Why was the Christchurch Earthquake so destructive?

RTR2HWJV.jpg

Image: Simon Baker / Reuters

New Zealand is no stranger to the results of plate tectonics. The country sits almost directly on top of the boundary between two chunks of the Earth's crust, the Pacific Plate and the Australian Plate. The two plates grind against each other, creating tension spots where potential energy builds up and is released in the form of earthquakes—a lot like pushing on a stuck door until it finally flies open. New Zealanders feel as many as 200 earthquakes every year, but most are nothing more than a minor jiggle. And even big, throttling shakes, like the 7.1 magnitude quake that hit the country five months ago, can come and go without killing anyone.

Today's earthquake in Christchurch, New Zealand is different. Although it was relatively powerful—6.3 magnitude—it was still weaker than the quake last Fall. And yet, it's already the deadliest earthquake to hit New Zealand since 1931. What made this earthquake so dangerous? It's all about location, says New Scientist:

Last year's 7.1-magnitude earthquake was more than 10 times as strong as today's but caused no deaths, probably because it occurred at greater depth and further away from Christchurch: its epicentre was 70 kilometres west of the city. And the focus of September's quake was some 10 kilometres below ground - today's was half as deep.

Via Discover magazine's 80 Beats blog