High-resolution Aeromagnetic Survey Research Articles

High resolution magnetic anomalies, volcanism and tectonics of the active “La Fossa” vulcanic system (Vulcano island) and Lipari island (South Italy)

In this paper we present the new high-resolution magnetic anomaly map of the La Fossa Caldera system and Lipari island (Southern Italy), obtained by merging two low-altitude aeromagnetic surveys. In these islands a variegated ensemble of magnetic anomalies develops in the north-south direction. The La Fossa Caldera is characterized by very high-intensity and short-wavelength magnetic anomalies, related to mafic intrusive/effusive sources, mainly aligned along the NNW-SSE and NS faults. Instead, the Lipari island is characterized by lower intensity anomalies related to sources with more evolved chemistry, elongated in the NE-SW, NNE-SSW and EW of the subordinate faults. Both the two sets of structures belong to the Tindari-Letojanni strike slip fault-system, a regional lineament along which the southern side of the Aeolian Archipelago is emplaced. The study identifies three distinctive magnetic zones on the Lipari island: the southern, the central, and the north-western ones. The southern zone is characterized by negative magnetic monopoles in correspondence with the younger rhyolitic domes and a Curie Isotherm upwelling. The central part of the island has an average lower intensity of positive anomalies, corresponding to the less evolved products of the intermediate Lipari volcanic epochs. The north-western side is characterized by higher intensity anomalies related to older volcanic epochs. The interplay among strike-slip tectonics, chemistry of the uprising magmas, and the thermal setting has contributed to the overall anomaly pattern in this sector of the Aeolian Archipelago. This interpretation is supported by the application of digital enhancement to the total intensity magnetic anomaly field and by the spatial correlation analysis of the magnetic and volcano-tectonic features. The obtained insights are useful to better understand the relationship between arc volcanism and tectonics. Moreover, they can also outline new inferences to forecast future eruptions of the active La Fossa volcanic system. In fact, recent unrest signals were registered at La Fossa Cone, which is one of the present-day active volcanoes of the Aeolian Archipelago, along with Stromboli island. Key pointsLa Fossa volcanic system of Vulcano and Lipari islands high resolution aeromagnetic surveys; Strike slip tectonics magnetic anomaly signature; Spatial correlation analysis of volcano-tectonic and magnetic features.

An ultra-high-resolution autonomous uncrewed helicopter aeromagnetic survey in Izu-Oshima Island, Japan

We conducted a high-resolution aeromagnetic survey using an autonomously driven uncrewed helicopter that flew as low as several tens of meters above the ground along precise flight tracks with 1 m accuracy. The geomagnetic total intensity was measured by a total intensity magnetometer suspended beneath the helicopter at a ~ 50 m or less flight spacing over the entire caldera of Mt. Mihara, located on Izu-Oshima Island, Japan. From the observed geomagnetic data, we estimated high-resolution subsurface magnetization intensity. A high average magnetization intensity of 13.5 A/m was obtained for the entire caldera. The distribution of the magnetization intensity was not only consistent with the results of conventional airborne surveys, but it also had a high spatial resolution of less than 100 m. Highly magnetized areas were observed along the NW–SE lines that intersected the summit pit crater, Crater A, which is consistent with the principal stress direction of Izu-Oshima Island. These highly magnetized areas might be solidified magma that did not reach the surface during past eruptions. A large and deep-rooted weakly magnetized area was found just outside of the NE side of the central cone, which corresponds to the location of Fissure B, and the conduit must have been demagnetized at the previous event. Other weakly magnetized areas were also observed at the N, E, and SW sides around the pit crater. These regions correspond to the location of fumaroles in the crater. The high-resolution subsurface magnetization imaged by the autonomous uncrewed helicopter will be helpful for the mitigation of future eruption damage by enabling the assessment of potential fissure eruption areas.

Interpretation of high resolution aeromagnetic data for structures study and exploration of polymetallic deposits in Kalatage area, eastern Tianshan (NW China)

A high resolution aeromagnetic survey of Kalatage area was carried out, aimed at providing detailed geological structures information and guiding for further mineral prospecting. The recently acquired data was processed and interpreted to better understand the mode of occurrence of the Cu-Au polymetallic deposits and associated structural features. Several analysis techniques, such as reduction to the pole, spectral analysis, low-pass filtering, were applied to process the aeromagnetic data to understand the distribution of magnetic sources. The depth of magnetic sources was estimated by spectral analysis, and the shallower and deeper sources anomalies were analyzed. The Euler deconvolution, total horizontal derivative, tilt angle derivative and theta map were used to study lineament structures. The new structural scheme was established by comparison of above derivative results and geological data of the Kalatage area. The results show that the study area is affected by sets of NWW-SEE/NW-SE, NNE-SSW/NE-SW and nearly E-W directions faults structures; various probable magmatic rocks may be the results of the ascent and intrusion of magma along these regional fractures in the process of large-scale and deep tectonic-magmatic activities. The polymetallic ore deposits are mainly distributed within the eastern portion of the study area and are confined probably along structure lineament suggesting that it is structurally controlled. Furthermore, the favorable area for mineralization was proposed. These analyses help the recognition of structure features of differing magnetizations, interpretation of tectonic evolution, which could have important reference for further mineral prospecting.

