Subscribe to our free daily newsletters
. Earth Science News .

Subscribe to our free daily newsletters

How strike-slip faults form, the origin of earthquakes
by Staff Writers
Amherst MA (SPX) Jul 07, 2017

file image

Structural geologist Michele Cooke calls it the "million-dollar question" that underlies all work in her laboratory at the University of Massachusetts Amherst: what goes on deep in the earth as strike-slip faults form in the crust? This is the fault type that occurs when two tectonic plates slide past one another, generating the waves of energy we sometimes feel as earthquakes.

Geologists have been uncertain about the factors that govern how new faults grow, says Cooke. In recent years she and colleagues have offered the first systematic explorations of such fault evolution. In their new paper, she and her team of students provide experimental results to illustrate the process, with videos, and report on how they re-enact such events in wet clay in the lab. Details appear in the current online edition of Journal of Structural Geology.

Cooke says, "When I give talks to other geologists I put up a picture of a fault and ask, wouldn't you love to be able to see exactly how that formed? Well, in my lab that's what we do. We set up the conditions for faulting on a small scale and watch them unfold. People have done this before, but we've developed methods so we can see faults grow in very, very fine detail, at a finer resolution than anyone has documented before."

The UMass Amherst researchers take a mechanical efficiency approach to understanding fault development. It states that faults in the crust reorganize in accord with "work optimization" principles, or what Cooke refers to as the "Lazy Earth" hypothesis. It focuses on fault systems' effectiveness at transforming input energy into movement along the faults. Like lightning striking the closest object, when forming a fault the earth takes the easiest path.

For this National Science Foundation-supported work, the researchers load a tray with kaolin, also known as china clay, prepared so its viscosity and length scale to that of the earth's crust. All the experiments involve two slabs of wet clay moving in opposite directions under one of three base boundary conditions, that is, different ways of "loading" the fault.

One scenario begins with a pre-existing fault, another with localized displacement beneath the clay, and a third that is characterized by a displacement across a wider zone of shear beneath the clay.

Data from the two-hour experiments record strain localization and fault evolution that represents millions of years at the scale of tens of kilometers during strike-slip fault maturation. Cooke says, "We have captured very different conditions for fault formation in our experiments that represent a range of conditions that might drive faulting in the crust."

She adds, "We found that faults do evolve to increase kinematic efficiency under different conditions, and we learned some surprising things along the way. One of them is that faults shut off along the way. We suspected this, but our experiment is the first to document it in detail. Another especially surprising finding is that fault irregularities, which are inefficient, persist rather than the system forming a straight, efficient fault."

The authors, who include graduate students Alex Hatem and Kevin Toeneboehn, identify four stages in fault evolution: pre-faulting, localization, linkage and slip. The process starts simply, advances to a peak of complexity, after which complexity suddenly drops off and the fault simplifies again, lengthening into a "through-going" or continuous single, surface crack.

In videos by Hatem, shear strain is clearly seen to distort the crust along the area where two base plates meet. In the next stage numerous echelon faults develop. These are step-like fractures parallel to each other that get pulled length-wise as strain increases until they suddenly link. In the last stage, these join to form a final single fault. Cooke says, "We were very excited to see that portions of the faults shut off as the system reorganized, and also that the irregularities persisted along the faults."

An interesting finding, but not a surprise is that for the most part all faults went through a similar process. Cooke says, "We tested the various extremes but came out of this with a common kind of evolution that's true for all.

If there's not already a fault, then you see echelon faults, small faults parallel to each other but at an angle to the shear. Probably the most insightful bit is the details of fault evolution within those extremes. What you're left with at the end is a long fault with abandoned segments on either side, which is something we see in the field all the time. It's a nice confirmation that our lab experiments replicate what is going on within the Earth."

Another insight, the researchers say, results from measuring the kinematic or geometric efficiency, the percent of applied displacement expressed as slip on the faults. "An inefficient fault will have less slip and more deformation around the zones," Cooke explains.

"We can see it happening in the experiments and it supports the idea that faults evolve to become efficient and the earth optimizes work. This is the Lazy Earth; the efficiency is increasing even though the fault is becoming more complex."

Finally the geologist adds, "We saw that when the faults eventually link up, they don't necessarily make a perfectly straight fault. That tells me that irregularities can persist along mature faults because of the material.

It's an insight into how you get persistent irregularities that we see in the real earth's crust. Structural geologists are surprised by irregularities, because if faults evolve to minimize work then all faults should be straight. But we have evidence now to show these irregularities persist. We have irregular faults that are active for millions of years."

Two dead as strong quake hits central Philippines: officials
Manila (AFP) July 6, 2017
A 6.5-magnitude earthquake killed at least two people in the central Philippines on Thursday, with more than five people still trapped inside a collapsed commercial building, officials said. An 18-year-old woman died after being hit by falling debris in Ormoc City on Leyte island, near the epicentre of the quake, police said. Elsewhere, rescuers pulled out eight survivors and one body fr ... read more

Related Links
University of Massachusetts at Amherst
Bringing Order To A World Of Disasters
When the Earth Quakes
A world of storm and tempest

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

Comment using your Disqus, Facebook, Google or Twitter login.

Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

The last survivors on Earth

Civilian deaths soar in Iraq, Syria: monitoring group

West Mosul residents start mammoth task of rebuilding

In IS-held Raqa, parched civilians risk lives for water

Sorting complicated knots

Engineers find way to evaluate green roofs

Nature-inspired material uses liquid reinforcement

Feel the heat, one touch a time

Trump envoy mediates water deal between Israel, Palestinians

Climate change deepens threat to Pacific island wildlife

Report: High seas in high danger as ecological tipping point nears

Big Muddy Missouri river needs a plan

Sentinel satellite captures birth of behemoth iceberg

Massive iceberg

US need for four polar icebreakers 'critical,' warns report

Warm Winter Events in Arctic Becoming More Frequent, Lasting Longer

Disneyland China falls a-fowl of huge turkey leg demand

Using treated graywater for irrigation is better for arid environments

Disneyland China falls a-fowl of huge turkey leg demand

Warmer Arctic harms crops in US, Canada: study

New research uses satellites to predict end of volcanic eruptions

4 killed, 6 missing in India's Gujarat amid monsoon floods

Slow earthquakes occur continuously in the Alaska-Aleutian subduction zone

How strike-slip faults form, the origin of earthquakes

Rwandan forces killing suspects without trial: HRW

AU chair questions US stance on African peacekeeping

3 killed in north Mali clashes as UN condemns violence

Gambian army 'hostile elements' working against government

Towards a High-Resolution, Implantable Neural Interface

DNA of early Neanderthal gives timeline for new modern human-related dispersal from Africa

Researchers document early, permanent human settlement in Andes

Analysis of Neanderthal teeth grooves uncovers evidence of prehistoric dentistry

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