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Radon earthquake precursor studies in Iceland

Hauksson, Egill and Goddard, John G. (1981) Radon earthquake precursor studies in Iceland. Journal of Geophysical Research B, 86 (B8). pp. 7037-7054. ISSN 0148-0227. doi:10.1029/JB086iB08p07037.

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Discrete samples of geothermal water have been collected from a network of nine stations for analysis of radon (^(222)Rn) content. The sampling network consisted of wells that range in wellhead temperature from 48°C to 100°C, and the depths range from 38 m to 1338 m. The sampling frequency at most stations was about once per week and twice per week at the station Fludir. The wells are either artesian or pumped more or less continuously. The network covered two regions of transform faulting in Iceland with seven stations in the Southern Iceland Seismic Zone (SISZ) and two stations in northern Iceland in the Tjornes Fracture Zone (TFZ). During 1978 and 1979 several anomalous changes in radon content were observed to precede some of the local earthquakes. Criteria based on tectonic regimes, a magnitude-distance relationship and time clustering were applied to select a set of 23 earthquakes that could be expected to be preceded by a radon anomaly. The magnitude of these earthquakes ranged between 1.0 and 4.3. Each of the 23 earthquakes was within the distance range of one or more stations such that altogether 57 potential observations of possible anomalies were available. The method of analysis applied to the radon and earthquake data consisted of identifying radon anomalies in retrospect, and resulted in nine precursory anomalies, 48 cases of failure to observe an anomaly, and seven false alarms. The probability of observing radon anomalies before earthquakes with magnitudes between 2.0 and 4.3 (the largest event observed) was found to be approximately 65% based on a weekly sampling rate. In the SISZ, five out of eight earthquakes (M > 2) were preceded by an anomaly. In two cases, anomalies were observed at two different stations prior to the same earthquake. The anomalies appeared to occur farther away for larger earthquake magnitude. An aquiclude that divides the SISZ did not seem to affect the occurrence of radon anomalies, but the amplitude of anomalies on the east side were larger than the ones on the west side. The duration times of the anomalies ranged from 17 to 37 days. The large number of failures to observe an anomaly indicated that the occurrence of an anomaly was more strongly dependent on local conditions and earthquake parameters than distance between epicenter and radon station. Some stations also appeared to be less sensitive than others and three stations never showed an anomaly. During periods of bursts in local seismicity, some stations reflected distinctively larger background fluctuations, which hampered the correlation of the seismicity with the radon data. Most of the false alarms were related to disturbances caused by changes in well operation. In the SISZ the high rate of failure to observe an anomaly and the occurrence of false alarms was partly compensated for by operating a dense network of sampling stations. Wells that are utilized at moderate flow rates are less likely to show false alarms than wells utilized at high flow rates. Wells situated close to rock formations rich in radioactive minerals may be more likely to show anomalies than others.

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Hauksson, Egill0000-0002-6834-5051
Additional Information:© 1981 by the American Geophysical Union. Received July 21, 1980; revised December 22, 1980; accepted February 10, 1981. This project is a cooperative effort between scientists at LDGO and the Science Institute, University of Iceland. The LDGO part of the effort was partly funded by the U.S. Geological Survey contract 14-08-001-17726. Financial support, which was provided by the Sergievsky Charitable Trust during the initial stages of this project, is sincerely acknowledged. The Science Institute made laboratory space available for the equipment that is used to analyze the samples. Gudbjorg Aradottir has analyzed nearly every sample and taken care of the daily routine running of the project in Iceland; without her efforts, the results of this project would have been much diminished. Sigurdur Emil Palsson participated in the summer field work and maintained the radon equipment in our absence. We owe special thanks to a group of nine volunteers who carried out the weekly sampling. Their contribution has made this logistically difficult project practically possible. Gillian Fougler and Bryndis Brandsdottir provided us with up to date accounts of the local seismicity. We thank John Lupton and Harmon Craig of the Scripps Institution of Oceanography for analysis of the He and gas data presented in Table 2. We are grateful to Wallace S. Broecker, Lynn R. Sykes, David Simpson, Sveinbjom Bjomsson, and Bragi Amason for their stimulating comments and suggestions. We thank Lynn R. Sykes, Wallace S. Broecker, Roger Bilham, and Pall Einarsson for their critical reviews of the manuscript. All the drawings were done by Patricia Catanzaro, and Mary Anne Avins skillfully typed the manuscript. Lamont-Doherty Geological Observatory contribution 3134.
Group:Seismological Laboratory, Division of Geological and Planetary Sciences
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Sergievsky Charitable TrustUNSPECIFIED
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Lamont-Doherty Geological Observatory3134
Issue or Number:B8
Record Number:CaltechAUTHORS:20130507-142954415
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Official Citation:Hauksson, E., and J. G. Goddard (1981), Radon earthquake precursor studies in Iceland, J. Geophys. Res., 86(B8), 7037–7054, doi:10.1029/JB086iB08p07037.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38332
Deposited By: Ruth Sustaita
Deposited On:07 May 2013 21:48
Last Modified:09 Nov 2021 23:36

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