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About This Plot
The above plot shows the seismic signals from an earthquake on all three channels (up-down, north-south, and east-west) of the ASU seismometer, filtered from 0.033 Hz to 2.0 Hz. The lower panel shows the location of the earthquake and the great-circle distance between the ASU Tempe campus and the earthquake.
The plot is automatically generated, a computer algorithm examines the signals and attempts to determine whether the earthquake signal is stronger than the background noise. The algorithm is not perfect, occasionally plots will be generated where local noise sources fell in time window which the program was examining for signal.
The ASU seismometer is a Guralp model CMG-3T broadband instrument, located in the basement of the Physical Sciences Building on the ASU Tempe campus. A concrete pier for the instrument extends approximately 40 feet below the foundations of the building, and is isolated from the rest of the building with an elastic gasket. While the gasket and deep pier isolate the instrument from some of the vibrations of the building, this is still a seismically noisy location due to the surrounding campus and city with the attendant traffic, light rail, and construction noises. Seismometers for scientific investigations are usually installed in remote locations to minimize the effects of civilization-generated seismic noise.