HR: 0800h
AN: S21B-0563    [Abstracts]
TI: Experimental study on deformation field evolution in rock sample with en echelon faults using digital speckle correlation method
AU: * Ma, S
EM: masp@bit.edu.cn
AF: Beijing Institute of Techhnology, 5#, Zhongguancun south street, Beijing, 10081, China
AU: Ma, J
EM: majin@ies.ac.cn
AF: State Key Laboratory Dynamics, Institute of Geology, China Earthquake Administration, Postal box 9803, Beijing, 100029, China
AU: Liu, L
EM: liuliqiang48@hotmail.com
AF: State Key Laboratory Dynamics, Institute of Geology, China Earthquake Administration, Postal box 9803, Beijing, 100029, China
AU: Liu, P
EM: liupeixun@sina.com
AF: State Key Laboratory Dynamics, Institute of Geology, China Earthquake Administration, Postal box 9803, Beijing, 100029, China
AB: Digital speckle correlation method (DSCM) is one kind of photomechanical deformation measurement method. DSCM could obtain continuous deformation field contactlessly by just capturing speckle images from specimen surface. Therefore, it is suitable to observe high spatial resolution deformation field in tectonophysical experiment. However, in the general DSCM experiment, the inspected surface of specimen needs to be painted to bear speckle grains in order to obtain the high quality speckle image. This also affects the realization of other measurement techniques. In this study, an improved DSCM system is developed and utilized to measure deformation field of rock specimen without surface painting. The granodiorite with high contrast nature grains is chosen to manufacture the specimen, and a specially designed DSCM algorithm is developed to analyze this kind of nature speckle images. Verification and calibration experiments show that the system could inspect a continuous (about 15Hz) high resolution displacement field (with resolution of 5μm) and strain field (with resolution of 50με), dispensing with any preparation on rock specimen. Therefore, it could be conveniently utilized to study the failure of rock structure. Samples with compressive en echelon faults and extensional en echelon faults are studied on a two-direction servo-control test machine. The failure process of the samples is discussed based on the DSCM results. Experiment results show that: 1) The contours of displacement field could clearly indicate the activities of faults and new cracks. The displacement gradient adjacent to active faults and cracks is much greater than other areas. 2) Before failure of the samples, the mean strain of the jog area is largest for the compressive en echelon fault, while that is smallest for the extensional en echelon fault. This consists with the understanding that the jog area of compressive fault subjects to compression and that of extensional fault subjects to tension. 3) For the extensional en echelon sample, the dislocation across fault on load-driving end is greater than that cross fault on fixed end. Within the same fault, the dislocation across branch far from the jog area is greater than that across branch near the jog area. This indicates the restriction effect of jog area on the activity of fault. Moreover, the average dislocation across faults is much greater than that across the cracks. 4) For the compressive en echelon fault, the wing cracks initialized firstly and propagate outwards the jog area. Subsequently, a wedge strain concentration area is initialized and developed in the jog area because of the interaction of the two faults. Finally, the jog area failed when one crack propagates rapidly and connects the two ends of faults. The DSCM system used in this study could clearly show the deformation and failure process of the en echelon fault sample. The experiment using DSCM could be performed dispensing with any preparation on specimen and not affecting other inspection. Therefore, DSCM is expected to be a suitable tool for experimental study of fault samples in laboratory.
DE: 5194 Instruments and techniques
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8010 Fractures and faults
DE: 8030 Microstructures
SC: Seismology [S]
MN: 2007 Fall Meeting