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: TRMM Satellite calculates Hurricanes Fay and Gonzalo rainfall

add to favorites email to friend print save as pdf

Related Stories

US company sells out of Ebola toys

4 minutes ago

They might look tasteless, but satisfied customers dub them cute and adorable. Ebola-themed toys have proved such a hit that one US-based company has sold out.

Partial solar eclipse over the U.S. on Thursday, Oct. 23

1 hour ago

People in most of the continental United States will be in the shadow of the Moon on Thursday afternoon, Oct. 23, as a partial solar eclipse sweeps across the Earth. For people looking through sun-safe filters, from Los Angeles, ...

UN biodiversity meet commits to double funding

24 minutes ago

A UN conference on preserving the earth's dwindling resources wrapped up Friday with governments making a firm commitment to double biodiversity aid to developing countries by 2015.

Recommended for you

Tropical Depression 9 forms in Gulf of Mexico

2 hours ago

Tropical Depression Nine formed over the western Bay of Campeche, Gulf of Mexico and is forecast to make a quick landfall on Mexico's Yucatan Peninsula. NOAA's GOES-East Satellite captured the birth of the ...

$58 million effort to study potential new energy source

7 hours ago

A research team led by The University of Texas at Austin has been awarded approximately $58 million to analyze deposits of frozen methane under the Gulf of Mexico that hold enormous potential to increase ...

And now, the volcano forecast

8 hours ago

Scientists are using volcanic gases to understand how volcanoes work, and as the basis of a hazard-warning forecast system.

User comments : 0