Full Tensor Gradient of Simulated Gravity Data for Prospect Scale Delineation

Gravity gradiometry measurement allows imaging of anomalous sources in more detail than conventional gravity data. The availability of this new technique is limited to airborne gravity surveys using very specific instrumentation. In principle, the gravity gradients can be calculated from the vertical component of the gravity commonly measured in a ground-based gravity survey. We present a calculation of the full tensor gradient (FTG) of the gravity employing the Fourier transformation. The calculation was applied to synthetic data associated with a simple block model and also with a more realistic model. The latter corresponds to a 3D model in which a thin coal layer is embedded in a sedimentary environment. Our results show the utility of the FTG of the gravity for prospect scale delineation

Constrained Two-Dimensional Inversion of Gravity Data

The non-uniqueness in the solution of gravity inversion poses a major problem in the interpretation of gravity data. To overcome this ambiguity, "a priori" information is introduced by minimizing a functional that describes the geometrical or physical properties of the solution. This paper presents a 2D gravity inversion technique incorporating axes of anomalous mass concentration as constraints. The inverse problem is formulated as a minimization of the moment of inertia of the causative body with respect to the axes of the mass concentration. The proposed method is particularly applicable to homogeneous, linear mass distributions, such as mineralization along faults and intruded sills or dikes. Inversions of synthetic and field data illustrate the versatility of the implemented algorithm

Identification Of Liquefaction-Potential Zones Using The Gravity Method In Lolu Village, Central Sulawesi

A seismic event of magnitude 7.5 struck the Palu region in Central Sulawesi on September 28, 2018, precipitating a subsequent calamity in the form of a tsunami measuring 4-7 meters in height. This catastrophe was further compounded by the occurrence of liquefaction, leading to extensive devastation and a significant loss of life. In order to identify areas susceptible to liquefaction, it is anticipated that the employment of the gravity method, renowned for its capacity to discern density fluctuations associated with the mass of voluminous materials over a considerable detection range, will prove instrumental. The investigation of parameters and the characterization of liquefaction phenomena in regions previously afflicted by liquefaction disasters can be instrumental in devising strategies for mapping zones that are predisposed to such occurrences. The present study seeks to employ geophysical methods, specifically the gravity method, to delineate zones with the potential for liquefaction within the Lolu Village at Palu City, Central Sulawesi. Through the application of techniques designed to isolate regional and residual anomalies, it is envisaged that a clearer understanding of anomalies situated in shallower regions can be attained, with a specific focus on residential areas. Notably, due to liquefaction, approximately half of the residential areas have shifted a considerable distance of around 132 meters from their original positions. To facilitate the interpretation of subsurface layers, two-dimensional cross-sections are modeled to intersect the displaced and stationary areas. The residual map reveals discernible variations in anomaly values, with lower values observed in the areas that experienced liquefaction-induced movement. Subsurface modeling further demonstrates the presence of three distinct rock layers, namely a sandy layer, a gravel layer, and a rock layer. Additionally, the modeling depicts the formation of canals composed of hard rock, exhibiting varying thicknesses within the surface layer as a consequence of the liquefaction event in 2018. The existence of these canals serves as an indicator that when the sandy layer becomes saturated with water, it will flow along the topographical gradient, following the path of the subterranean canals that have formed.A seismic event of magnitude 7.5 struck the Palu region in Central Sulawesi on September 28, 2018, precipitating a subsequent calamity in the form of a tsunami measuring 4-7 meters in height. This catastrophe was further compounded by the occurrence of liquefaction, leading to extensive devastation and a significant loss of life. In order to identify areas susceptible to liquefaction, it is anticipated that the employment of the gravity method, renowned for its capacity to discern density fluctuations associated with the mass of voluminous materials over a considerable detection range, will prove instrumental. The investigation of parameters and the characterization of liquefaction phenomena in regions previously afflicted by liquefaction disasters can be instrumental in devising strategies for mapping zones that are predisposed to such occurrences. The present study seeks to employ geophysical methods, specifically the gravity method, to delineate zones with the potential for liquefaction within the Lolu Village at Palu City, Central Sulawesi. Through the application of techniques designed to isolate regional and residual anomalies, it is envisaged that a clearer understanding of anomalies situated in shallower regions can be attained, with a specific focus on residential areas. Notably, due to liquefaction, approximately half of the residential areas have shifted a considerable distance of around 132 meters from their original positions. To facilitate the interpretation of subsurface layers, two-dimensional cross-sections are modeled to intersect the displaced and stationary areas. The residual map reveals discernible variations in anomaly values, with lower values observed in the areas that experienced liquefaction-induced movement. Subsurface modeling further demonstrates the presence of three distinct rock layers, namely a sandy layer, a gravel layer, and a rock layer. Additionally, the modeling depicts the formation of canals composed of hard rock, exhibiting varying thicknesses within the surface layer as a consequence of the liquefaction event in 2018. The existence of these canals serves as an indicator that when the sandy layer becomes saturated with water, it will flow along the topographical gradient, following the path of the subterranean canals that have formed

