Interpret Displays - Pacific Northwest Seismic Network

Displays Interpretation Primer

Seismograms (including hawk-o-grams, fan-o-meter2 and QuickShake displays) are graphical representations of ground vibrations over time at the respective sensor locations. Time increases from left to right (and for Hawk-o-grams top to bottom). The size of the wiggles on the traces is proportional to ground acceleration at the site. These are very sensitive instruments and thus most signals observed in this football game monitoring case are very small with motions much less than 1% g (Where 1.0 g is the acceleration of gravity, ie what we feel just living on the earth). Ground motion in excess of 1 g (ie 100% g) would throw you in the air. Normally one can start feeling ground vibrations as small as 0.1% g and vibrations in excess of 10% g can damage buildings. All of our displays have constant scaling (though for the QuickShake display you can change that with a slider). See our FAQ for comparing ground motion for Seahawk games with real earthquakes.

Our three different displays have different characteristics based on the length of the displayed record and how many channels. It may be interesting to compare a particular signal, such as a train passing near the stadium, on all three display types.

Some examples of what we think different signals mean:

A seismogram from the station HWK3 on the vertical channel. A red circle points out a spike in the seismogram likely caused by someone jumping or walking nearby, and a long blue oval encircles a steady increase and eventual decrease in the seismogram overtime likely caused by a train passing.

The fan-o-meter shows every channel from the HWK and KDK stations, with some seismic activity occurring on the HWK1 and HWK3 channels.

Seismogram taken from QuickShake showing several spikes from the vertical channel of HWK3, where someone might have been walking or jumping nearby.

Fan-o-meter showing all of the channels from each HWK and KDK station. There are several large spikes on the HWK3 seismogram channels.

Here are examples on QuickShake and fan-o-meter2 of short, sharp signals on only station HWK3, probably due to someone walking/jumping very near the instrument.

By the way, we are only showing the vertical component (HNZ) on QuickShake because it is the most interesting.

The different colors on the fan-o-meter2 (and the hawk-o-grams) are only to aid the eye and have no other significance.

PNSN Station KDK

Seismogram from station KDK on the ENZ channel. Normal background seismic activity is shown, with small spikes at somewhat regular intervals largely due to traffic nearby.

Station KDK is located very near the US-99 ramp leading up to the Alaska Way Viaduct and so any vehicle starting up the ramp will shake the ground. Trucks in particular are probably producing the larger signals. Thus, Seahawk fans need to be bigger and stronger than vehicles on the nearby roadway to show above the traffic signals.