Co-seismic multilayer water temperature and water level changes associated with Wenchuan and Tohoku-Oki earthquakes in the Chuan no. 03 well, China

The present paper shows analysis of water level (the distance from the land surface to the water in the well under static condition) and water temperature observed at three different levels of Chuan no. 03 well to study the changes associated with the Wenchuan earthquake of 2008 and the 2011 Tohoku-Oki earthquake. Our analysis shows co-seismic changes in water level and water temperature associated with the increase in compressive stress associated with the Wenchuan earthquake. The water level shows an increase, whereas there was drop in water temperature at the shallow depth (395 m) and enhancement of water temperature at the middle (595 m) and the bottom (765 m) layers. However, no step change in water level or temperature of Chuan no. 03 well is observed associated with the Tohoku-Oki earthquake, only seismic wave propagation-induced water level oscillation and led to co-seismic response of water temperature. The analysis of the co-seismic responses and post-earthquake adjustment processes combined with the borehole histogram and the borehole temperature gradient data clearly show co-seismic changes in water temperature that could be closely associated with the changes in the regional stress and strain state and the distribution of the aquifer and the characteristics of the aquifer. The observed temperature variation of different layers in the borehole is likely to be controlled by the flow of water in the horizontal direction.