Loma Prieta fault not so weak?

Dec 19, 2007

A new study adds to evidence that the fault responsible for the 1989 Loma Prieta earthquake is not as unusually weak as had been thought.

In general, a "weak" fault is one that ruptures relatively easily, resulting in smaller but more frequent earthquakes, while a "strong" fault can accumulate more strain before breaking in larger shocks, said Robert Twiss, professor emeritus of geology at UC Davis and co-author of the study with Jeffrey Unruh of William Lettis and Associates of Walnut Creek, Calif.

The Loma Prieta fault has been described as unusually weak based on studies of the aftershocks from the 1989 earthquake. By looking at the direction and movement of the aftershocks, researchers could calculate the strains in the fault. Previous studies looked at the aftershocks in total.

Twiss and Unruh took a new approach, breaking the aftershocks up into 17 separate clusters. They found that the fault is complex, with different kinds of deformation in different places. When they looked at the aftershocks in greater detail, they found more stresses in the structure.

"You're losing most of the essential mechanical information about the fault by piling these details together," Twiss said.

The researchers also found that the stresses and slip directions of the main earthquake were reproduced in the aftershocks, implying that the stresses continue to be present.

Twiss said that there is "no way" to predict the strength or timing of future earthquakes on the same fault using these results. But the findings would be relevant for other researchers seeking to build models of earthquake faults in the Bay Area, he said.

The paper was published in the September/October 2007 issue of the Geological Society of America Bulletin.

Source: University of California - Davis

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

add to favorites email to friend print save as pdf

Related Stories

A global murmur, then unusual silence

Apr 19, 2013

In the global aftershock zone that followed the major April 2012 Indian Ocean earthquake, seismologists noticed an unusual pattern. The magnitude (M) 8.6 earthquake, a strike-slip event at intraoceanic tectonic plates, caused ...

Quake off Indonesia causes panic in East Timor

Feb 24, 2013

(AP)—An undersea earthquake has rocked eastern Indonesia, causing panic among residents in neighboring East Timor. There were no immediate reports of injuries or damage.

Recommended for you

Strong quake hits east Indonesia; no tsunami threat

13 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.

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.

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 ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

out7x
1 / 5 (1) Dec 20, 2007
Any implications for the SanAndreas, strong or weak fault, in the Loma Prieta Area?????

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.