Latest Quaternary paleoseismology and slip rates of the Longriba fault zone, eastern Tibet: Implications for fault behavior and strain partitioning

Abstract

[1] Although much work has been done on active tectonics of eastern Tibet, little is known about the Longriba fault zone and its role in strain partitioning. Whether its two sub-parallel strands (Longriqu and Maoergai faults) can rupture simultaneously in a large earthquake remains unknown. We conducted trenching combined with the interpretation of satellite imagery, field investigations, topographic surveys, and radiocarbon and Optically Stimulated Luminescence (OSL) dating to reconstruct paleoseismic history, and we used displaced terrace risers to estimate geological slip rates. Our results demonstrate that the Longriba fault zone is predominantly right-lateral with a small southeast-verging thrust component. Four surface-rupturing events occurred on the Longriqu fault at 5080 AE 90, 11,100 AE 380, 13,000 AE 260, and 17,830 AE 530 cal yr B.P. Together with our previous trenches on the Maoergai fault, we found that the last event probably ruptured both the Longriqu and Maoergai faults. Prior to the last event, the two strands of the Longriba fault zone experienced alternating earthquakes. The fault zone has a high potential for an earthquake larger than Mw 7. The slip rate of the Longriba fault zone decreases from 7.5 mm/yr in latest Pleistocene to~2.1 mm/yr in the Holocene, probably related to a slowing down of the eastern motion of the Tibetan Plateau. The comparison with slip rates at the Longmen Shan fault zone suggests that the Longriba fault zone has an equally important role in strain partitioning in eastern Tibet. This study is helpful to seismic hazard assessment and an understanding of deformation mechanism in eastern Tibet.Citation: Ren, J., X. Xu, R. S. Yeats, and S. Zhang (2013), Latest Quaternary paleoseismology and slip rates of the Longriba fault zone, eastern Tibet: Implications for fault behavior and strain partitioning, Tectonics, 32, 216-238,

Heterogeneous strain regime in the eastern margin of Tibetan Plateau and its tectonic implications

“…Longmenshan fault displayed slow activity, with a fault-normal rate at 0.8 ± 2.5 mm/a, and a fault-parallel rate at 1.8 ± 1.7 mm/a. This result contrasts with the geological solution of Ren et al's (2013) that the slip of the Longriba fault in the latest Pleistocene is up to *7.5 mm/a, indicating an apparent decrease of slip rate from the latest Pleisstocene to the Holocene. Using elastic subblocks model, Cheng et al (2012) documented that Longriba fault is characterized by an evident dextral slip and negligible contraction; the difference likely results from their short spanning data and their modeling approach, which employed subblock motion to fit the velocities of GPS sites within respective subblocks.…”

Denudation pattern across the Longriba fault system and implications for the geomorphological evolution of the eastern Tibetan margin

“…The Longriqu fault accommodates lateral and reverse components, whereas the Maoergai fault is a pure right-lateral strike-slip fault. The right lateral slip rate on the LFS decreased from 7.2 to 2.1 mm/y over the Pleistocene (Ren et al, 2013a). The LFS appears to act as an important partitioning structure for the accommodation of the eastward motion of the Aba block Shen et al, 2009;Ren et al, 2013a).…”

“…1 and 3). Paleoseismological investigations suggest a late Quaternary sequence of four earthquakes along the Longriqu fault and three on the Maoergai fault with an estimated seismic recurrence interval of 2000 years on the whole system (Ren et al, 2013a). The Longriqu fault accommodates lateral and reverse components, whereas the Maoergai fault is a pure right-lateral strike-slip fault.…”

“…This fault system is made of two~300-km-long, N50E-trending, NW-dipping, dextral strike-slip faults: the Longriqu and the Maoergai faults Guo et al, 2013b;Ren et al, 2013a) (Figs. 1 and 3).…”

“…1). However, recent geodetic results and field observations have highlighted the importance of the Longriba fault system (LFS), located 200 km northwest of the Longmen Shan, as a major structural boundary between crustal blocks, with an important role in stress and strain field distribution Shen et al, 2009;Ren et al, 2013a). While some results are available concerning the tectonic activity of the LFS, from a geomorphological perspective little is known about its contribution to the evolution of the eastern Tibetan margin.…”