Abstract: Strain data in both the NS and the EW component obtained by vault-housed extensometers at the Geodynamic Observatory Qianling, are dominated by annual fluctuations since 1981, the casual mechanism is unclear till now. We show that a significant part of the annual data may result from thermoelastic strain induced by atmospheric temperature variations. We test this hypothesis by computing thermoelastic strain in an inclined homogeneous elastic half-space from atmospheric temperature and comparing the results to the extensometric strain records. The theoretical results suggest that fluctuations in temperature of 5.4 K approximately produce thermoelastic strain amplitudes of up to 2.2×10^-7. Furthermore, the model provides reasonable fits to the amplitudes and patterns of the annual signals recorded by extensometers. Thus, thermal effects on the extensometric strain are a very important factor to explain the annual fluctuations observed by extensometers. Our analysis could potentially contribute to improve the correction models of annual thermoelastic deformation, as well as refine the observation strategy aiming to reduce the signals of annual thermoelastic strain for the Qianling observatory. Especially, these methods will enhance the value of the data for geodynamic studies in the southwestern Ordos margin.

Key words: Qianling observatory, Extensometric strain, Thermoelastic strain, Annual variations, Dynamic diagnosis