Newsgroups: ca.earthquake,ba.general
From: rchilder@us.oracle.com (Richard Childers)
Subject: Earthquake Research in Santa Cruz
Followup-To: ca.earthquake
Summary: USGS fracture network research
Keywords: USGS fracture network research NSF water table stress
Organization: Memes-R-Us
Distribution: ca
Date: Mon, 27 Jul 1992 20:35:14 GMT
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I was up on Skyline Boulevard - Highway 35 - this weekend, and happened
to pass by the research site mentioned by a few people in ca.earthquake.
The site is perhaps a thousand feet west of the intersection of 35 and 9,
on the Santa Cruz side of the mountain range, just down highway 9, in a
pullout area. It's a couple of trailers full of equipment, a drill, and
some cyclone fencing, with the United States Geological Survey logo upon
one of the trailers.

Returning from a few hours of happy bookshop browsing in Santa Cruz, back
up 9, I noticed that there were now people present at the site, and stopped
to pester them with questions. I'd stopped and reconnoitered on my previous
pass, but had been unable to glean much from what I could see.

The story, as far as I am able to accurately relay it, is that one of the
geologists there happens to live a few miles away from the intersection,
up near the ridge line, and just after the Loma Prieta Earthquake, he and
everyone else's water level dropped several hundred feet ... then grad-
-ually came back.

This provoked the geologist's curiosity - not to mention his thirst (-: -
and his neighbors bombarded him with questions, knowing him to be a geo-
-logist and employee of the USGS, after all, such that he came up with a
hypothesis, wrote a paper with one of his then-coworkers ( who is still
involved ), got it published, and applied, successfully, for a grant from
the National Science Foundation. With that grant money, and the approval
of his superiors in Menlo Park, he drilled two test holes about fifteen
feet apart, just off Highway 9, where you see them now.

My understanding is that these two holes are radically different, in that
they encounter the water level at two radically different locations even
though they are only fifteen feet apart. This has led to difficulties
with keeping the holes open, but so far they are remaining usable.

The purpose of the holes is twofold. First, they lower a device which is
designed to maintain a magnetic north orientation within the hole, until
it is immersed. Spring-loaded vanes hold it in the center, while it vib-
-rates at a frequency appropriate to map the walls in considerable detail,
making what I understand to be the equivalent of a 5-foot-tall picture
that wraps around the 360 degrees of wall surface and shows it in detail,
a sort of sonar application. They take these pictures 5' at a time, so
that they have a detailed picture of the layering all the way down.

Once this is done, they will lower another device, which will be used to,
at appropriate points, force the rock 'collar' which can be visualized
as surrounding the drilled hole, to fracture. The energy required to make
the rock fracture will give them an idea of how much pressure the rock is
under at present, and give them a way to map stress in three dimensions.

I cannot pretend to understand the theories behind this research ... I am
not a geologist or a hydrologist. However, my dad happens to be a hydrol-
-ogist for the USGS, so maybe I can do it justice. Essentially, the idea
is that there are a fine network of fractures running through the rock's
infrastructure, throughout the mountain range, and that when the quake
happened, this fracture web opened up and all the water drained down. If
I understand the explanation correctly, there is a hypothesis that this
network of fractures can be used to measure the stress of the whole system,
and possibly warn of problems forthcoming.

My host referred to several other peculiar precursor phenomena which occurred
in the vicinity and general time frame which suggested interconnections that
existed between these tangential phenomena and the quake, but which classic
geologists poo-poo'd. I asked him if he'd ever heard of Jack Coles, and he
professed a total lack of knowledge, but he *had* heard of the research at
Stanford, and thought it was great.

If there is any *public* interest, I will ask him if it would be possible
to arrange a tour some weekend morning. I say *public*, because I want
to avoid dozens of people making private commitments, and then not showing.

On the other hand, you can also cruise by the site and trust your luck that
they'll be on site ...

I would be really interested in asking him for a thorough tour, they have
a cab full of interesting hardware I didn't get to see.		)-:


-- richard

-- 
-- richard childers		rchilder@us.oracle.com		1 415 506 2411
         oracle data center  --  unix systems & network administration

                   Klein flask for rent. Inquire within.
Newsgroups: ba.general