Tuesday, September 13, 2005

Eternal Vigilance

At the Bottom of The Sea

by Gene Barth

Scattered over an area of the Pacific Ocean floor greater than North America are six exotic pieces of quartz. Under several miles of water, each tiny piece of quartz-a small fraction of an inch in extent- is the sensor element of a remarkable pressure gauge. Mechanically pulled taught ("loaded") by the pressure of the ocean itself, each piece of quartz oscillates at an ultrasonic
frequency that responds to sea floor pressure with enormous precision. This device can register a change in pressure of less than one millionth of its full scale reading. Since the pressure at the bottom of the ocean is simply the weight of the column of water overhead, ocean floor pressure is a direct measure of ocean depth. See reference.

Maintained by NOAA as part of the Deep Ocean Assessment and Reporting of Tsunamis (DART) program, these ocean floor sentinels ("bottom pressure recorders", or BPRs) can reliably detect a one inch tsunami wave at the top of a column of water several miles high - against the background of much larger wind generated waves and the tides. See reference.

Incorporating an acoustic modem, each BPR can immediately transmit an announcement of "event detection", along with the actual data, to a tethered ocean buoy miles over head. In turn, the buoy transmits the BPR data by GOES satellite to the West Coast/Alaska Tsunami Warning Center, the Pacific Tsunami Warning Center, and NOAA's Pacific Marine Environmental Laboratory. Within minutes of mid-ocean detection of a one inch wave, a rock solid warning goes out to shore land communities in the Pacific basin likely to be hit by the tsunami. See reference. Be sure to click on the animation!

This feat of detection is a remarkable demonstration of Industrial Civilization's full devotion to Man's Life on Earth. It is not enough to pinpoint a large, shallow earthquake in the ocean minutes after it has occurred and then issue a warning for a possible tsunami. Most seaquakes do not cause tsunamis. Evacuations are an enormous disruption to productive, everyday life. In the United States, the prospect of detecting every tsunami that occurs, while avoiding a single "false positive", has sustained a decades long effort culminating in the ability to observe in mid-ocean a one inch tsunami wave atop several miles of water.

Enter this URL to observe BPR detection of the magnitude 9 Christmas 2004 earthquake off the coast of Sumatra.

Gene Barth (ebarth@rover.bsd.uchicago.edu) works in a research lab at the University of Chicago Medical Center and is a regular contributor to TIA Daily.

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