Land Gravity Measurements Research Articles

Determination of a gravimetric geoid model for Eastern Province in the Kingdom of Saudi Arabia

Abstract A high-resolution gravimetric geoid model was developed for the Eastern Province Kingdom of Saudi Arabia region. The model was created using various datasets, including 320,434 land gravity measurements, 5442 shipborne marine gravity data, the DTU17 altimetry gravity model, and the XGM2019e global geopotential model. The computation strategy employed for modeling the gravimetric geoid involved the Remove-Compute-Restore method with Residual Terrain Model reduction and the 1D-Fast Fourier Transform approach technique. Geoid heights were determined using the Stokes integral with the Wong-Gore modification. To assess the accuracy of the resulting geoid models, they were compared with 4401 GNSS/Levelling points. The geoid accuracy throughout the entire area is better than 1.6 cm in terms of standard deviation (STD) after fitting.

Use of Land Gravity Data in Small Areas to Support Structural Geology, a Case Study in Eskişehir Basin, Turkey

Various researchers have contributed to the literature on the locations and lengths of existing faults in the Eskişehir Basin, Turkey. However, the majority of the literature on the subject bases its results on fault indications observed on the surface, for example, surface ruptures. In addition, studies using geophysical methods in order to reveal buried faults have also fallen short regarding depth compared to gravity. In order to have a better understanding, the gravity method was applied with a total of 448 gravity measurements on five parallel lines in the north–south direction of the study area, which also includes the urban area of the Eskişehir Basin. Considering the neotectonics of the Eskişehir basin, the measurement lines were chosen to perpendicularly cut the east–west extending faults of the Eskişehir fault zone. For the first time in the literature, a detailed Bouguer gravity anomaly map has been obtained for the Eskişehir Basin using land gravity measurements. The edge detection Horizontal Gradient Magnitude (HGM) and Euler Deconvolution (ED) methods were applied to obtained Bouguer anomaly data. Both of these use spatial analysis of Bouguer gravity anomalies. An HGM map shows the presence of maximum amplitude areas in the south and north of the study, and these areas were found to be compatible with the known faults in the literature. ED solutions also support HGM maximums. The relationship between the lineaments obtained from the edge detections and the seismicity of the region were examined. It can be seen that the results obtained from both the HGM and ED edge detection methods are highly compatible with each other, and highly related to the structural geology of the region. Although great agreement with the faults in the literature was determined by both methods, only the ED method showed a number of newly found faults in the area. In addition, the locations of the known faults in the region were supported by the geo-physical gravity method for the first time.

Bouguer anomaly comparison using elevation data measured with hand-held device and geodetic GPS in Blora and Pandan Mountain

Land gravity measurements for subsurface studies require good accuracy for three-dimensional measurement of station’s coordinate (X, Y, Z). These coordinate data will contribute to calculation of Bouguer anomaly correction in the research area. In this study, we compared the coordinate data measured using hand-held devices and geodetic GPS devices. A more accurate tool is a Trimble R4 geodetic GPS and then we select the acquired data as a reference (Ground Control Points). The hand-held devices that we used are consist of the SUUNTO Escape 203 altimeter and the Garmin GPSMAP 60CSx. The research areas of this studi are in Blora and Pandan Mountain. At that location, we conducted acquisition of elevation data and also gravity. The relative gravimeter used to observe variations of gravity in this study is Scintrex CG5. Gravitational data processing is performed until we obtain Complete Bouguer Anomaly (CBA). The results of this study, we get statistical comparison of the accuracy of elevation data as well as differences in CBA values from the study area. Accuracy of elevation data with hand-held devices based on field measurements in Blora and Mount Pandan reaches 6-53 and 54-95 times lower than a geodetic GPS device. The Bouguer anomaly comparison of the 50 point measurements at the two sites gave the difference range of -1.03 to 2.93 mGal.

A high-resolution gravimetric quasigeoid model for Vietnam

A high-resolution gravimetric quasigeoid model for Vietnam and its surrounding areas was determined based on new gravity data. A set of 29,121 land gravity measurements was used in combination with fill-in data where no gravity data existed. Global Gravity field Models plus Residual Terrain Model effects and gravity field derived from altimetry satellites were used to provide the fill-in information over land and marine areas. A mixed model up to degree/order 719 was used for the removal of the long and medium wavelengths and the calculation of the quasigeoid restore effects. The residual height anomalies have been determined employing the Stokes integral using the Fast Fourier Transform approach and deterministic kernel modification proposed by Wong–Gore, as well as by means of Least-Squares Collocation. The accuracy of the resulting quasigeoid models was evaluated by comparing with height anomalies derived from 812 co-located GNSS/levelling points. Results are very similar; both local quasigeoid models have a standard deviation of 9.7 cm and 50 cm in mean bias when compared to the GNSS/levelling points. This new local quasigeoid model for Vietnam represents a significant improvement over the global models EIGEN-6C4 and EGM2008, which have standard deviations of 19.2 and 29.1 cm, respectively, for this region.

