Living with Earthquakes - Earthquake Engineering for Structural Design - page 63

(b)
Figure 2.18 2004 Indian Ocean earthquake. (a) Location of epicenter and tsunami;
(after NGDC, nd) (b) Produced tsunami (NOAA, 2004)
The 2005 Kashmir earthquake (Wikipedia, nd) occurred not far from the border
of Afghanistan and India along a fault associated to the Indian and Eurasian
tectonic plates. It was the strongest natural disaster in Pakistan's history in terms of
victims, destruction of infrastructure and economic assets.
For other earthquakes that occurred in this period, even if their magnitude was
high, there were no reports about a high number of deaths and important damage,
because they were located in scarcely populated areas.
The 2008 Sichuan (China) earthquake (known also as Wenchuan earthquake)
(Wikipedia, nd), magnitude 8.0 M, occurred on 12 May 2008, with the epicenter in
the Wenchuan County, Sichuan Western province of China (Fig. 2.19a). The
seismicity of this region is a result of Northward convergence of the Indian Plate
(represented by Himalayan Mountains and Tibetan Plateau) against Eurasian Plate
(represented by the very rigid Sichuan Plateau of South China Block). As a result
of this collision the Logomen Shan Fault formed, a collision thrust fault type.
Along this fault a high degree of stress concentration occurs and, finally, this
caused a sudden dislocation in fault, leading to the violent Sichuan earthquake. The
earthquake lasted about two minutes and released 30 times the energy of the 1995
Kobe (Japan) earthquake. The shallowness of epicenter (about 19 km), the density
of population of this region and the presence of many non-resistant structures and
school buildings, greatly increase the severity of the earthquake, producing the
collapse of many unprepared buildings (Fig. 2.19b,c). The main lesson learned
after this earthquake is that even an earthquake measuring magnitude 8.0 M, which
is considered a big one, need not necessarily be a calamity, it is the building
vulnerability which changes it into a disaster.