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Bulletin of the Seismological Society of America; February 2006; v. 96; no. 1; p. 48-58; DOI: 10.1785/0120040176
© 2006 Seismological Society of America
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Article

New Constraints on Recent Large Earthquakes along the Xidatan–Dongdatan Segment of the Kunlun Fault, Western China

Jianming Guo1, Aiming Lin1, Tadashi Maruyama2, Jianjing Zheng3 and Guoqiang Sun3

1 Institute of Geosciences, Faculty of Science
Shizuoka University
Shizuoka 422-8529, Japan
gjm2001cn{at}yahoo.com
 (J.G., A.L.)

2 Active Fault Research Center
Geological Survey of Japan / AIST
Tsukuba 305-8567, Japan
 (T.M.)

3 Key Lab of Gas Geochemistry
CAS, Lanzhou 730000, China
 (J.Z., G.S.)


   Abstract
Top
 Abstract
Introduction
 Activity of the Kunlun...
 The Offset of the...
 Paleoseismicity
 Discussion and Conclusions
 Appendix
 
Field investigation and paleoseismic study constrain the offset and timing of recent large earthquakes on the Xidatan–Dongdatan segment of the strike-slip Kunlun fault, northern Tibet. Displaced terrace risers and gullies preserved on the lowest and youngest terrace in the central part of the Xidatan–Dongdatan valley indicate that the offset produced by the most recent earthquake is 3–6 m, which is much smaller than what has been previously estimated; however, it is consistent with the slip of historical earthquakes along the Kunlun fault and recent well-recorded large earthquakes on other strike-slip faults. Accumulated offsets on higher terraces indicate repeated seismic activity of the Kunlun fault. We assume a 150 ± 20-km- long surface rupture for the most recent event based on roughly continuous linear features on remote-sensing images and distinct mole tracks in the field. The lack of seismicity records in the region earlier than 100 years ago led us to carry out paleoseismic investigation. Samples collected from the faulted upper layer show that the most recent large event on the Xidatan–Dongdatan segment is not older than 663 yr B.P. At least three prehistoric events are identified on the trench wall. Due to a lower constraint on the offset produced by the most recent earthquake, it would be necessary to reevaluate the seismic behavior of the Xidatan–Dongdatan segment.


   Introduction
Top
 Abstract
 Introduction
Activity of the Kunlun...
 The Offset of the...
 Paleoseismicity
 Discussion and Conclusions
 Appendix
 
The Kunlun fault is considered one of the major left- lateral strike-slip faults to accommodate the eastward extrusion of Tibet (e.g., Molnar and Tapponnier, 1975; Tapponnier and Molnar, 1977; Meyer et al., 1998; Tapponnier et al., 2001; Van der Woerd, Tapponnier, et al., 2002). Some studies have been focused on the late-Quaternary activity of the 600-km-long central Kunlun fault including the Xidatan– Dongdatan and the Tuosuo lake segments (Fig. 1; Table 1; Li and Jia, 1981; Kidd and Molnar, 1988; Jia et al., 1988; Xiao et al., 1988; Ren et al., 1993; Zhao, 1996; Van der Woerd et al., 1998, 2000, Liu, 1999; Van der Woerd, Meriaux, et al., 2002; Van der Woerd, Tapponnier, et al., 2002). characteristic offset of 9–12 m and slip rate of 10–15 mm/ yr on the Xidatan–Dongdatan segment are generally accepted (Table 1). However a smaller offset of 5–7 m was also reported (Ren et al., 1993), and three large historical earthquakes along other segments of the Kunlun fault indicate that the average offset produced by these earthquakes is much smaller than that published for the Xidatan–Dongdatan segment (Fig. 1; Xiao et al., 1988; Peltzer et al., 1999; Lin et al., 2002). Recent well-recorded large earthquakes on other strike-slip faults also show similar offset (Reilinger et al., 2000; Eberhart-Phillips et al., 2003). Because the offset is a vital parameter for understanding the activity of the fault and assessing the seismic hazards, further work is needed to clarify whether the seismic behavior of the Xidatan–Dongdatan segment is an exception.


