Monday, September 15, 2014

Salty Seismic Station Servicing in the Outer Banks

Over the last three days Celia and I (both geophysics graduate students at Columbia University – Lamont-Doherty Earth Observatory) have been servicing ENAM’s three land-based broadband seismometers that sit on the Outer Banks of North Carolina.  These seismometers, installed in May of this year, represent a critical extension of ENAM’s ocean work as they expand the project’s scientific footprint across the western expression of the Eastern North American Margin magnetic anomaly.  This feature is one of ENAM’s key scientific targets as it is believed to be intimately tied to the complex rifting history of the Atlantic Ocean. 
Map showing the locations of existing USArray seismic stations (white), ENAM offshore seismic stations (yellow), and ENAM onshore seismic stations (red).
For our part, the goals for this service run were simple: 1) Safely retrieve the previously recorded data from the seismometers and 2) Check to make sure the instruments have been and currently are running well.  After spending a few days working in the sun and sand we are cautiously happy to report that we were successful on both fronts! First let’s talk about data.  
Station CHPH located near Cape Hatteras Middle School.  The solar panel sits on the right and the computer and seismic instrument sit buried beneath the sand on the left.  Their location is marked by the line of logs.
These instruments were installed in May 2014 and have been sitting quietly, buried beneath the sand recording ground motions from distant earthquakes ever since.  Amongst the treasure trove of data that we retrieved from the instruments are gorgeous records of both the Mw 6.9 Chiapas, Mexico event and of the recent Mw 6.0 Napa Valley earthquake, just to name a few.  Scientists will utilize traces of events such like these recorded at these stations to image the subsurface along the North Carolina coast with the aim to reveal the tectonic and deformational history of the region. 

Seismic records from the recent Mw 6.0 Napa Valley earthquake (left) recorded on ENAM station FFMS (located at First Flight Middle School) and the Mw 6.9 Chiapas, Mexico earthquake (right) recorded on station CHPH (located at Cape Hatteras Middle School).
With the data safely retrieved and stored on backup hard drives, we next moved onto checking on the instruments themselves or as we call it, their “state of health” (SOH).  The term SOH includes a variety of checks including the temperature of the digitizer (the computer that interacts with the seismometer), the accuracy of the clock used to keep time for the seismometer, the voltages of the batteries that power the instrument and the computer, …  By looking at the SOH we make sure that the entire package from the instrument to the computer to the solar panel (used to charge the battery) is performing adequately and that all components are successfully interacting with each other.
Natalie (left) and Celia (right) stand proudly in front of recently serviced seismic stations ECHS (located at East Carteret High School) and FFMS (located at First Flight Middle School).
With the data collected and health of the stations verified, it’s time to leave the seismometers to collect data silently by themselves for another few months.  More students and scientists will come to check on them again and retrieve their records this winter.  With such an active and dynamic world around us, who knows what geophysical treasures will be hidden amongst the data that will be collected then!

- Natalie Accardo, Columbia University - LDEO

Rosette Test

 September 15, 2014

Testing one, two, three! We successfully completed a Rosette test of the Scripps acoustic transducers at 4000 meters water depth. We wanted to be sure we could talk to the ocean bottom seismometers once deployed to the bottom of the Atlantic where the pressure is around 40 MPa and the temperature at about 4 °C. The test went smoothly, and now we are ready to deploy! While we were at it, we had a little fun with Styrofoam cups sending them down as well with messages and pictures making styrocasts.

Recovery from the Rosette test (photo credit: Gary Linkevich)

See you later,

Kate Volk aboard the R/V Endeavor