One ofthe lessons learned from the catastrophic Wenchuan earthquake is that extremely strong event has occurred first time within peoples' memory in the region with millennia-long seismic record. It clearly shows that extreme events that can occur in favorable seismotectonic conditions should be considered for seismic hazard and slope stability assessment irrespective of presence or absence of similar phenomena in the historical and instrumentally recorded occurred along the northern and southern boundaries of this mountain system, while its central part have no record of such events in the past. However, this record hardly extends for 200 years. At the same time Central (Inner) Tien Shan is extremely rich of surface ruptures, rockslides and other features that can be interpreted as geological traces of strong past earthquakes. It hydraulic projects are proposed and implemented here. Possibility of a very strong earthquake occurrence should be considered both for dams' design and for the reservoir slopes stability assessment.
The catastrophic 2008 M8.0 Wenchuan earthquake gave us several tragic lessons, one of which, may be the most important, is that this extremely strong event has occurred first time within people' memory in the region with the millennia-long seismic record (Catalogue … 1989, Wang 2004). None of this numerous strong earthquakes that have occurred in this seismotectonic zone exceeded M7.0–7.5.
Another lesson is that location and kinematics of surface ruptures, which mark the causative fault, play a critical role in the spatial distribution of the earthquake- triggered landslides. Most of slope failures occurred within the hanging wall of the 180-km long surface rupture with up to 6-m lateral displacement (Chigira et al. 2008). Largest river-damming rockslides also concentrate just along main active faults (Yin et al. 2008). The same phenomena were observed at the 1999 M7.3 Chi-Chi earthquake in Taiwan (Lin et al. 2004), at the 1911 M8.2 Kemin earthquake in Kyrgyzstan (Bogdanovich et al. 1914, Delvaux et al. 2001) and in many other cases.
These lessons mast be applied to other seismically active regions, where the historical record of hazardous natural phenomena is much shorter than expected recurrence interval of strongest earthquake and where the possibility of large-scale slope failures is high enough due to rugged terrain and geological conditions.
One of such regions is the Tien Shan, its inner (Kyrgyzian) part in particular. Spatial distribution of strong earthquakes, both historical and instrumentally recorded along the northern and southern boundaries of this mountain system, while its central part, which is neotectonically as active as boundary zones, has almost no records of such events in the past (Figure 1). It should be poited out, however, that the Tien Shan historical record of earthquakes hardly extends up to 200 years, since this region was inhabited by nomads lacking written history.
At the same time the entire Tien Shan, including its central part, is extremely rich of surface ruptures, rockslides and other features that can be interpreted as geological traces of strong past earthquake (Figure 2).