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Russian Geology and Geophysics

2012 year, number 3


D.Yu. Demezhko, A.K. Yurkov, V.I. Utkin, and A.V. Klimshin
Institute of Geophysics, Ural Branch, Russian Academy of Sciences, 100 ul. Amundsena, Yekaterinburg, 620016, Russia
Keywords: Temperature monitoring, borehole, tide, thermal convection, tectonic regime, Kunashir Island
Pages: 313-319


The study presents the result of continuous temperature monitoring in a 300 m deep borehole located on the Pacific coast of Kunashir Island. Temperature variations at 20-240 m depths with periods from a few tens of minutes to a few tens of days and amplitudes of thousandths to tenths of degree are found to result from three main causes: tidal variations of groundwater level in the borehole, natural convection in the borehole, and nonperiodic and spatially heterogeneous changes of the pore pressure resulting in an anomalous subsurface fluid regime and generating crossflow between the different aquifers through the annular space. Joint analysis of temperature and seismic data revealed that shallow-focus (up to 30 km) earthquakes with M > 5 occurred southeast of the seismic station created more expressed temperature response at 240 m depth. This response has the form of a 0.05-0.3 K temperature drop, which precedes a seismic event within a period of a few hours to a few days. Tidal analysis of borehole temperature measurements can be used to calculate the strain sensitivity, and the method of borehole temperature monitoring can be used to investigate the tectonic regime of the Earth's crust.