Subscribe to our free daily newsletters
. Earth Science News .




Subscribe to our free daily newsletters



SHAKE AND BLOW
Tide-triggered tremors give clues for earthquake prediction
by Staff Writers
Los Alamos NM (SPX) Jul 22, 2016


illustration only

The triggering of small, deep earthquakes along California's San Andreas Fault reveals depth-dependent frictional behavior that may provide insight into patterns signaling when a major quake could be on the horizon, according to a paper released this week by the Proceedings of the National Academy of Sciences (PNAS).

The study, which was led by the U.S. Geological Survey and Los Alamos National Laboratory, reports that the deepest part of California's 800-mile-long San Andreas Fault is weaker than expected and produces small earthquakes in response to tidal forces.

"These findings provide previously inaccessible information about the San Andreas Fault activity and strength," said Los Alamos National Laboratory's Paul Johnson, a coauthor on the paper and geophysicist in the Lab's Earth and Environmental Sciences Division.

"The study's discovery of low-frequency-earthquake (LFE) and tidal triggering of the San Andreas Fault gives seismologists new warning signals and information about slightly more predictable triggers of quakes to come."

Los Alamos maintains technical expertise in seismology and the behavior of Earth's crust as a part of its role monitoring underground nuclear testing globally and applies that expertise to other national challenges, including earthquakes.

The team used a data set of 81,000 LFEs since 2008 to match LFEs to tides. They determined in addition to being modulated with the semidiurnal (twice daily) tides, LFEs are also modulated by fortnightly tides.

The contrasting relationship between the LFE responses observed at two different tidal timescales should serve as a powerful constraint on understanding frictional behavior and stress transfer on the deep San Andreas.

"The findings provide new information regarding the fault zone structure with depth," Johnson said.

The authors found that deep, small, low-frequency earthquakes (LFEs) on the San Andreas Fault are most likely to occur during the waxing period approaching a full or new moon within the fortnightly tide period of 14.7 days.

The fortnightly tide modulates the semidiurnal (twice a day) tide. LFEs preferentially occur not when the tidal amplitude is highest, as might be expected, but when the tidal amplitude most exceeds its previous value, the authors found. LFEs correlate more strongly with larger-amplitude shear stress.

Previous studies have found stronger tidal semidiurnal variation for deeper, continuously active LFE families. The team used two models to explain variations: One, based on friction studies, posited LFEs occur when stress accelerates slip.

The other model suggests LFEs occur by simple threshold failure but are driven indirectly by tidally modulated creep. Regardless of which tidal triggering model is correct, the inverse relationship between the strength of the semidiurnal and fortnightly modulations provides a key insight into the mechanics of LFEs and the structure of the deep fault, according to the paper.

"The pattern of LFEs tells us something about loading rates and stress conditions in the deep part of the fault," said Andrew Delorey, a seismologist with Los Alamos.

"We don't know to what extent the deep part of the fault where LFEs occur is coupled to the shallow part of the fault where regular earthquakes occur. We may find that as stress increases and approaches failure in the shallow fault, where large earthquakes occur, it will affect the pattern of LFEs in a way that allows us to use LFE behavior to infer conditions in the shallow fault."

While tidal triggering of earthquakes is found only for select environments, triggering of tremor has been found almost everywhere that tectonic tremor is observed, generating insights into the mechanics of the brittle transition zones. The response to the tidal stress carries otherwise inaccessible information about fault strength and rheology.


Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only

.


Related Links
Los Alamos National Laboratory
Bringing Order To A World Of Disasters
When the Earth Quakes
A world of storm and tempest






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Previous Report
SHAKE AND BLOW
Tokyo jolted by third quake in four days
Tokyo (AFP) July 20, 2016
Tokyo was struck by a third earthquake in four days on Wednesday, but there were no reports of damage or casualties. The 5.0 magnitude jolt was felt in Tokyo and areas of eastern Japan at 7:25 am (2225 GMT Tuesday), the US Geological Survey said. It was the third quake to shake the capital's high-rise buildings in recent days - following a 4.8 magnitude quake on Tuesday and one of 5.0 o ... read more


SHAKE AND BLOW
Taiwan buses recalled after deadly fire disaster

Ex-Marine 'assassinated' Baton Rouge cops: police

Ex-Marine 'assassinated' Baton Rouge cops

Natural catastrophe losses up sharply in first half 2016: Munich Re

SHAKE AND BLOW
Rice's 'antenna-reactor' catalysts offer best of both worlds

'Green' electronic materials produced with synthetic biology

'Jumping film' harnesses the power of humidity

Exploring superconducting properties of 3-D printed parts

SHAKE AND BLOW
Massive sewage spill forces closure of Los Angeles beaches

South Africa's great white sharks face extinction: study

Ocean acidification - the limits of adaptation

Ocean Glider tells quite a tale after 74 days at sea

SHAKE AND BLOW
Ocean warming to blame for Antarctic Peninsula glacier retreat

Warming Arctic could disrupt migration patterns of millions of birds

More Chinese vessels to sail the Arctic: shipping firm

NASA's Field Campaign Investigates Arctic North American Ecosystems

SHAKE AND BLOW
ANU leads effort to develop drought-proof crops

Scientists sequence genome of 6,000-year-old barley

How plants can grow on salt-affected soils

Researchers build trenches to curb nitrogen runoff, algae growth

SHAKE AND BLOW
Tokyo jolted by third quake in four days

Record-breaking volcanic kettle on Iceland explored

China rain leaves one dead, 34 missing: report

Better understanding post-earthquake fault movement

SHAKE AND BLOW
NASA, USAID Open Environmental Monitoring Hub in West Africa

Armed group kills 17 soldiers at Mali base: ministry

Bashir reshuffles senior Sudanese military officials: army

Low uptake of space technology science slows Africa's growth: experts

SHAKE AND BLOW
Technological and cultural innovations amongst early humans not sparked by climate change

Cave art reveals religious encounters between Europeans and Native Americans

Genomes from Zagros mountains reveal different Neolithic ancestry

Changes in primate teeth linked to rise of monkeys




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News






The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement