Magazine article Science News

Demise of Ice Age Sparked Great Quakes

Magazine article Science News

Demise of Ice Age Sparked Great Quakes

Article excerpt

In geology, as in international relations, Scandinavia has a reputation for keeping a low profile. By the rules of plate tectonics, the extremely old crust in this region should not suffer the vicissitudes that rattle younger parts of the globe. New seismic studies, however, are threatening Scandinavia's image of stability.

Evidence from northern Sweden suggests that this area may have unleashed monster earthquakes when the ice age ended, only a short geologic span ago, says Ronald Arvidsson, a seismologist at Uppsala University in Sweden. The uncharacteristic quakes within a tectonic plate occurred because the land sprang up after the heavy European ice sheet melted away, he reports in the Nov. 1 Science.

Arvidsson studied a series of northern Scandinavian faults that formed 9,000 years ago, just after the disappearance of the ice sheet there. Geologists began discovering these postglacial faults 20 years ago, but the remoteness of the faults has hindered investigations.

When Arvidsson determined the locations of minor, unmapped earthquakes that occurred between 1963 and 1993, he found signs that the faults remain active. To determine the depth of the faults, he studied seismic data taken close to one of the smaller ones. Recordings of tiny shocks revealed that the fault extends unusually deep, all the way to the base of Earth's crust, some 40 kilometers down.

Knowing the scale of the faults, Arvidsson could calculate the size of the earthquakes that ripped the crust long ago. …

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