ANALYSIS THE EFFECT OF STRESS ON IGNEOUS ROCK SAMPLES IN FAULT AREAS USING ANISOTROPY MAGNETIC OF SUSCEPTIBILITY (AMS) DATA AND PETROGRAPHIC (CASE STUDY : CIMETA SEGMENT, LEMBANG FAULT)

• Main Author: Nur Sarianna, Faradilla
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/81026
• Institution: Institut Teknologi Bandung

Research on the analysis of magnetic susceptibility anisotropy (AMS) was carried out in the Cimeta Segment of the Lembang Fault. The principle of this method involves measurements using a reference direction, so that during the data collection process, magnetic susceptibility values are obtained in different directions. The main aim of this study is to assess the degree of anisotropy of igneous rocks related to the sample positions in the fault area, because anisotropy can be caused by the influence of stress occurring in faults. If there is an increase in stress effects on the rocks, the resulting degree of anisotropy will change significantly. Moreover, the samples also carried out petrographic analysis to determine if the samples belonged to the same rock type. The samples taken were core samples formed into several cylindrical specimens with a diameter of 2.5 cm and a height of 2.1 cm for magnetic susceptibility measurements. AMS measurements were carried out of nine directions to obtain anisotropy parameter. These core samples were then thin sheet for petrographic analysis to identify the rock type and mineral composition of the research samples. The study revealed that the rock samples were of the same rock type, namely pyroxene andesite, with ellipsoidal susceptibility shapes tending to be prolate or more elongated, with a degree of anisotropy that is considered high (>20%). The high degree of anisotropy near the fault had higher values compared to samples taken far from the fault, which could be related to stress effects caused by the fault structure. The stress orientation in this area tends to have a vertical trend, as indicated by the orientation of the maximum susceptibility, with the minimum susceptibility orientation tending to have a horizontal trend.