**3.1 Investigations in Ara-Beyik – Kara-Kasmak interfluve**

In the most west of Kyrgyzstan (the Ara-Beyik river valley) the TFF trace is unclear. Probably, it is divided into several zones parallel to each other and differing in character of the Holocene slip. The fault zone can be identified in outcroppings of rocks along the right slope of the river valley where there is a wide zone of crushed basement rocks.

Fig. 3. The right-lateral deviation of dry channels (shown by black arrows) along the Talas-Fergana trace on the left slope of the Sulu-Bakair river valley.

In the Sulu-Bakair River valley the TFF zone cuts a moraine of Middle and Late Pleistocene age and is expressed as a deep and wide upslope facing scarp. Although the moraine is several tens meter thick, the fault zone is marked by springs. Above the TFF line there is a stairs on the slope consisting of upslope facing scarps located one above another and formed in loose colluvial and moraine deposits. Slip displacements are not clearly seen here excluding some cases. Thus, for example, two neighboring scours on the left slope of the Sulu-Bakair river valley within the TFF zone have experienced a right-lateral bending (Fig. 3). On the right bank of the river a small stream channel was beheaded along the fault, and now its upper reaches are at a distance of 128 m from the lower ones (Fig. 4). A neighboring stream channel was shifted to the right on the distance of 57 m, but its valley is smaller than that of previous one.

In a place of crossing of the Korumtor Spring by the Talas-Fergana Fault (Shilbilisay River basin) the fault is expressed by a visible depression in relief. An upslope facing scarp is located along it. Its width – 30 m, depth – down to 3 m (Fig. 5). The upslope facing scarp is also visible in a body of Late Pleistocene (QIII2) moraine.

Fig. 4. The right-lateral deviation of channels on the distance of 128 m in the Late Quaternary moraine on the right slope of the Sulu-Bakair river valley within the TFF zone.

The Talas-Fergana Fault zone is well exposed in the region of the Kara-Bura pass due to building an automobile route. Here the fault is represented by a zone of hundreds meter wide composed of completely crushed cataclasites and milonites and rocks with traces of initial structural-material features. There are also lenses not modified by tectonic processes. The TFF line is clearly identified by lows in the relief and saddles on watershed spurs.

Probably to the west of the Kara-Bura pass the right-lateral slip turned to a fault plane to the north of the TFF. Thus, in the upper reaches of the Kara-Bura river on the northern slope of

several tens meter thick, the fault zone is marked by springs. Above the TFF line there is a stairs on the slope consisting of upslope facing scarps located one above another and formed in loose colluvial and moraine deposits. Slip displacements are not clearly seen here excluding some cases. Thus, for example, two neighboring scours on the left slope of the Sulu-Bakair river valley within the TFF zone have experienced a right-lateral bending (Fig. 3). On the right bank of the river a small stream channel was beheaded along the fault, and now its upper reaches are at a distance of 128 m from the lower ones (Fig. 4). A neighboring stream channel was shifted to the right on the distance of 57 m, but its valley is smaller than

In a place of crossing of the Korumtor Spring by the Talas-Fergana Fault (Shilbilisay River basin) the fault is expressed by a visible depression in relief. An upslope facing scarp is located along it. Its width – 30 m, depth – down to 3 m (Fig. 5). The upslope facing scarp is

Fig. 4. The right-lateral deviation of channels on the distance of 128 m in the Late

Quaternary moraine on the right slope of the Sulu-Bakair river valley within the TFF zone. The Talas-Fergana Fault zone is well exposed in the region of the Kara-Bura pass due to building an automobile route. Here the fault is represented by a zone of hundreds meter wide composed of completely crushed cataclasites and milonites and rocks with traces of initial structural-material features. There are also lenses not modified by tectonic processes. The TFF line is clearly identified by lows in the relief and saddles on watershed spurs. Probably to the west of the Kara-Bura pass the right-lateral slip turned to a fault plane to the north of the TFF. Thus, in the upper reaches of the Kara-Bura river on the northern slope of

that of previous one.

also visible in a body of Late Pleistocene (QIII2) moraine.

the Talas range we observed an upslope facing scarp causing beheading and right-lateral shifting of dry channels and scours (Fig. 6 and 7).

Fig. 5. A photograph of the Talas-Fergana Fault zone. A view NW-ward from Korumtor river basin.

To the south-east of the Kara-Bura pass the Talas-Fergana Fault is well pronounced in three recessional moraines filling the upper valley of the Karakasmak river. Here it is represented by a zone of sagging located at oblique angles to each other and cutting moraine and fluvioglacial sediments. Along the southern line one can observe right-lateral deviation of dry channels (up to 34.7 m) and watersheds between them. We also observed a recessional moraine body deposited at the end of the Late Pleistocene and shifted on 28.3 m. Further to the south there is a stairs consisting of upslope facing scarps on a steep slope.

As we described above, along the whole its length the Talas-Fergana Fault is expressed in relief in a form of a deep depression – upslope facing scarp which cuts both basement rocks and Quaternary deposits (Fig. 8).

Fig. 6. Beheaded dry scours (shown by dashed lines) on the right slope of the upper Kara-Bura river valley. The rupture of upper and lower parts of the scours occurred along the slip fault (show by arrows) located in the north of the main trace of the Talas-Fergana Fault.

Mentioned above upslope facing scarp testifies on active seismic life of NW chain of the Talas-Fergana Fault. A number of features point on the fact that it is a real seismic-rupture form and not a depression of weathering developed along a zone of milonites and cataclazites.


fluvioglacial sediments. Along the southern line one can observe right-lateral deviation of dry channels (up to 34.7 m) and watersheds between them. We also observed a recessional moraine body deposited at the end of the Late Pleistocene and shifted on 28.3 m. Further to

As we described above, along the whole its length the Talas-Fergana Fault is expressed in relief in a form of a deep depression – upslope facing scarp which cuts both basement rocks

Fig. 6. Beheaded dry scours (shown by dashed lines) on the right slope of the upper Kara-Bura river valley. The rupture of upper and lower parts of the scours occurred along the slip fault (show by arrows) located in the north of the main trace of the Talas-Fergana Fault.

Mentioned above upslope facing scarp testifies on active seismic life of NW chain of the Talas-Fergana Fault. A number of features point on the fact that it is a real seismic-rupture form and not a depression of weathering developed along a zone of milonites and

1. Localization to the fault of a number of seismic-gravitation forms (rock- and landslides). For example, a limestone rockslide which locates in 500-600 m east of the Kara-Bura

2. Linear upslope facing scarp is well traced, in spite of it crosses different relief forms, as well as different rock formations. It is particularly well expressed in moraine bodies. 3. The up slope facing scarp cuts channels of temporary springs where the tectonic dams are formed. An existence of the tectonic dams is the direct evidence of impulse

the south there is a stairs consisting of upslope facing scarps on a steep slope.

and Quaternary deposits (Fig. 8).

cataclazites.

pass (Khodzhaev, 1985).

movements along the fault during a moment of its seismic refreshment (Khromovskikh and Nikonov, 1984).

Fig. 7. Upper reaches of the Kara-Bura river, right slope of the valley. Picture of one of beheaded scours (shown by dashed line) along a slip fault (shown by two arrows) in the north of the TFF. The upper portion of the scour is shifted to the right.

Fig. 8. A map of the Talas seismogenic structure (modified after A.K. Khodzhaev, 1985): 1 – watershed line of the Talas Range; 2 – contour lines in 200 m; 3 – seismogenic ruptures (a – normal faults, b – cracks); 4 – rivers and springs' beds; 5 – river captures; 6 – seismically induced rockslide.

4. An intake of frontal parts of recent taluses by the upslope facing scarp testifies on youth and instantaneity of its formation. This phenomenon one can observe east of the Kara-Bura pass. If not, an ancient upslope facing scarp would be covered by the colluvial material, the talus would gush over the scarp and will continue its movement down the slope.
