Oct 19 2010 - Strong aftershock close to Christchurch

A magnitude 5.0 earthquake rocked Canterbury at 11:32 am today.

A further aftershock of the 4 September magnitude 7.1 Darfield earthquake occurred 10 km south-west of Christchurch city centre at a depth of 9 km.

There have been reports of power outages and further damage to buildings. This earthquake will have felt particularly strong to the residents of Christchurch, comparable to the magnitude 5.1 aftershock on 8 September, due to their close proximity to the city. As seen on the accompanying map, those two earthquakes have been the closest to the city, with the rest at varying distances to the west. How big the earthquake feels to people is dependent on how close they are to it. That is why the Modified Mercalli intensity scale is a better way of comparing shakes, as it grades the impact upon people and the environment.

The occurrence of this earthquake falls within the expected number and size of aftershocks for this month: between 0 and 5 magnitude 5.0 or greater quakes could be expected - this is the third earthquake of that size since 4 October.

The top 5 shakes as recorded at the Christchurch Botanic Gardens (CBGS) seismograph, close to the city centre, are:

Christchurch Botanic Gardens (CBGS)

Date

Magnitude

Peak Ground Acceleration

4 Sep 2010 4:35 am7.118.124 %g
8 Sep 2010 7:49 am5.115.685 %g
19 Oct 2010 11:32 am5.07.229 %g
25 Sep 2010 7:58 pm4.14.132 %g
4 Sep 2010 7:56 am5.22.741 %g

Contrast this top 5 with a list for Darfield (DFHS):

Date

Magnitude

Peak Ground Acceleration

4 Sep 2010 4:35 am7.152.653 %g
4 Sep 2010 11:12 am5.319.927 %g
8 Sep 2010 3:59 am4.511.085 %g
11 Sep 2010 9:01 am4.09.800 %g
5 Sep 2010 12:57 am3.87.191 %g

and Lincoln (LINC):

Date

Magnitude

Peak Ground Acceleration

4 Sep 2010 4:35 am7.191.426 %g
4 Sep 2010 7:56 am5.221.83 %g
5 Sep 2010 1:04 pm5.015.473 %g
6 Sep 2010 11:24 pm5.215.116 %g
15 Oct 2010 10:31 pm4.612.743 %g

Clearly where you are in relation to the epicentre is just as important as the magnitude of the earthquake.

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