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Blobrana


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A three-man team from the US Geological Survey is digging a large hole for a new batch of measuring instruments that will soon become part of America's first earthquake early warning system.
The southern San Andreas is being wired by government scientists and technicians from the USGS staff, so that cities like Los Angeles can have up to a minute's warning of a major quake.
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Blobrana


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For the first time, rocks have been extracted from California's San Andreas Fault by scientists drilling some three kilometres below the surface.
They say this new material may answer a number of long-standing questions about the fault's composition and properties.

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Blobrana


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A team of scientists on Thursday showed off the first rock samples taken from a borehole being drilled into the mighty San Andreas Fault to better understand how earthquakes are born.
The 4-inch-wide rock cores were pulled earlier this month from two miles beneath a seismically active section of the fault halfway between San Francisco and Los Angeles.
Researchers hope the core collection, weighing about a ton in total, will help answer questions about the fault's makeup and determine what happens during stress buildup at great depths.

"Now we have samples that we can literally hold in our hands and study in the lab" - Mark Zoback, a geophysicist at Stanford University and one of the project leaders.

As excited as scientists worldwide are about the rock cores, they likely won't help in earthquake prediction. That goal is still out of reach despite a century of research into earthquake physics.
Since 2004, a team of geophysicists and seismologists has been drilling in the town of Parkfield using a technique common in the oil industry. The site in Parkfield, the self-proclaimed "Earthquake Capital of the World," was chosen because it sits atop a creeping segment of the 800-mile San Andreas Fault. Creeping occurs when two sides of the fault gently slide past each other, triggering small temblors.
Last summer, scientists penetrated an active section of the fault for the first time and began the arduous process of extracting rock samples to the surface.

"These are kind of like moon rocks for people studying earthquake mechanics" - Stephen Hickman of the U.S. Geological Survey.

A preliminary analysis revealed the rupture zone contains very fine ground-up rock containing a greenish mineral called serpentine that may explain why the region of the fault creeps slowly to relieve stress. Scientists plan to study the mineral in the lab to find out the exact process by which it causes the fault to creep.
While the rock cores should reveal abundant clues about the middle section of the San Andreas, the findings may not apply to other regions of the fault. Seismologists are particularly concerned about the southernmost section, which has not popped since 1690 and is capable of producing devastating quakes.
Scientists next year plan to rig the borehole in Central California with sensors to try to catch an earthquake in the making. When completed, it will be the world's first underground earthquake observatory designed to study temblors up close.

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Blobrana


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San Andreas Fault
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The Los Angeles basin appears to be in a seismic lull characterised by relatively smaller and infrequent earthquakes, according to a study in the September issue of Geology.
By contrast, the Mojave Desert is in a seismically active period. The study suggests that seismic activity alternates between the two regions, and that seismic hazard models assuming random quake activity may need to be updated.
The lull in the Los Angeles basin began 1,000 years ago, said the authors, led by James Dolan, associate professor of earth sciences at the University of Southern California.

The past 1,000 years has been relatively quiet - James Dolan, referring to what he calls the urban fault network under the Los Angeles metropolitan area.

The claim will come as news to anyone who has lived through a big quake in Southern California.
But Dolan said that even the Northridge earthquake of 1994, the costliest natural disaster in U.S. history at the time, was a drop in the bucket compared to the massive jolts that would strike the basin during a period of high seismic activity.

The study comes with some caveats. Among them:

The urban fault network does not include the more distant San Andreas fault. Though the San Andreas is storing energy at a slower than average rate, a major quake along the fault is always possible. About 10 San Andreas big ones have occurred during the current lull on the urban fault network.

The authors developed their theory from the discovery of several clusters of intense seismic activity in the geological record. It is not yet known if the clusters are statistically significant.

The authors studied the geological record going back 12,000 years. During that period, they found several clusters of seismic bursts, with the most recent lasting 4,000 years and ending about 1,000 years ago.
The seismic clusters were separated by periods of relative calm lasting about 1,500 to 2,000 years.
Remarkably, the lulls in the Los Angeles region corresponded with seismic clusters in the Mojave Desert, as described in 2000 by Thomas Rockwell of San Diego State University and his colleagues.

When were having earthquakes in L.A., generally we dont have as many earthquakes in the Mojave, and vice versa, Dolan said.

