Artist’s impression of GOCE satellite. European Space Agency


Earthquakes’ booms big enough to be detected from orbit

Satellites listened to the 2011 Japan quake and located fault beneath Spokane.

by Scott K. Johnson – Feb 25 2013, 11:00am EST

Last year, we reported on some mysterious booms in a small Wisconsin town that turned out to be small earthquakes. While it was an unusual story, it’s actually not that uncommon of an occurrence. Early in the summer of 2001, folks in Spokane, Washington started reporting similar booms. The sounds continued, off and on, for about five months. The mystery didn’t last long, as the earthquakes responsible were picked up by seismometers in the area. (A particularly loud one that took place exactly one month after the September 11, 2001 terrorist attacks in New York did rattle some nerves, however.)

In total, 105 earthquakes were detected, with a couple as large as magnitude 4.0. For most of them, there wasn’t good enough seismometer coverage to really pinpoint locations, but some temporary units deployed around the city in July located a number of events pretty precisely: the earthquakes were centered directly beneath the city itself.

While a dangerously large earthquake is pretty unlikely in Wisconsin, the possibility can’t be ignored in Washington. The 2011 earthquake in Christchurch, New Zealand was only a magnitude 6.3, but the damage was extensive because the epicenter was so close to the city. In L’Aquila, Italy, a swarm of small earthquakes in 2009 was followed by a deadly magnitude 6.3. (The poor public communication of risk during that swarm netted six seismologists manslaughter convictions.)

For obvious reasons, it’s important to learn more about what’s going on beneath Spokane. A group of researchers from the US Geological Survey and the Pacific Northwest Seismic Network have turned to satellites to start piecing the story together.

InSAR (or interferometric synthetic aperture radar) data from satellites allows scientists to detect exceedingly small changes in land surface elevation, such as occurs when crustal blocks shift during an earthquake. Data collected by European Space Agency and Canadian Space Agency satellites show surface movement along a fault running northeast from the center of the city. Despite the fact that the data were gathered from space, they were able to show a maximum change of about 15 millimeters.

Read more: Earthquakes’ booms big enough to be detected from orbit | Ars Technica.

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