Figure 001
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  		Figure 1. (a) Topography and major faults of Tibet and adjacent regions (GTOPO30; Avouac and Tapponnier, 1993; Tapponnier et al., 2001). (b) Segmentation and earthquakes of M ≥6.0 occurring in the past 70 yr along the Kunlun fault (Landsat Thematic Mapper (TM); International Seismological Centre, 2001; Van der Woerd, Meriaux, et al., 2002). Beach balls show the focal mechanism. From west to east, red lines indicate the surface rupture of the 1997 Mw 7.6, 2001 Mw 7.8, and 1937 M 7.5 earthquakes, respectively.

 

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  		Table 1 Summary of the Seismic Behavior along the Xidatan–Dongdatan Segment and the Tuosuo Lake Segment of the Kunlun Fault
 

Although distinct mole tracks show evidence for a recent earthquake, and accumulated offsets indicate multiple events on the Xidatan–Dongdatan segment (Kidd and Molnar, 1988; Van der Woerd, Tapponier, et al., 2002), the earthquake history of the segment is poorly known.

In this study, we selected the youngest and lowest terrace in the Xidatan–Dongdatan valley as the most favorable site to measure the offset produced by the most recent earthquake. Displaced terrace risers and gullies were measured to constrain the offset produced by the event. Accumulated offsets on higher terraces were also observed. Moreover, paleoseismic studies provide age information on recent earthquakes.


   Activity of the Kunlun Fault
Top
 Abstract
 Introduction
 Activity of the Kunlun...
The Offset of the...
 Paleoseismicity
 Discussion and Conclusions
 Appendix
 
The Kunlun fault strikes east–west to west-northwest– east-southeast over 1600 km in northern Tibet. On the basis of the geometry of the fault trace, the fault may be roughly divided into seven principal segments (Fig. 1; Van der Woerd, et al., 2002). The Kunlun fault generally cuts the alluvial fans and bajadas that bound the Kunlun range, and is recognized as a straight lineament on satellite images (Figs. 1 and 2).


Figure 002
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  		Figure 2. (a) SRTM (90 m resolution) color shaded relief map of the Xidatan– Dongdatan segment. (b) East-looking perspective view of the western part of the Xidatan–Dongdatan valley, generated by draping the Landsat Enhanced Thematic Mapper Plus (ETM+) images over Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM). The size of the image is about 40 km wide by 90 km long. The image has 2.5 times vertical exaggeration. Landsat bands 7, 4, 1 (30 m resolution) are used as red, green, and blue, respectively. White circles with numbers correspond to the sites studied by Van der Woerd, Tapponnier, et al. (2002).

 

Three large historic earthquakes of M ≥7.5 producing obvious left-lateral offsets along the Kunlun fault during the last century indicate that the fault is currently active and is the source for large earthquakes. The first is the 1937 M 7.5 Tuosuo lake earthquake that ruptured the Tuosuo lake segment (Li and Jia, 1981; Liu, 1999). The second is the 1997 Mw 7.6 (Ms 7.9) Manyi earthquake that produced a 170-km- long surface-rupture zone along the westernmost strand of the Kunlun fault (Peltzer et al., 1999). And the last is the 2001 Mw 7.8 (Ms 8.1) Kunlun earthquake that produced a 400-km-long surface-rupture zone along the Kusai lake segment (Lin et al., 2002, 2003; Van der Woerd, Meriaux, et al., 2002; Xu et al., 2002; Fu and Lin, 2003; Klinger et al., 2003) between the 1937 Tuosuo lake and 1997 Manyi surface-rupture zones (Fig. 1). There is no known historical earthquake recorded in the Xidatan–Dongdatan segment.

