Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

San Jacinto fault is younger than thought, rises in seismic importance

25.10.2006
Slip rate of southern California fault may be faster than previously believed

A detailed study of sedimentary rocks exposed along a portion of southern California's San Jacinto fault zone shows the fault to be no older than 1.1 million to 1.3 million years and that its long-term slip rate is probably faster than previously thought.

Researchers at three universities conducted a National Science Foundation-funded study of the earthquake-active region, concluding that sedimentation related to slip in the San Jacinto fault zone began about 1 million years ago, significantly later than predicted by many models for faulting in southern California. Their findings appear in the November-December issue of the Geological Society of America Bulletin.

"Our findings suggest that the San Jacinto fault absorbs a large share of the relative motion between the Pacific and North American plates," said principal investigator Rebecca J. Dorsey, a professor of geological sciences at the University of Oregon. "This is important both for understanding the development of this active plate boundary and for helping to constrain estimates of seismic hazards in southern California."

Until now the birth of the San Jacinto fault in the area of Anza-Borrego Desert State Park had not been pinned down.

Geologists from the University of Oregon, Western Washington University and Utah State University carried out detailed geologic mapping, measuring and analysis of samples from Pleistocene (12,000 to 1.8 million years ago) sedimentary rocks in the western Salton Trough, including the Ocotillo Formation and the Font's Point Sandstone in the Borrego Badlands.

Using geologic, stratigraphic and paleomagnetic techniques, they determined that sedimentation related to slip in this fault zone began about 1 million years ago; the fault itself could have started a little earlier than that. A second fault reorganization about 400,000 years later produced a thin sheet-like alluvial deposit that created the Font's Point Sandstone, triggering modern uplift and erosion that has produced the popular Font's Point escarpment.

"The revised younger age of the San Jacinto fault indicates it is an important player in southern California's seismically active fault zones," Dorsey said.

However, she noted, "a rigorous assessment of long-term slip rate on this fault must await a complete analysis of the total offset on the fault," which already is underway. "Based on our current knowledge, it appears that the geologic slip rate could be as high as about 20 millimeters a year," she said.

Slip rate is the speed at which one side of a fault moves with respect to the other. Any rate over 10 millimeters a year is considered "fast," although the movement measured is an average occurring over long periods of time and many earthquakes. Previous studies concluded that fault has slipped about 25 kilometers (15.5 miles) in a right-lateral sense, at a rate of 10-12 millimeters a year during the last 2.0 million to 2.4 million years.

Jim Barlow | EurekAlert!
Further information:
http://www.uoregon.edu

More articles from Earth Sciences:

nachricht Massive impact crater from a kilometer-wide iron meteorite discovered in Greenland
15.11.2018 | Faculty of Science - University of Copenhagen

nachricht The unintended consequences of dams and reservoirs
14.11.2018 | Uppsala University

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: UNH scientists help provide first-ever views of elusive energy explosion

Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.

Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...

Im Focus: A Chip with Blood Vessels

Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.

Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...

Im Focus: A Leap Into Quantum Technology

Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.

In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...

Im Focus: Research icebreaker Polarstern begins the Antarctic season

What does it look like below the ice shelf of the calved massive iceberg A68?

On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.

Im Focus: Penn engineers develop ultrathin, ultralight 'nanocardboard'

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure

Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

“3rd Conference on Laser Polishing – LaP 2018” Attracts International Experts and Users

09.11.2018 | Event News

On the brain’s ability to find the right direction

06.11.2018 | Event News

European Space Talks: Weltraumschrott – eine Gefahr für die Gesellschaft?

23.10.2018 | Event News

 
Latest News

Purdue cancer identity technology makes it easier to find a tumor's 'address'

16.11.2018 | Health and Medicine

Good preparation is half the digestion

16.11.2018 | Life Sciences

Microscope measures muscle weakness

16.11.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>