PSN-L Email List Message

Subject: Re: predictions
From: John Hernlund hernlund@.......
Date: Mon, 18 Sep 2000 11:17:03 -0700 (MST)

On Sun, 17 Sep 2000 ddiffenderfer@........ wrote:
> I live about 100 miles east of the San Andreas in Southern California  at
> Palo Verde and remain interested in predictions done scientifically.  So
> far I am not aware of anyone that can predict quakes with any accuracy by
> any method.
> David. W. Diffenderfer
> ddiffenderfer@........

Hi All,
   I just moved to LA, and have just been going through the messages
concerning prediction. This is a very interesting topic indeed.  I had the
pleasure of attending a symposium last week which went through several
statistical models and fancy number schemes which may be applied to
prediction.  The best talk was given by Dave Jackson, who has been interested
in this topic for some time now.  He used only raw data from the past to try
and model future activity...and the result: you have a better idea of
earthquake risk from looking at a map of previous seismicity than just about
any other method.  I think that anybody will find this simple method hard to

   There have been many studies over the years, with little success.  One
such was that a temporal gap in seismicity should usually preclude a large
earthquake.  However, looking at plots of the rates of seismicity for many
fault zones it was easy to see that this rarely works.  There are also papers
I have seen that report ULF magnetic field variations, but this stuff is still
locked into the problem of "statistics of small numbers" and has to be studied
much further to understand both the mechanism for changing the magnetic field
as well as the character of a signal before a large quake.

   Also, a lot does not make sense yet to the field seismo people.  For
instance, a section of the San Andreas is creeping and just next to it is a
section which is locked.  How the kinematics of the transition between the two
styles along the fault work is anyone's guess.  Recently this year, I sent two
references to the group from a paper in Science and one from Nature that
report annual variations in seismicity for some spherical modes and also for
aftershocks following the Landers quake.  This is probably some kind of
atmospheric effect which is not totally understood either.  Another paper
coming out soon shows that the San Andreas speeds up and slows down in its
average motion over I guess what I am trying to say is that there is
a lot about earthquakes that is not yet understood.  New information and
findings are constantly coming in, any of which can effect the over all

John Hernlund
Department of Earth and Space Sciences
University of California, Los Angeles
E-mail: hernlund@....... or hernlund@............


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Larry Cochrane <cochrane@..............>