Experimental and numerical investigation of the temperature response to stress changes of rocks

Abstract

The temperature response to stress changes of rocks is key to understanding temperature anomalies in geoscience phenomena such as earthquakes. We developed a new hydrostatic compression system in which the rock specimen center can achieve adiabatic conditions during the first ~10 s following rapid loading or unloading and systematically measured several representative sedimentary, igneous, and metamorphic rocks sampled from two seismogenic zones (the Longmenshan Fault Zone in Sichuan and the Chelungpu Fault Zone (TCDP Hole‐A) in Taiwan) and several quarries worldwide. We built a finite element model of heat conduction to confirm the measured results of temperature response to stress changes of rocks. The results show that (1) the adiabatic pressure derivative of the temperature (β) for most crustal rocks is ~1.5 mK/MPa to 6.2 mK/MPa, (2) the temperature response to stress of sedimentary rocks (~3.5–6.2 mK/MPa) is larger than that of igneous and metamorphic rocks (~2.5–3.2 mK/MPa), and (3) there is good linear correlation between β (in mK/MPa) and the bulk modulus K (in GPa): β = (−0.068K + 5.69) ± 0.4, R2 = 0.85. This empirical equation will be very useful for estimating the distribution of β in the crust, because K can be calculated when profiles of crustal density (ρ) and elastic wave velocities (Vp, Vs) are obtained from gravity surveys and seismic exploration.

Experimental Study of the Thermal Infrared Emissivity Variation of Loaded Rock and Its Significance

“…Based on previous studies, 6 factors can cause temperature changes during the rock loading process: the thermoelastic effect [25,45,47,61], f 1 (t); porous gas release and escape behavior, f 2 (t); fracturing behavior of the rock, f 3 (t); friction heating, f 4 (t); heat transfer, f 5 (t); and environmental radiation, f 6 (t), where t is time [20,21]. Therefore, the temperature change, ∆T s , can be expressed by the following:…”

“…To explore the internal mechanisms of the TIR anomalies caused by crustal stress changes before earthquakes, a series of experimental studies of TIR imaging observations of loaded rock were performed [16,[19][20][21][22][23][24][25][26]. The results showed that different TIR changes appeared at different loading stages.…”

“…According to Stefan-Boltzmann's law, the TIR information is determined by both the surface emissivity and physical temperature. In previous TIR studies of loaded rocks, the emissivity was regarded as constant in the loading process, and thus the TIR change was attributed only to the change in physical temperature [19][20][21]25]. However, research on the surface emissivity change for loaded rocks is lacking.…”

Experimental Study of Extracting Weak Infrared Signals of Rock Induced by Cyclic Loading under the Strong Interference Background

“…Wu et al [22][23][24] conducted wide research on the spatiotemporal evolution characteristics and anomalous precursors of TIR for loaded rocks under different stress conditions; two main thermal effects were proposed for explaining the experimental phenomenon. One is the thermoelastic effect, which is present throughout the entire loading process [20,25]; the other one is the frictional-thermal effect, which only occurs during microfracturing and fracturing stage [26][27][28][29]. Therefore, the stress condition and fracture process of loaded rock can be monitored in the experimental condition.…”

“…However, studies have shown that the TIR changes induced by the thermoelastic effect during loading are relatively small with the increasing temperature rate of approximately 3 mK/MPa under the normal temperature and pressure conditions [22][23][24][25]. Additionally, the wavelength features in the spectral radiance change for loaded rocks were observed and can be used for stress monitoring [33][34][35][36][37].…”