Experimental Study on the Thermal Infrared Spectral Variation of Fractured Rock

Jianwei Huang,Wenfang Liu,Shanjun Liu,Min Yu,Lixin Wu,Shuiping Li,Chunju Zhang

doi:10.3390/rs13061191

Abstract

Previous studies have shown that thermal infrared radiation (TIR) anomalies occur in the vicinity of fractures that form when a rock is loaded to failure. Different types of fracturing modes correspond to different TIR anomaly trends. However, the spectral features and the mechanisms responsible for the TIR changes in the fracturing stage remain poorly understood. In this paper, experiments involving observations of the thermal infrared spectrum (8.0–13.0 μm) of loaded sandstone during the fracturing stage were conducted under outdoor conditions. The experiment yielded the following results: (1) Different fracturing modes can lead to different trends in the spectral radiance variation; (2) when an extensional fissure appeared on the rock surface, the radiance increased with a local peak in the 8.0–9.7 μm range; (3) when local bulging formed at the surface, the radiance decreased, with a local valley in the 8.0–9.7 μm range. The radiance variation caused by morphologic changes is the combined result of changes in both the temperature and the emissivity. The characteristic waveband corresponding to the reststrahlen features (RF) of quartz was mainly related to the emissivity change. This study provides a preliminary experimental foundation for the detection of crustal surface fractures via satellite-based remote sensing technology.

Highlights

Rocks are the main constituent of the crust, and surface rocks experience dynamic crustal stress
The spectral radiance field reaching the sensor in the static condition, L0 (h,θ,λ), can be defined as follows [29,30]: L0 (h, θ, λ) = ε(θt, λ) Lbb ( Ts, λ) + [1 − ε(θt, λ)] Ldwr (λ) where Ts is the temperature of the sample surface (K), λ is the wavelength; h is the height of the instrument above the sample (m); θ is the zenith angle of the sensor with respect to the earth normal; θ t is the zenith angle of the sensor with respect to the target normal; ε(θ t,λ) is the static spectral emissivity at a zenith angle of θ t
Previous studies have shown that thermal infrared radiation (TIR) anomalies are mainly related to temperature changes caused by the frictional heating effect and stress relaxation in the fracturing stage

Summary

Introduction

Rocks are the main constituent of the crust, and surface rocks experience dynamic crustal stress. The increase and accumulation of crustal stress can lead to deformation and fracturing of rocks, resulting in rock failure and geological disasters, such as earthquakes, landslides, rock bursts, and crustal ruptures. Rock failure can result in different types of surface fracturing modes, including extensional fissures, local bulging, and subsidence, along active faults [1,2,3]. Basic information on crustal activity, including the deformation mode, motion state of a fault and the fracture process, can be reflected by the movement characteristics of surface rupture [4,5,6]. Studies on the correlation between crustal movement and fault activity have rapidly progressed with the development of satellite-based remote sensing technology, such as GPS [7], InSAR, and gravimetry systems [8,9]. Studies have shown that the analysis of the correlation between the TIR features and the seismic activity in an active fault area is helpful for improving the accuracy of seismic TIR recognition [13,14]

Methods

Results

Discussion

Conclusion