Chinese dam triggers earthquake, rattles Hong Kong

Chinese dam triggers earthquake, rattles Hong Kong

(Probe International, February 16, 2012) An earthquake that shook Hong
Kong early this morning was triggered by the Xinfengjiang dam on China's
mainland, say officials from the Guangdong Provincial Seismological Bureau.

by Patricia Adams

Zhong Yijun, the vice director of the Guangdong Provincial Seismological
Bureau, told China News Service (Zhongguo xinwen she), today's
earthquake in Hong Kong was caused by the filling of the Xinfengjiang
reservoir.

The magnitude 4.8 quake, which hit at 2:34 AM local time, occurred in
Heyuan prefecture in the northern part of Guangdong Province and could
be felt in Guangzhou, Shenzhen and Hong Kong. There were no reports of
injuries.

This isn't the first time the dam has triggered a temblor. Xinfengjiang
caused China's largest and most famous reservoir-induced seismic event
in 1962 when it triggered a 6.1 magnitude earthquake that toppled
buildings and cracked the dam.

The phenomena, known as "reservoir-induced seismicity" (RIS), occurs
when a full reservoir creates extra pressure in the micro-cracks and
fissures in the ground under and near the reservoir, in essence
lubricating them. When the reservoir is drawn down, the friction caused
by the mass of the reservoir relaxes, allowing slippage to occur.

According to data from the Guangdong Provincial Seismological Bureau,
six earthquakes with magnitudes greater than 5 (including the largest
M6.1 quake in 1962) have occurred since the Xinfengjiang reservoir began
filling in 1959. Since then, small and medium earthquakes in the area
has been relatively active, with 44 seismic events greater than a
magnitude of 4 on the Richter scale occurring since impoundment began.

Zhong says that larger magnitude earthquakes are unlikely in the near
future.

The geological phenomena of reservoir-induced seismicity has gathered
intense interest since scientists began investigating the likelihood
that China's massively destructive 2008 earthquake in Sichuan was
triggered by the Zipingpu dam. That magnitude 7.9 quake killed an
estimated 90,000 people.
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