Abstract
The role of large-scale strike-slip faults in high-elevation areas in absorbing the strain resulting from plate convergence has yet to be scientifically understood. The Dang Jiang Fault (DJF), as the NW continuation of the Xianshuihe Fault Zone (XFZ) in the central Qinghai-Tibetan Plateau, may provide an excellent testing ground for this question, given its high slip rate, sparse vegetative cover, minimal modification, and possible relationship with the CE 1738 Dangjiang destructive earthquake. However, co-seismic surface ruptures and seismotectonics remain in dispute because of inconvenient transportation and lack of oxygen at high altitudes. Thus, field investigations are conducted here to determine co-seismic surface ruptures. The newly synthesized data from geologic observations, historical record reviews, geomorphic mapping, trench logging, and sample dating indicate that the CE 1738 Dangjiang earthquake produced an ∼100 km-long surface rupture that includes offsets of gullies, linear scarps and troughs, sag ponds,en echelonfractures, and pressure ridges. The magnitude is re-estimated asM7.6, with average and maximum strike-slip displacements of ∼2.1 ± 0.1 m and ∼3.5 ± 0.1 m, respectively. The DJF has undergone multiple seismic faulting events, and the linear fitting surface displacement rate in the Holocene is ∼6.3 ± 1.9 mm/yr with a 95% confidence interval. This study implies that the seismic hazard of the DJF cannot be underestimated given that its elapsed time is close to or beyond the recurrence interval of major earthquakes and that the oblique convergence of the Qiangtang Block might be accommodated by the clockwise rotation of the block through repeated left-lateral strike-slip movements along the southern boundary of the Bayan Har Block.
Highlights
The large-scale strike-slip faults in continental interiors have played important roles in the process of the adjustment and absorption of tectonic deformation that has resulted from the collision between the Indian plate and the Eurasian plate since 45 ± 5 Ma (Molnar and Tapponnier, 1975; Rowley, 1996; Tapponnier et al, 2001; Lin et al, 2002; Yin, 2010), their geodynamic processes have yet to be thoroughly understood
Field investigation reveals that the strike of the Dang Jiang Fault (DJF) is oriented more east–west than other branches of the Xianshuihe Fault Zone (XFZ) and can be traced for ~170 km in length (Figure 1 and Figure 2)
The DJF ends to the east near Anchong town (Figure 2), and an ~20 km wide uplift area can be observed near Jielong town because the Yushu fault overlaps the southeastern end of the DJF with a right en echelon stepover of approximately 25 km
Summary
The large-scale strike-slip faults in continental interiors have played important roles in the process of the adjustment and absorption of tectonic deformation that has resulted from the collision between the Indian plate and the Eurasian plate since 45 ± 5 Ma (Molnar and Tapponnier, 1975; Rowley, 1996; Tapponnier et al, 2001; Lin et al, 2002; Yin, 2010), their geodynamic processes have yet to be thoroughly understood. Many achievements in the middle and eastern sections of the XFZ have been attained by geologists around the world, the active tectonics and seismogenic behavior, recurrence interval of great earthquakes, slip rate, and maximum magnitude estimation along the western portion of the XFZ remain debated (Wang et al, 2007). These basic data are crucial for assessing the seismic hazard and activity habit along the whole structure, as well as for deciphering the strain distribution and tectonic deformation model in the central Tibetan Plateau. The CE 1738 Dangjiang earthquake, despite matching the area crossed by the
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