Could crustal strain form 'Texachusetts'?

Could crustal strain form "Texachusetts'?

The theory of plate tectonics holds that the earth's outer shell is composed of a dozen or so floating pieces that spread away from and grind into one another as new plate material is created and destroyed. In the last few years, geodesists, using a technique called Very Long Baseline Interferometry (VLBI), have been able to detect these motions directly by comparing the arrival times of quasar radio signals on opposite sides of plate boundaries (SN: 12/21 & 29/85, p. 388).

Now two scientists argue that measurements indicate that VLBI stations at Westford, Mass., and Fort Davis, Texas--two points on the same plate--are converging at about 1.2 centimeters per year. Steven A. Musman of the National Geodetic Survey in Rockville, Md., and Tom Schmitt of the Georgia Geological Survey in Atlanta propose that this compression is responsible for earthquakes in the eastern United States.

While some scientists suggest the apparent convergence of two regions within one plate is due is due to systematic errors, Schmitt thinks the movement is real. "If so,' he says, "it makes a lot of sense from a geophysics point of view.' Musman and Schmitt have shown that the measured strain rate is consistent with values, obtained by other methods, for the viscosity of the crust and for the depth at which rocks deform rather than break from tectonic stresses. They also found that the amount of energy being stored by the compression is more than adequate to produce eastern U.S. quakes. The VLBI measurements, says Schmitt, do not indicate where or how often quakes will occur, but they do help seismicity modelers make more intelligent guesses.