Normally, we pay very little attention to Richter 5.0 to 5.9
earthquakes - however, if they are shallow enough and close to an
urban center, such events can still be destructive as residents of
Christchurch New Zealand can attest. Shown here is the only Richter
6.0 known to have struck in the last 40 years - It was on 10/24/2002
and was a Richter 6.2. The map is somewhat deceptive - there was a
Richter 5.5 aftershock at the same place an hour later, followed by a
Richter 5.0 an hour after that. There had been a cluster of four
events (all 5.1s) nine months earlier. Given the location, our models
assert that a more powerful earthquake (>7.0) would have triggered an
overturn and explosion. Almost ten years later the saturation of gases
has increased so the power of the earthquake needed to trigger a
disaster has decreased.