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Experts on Christchurch earthquake


Experts on Christchurch earthquake 
 
22 Feb 2011 

The Prime Minister John key said this evening that the confirmed death toll resulting from today's 6.3 magnitude earthquake near Christchurch stands at 65.

This is the second major earthquake event to occur in the region in recent months.

Twitter posts related to the earthquake are using hash tag #EQNZ.


Our colleagues at the Australian Science Media Centre gathered the comments below from Australia-based experts in earth sciences:

The answers to 12 questions are given below, feel free to use these quotes in your stories. Any further comments will be posted on our website at www.aussmc.org.

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Q1: Just how bad is an earthquake of magnitude 6.3?

Dr Gideon Rosenbaum is a Lecturer in the School of Earth Sciences, at The University of Queensland:

"A magnitude 6.3 earthquake can be devastating in one place and quite harmless in another. It depends on many factors. Most important is the distance of the epicentre from populated areas. As far as I understand, the earthquake today was shallower and closer to Christchurch in comparison to the September earthquake. The type of rocks in the affected areas are also very important. Hard rocks are stronger and more resistant, whereas soft rocks, particularly if wet, can amplify the seismic effect (a process called liquefaction). I think that Christchurch is built on silt that was affected by this process."

Dr Gary Gibsonis Principal Research Fellow in the School of Earth Sciences ,University of Melbourne:

"A magnitude 6.3 earthquake will occur when an active fault area approximately 15 km square ruptures, and one side moves about one metre relative to the other. Its effect depends on how close it is, and ground shaking will be severe within 10 to 20 kilometres of the rupture."

Q2: Should we expect further large earthquakes in the area? Are aftershocks likely?

Dr Gideon Rosenbaum is a Lecturer in the School of Earth Sciences, at The University of Queensland:

"Aftershock are common after big earthquakes."

Dr Gary Gibson,is Principal Research Fellow in the School of Earth Sciences ,University of Melbourne.

"The September earthquake and this earthquake will have relieved the majority of stress in the regions in which they occurred, so another larger earthquake is unlikely. However, aftershocks will certainly occur over the next few days and weeks which may cause further damage in weakened buildings, and will be very distressing for residents."

Q3: Is there a geological reason for multiple large earthquakes occurring within such a short time? (Both worldwide and also in that area of NZ)

Dr Gary Gibson,is Principal Research Fellow in the School of Earth Sciences ,University of Melbourne:

"Earthquakes always cluster in time and space with some large earthquakes having foreshocks and most large earthquakes have many aftershocks. Multiple large earthquakes are not uncommon, often when the main rupture of the earlier event is extended into an adjacent segment of the active fault."

Q4: Why is the New Zealand south island so geologically active?

Dr Gideon Rosenbaum is a Lecturer in the School of Earth Sciences, at The University of Queensland:

"The New Zealand South Island is dissected by a plate boundary zone. The Pacific and Australian plate are moving in respect to each other. The boundary itself is in the West coast (Alpine Fault), but some active faults are leaked to the East."

Dr Gary Gibson,is Principal Research Fellow in the School of Earth Sciences ,University of Melbourne:

"New Zealand is on the tectonic plate boundary between the Pacific Plate and the Australia-India Plate. The plate boundary is east of the North Island and crosses to the west of South Island. Christchurch is not on the plate boundary, but is near to related secondary faults that result from the bend in the plate boundary to the north. On average large earthquakes will occur less frequently in Christchurch than along the plate boundary, as has been the case for the last 200 years. However all earthquakes in the Christchurch region will be shallow, so the effect of a given earthquake will be worse than from a deeper plate boundary earthquake of the same magnitude."

Q5: How does this rate historically against other earthquakes?

Dr Gary Gibson,is Principal Research Fellow in the School of Earth Sciences ,University of Melbourne:

"This is by far the largest earthquake to have occurred in the Christchurch region in historic time. Earthquakes larger than magnitude 6.0, usually deeper than this event, occur about annually in New Zealand, including one of magnitude 7.8 that occurred in the remote southwest of South Island in July 2009 with little damage."

Q6: Why is NZ seemingly more prone to earthquakes than Australia? Is a similar earthquake likely to occur in Australia?

Dr Gideon Rosenbaum is a Lecturer in the School of Earth Sciences, at The University of Queensland:

"The Australian continent is quite far from the boundaries of the Australian plate. There are quite a lot of so called intraplate earthquakes, but these are normally quite small."

