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98347 |
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Date: August 10, 2024 at 09:49:52
From: eaamon, [DNS_Address]
Subject: Grapevine area and questions |
URL: Grapevine section |
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I see today looks to be over 500 quakes in or around there.
but it is mostly in one spot!?
I remember some of what Redfern's 'the making of a continent' PBS/BBC series did show.
but at this location I am not sure.
the West coast has some continent spreading as almost everything West of the
SAF/ San Andres fault is lands scraped off the subducting plate-plates.
some to the East too like in San Jose, shell fish pieces can be found high in the hills there.
it is possible that one of the two plates is moving once again.
what happens when it stops vibrating or it moves it's location?
like watching a pot boil or a volcano emit smoke.
any geological help in this area might help us understand the actions...
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Responses:
[98348] [98349] |
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98348 |
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Date: August 10, 2024 at 11:09:22
From: Redhart, [DNS_Address]
Subject: Re: Grapevine area and questions |
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What you're seeing on the map is all the aftershocks
to a 5.4 quake earlier this week.
This area above the "big bend" of the San Andreas is
being squeezed and you find both thrust and normal
(down dropping quakes) on a regular basis in response
to those stresses. This area lies on the "northern
American" plate.
The other side of the San Andreas is the Pacific plate
and it is moving north-north west in tiny bits, as well
as elevating as it's compressed by the north american
plate on it's east.
The aftershocks are following a normal (but very
robust) patter slowly declining with time from the main
shock.
I grew up in the San Jose area, and the east hills were
at one time under a sea until tectonic forces pushed up
sequences of both volcanic arcs, then later, accretion
folding. It's been through several different phases of
geological remodeling.
The plates are always moving, or storing energy for
their next move.
The Central Valley used to mark the decending slab of a
subduction trench millions of years ago. When the San
Andreas started moving about 30 mil ago, it slowly cut
off the trench from new slab. The end of the San
Andreas near Mendocino marks where volcanism begins
again in the Cascades. Some day, those will also become
extinct as the San Andreas cuts off it's descending
slab.
The old cold slab that was cut off under the Central
Valley, continues to sink, however. This is partially
what creates the interesting foot print in tne middle
of the state...but no longer active enough to create
the volcanics that once built the Sierras.
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Responses:
[98349] |
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98349 |
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Date: August 12, 2024 at 09:08:36
From: eaamon, [DNS_Address]
Subject: Re: Grapevine area and questions |
URL: Book titled by Ron Redfern |
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lived in SJ since 1971 to 2007 and am very familiar of that area geologically.
Cambrian Park for sure next to LG block.
I did walk many of the East foothills creek beds working for the
water district, lots to find there.
same as the cliffs North of Seacliff and South of Capitola a lot of specimens
embedded in those cliffs.
movement was said to be about 2.2" per year.
there is a lot stored up both North and South.
perhaps you missed the Redfern's story about the older Pacific plate both subsiding.
there was a spreading action between them similar to the Mid-Atlantic rift.
if that spreading action approaches the SAF will it act as a lubricant floating a boat?
will it make the 30 feet of movement at the Grapevine move a distance 10 times
what is stored. like 300 feet?
it is funny we can not see what is underfoot!
I still have the BBC version of the movie depicting it.
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