Maps United States Fault Lines
November 6, 2011 by staff
Christchurch’s magnitude-6.3 quake had far more serious repercussions than scientists would have expected for a quake of “relatively moderate” size, according to a review released in the United States this morning.
Because the quake was extremely well recorded by equipment set up to measure aftershocks of the larger September 4 magnitude-7.1 earthquake, scientists could compare them and focus on why the second was so devastating.
The shallow quake at 12.51pm on February 22, centred under the Port Hills between Ferrymead and Rapaki, killed 182 people.
Today’s special issue of Seismological Research Letters is dedicated to the February quake, with 19 technical papers covering the seismology, geology and engineering geology of the quake.
Christchurch’s liquefaction receives extensive coverage, with scientists suggesting damage caused by it was “unprecedented and may be the greatest ever observed in an urban area”.
Millions of people live on similar soft sediments in Los Angeles and San Francisco.
Journal editor-in-chief Jonathan Lees, professor of geosciences at the University of North Carolina at Chapel Hill, said the papers could help “transform the way scientists assess the potential threat of faultlines that run through urban centres”.
“The March Japan earthquake and tsunami overshadowed the Christchurch earthquake, which was absolutely devastating in its own right. Compared to the earthquake that destroyed much of Haiti, the scale of disaster in Christchurch may seem small.
“Christchurch, however, was constructed using much better technology and engineering practices, raising a very sobering alarm to other major, high-density Western urban centres.”
Guest editor Erol Kalkan, manager of the United States Geological Survey’s national strong-motion network, said the February earthquake was “remarkable on several counts”.
“The ground motion was much larger than previously recorded, the high intensity of shaking was greater than expected, particularly for a moderate-size earthquake, and the liquefaction-induced damage was extensive and severe within the central business district of Christchurch.
“Many urban areas are built over soft sediments and in valleys or over basins, for example the San Francisco Bay area and Los Angeles metropolitan. These are urban areas that sit atop geological features that may exaggerate or amplify ground motion, just as Christchurch experienced.
“The question is how to apply or account for such significant, higher-than-expected ground motions, as seen in Christchurch.”
The Christchurch quake would have a long-lasting and significant impact on engineering practices and provided a huge opportunity to fuel scientific knowledge, Kalkan said.
Six of the papers were written or co-written by GNS Science researchers. University of Canterbury civil engineer and liquefaction expert Misko Cubrinovski also wrote or co-wrote six papers.
GNS Science’s John Callan said the quantity and quality of data collected during the quake was “almost unprecedented internationally”.
“Analysis of this data is already having a significant impact on seismology worldwide.”
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