Contributions of thermoelastic strain to apparent annual variations in four-component borehole strain: A case study from Gaotai station in the NE margin of the Tibetan Plateau

Abstract

Clarifying the physical mechanisms underlying near-surface annual deformation remains a major challenge in crustal dynamics research. For the four-component borehole strain observation networks in mainland China, a few stations are apparently dominated by annual fluctuations. However, only a limited number of specific studies have been carried out to dynamically assess the physical characteristics of these signals. Considering the fact that atmospheric temperature is a major factor inducing annual variations in crustal deformation, the Gaotai station was thus selected as a typical example diagnosis and a half-space model with a decoupling layer was used to quantitatively assess the thermo-effects of annual atmospheric temperature variation on the four-component borehole strain. The results show that an annual temperature variation with amplitude of 16.60 ℃ can induce a theoretical thermal strain of the 10^-6 magnitude at a borehole depth of 44.97 m; additionally, both amplitude and phase of the modeled values closely align with the measured strain time series, suggesting that the annual variation signal of the four-component borehole strain recorded at Gaotai station mainly originates from the annual atmospheric temperature changes. This geodynamical investigation can help to quantitatively elucidate the annual variation mechanism of the multi-component borehole strain and advance our understanding of thermo-deformation processes in shallow crust.