(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.