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
