). Tapponnier, P., Xu, Z., Roger, F., Meyer, B., Arnaud, N., Yeats, R.S., Seih, K., and Allen, C.R. (1997) The geology Wittlinger, Yang, J. (2001) Oblique stepwise rise and of earthquakes. Oxford University Press, New York, growth of the Tibet Plateau. Science, 294, 1671-1677. 568 p. Van der Woerd, J., Ryerson, F. J., Tapponnier, P., Zhang, P., Mao, F., and Slemmons, D. B. (1999) Rupture Gaudemer, Y., Finkel, R.C., Meriaux, A.S., Caffee, termination and size of segment boundaries from M. W., Zhao, G., and He, Q. (1998) Holocene left historical earthquake ruptures in the Basin and slip-rate determined by cosmogenic surface dating Range Province. Tectonophysics, 308, 37-52. on the Xidatan segment of the Kunlun Fault (Qinghai, Zhao, G. (1996) Quaternary faulting in the north Qinghai- China). Geology, 26, 695-698. Tibet Plateau. Earthquake Research in China, 12, Van der Woerd, J., Ryerson, F. J., Tapponnier, P., Meriaux, 107-119 (in Chinese with English abstract). A.S., Gaudemer, Y., Meyer, B., Finkel, R.C., Caffee, Zhao, R., Li, J., Xiang, Z., Ge, M., and Luo, G. (2002) M. W., Zhao, G., and Xu, Z. (2000) Uniform slip- Expedition of the west segment of the surface
rate along the Kunlun Fault: Implications for seismic rupture zone of the Ms = 8.1 earthquake in the west behavior and large-scale tectonics. Geophys. Res. of Kunlun Pass. Inland Earthquake, 16, 175-179 (in Lett., 27, 2353-2356. Chinese). Van der Woerd, J., Tapponnier, P., Ryerson, F. J., Meriaux, A.S., Meyer, B., Gaudemer, Y., Finkel, R.C., Caffee, (Received 19 August 2004, Accepted 5 October 2004)
249 Bihong Fu, Yasuo Awata, Jianguo Du, Wengui He 1 m u 0 u e t 0 o m o s E 2 h h k o y z z e s 4 h n n 0 t t 0 l a a 4 f u 1 L L a o 2 f r e n t u n l e 6 n c u i p K e e s s e g h g o t h n n r r n n i i 2 i f i T e e 0 o a a n . n v i v i t t y 1 i l n X X n n e o R i v u u t
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250 Rupture geometry and multi-segment rupture of the November 2001 earthquake in the Kunlun fault system, northern Tibet, China
a N
Golmud Buka Daban Peak 6860m 36oN
USGS & ERI Kunlun Pass
90o 92o 94oE b N er Riv Fiig.. 3 i u Gollmmuudd h Fig. 6 s g n 6860 m o H Fig. 9 SL Seg. BK-HR Seg. KL Seg. HB Seg . Fiig.. 13 K 6056 m KP Seg.. Xidattaann Sun 5805 m 5863 m Lake Kusai Kekexili Kunlun Lake 6178 m Lake Pass
0 100 km
Quaternary and Active strike- Pre-Tertiary Rupture zone Ice-cap Lake Tertiary rocks rocks slip fault
Fig. 2. (a) Landsat ETM mosaic image of the Kusai Lake and Kunlun Pass faults of the Kunlun fault system. Fault traces indicated by arrows.
The epicenter and focal mechanism of the 2001 Mw 7.8 Kunlun earthquake were determined by the USGS and Earthquake Research Institute (ERI) of the University of Tokyo, respectively. (b) Spatial distribution of the surface rupture zone produced by the 2001 Kunlun earthquake (Modified after Fu and Lin, 2003). SL Seg.: Sun Lake segment; BK-HR Seg.: Buka Daban-Hongshui River segment; KL Seg.: Kusai Lake segment; HB Seg.: Hubei Peak segment; KP Seg.: Kunlun Pass segment.
