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Thursday, March 4, 2010

Tsunami Center in an Inundation Zone?

Eagle-eyed HONOLULU Magazine reader Ken Agena emailed me recently with a pertinent question and a couple links:

“Why is the Pacific Tsunami Warning Center located inside a tsunami inundation zone?

“Here’s a map of the Pacific Tsunami Warning Center's location.”

“Here’s the apppropriate evacuation zone map.”

The expression “close enough for government work” came to mind, but instead of assuming that was the explanation, I asked the PTWC about this. The reply from geophysicist Gerard Fryer included such an interesting history lesson, along with an explanation, I’ll post it here in full:

Your eagle-eyed reader is almost correct. The Pacific Tsunami Warning Center is actually just outside the evacuation zone (the zone stops at our flag pole out front). Nevertheless, tsunamis do cause us some concern: a tsunami could conceivably interfere with our access on Fort Weaver Road, and it could mess up both our water supply and our sewage (fortunately, power comes via an overland line farther inland).

Of greater concern is a hurricane. The land is very flat—PTWC is only five feet above sea level—so storm surge could inundate the property.

So why are we there? We are a bit embarrassed by our proximity to the ocean. That fact that we are 25 miles from town is also a bit of a nuisance for our visitors. The location is not optimal, so why Ewa Beach?

It all started about 1920 (I’m not sure of the exact year), when the US Coast and Geodetic Survey (USCGS) were looking to move their magnetometer away from the increasing cultural activity at Barbers Point. A magnetometer measures the Earth’s magnetic field, which was a big deal in the days when people navigated with the aid of a compass. It’s still a big deal: now we are worried about the effects of magnetic storms on communications equipment. In the old days, measuring the geomagnetic field demanded an instrument called an astatic magnetometer, which had to be located far from sources of magnetic interference. Even tiny quantities of iron could throw the thing off: ships, cars, rebar in buildings, even crystals of magnetite in lava. In Ewa Beach, USCGS found an unused chunk of land (too hard for sugar cane), that was far from civilization and at least a thousand feet above the nearest lava. It was the perfect place to put a maggie (“maggie” is the diminutive nickname for magnetometer—hey, scientists are human too). The place was called Honolulu Observatory.

Soon after the first maggie was installed at Ewa Beach, it was decided to set up a seismographic station. With the maggie already installed, it made sense to install the seismometer at Honolulu Observatory as well. Then, in 1946, the Islands were walloped by the Aleutian tsunami. 159 people died. By then the link between earthquakes and tsunamis had been well established, so the new Seismic Sea Wave Warning System was set up with headquarters at Honolulu Observatory where there was ready access to the locally recorded seismograms. What was to be renamed the Pacific Tsunami Warning Center started operations in 1948.

So we are near the coastline at Ewa Beach because of the needs of geomagnetic recording. There is still a maggie on our site, though it is a modern instrument which is far less affected by nearby traffic. We operate the maggie on behalf of the Geomagnetic Program of the U.S. Geological Survey.

Sometime in late 2013 we are expecting to move into a new facility on Ford Island in Pearl Harbor. For its new Pacific Regional Center, which will bring together disparate NOAA [National Oceanic and Atmospheric Administration] activities, including marine operations, NOAA is constructing a building among the WWII-vintage hangars on the north side of the Ford Island runway. The two largest hangars are to be incorporated into a generous three-story structure with PTWC getting one of the best spaces on the top floor. Our present facility is a collection of tiny ancient structures supplemented by temporary buildings; it will be a relief to move into permanent building with full hurricane protection, hardened power and all modern conveniences. Some have wondered about the tsunami hazard (Ford Island is only ten feet above sea level), but any tsunami scientist can tell you that, unlike Ewa Beach, the hazard at Ford Island is almost negligible. Pearl Harbor is like a saucer connected to the ocean by a straw; the time needed to get appreciable water through the straw is far longer than the time from one tsunami wave to the next, so tsunamis will not be a problem.


Thanks, Ken and Gerard!

  

Posted on Thursday, March 4, 2010 in Permalink

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