UTILIZATION OF HIGH-RESOLUTION AMBIENT NOISE TOMOGRAPHY TO DELINEATE BANYUMAS SEDIMENTARY BASIN, CENTRAL JAVA, INDONESIA

• Main Author: Setiawan, Ahmad
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/47932
• Institution: Institut Teknologi Bandung

Ambient Noise Tomography (ANT) studies in volcanic areas are relatively rare and conventional seismic exploration (seismic reflection) results were not good enough (poor) to image subsurface structures. The applications of crosscorrelation from ambient noise have been widely applied to understand subsurface structures. This application uses the principle of seismic interferometry to get a new signal from cross-correlation of ambient seismic noise. In this thesis, the method of cross-correlation of ambient seismic noise is used to describe the structure in the Banyumas Basin, Central Java, Indonesia. This location is believed to be related to relatively thick volcanic layers. The temporary seismic network used was 68 broadband seismometer stations for 60 days of observation. More than 1000 pairs of vertical component crosscorrelations can be used to estimate the Green’s Function of the Rayleigh wave. Multiple Filter Technique (MFT) was used as a Time-Frequency Analysis and 1,291 dispersion curves were obtained. Each dispersion curve is extracted to obtain travel time for different periods. Tomographic inversion of the group velocity models was performed to obtain a map of Rayleigh wave group velocity variation in the study area in the 1s-6s period. The low group velocity anomaly of Rayleigh waves tends to be northwest-southeast. Neighbourhood Algorithm (NA) is used to inverse dispersion curves at 121 grid points created to obtain a vertical profile of 1D Vs with respect to depth. All vertical profiles of 1D Vs are then interpolated to obtain maps of Vs variation in the study area. The variation map of Vs value shows that the low anomaly pattern of Vs tends to be trending in the northwest-southeast direction associated with two sediment sub-basins, the Majenang sub-basin, and Citandui sub-basin. The presence of low anomaly Vs value in response to Middle Miocene – Pliocene sedimentary rocks.While high anomaly Vs value in response to Oligocene – Early Miocene volcanic products and Eocene sediment. The high and low anomaly patterns Vs are relatively following the distribution of rock from surface geology studies and the high-low anomaly patterns of gravity method studies. The results of the vertical cross-section Vs show the unconformity boundary between volcanicrock and the sedimentary layer above it at ~6 km depth. This study is expected to be additional knowledge in responding to the challenges of exploration in volcanic cover areas associated with hydrocarbon potential.