Dr Gary Gibson,is Principal Research Fellow in the School of Earth Sciences ,University of Melbourne:

"New Zealand is more prone to earthquakes because it is on the plate boundary and has many plate boundary earthquakes. Large earthquakes occur infrequently in Australia. In all of Australia a magnitude 6.0 or larger event occurs on average every ten years. In the capital cities of Australia, a nearby magnitude 6.0 will occur on average every few thousand years. All earthquakes in Australia are at shallow depth, similar to those in about Christchurch."

Q7: Is it possible to predict earthquake activity? How much better are we at predicting them and how good can we hope to get?

Dr Gary Gibson,is Principal Research Fellow in the School of Earth Sciences ,University of Melbourne:

"It is not possible to predict earthquakes, giving location, time of occurrence and magnitude, with certainty. Aftershocks have continued at a decreasing rate since the September earthquake. Recent aftershocks have been east of the original rupture."

Q8: Are there engineering or town planning measures which could be improved to reduce the impact of earthquakes?

Dr Gary Gibson,is Principal Research Fellow in the School of Earth Sciences ,University of Melbourne:

"Building standards are already very high in New Zealand, but are upgraded as knowledge develops, and as higher standards become economically viable."

Q9: Any other comments or thoughts about the subject would also be extremely appreciated!

Dr Gary Gibson,is Principal Research Fellow in the School of Earth Sciences ,University of Melbourne:

"The critical issue with this earthquake was that the epicentre was at shallow depth under Christchurch, so many people were within 10 to 20 km of the fault rupture. The magnitude 7.0 earthquake on 4 September 2010 was 30 to 40 kilometres west of Christchurch and ruptured mainly to the west."

Q10: Is there a connection between Christchurch and Manilla (stories just starting to run on wires that Manilla has been shaken by a quake).

Dr Gary Gibson is Principal Research Fellow in the School of Earth Sciences ,University of Melbourne:

"The earthquake south-west of Manilla was not unusual for the Philippines. There is no connection to the Christchurch activity."

Adam Pascale is Head of Seismology at Environmental Systems & Services:

"Highly unlikely. Earthquake energy can only trigger faults in the immediate area in a short time frame - there is simply not enough energy from an event of this size to directly trigger an event in a very distant location."

Q11: Why was this quake more damaging than the last one - the Wires say it's because it was much shallower? Why does a shallower quake cause more damage than a deeper one?

Dr Gary Gibson is Principal Research Fellow in the School of Earth Sciences ,University of Melbourne:

"The earthquake fault rupture in September began about 40 km west of Christchurch and ruptured for another 40 km heading off to the west, away from Christchurch. The earthquake this morning was smaller with a rupture of about 15 x 15 km at shallow depth immediately under Christchurch, so the shaking was much stronger."

Adam Pascale is Head of Seismology at Environmental Systems & Services:

"This earthquake was only 10km from Christchurch and 5km deep. The Darfield event was 40km away from Christchurch and 10km deep. Although the Darfield earthquake was almost 10 times larger, the ground motion had significantly attenuated by the time it reached Christchurch."

Q12: Also, is this quake part of the classic scene were somewhere hit by a quake gets more in the months afterwards? If so why does this happen?

Dr Gary Gibson is Principal Research Fellow in the School of Earth Sciences ,University of Melbourne:

"All shallow, large earthquakes are followed by many aftershocks that can last from days to months. Sometimes the rupture from the earlier earthquake is extended by another relatively large earthquake."

Adam Pascale is Head of Seismology at Environmental Systems & Services

"Earthquakes tend to cluster in time and space. The stress built up in a particular area will release over a geologically short period of time assuming the area is comprised of similar strengths of rock. It is likely that events will continue to occur in the area until the underlying structure has settled back into a formation where it can again start to absorb the stress from tectonic plate movements."
 


ENDS

Note to editors

The Science Media Centre (NZ) is an independent source of expert comment and information for journalists covering science and technology in New Zealand. Our aim is to promote accurate, evidence-based reporting on science and technology by helping the media work more closely with the scientific community. The SMC (NZ) is an independent centre established by the Royal Society of New Zealand with funding from the Ministry of Research, Science and Technology. The views expressed in this Science Alert are those of the individuals and organisations indicated and do not reflect the views of the SMC or its employees. For further information about the centre, or to offer feedback, please email us at smc@sciencemediacentre.co.nz.

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