Abstract
We have studied the characteristics of the active faults and seismicity in the vicinity of Urumqi city, the capital of Xinjiang Autonomous Region, China, and have proposed a seismogenic model for the assessment of earthquake hazard in this area. Our work is based on an integrated analysis of data from investigations of active faults at the surface, deep seismic reflection soundings, seismic profiles from petroleum exploration, observations of temporal seismic stations, and the precise location of small earthquakes. We have made a comparative study of typical seismogenic structures in the frontal area of the North Tianshan Mountains, where Urumqi city is situated, and have revealed the primary features of the thrust-fold-nappe structure there. We suggest that Urumqi city is comprised two zones of seismotectonics which are interpreted as thrust-nappe structures. The first is the thrust nappe of the North Tianshan Mountains in the west, consisting of the lower (root) thrust fault, middle detachment, and upper fold-uplift at the front. Faults active in the Pleistocene are present in the lower and upper parts of this structure, and the detachment in the middle spreads toward the north. In the future, M7 earthquakes may occur at the root thrust fault, while the seismic risk of frontal fold-uplift at the front will not exceed M6.5. The second structure is the western flank of the arc-like Bogda nappe in the east, which is also comprised a root thrust fault, middle detachment, and upper fold-uplift at the front, of which the nappe stretches toward the north; several active faults are also developed in it. The fault active in the Holocene is called the South Fukang fault. It is not in the urban area of Urumqi city. The other three faults are located in the urban area and were active in the late Pleistocene. In these cases, this section of the nappe structure near the city has an earthquake risk of M6.5–7. An earthquake MS6.6, 60 km east to Urumqi city occurred along the structure in 1965.
Highlights
To achieve earthquake prevention and disaster reduction, extensive investigations of active faults and assessment of seismic hazards are currently under way in city areas across the Chinese mainland
Based on analysis of the relationship between active faults and seismotectonics, Urumqi city is associated with two seismogenic structures (Yeats 1986); one is to the west of the Urumqi River and the other is to the east
This work focuses on the seismotectonics of Urumqi city which lies in the frontal area of the North Tianshan Mountains
Summary
To achieve earthquake prevention and disaster reduction, extensive investigations of active faults and assessment of seismic hazards are currently under way in city areas across the Chinese mainland. Cenozoic tectonic deformation of the Tianshan is characterized by expansion to the north and south sides in the meantime and development of reverse fault and fold belts (Avouac et al 1993; Liu et al 1994; Zhang et al 1996; Abdrakhmatov et al 1996; Ghose et al 1998; Allen et al 1999; Burbank et al 1999; Burchfiel et al 1999; Deng et al 2000; Fu et al 2003) These nappe structures developed in Quaternary are of the most intense regions of tectonic deformation, and the strongest earthquakes have occurred along these structures (Yang et al 2008; Wu et al 2011, 2016). This position corresponds to the western end of the first row of the North Tianshan range-frontal anticline zone, and the western flank of the second and third rows of the thrust zone in the Bogda reverse fault-fold structure
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