A uniform long-term slip rate of 11.5 ± 2.0 mm/yr was derived from 26A1, 10Be, and 14C dating of accumulated offsets along the central 600 km of the Kunlun fault (Van der Woerd et al., 2000; Van der Woerd, Tapponnier, et al., 2002). However, although based on a limited number of stations, Chen et al. (2000) suggested a smaller GPS slip rate of 6 ± 2 mm/yr across the Kunlun fault. Recent GPS results gave a 10–12 mm/yr left-lateral shear over a ~400-km-wide zone including the Kunlun fault, but Zhang et al. (2004) argued against the assignment of this broadly distributed 10– 12 mm/yr shear to elastic strain associated with slip on the Kunlun fault, because other active faults within the 400-km- wide deformation zone might accommodate some of the relative movement.


   The Offset of the Most Recent Earthquake
Top
 Abstract
 Introduction
 Activity of the Kunlun...
 The Offset of the...
Paleoseismicity
 Discussion and Conclusions
 Appendix
 
The Xidatan–Dongdatan segment splays from the Kusai lake segment and trends in a roughly west–east direction for about 200 km between 93.6° E and 96° E along the flat- floored Xidatan–Dongdatan valley and Xiugou valley with an elevation of ~4000 m in northern Tibet. The fault trace bends away from the southern range front to north in Xidatan–Dongdatan valley (Fig. 2). The basement of the study area consists mainly of pre-Tertiary rocks (Chengdu Institute of Geology and Mineral Resources, Chinese Academy of Geological Sciences, 1988). The fault trace is marked by sag-pond and push-up structures on the alluvial fans fed by north-flowing streams from the snow-capped Burhan Budai Mountain peak with an elevation of up to ~6000 m (Fig. 2). Glacial and alluvial processes modulated by climate variability are the primary agents to affect the landscape formation of the region; stream entrenchment and terrace emplacement responding to such processes left abandoned terrace risers as passively preserved topographic markers to record the displacements of past earthquakes (Van der Woerd, Tapponnier, et al., 2002). Gullies on terraces also record the offset of past earthquakes.

Mole tracks can be preserved for a long time due to the arid climate in the region. However, after several hundred years, the fresh features of the earthquake will be eroded, and it becomes difficult to distinguish the offset of the most recent earthquake from those of previous earthquakes, when they overlapped each other on higher terraces.

In theory, the terrace abandoned between the penultimate earthquake and the most recent earthquake is the only site to preserve the offset of the most recent earthquake from overlapping with previous earthquakes. Because it is difficult to identify the terrace formed in this period in the field, in practice, we assume the lowest and youngest terrace is the most likely site to record the most recent event. Larger offsets on higher terraces indicate slip produced by repeated events.

We measured offsets along the Xidatan–Dongdatan valley (Fig. 2b) ranging from 3 m to ~50 m with a tape. Well- preserved offsets on the lowest terrace were found in the central part of the valley (Fig. 2b). The typical examples of offset of terrace riser and gully on the surface rupture zone are presented as follows (Figs. 3, 4, and 5). Ten offsets ranging from 3 m to 6 m were recorded in this area (Fig. 6). The measurement uncertainty was estimated to be ±0.5 m.


Figure 003
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  		Figure 3. (a) South-looking perspective view in the Xidatan–Dongdatan valley (see Fig. 2b for location). (b) Aerial photograph, and (c) corresponding sketch, where the Kunlun fault offsets left-laterally the terrace risers. T0–T3 indicate the terrace surfaces from lower to higher (i.e., younger to older). Numbers indicate the left-lateral strike-slip amounts of the terrace risers along the fault: the terrace risers T0/T1 and T1/T2 are displaced by 4.8 ± 0.5 m and 18.5 ± 2 m, respectively.

 

Figure 004
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  		Figure 4. Photographs showing mole tracks and offset terrace risers observed in Figure 3.

