Canterbury – Aftershocks Ease

Aftershock activity in Canterbury has eased this morning.

Monday 6th September 2010

Aftershocks of Saturday’s seventh magnitude Darfield earthquake have eased in number and strength this morning.

GeoNet has recorded hundreds of aftershocks across the region during the last two days, and nearly a hundred of these have now been analysed.

Darfield Quake Aftershocks to 6 September 2010

[click for larger image]
This map (courtesy of GeoNet) shows a snapshot of the aftershocks analysed by GeoNet during the 52 hours to midday today. The map shows that the aftershocks are spread across the Canterbury Plains and even out on Banks Peninsula and under Pegasus Bay.

The dynamic version of the earthquake map for Canterbury, which includes new aftershocks as they are analysed, can be found here. It show earthquakes analysed by GeoNet during the past 60 days and will age as time passes.

The decline in earthquake activity is part of the expected pattern of aftershocks. However, bursts of activity can still be expected, with aftershocks clustering together around larger events. After a string of magnitude 3 events in recent hours, a magnitude 4.5 aftershock struck at 12:35 today. A magnitude 6 aftershock is still possible.

Surface water is an ongoing problem throughout the Canterbury region, and it will be some time before many of the causes of the flooding can be determined. Some will be due to water being forced out of the ground as it liquefied during the intense shaking that also caused mud and sand to burst out onto the surface of the ground.

Reports of bores and wells now flowing to the surface are also being made. In one case discussed this morning, a farm well normally pumped from 70 metres below the surface is now expelling water at the surface.

Burst water mains will have contributed to the surface water and the reported surge of water along the Avon River soon after the main quake may have affected nearby low-lying properties.

The cause of all these phenomena will become more clear in the coming days.

Meanwhile, the assessment phase continues and the first building demolition has commenced in Victoria Street in central Christchurch.

One Response to “Canterbury – Aftershocks Ease”

  1. Ken says:

    Radio NZ National’s 2 p.m. news reports that a badly quake-damaged building in the Christchurch suburb of St. Albans has collapsed, and some people have had a narrow escape. Whether an aftershock, the strong wind or some other event caused the collapse is not clear at this stage.

    It makes you think – Canterbury has been remarkably lucky that no deaths have resulted from the quake so far. There have been few serious fires (a major killer in Hawke’s Bay in 1931) and sudden building collapses have been rare even though residents have reported seeing material being shed by damaged structures during aftershocks.

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