**1. Introduction**

32 Earthquake Research and Analysis – Seismology, Seismotectonic and Earthquake Geology

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#### **1.1 Geological-tectonic structure and evolution of the Talas-Fergana Fault in the Cenozoic**

The Talas-Fergana Fault (TFF) is the largest strike-slip structure in the central Asia. It forms an obliquely-oriented boundary between the north-eastern and south-western parts of the Tien Shan (Fig. 1). The last one includes the Fergana depression, Chatkal-Kurama mountain system and Alay valley. A wide belt of latitudinal oriented ranges, which are located between the Kazakh platform and Tarim basin, represents the north-eastern Tien Shan.

Many scientists were engaged and are still interested in studying the problem of recent movements along the Talas-Fergana Fault (K.E. Abdrakhmatov, T.P. Belousov, V.S. Burtman, O.K. Chediya, A. Khodzhaev, V.I. Knauf, A.M. Korjenkov, N.P. Kostenko, V.N. Krestnikov, I.N. Lemzin, V.I. Makarov, P. Molnar, V.A. Nikolaev, V.N. Ognev, A.V. Peive, V.I. Popov, G.N. Pshenin, E.Ya. Rantcman, S.V. Ruzhentsev, V.M. Sinitsyn, N.M. Sinitsyn, S.F. Skobelev, D.V. Shtange, A.L. Strom, L.D. Sulerzhitsky, A.I. Suvorov, V.G. Trifonov, N.N. Verzilin, R.E. Wallace, and others. Most researchers interpret the TFF as a right-lateral strike-slip fault active since Palaeozoic time. Right-lateral movements rejuvenated in the late Cenozoic because of crustal shortening linked to the India-Eurasia collision. The tectonic movements along the intracontinental strike-slip faults contribute to absorb part of the regional crustal shortening, thus strike-slip motions along the TFF are necessary for the complete assessment of the active deformation of the Tien Shan orogen.

Our focus is to improve the understanding of the intracontinental deformation of the Tien Shan mountain belt as a whole and the occurrence of strong earthquakes along the whole length of the TFF. The aim of the work is an attempt to reveal features of relief occurred during strong paleoearthquakes along the Talas-Fergana Fault, TFF fault segmentation, length of the seismogenic ruptures, energy and age of ancient catastrophes. Mentioned data are critical for complete seismic hazard assessment for a territory with absence of materials on historical seismicity.

Fig. 1. The map of the Talas-Fergana Fault's line and adjacent territories (modified after Burtman et al., 1996). Dashed rectangulars shows studied portions of the fault. Sedimentary basins are indicated by regular dotty filling. Irregular dotty area shows lakes and reservoirs. Numbers along the fault's line are observation points N12 and 13 from Burtman et al. (1996).

Many authors (Khodzhaev, 1985; Burtman et al., 1987, 1996; Trifonov et al., 1990, 1992; Abdrakhmatov and Lemzin, 1991; Korjenkov, 1993, 2006; Korjenkov et al., 2006, 2009, 2010 and others) were occupied also by a detailed paleoseismological study of the TFF zone. Some of them (Burtman et al., 1987, 1996; Trifonov et al., 1990, 1992; Rust et al., 2008; Korjenkov et al., 2009, 2010) collected samples for the radiocarbon dating. Because the organic material has deposited later than the formation of the upslope facing scarp, displacing channels of gullies and watersheds, the radiocarbon dates (Table 1) point on minimum ages of the events which led to relief forms' displacement along the fault zone.

All features pointing on seismic-rupturing character of the upslope facing scarp, developed along the fault zone, are testifying that the Talas-Fargana Fault is "alive" until present. As related to its morphologic-kinematic characteristics, most of scholars believe that the fault is right-lateral strike-slip fault's structure, they point on amplitude of displacement along it from hundreds meters to 12-14 kilometers during Cenozoic time (Ranzman and Pshenin, 1963; Trifonov et al., 1990 and others).

Last summary of materials of previous investigations along the Talas-Fergana fault is cited in papers by Korjenkov (2006), Korjenkov et al. (2006, 2007, 2009, 2010), Rust et al. (2008).


Table 1. Radiocarbon dates of the samples collected from the displaced gullies along the TFF (by Trifonov et al., 1990, 1992 и Burtman et al., 1996)