 

Figure 005
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  		Figure 5. (a) North-looking perspective view in the Xidatan–Dongdatan valley (see Fig. 2b for location). (b) Aerial photograph showing the surface- deformation features on lowest and higher terraces. (c) A small gully on the lowest terrace is offset 3.4 ± 0.5 m. Spade (0.6 m high) for scale.

 

Figure 006
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  		Figure 6. Offsets measured on the lowest terrace in the central part of the Xidatan–Dongdatan valley.

 

At a north-flowing stream, the fault trace is developed on the alluvial fans and terraces that are sinistrally offset (Figs. 3 and 4). There is a tendency that the higher the terraces from the streambeds are, the larger the offsets of the terrace risers are. As shown in Figures 3b and 3c, four main terraces (T0–T3) developed on the west bank of the stream are systematically offset. T0 is the lowest and youngest terrace, about 0.5 m higher than the present streambed; T1 is ~4 m above T0; T2 is ~1.5 m above T1; and T3 is the highest level. The principal terrace risers of T0/T1 and T1/ T2 are displaced by 4.8 ± 0.5 m and 18.5 ± 2 m, respectively (Figs. 4b and 4c).

The terrace riser on the active streambed is constantly refreshed by flood and glacier; only after the incision of the stream does the terrace riser on the lowest terrace begin to record lateral displacement of the fault as a passive marker (Van der Woerd, Tapponnier, et al., 2002). Comparing with strike-slip offsets by the other recent large earthquakes (Reilinger et al., 2000; Eberhart-Phillips et al., 2003), we assume that the T0/T1 riser with 4.8 ± 0.5 m offset only recorded the most recent earthquake after the abandonment of terrace T0. If more than one earthquake was recorded on the T0/T1 riser, the offset of the most recent earthquake would be much smaller than 4.8 m at this site. Mole tracks produced by the most recent event are not clear on the T0 terrace. One possible reason is that sometimes floods reached to the T0 surface and wore down the fault trace due to the narrow and shallow active streambed. The well-preserved deformational features of the surface rupture on the T0/T1 riser indicate that after the last faulting event floods have had little effect on the terrace riser, because it is a little far from the active streambed. Therefore, T0/T1 acts as a passive marker to record the displacement of the most recent earthquake. The T1/ T2 riser with 18.5 m offset would record several large earthquakes after the abandonment of the T1.

On a north-sloping youngest terrace surface a small gully is offset 3.4 ± 0.5 m (Figs. 2b and 5). Here, distinct mole tracks such as those observed along the coseismic surface-rupture zone produced by the 2001 Mw 7.8 Kunlun earthquake (Lin et al., 2004) indicate a recent event occurred on the surface. Thus, the low and narrow deformation zone on the surface makes us consider that only one earthquake occurred after the abandonment of this terrace.

The offset of 3–6 m measured in this study is much smaller than that of 10 m reported by Kidd and Molnar (1988) and 9–12 m reported by Van der Woerd et al. (1998, 2000; Van der Woerd, Tapponier, et al., 2002) in the same area. Kidd and Molnar (1988) published two photos to show that gullies were offset about 10 m. However, high and wide mole tracks suggest that more than one earthquake occurred at these sites. Van der Woerd et al. (1998, 2000; Van der Woerd, Tapponier, et al., 2002) provided only remote- sensing images and a photo to show accumulated offsets on the Xidatan–Dongdatan segment. So the likely explanation for the difference between these measurements is that in this work we measured the offset on different terraces with the possibility of distinguishing the slip produced by the most recent event and that cumulated by more events, whereas in the other works it was measured only by the cumulative slip.

Linear and generally continuous features revealed in satellite images and air photos, and distinct surface breaks observed in the field, indicate that a surface faulting event occurred along the Xidatan–Dongdatan segment at a recent time. From longitude 93.6° E to 95° E, a 125-km-long surface rupture was followed on satellite images, and more than half of it was observed directly in the field. The fault trace becomes discontinuous when the fault extends eastward from the Xidatan–Dongdatan valley to Xiugou valley. Due to erosion and uncertainty of rupture terminations, we can assume that the most recent large earthquake produced a 150 ± 20-km-long surface rupture.


