Radon in soil gas: How to identify anomalies caused by earthquakes |
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| Institution: | 1. Departamento de Geología, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Ensenada, Baja California, Mexico;2. Centro de Geociencias, Universidad Nacional Autónoma de México, Campus UNAM Juriquilla, Querétaro, Mexico;3. Department of Volcanology, GNS Science, Taupo, New Zealand;4. Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México, Mexico;5. Instituto Nacional de Electricidad y Energías Limpias, Cuernavaca, Morelos, Mexico |
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| Abstract: | Anomalies have been observed in Rn content in soil gas from 3 boreholes at the Orlica fault in the Kr?ko basin, Slovenia. To distinguish the anomalies caused by environmental parameters (air and soil temperature, barometric pressure, rainfall) from those resulting solely from seismic activity, the following approaches have been used: (i) deviation of Rn concentration from the seasonal average, (ii) correlation between time gradients of Rn concentration and barometric pressure, and (iii) regression trees within a machine learning program. Approach (i) is much less successful in predicting anomalies caused by seismic events than approaches (ii) and (iii) if ±2σ criterion is used and is equally successful if ±1σ is used. Approaches (ii) and (iii) did not fail to observe an anomaly preceding an earthquake, but show false seismic anomalies, the number of which is much lower with (iii) than with (ii). Model trees are shown to outperform other approaches. A model has been built which, in the seismically non-active periods when Rn is presumably influenced only by environmental parameters, predicts the concentration with a correlation of 0.8. This correlation is reduced significantly in the seismically active periods. |
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