The study in Geology proposes a mechanism by which periods of high seismic activity alternate between the urban fault network and the Mojave Desert.
The two main cogs in the mechanism are the section of the San Andreas fault north of Los Angeles and the desert fault system known as the eastern California shear zone.
Rapid motion along one fault causes slower motion along the other, the authors suggest. During relatively rare periods when the San Andreas fault is moving slowly, the strain in the urban fault network drops accordingly, leading to a seismic lull in Los Angeles and to more seismic activity in the desert.

The San Andreas is always dominant. Its always the big brother. But at times the eastern California shear zone takes up its share of the load -  James Dolan.

During the current lull in Los Angeles, major earthquakes in the eastern California shear zone have included the magnitude 7.1 Hector Mine of 1999, the 7.3 Landers of 1992 and the 7.6 Owens Valley of 1872.
Each packed four to 20 times the energy of the Northridge quake.
While all three quakes occurred in sparsely populated areas, Palm Springs and other desert communities lie close to the eastern California shear zone and could be vulnerable.

These are very large earthquakes .

If the authors theory is confirmed, detecting the start and end of a lull will become extremely important. Predicting the end of the current lull is impossible at present.

We do know that the Mojave part of the eastern California shear zone is still storing energy much more rapidly than usual (by a factor of about two), so I would tend to doubt that the recent 1994 (magnitude) 6.7 Northridge and 1971 (magnitude) 6.7 San Fernando earthquakes indicate that we are coming out of the current lull - James Dolan.

Dolan studies fault systems in Southern California and in Turkey, whose simpler fault geography helps Dolan to understand the extremely complicated place that he calls home.
In a study published in Science in 2003, he estimated the size and frequency of past earthquakes on the Puente Hills fault, one of the Los Angeles-area faults currently in a lull.
The study found that all four major earthquakes on the Puente Hills fault in the past 11,000 years exceeded magnitude 7.0.

Were stuck with living here, so we have to understand what we can about this system .

Dolans co-authors were Charles Sammis, professor of earth sciences at USC, and David Bowman, associate professor of geological sciences at California State University, Fullerton.
Funding for the research came from the National Science Foundation and the U.S. Geological Survey through the Southern California Earthquake Centre as well as from the California Department of Transportation and the City and County of Los Angeles.
Geology is published by the Geological Society of America.

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Blobrana


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San Jacinto Fault
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San Jacinto Fault is younger than thought, rises in seismic importance
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.

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Blobrana


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San Andreas Fault
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Tremors within the Earth are usually--but not always--related to the activity of a volcano. Now, such vibrations have been recorded nowhere near a volcano, but at a geologic observatory at the San Andreas Fault. Scientists believe the fault tremors may be related to activity at a subduction zone--a place where one of Earth's constantly moving tectonic plates slips beneath another.

To determine whether the San Andreas Fault is moving with the tremors, scientists with the San Andreas Fault Observatory at Depth (SAFOD) are installing instruments to measure the tremors' activity. Located near Parkfield, California, SAFOD is part of the EarthScope Project, an effort to study the North American continent's geology.

"Unlike the sharp jolt of an earthquake, tremors within Earth's crust emerge slowly, rumbling for longer periods of time. Although not in this case, tremors are usually produced by magma moving in cracks or other conduits beneath a volcano"- Kaye Shedlock, program director for EarthScope at the National Science Foundation (NSF), which funds the project.

The rumblings are the first recordings of non-volcanic tremors in a deep borehole, providing scientists with data to better understand such mysterious underground movements.
The results will help geologists understand whether the deeply buried rocks of the San Andreas Fault - which are derived from an ancient subduction zone - behave in a similar way to the rocks of the Cascadia Subduction Zone, still active today.

"In the Cascadia Subduction Zone off the Pacific Northwest, for example, tremors are associated with the slow slip of the undersea Juan de Fuca tectonic plate as it submerges beneath the North American tectonic plate" - Greg van der Vink, EarthScope facility project director.

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Fault Observatory
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The San Andreas Fault Observatory at Depth (SAFOD) reached a significant goal on Aug. 2 when scientists drilled into a seismically active section of the fault approximately two miles below the surface of the Earth.

"This is a milestone for SAFOD," says Mark Zoback, a professor of geophysics at Stanford University. "For the first time, scientists have drilled directly into the San Andreas Fault Zone at a depth that will allow us to observe earthquakes up close for decades to come."

Zoback is co-principal investigator of the SAFOD project, along with geophysicists Steve Hickman and Bill Ellsworth of the U.S. Geological Survey (USGS) in Menlo Park, Califonia.

"It’s the first time we’ve been inside the earthquake machine," Ellsworth says. "We’ve looked at the fossil earthquakes, we’ve made computer models, and we’ve made laboratory earthquakes. We’ve studied them from afar, but we’ve never been inside the machine where the action is."

