Picking up strange signals

We carefully monitor all of the data that we are collecting from the main lab, located in the bowels of the ship, below the water line.  This is mission control for the scientific operations.  A bank of 46 screens (!) display every conceivable kind of information about data that we are collecting, including the position and status of equipment towed behind the vessel and real-time displays of the raw data themselves.   There are also 20 mice and 18 keyboards – good luck finding the right mouse the first time if you are not intimately familiar with the set up!  Because we are collecting data 24 hours a day, 7 days a week, members of the R/V Langseth’s crew and scientific technical team and the science party work in shifts to monitor all aspects of the operations around the clock. 

The main lab on the R/V Langseth.

If anything strange or unexpected occurs – for example, we see something odd in the data – we make detailed notes.  On October 1 at 1:25 am local time, the watchstanders noticed some strange signals in the data recorded by the streamer and made a note of it.  Today, we realized that a magnitude 5.3 earthquake occurred about 30 miles away at that time.  The strange signals were actually sound waves generated by the earthquake!  Although the main signal we intend to record are sound waves generated by the seismic source towed behind the ship, the sensitive recorders in the streamer will also detect any other sound waves.  Our study area is a seismically active region that regularly produces earthquakes, so it is likely that we recorded quite a few earthquakes on the seismic streamer and the ocean bottom seismometers that we deployed during the first phase of this project.  We also record ocean waves and whales.  Thanks to Jim Gaherty (NAU) for bringing this earthquake to our attention!  Every so often, it is useful having a seismologist husband….

Map showing location of all earthquakes during our study (red circles), including the one that occurred on Oct 1 (labeled with text). The orange star shows where the ship was at the time of the Oct 1 earthquake.
Recording from seismic streamer showing the arrival of sound waves generated by the Langseth’s seismic source (first couple of seconds of record) and from a magnitude 5.3 earthquake (last ~5 seconds of record).

Donna Shillington (NAU)

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