About the PNSN Webicorders Experimental Spectrograms -- Links to other dates

Webicorders and Spectrographs for Rainier Debris Flows

On the evening of August 14, 2001 starting around 20:40 Pacific Daylight time (8:40 PM), unusual seismic signals showed up on three seismographs located on Mount Rainier. These long-lasting low-level signals resulted from debris flows down Van Trump Creek and the Nisqually River.

Webicorder and spectrogram records for this period are shown here. Signals are given in Universal time (UTC), which is 7 hours ahead of PDT.

The 8/15/2001 (UTC) RCM WEBICORDER record shows:

• A long-lasting higher signal amplitude starting at 03:40 UTC (20:40 PDT).
• The higher signal level comes and goes over the next few hours, quitting a little after 08:00 UTC (01:00 PDT), though there may be a much smaller similar signal around 09:00 UTC (02:00 PDT).
• These signals are also visible (but less prominent) on FMW and LON.

The accompanying Spectrograms are for the same time periods as the webicorders. A Spectrogram is made by analyzing the frequency content of a time-window of trace data. The x-axis of the spectrogram represents frequency. Info on Spectrograms from the USGS
The 8/15/2001 (UTC) RCM SPECTROGRAM record shows:

• Red color indicates signal frequencies are concentrated between 1 Hz and 6 Hz (see frequency scale at bottom).
• The signal waxes and wanes over several hours; 03:40-08:30 UTC (20:40-01:30 PDT) (see vertical time axes)
• The most intense signal occurred in the first 15 minutes of the event.
• The average amplitude was low, as indicated by the spike-trace on the right.

Click on a date-time below to view the data from that time period.