ASRA Earthquakes Module 2007

Seismometer Sites

Seismometers must be placed in areas that meet certain criteria. These criteria are listed below.

• Noise - this is anything that causes vibrations other than earthquakes, such as cars, avalanches, wildlife, people, or buildings.
• Tampering - any disturbance of the seismic instruments or surrounding area by humans or animals.
• Skyview - the GPS needs an unobstructed view of the sky in order to communicate with the GPS satellites to acquire an accurate time.
• Stable soil - the ground where the seismometer is placed must be able to transmit vibrations well (loose ground can insulate the seismometer so it doesn't register vibrations).

We placed three seismometers in the park which we called ARPT, GRVL, and PATH. Following is a brief description of where each site was, how well the site met the above criteria, and pictures of the site taken facing north, south, east, and west.

ARPT

This site was located at the end of the Denali Park road near the Kantishna airstrip. A walking trail made it easy to access but its proximity to humans and the airstrip created a source of noise. The possibility of human tampering was relatively high because of the trail, but the soil and skyview were adequate.

PATH

This site was a few miles beyond the Wonder Lake Ranger Station. It was the most promising because it was located away from the road on a rarely used trail, making the noise level and chance of tampering small. It also had a good clear skyview and stable soil.

GRVL

This site was located at mile 74 of the park road on the edge of an old gravel pit. It was close to the road and therefore had a high probability of being noisy. To avoid tampering, we not only buried the seismometer but also covered the other pieces of the monitoring system. We placed the instruments along the edge of the pit in order to have the most stable soil. There was a very clear skyview for the GPS.

Procedure for installing a seismometer:

1. Find a suitable area.
2. Dig a hole for the seismometer.
3. Orient the sensor towards geographic (true) north.
4. Double check sensor orientation.
5. Level the sensor.
6. Lock the feet down and make it stable and secure.
7. Conect sensor to sensor cable.
8. Connect GPS antennae to cable and cable to breakout box.
9. Test output of the batteries (the charge must be positive).
10. Attach power cable to the battery and visually check the polarity.
11. Check the polarity at the power cable connector.
12. Connect battery to breakout box.
13. Listen for the starter click (it's in the seismometer and it's very quiet so listen carefully) If no click run a diagnostic check with the computer.
14. Take pictures of the site from North, South, East and West
15. Document the site and record the picture numbers for later reference