Katrina"s Waves Felt in Calif.

[Christina]

Hurricane Katrina's waves felt in California11:00 24 September 2006 From New Scientist Print Edition. On 29 August 2005, as hurricane Katrina was rumbling towards New Orleans, a seismic hum more than 1000 times the strength of the average volcanic tremor was felt nearly 3000 kilometres away in southern California. Its source was the hurricane itself.Hurricanes create large ocean waves, which send energy pulsing through the Earth as they pound the shoreline. To determine the power of Katrina's seismic waves, Peter Gerstoft of the University of California, San Diego, and colleagues analysed the signals recorded by a network of 150 seismic stations in southern California just before Katrina hit the Louisiana coast. They used a method known as beamforming, which preferentially picks up signals from a particular direction, to decipher the seismicity generated by Katrina (Geophysical Research Letters, vol 33, p L17805).Seismic surface waves, which travel through the Earth's crust, were detected 30 hours before the hurricane made landfall, while body waves, which bounce down into the mantle, arrived some 18 hours later. "The body waves had travelled down to 1100 kilometres inside the Earth," Gerstoft says. This is the first time that a hurricane's seismic signal has been detected so far away.