Both stations are located in the seismically quiet state of Maine, USA. RCB43, the station in Poland, ME, is located within a meter of bedrock. R06AC is located on a glacial deposit and is not near bedrock, which makes it much more sensitive to surface environmental noise like passing vehicles. Small seismic events have been observed nearby, and major earthquake events (magnitude 7+) from around the world are detected at both stations.
Availability plot for today, 2017/11/21
Plots are updated every minute at 15 seconds past. Both stations are located in basements about 50 feet from residential streets. Vehicles driving by at speed account for a large portion of the spikes seen in the data. Other potential sources of noise include washer/dryer vibration, indoor foot traffic, and cars entering and exiting the driveway. During the warmer months, lawnmower noise may contribute as well. The anthropogenic noise sources generally fall in the 10-15Hz range of the frequency spectrum as observed at this station. Earthquakes, should they be detected, will likely cover a much larger portion of the observable spectrum than the rest of the noise sources.
Plots rendered at 2017/11/21 17:34:18 UTC.
Page loaded at 2017/11/21 17:34:56 UTC.
Spectrogram of the past five minutes (unfiltered):A plot of energy density over time. Spectrogram z-axis (color) units are dimensionless.
0.7 - 2 Hz bandpass:
Helicorder plot since UTC 0000hrs:
0.7 - 2 Hz bandpass helicorder plot (can detect P waves from large, faraway earthquakes):
These plots are made with a combination of ObsPy and Matplotlib formatting. The spectrogram above scales based on the density of energy at the given frequency, based on a moving window with an overlap of 0.9/1. The helicorder plot resets every day at 0000hrs UTC. Traces plotted on the helicorder are scaled down by 800 and 70 respectively for readability, although this is subject to change as I get more familiar with the signatures of environmental noise that the geophone picks up.
RCB43 was moved to Poland, ME in the summer of 2017. Previously, it was located in Greenwich, CT, near the downtown area, and as such, all of the examples below are from the Greenwich location. As it turns out, there are plenty of sources of environmental noise associated with placing a geophone in the heart of a fairly busy suburban town. My hypothesis is that these sources of noise were somewhat amplified by unconsolidated Holocene material that underlies the property. I do not know the depth to acoustically "fast" unweathered bedrock, but based on characteristics of nearby outcrops (and observed belowground conditions of a recent road excavation) I assume it's probably at least 3-5 meters below where the station sat.
R06AC was brought online in November, 2017. It is located on what geologists call an esker—a hill composed of sand and gravel from a stream that ran beneath a glacier. That glacier was the Laurentide Ice Sheet, a 3-4 kilometer thick blanket of ice that covered much of Canada and New England during the end of the last ice age, approximately 25-15 thousand years ago. What this means is that since esker sand and gravel is loose and less stable than bedrock, vibration from nearby roads is picked up really well by the geophone on the seismic instrument.