Re: Core Drilling the San Andreas Fault


"SBC Yahoo" <atilla.the.hun@xxxxxxxxxxxxxxxxx> wrote in message
news:hYtNi.665$R95.16@xxxxxxxxxxxxxxxxxxxxxxx
http://www.latimes.com/news/local/la-me-fault5oct05,0,4466797.story?coll=la-home-center

Core samples taken 2 miles deep reveal that the answer to having plates
slip past one another without a quake may be baby powder.

Are we meant to assume they mean talc? It's not mentioned anywhere in the
article
other than the inference in the title.
cheers
Bill


By Richard C. Paddock, Los Angeles Times Staff Writer
October 5, 2007
PALO ALTO -- Rock samples extracted from two miles deep within the San
Andreas fault -- the first samples of their kind -- are a breakthrough
that could provide new understanding of how earthquakes function,
scientists said Thursday.

Earthquake scientists from Stanford University and the United States
Geological Survey said that the minerals taken from the core of the active
fault could help scientists learn what triggers an earthquake and whether
quakes can be predicted.

"Now we can hold the San Andreas fault in our hands," said Mark Zoback, a
Stanford professor of earth sciences and a leader of the project. "We know
what it's made of. We can study how it works."

Until now, geologists studying the physical evidence of faults have
focused on outcrops that were uplifted to the surface and weathered over
millions of years.

The rock samples taken from the San Andreas fault near Parkfield in
Central California are so fresh that they were 240 degrees Fahrenheit when
they were extracted.

"This is very significant," said Thomas Jordan, a USC professor of
geophysics and director of the Southern California Earthquake Center who
is not involved in the project. "For the first time we have samples from
the core of the fault zone at the depths where these earthquake processes
are actually happening."

Jordan added: "These may turn out to be as precious as the rocks brought
back from the moon."

The core samples are part of an ambitious $197-million federal project
called EarthScope to gather detailed data on the geologic structure and
evolution of North America. In California, it includes the $24-million San
Andreas Fault Observatory at Depth, which is establishing the world's
first underground earthquake observatory at Parkfield.

The small town near Paso Robles was chosen as the site for the study
because it is an unusual spot on the San Andreas fault where small
earthquakes occur frequently, many of them unnoticed at the surface.

Scientists have long wondered why the two huge tectonic plates that are
separated by the San Andreas slide by each other at Parkfield with few
major jolts, unlike other sections of the fault. They hope the core
samples will provide the answer.

"The story of how it moves is contained in these rocks," said William
Ellsworth, a USGS geophysicist who is another leader of the project. "We
are going to get some of the secrets of the San Andreas fault out of these
rocks."

The drilling at Parkfield began in 2004, and scientists recovered
ground-up soil from the fault in 2005. In drilling the hole, they
discovered two active strands of the fault about 350 feet apart.

This year, they drilled diagonally through the two strands at a depth of
about two miles and extracted intact core samples from both. The final
samples were brought up Sept. 7. On Thursday, project leaders displayed
several sections of the core at a Stanford news conference.

The scientists are confident that they extracted minerals from the fault
because the steel casing they inserted into the ground was deformed by the
shifting of the tectonic plates during the project. The plates move about
an inch a year along the fault line.

"That was the proof," Ellsworth said.

. . . . . . . . . .



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Relevant Pages

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