New free-air and Bouguer gravity fields of Taiwan from multiple platforms and sensors

We construct 1′ × 1′ grids of free-air and Bouguer gravity anomalies around Taiwan with well-defined error estimates for quality assessment. The grids are compiled from land, airborne and shipborne gravity measurements, augmented with altimeter gravity at sea. Three sets of relative land gravity measurements are network-adjusted and outlier-edited, yielding accuracies of 0.03–0.09 mGal. Three airborne gravity sets are collected at altitudes 5156 and 1620 m with accuracies of 2.57–2.79 mGal. Seven offshore shipborne gravity campaigns around Taiwan and its offshore islands yield shallow-water gravity values with 0.88–2.35 mGal accuracies. All data points are registered with GPS-derived geodetic coordinates at cm–dm accuracies, allowing for precise gravity reductions and computing gravity disturbances. The various datasets are combined by the band-limited least-squares collocation in a one-step procedure. In the eastern mountainous (or offshore) region, Bouguer anomalies and density contrasts without considering the oceanic (or land) topographic contribution are underestimated. The new grids show unprecedented tectonic features that can revise earlier results, and can be used in a broad range of applications.

Sofalica Region (GAZIANTEP) Chromium on Microgravity Anomalies Modelling of Normalized Full Gradient and Nonlinear Inversion

In this study, the province of Gaziantep, Sehitkamil district, there are thought to be chrome-metallic mine in the village of Sofalica the localization of gravity and economical method was to investigate whether it has a reserve. Approximately 189 hectares of land gravity measurements over the measurement point in the study area was 220. By differentiating regional and residual Bouguer gravity map of the generated residual maps were obtained on areas likely to be created on the source. The inversion method of pre-NTG was required for the selection model is the appropriate start. On the structure of polygon slices as a result of application received in the form of the inversion in the range of 125 meters and 450 meters long, 25 meters to 70 meters in thickness in the range of existence of geometric structures have been identified.

Subsurface Structure of the Eastern Edge of the Zagros Basin as Inferred from Gravity and Satellite Data

A data set of 10,505 points of land gravity measurements from southeast Iran obtained from the Bureau Gravimetrique International, combined with Landsat imagery, was used to investigate crustal and Cenozoic lithospheric structure. Interpretation of the Bouguer anomalies reveals three primary structural features. The Zagros Mountain belt is characterized by a progressive decrease in gravity values from -70 mGal near the Persian Gulf to -160 mGal over the suture zone between the Arabian margin and central Iran crustal blocks. The second feature is marked by a backward-L-shaped pair of anomalies that extends from the eastern peripheries of the Zagros basin and wraps around southern Iranian shores. These 15- to 20-km-deep source anomalies, with amplitudes of as much as 10 mGa , are interpreted as intrabasement intrusions demarcating an ancient rift axis. The shallow (6-8 km) east-west-trending anomalies are perhaps interbasement uplifts bordered by reverse faults. The third structure, observed on both gravity and Landsat displays, a north-striking eastward-facing topographic escarpment, has a gravity gradient of 0.85 mGal/km, and is right laterally offset approximately 100 km by the Zagros main recent fault. On Landsat, this escarpment is manifest by a system of north-trending faults that seem to diverge into a horsetail pattern toward the east, and by a set of north-trending dike swarms that cut Jurassic volcano-sedimentary rocks. It separates two distinct structural and sedimentary styles, the Zagros foreland basin anticlines of shallow marine Precambrian to Pliocene rocks on the west and the Makran deep-water Eocene flysch belt on the east. A comparison of gravity features with surface structures on Thematic Mapper and Landsat Multispectral Scanner imagery indicates that a northeast-trending fault system is the result of post-Miocene pervasive transpressive stress coupled with clockwise rotation of underlying basement blocks following the collision of Arabia and Iran. Accommodation structures such as forced folds and rabbit-ear anticlines may develop over and on the flanks of the basement blocks, providing remigration and trapping mechanisms for new oil and gas plays.