   Paleoseismicity
Top
 Abstract
 Introduction
 Activity of the Kunlun...
 The Offset of the...
 Paleoseismicity
Discussion and Conclusions
 Appendix
 
The seismic history of the Xidatan–Dongdatan segment is poorly known due to the lack of historical and instrumental records of earthquakes in the remote mountain area (International Seismological Centre, 2001; Center for Seismic Data and Information, China Seismological Bureau, 2004). Geological and geomorphologic evidences show that the late-Quaternary deposits and terraces have been deformed and displaced by the Xidatan–Dongdatan segment of the Kunlun fault (Kidd and Molnar, 1988; Van der Woerd, Tapponier, et al., 2002). Kidd and Molnar (1988) suggested that the most recent event occurred between A.D. 1500 and A.D. 1700 on the basis of the clearness and freshness of surface ruptures. Van der Woerd, Tapponier, et al. (2002) inferred that the last event took place prior to the youngest undisturbed alluvial flash-flood deposits whose cosmogenic age is 280 ± 89 yr B.P.

In order to better constrain the timing of past earthquakes, we carried out a paleoseismic study by trench excavation and outcrop observation in the field. 14C dating of four silt samples that include grass roots and other organic matter were collected for constraining the depositional and earthquake history (results are shown in Table 2).


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  		Table 2 Radiocarbon Dates of Samples
 

Trench Excavation
The trench site was selected on an abandoned alluvial fan (Figs. 2b and 7). At this location, the surface-rupture zone is characterized by a series of sag-pond and push-up structures on the fan (Fig. 7b). The 6.5-m-long hand-dug trench exposed the main fault zone in its central northern part (Fig. 8), but it was too short to expose the whole fault zone.


Figure 007
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  		Figure 7. (a) Aerial photograph of the trench site area (see Fig. 2b for location). (b) East view of the surface fault ruptures near the trench. Here the fault is characterized by alternating fault-sag and push-up structures. (c) Fault exposure at outcrop B in a remnant of terrace riser.

 

Figure 008
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  		Figure 8. (a) Photograph, and (b) corresponding sketch of the east wall of the trench. See text for explanation. MRE is the most recent event, PEN the penultimate event, 3rd the third event, and 4th the fourth event. Grid interval is 0.5 m.

 

Deposits exposed on the trench wall consist mainly of unconsolidated slope-wash sediment, wind-blown sediment, and alluvial sediment, which can be divided into three main stratigraphical units (Fig. 8, from top to bottom). Unit 1 consists of brownish gravels with a silt–sand matrix yielding calibrated 14C age of 551–663 yr B.P. (030828-C06) at the top (Fig. 8; Table 2). Material composing the unit was mainly transported from the upper slope of the fan surface by rain, some silt might be deposited by wind, and gravels are reworked from the top of the pressure ridge. Unit 2 consists of light-gray silt that is discontinuously distributed in the exposure wall and bounded by faults. Two samples collected from both top and bottom of this unit yielded calibrated 14C age of 1952–2307 yr B.P. (030828-C04) and 3355–3548 yr B.P. (030828-C03; Fig. 8; Table 2), respectively. Unit 3 is mainly composed of light-blue boulder- to pebble-size alluvial gravels with a coarse-grained sandy matrix. Loose and strongly sheared gravels in a main fault zone suggests that repeated events have occurred.

Eight main faults (F1–F8) can be recognized by discontinuities and deformational structures in the deposits of the trench (Fig. 8b). Faults F3 and F5 bound a prominent pressure ridge. F1, F2, F7, F8, and a branch of F3 do not reach to the surface. Some fractures filled by upper deposits are observed in the silt layer to the south of the main fault zone (Fig. 8).

