Abstract
We demonstrate that a continental interior reverse fault is deforming by aseismic creep, presently, and likely also in the long term. The Karkara Rangefront Fault, part of the larger Main Terskey Front, forms the northern boundary of the high Terskey Tien Shan in southeastern Kazakhstan and is a mature structure with evidence for high slip rates throughout the late Cenozoic. Combining field studies with a satellite stereo-image derived digital elevation model (2 m resolution), we map a series of fluvial terraces along the rangefront which are uplifted by up to ∼300 m above the present river level. Radiocarbon ages from one catchment constrain the ages of the lowermost two terraces to be ∼4–5 ka and ∼10–15 ka, consistent with prominent, regionally extensive terraces observed elsewhere in the Tien Shan. Based on conservative estimates for the fault dip under the displaced terraces, we estimate a slip rate along the fault plane of 3.5+1.7−0.4 mm yr–1 on the Karkara Rangefront Fault and a further >0.8 mm yr–1 on a fold structure in the Kegen basin that we infer is driven by a detachment from the main rangefront. We therefore estimate a minimum shortening rate across the rangefront of 1.1–3.3 mm yr–1. Elastic modelling of the regional GPS velocity field suggests that the fault is presently creeping at ∼3 mm yr–1 (horizontal shortening), consistent with the upper limit of our Late Quaternary slip rate estimate. This is the fastest known slip rate in the northern Tien Shan and the only individual structure resolved in the regional velocity field. At present the fault is accumulating minimal strain, and there is evidence in the geomorphology that this creep is sustained in the long term, but whether or not it is also capable of generating earthquakes requires further study.
Highlights
34 The classical model of earthquakes and faulting in the continents is that of stick-slip be[35] haviour on discrete faults
We demonstrate that a continental interior reverse fault is deforming by aseismic creep, presently, and likely in the long term
Here, we present a case study of the northern rangefront fault of the high Tien Shan, adjacent to the highest peaks of the range, where creep on a continental interior thrust fault is suspected (Figure 1)
Summary
34 The classical model of earthquakes and faulting in the continents is that of stick-slip be[35] haviour on discrete faults. We present a case study of the northern rangefront fault of the high Tien Shan, adjacent to the highest peaks of the range, where creep on a continental interior thrust fault is suspected (Figure 1). The regional GPS velocity field shows that the Tien Shan accommodate ∼20±2 mm/yr of shortening (at the longitude of this study), amounting to around half the total India–Eurasia plate convergence (Tapponnier & Molnar 1979; Abdrakhmatov et al 1996; Zubovich et al 2010). Half of this shortening, ∼10 mm/yr, is taken up across the northern and central Tien Shan, with the other half accommodated along the northern margin of the Tarim Basin.
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