By IRIS - Winter 2013
The USArray’s Transportable Array (TA) seismometers and barometers have documented ground motion and atmospheric pressure changes due to Hurricane Sandy. The image below shows the TA sensors and the ground vibrating in the up-down direction (red dots) as the hurricane approaches (offshore concentric circles). Snapshots of ground motion are shown over a six day period at midnight. As the hurricane approaches, the stations furthest south start vibrating; as it sweeps north, the whole TA lights up with activity, and eventually returns to normal as the hurricane moves on land and loses its energy. This weak ground motion is not detectable by humans, but the sensitive TA instruments routinely record microscopic motions (or hum) of the Earth, called microseisms. This motion is generated by the ocean waves from the hurricane, which beat on the ocean shore with a dominant period of seven seconds, which these snapshots highlight. The images were taken from an animation made by Dr. Alex Hutko, at the IRIS Data Management Center. For more information, seehttp://www.iris.edu/dms/products/hurricanesandy.