Atmospheric Pressure Sensors Help Earthquake Magnitude Determination
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Infrasound sensors cost less than seismometers, are reliable and exist in large numbers in Alaska for other uses.
“What we’ve done is use infrasound for a purpose it wasn’t really intended for,” said Ken Macpherson
Macpherson details the use of infrasound sensors for seismology in a research paper published April 21 in the
Macpherson is a
Infrasound sensors can register the full range of an earthquake’s ground motion by detecting air pressure changes caused by the ground’s up and down movement during an earthquake.
Upward movement of the ground compresses the air, increasing air pressure much like a piston does. Downward movement reduces the pressure.
Pressure changes from even the largest earthquakes are far below infrasound sensors’ upper limit.
In contrast, seismometers, which record the actual movement of the ground, have an upper limit, meaning top-end data can be absent for large earthquakes. They can also miss data of smaller earthquakes if those occur too close to a seismometer.
Seismologists call that data loss “clipping.”
“If you crank up your stereo too high, you get a horrible sound,” Macpherson said.
As one example, Macpherson and his colleagues compared infrasound data of the magnitude 7.1 Anchorage earthquake of Nov. 30, 2018, to data from a seismometer. Both instruments were in the same location 18.6 miles from the epicenter.
“The seismometer recording of that earthquake went right to the dynamic range of the instrument and stopped,” Macpherson said. “So there’s a loss of amplitude information.”
The seismometer was one of several in the Southcentral Alaska region missing top-end data from that earthquake. Data from the infrasound sensor was not clipped.
To check the accuracy of the infrasound monitor’s top-end data, Macpherson matched it against the data from a strong-motion seismometer at the same location. They matched.
Infrasound sensors can also provide data just as timely as seismometers. That’s especially important if a tsunami is possible. The National Tsunami Warning Center has just four minutes to issue a warning from the time of a quake’s occurrence.
“If all of the close seismometers clip, and the Tsunami Warning Center is trying to get an accurate magnitude for warning of a tsunami, they could quickly compute magnitudes from a nearby infrasound station that’s colocated with a seismometer,”
Some of these were part of the EarthScope
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