Identifikasi Jalur Sesar Opak Berdasarkan Analisis Data Anomali Medan Magnet dan Geologi Regional Yogyakarta

Abstract

This research was aimed to know the magnetic field anomaly pattern upon Opak's fault, to identify the direction of Opak's fault and the structure of Opak's fault based on Geomagnetic data. It was conducted in the vicinity of Opak's fault in Pundong sub-district, Yogyakarta. It used magnetic method which is based on rocks magnetic susceptibility. The data were taken by G-856AX Proton Precision Magnetometer (PPM) using looping method. Data analysis was done using diurnal variation and IGRF correction, reduction to pole, upward continuation and under surface structure modelling. From magnetic field anomaly analysis, it was discovered that magnetic field anomaly on Opak's fault has -50 nT negative closure in the East, and 100 nT positive closure in the West. According to the result interpretation of 2.5D model on two slices using Mag2DC software, it can be obtained that the under surface structure of Opak's fault consist of Young Alluvial formation, Nglanggran formation, Semilir formation, Kebo Butak formation, and Wungkal Gamping with various thickness. The location of this Opak's fault is almost the same with the location of Opak's fault in Yogyakarta geology map. Opak's fault around Pundong sub-district is a normal fault directed to N 35º E. The eastern part of the fault has a relatively constant movement, while the western part is relatively moving down.

Geopedology in complex landform setting: A case study in eastern Parangtritis Village, Indonesia

“…These geological activities lead to elevation changes, forming the Baturagung Hills. The Opak Fault is categorized as a normal fault [11]. According to Rahardjo et al, this fault zone is directly beneath the course of the Opak River [12].…”

Was the Pesawaran Swarm Induced by Magmatic Fluids? Insight from Magnetic Method Analysis

“…Transforming TMI to RTP anomalies has an objective to facilitate magnetic interpretations where the magnetic field direction has transformed from dipole to monopole, especially in areas with lower latitude [3], [5]. In order to change the direction, the inclination and declination have to be 90 and 0 degrees, respectively, so that the resulting anomalies represent the actual position of concerned mediums.…”

“…Extracting regional information in magnetic fields is an advantage of implementing upward continuation because this method eliminates local influences near the surface so that the effect of background magnetic fields is more visible [3]. More visible background magnetic fields can be obtained by inserting higher distance values as the parameter.…”

“…Even though the existence of inferred Menanga fault is still debated, an earthquake swarm collocated with the indicated area of this fault should be the initial step to investigate its presence by other approaches. Actually, magnetic anomalies have been successfully studied to identify the possible existence of faults due to their susceptibility [2], [3]. Therefore, this research will perform anomalies by magnetic measurements, which may represent inferred Menanga fault and activities around the fault.…”

Acceleration Response Spectrum and Effective Duration of Lebak Earthquake January 23, 2018 in Jakarta Region

“…It caused Jakarta to be vulnerable to natural disasters, one of which was an earthquake. Jakarta is in the area affected by seismic sources, there is the subduction zone resulting from the subduction of the Indo-Australian and Eurasian plate collisions, on the east side there are local faults such as Cimandiri and Lembang in West Java that have a sinistral mechanism [2] [3] also the Baribis fault [4]. On the other side, based on geological conditions, Jakarta is located on a basin of groundwater, known as the Jakarta Groundwater Basin where the entire land of the DKI Jakarta area consists of alluvial deposits in the Pleistocene era ± 50 m thick [5].…”