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Investigating the polar regions from the inside out

Building an Antarctic Seismic Station — by Rachel Gesserman

It has been almost 2 weeks since I arrived at Byrd camp in the middle of the West Antarctic ice sheet and our project is off to a great start. The camp itself is pretty remote and home to about 35 people. This includes the scientists working on the POLENET project, pilots from Kenn Borek Air who fly the Twin Otter and Basler airplanes to our seismic and GPS sites, and a hard-working camp staff made up of weather observers, kitchen staff (who happen to be excellent cooks!), and people who do daily tasks around camp. You can probably imagine with only 35 people, the camp is not too big. There are several semi-permanent tents that house the galley, washroom (aka Byrd Bath), science equipment, pilot sleep quarters, and a meeting tent where we can watch movies and hold science lectures. There is also a big plot of mountain tents where everybody else sleeps called “tent city” that is further away from some of the loud, heavy equipment used at camp. 




One challenging aspect of working here is figuring out what GPS and seismic sites to fly to each day. The process is a little tricky because in order to fly, the weather must be good at Byrd camp, at the site we are flying to which can range from 100-600 miles away from Byrd, and at a fuel cache along the route if the plane needs to re-fuel during the trip. If the weather forecast does not look good at any of these places, we cannot fly for safety reasons. Another complication is that the weather in Antarctica is rapidly changing, and the plan that we develop each night for where we want to fly can often change in the morning when the pilots get an updated forecast. This makes for some hectic mornings of getting the right people and equipment organized to fly because the planes can only hold a certain amount of weight and the equipment needed varies from site to site. Since I have arrived we have been able to visit 5 seismic sites. Some are only temporary stations that have been fully removed, and others we are collecting data from and performing maintenance on to keep them running for another year. Although the setup of a seismic site may not look like much on the surface of the snow, inside all the buried boxes is an intricate setup of equipment that will record earthquakes from around the world. The following picture is of a temporary site that we had to completely dig out and remove.




On the right side of the photo you can see a circular red dome. Under this dome is the actual seismometer, which is insulated in a foam box. Burying the sensor helps to keep out a lot of unwanted noisy signal created from wind because it is shielded by the dome and the snow. The sensor is extremely delicate and sensitive, and is composed of three masses in a spring-like system. Each mass is positioned differently in order to record ground motion in the east-west, north-south, or up-down direction. You can’t see it, but there is a cable running from the sensor through the snow and into the orange box on the left side of the photo where it is connected to a piece of equipment called a datalogger. The datalogger records these mass movements as digital data that can be viewed on a computer. Several times a day, the datalogger will transfer the digitized data to a small box called a baler that contains memory sticks. When we visit a seismic site, we can remove the baler to get all of the seismic data recorded over the last year or two. 




But how do we keep this station powered up and running all year long in the harsh Antarctic weather? In the back of the station photo is a set of three solar panels. There is a cable running from these solar panels through the snow and into the orange box where it is connected to a power module. The datalogger that I discussed before is also connected to this power module, along with 10 car batteries. During the 6 months of sunlight in Antarctica, referred to as austral summer, the solar panels charge the car batteries that provide power for the station. During austral winter when there is no sunlight, the batteries provide enough power to keep the station running. Just for comparison, when we install sites in other parts of the world we only need 1 car battery because the solar panels receive sunlight every day. You also might notice an antenna on top of the solar panels. This is a GPS antenna that is extremely important because it allows the station to know the exact time. The timing needs to be accurate to about 1/100 of a second; otherwise our data will be useless because we won’t know how long it takes seismic waves from an earthquake to reach the station. But when everything is set up correctly and functions without a problem throughout the year, we get excellent data like this signal from the March 11, 2011 Japan earthquake recorded at one of our seismic sites called Siple Dome. You can see how the earthquake looks on the up-down, north-south, and east-west components of the seismometer. We can use this data along with data from many other earthquakes around the world to make a map of the structure of the earth beneath Antarctica.  Here’s hoping that the rest of our data collected this season looks as good! 




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