ANALYSIS OF VP, VS, AND VP/VS STRUCTURES EVOLUTION THROUGH 4D TOMOGRAPHY IN THE “UC” UNDERGROUND MINING FIELD

• Main Author: Putu Raditya Ambara P, I
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/51612
• Institution: Institut Teknologi Bandung

Mining activities are activities that change subsurface structures quickly and continuously. The structure changes include changes in pressure distribution, subsidence, and fault slips. These structural changes cause earthquakes of small to large magnitudes. Therefore monitoring in underground mining fields is very important in order to prevent losses in the form of lives and material. Monitoring the parameters of the wave velocity P (Vp), wave S (Vs), and Vp / Vs is expected to know the development of the condition of the subsurface structure. To get the evolution of the subsurface velocity structure, time-lapse Double-Difference Tomography method is used by utilizing micro earthquake data that occurred in the underground mining area. In carrying out time-lapse tomography methods there is a bias caused by the amount and distribution of data that is very diverse in each time interval. In this research time-lapse tomographic inversion has been done using several configurations of the distribution of earthquake events. From the synthetic test it can be seen that the distribution of data is more influential than the amount of data in determining the quality of the tomogram results. A large amount of data does not always produce a better tomogram if the data distribution is not good. The pattern of velocity structures every two weeks obtained from this study is always changing. This shows how underground mining activities are very dynamic and can change the velocity structure in a short time. The mainshock incident that occurred on October 30, 2019 caused a decrease in the value of Vp towards aftershock and a decrease in the value of Vp and Vs in the area of rockburst. The reduced velocity value is related to the stress release due to the mainshock and rockburst. Changes in the value of Vp and Vs after and before the occurrence of the mainshock 30 October 2019 can reach 15%.