Airborne gravimetry from a small twin engine aircraft over the Long Island Sound

In January 1990, a test of the feasibility of airborne gravimetry from a small geophysical survey aircraft, a Cessna 404, was conducted over the Long Island Sound using a Bell Aerospace BGM-3 sea gravity meter. Gravity has been measured from large aircraft and specially modified de Havilland Twin Otters but never from small, standard survey aircraft. The gravity field of the Long Island Sound is dominated by an asymmetric positive 30 mGal anomaly which is well constrained by both marine and land gravity measurements. Using a Trimble 4000 GPS receiver to record the aircraft’s horizontal position and radar altimeter elevations to recover the vertical accelerations, gravity anomalies along a total of 65 km were successfully measured. The root mean square (rms) difference between the airborne results and marine measurements within 2 km of the flight path was 2.6 mGal for 15 measured values. The anomalies recovered from airborne gravimetry can also be compared with the gridded regional free air gravity field calculated using all available marine and land gravity measurements. The rms difference between 458 airborne gravity measurements and the regional gravity field is 2.7 mGal. This preliminary experiment demonstrates that gravity anomalies, with wavelengths as short as 5 km, can be measured from small aircraft with accuracies of 2.7 mGal or better. The gravity measurements could be improved by higher quality vertical and horizontal positioning and tuning the gravimeter’s stabilized platform for aircraft use.

The Role Of High Degree Potential Coefficients And Satellite Altimeter Data In Gravity Field Aproximation In The Malaysian Region

Earth Gravity models (OSU81, OSU86E,and F) defined by a set of high degree potential coefficients were used to generate the geopotential geoid in the Malaysian region. In the very near future, land gravity measurements can be carried out where the station positioning in the survey will be by Global Positioning System (GPS) operating in differential mode. In areas with scarce height benchmark, especially in the remote areas of Peninsular Malaysia, the geopotential geoid can be utilized in conjunction with the satellite derived ellipsoidal heights to yield the orthometric heights of the gravity stations. Satellite altimeter data has the ability to provide high frequency gravity field information in the surrounding marine areas. The method of gravity anomaly recovery in the Tioman test area was based on the theory of least squares collocation. Gravity anomaly maps derived from satellite altimeter data can be used to scan large off-shore areas for detecting density contrasts within the oceanic's outer crust, and thus providing an indirect indication of potential hydrocarbon deposits.

Structural profiles in the New Britain / New Ireland region

Abstract Seismic interpretations along lines of shots and stations in the New Britain/New Ireland region have revealed structural detail in this tectonically complex region. When correlated with marine and land gravity measurements, they indicate a comparatively uniform crust 18 km thick in the eastern Bismarck Sea, thickening to between 30 and 40 km approximately under New Britain and New Ireland. The interpretations indicate crustal thinning of the order of 8 km under the gravity high of central New Britain, and it is suggested that this is upwarping due to northsouth compressional forces. The gravity data indicate that a similar structure could apply to other islands in the Solomon chain. Shear forces seem to dominate the geological structure in the region of the Gazelle Peninsula and southern New Ireland, and the 30 km thick crust there contrasts sharply with an 18 km Bismarck Sea crust along the west coast of the Peninsula. The crustal thickness under New Ireland is the same as that under the islands...

Bouguer gravity anomalies and magnetic anomalies off the Coast of Southern California

Marine and land gravity measurements in the area bounded to the east and west by the 117°00′ and 120°00′ meridians and to the north and south by the 34°30′ and 32°30′ parallels of latitude have been compiled and a map of Bouguer anomalies drawn. A spatial filtering technique was used to separate the anomalies into short-, intermediate-, and long-wavelength components. The features outlined by the short-wave-length components show a pronounced NW-SE strike, and, wherever geologic or seismic evidence is available, there is an excellent correlation between the anomalies and geologic structures aligned parallel to the Coast Ranges. A greater continuity or alignment of these features is noticeable in the filtered anomalies than in the unprocessed gravity data or in the bathymetry. The pattern shown by the intermediate wavelengths has a pronounced east-west strike, parallel to the Transverse Ranges but extending far outside the Transverse Range province. There is a very abrupt transition between the oceanic crust of the Pacific Ocean and the intermediate borderland crust. The dip of the Mohorovicic discontinuity appears to exceed 45° beneath the continental slope. A map of total magnetic field anomalies in the offshore area has also been drawn. Two features have been interpreted in terms of intrusive masses which may be sources for the extensive volcanic rocks in the vicinity of Santa Barbara and San Clemente islands.