CERI - Microseismic Effects of Hurricane Katrina

CERI - Microseismic Effects of Hurricane Katrina: "Microseisms (from the Greek micro for 'very small' and seism for 'shaking') are faint, continuous tremors of the Earth caused by natural processes. Most seismologists consider them to be annoying background noise that interfere with the detection of earthquakes, underground explosions, or oil exploration sources. However, microseisms sometimes become interesting in their own right.

As hurricane Katrina plowed its way over the Gulf of Mexico during the last week in August, its high winds whipped the sea surface into a frenzy of huge waves. The low atmospheric pressure in the eye of the storm raised the sea surface and as the storm moved onto the shallow continental shelf the shoreward winds east of the eye piled additional water onto the coast. All of these processes generated microseisms that traveled as sound vibrations through Earth's solid crust to the shore, and were recorded at seismograph stations.

The images on this page illustrate this story, as told by one seismic station at Livingston, Louisiana, operated by the LI.LTL (LIGO-SCSN) operated jointly by the LIGO Livingston Observatory of Caltech and the Southern California Seismic Network. LIGO is supported by the United States National Science Foundation. Each 'helicorder' record shows the ground motion in a 12 hour period, with time increasing in 15 minute lines (each of a separate color) from top to bottom. The microseisms grow relentlessly as Katrina approaches slowly for at least 2 days. On August 28 the microseisms are so strong that the lines are overwriting each other. Finally on the 29th of August Katrina slams ashore at just after 6 a.m. Central Daylight Time. At about 6:10 the seismic station loses communications with the network."

This may not explain the ominous rumbling my mother and I heard and felt on August 28th as Katrina approached -- but at least we know that the seismic station at Livingston, Louisiana heard it too....

View the helicorder record for August 26, 2005 - According to CERI it is possible that the monitor was already picking up noise from Hurricane Katrina even at this early date. I have been checking out the readings from this station (LI.LTL) for several weeks now and have found that such 'noise' is not uncommon. For contrast - view the helicorder record for August 28, 2005. Scary stuff.

(See my Katrina Journal entry from August 28th, At least we don't have to worry about the water... where I describe the sound:

"It has rained a little - a sprinkling... And now there is a sound out on the southern horizon. My mother and I can hear it but I am not sure that Dave can. It's a low roaring sound and we find it rather spooky. A neighbor suggested that maybe it's the sound of the Chevron refinery shutting down, but I'm not convinced. I can hear Chevron too - to the East. This is different and it's frankly making me a little more nervous than I had intended." )