251 Bihong Fu, Yasuo Awata, Jianguo Du, Wengui He t g n n d e o n l a - m t g m s e r N N o k N i s f r 0 f e 3 o d r a y o r - s . a i d d n g e n r o u e e c o h e S t B s t a R h t H a e - t o 7 K . N B . g l e i e n m n F o a n z e a r t e h r S c u t p u r ' ' e 0 c 0 e a 0 f p k 0 o r o a a u 1 L 1 s 9 G f 9 o n t r m n a a m a r b 0 p b e 0 k a 6 t i k a s 6 c a 8 D e a a 8 l e D 6 e w g a 6 P a k P e & k h u t w u B f o B n o S y r t e m o e g e g n i n i a r w o o e M h k s a p L a e m n k . u e a b v S i 2 L t t l . a u t g a i ) e f r F n S e p e r v u i e e t b G t s c S n 4 S A n I . o ) i U t g b ( ' ( a i ' e c 0 . 0 d ) c F o 3 l n 2 3 a o r o 0 a e l 0 o 0 0 s P F 2 e 9 I 9 . n , s o 6 e z 1 l m m g t e r s n 1 1 u u a t i 8 8 g p r 9 9 t u u 4 4 R A w ( o t l l n e e y m y g b . e s y d g r e e a t e k n a r a c S e i t L d a L n n u i u S Q s S - m m E k ' e c e r 7 k k o h 0 P r t ° 0 0 f 1 2 2 o 9 e d a g n n 4 a a . a m m E i ' g w n 0 4 i y i e r a 5 s 0 M t u ° a k F 0 n w T 0 n h e i a r e 6 9 E s e k u L t m t n i u a a h a e d s u L K s e e d Q s u w n t a K E e ' E L ' b N 0 N ) ' 0 ' p a 0 a 0 ( 0 0 o g o . 0 0 0 3 o 0 o 9 . b a 6 9 0 0 6 g i 3 3 F
252 Rupture geometry and multi-segment rupture of the November 2001 earthquake in the Kunlun fault system, northern Tibet, China
a N
0 5 km
b
Fig.5a
Fig.5b
0 5 km
Fig. 4. Post earthquake (January 05, 2002) ASTER images exhibiting geometry of the surface rupture zone. (a) Ruptures appearing as right-stepping en-echelon pattern in the westernmost termination. (b) Ruptures displaying a tail pattern in the Sun Lake. Locations of Figs. 4a and 4b are shown on Fig. 3a.
253 Bihong Fu, Yasuo Awata, Jianguo Du, Wengui He
a N
a b c d e f
0 1 km
b SES
Sun Lake
Fig. 5. (a) IKONOS image (September 24, 2002) showing detailed features of surface ruptures to west of the Sun Lake. For location see Fig. 4b. (b) Photograph showing a distinctive rupture in west bank of the Sun Lake (provided by Seismological Bureau of Xinjiang, CSB) .
254 Rupture geometry and multi-segment rupture of the November 2001 earthquake in the Kunlun fault system, northern Tibet, China . N N ' ' g 0 0 e 0 0 o o a o o S 8 6 6 . 3 3 L g i K F
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255 Bihong Fu, Yasuo Awata, Jianguo Du, Wengui He
91o05' o 91o10'E a N
Fig.7b
Moraine 36o00'N
0 1 km
b N
0 50 m
Fig. 7. (a) Post-earthquake (December 26, 2001) SPOT image showing tail pattern of surface rupture in the west end of Buka Daban-Hongshui River segment. For location see Fig. 3a or Fig. 6a. (b) IKONOS image (September 24, 2002) showing that the surface ruptures appear a right-stepping pattern in southeast of the Buka Daban Peak. For location see Fig. 7a.
256 Rupture geometry and multi-segment rupture of the November 2001 earthquake in the Kunlun fault system, northern Tibet, China
a R N i v e r
H
o
n
g
s
h
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i Fig.8b
0 2 km
b N
PR
0 500 m PR
Fig. 8. (a) IKONOS image (January 9, 2002) showing that the segment boundary between the Buka Daban-Hongshui River and Kusai Lake segments appears as a step-over, 10 km long and 500 m wide. (b) Enlarged IKONOS image showing the detailed geometric and geomorphic features of the ruptures. Note that the ruptures are separated by third-order step-overs or bends. PR: pressure ridge.
257 Bihong Fu, Yasuo Awata, Jianguo Du, Wengui He k a e P i N N e b u H d a n ' ' a 2 0 0 e 1 . 3 3 k o o a g i 3 3 L i 9 9 F a s b u 1 K 1 . e h g t i f F o y r t e m m a o 6 e 1 4 g 1 6 . g 5 n g i i t i F b t i n h d e x n e . a m p t g g a s e r e i s f m r f S e e o v d i r y t r B o a t - a e d d H r n n p o u r c e o t e B n s I r ) e i b ( c . a ' ' l l s t e g 0 0 m n n m 0 0 a e & n o o i e 9 a r m k e 3 3 w t h 6 g a o b 9 9 S c e 7 e n u s 5 S P H k a e P e i k e b a p u r L a H a c d s 0 . n b 1 n a . 2 o e i e . g k s k i g a o i a r L F i i F L E a i a e a e s s s s u u u n K K K o i t e a h t c o f l o e r t s n l o e o u F r . z a . u f t e e l g a r n a e u e o f t m z p r c S i e u o r h R N u p L t r p o K u r m o e e E E c ' ' g a f 0 0 r g 3 3 u n o o i s 2 2 y w c r i o 9 9 a h m n s r s y m m i r e s e e t t k k a g s a n n a o r u e 0 0 c e m Q s t m i i - 1 2 2 k a d e c 0 c u r i e 0 o a P r Q s 2 s o e h m t e f t o i l l s t e t n a e S m ) g a e ( N N ' ' ' ' s . 0 0 0 0 9 4 4 . 5 5 o o o o g i 5 5 5 5 a b F 0 0 3 3 3 3
258 Rupture geometry and multi-segment rupture of the November 2001 earthquake in the Kunlun fault system, northern Tibet, China
a N
Fig.10b
Kusai Lake
0 5 km
b S
Kusai Lake
Fig. 10. (a) ASTER VNIR image (December 6, 2001) showing distinctive coseismic ruptures in the north of the Kusai Lake. For location see Fig. 9a. (b) Photograph showing the surface rupture zone in the northern bank of Kusai Lake. For location see Fig. 10a.
