In the last four decades, water and soil radon measurements in earthquake prone areas gave an indication of potential precursor of an earthquake based on short period data. However, at many earthquake prone areas no anomalous radon concentrations were observed. Radon fluctuations prior to L’Aquila earthquake of April 6, 2009, in Italy created lots of controversies and scientists were dragged into the Italian court for not using radon anomaly to give an early warning of the earthquake. US Scientists were always skeptical to use radon emissions as a reliable precursor since no definite pattern in fluctuations were observed. Earth is complex and geological, hydrological, seismological and geophysical settings of earthquake prone areas vary from one earthquake to another. In China numerous land, ionosphere and borehole parameters are being monitored through a large network of stations distributed in China which are sponsored by China Earthquake Administration (CEA). All the data from this network is managed by China Earthquake Network Center (CENC).
Ramesh Singh, Ph.D., professor in the Schmid College of Science and Technology at Chapman University, in collaboration with Chinese visiting scholars (Qing Ye and Anhua He), used water and gas radon, water level and water temperature data measured at six stations during the period 2002-2014 along Longmenshan fault and studied the behavior and characteristics of water radon. The detailed analysis shows pronounced changes in the observed water and gas radon prior to the Wenchuan (Ms = 8.0) and Lushan (Ms = 7.0) earthquakes that occurred along Longmenshan fault. The results are recently published in the Radiation Measurements (http://www.sciencedirect.com/science/article/pii/S1350448715300020) published by Elsevier Pub.
The Wenchuan earthquake occurred at the steep eastern margin of the Tibetan plateau in the Sichuan province of China on May 12, 2008, which killed about 70,000 people, left 18,000 people missing, damaged millions of dollars’ worth of infrastructure, and caused widespread surface manifestations and landslides in epicentral and surrounding regions. The long-term data analysis of water radon and water level at various locations around epicenters of two major earthquakes along Longmenshan fault show a positive and negative relation of water radon and water level prior to these two earthquakes. It was difficult to find any trend of water radon and changes in water radon pattern with these two earthquakes that could prove as a reliable precursor of earthquakes. Changes in the water radon concentrations from one location to another may be associated with the numerous parameters, such as in-situ configurations, tectonic regime, hydrological regime, and land and ocean proximity, etc.
Water radon shows strong seasonal variability with higher radon concentrations from July to September and minimum variations during winter seasons. The rainfall and water radon concentrations show one-to-one correspondence. However, the rainfall reduces the gas emanation in the atmosphere which can influence the gas radon. The two major earthquakes occurred along Longmenshan fault in the increasing/decreasing trend of water radon concentrations. The magnitude of variations of water radon concentrations changes from one location to other locations which may be associated with the fluctuations in ground water levels due to change in stress regime in the epicentral area. The temporal and spatial variations in water radon concentration near the fault seems to be reasonable to believe that these anomalies are due to the readjustment during the pre-seismic and post-seismic phase having close relation with the ground water level. Long-term water radon concentrations change around the Longmenshan fault reflects changes in the in-situ stress regime which is related to the formation of micro-cracks in the epicentral areas with the fluctuations of the water table. The sharp water radon increase or decrease 1-7 days prior to the earthquake is likely due to formation of micro-cracks that enhances the permeability of the underground rock formation. On the other hand, the radon concentrations and groundwater level show a negative correlation prior to the Wenchuan earthquake.
The long-term 2002-2014 trend of water radon concentrations and water level associated with the deadly Wenchuan earthquake of 2008 and Lushan earthquake of 2013 do not show any definite changes prior to earthquakes that can be used as an indicator of an impending earthquake.