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March 2, 2010

Virginia well dropped 2 feet after Chile quake

Water in a hydrological monitoring well in Christiansburg, Va. briefly dropped almost 2 feet in response to the Mag. 8.8 earthquake in Chile on Feb. 27.

The Christiansburg site is well-known to hydrologists for its sensitivity to the seismic waves that travel around the globe after major quakes. It had a similar response to the earthquake in Haiti on Jan. 12 and to others as far away as the South Pacific and the Indian Ocean.

Here's the tracing from the Chilean quake. The regular sine-wave variations are due to the effect of lunar tides on the Earth's crust:

USGS

Posted by Frank Roylance at 2:28 PM | | Comments (1)
Categories: Cool pictures
        

Comments

Why?

FR: Think of it as a giant hand squeezing a sponge. Or maybe a breeze blowing across a grassy field. As seismic waves from the quakes pass through the Earth's crust, the rocks that contain the ground water are squeezed slightly and released. The water level in the well responds by rising and falling a few inches - or feet - as the waves pass through, then returning to their previous level. The same thing happens twice a day as the Earth turns, and the gravitational effects of the moon (and sun) create an "Earth tide" in the planet's crust. The slight crustal movement changes the water level in the well, which is quite visible in the regular, twice a day rise and fall of the water table, similar to ocean tides.

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About Frank Roylance
This site is the Maryland Weather archive. The current Maryland Weather blog can be found here.
Frank Roylance is a reporter for The Baltimore Sun. He came to Baltimore from New Bedford, Mass. in 1980 to join the old Evening Sun. He moved to the morning Sun when the papers merged in 1992, and has spent most of his time since covering science, including astronomy and the weather. One of The Baltimore Sun's first online Web logs, the Weather Blog debuted in October 2004. In June 2006 Frank also began writing comments on local weather and stargazing for The Baltimore Sun's print Weather Page. Frank also answers readers’ weather queries for the newspaper and the blog. Frank Roylance retired in October 2011. Maryland Weather is now being updated by members of The Baltimore Sun staff
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