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

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.)

View larger version (146K): [in this window] [in a new window]   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.

View larger version (130K): [in this window] [in a new window]   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).

View larger version (72K): [in this window] [in a new window]   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.

View larger version (83K): [in this window] [in a new window]   Figure 4. Photographs showing mole tracks and offset terrace risers observed in Figure 3.

View larger version (90K): [in this window] [in a new window]   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.

View larger version (6K): [in this window] [in a new window]   Figure 6. Offsets measured on the lowest terrace in the central part of the Xidatan–Dongdatan valley.

View larger version (89K): [in this window] [in a new window]   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.

View larger version (76K): [in this window] [in a new window]   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.

View larger version (75K): [in this window] [in a new window]   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.