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Determining thermal diffusivity using near‐surface periodic temperature variations and its implications for tracing groundwater movement at the eastern margin of the Tibetan Plateau
Author(s) -
Liu Qiongying,
Chen Shunyun,
Jiang Liangwen,
Wang Dong,
Yang Zhuzhuan,
Chen Lichun
Publication year - 2019
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.13399
Subject(s) - thermal diffusivity , amplitude , thermal conduction , heat transfer , convection , geology , thermal , plateau (mathematics) , tracer , convective heat transfer , thermal conductivity , phase (matter) , fault (geology) , thermodynamics , mechanics , chemistry , physics , optics , mathematical analysis , mathematics , organic chemistry , seismology , nuclear physics
The thermal diffusivity is the key parameter that controls near‐surface temperature where periodic temperature variation is progressively attenuated and delayed with depth. This article presents the results of apparent thermal diffusivity using temperatures recorded by a bedrock temperature measurement network in the fault zones of western Sichuan. High sensitivity temperature sensors (10 −4 K) were installed at a maximum depth reaching 30 m. The apparent thermal diffusivities were deduced from both amplitude damping and phase shifting of annual temperature variations between two different depths. Under pure conduction, the thermal diffusivity determined through the phase method ( α Φ ) should be equivalent to that determined through the amplitude method ( α A ), whereas effects of the upward (downward) water flow are evidently reflected in the amplitude decay to make α Φ larger (lesser) than α A . The discrepancy between α Φ and α A can thus be a tracer of water movement or convective heat transfer. The calculated α Φ of the measurement stations varies from 1.22 × 10 −6 to 3.00 × 10 −6 m 2 /s, and the estimated α A ranges from 0.93 × 10 −6 to 2.41 × 10 −6 m 2 /s. Two regimes of heat transfer underground were suggested from the results. Conductive heat transport prevails over the nonconductive processes at five stations, which is characterized by α Φ coincident with α A for the same depth pair. On the contrary, the values of α Φ differ from α A at six stations in the intersection area of the Y‐shaped fault system, implying that convective heat transfer also plays a comparably important role. This finding is consistent with the hot springs distribution of the area. The results also indicate that water moves upward with an average Darcy velocity of approximately −1 × 10 −7 m/s in this region. Our research provides new evidence for the hydrothermal activity in the fault zones at the eastern margin of the Tibetan Plateau.