2011-06-14
By Deborah Ritchie
An M6 earthquake occurred near Christchurch, New Zealand yesterday, Monday 13th June at 02:20:50 UTC (2:20 PM local time). According to reports from risk analysts, Eqecat, the reported epicentre (43.58S, 172.74E) is just six miles southeast of Christchurch’s central business district, where buildings previously damaged by large earthquakes over the past nine months suffered additional damage.
This latest event is expected to cause an additional US$3-5bn in insured losses to the region. Monday’s M6 event was preceded by a M5.2 earthquake immediately to the west just 1 hour and 20 minutes before the main shock.
Since the M7 earthquake on 3rd September, two M6 events have occurred – one on February 21 and another on June 13 – as well as 11 M5 events. The epicentre of Monday's earthquake is very close to the epicenter of the 21st February M6.1 event.
This latest quake ruptured dominantly as a strike-slip fault near the eastern end of the inferred rupture of the February M6.1 event
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This latest earthquake is affecting an area already significantly damaged by earlier earthquakes. The larger, distant M7 Darfield earthquake in September caused an estimated US$4-6bn in insured losses, while the urban M6 earthquake in February caused an estimated US$8-12bn in additional losses.
The February event destroyed an estimated one-third of the buildings within the Christchurch CBD. The primary factors in the damage in February were heavy, brittle construction (unreinforced masonry or non-ductile concrete), and liquefaction of poorly consolidated soils throughout Christchurch both along the Avon River and throughout the region.
Eqecat suggests reports of newly collapsed buildings from Monday’s event, along with additional disruptions to electrical, gas, and water utilities. Roads have become disrupted as additional liquefied soils tear up road surfaces.
Monday’s earthquake is not expected to cause significant damage to buildings undamaged by the February M6 event, but will cause incremental damage and loss.
The continuation of this sequence of damaging earthquakes to Christchurch along unknown fault structures is delaying the recovery and restoration efforts.
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