ScienceIQ.com

Is The Sea Really On The Level?

When we measure the height of mountains, we measure from a constant number called sea level. For instance Mount Whitney in California is 14,494 feet (4,418 m) above sea level. We start at 0 feet and end up precisely, by careful measurement, at 14,494 feet (4,418 m) . That sounds well and good until you consider that sea level IS NOT a constant. It ...

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SeaLevel
Biology

The Art of Hunting

Most of us have seen a praying mantis. Two thousand species of praying mantis are scattered throughout the world, ranging in size from less than half an inch (1.27 cm) to more than five inches (12.7 ... Continue reading

PrayingMantis
Engineering

Solid Smoke

Ever wondered what is the least dense solid in the world? Well, it is the so called Solid Smoke aerogel developed decades ago by aerospace engineers and recently perfected to its newest, lightest ... Continue reading

SolidSmoke
Biology

Water, Water Everywhere, But Not A Drop To Drink

That line, from The Rime of the Ancient Mariner, by Samuel Taylor Coleridge, captures a truism -- we cannot drink salt water to quench our thirst. But why not? The answer lies in understanding the ... Continue reading

WaterWater
Engineering

Barn Yard Aeronauts

The word aeronaut is derived from the Greek terms 'aero' meaning air or atmosphere and 'nautes' meaning sailor. Originally, individuals who piloted balloons or airships (blimps or dirigibles) were ... Continue reading

BarnYardAeronauts

Silent Earthquakes

SilentEarthquakesTry this demonstration of earthquake movement. Shape modeling clay into two blocks or get two firm sponge blocks. Press the sides of the blocks together while trying to slide them slowly past each other. You may notice that they stick at first, then suddenly slide. This is much like what happens when earth's plates (large sections of earth's solid upper layers) are forced past each other causing earthquakes, whether one plate slides and bumps past another or one moves over the other. However, slow moving 'silent' quakes have been discovered occurring deep beneath Washington state and British Columbia, Canada. Here the Juan de Fuca Plate is being forced below the North American plate, but the movement has been so slow, it was not originally detected by seismograph analysis. It was data from the satellites in the GPS (Global Positioning System) that detected the very slight movements of stations on the ground.

Far offshore from Oregon, Washington, and British Columbia, the Pacific Plate and the Juan de Fuca Plate are being forced apart by convection currents in earth's mantle. (See the ScienceIQ Geology fact on Plate Tectonics from 11/02.) This moves the Juan de Fuca plate eastward where it collides with and is subducted under the North American plate. But not all parts of the massive plates move equally. Deeper in the earth, the subducted portion of the plate becomes pliable as it is heated, and it moves more easily, while colder, shallower sections of the plate get stuck, and pressure continually builds. This would be like forcing your fingers into a narrow opening. Some fingers might slide in easily, but you would feel pressure build up on the stuck fingers. The continued sliding of the moving fingers - or plate sections - does not reduce total stress because it causes stress to increase in the locked zones.

Since plate movement in the pliable regions is so slow, the massive earthquake energy is also being released very slowly, and no quaking is noticed. Scientists think the energy being released is equivalent to what would normally occur during a 6 to 7 magnitude quake, but is being released over weeks, not seconds, so the smaller quakes are much less powerful. The end result, however, may not be less destructive earthquakes. Since pressure builds up in the locked zones of plate boundaries, the energy may later be released in a quake of much greater magnitude. If the movement occurred at the western edge of the Juan de Fuca plate, devastating tsunamis could be generated and the entire region would be shaken. Such a release is believed to occur somewhere along the Juan de Fuca's boundaries about every 500 years in massive 8 or 9 magnitude earthquakes. The sensitive GPS detection of even very slight surface movements may provide a means of predicting such quakes, allowing advance warning.