Mobile Earthquake Network Widens Pulse Readings on Planet

It's no secret that scientists have extracted an abundance of data from the National Science Foundation's EarthScope-USArray and its unique transportable seismic network of 400 sensor stations leapfrogging across the United States.

But now scientists at Scripps Institution of Oceanography at UC San Diego are
piggybacking onto the mobile network with instruments that go beyond seismology to capture groundbreaking data and new perspectives of a range of phenomena.

For example, the value of monitoring infrasound-sound waves inaudible to humans-has been known for years for tracking events ranging from human-produced acoustic disturbances such as clandestine nuclear testing to natural phenomena such as bolide events in which meteors explode in the atmosphere.

With recent installations of infrasound instruments on USArray stations, scientists now have a dense cluster of listening devices to track acoustic phenomena. Michael Hedlin of Scripps will present examples of such events at the 2011 American Geophysical Union (AGU) Fall Meeting in San Francisco. (A31A-0037 · Wednesday, Dec. 7, 8 a.m. - 12:20 p.m. Moscone Halls A-C)

"Infrasound recordings have never been made before at this scale," said Hedlin, who indicated that the network places a station every 70 kilometers (44 miles) across an area of 2 million square kilometers (772,000 square miles). If a significant event occurs anywhere within the network, we should have a station nearby."

Hedlin said access to a cluster of stations within 1,000 kilometers (621 miles) of an event within the network is highly valuable to not only study the source but probe the atmosphere through which the sound waves propagate.

"Our new work shows we can use these stations to not only study large-scale features in the atmosphere but very small-scale structures, such as those due to gravity waves," said Hedlin. "We believe these small-scale features that change constantly have a huge effect on the propagation of sound."

The new data also are revealing tantalizing new views of powerful weather events. Scientists are studying real-time data streams from severe weather events, from mighty gust-front passages to severe thunderstorms.

Scripps Research Geophysicist Frank Vernon will describe studies of a cluster of tornadoes in April and May of 2011 in several areas of the United States-some that passed as close as four kilometers (2.5 miles) from network stations. (A43E-07 · Thursday, Dec. 8, 3:10 p.m. - 12:20 p.m. · Moscone Room 3004)

"Currently there are many unidentified signals that are recorded by seismic monitoring systems-it turns out that many of these signals have sources in the atmosphere," said Vernon. "They could be storm fronts passing over the seismic station, thunderstorms, nearby tornadoes or other large scale meteorological phenomena. Our new observations give us better understanding of the seismic noise as well as opportunities to study the interface between the atmosphere and the surface of the earth."