Outcrop Exposures
An exposure of a stream bank (outcrop A) located 11 km west of the trench shows a distinct push-up structure (Figs. 3a and 9). The deposits are mainly composed of alluvial gravels that are covered in the southern part by a 30- cm-thick silt layer. The silt layer is cut and sheared by the fault. Along the fault planes, the gravels are dragged and reoriented parallel or subparallel to the fault plane, which dips south with a steep angle of >66°. A silt sample (030827-C01) collected from the bottom of the silt layer yields a calibrated 14C age of 564–726 yr B.P. (Table 2).


Figure 009
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  		Figure 9. (a) Photograph, and (b) corresponding sketch of outcrop A (see Fig. 3a for location). Note that the gravels are dragged and reoriented along the fault plane and the silt layer is faulted. Grid interval is 1 m.

 

Another outcrop (outcrop B) was observed in the remnant of an abandoned terrace located 2.2 km east of the trench (Fig. 7). Similarly to outcrop A, also here the fault shows an apparent vertical component and reaches the surface (Fig. 7c).

Paleoseismic Events
Past earthquakes are generally identified in trenches and natural exposures by the fault upward terminations and disturbed deposits capped by continuous beds (Yeats et al., 1997). On the basis of the relationships observed in the trench, we recognized evidence for at least three paleoseismic events.

The most recent event (MRE in Fig. 8) is identified both in the trench and outcrops. In the trench, F3–F5 cutting all deposits in the uplifted main fault zone indicate that the most recent event occurred along them. Sample 030828-C06 collected near the top of the deposits shows that the maximum age of the event is cal. 663 yr B.P. All layers are disturbed by the fault in outcrop A, and the sample 030827-C01 obtained from the upper layer also gives a consistent maximum age of cal. 726 yr B.P. for the recent earthquake. Therefore, we can infer that the most recent event along the segment occurred in the past 663 yr. The termination of a branch of F3 within unit 1 is identified as evidence for the penultimate event (PEN in Fig. 8). A third event (3rd in Fig. 8) is recognized because F5–F8, F1, and F2 offset the silt and gravel layers, and fractures developed in the correlative silt layer on the south side of the main fault zone. Sample 030828- C04 provides a maximum age of cal. 2307 yr B.P. for this event.

One more possible event (4th in Fig. 8) is inferred because of the deformation of the gravel layer of unit 3 under the silt layer of unit 2. The earthquake disturbed gravels, when they were at the ground surface, and then wind-blown silt deposited on them. Sample 030828-C03 gives a minimum age of cal. 3355 yr B.P. for this possible event.


   Discussion and Conclusions
Top
 Abstract
 Introduction
 Activity of the Kunlun...
 The Offset of the...
 Paleoseismicity
 Discussion and Conclusions
Appendix
 
The knowledge of recent earthquakes can be linked directly to assess prehistoric and future earthquakes along active faults (Yeats et al., 1997). Historical large earthquakes along the Kunlun fault in the past century show that coseismic offsets are generally smaller than 7 m (Xiao et al., 1988; Peltzer et al., 1999). Other recent well-recorded large earthquakes along strike-slip faults, such as the 1999 Mw 7.5 Izmit, Turkey, earthquake (Reilinger et al., 2000; Aydin and Kalafat, 2002) and the 2002 Mw 7.9 Denali fault earthquake, Alaska (Eberhart-Phillips et al., 2003; Haeussler et al., 2004), also show similar amounts of offset. Moreover, paleoseismic investigation along the Altyn Tagh fault, another major strike-slip fault in northern Tibet, also gets coseismic offset of ~7 m (Washburn et al., 2001). Therefore, we can consider that 3–6 m offset measured in this study was generated by the most recent large earthquake along the Xidatan–Dongdatan segment. Larger offsets observed on higher terraces are evidence for repeated surface faulting events on the fault.

