Wednesday, 28 December 2011

Major Earthquake in southwestern Siberia. 27 December 2011.

Slightly after 11.20 pm local time (slightly after 3.20 pm, GMT) on Tuesday 27 December 2011 a severe Earthquake shook a remote part the Kaa-Khem District of the Tuva Republic, southwestern Siberia, close to the Mongolian border, roughly 96 km to the east of Kyzyl, the capitol of the Tuva Republic. The quake was measured as having a magnitude of 6.6 on the Richter Scale and occurring at a depth of 6.9 km by the United States Geological Survey, and as having a magnitude of 6.5 on the Richter Scale and having a depth of 10 km by the Russian Academy of Sciences, which is slightly less severe but still pretty bad; the larger the magnitude and the shallower the depth, the more severe any effects felt at the surface will be. There have been at least three aftershocks, with magnitudes of 4.7-4.8.

Population exposure map from the United States Geological Survey, showing the epicenter of the quake (black star), the intensity of the shaking at the surface (coloured lines, yellow more severe than green), and local population centers (grey writing)

The quake has also been described as a magnitude 9.5 quake in some Russian press releases; this is a Medvedev-Sponheuer-Karnic (MSK) scale number; the MSK scale is an intensity measure used by Russian seismologists, it is an indication of the likely damage caused by a quake rather than the actual energy released as in the Richter Scale. A magnitude 9.5 quake on the MSK scale is considered to be Destructive to Devastating, with general panic, people thrown to the ground, severe damage to non-earthquake proofed buildings, damage to earthquake proofed buildings, and the potential of massive landslides and flooding.

The quake was felt in Kyzyl, where there are reports of minor damage to buildings but no casualties, but not as yet from the area where the quake was centered. The area is sparsely populated, with the majority of homes in the area being holiday homes owned by Russian city dwellers, which are unlikely to have been in use in mid-winter, but it is still thought highly likely that there will have been casualties, as buildings in the area are not generally Earthquake-proofed, and people forced to leave their homes abruptly in the middle of the night during the Siberian winter are deemed to be at extreme risk of hypothermia; temperatures are likely to have been between -20°C and -30°C in the area at the time of the quake. Emergency teams have been dispatched to the area, and a state of emergency declared by authorities in the Tuva Republic.

Major Earthquakes in southwestern Siberia are rare, the most recent was a quake in the neighboring Altai Republic in September 2003 that measured 7.2 on the Richter Scale, prior to which there had been no major quakes in the region for over 70 years. These quakes are a product of India pushing into the Eurasian Plate far to the south, which causes the eastern part of the Eurasian Plate to rotate clockwise, provoking pressure to build up in Central Asian rocks and eventually faulting within the mountains of southwestern Siberia.

2 comments: