Russian Geology and Geophysics Vol. 42, No. 10. pp, 1583-1592. 2001 LANDSLIDES AND SURFACE BREAKS OF THE 1911 M- 8.2 KEMIN EARTHQUAKE (Kyrgyzstan) D. Delvaux, K. E. Abdrakhmatov*, I. N. Lemzin*, and A. L. Strom** Royal Museumfor Central Africa, B-3080 Tervuren, Belgium * Kyrgyz Institute of Seismology, Asanbai 52/1, Bishkek, 720060, Kyrgyzstan ** Gidroproekt Institute, Volokolamskoe shosse 2, Moscow, 125812, Russia Geologiya i Geofizlka UDe 550.34(575.2) The 1911 Ms = 8.2 Kemin (Kebin) earthquake in the northern Tien Shan (Kazakhstan, Kyrgyzstan) formed a complex system of surface ruptures nearly 190 km long and numerous landslides and rock avalanches up to tens of millions of cubic meters in volume. Judging from their distribution, six fault segments of the Kemin-Chilik and the Aksu fault zones with different strikes, dips, and kinematics were activated. The Kemin earthquake was one of the strongest events of a sequence of seismic catastrophes that affected the Kungei and Trans-iii-Alatau mountain ranges between 1887 and 1938. The effects of the Kemin earthquake are well documented in a monograph published soon after the event by K. I. Bogdanovich. In the framework of the European INCO·COPERNICUS program, the surface ruptures, landslides, and rockslides associated with this earthquake have been re-examined in detail. In addition, the large-scale tectonic setting of the Kemin-Chilik and Aksu fault zones has been re-evaluated, and their segments have been identified and described. The whole system forms a sinistral transpressional structure, which controls the formation of the mountain ranges between the Issyk-Kul' depression and the Kazakhstan block. The surface ruptures of the 1911 earthquake can presently be observed in the field over a total length of nearly 100 km and : generally reactivate longer-term cumulative paleoseismic fault scarps. The presence of well-expressed paleoseismic fault scarps and several tremendous ancient landslides in the Chon-Kemin, Chon-Aksu, and Aksu valleys can be considered as evidence for strong prehistoric earthquakes. Active fault, landslides, 1911 Kemin earthquake, Tien Shan, Kyrgyzstan INTRODUCTION The 1911, M s 8.2 Kemin earthquake occurred along the Chon-Kemin-Chilik fault zone, at the interaction between the Kazakhstan platform and the Tien Shan fold belt. It was part of a sequence of strong earthquakes, starting with the 1887, M s 7.3±0.5 Verny earthquake near Alma-Ata [1, 2], and followed shortly by the 1889, M s 8.3 Chilik [3], the 1911, M s 8.2±0.3 Kemin (Kebin) [4], and the 1938, M s 6.9±0.5 Kemin-Chu earthquakes [5, 6]. The last three marked an east-to-west propagation of stress release along the Chon-Kemin-Chilik fault zone (Fig. 2). The Kemin earthquake killed 452 and injured 740 people [4]. The number of casualties was relatively low for such a strong earthquake, because it affected mainly mountainous areas of the Kyungei-Alatau and Trans-IIi-Alatau Ranges, between Lake Issyk-Kul' and Alma-Ata (formerly Verny). It generated surface ruptures along several fault segments and caused landslides, rockfalls, debris flows, and secondary soil dislocations over a total area of 10,000 km 2 , 200 km long and 70 km wide, elongated parallel to the fault zone [4, 7]. The surface effects of the 1911 Kemin earthquake were investigated beginning a few months after the event by an expedition led by K. I. Bogdanovich in spring 1911 [4]. This team explored the mountainous area affected by the earthquake, mainly by horses, following the major valleys. They mapped and described all the observed surface deformations and differentiated primary effects, of postulated tectonic origin, from secondary ©2003 by Allerton Press, Inc. 1583 Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by Allerton Press, Inc. for libraries and other users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that the base fee of $50.00 per copy is paid direclly to CCC, 222 Rosewood Drive, Danvers, MA 01923.