PNSN Logo PNSN | Fall 2006 Tremor Episode | Summer 2005 deep tremor

Average Signal Amplitudes at selected stations

Average (root-mean-square) signal amplitudes (or "RSAM") of vertical ground velocity recorded at selected stations of the Pacific Northwest Seismograph Network. The stations are (top to bottom on the graphs, ie north to south) MCW, STW, JCW, GNW, HDW, CPW

Smoothed RSAM data for three day period of strongest tremor for selected stations shows periods of deep tremor. Episodic tremor shows up as an increase in signal that appears simultaneously on several stations.

    Two weeks for the last part of this ETS RSAM data
    ETS tremor was considered over on Feb 2, 2007. Regular daily pulses, particularly on JCW are due to cultrual/telemetry noise.
Average (rms) amplitudes are displayed as a function of time. Each dot on the graph is the average amplitude computed for a 60 sec window.

Signals are converted to true ground velocity in millimicrons per second before the rms is computed. The data are filtered between 1.5 and 5 Hz before the average (rms) amplitude(over a 60 sec window) is computed. The average amplitude is de-glitched and then further smoothed (running average) over a time window of 20 minutes RMS amplitude will also reflect any earthquakes that occur, changes in cultural noise, and other artifacts. Note the daily cycle on some stations, probably due to higher cultural noise (trucks, trains, human activity) during the day.

Map of stations in above plots.