APPLICATION OF 4D DOUBLE-DIFFERENCE TOMOGRAPHY METHOD IN “CY” UNDERGROUND MINING AREA

• Main Author: Hermadianti, Dita
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/77953
• Institution: Institut Teknologi Bandung

Mining activities are activities that change the subsurface structure rapidly and continuously. Changes in the structure include changes in pressure distribution, subsidence, and fault shifts. Changes in the structure cause small to large magnitude earthquakes. Therefore, monitoring in mining areas is very important to prevent losses in the form of both lives and materials. One of the parameters that can be monitored is the change in the structure of P (Vp) wave and S wave (Vs) velocity below the surface due to these mining activities. The Double-Difference Tomography method is applied to obtain the 3D velocity structure of P wave and S wave. This method can simultaneously resolve hypocenter locations and 3D seismic wave velocities using catalog absolute data and differential data. Tomography inversion was carried out in 4D to obtain velocity structures in November – December 2022 with the aim of monitoring cave propagation and stress redistribution. The data used has a total of 38,366 events, 405,619 phases of P waves and 319,364 phases of S waves. To see the evolution of speed based on cave propagation, the data is divided into 4 (four) subsets of data. The results of tomography inversion consistently show anomalous patterns of low Vp and Vs in the area around the cave which is a result of empty volume, lose stress and indications of cave propagation. While there are high anomalies of Vp and Vs distributed, it is caused by stress redistribution and compensation from cave propagation in other areas.The cave propagation cycle was detected at an elevation of 2680 masl in the cave area and propagation occurred in subset 2 which was seen based on Time Domain Reflectometry (TDR) data. This is in accordance with the results of Vp and Vs tomograms that changes from high anomalies to low anomalies from subset 1 (one) to subset 2 (two). The Vp/Vs ratio also decreased in subset 2 (two) due to the fracturing process and along with cave propagation. To increase confidence in the results of this tomogram, a Checkerboard Resolution Test (CRT) resolution test was carried out.