Taking the stress out of earthquakes

The Swedish Defence Research Agency, FOI, has developed a method of stress analysis in earthquake research which could lead to earlier and more accurate earthquake predictions.

The analysis method makes it possible to estimate the complete stress tensor and monitor changes in the magnitude of stress and the instability of faults. This makes it more accurate, facilitating efforts to provide warnings.

The technique also uses micro-tremor data, for quakes with a magnitude of between -1 and 5, which offer the greatest possible amount of information for the analysis.

Tests with Icelandic micro-tremors from 1990 to 2005 yielded excellent results, with the major earthquakes occurring precisely when they were predicted by the stress analysis. This experiment indicated that the sites of coming earthquakes can be determined years before they occur.

‘What is crucial to whether the analysis is reliable is to what extent the small quakes are analysed,’ said the scientist behind the method, Ragnar Slunga.

‘It is necessary to analyse very minor micro-tremors as well, especially if the method is to be used to warn people immediately before a coming earthquake, a few days or a few hours before the quake.’

The Icelandic seismological network where the metering took place started as a Nordic collaborative project in 1988 and has continued as the largest EU project devoted to earthquake warnings. In 2006 the network comprised some 45 metering stations covering most of Iceland. Around 250,000 micro-tremors were analysed.