Using Digital Photogrammetry Method to Monitor Surface Deformation of Active Creep Fault: A Case Study of the Chihshang Fault in Eastern Taiwan

One of the most active faults in eastern Taiwan, the Chihshang fault, has been identified and studied for decades. Many surface ruptures of the Chihshang fault were found in the southern part of the fault. In Tapo and Jinyuan, five creep meters have been set up since 1990s to monitor the surface deformation of the fault and found the shortening rate to be 20 to 30 millimeter per year. The creep rate varies during dry and rainy seasons with faster rate in rainy season. We propose a new economic and precise approach to monitor the surface deformation of the fault by using the digital photogrammetry technique with a commodity-grade digital single-lens reflex camera (DSLR). Five concrete structures, all of which broken by the activities of the Chihshang Fault, in Jinyuan are chosen as the study targets. We measured the sites every month from April 2016 to January 2017 and one indoor calibration. After each measurement, the photos was first transform into monochrome images. We found that the autofocus function of camera does produce some noise signal in a single measurement. We tried to eliminate the noise signal by image averaging tool, which makes the measurement more stable and representative. Afterward, two period images are used to calculate the velocity by the image cross-correlation technique. We are able to observe the two dimensional surface deformation at the millimeter scale. The proposed method may be ecomonically used to complement existing measurement techniques providing suitable calibrations are carried out using a regular single-lens digital camera.