HKNIC - Earthquake Threats

Earthquake Threats
Earthquakes may occur in areas where there are "capable faults". These are dividing boundaries between two plates of the earth's crust which have experienced at least one significant seismic activity during the last 35,000 years, or several significant activities during the last 500,000 years. Regulations governing nuclear power stations in the United States specify that there should be no capable faults within 8 kilometres of a nuclear power station.

Daya Bay has no capable fault within 20 kilometres. In recent centuries, the most severe earthquake on record to affect the Daya Bay region occurred in 1918 near Nanao Island, which is about 280 kilometres from the Daya Bay site. The earthquake was rated 7.25 on the Richter Scale and had an effect at the Daya Bay site of Level VI on the Modified Mercalli Earthquake Intensity Scale (MMEIS).

The Richter Scale measures the energy released in an earthquake. It has no upper limit and earthquakes measuring as high as 9 have been recorded. MMEIS measures the power of an earthquake at a particular location, with the scale running from a low of I to a high of XII.

An earthquake will have only a single reading on the Richter Scale. While the scale is useful in measuring the strength of an earthquake, it does not describe the consequential damage. MMEIS, by contrast, assigns ratings to each of the many locations affected by an earthquake, and because the effects of the earthquake diminish the further away a location is from its epicentre, those closer will generally rate higher on MMEIS than those further away.

The Guangdong Seismological Bureau has estimated that the maximum earthquake intensity at Daya Bay will be no higher than Level VII on the MMEIS scale over the next century. To protect Daya Bay from the threat of earthquakes, key buildings, structures, systems and facilities are designed to withstand an earthquake with an intensity of up to Level VIII on the MMEIS scale.