259 Bihong Fu, Yasuo Awata, Jianguo Du, Wengui He
a N
Step-over
0 1 km
b N
Bend
0 1 km
Fig. 11. (a) ASTER VNIR image (November 29, 2001) showing a right-stepping en-echelon pattern of the ruptures. Note that a pressure ridge formed between two ruptures in the northeast of the Kusai Lake. (b) SPOT image exhibiting a bend between two second-order segments in the Hubei Peak segment. For locations see Fig. 9a.
260 Rupture geometry and multi-segment rupture of the November 2001 earthquake in the Kunlun fault system, northern Tibet, China
a N
0 5 km
b N 5933 m 5559 m
0 5 km
Quaternary Rupture zone Snow & glacier Stream sediments channel Pre-Quaternary Avalanch of snow Normal fault rocks and glacier triggered by earthquake
Fig. 12. (a) SPOT image (January 16, 2002) showing the segment boundary between the Hubei Peak and Kunlun Pass segments. The segment boundary appears as a step-over, where the ruptures display a complicated pattern. (b) Interpretative map displaying the step-over between two segments. For location see Fig. 9a.
261 Bihong Fu, Yasuo Awata, Jianguo Du, Wengui He . b 2 . g ' ' i 0 0 F 0 0 e o o e 5 5 s a 9 9 n 4 o i 1 t . a g c i o l F r o F . t n N e N m g e s s s a P n u l n u K e h t f o y r t m e m k m k o e 0 0 g 2 2 g n i ' ' w 0 0 o m 3 3 h o o s 0 . 4 4 9 p g a 9 9 5 5 e m e S v i t P a t e K r p r e t n 0 I 0 ) b ( u k . t t h n a d n z e e n e u a m P m t Y g s e g r i s e f s r f n n e s o a a d m s t r t y a r o a 8 a - a P d 7 d d d i i n n n 1 X u o u X 6 l c o n e B r s u e i K c e a l l h e g t m n a f & n e o a r w t h s o S c e n r S u n n t s s a u u s s l l E E e ' ' a a f n n 0 0 P P c u u i 0 0 - K e h K o o e n p 4 4 r k o i r z o
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262 Rupture geometry and multi-segment rupture of the November 2001 earthquake in the Kunlun fault system, northern Tibet, China
a N
A
C
B
D
E
0 2 km
b SW
Fig.14. (a) SPOT image (January 25, 2002) showing that the easternmost termination of the 2001 surface rupture zone, appearing as a flat-lying Y-shape pattern. Location is shown on Fig. 13a. (b) Photograph showing that rupture zone gradually disappeared near the easternmost end, where the ruptures appearing an en-echelon pattern. For location see point E in Fig. 14a.
263 Bihong Fu, Yasuo Awata, Jianguo Du, Wengui He
a
r Buka Daban e v i Peak R
i
i
u Sun (6860 m) u Sun h
h
s 6004 m s
g LLakee g
n
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o o 36 00'N
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0 100 km aftershock o o 92 00'E 94 00'
b ) m ( t n e m e
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c
Xidatan-Dongdatan fault dary boun Seg. boundary Seg. Seg. boundary Seg. boundary
Fig.15. (a) Geometry and segmentation of the surface rupture zone associated with the 2001 large seismic event. The
distribution of major aftershocks (ML>3.0) occurred during 14 November 2001 and 27 November 2001 (modified from Xu and Chen, 2004). (b) Slip distribution along the surface rupture zone, compiled from our field measurements and previous published results (CSB, 2002; Zhao et al., 2002). Locations of three major sub-events are same with the USGS`s epicenter, Harvard Moment Centriod, and third sub-event suggested by Xu and Chen (2004), respectively. (c) Rupture propagation model showing a complex multiple rupture process related to the 2001 seismic event.
264