Irregular earthquake cycle along the southern Tianshan front, Aksu area, China

Abstract

[1] A long deformation record ($16.5 ka) showing nonsteady earthquake recurrence is established for the Aksu thrust (Tianshan, China) on the basis of cosmogenic 10 Be dating of faulted surfaces. Topographic leveling across the Aksu fault scarp indicates up to $10 m uplift across a moraine abandoned $16.5 ka and similar uplift of $6 m across two inset surfaces yielding ages of $12.5 and $5 ka. Successively smaller uplifts of terraces younger than 5 ka indicate that three or more major earthquakes occurred during this period. These data show that the Aksu thrust fault was quiet for at least 7500 years and active in the last $5000 years and probably in the interval 16.5-12.5 ka. The seismic cycle along the Aksu thrust fault over the last $16,500 years was thus strongly irregular showing long quiescence and clustering, which is a challenge for paleoseismology and hazard assessment. This irregularity also makes it more difficult to estimate long-term shortening rates. Nevertheless, we are able to constrain a minimum total shortening rate (>7 mm/yr) across the southern Tianshan front for the last 12,500 years that is about a third of the total geodetic rate for the western Tianshan ($20 mm/yr).

Temporal constraints and pulsed Late Cenozoic deformation during the structural disruption of the active Kashi foreland, northwest China

“…Line length calculations along the highest terrace indicate 11 m of shortening across the 8‐km‐long terrace. Similar broad terrace levels from the Kuqa Basin ∼1000 km east have been dated at 12.5 ka [ Hubert‐Ferrari et al , 2005]. Using 12.5 ka as an estimated age for the terrace, shortening of ∼1 mm/a is calculated for the Atushi Anticline.…”

Three‐dimensional numerical models with varied material properties and erosion rates: Implications for the mechanics and kinematics of compressive wedges

“…These cycles last on the order of 15 -200,000 model years. Our models, along with other numerical [Naylor and Sinclair, 2007] and analog models [Hoth et al, 2006; and some well dated examples from active orogens [Masaferro et al, 2002;Hubert-Ferrari et al, 2005;Sinclair et al, 2005], suggest that transient accommodation of strain may be common. Thus, caution should be applied when extrapolating long-term slip rates from varying temporal scales.…”

“…Cosmogenic 10 Be dating along the Asku Fault (Tian Shan, China) reveals a record of activity followed by a long quiescence (at least 7.5 ka) and recent activity over the past 5 ka [Hubert-Ferrari et al, 2005]. Masaferro et al [2002] showed that the Neogene-Quaternary growth of the Santaren anticline (Cuban fold and thrust belt) is characterized by several tectonic uplift pulses of different duration and intensity, interrupted by periods of variable duration in which no fold growth occurred.…”

Mechanisms of active folding of the landscape (southern Tian Shan, China)

“…It is one of the largest and most active intracontinental mountain ranges (Figure 3) [ Avouac et al , 1993; Molnar and Deng , 1984]. Up to 20 mm/yr of shortening [ Abdrakhmatov et al , 1996; Reigber et al , 2001; Molnar and Ghose , 2000] is accommodated in thrust belts on both sides and within the range [ Allen et al , 1999; Burchfiel et al , 1999; Burbank et al , 1999; Chen et al , 2002; Thompson et al , 2002; Hubert‐Ferrari et al , 2005b]. In the eastern part of the southern Tian Shan between 80°30′ and 85°E, the main locus of deformation is the 350‐km‐long Kuche fold‐and‐thrust belt that deforms an 8‐ to 10‐km‐thick Triassic to Recent sequence of continental strata [ Yin et al , 1998].…”