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Abstract. Landslides triggered by strong earthquakes often caused most of the global damage and most of all casualties related to the events, such as shown by the M = 7.7 Peru earthquake in 1970, by the M = 7.6 El Salvador earthquake in 2001 or by the M = 7.4 Khait (Tajikistan) earthquake in 1949. The obvious impact of a landslide on the population is directly related to its movement. Yet, prediction of future failure potential and hence future risk to population is necessary in order to avoid further catastrophes and involves the analyses of the origin of seismic instability. The seismic landslide potential is mainly determined by the interaction between the regional seismic hazard and local geological conditions. At a local scale, seismic factors interfering with geological conditions can produce site-specific ground motions. The influence of such Site Effects on instability is the principal topic of this paper, which is divided into two parts, A and B. The present Part A is concerned with the correlation of field data with observed instability phenomena. Field data were obtained on mainly three landslide sites in the Northern Tien Shan Mountains in Kyrgyzstan, Central Asia. Geophysical prospecting, earthquake recordings, geological observation, trenching and geotechnical tests were the main investigation tools. The collected information gives an insight in the geological background of the slope failure and allows us to roughly infer failure mechanisms from field evidence. A detailed analysis of the susceptibility of a mechanism to specific geological conditions will be shown in Part B.

We present 24 new apatite fission track (AFT) ages and 18 track length measurements from the Baikal region, SE Siberia. Most samples have AFT ages between 140 and 100 Ma, with relatively high mean track lengths ( c. 13.2 μ m). The relationship between AFT ages, elevation and mean track lengths indicate that the samples record rapid cooling during the Early Cretaceous (140–120 Ma), as also shown by thermal history inversion of track length distributions. Cooling took place during a Late Jurassic-Early Cretaceous orogenic phase, related to closure of the Mongol-Okhotsk ocean and reflected in the exhumation of metamorphic core complexes followed by thrusting and reverse faulting, basin inversion and large vertical motions. The variation in AFT ages throughout the study area can be partly explained by differences in geothermal structure but differential denudation also played a role. Minimum amounts of Early Cretaceous denudation are estimated at 2–3 km.

The paper presents a geodynamic interpretation of the deep structure and active tectonics of the northern Tien Shan, with particular emphasis on strike-slip motions, which produced a pull-apart in the centre of the Issyk-Kul basin. The study is based on a detailed interpretation of satellite imagery, fault plane solutions of earthquakes, seismic, and geodetic data.Seismic and magnetotelluric studies show tectonic layering of the Tien Shan lithosphere, with several nearly horizontal viscoelastic layers and the lower layer underthrust northward in the northern Tien Shan. This active process may be responsible for the intricate present-day tectonic framework of the northern Tien Shan.The recent tectonics of the northern Tien Shan inherits the earlier structure: The lens-shaped Issyk-Kul microcontinent comprising Precambrian-Palaeozoic metamorphic and magmatic rocks is surrounded by thick shear zones which have been involved in the activity over most of the Cenozoic. In the Quaternary the strain propagated as far as the central part of the Issyk-Kul basin.