Characterization of Magnetic Properties of the Coastal Sand Deposits in South Beach of Manokwari, West Papua

Coastal sand deposits containing iron particles (magnetic) can be regarded as iron sand and it generally has color from gray to shiny black yet while it is mixed with other minerals, the mineral will have a certain color combination. Coastal sand in the South of Manokwari Regency, West Papua especially in Wosi Beach, Arfai Beach, and Maruni Beach has a different color of the grain according to the source rocks and the sedimentation process. To characterize the magnetic properties of the three coastal sand deposits, several experimentations were done through measurements of the density, magnetic degree, magnetic susceptibility, and also SEM (Scanning Electron Microscopy) and EDS (Energy Dispersive X–Ray Spectroscopy) tests. The coastal sand deposition has a density ranging from 2.50–5.00 g cm-3 with the magnetic degree between 0.28–36.29 % and its magnetic susceptibility ranged 80.9×10-8 – 7447.7×10-8 m3 kg-1. The coastal sand from Arfai Beach has a magnetic susceptibility between the coastal sand from Wosi and Maruni Beach with the highest value reaching 5135.4 × 10-8 m3 kg-1. This is also supported by SEM and EDS data. The percentage of iron element mass (Fe) of the identified magnetic grain distribution in Wosi Beach sand is 6.71–33.90%, Arfai Beach sand is 11.35 – 38.45% and Maruni beach sand is 15.84–44.41%. ©2018 JNSMR UIN Walisongo. All rights reserved

Characterization of Magnetic Properties of the Coastal Sand Deposits in South Beach of Manokwari, West Papua

Coastal sand deposits containing iron particles (magnetic) can be regarded as iron sand and it generally has color from gray to shiny black yet while it is mixed with other minerals, the mineral will have a certain color combination. Coastal sand in the South of Manokwari Regency, West Papua especially in Wosi Beach, Arfai Beach, and Maruni Beach has a different color of the grain according to the source rocks and the sedimentation process. To characterize the magnetic properties of the three coastal sand deposits, several experimentations were done through measurements of the density, magnetic degree, magnetic susceptibility, and also SEM (Scanning Electron Microscopy) and EDS (Energy Dispersive X–Ray Spectroscopy) tests. The coastal sand deposition has a density ranging from 2.50–5.00 g cm-3 with the magnetic degree between 0.28–36.29 % and its magnetic susceptibility ranged 80.9×10-8 – 7447.7×10-8 m3 kg-1. The coastal sand from Arfai Beach has a magnetic susceptibility between the coastal sand from Wosi and Maruni Beach with the highest value reaching 5135.4 × 10-8 m3 kg-1. This is also supported by SEM and EDS data. The percentage of iron element mass (Fe) of the identified magnetic grain distribution in Wosi Beach sand is 6.71–33.90%, Arfai Beach sand is 11.35 – 38.45% and Maruni beach sand is 15.84–44.41%. ©2018 JNSMR UIN Walisongo. All rights reserved

GEOKEMIJA I MAGNETSKA ANALIZA STIJENA POVRŠINSKOGA SEDIMENTA RIJEKE LAMPENISU: POTRAGA ZA IZVOROM MAGNEZIJA U JEZERU TOWUTI, INDONEZIJA

Sediment from Lake Towuti has been extensively studied to reconstruct past climate and environmental changes. One of the remaining questions is the source of magnesium (Mg) and calcium (Ca) in the northern part of Lake Towuti. In this study, the source of high Mg and Ca content is examined by analysing surface sediment from the Lampenisu River (LR) and Mahalona River (MR) that merge before entering Lake Towuti. Twelve surface sediments from MR, LR, and the confluence of the two rivers (LMR) were subjected to geochemical (XRF), mineralogical (XRD), and rock magnetic (susceptibility and hysteresis parameter) analyses. The result shows that the Mg and Ca content in LR samples are higher than in MR samples. LR samples have a higher susceptibility and a lower frequency dependent susceptibility than MR samples. XRD analyses on extracted magnetic grains show the presence of minerals with a sodalite crystal structure, possibly valleyite in LR but not in MR samples. If valleyite indeed occurs in LR samples, it may contribute to their relatively high Ca content. At the same time, the high content of Mg in LR samples is likely due to the serpentinized peridotite rocks. LR is thereby considered to be the source of high Mg and Ca content in the northern portion of Lake Towuti. This study shows the importance of sediment-source identification in big lakes such as Lake Towuti, where the influx could come from several rivers around the lake.Sediment iz jezera Towuti opsežno je istraživan kako bi se rekonstruirale klimatske i okolišne promjene u prošlosti. Jedno od preostalih pitanja jest izvor magnezija (Mg) i kalcija (Ca) u sjevernome dijelu jezera Towuti. U ovome istraživanju izvor visokoga sadržaja Mg i Ca ispitan je analizama površinskoga sedimenta iz rijeke Lampenisu (LR) i rijeke Mahalona (MR) koje se spajaju prije ulaska u jezero Towuti. Dvanaest površinskih sedimenata iz MR, LR i ušća dviju rijeka (LMR) podvrgnuto je geokemijskoj (XRF), mineraloškoj (XRD) i magnetskoj analizi stijena (susceptibilnost i parametar histereze). Rezultat pokazuje da je sadržaj Mg i Ca u LR uzorcima veći nego u MR uzorcima. LR uzorci imaju veću susceptibilnost i manju susceptibilnost ovisnu o frekvenciji od MR uzoraka. XRD analize ekstrahiranih magnetskih zrnaca pokazale su prisutnost minerala s kristalnom strukturom sodalita, moguće valleyita u LR, ali ne i u MR uzorcima. Ako se valleyit doista pojavljuje u LR uzorcima, to može pridonijeti njihovu relativno visokom sadržaju Ca. Istodobno, visok sadržaj Mg u uzorcima LR vjerojatno je posljedica serpentiniziranih stijena peridotita. S obzirom na navedeno, LR se smatra izvorom visokoga sadržaja Mg i Ca u sjevernome dijelu jezera Towuti. Ovo istraživanje pokazalo je važnost identifikacije izvora sedimenta u velikim jezerima kao što je jezero Towuti, gdje donos materijala može dolaziti iz nekoliko rijeka oko samoga jezera

