New Zealand: Aftershocks Continue Following the 2010 Canterbury Earthquake
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Pastor Dale Morgan
Oct 7, 2010, 9:35:22 PM10/7/10
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Great Earthquakes In Diverse Places
New Zealand: Aftershocks Continue Following the 2010 Canterbury Earthquake
By Brian Cross
Published Oct 7, 2010
In the weeks following the 2010 earthquake, Canterbury residents have learned to endure numerous aftershocks as they rebuild their lives.
At 6.29am on Friday 8 October 2010 an earthquake measuring 4.2 on the richter scale rattled Christchurch. It came 12 minutes after a 4.4 shake, another early morning wake-up for people forced to become accustomed to seismic activity since the big one struck on 4 September. That most recent aftershock was number 325 on the basic data list of Canterbury aftershocks published by New Zealand’s GeoNet service.Several Large Aftershocks Rocked Canterbury
The smallest aftershock registered on GeoNet’s website was a 2.5, barely big enough to be noticed by a person at rest. But there have been some sizeable ones too, sufficient to cause concern for homes and commercial buildings damaged in the main shock of maginitude 7.1. That’s not to mention the psychological effect of the ongoing series of aftershocks on Christchurch and Canterbury residents who have much to endure due to loss of property and home comforts in the initial event.
The largest Canterbury aftershocks to date were a couple of 5.4s, one on 6 September and the other a day later. In the first week after the initial earthquake there were 74 registered aftershocks, in the following week 84. Week three saw 29 aftershocks as published by GeoNet, and there were another 44 in week four.
Gradually the earth beneath the Canterbury Plains was showing some sign of settling down after the main earthquake that was centred under the town of Darfield. But the seismic shift along the previously unknown Canterbury faultline was not done with by any means. For week five the GeoNet list shows 25 aftershocks - with 20 hours remaining in the seven-day period for potentially more.
The aftershocks have been predominantly located around Darfield, the epicentre of the main shock. That’s normal, although movement along the faultline during main shocks can cause aftershocks some distance away. So it is, with many aftershocks centred some kilometres to the east, closer to where the population is greatest.
Many Aftershocks are not Recorded
The above figures are only part of the seismic picture. Geonet’s website explain that scientists are working through a myriad of data to identify all the aftershocks that are cluttering their equipment. It will take months for the true number to accurately be known, but many more there certainly have been. That is reflected in some of the media reports, which at first glance appear to exaggerate the real number of aftershocks.
According to the scientists, one to two thousand aftershocks of magnitude three could be identified over the course of the entire aftershock sequence. With a difference of roughly ten-fold for each of the Richter scale ranges, “that means there are probably up to 20,000 magnitude twos!”, Geonet states on its website. In applying resources to tracking all the aftershocks, scientists must “strike a balance between the people we have to do the work and what gives us the best scientific outcome.”
Documenting an Aftershock Sequence is a Huge Task
The nature of an aftershock sequence is that it can be expected to gradually diminish over time, with the incidence of larger events more rapidly reducing. 12 aftershocks of magnitude five or greater have been recorded in Canterbury, all in the first week after the main earthquake. (Elsewhere GeoNet records that figure as nine, suggesting three may have been reassessed downwards).
So the earthquake statistics and the variously reported number of aftershocks throw up anomolies in the recoded data. That only shows the immensity of the job on hand for scientists when a large earthquake strikes. There are some 15,000 earthquakes recorded in New Zealand in a typical year. That’s a year without an aftershock sequence as currently being experienced and endured by the people of Christchurch and their rural Canterbury neighbours.
Read more at Suite101: Aftershocks Continue Following the 2010 Canterbury Earthquake http://www.suite101.com/content/aftershocks-continue-following-the-2010-canterbury-earthquake-a294468#ixzz11j88t2ve
New Zealand: Aftershocks Continue Following the 2010 Canterbury Earthquake
By Brian Cross
Published Oct 7, 2010
In the weeks following the 2010 earthquake, Canterbury residents have learned to endure numerous aftershocks as they rebuild their lives.
At 6.29am on Friday 8 October 2010 an earthquake measuring 4.2 on the richter scale rattled Christchurch. It came 12 minutes after a 4.4 shake, another early morning wake-up for people forced to become accustomed to seismic activity since the big one struck on 4 September. That most recent aftershock was number 325 on the basic data list of Canterbury aftershocks published by New Zealand’s GeoNet service.Several Large Aftershocks Rocked Canterbury
The smallest aftershock registered on GeoNet’s website was a 2.5, barely big enough to be noticed by a person at rest. But there have been some sizeable ones too, sufficient to cause concern for homes and commercial buildings damaged in the main shock of maginitude 7.1. That’s not to mention the psychological effect of the ongoing series of aftershocks on Christchurch and Canterbury residents who have much to endure due to loss of property and home comforts in the initial event.
The largest Canterbury aftershocks to date were a couple of 5.4s, one on 6 September and the other a day later. In the first week after the initial earthquake there were 74 registered aftershocks, in the following week 84. Week three saw 29 aftershocks as published by GeoNet, and there were another 44 in week four.
Gradually the earth beneath the Canterbury Plains was showing some sign of settling down after the main earthquake that was centred under the town of Darfield. But the seismic shift along the previously unknown Canterbury faultline was not done with by any means. For week five the GeoNet list shows 25 aftershocks - with 20 hours remaining in the seven-day period for potentially more.
The aftershocks have been predominantly located around Darfield, the epicentre of the main shock. That’s normal, although movement along the faultline during main shocks can cause aftershocks some distance away. So it is, with many aftershocks centred some kilometres to the east, closer to where the population is greatest.
Many Aftershocks are not Recorded
The above figures are only part of the seismic picture. Geonet’s website explain that scientists are working through a myriad of data to identify all the aftershocks that are cluttering their equipment. It will take months for the true number to accurately be known, but many more there certainly have been. That is reflected in some of the media reports, which at first glance appear to exaggerate the real number of aftershocks.
According to the scientists, one to two thousand aftershocks of magnitude three could be identified over the course of the entire aftershock sequence. With a difference of roughly ten-fold for each of the Richter scale ranges, “that means there are probably up to 20,000 magnitude twos!”, Geonet states on its website. In applying resources to tracking all the aftershocks, scientists must “strike a balance between the people we have to do the work and what gives us the best scientific outcome.”
Documenting an Aftershock Sequence is a Huge Task
The nature of an aftershock sequence is that it can be expected to gradually diminish over time, with the incidence of larger events more rapidly reducing. 12 aftershocks of magnitude five or greater have been recorded in Canterbury, all in the first week after the main earthquake. (Elsewhere GeoNet records that figure as nine, suggesting three may have been reassessed downwards).
So the earthquake statistics and the variously reported number of aftershocks throw up anomolies in the recoded data. That only shows the immensity of the job on hand for scientists when a large earthquake strikes. There are some 15,000 earthquakes recorded in New Zealand in a typical year. That’s a year without an aftershock sequence as currently being experienced and endured by the people of Christchurch and their rural Canterbury neighbours.
Read more at Suite101: Aftershocks Continue Following the 2010 Canterbury Earthquake http://www.suite101.com/content/aftershocks-continue-following-the-2010-canterbury-earthquake-a294468#ixzz11j88t2ve
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