Humans can make rockfalls from earthquakes more dangerous

By Mark Quigley and Josh Borella

Earthquakes (including the tsunamis they generate) are Earth’s most fatal natural hazard, accounting for approximately 55% of the more than 1.35 million disaster deaths in the last two decades. The US Geological Survey predicts that more than 2.5 million people will die from earthquakes this century alone.

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Landslides and other mass movements, such as rockfalls, are another important cause of earthquake fatalities. In the magnitude 7.9 Wenchuan earthquake in China in 2008, landslides caused more than 20,000 of the estimated 80,000 fatalities.

Landslides caused approximately 26,000 fatalities in the magnitude 7.6 Kashmir earthquake in 2005.

Of the 185 fatalities in the magnitude 6.3 earthquake at Christchurch in New Zealand in 2011, five were caused by rocks that hit people after falling from steep basaltic bedrock cliffs.

In the aftermath of the Christchurch earthquakes, the annual fatality risk posed by future rockfalls was calculated by a team led by GNS Science for individuals living in areas of Christchurch susceptible to mass movements. Some residents were estimated to have a greater than 1 in 1,000 annual chance of dying from future rockfalls.