3D Modeling of Subsurface Lawanopo Fault In Southeast Sulawesi, Indonesia Using Grablox and its Consequence to Geohazard

Lawanopo Fault is a horizontal shear fault (sinistral strike-slip) found in Southeast Sulawesi province and is thought to be active during Plio-Pleistocene or mid-late Miocene to the present. This study has been carried out which aims to find out the geometric shapes below the surface of the Lawanopo fault using complete Bouguer anomaly (ABL) data. The ABL data is projected onto a flat plane using the Dampney method at an altitude of 8 km, and the separation of local and regional anomalies is carried out using the upward continuation method at an altitude of 60 km. Three-dimensional (3D) modeling under the surface of the Lawanopo fault is done using the computer program Grablox. Data processing techniques using Singular Value Decomposition (SVD) and Occam inversion. The results showed that a high gravity anomaly of 190-225 mGal was caused by an igneous rock below the surface with a density of 2.7-3.33 gr/cm3 and a thickness of about 13 km, a moderate anomaly of 175-187 mGal caused by Paleozoic igneous rocks aged Carbon with a density of 2.6-2.9 gr/cm3 and a thickness of about 25 km. Low anomaly 115-160 mGal is caused by rocks with a density of 2.0-2.5 gr/cm3 and a thickness of about 22-23 km. The Lawanopo fault constituent rocks consist of alkaline rocks in the basement covered by sediment and metamorphic with a depth of Lawanopo fault more than 15 km and begin to be seen at a depth of 4.3 km of the surface. it is known that the area around the Lawanopo fault is an area prone to earthquakes. But, based on the soil and rock structure around the Lawanopo fault, the compactness and attenuation levels in reducing earthquake waves are quite good, so that land use around the Lawanopo fault tends to be safe.

Investigation of Groundwater In-rush Zone using Petrophysical Logs and Short-offset Transient Electromagnetic (SOTEM) Data

The water burst from the Ordovician limestone underlain by the Permo-Carboniferous coal seams have potential to trigger coalmine hazards in Northern China. Therefore, it is crucial to identify and accurately map the water enrichment zones and delineate coal seams using an integrated approach based on surface TEM and subsurface wireline log information to avoid water-inrush hazard and ensure safe production of coal. We inverted surface based TEM data using 1-D Occam inversion to identify the conductive anomaly and then further quantified the zone of interest by gamma and resistivity logs. 1-D Occam inversion results show conductive zone around 370 m while higher resistivity and lower gamma ray log signatures were observed against coal seams. Groundwater inrush zone falls within the mid-range gamma ray and resistivity interval as shown on the petrophysical logs. The distinct log signatures (low gamma-ray and high resistivity values) clearly indicated coal seams at depth of 410 and 470 m and subsequently the log trends were used to distinguish between coal units and more permeable sands. The magnitude and the variability of these parameters in the borehole are attributed to the subsurface stratigraphic heterogeneity. They can be key clues for interpretation of depositional facies of coal-bearing sequence and may also be used as a constraint in characterization of groundwater enrichment zone.

Optimation of Least Squares Methods Smooth Constrain Using Occam’s Inversion Geoelectric Resistivity Dipole-Dipole Consfiguration for Estimation Slip Surface

The volumes of the landslide depend on the depth of the slide surface. The depth of the slide surface can be predicted by using the least squares inversion methods of data geoelectrical. Method of Least Squares Inversion of the data Geoelectrical cannot get smooth results. Based on the above, the aims was optimalitation leastsquares smooth constrain inversion methods with Occam’s inversion for geoelectrical data and to determine the depth and tilt angle of the slide surface in in Bukit Lantiak Padang . This exploratory study was use the method Geoelectrical resistivity Dipole-Dipole configuration. The depth and tilt angle of the slide surface in Bukit Lantiak Padang was interpretated by combined Occam’s inversion with least-squares smooth constrain inversion methods. The type of slip surface is translation slip with 33.45 degrees in tilt angle and 19.3 meters in depth. Research show that the result interpretation by used combined Occam inversion with least-squares smooth constrain inversion methods more sharpness than least-squares smooth constrain inversion.

OPTIMITION OF LEAST SQUARES METHODS SMOOTH CONSTRAIN USING OCCAM’S INVERSION GEOELECTRIC RESISTIVITY DIPOLE-DIPOLE CONFIGURATION FOR ESTIMATION SLIP SURFACE

The volumes of the landslide depend on the depth of the slide surface. The depth of the slide surface can bepredicted by using the least squares inversion methods of data geoelectrical. Method of Least Squares Inversionof the data Geoelectrical cannot get smooth results. Based on the above, the aims was optimalitation leastsquaressmooth constrain inversion methods with Occam’s inversion for geoelectrical data and to determine thedepth and tilt angle of the slide surface in in Bukit Lantiak Padang . This exploratory study was use the methodGeoelectrical resistivity Dipole-Dipole configuration. The depth and tilt angle of the slide surface in BukitLantiak Padang was interpretated by combined Occam’s inversion with least-squares smooth constraininversion methods. The type of slip surface is translation slip with 33.450 tilt angle and 19.3 meters in depth.Research show that the result interpretation by used combined Occam inversion with least-squares smoothconstrain inversion methods more sharpness than least-squares smooth constrain inversion.

Analysis of Long-offset Transient Electromagnetic (LOTEM) Data in Time, Frequency, and Pseudo-seismic Domain

Long-offset transient electromagnetic (LOTEM) has received great attention in mineral, hydrocarbon and hydrogeological investigations for the last several years. Conventionally, TEM soundings have been presented as apparent resistivity curves as function of time. With development of sophisticated computational algorithms, it became possible to extract more realistic geoelectric information by applying inversion programs to 1-D and 3-D problems. Here, we analyze LOTEM data by carrying out analysis in time, frequency and pseudo-seismic domain supported by borehole information. At first, H, K, A & Q type geoelectric models are processed using a proven inversion program (1-D Occam inversion). Second, time-to-frequency transformation is conducted from TEM ρ a ( f) curves for the same models based on all-time apparent resistivity curves. Third, 1-D Bostick's algorithm was applied to the transformed resistivity. Finally, EM diffusion field is transformed into propagating wave field and constructed pseudo-seismic section. The transformed seismic-like wave indicates that some reflection and refraction phenomena appear when the EM wave field interacts with a geoelectric interface at different depth intervals due to contrast in resistivity. In all three cases, synthetic tests showed that conductive anomaly in resistive host environment can be retrieved more clearly than resistive target. A case study illustrates the successful application of proposed approach in recovering a water-filled mined-out area in a coal field located in Ye county, Henan province, China. The results support the introduction of pseudo-seismic imaging technology in long-offset version of TEM which can also be an useful aid if integrated with seismic reflection technique to explore possibilities for high resolution EM imaging in future. [Figure: see text]