From: eugene@amelia.nas.nasa.gov (Eugene N. Miya)
Subject: [lm 10/27/92] Frequently asked earthquake references (where to find)
Keywords: Wegener,
Followup-To: poster
Organization: NAS Program, NASA Ames Research Center, Moffett Field, CA
Date: Fri, 13 Nov 92 12:30:56 GMT
Summary: This file exists to combat scientific illiteracy
Reply-To: eugene@amelia.nas.nasa.gov (Eugene N. Miya)
Distribution: ca

Sources to most general questions about earthquakes can be found
in THE classic reference work on the subject:

%A Charles F. Richter
%Z Caltech
%T Elementary Seismology
%I W. H. Freeman Publishers (company now defunct, try a library)
%C San Francisco
%D 1958

Although this text was published before the theory of plate tectonics,
it is quite readable by the general public (the extensive math being
in the Appendix).  It covers quake dynamics, questions like animals,
weather, etc.  And it is by THE authority.

For instance page 133:
"Earthquake weather," as commonly described, is merely a popular fable.
 . . .can be traced to classical writing.  The Greeks . . .

Visit a library to find this book to answer your questions before thinking
about posting to the net.  Do you really think an 104 line net posting can
answer everything?  Richter's 1.5 inches thick and packed with information.
There are numerous other good books.  Bruce Bolt (UC Berkeley),
Norris (UCSB), and others.  Just check a library out.  Community
college classes are fun and useful (field trips!).  Additionally,
the Bay Area is especially fortunate to have the Menlo Park offices
of the US Geological Survey.  The USGS does work on cartography
(map making), seismology, volcanology, land slides, hydrology, etc.
They have tours, open house, and have speakers available on a wide
variety of subjects.  Just visit them.  They have maps, reports, etc.

On predictions specifically: earthquakes happen practically everyday
around the world.  Any GOOD prediction will have:
	latitude
	longitude
	depth
	date (with time)
	magnitude
Simplying saying "A quake will happen" is like dowsing for water.

The front of your phone book (in California), the Red Cross, Sunset
Magazine, your state and county offices of emergency services are
all good sources of information concerning earthquake preparedness.
Topics include:

+Preparing your home to prevent property damage and injury
 from falling objects (e.g. bolting houses to foundations,
 securing water heaters and bookcases, NOT having your bed under a window).

+Stocking a few days of food and water (albeit it could do you little good
 if you are not near your cache).

+Knowing what to do during (get under a doorway or desk, DO NOT run outside)
 and after an earthquake (Do you know how to turn off your utilities?).

+Try to stay off of the telephone except in EXTEREME emergencies.
 Emergency services personnel need the lines for disaster assistance.
 Temporarily disable UUCP connections as well.  If you need to make a
 call, wait patiently for a dial tone.  Clicking the receiver will
 prevent you from ever getting one.  To contact family, set up a contact
 person out of state whom everyone can call.  Calls out are given
 preference over calls into the damaged region.  Pay telephones (at
 least the ones run by Pacific Bell) are on priority service and should
 provide reliable service.

+LEARN FIRST AID.  SF 1989 showed that volunteer rescuers are critical.
 If you want to learn something useful, get a Red-Cross certification
 card, and even then, that's not a guarantee, it's First-Aid.  Any smart
 class will prepare you with pre-cautions.

 Remember STOP!
	  Think
	  Observe
	  Plan

+One past net.discussion involved fire-arms.  Guns have no use in this
 natural disaster.  That silly discussion belongs in other newsgroups.

Lastly, on a frequently mentioned topic peripheral to earthquakes:
The following message comes from a former Vice-President of Caltech:
As for "Caltech" vs. "Cal Tech," it is DEFINITELY supposed to be CALTECH,
one word, not Cal Tech.  Linda is a stickler on this, and woe unto him
who makes this mistake! She frequently finds the error in written stuff,
often stuff coming from Caltech itself.  She blasts the miscreant.
Best wishes  -----Barclay
As far as I know, it was always one word.  Supposedly, the powers that
be (or were) -- Millikan, Hale, and Noyes -- decided at the beginning that
Caltech would be different from Georgia Tech etc.  -----Barclay

Kill line:
/: [lm 5.2.92] Frequently /h:j

From: stead@seismo.CSS.GOV (Richard Stead)
To: eugene@nas.nasa.gov
Subject: Re: Ferndale shocks south

Yeah, I did those kinda quick.  Arrows are nice.  3d perspective is even
better, but ascii characters are a bit limiting ...

As for the FAQ, I'm all for short FAQs, but thrust, normal and strike-slip
is such a fundemental concept (like magnitude and intensity, which
everyone has trouble with as well), that a case could be made for putting
it in a FAQ.  CA is pretty much strike-slip so it may be of only marginal
value for ca.earthquakes.  Maybe next time I'll try to explain beach balls 8-).

