For earthquakes 'speed kills'

Aug 17, 2007
For earthquakes 'speed kills'
A box canyon on the San Andreas fault: High speed ruptures travelling along the straight section of the fault could see Santa Barbara and Los Angeles worst hit in future earthquakes. Credit: iStockphoto/William Royer.

High-speed ruptures travelling along straight fault lines could explain why some earthquakes are more destructive than others, according to an Oxford University scientist.

In this week’s Science, Professor Shamita Das suggests that ruptures in the Earth’s surface moving at 6km per second could make future earthquakes along California’s San Andreas fault much more destructive than current models predict.

Professor Das compared data from the 1906 California earthquake with data from a similar earthquake that occurred in 2001 in Kunlunshan, Tibet. The comparison suggests that, in both, the long straight portions of the fault enabled ruptures to travel twice as fast as the original ‘shear’ wave travelling through the rock. Such ‘super-shear’ waves were once thought to be impossible but could now explain why similar magnitudes of earthquake can cause much greater devastation in some areas than others.

‘Long straight faults are more likely to reach high rupture speeds,’ said Professor Das of the Department of Earth Sciences. ‘The fault starts from rest, then accelerates to the maximum permissible speed and continues at this speed until it reaches an obstacle such as a large ‘bend’. If the next earthquake in southern California follows the same pattern as the ones in California in 1857 and 1906, and in Tibet in 2001, a super-shear rupture travelling southward would strongly focus shock waves on Santa Barbara and Los Angeles.’

The 2001 Kunlunshan earthquake is of particular interest to scientists because it was so well preserved owing to its remote location and dry desert environment. Studies of the earthquake revealed telltale off-fault open cracks only at the portions where it was found to have a very high rupture speed. ‘These cracks confirm that the earthquake reached super-shear speeds on the long, straight section of the fault. This is the first earthquake where such direct evidence is available and it is exactly the kind of evidence that we do not have for the similar earthquake in California 1906, due to the heavy rains and rapid rebuilding that occurred there immediately afterwards.’

Professor Das believes that future research into rupture speeds could take scientists one step closer to predicting the potential impact of earthquakes in particular regions.

She commented: ‘It appears that the 1857 and 1906 California earthquakes may have propagated faster than was previously thought. If this is the case then we need to apply the same analysis to other similar faults around the world. By developing a measure of the ‘straightness’ of faults and finding and recording evidence such as off-fault open cracks we hope to better understand these potentially devastating phenomena.’ The full article, entitled ‘The Need to Study Speed’, is published in Science on 17 August 2007.

Source: University of Oxford

Explore further: Strong quake hits east Indonesia; no tsunami threat

add to favorites email to friend print save as pdf

Related Stories

Strong quake hits east Indonesia; no tsunami threat

6 hours ago

A strong earthquake struck off the coast of eastern Indonesia on Sunday evening, but there were no immediate reports of injuries or damage, and authorities said there was no threat of a tsunami.

Indonesia volcano erupts, injuring 4; 1 missing

Dec 19, 2014

A volcano in eastern Indonesia erupted Friday, spewing towering clouds of hot ash into the air and leaving four hikers injured and one missing when they scrambled to safety, an official said.

Scientists make strides in tsunami warning since 2004

Dec 19, 2014

The 2004 tsunami led to greater global cooperation and improved techniques for detecting waves that could reach faraway shores, even though scientists still cannot predict when an earthquake will strike.

California gets funds for quake warning system

Dec 15, 2014

California has received a spurt of federal funding to expand an earthquake warning system intended to provide enough time for trains to brake, utilities and factories to shut off gas lines, and people to dive under a table ...

Deep fault drilling project

Dec 15, 2014

It rains a lot in the tiny south Westland town of Whataroa. Every year, this region gets some of the highest rainfall totals recorded anywhere in the World and Whataroa is one of the wetter parts. The town is nestled beneath ...

Recommended for you

Trade winds ventilate the tropical oceans

Dec 19, 2014

Long-term observations indicate that the oxygen minimum zones in the tropical oceans have expanded in recent decades. The reason is still unknown. Now scientists at the GEOMAR Helmholtz Centre for Ocean Research ...

NASA's spaceborne carbon counter maps new details

Dec 19, 2014

The first global maps of atmospheric carbon dioxide from NASA's new Orbiting Carbon Observatory-2 mission demonstrate its performance and promise, showing elevated carbon dioxide concentrations across the ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.