When completed in 2007, SAFOD will be the only earthquake observatory with instruments installed directly within an active fault where earthquakes form or "nucleate." Scientists also will be able to bring up actual rock and mineral samples from the earthquake zone. "With SAFOD, we’ll be able to recreate the earthquake process in the laboratory using real materials and under real conditions that exist in the San Andreas Fault Zone at depth," Hickman says. "That’s unique."

Launched in 2003, SAFOD is one of three major components of EarthScope, a National Science Foundation-funded initiative being carried out in collaboration with USGS. EarthScope is designed to investigate the powerful geological forces that shape the North American continent. The other EarthScope projects, USArray and the Plate Boundary Observatory, are large-scale research efforts focusing on deformation and properties of the Earth’s crust in North America.

EarthScope is combining data from the SAFOD borehole with thousands of seismic, strainmeter and GPS measurements from across the continent. "We now have the first opportunity to measure directly the conditions under which earthquakes initiate and grow," says Herman Zimmerman, director of the NSF Division of Earth Sciences. "This is an unprecedented step forward in understanding these dangerous phenomena."



SAFOD is being built on private ranchland near the rural town of Parkfield in central California, about halfway between San Francisco and Los Angeles. The ranch straddles the San Andreas Fault, an 800-mile-long rift that marks the boundary between the Pacific and North American tectonic plates. These two enormous landmasses constantly grind against each other in opposite directions, triggering earthquakes of various magnitudes up and down the fault.

"Almost everything we know about earthquakes has been gathered either at or very close to the Earth’s surface, where all we see is the elastic part of the process, the part that carries seismic waves to great distance," Ellsworth says. "SAFOD gets into the inelastic part where things are actually breaking. That’s the part we can only see by getting into the fault zone."

Drilling of the observatory borehole began in June 2004 and continued until mid-October, the end of the dry season in California. Drilling resumed on June 10, 2005, and on Aug. 2 drill operators finally entered the San Andreas Fault Zone, reaching a maximum depth about 2 miles below the surface of the Earth.

The borehole begins on the Pacific plate just west of the fault, passes through the active earthquake zone and winds up in the North American plate east of the fault--a distance of 3 miles. Seismic instruments will be installed along both plates in a section of the fault where small temblors of magnitude 2.0 are frequent. While these microearthquakes usually aren’t felt at the surface, they can offer important clues about the origin of bigger, more destructive quakes. "Microearthquakes provide scientists an exciting opportunity to study events that occur about every two years in roughly the same place," Zoback explains. "It’s a live, active system, and we’re building an observatory directly within it."

SAFOD instrumentation will provide around-the-clock observations of temperature, fluid pressure, strain accumulation and other processes before, during and after microearthquakes occur. "That’s really at the heart of determining whether earthquake prediction is possible, and if it is, how you might go about doing it," Hickman notes. "You cannot do those kinds of in-depth observations in parts of the fault that only produce big earthquakes, because those usually occur at intervals of 100 to 150 years or so."



In addition to monitoring the earthquake nucleation process, SAFOD researchers plan to address a number of fundamental scientific questions. For example, in what ways are plate boundaries such as the San Andreas unique? Why are they so narrow? Why do they persist for millions of years? What makes them so weak relative to that crust that’s adjacent to them?

"We have numerous theories about how earthquakes work that have been developed over the last 20 years based on remote geophysical observations of active faults or geologic examination of faults exhumed by erosion that are no longer active," Hickman says. "For the dozens of scientists involved in SAFOD, this is really their first opportunity to test these ideas and see which ones are right."

When drilling is completed in August, the entire borehole will be encased in steel and cement so that sensitive instruments--such as seismometers, strainmeters, and fluid and temperature gauges--can be installed underground. Meanwhile, scientists will begin to collect rock, gas and mineral samples from the fault zone for laboratory analysis.

Over the next two years, geophysicists also will try to identify precise areas in the fault zone where microearthquakes regularly occur. In 2007, project engineers will begin drilling into those active areas and installing the instruments. The observatory is expected to operate for 20 years and give researchers a unique window into the process of stress buildup and release in the fault zone during numerous microearthquakes.

"It’s a whole new type of experiment," Zoback concludes. "It’s opening doors to research we haven’t been able to consider before because we’ve never been able to do experiments within an active fault. It’s a very exciting time for earthquake science."

http://www.innovations-report.com/html/reports/earth_sciences/report-47468.html


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