but on the other hand the p-wave now since is moving back and
forth and back and forth in the direction of propagation at least half the time energy is being
spent moving in the direction of propagation so I don't exactly know that's why that this the velocities are different
but that's how I've remembered lo these many years soapy ways are all gone awry first then
ass ways and finally the the the surface wager
gonna come in so you look at a typical trace here comes a trace along the first one
is the p-wave the body P wave member now not much motion so it will be
very low amplitude and then some time right after that
there's going to be the s-wave come through again in not much motion because there's not
much motion the rocks and then funny the great be 11 you always see sweeping across the chart those are the
surface waves and funny to me
okay what he wanna tell you first you
gotta seismograms here what he wanna tell from it well 10
things you want to tell from it is a where was the focus where was the
epicenter and then how big was this earth but what
was the richter Richter scale reading lists a at the upper center can you do that well yes you can so here's here's the way it's done let's
say we take first the ball those body wave arrivals the p-wave and
the s-wave now here's the deal I love picture these as two racers our race European racer
ass and just picture now our rates between these two people
running around a track and we're gonna make a plot now were in
a plot time on the vertical axis versus distance on the horizontal axis and firstly first well as plots a the
racer p so all we have to do is watch in time
and make a plot of time versus distance and if you do that
as he races along time versus distance you get a line now
adjust a simple straight line which describes that performance of the
racer p now was put on top of that the
performance a racer ass now remember ass is not as fast so
for the same time interval he will not have gone as far and then so if we keep doing that for
for racer ass you'll get another curve shorter diverging from 00 reparative representing racer s know two
things you are two diverging now curves was a really tell you well for
example is so you're watching the race what it really says as time goes on
we're talking about the vertical component now as time goes on what it really says is
the distance between those two racers Wally grace and you say that you just
watch him run around the track in you can see right off the bat the pier azure pools away from the S
racer and the gap between a distance gets bigger and bigger well thats with his plot says so note on besides that is says the as the further
they were Ron the further they go the time
interval between them gets bigger and bigger sees another word
for any given distance you can look at this chart and you can
tell how far they would be a part in time well let's say for example this was
America lot and you wanted to get to the start but you couldn't find out you'd
get the time you gonna were started anyway so you're you're standing along the
course someplace and the first runner came by writer P and you started a stopwatch and
then writer s came by and you stopped at so
you know the time interval now the dissed the time interval between these
two racers note if you have this plot all you have to do is take their time in
a row now find out where those two curves are
separated by that time interval