According to the moment magnitude law, if we assume a uniform slip distribution over a depth of 15 km and an elastic shear modulus of 3.0 x 1010 N/m2, a 150-km-long rupture with an average slip of 4.5 m earthquake corresponds to an Mw 7.6 earthquake, which is consistent with other historical large events of the Kunlun fault (M 7.5–M 7.8).

Paleoseismic investigation in this study shows that the deposits with ages of cal. 551–663 yr B.P. are sheared and offset during the most recent earthquake. Combining this result with the minimum age of unfaulted features of 280 ± 89 yr B.P. suggested by Van der Woerd, Tapponnier, et al. (2002), we conclude that the most recent earthquake occurred between 191 B.P. and 663 B.P.

Although three paleoseismic events are identified, we only get the maximum age for the events due to a limited number of samples that may have been reworked by wind and water. Moreover, because of the type of sediments exposed, which are characterized by intermittent deposition and erosional events, we may have missed some events in the paleoseismological reconstruction; thus, it is hard to estimate a recurrence interval along the Xidatan–Dongdatan segment from this study and previous ones. However, based on an average slip of ~4.5 m per event from this study and published slip rates, a firsthand average recurrence interval on the segment can be calculated. Using the slip rate of 11.7 ± 1.5 mm/yr determined by dating accumulated offsets of Quaternary landforms (Van der Woerd, Tapponnier, et al., 2002) yields a recurrence time of 380 ± 50 yr, whereas using the slip rate of 6 ± 2 mm/yr determined from GPS (Chen et al., 2000) yields a recurrence time of 750 ± 300 yr. Given the uncertainty of the recurrence interval along the Xidatan–Dongdatan segment and the wide interval of the MRE age, it is difficult to estimate the present seismic potential of this fault segment within the next decades. However, it should also be taken in account that the 2001 Mw 7.8 earthquake increased Coulomb stress on the Xidatan– Dongdatan segment (Wan et al., 2003), and this poses potential seismic hazards to important infrastructures, such as the Golmud–Lhasa railway, highway, and oil pipeline, which cross the Kusai lake and Xidatan–Dongdatan segments near the Kunlun Pass, and have been damaged by the 2001 Mw 7.8 earthquake on the Kusai lake segment (Fig. 2; China Seismological Bureau, 2003).

In summary, this study provides a possible average slip and magnitude for the future large earthquake on the Xidatan–Dongdatan segment of 3–6 m and Mw 7.6, respectively. This should be taken in consideration for seismic- hazard evaluation on existing and future infrastructures in the area, as highlighted by the successful design of the Trans-Alaska Pipeline, which withstood the 2002 Mw 7.9 Denali fault earthquake, demonstrating the value of geological studies in earthquake-risk mitigation (Eberhart-Phillips et al., 2003).


   Appendix
Top
 Abstract
 Introduction
 Activity of the Kunlun...
 The Offset of the...
 Paleoseismicity
 Discussion and Conclusions
 Appendix
 
We are grateful to the U.S. Geological Survey Land Processes Distributed Active Archive Center for releasing GTOPO30 data, the University of Maryland Global Land Cover Facility for Landsat ETM+ images, the NASA Applied Sciences Directorate for mosaic Landsat TM images, and the NASA Shuttle Radar Topography Mission Project for SRTM data. We thank R. Arrowsmith, D. Pantosti, and an anonymous reviewer for constructive reviews that greatly improved the manuscript. Thanks are also due to M. Zhang and P. Zhou for assistance in the field, and K. Kano for helpful discussions. This work was supported by the Nuclear and Industrial Safety Agency, Japan; the Science Project (No. 14403009 for A. Lin) of the Ministry of Education, Culture, Sports, Science, and Technology of Japan; the Important Direction Project of Knowledge Innovation in Resource and Environment Field, the Chinese Academy of Sciences (KZCX3-SW-128); and Grant-in-Aid of Graduate School of Science and Engineering, Shizuoka University.

Manuscript received August 25, 2004

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