A Note on the Use of the Second Vertical Derivative (SVD) of Gravity Data with Reference to Indonesian Cases

Gravity data analysis and interpretation are based, among others, on their spatial variation represented by horizontal and vertical gradients. The gradient or derivative of a gravity field can be calculated either in the spatial domain or the wave-number domain. Historically, the second vertical derivative (SVD) of gravity data can be used to delineate the boundaries of anomalous sources. This paper addresses inappropriate use of the SVD of gravity data, with reference to current practices in Indonesia. The SVD's relative magnitude along a profile is widely used to define whether a density contrast and its dipping orientation correspond to a normal or reverse fault, which may be geologically incorrect. Furthermore, the SVD is calculated by approximation using the horizontal derivative, which may be erroneous especially with poorly distributed data and anomalous 3D sources. We exemplify our analysis with synthetic data and propose a more appropriate spectral-based analysis using field data

Pendeteksian Batas-batas Zona Steamflood Menggunakan Data Anomali Gayaberat-mikro 4d Yang Diberi Konstrain

Recently, the oil industry has emphasized enhancement oil recovery (EOR) process. The steamflood are ones EOR process can used to increase the heavy oil production. Effective management of EOR process requires detailed reservoir description and observation of the reservoir being swept at time. The 4D microgravity method can be applied in obtaining reservoir description such as steamflood zone mapping. Combination between the rock physics analysis with ideal model of steamflood used to calculate the synthetic 4D microgravity anomaly. This result suggest the negative 4D microgravity anomaly changes at time represented steamflood zones causes by density contras between steam at the high temperature after injection and pressure with heavy oil at the low temperature and pressure before injection. But the 4D microgravity anomaly can't detect steamflood zone boundaries causes the anomaly shape with respect to shape of source. We proposed the 4D microgravity anomaly constrained with high resolution horizontal derivative to detect steamflood zones boundaries. The field data showed gravity change of up to -300mGal have occurred in area near ones the oil production well. The maxima value of the field constrained 4D microgravity anomaly represented the steamflood zones boundaries with its surrounding

Lithogenic and Anthropogenic Components in Surface Sediments from Lake Limboto as Shown by Magnetic Mineral Characteristics, Trace Metals, and REE Geochemistry

Lake Limboto is one of the major lakes in Sulawesi, Indonesia. It is currently undergoing serious degradation due to population pressure. As more residential areas have been established around the lake, the sedimentation rate has increased because of the contribution of anthropogenic particles. In this study, the lithogenic and anthropogenic components in surface sediments from 17 points in the lake were studied and identified using a combination of magnetic and geochemical analyses. The results showed that although the magnetic susceptibility values in R (residential) and NR (non-residential) areas were relatively similar, the values of saturation isothermal remanent magnetization (SIRM) as well as those of SIRM/χLF differed significantly, implying that the magnetic characteristics of the lithogenic component (in the NR area) differ from those of the anthropogenic component (in the R area). The discrepancy between the anthropogenic and lithogenic contributions was further supported by trace metals and rare earth element (REE) contents. Sediment samples in the R area contained higher levels of Mn, La, Pr, and Gd, while in the NR area they contained higher levels of Fe, Sc, Nd, and Ce. The magnetic susceptibility also correlated strongly with Fe, Cu, Zn, and Mn contents in the NR area. A similar correlation was not observed in the R area. The results above imply that a combination of magnetic and geochemical analyses can successfully differentiate lithogenic and anthropogenic components or contributions in lake sediments