Featured Research

from universities, journals, and other organizations

Structure, Deformation, and Strength of the Loma Prieta Fault In California

Date:
September 28, 2007
Source:
Geological Society of America
Summary:
Researchers analyzes over a thousand aftershocks of the 1989 Loma Prieta earthquake, which occurred along the San Andreas Fault system in northern California. It determines details of the fault structure from aftershock alignments at different scales in the fault zone, and the authors used the slip directions on local groups of aftershock faults to map the variations in deformation throughout the fault zone. The main fault is about 60 km long, and is defined by three segments that form a 20 bend, shaped like an open 's'.

Researchers analyzes over a thousand aftershocks of the 1989 Loma Prieta earthquake, which occurred along the San Andreas Fault system in northern California.

Related Articles


It determines details of the fault structure from aftershock alignments at different scales in the fault zone, and the authors used the slip directions on local groups of aftershock faults to map the variations in deformation throughout the fault zone. The main fault is about 60 km long, and is defined by three segments that form a 20 bend, shaped like an open 's'.

Aftershock slip was dominantly in a horizontal, west-side-north sense on the Southern Segment, a mixture of west-side north and west-side-up on the Central Segment, and a complex distribution of slip directions characterized by west-side-north with a large to dominant component of west-side-up on the Northern Segment. These three segments of the fault do not reach the surface, but are overlain by a Shallow Zone comprising another set of faults that are distributed along the main trend of the three fault segments but are oriented at an angle to them.

The slip on faults in the Shallow Zone is dominantly west-side-up. These zones of the fault all have a substructure of smaller faults at length scales of several kilometers to several tens of meters on which the deformation actually accumulates. The patterns of slip and the relation between the orientations of these smaller faults and the deformation, can be interpreted to show that the Loma Prieta fault zone had the strength of normal crust when the earthquake and its aftershocks occurred.

This conclusion contradicts numerous previous studies, which inferred that the fault was abnormally weak. The detailed analysis of the aftershock deformation has also provided evidence for a newly recognized mechanism of brittle deformation by which a three-dimensional deformation is split into two two-dimensional deformations, both of which occur within the same volume of rock at the same time.

This provides a new model for understanding this type of brittle deformation in the Earth's crust. Constraints on the rotations of fault blocks in the shear zone also can be inferred from the seismic data, a result that supports a model we have proposed previously but that is not predicted by classical seismology.

Reference: Structure, Deformation, and Strength of the Loma Prieta Fault, Northern California,U.S.A., as Inferred from the 1989-1990 Loma Prieta Aftershock Sequence, Robert J. Twiss and Jeffrey R. Unruh, Geology Department, University of California at Davis, Davis, California 95616, USA., Geological Society of America Bulletin, Pages 1079-1106.


Story Source:

The above story is based on materials provided by Geological Society of America. Note: Materials may be edited for content and length.


Cite This Page:

Geological Society of America. "Structure, Deformation, and Strength of the Loma Prieta Fault In California." ScienceDaily. ScienceDaily, 28 September 2007. <www.sciencedaily.com/releases/2007/09/070926191844.htm>.
Geological Society of America. (2007, September 28). Structure, Deformation, and Strength of the Loma Prieta Fault In California. ScienceDaily. Retrieved December 21, 2014 from www.sciencedaily.com/releases/2007/09/070926191844.htm
Geological Society of America. "Structure, Deformation, and Strength of the Loma Prieta Fault In California." ScienceDaily. www.sciencedaily.com/releases/2007/09/070926191844.htm (accessed December 21, 2014).

Share This


More From ScienceDaily



More Earth & Climate News

Sunday, December 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Lava Inches Closer to Highway

Raw: Lava Inches Closer to Highway

AP (Dec. 21, 2014) Officials have opened a new road on Hawaii's Big Island for drivers to take care of their daily needs if encroaching lava from Kilauea Volcano crosses a highway and cuts them off from the rest of the island. (Dec. 20) Video provided by AP
Powered by NewsLook.com
Raw: Scuba Diving Santa Off Florida Keys

Raw: Scuba Diving Santa Off Florida Keys

AP (Dec. 20, 2014) A scuba diving Santa Claus explored the waters of the Florida Keys National Marine Sanctuary. Dive shop owner Spencer Slate makes the dive each year to help raise money for charity. (Dec. 20) Video provided by AP
Powered by NewsLook.com
Obama: Better Ways to Create Jobs Than Keystone Pipeline

Obama: Better Ways to Create Jobs Than Keystone Pipeline

AFP (Dec. 19, 2014) US President Barack Obama says that construction of the Keystone pipeline would have 'very little impact' on US gas prices and believes there are 'more direct ways' to create construction jobs. Duration: 00:47 Video provided by AFP
Powered by NewsLook.com
Raw: Lava on Track to Hit Hawaii Market

Raw: Lava on Track to Hit Hawaii Market

AP (Dec. 19, 2014) Lava from an active volcano on Hawaii's Big Island slowed slightly but stayed on track to hit a shopping center in the small town of Pahoa. (Dec. 19) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins