Chlorine cues to quakes?

Scientists hoping to predict earthquakes have for many years been on the lookout for changes in radon levels in the soils and groundwater near faults. Indeed, high concentrations of the inert radioactive gas have often preceded seismic activity (SN: 5/5/79, p. 297). But according to Naoji Koizumi and colleagues at the Disaster Prevention Research Institute of Japan's Kyoto University, it may be easier, in practice, to monitor concentrations of other elements, especially the major chemical ions -- some of which have also been loosely tagged in past studies as seismic precursors.

These ion studies, however, have been limited, so Koizumi's group set out to do a more thorough job. The researchers measured chlorine ion concentrations in a mineral spring near the Yamasaki fault in southwest Japan almost every day for seven years. During that period, eight earthquakes with magnitudes greater than 3.5 shook the region.

The scientists report in the August GEOPHYSICAL RESEARCH LETTERS that chlorine ion levels radically changed in association with these quakes, but that the character of these changes was not the same for every event. In some cases, for example, earthquakes occurred several days after chlorine levels had gradually increased and then rapidly dropped; in other cases the drop in chlorine concentrations happened during or just after quakes. Nonetheless, the researchers conclude in their paper that chlorine ion "concentration measurement at carefully chosen mineral springs along an active fault may be useful for earthquake prediction even if some problems remain to be solved in the future."