Long-term faulting behavior of eastern Altyn Tagh fault, north Tibetan Plateau

Abstract:

The Altyn Tagh Fault (ATF) bounds the Tibetan Plateau to the north and is the longest continental active strike-slip fault at lithospheric scale within the India-Eurasia collision zone (Wittlinger et al., 1998). Together with other mega strike-slip faults, e.g., the Kunlun, Haiyuan, Xianshuihe and Jiali faults, it plays an important role in both the two end member models, eastward block-like motion and distributed deformation or channel flow, to accommodate the India-Eurasia convergence. However, how much amount of northward motion, from convergence between Indian and Eurasian plates to the south, has been transferred by localized slip on the ATF into eastward motion of the Plateau relative to the Tarim basin is still unclear. Its main reason may be originated from disagreements over quite scattered Quaternary left-slip rates from 2 mm/yr up to 30 mm/yr and also difference in slip rate over time scales of 10 yr from GPS and InSAR to 10 kyr from Quaternary offset-landforms. However, accurate Quaternary long-term average slip rate is the first step for quantitatively evaluating the role of the ATF in transferring northward convergence of the India-Eurasia collision into eastward escape and then for understanding the kinematic model of the Tibetan Plateau.

Here we present a synthetic approach to well constrain long-term left-slip rate by identifying paleo-earthquake sequence as precise chronologic bounds for the associated measured cumulative displacements at two sites on the Aksay segment of the ATF. This result is very important not only to establish surface-rupturing earthquake recurrence model to reduce its potential earthquake hazards along the ATF, but also to solve the long-standing dispute over the high or low Quaternary slip rates by using diferent terrace models and geodetic strain rate.

Analysis of the paleo-earthquakes from trenches and recent cumulative offsets reveals a Holocene surface-rupturing faulting process, which well constrains the long-term slip rate of the ATF on its eastern segment. These long-tern slip rates may help us to legitimately understand how much of the convergence between the Indian and Eurasian plates has been accommodated by the ATF.