PSN-L Email List Message

Subject: something else about microseisms
From: Randall Peters PETERS_RD@..........
Date: Sun, 20 Dec 2009 10:15:12 -0500

For those of you who have both a vertical as well as a horizontal seismogra=
ph, I would like for you to consider the following.
    Conventional wisdom says the microseisms are fundamentally of Rayleigh-=
wave type.  If they are generated by ocean pressure waves as is thought by =
most (including myself because I have seen them increase dramatically durin=
g hurricanes) then I don't believe they are Rayleigh waves.  The reason has=
 to do with the mechanism of their generation by this means.  Water cannot =
support shear, as is well known; so what gets propagated away from the ocea=
n bottom where the pressure is fluctuating--must be a vertically polarized =
wave that I think of as a 'guided' wave in the crust of the earth.  Because=
 of the granular nature of the crust, rotation effects cause the vertically=
 polarized vibration to take on horizontal components of accceleration.  Th=
us the waves begin to masquerade as Rayleigh waves.  My first occasion to t=
hink about this was when I moved my VolksMeter from a building basement sla=
b to a pier that extends 20 feet down into the ground.  Surprisingly, I fou=
nd a dramatic difference in micro-signal for these two cases.  The slab cas=
e showed micro's nearly all the time, whereas the pier-case showed them onl=
y occasionally and smaller when present.  So what physics-experience is the=
 basis for my belief?  My PhD was concerned with the propagation of ultraso=
und (acoustic) waves in solids.  The waves were introduced to the samples u=
sing an x-cut quartz crystal.  Anybody who has done such work knows that bo=
nds to couple transducer and sample are crucial to the success of the work.=
  They also know that you can't transmit shear waves through a liquid.  Thi=
s is in fact the reason we know (from seismic studies) that the earth's cor=
e includes a liquified one that surrounds the innermost solid one.  I am su=
rprised by the fact that this property of liquids is apparently thus well k=
nown to seismologists, while at the same time they believe that water (pres=
sure) waves working on the floor of the ocean could generate horizontal mot=
ions of that floor as well as vertical ones.  =

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