What are the noises I hear before the small quakes that hit Berkeley?
Two examples, both about 3 a.m., so all else was quiet, both small
quakes, under 3.0. I'm inside, I hear these sounds a few moments
before the jiggle. The first of these two was especially interesting
in that it sounded exactly as a small but definite car crash, two cars
colliding; in fact, I got up to look, and then the quake hit.

The second, and most recent, was the more common rumble, then all was
quiet for a moment, then the jiggle. The first quake was also much
sharper, which is probably relevant, but what is one really hearing?
And why does the sound arrive so distinctly before the quake?

Hi maria219:

Thanks for the fascinating question. I've weeded through quite a few
websites that touch on this subject and the best (and most
scientifically plausible) explanation I've found is:

Why do we hear an earthquake before it arrives?
URL: http://visindavefur.hi.is/svar.asp?id=4825
Quote: "We normally sense P-waves as an earthquake to a lesser degree
than for instance the S-waves following them. If an earthquake has not
been very strong or we are reasonably far away from its center we will
not at all sense the P-waves as an earthquake but only hear the sound
induced by them in the air. Still, we may feel the S-waves quite
clearly and then other waves which often arrive later, especially at a
distance. The reason for this incoherence of sensation is thus found
in the different sensitivity of our sensing organs."

Read the entire article for even more detail. 

An earthquake produces both P-waves and S-waves. for more detail see:

How Earthquakes Work
URL: http://science.howstuffworks.com/earthquake4.htm

So, you are basically hearing the P-waves (which are too subtle to be
felt) before you get smacked with the S-waves. So, I guess you can say
that you aren't hearing sounds before an earthquake - you are *in an
earthquake and hearing part of it before you can feel it*.

More information on this can be found at: 

Perception Diary
URL: http://psy.otago.ac.nz/r_oshea/PSYC323/perception_diary.html
Quote: "The first sound my friend heard in the Secretary-Island
earthquake (and which I heard at my first earthquake, see ``Can the
earth move? 1981'', above), the sound of the wind in the trees, was
the sound of P waves reaching her location. These waves must have been
of a frequency high enough to hear and too high to feel. The first
shaking I felt must have come from S waves reaching my location. These
waves must have been of a frequency too high to hear and low enough to
feel. The slow rolling I felt must have been from L waves, which would
have been much attenuated by the time they reached Dunedin. They were
clearly of a frequency too low to hear (I estimate them at about 1
Hz), but high enough to feel. I suspect they had the highest amplitude
of all the waves."

Earthquake House - Awesome Forces 
URL: http://www.tepapa.govt.nz/TePapa/English/Learning/OnlineResources/SGR/EarthquakeHouse.htm
Quote: "?P? waves or (primary or ?push?) waves are the waves that
travel at 20,000 km per hour and are responsible for the low rumbling
sound that you may hear just before an earthquake. ?S? waves are the
(secondary or ?shear?) waves that travel at10,000 km per hour. They
shake the ground sideways and cause the most damage."

The difference in the sounds you heard before the two earthquakes are
probably attributable to the direction from which the sound is coming
and the magnitude (energy) and wavelength (pitch) of the sound itself.

Search Strategy (on Google):
* earthquake "sounds before"
* "immediately before an earthquake" sounds OR sound
* "just before an earthquake" sound OR sounds OR noise OR noises
* "p waves" earthquake
* "p waves" earthquake audible 
* "p-waves" "s-waves"

I hope this helps!

websearcher

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Clarification of Answer by websearcher-ga on 17 May 2005 14:32 PDT

One other thing. In many cases earthquakes feel "small" to you because
the epicenter is far away from your location. If that is the case,
because P-waves (which you might only hear) travel faster than S-waves
(which you feel), that would mean that you would spend more time with
*onlt* the P-waves. This could give you a better chance of being able
to discern the sounds before the *shake* of the S-waves.

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Request for Answer Clarification by maria219-ga on 17 May 2005 15:52 PDT

Thanks, I shall read more widely. I just couldn't come up with any
good search terms, so thanks for that too. Seems to me that there must
be some noise, too, from everything being jostles, the city around me.
We'll find out. I hope to discover too why one quake might sound so
very different. The indistinct rumble is common--the sound of a
collision, not! Perhaps a geologist could tell, by the data--maybe
it's the rock, or the type of movement. I always look online, but of
course, the figures mean nothing to me.

Great answers!

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Clarification of Answer by websearcher-ga on 17 May 2005 17:03 PDT

Hi maria219:

Thanks for the kind words - and for one of the more interesting
questions I've had to research in a while. :-)

websearcher

very cool and interesting. i've heard it too many times. last time i
heard it, my father ran out of his room thinking i had crashed into
the house.

Are you kidding? Like with a vehicle? Cuz that crash sound, that one
quake not long ago--I think it was the one under Canyon--was totally a
car crash

I should probably buy another question. I have heard slammers
(slamming against the house. The big one, in '89, every little thing
in the house made too much noise--(and the scenery was mesermerizing.)

Thanks, all!