On the Hot Seat

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Science  03 Sep 2004:
Vol. 305, Issue 5689, pp. 1371
DOI: 10.1126/science.305.5689.1371b

Iceland straddles a plate boundary, the mid-oceanic ridge that separates the North American and Eurasian plates, and a hotspot plume. This placement results in the many volcanoes, geothermal systems, and earthquakes that are all carefully monitored in an attempt to understand subsurface complexity.

Claesson et al. have been sampling fluid from a 1.5-km-deep borehole that taps into four aquifers at one end of the Húsavík-Flatey fault. They measured sharp increases in Cu, Zn, Mn, and Cr at 1, 2, 5, and about 10 weeks, respectively, prior to a moment magnitude 5.8 earthquake (16 September 2002) whose epicenter was 90 km north of the borehole. They theorize that the elemental transients were caused by the accumulation of stress that then squeezed the hydrothermal system and allowed fluids that had recently been in contact with hotter basaltic rock to enter the borehole; therefore, these chemical signals may be useful for earthquake prediction. About 2 to 9 days after the earthquake, the chemistry shifted again, even more rapidly, with increases in B, Ca, Na, and S, and with changes in oxygen and hydrogen isotopes. These postseismic shifts imply that the borehole is now tapping a 10,000-year-old aquifer from the last ice age. — LR

Geology 32, 641 (2004).

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