--Richard

Article 2923 of ca.earthquakes:
From: stead@skadi.CSS.GOV (Richard Stead)
Newsgroups: ca.earthquakes
Subject: Re: Ferndale shocks south

I'll take this as an opportunity to try and explain faulting to those
who may be novices.

> Does the proximity to the San Andreas have anything to
> do with it? (ie, do waves propagate down a fault in 
> an enhanced fashion?)
> John McDonald

Those are definitely part of it.  The problem here is the earthquake mechanism.
An earthquake (with a very small number of bizarre exceptions) always
occurs on a planar fault and always involves one side sliding in some
direction relative to the other.  However, the plane can be in any
orientation (vertical, horizontal or at some angle to the surface), and
the slip direction can be at any angle.  We can divide all that up into
three basic cases for shallow events (events occurring within 15 kilometers
of the surface).  These are thrust, normal and strike-slip.  A thrust
occurs on a plane that is at an angle to the surface such that one side
slides up over the other.  Normal faults (so named by their appearance
in mines in England) are also on angled fault planes, but one side moves
down and away from the other.  Strike-slip events occur on vertical
faults and one side slides by the other.

 ----------/                     /-----
 |        /                     /     |       ---------|--------
 |       /-------      --------/      |       |        |       |
 |      /       |      |      /       |       |        |       |
 ------/        |      |     /---------       |        |       |
      /         |      |    /                 ---------|--------
      -----------      -----

    thrust                normal                strike-slip

(In the doodles, the top of the page is the surface of the earth and the bottom
is deep in the earth, so it's like you were in a deep trench looking at the
fault from the side.  The strike slip shows no motion, because on side
moved toward you and the other moved away).

There is a good reason why there are three types for shallow events.
The surface of the earth is called a "free surface", basically, no one
prevents the surface of the earth from moving (the atmosphere doesn't
provide much resistance), whereas other surfaces in the earth have rock
on both sides.  A free surface means that the force in the vertical
direction is the smallest force.  In each of these fractures, the force
is strongest in a direction parallel to the surface.

Anyway, regardless of orientation, the wave field generated when a fault
slips is a "quadrupole".  All you EE's will know that one.  All a quadrupole
means is that there are four regions away from the qauke that will get
strong waves and four regions that get weak waves.  (For the EE's who haven't
heard this about quakes before, there are actually 2 quadrupoles, one for
P and one for the more substantial S waves.  The P-wave quadrupole is oriented
such that the four poles lie in a plane perpendicular to the fault plane
that includes the direction of motion.  One node coincides with the
direction of motion.  For the S-wave one peak coincides with the direction
of motion).

Anyway, the first quake was a thrust on one fault, the next two were strike-slip
on another.

More things affect the pattern of perceptible shaking.  One is "directivity".
This occurs when a very large portion of fault surface breaks (generally,
directivity has been measured on quakes of M5 and larger).  The break
starts on one part of the fault and moves at about the S-wave speed along
the fault.  Like a sonic boom, this causes reinforcement of energy in the
driection that the fault ruptured.  There is also "focusing" - afterall,
these are waves we're talking about, and certain structures deep in the
earth act exactly like lenses.  Since the first quake was in a somewhat
different spot than the later two, it is possible that it's waves are
focused slightly differently than thsoe of the other two.

Finally, there's just our own human perception capability.  We are most
sensitive to motion at certain frequencies.  But earthquakes can have
different distributions of energy in different frequency ranges, even
when they're the same magnitude (this is related ot the "stress drop"
you've heard other seismologists mention).

Hope this helps explain things a bit.
--
Richard Stead
Center for Seismic Studies
Arlington, VA
stead@seismo.css.gov


From: "Jack C. LOCKHART" <LOCKHART@uci.edu>
To: eugene@amelia.nas.nasa.gov (Eugene N. Miya)
Subject: AVAILABILITY OF USGS EARTHQUAKE DATA VIA MODEM
Keywords: Earthquake Maps & Reports

It is not certain if the Southern California postscript maps will be
posted again.  However, there are several ways for you to get this
information.  Data is available via this news network, FTP, and MODEM.

Two sites available via modem are listed below.  One site is located
in Northern California (Sacramento area); the other is in Southern
California (Anaheim area).

I compile each weeks earthquake data posted or submitted by Kate at
Caltech and Andy at USGS; into a ".zip" file and upload it to the
California Public-Safety Radio Association (CPRA) Communications
Bulletin Board System (PSCBBS), located in Anaheim, California.

Earthquake files are located in file directory #19.  Each weeks ".zip" file
is named "usgsYYWW.zip" where "YY" is the year, i.e., 92 and "WW" is the week
of the year, i.e., 01, 02, 03...  The file "usgs9201.zip" would be the weeks
data from 00:00:01 January 02, 1992 to 23:59:59 January 08, 1992.

Contact Gary David Gray - assistant sysop - (voice line) (714)
938-4311 for BBS access.  Speeds are: 300/1200/2400/9600; error
correction and data compression are also supported.  Access is granted
more favorably to those who work for a public-safety agency.



Article: 2054 of ca.earthquakes