Using the AmaSeis seismogram viewer and downloading - QuarkNet

Using AmaSeis… Page 21 of 69
Figure 27. AmaSeis screen image showing seismogram (“zoomed in” on the P arrival using
extraction tool) and the use of the amplitude measuring capability of the software. The amplitude
(146 digital units) of the mouse location is displayed in the window in the lower right hand corner
of the screen. The seismogram is from the September 22, 2003 Dominican Republic earthquake.
3.8 Real time playback of seismograms using AmaSeis: Extracted or saved seismograms can
be played back in real time (or speeded up time) by clicking on the “Play Record” button at the
bottom of the AmaSeis extracted seismogram screen. This capability is useful to illustrate the
ground shaking during an earthquake, particularly for seismograms recorded very near to the
epicenter of a strong earthquake. By watching the screen as the ground motion appears in real
time and displays the amplitude, frequency content and duration of the shaking, one can get a
sense of the actual shaking that occurred at that location. An example seismogram that is useful
for real time playback is shown in Figure 28. This seismogram is called an accelerogram
because it is a record of acceleration of the ground in a particular direction, in this case
horizontal. The accelerogram shown is only 28 seconds long and show that ground motions in
this location reached peak accelerations of about 40% of the acceleration of gravity (enough to
be very strongly felt and cause significant damage) and that the strong shaking lasted for about 6
seconds. Also notice that the ground motion begins with relatively low-amplitude and highfrequency
shaking (corresponding primarily to P-wave arrivals) and then becomes much larger
and of lower frequency as S- and surface-waves arrive at the station. This seismogram can be