**2. Methodology**

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

are critical for complete seismic hazard assessment for a territory with absence of materials

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,

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).

on historical seismicity.

1963; Trifonov et al., 1990 and others).

Besides traditional route field investigations, forestalling by interpretation of air-photos and satellite images, study of existing archive and published literature, we have conducted a detailed mapping of selected key test sites:



Fig. 2. Digital map of relief of the western Tian Shan. The locations of the investigated test sites are shown in the map.

On the prospected ranges the TFF line usually goes across the slope of one of river valleys or a ridge (range) slope. Along the line there is usually a fault scarp in the form of a swell. Height of this scarp is usually equal to several dozens centimeters - the first meters. On the investigated ranges the numerous broken forms of a modern relief were found: valleys of temporary waterways and watersheds between them, upper parts of which are shifted in a horizontal direction - to the right to a distance from several dozens to several hundreds meters. The identical width and morphology of the shifted parts of dry valleys above and below the fault line testifies that the shift occurred quickly. It allows linking such shifts with earthquakes (Burtman et al., 1987).

The majority of the shifted valleys of temporary waterways have remained below the fault line, where on the slope at earthquake a fault scarp was formed in the shape of a swell. This scarp has isolated the lower continuation of the broken valley, while seasonal waters found other drain, washing away the scarp in the lowest place. Further the isolated part of the valley could continue to be displaced along the fault.

For definition of time of movements along the TFF indirect method of V.G. Trifonov (1985) was used. At formation of a scarp on the slope along the fault line a depression was also formed. This scarp has impound the waters flowing down the slope and filtering along the fault plane, which created conditions for swamping of the depressions in the vicinity of the fault. The beginning of formation of a peat swamp and a thick soil layer testifies to occurrence of a fault scarp which formed because of horizontal displacement along the fault. For definition of age of these formations samples of organic material for the radiocarbon analysis in bore pits, prospected in impounded parts of valleys, were taken. The received radiocarbon dates, based on the sum of the organic substance which was accumulated during some period of time, are always later dates as compared to the moment of beginning of accumulation. Determination of residual activity of carbon in our samples was carried out on a device QUANTULUS-1220 (Liquid Scintillation Counters) at the Institute of Geology and Mineralogy of the Siberian Branch of the Russian Academy of Science, Novosibirsk. For age calculation the half-life period of 14C was used equal to 5570 years. The age was calculated from 1950. Age determination was done based on fraction of humic acids.
