Avian Flu Diary: 5.5 & 6.0 Aftershocks Strike Christchurch

# 5623

An Active Ring of Fire

Original Map – USGS

Overnight here in the USA, and early afternoon local time (1pm & 2:20pm), two strong and very shallow earthquakes struck near Christchurch, New Zealand, reportedly injuring a small number of people and causing major power outages and widespread local damage.

This comes a little less than four months after the devastating 6.3 mag aftershock (see NZ: Aftershocks, Rescue Attempts, Casualties, And The Mounting Toll) of the September 2010 quake, and at a time of year when winter nighttime temperatures are dropping uncomfortably to near freezing.

Kiwibird, an editor and senior moderator of FluTrackers, has started a new news thread on the new quake. You’ll find local news stories, photos, and first hand accounts posted there.

As the residents of Japan and Chile can testify, aftershocks – sometimes only a magnitude less than the original quake – are common during the months and years following a major earthquake.

They can pose a continual physical danger, and ongoing psychological challenge, to the to residents of the stricken area.

The USGS has released this Tectonic Summary on these latest temblors.

The June 13, 2011 South Island, New Zealand earthquake is a continuing part of the earthquake sequence that initiated with the magnitude 7.0 September 3, 2010 Darfield, New Zealand earthquake. The June 13, magnitude 6.0 earthquake is a dominantly strike-slip faulting earthquake that is at the eastern end of the inferred rupture of the 21 February 2011 magnitude 6.1 earthquake. Both this magnitude 6.0 event and the previous magnitude 6.1 event have an inferred fault plane striking approximately east-northeast. The entire earthquake sequence is broadly associated with regional plate boundary deformation as the Pacific and Australia plates interact in the central South Island, New Zealand.

This latest earthquake, similar to the February 21 earthquake, is close to the main population centers of Christchurch, New Zealand. This region has suffered substantial casualties and damage to buildings, infrastructure, and lifelines from a series of events starting with the February 21 earthquake. Additionally, the earthquakes close to Christchurch caused substantial liquefaction in residential areas. The June 13 earthquake was preceded by a nearby magnitude 5.2 foreshock, about 1 hour and 20 minutes earlier. There is no specific surface fault that has been observed for the post-September 3 earthquakes near Christchurch, or directly linking them to the observed September surface fault rupture. There have however been a substantial number of aftershocks forming a continuous swath extending from the September 3 events to the June 13 earthquake.

As I wrote last March in The Ring Of Fire, we live on a seismically active planet, and while `Great Quakes’ are relatively rare (happening somewhere in the world – on average – of once a year), very damaging quakes of between 7.0-7.9 happen on practically a monthly basis.

(USGS chart)

And quakes the size of the one that struck Christchurch today happen about 10 times each month.

Many, of course, don’t occur this close to a populated area and this shallow, and so their impact isn’t always felt.

Tens of millions of people, however, live in high risk zones - and yet - many are unprepared for these all-too-common disasters.

No matter where you live, the images coming out of Japan, New Zealand, Haiti and Chile over the past couple of years should serve as a wake-up call to become better prepared.

From the USGS Great Southern California Shakeout website, we’ve this 4 and 1/2 minute video called Preparedness Now (Streaming | Video) that “depicts the realistic outcome of a hypothetical, but plausible, magnitude 7.8 earthquake on the San Andreas fault in Southern California.”

Which makes this a pretty good time to remind my readers about the study last year (see Revised Risk Of `The Big One’ Along San Andreas Fault) that suggests that Southern California may be more overdue for another major quake than previously thought.

For more on earthquake and general disaster preparedness, you might wish to look at these essays as well.