Realtime recordings of the active shots

Steve Malone
July 20, 2014
Sets of shots for the active seismic experiment are scheduled for the nights of July 23, July 24 and July 31 (NOTE this is one day later than previously planned).  Eight shots are planned for each night starting after 10pm PDT and finishing by 2am PDT, but exact schedule depends on weather conditions. These shots are done at night to give the best chance of recording good signals without other vibrations being present (such as from wind or vehicle traffic or other explosions such as from active quarries).  Some of the permanent seismic stations of the Pacific Northwest Seismic Network (PNSN) will likely record some or all of these shots.  These stations have realtime telemetry to the PNSN labs at the University of Washington.  The PNSN provides visual records of most stations on their web site.  Any of these seismograms (sometimes called "webicorders" when on the web) can be viewed anytime via the PNSN web interface.
The list below (with links to the current record) give the names for those stations most likely to have good signals from the iMUSH shots.  The location of these stations along with the approximate shot locations are shown on the map.  The shot locations are in three groups.  Those with "X" (pink) labels will be shot on Wednesday night, those with "A" (yellow) labels will be shot on Thursday night and those with "Y"  (blue) labels will be shot the following Thursday night (July 30).


(clicking on a station in list above on the right will open a new window for today's seismogram. It may take a few seconds to draw, but will update every 2 minutes.)


For those interested in watching the signals from shots arrive in realtime we provide a realtime interface showing 16 stations all at the same time with only about a 10-15 second delay behind realtime. This graphic is automatically updated every 10 seconds and shows the last 10 minutes of signals.  Wiggles on only one station are likely due to something local to that station such as,a wind gust, animals walking nearby or a vehicle or aircraft in the vicinity. Signals on volcano stations such as SEP and HSR often are due to rock fall or glacier motion.  A signal showing up on several or all of the stations is from an earthquake (near or far) or, on the shooting nights one of the shots.
Clicking on the realtime display will open a new window.  Note, on Jul 24 the amplitude scaling was reduced and it now displays 6 minutes rather than 10 to give better resolution.  If you have a big screen expanding this window horizontally will give you the best resolution.  Note that the time axis is in Universal Standard Time or GMT which is 7 hours ahead of local time (PDT).
After the first night of shooting this blog will be updated with example records including brief interpretations of what can be seen.  So stay tuned….

UPDATE July 24, 2014

It looks as if all 8 shots went off last night as planned.  Two crews were active, each doing four shots over a 9 hour period.  One crew shot on an even multiple of 10 minutes and the other on 5 minutes to avoid both crews setting of a shot at the same time and generating confusing seismic signals.  Here is an example of one of the PNSN station seismograms for yesterday with annotations for what can be seen. Red arrows point to shot signals and blue mark other things on the record.


Screen captures of the realtime seismograms taken shortly after different shots.  Shots 1 and 2 went off at 10:05 and 10:10 pm PDT, July 23, 2014 (05:05 and 05:10 Z, July 24, 2014).  Note the times at bottom left and right are GMT (Z), not local time. The amplification of this plot is quite high so that the shot signals are very strong, but it also allows one to see other wiggles on individual stations not related to the shots and likely due to something near the station such as an animal or wind gust.  Station MTM is known for being susceptible to wind generated noise and both ELK and and FL2 often seem to have animals (deer?) nearby.



Here is the same sort of screen capture for the 4th shot that took place 10 minutes past midnight PDT (07:10 Z).  Not that there is a sharp signal on SEP about a minute later. Such rock fall signals are very commonly seen on this station and not related to the shot. Note the "move out" or delay in arrivals for those stations near the top of the plot.  These stations, with smaller signals are located at some distance from Mount St. Helens.



The automatic earthquake detection and location software of the PNSN detected and located all of the shots as if they were earthquakes. Seismologists have reviewed them, making minor corrections to the automatic analysis and they show up on the PNSN Recent Event page as stars (meaning explosions, not earthquakes).  Here is a subset of events from this page for just the past two days. Note that there are two explosions unrelated to iMUSH, one near Centralia, WA and one east of Vancouver, WA.  These are probably related to mining or quarry activity. Note also that there are some regular earthquakes during this period (circles).  The symbol color represents the event depth, red for very shallow and yellow and blue progressively deeper.



By The Way: Some may have noticed on the PNSN web pages that there seems to be an uptick in the number of earthquakes over the past month.  This is an artifact of the additional attention and some special processing software that the iMUSH experiment is inspiring.  Very small earthquakes that normally would be undetected or ignored are being searched out and analyzed in detail because of the extra instrumentation installed in the region.

NOTE:  On Jul 24 the amplitude scaling for the realtime display was reduced and it now displays 6 minutes rather than 10 minutes to give better resolution.


UPDATE: July 25, 2014

Seven more shots were fired last night, all of which were well recorded on the PNSN stations.  There also were a number of earthquakes that the PNSN detected and should have been recorded on many of not most active source portable stations.  Some hours before the shots there was a very tiny bunch of events right under Mount St. Helens in a zone that often has had such earthquakes.  At 11:53pm PDT there there was a Magnitude 2.3 earthquake just west of Vancouver, WA and then at 3:01 am PDT there was a Magnitude 2.8 earthquake just east of Kirkland, WA.  And finally at 3:54am PDT there was a magnitude 5.9 earthquakereported by the USGS  in southeast Alaska that was well recorded on all PNSN stations.

Here is a selection of the seismogram from station, FL2, to the southwest of Mount St. Helens.  The seven shots are marked with red arrows and earthquakes are marked with blue arrows and annotations.  Note that the southeast Alaska earthquake signals last for more than 15 minutes.  Seismic waves spread out in time so the further you are away the longer the signals last (as long as the source is large enough to be recorded at greater distances).




Here is a screen capture from the realtime display showing a very small event in the crater of Mount St. Helens (recorded only on SEP, HSR and SHW) followed several minutes later by one of the shots that was located to the southwest of the mountain.  Note the later and smaller signals on ASR near Mount Adams) and FMW (just north of Mount Rainier).



Crews are now heading to the field to pick up all the active source seismic stations.  They will then spend a couple of days down-loading data from them and preparing for another deployment next week with shots scheduled for Thur. night.