One of the consequences of the continental collision is high seismic activity across
the southern margin of the FSU (Figure 16.3).
Fig. 16.3 Seismic regionalization in Central Asia. After Alpatiev (1976)
The Complex Seismological Expedition, established in the region of Garni in the
aftermath of the Khait earthquake of 1949, has recorded more than 90000 crustal
earthquakes since 1955 (Hamburger et d., 1992). The Central Asian mountains have also been
a scene for many devastating historical earthquakes. Thus between 1914 and 1957, there
were four earthquakes with a magnitude of 8-9 points on the Richter scale in the Kopetdagh
alone and in ten years between 1985 and 1995, there were sixteen earthquakes with a
magnitude exceeding 6.5 points across the region (Vysokogornye issledovamya, 1996). In
earlier history, the world's most devastating earthquakes occurred in the densely
populated valleys: in the Chuisky oasis in 1885, in Alma-Ata in 1887, in the Gissar valley
in 1907, in Ashgabat in 1948, in the Surkhob valley in 1949, and in Tashkent in 1966. The
Surkhob earthquake of 1949, which reached 10 points, completely destroyed the ancient town
of Khait, claiming over a thousand lives. The Surkhob valley was one of the richest
agricultural areas in the Pamir-Alay whose slopes, covered with thick loess and loess-loam
mantles were intensively cultivated over 300 years. Much of the devastation was due to
gigantic landslides and mudflows which followed the earthquake, transporting over 4 x
1010m3 of material and destroying over a half of the highly productive arable
land (Merzlyakova, 1996). Landslides and rockfalls are often responsible for damming the
rivers and the formation of lakes. Perhaps the most dramatic example is the formation of
Lake Sarezskoe in 1911 by a landslide which formed a 750 m high dam across the river
Murgab. The lake, which is over 60 km long and over 500 m deep, is the second deepest lake
in the region after the Issyk-Kul. Earthquakes are often accompanied by land subsidence.
The formation of grabens occurred during the Alma-Ata earthquake in 1911 and numerous
fissures appearing as overthrusts occur on the northern shore of the Issyk-Kul.