The development of a regional-scale intraplate strike-slip fault system; Alpine deformation in the north of Ireland

A paucity of displacement markers can make constraining the kinematics and interaction of regional-scale strike-slip faults difficult. In this study, a high-resolution aeromagnetic survey allows quantitative analysis of kilometre-scale Paleogene faulting in the north of Ireland. Mapping offset dykes and igneous centres reveals the presence of two orientations of Cenozoic strike-slip faults attributed to broadly N-S Alpine shortening arising from the convergence of Africa and Europe. Reactivated NE-SW striking faults accommodated up to 2.3 km of sinistral displacement mainly during the Paleocene. Following tectonic quiescence, up to 2.5 km of Oligocene-aged dextral movement was accommodated on newly-formed NNW-SSE striking faults. Displacement analysis suggests that the faults were kinematically linked and experienced a switch in polarity of the predominantly active fault orientation during the Paleogene, forming an apparent conjugate system with asymmetric displacement distributions. The switch in fault polarity is attributed to a rotation in the regional maximum horizontal stress orientation and the locus of deformation moving from pre-existing reactivated structures to newly formed faults. The analysis also illustrates that, despite low strain rates, the interaction of the principal components of the fault system controlled the formation of sedimentary basins and defined the present-day geography of the region, far from an active plate boundary.

This issue of Earth Science Research Journal

We at the Earth Sciences Research Journal hope all our readers have a happy and productive 2018. Our last issue of ESRJ in 2017 presents a number of papers on different topics within the Earth Sciences. In Alvarez-Ysabel et al. a 150+ year database of tropical cyclone activity is analyzed for the Dominican Republic (DR). A total of 112 events have tracks at most 300 km from the DR are studied in terms of their seasonal distribution and long-term distribution, their frequency and landfall probability. The authors also present a review of trocial cyclone activity in the region. Ogly Gahramanov uses a combination of geological and geochemical information to model the formation of hydrocarbon deposits in the South Caspian Basin, in particular for the South Caspian Depression. The authors argue that large pressures and tectonic history have a large effect on the appropriate selection of potential drilling sites. Using high-resolution aeromagnetic survey data in combination with other geological-geophysical thematic maps, XXXX.et al. take advantage of GIS tools for identifying different tectonic regimes in the Sabinas Basin, northeastern Mexico. Regions where the basin is deepest and the delineation of faults allows for the determination of block boundaries as well. He et al. use a modified direct shear test apparatus to determine shear strength parameters of unsaturated soils under various conditions. The paper proposes that the direct shear test analysis is an efficient way to analysis soil samples. Zhuo and Chen explore the improved water retention capacity of sandy soils by adding nanocarbon made from coconut shells. Different amounts and thicknesses of nanocarbon were added to the soil, increasing water content with increased nanocarbon. Loess deposits can have very large thicknesses, and for engineering purposes it is important to better understand the geotechnical response of the loess deposits. Wang et al. investigate the collapsibility of loess deposits in the Xixian New Region using compressions tests under different pressure and water content conditions. Results presented may have important application in future geotechnical studies in the region.

Mapping and characterization from aeromagnetic data of the Foum Zguid dolerite Dyke (Anti-Atlas, Morocco) a member of the Central Atlantic Magmatic Province (CAMP)

A high-resolution aeromagnetic survey was carried out in the Anti- Atlas, Morocco covering the main areas traversed by the Great CAMP Foum Zguid dyke (FZD). This “doleritic” dyke belongs to the Central Atlantic Magmatic Province (CAMP), a Large Igneous Province which is associated with the fragmentation of the supercontinent Pangaea and the initial stages of rifting of the Central Atlantic Ocean. It also coincides in time with the mass extinction of the Triassic - Jurassic boundary. Based on the study of geological maps and Google Earth satellite images, it appears that the FZD is poorly exposed and, often covered by Quaternary deposits. This work proposes aeromagnetic modelling and interpretation of the FZD in order to better constrain its structural extent. The data have allowed (i) mapping of the dyke over great distances, under the Quaternary deposits and through areas where it was poorly characterized on the geological map; (ii) identifying major tectonic lineaments interpreted as faults; (iii) recognizing magnetic anomalies related to mafic intrusive bodies; and (iv) informing about regional structural context.

High-resolution aeromagnetic survey of Calabria (Southern Italy)

ABSTRACTWe present a 1:350,000 high-resolution magnetic anomaly map of Calabria (Southern Italy), obtained by merging the results from two low-altitude aeromagnetic surveys performed in southern and northern Calabria. Magnetic anomalies of Calabria are of low intensity, and mostly range from 11 to –9 nT. Northern Calabria is characterized by positive anomalies in the Tyrrhenian margin (Coastal Chain) that turn into negative values moving eastward in the Sila Massif. Southern Calabria is characterized by slightly positive anomaly values, interrupted by a null magnetic anomaly corridor roughly corresponding to the eastern margin of the Gioia Tauro basin. Finally, anomaly values turn systematically negative in the Messina Straits. Due to the unprecedented resolution (low flying height, spatial sampling along the flight line of ∼5 m and 1–2 km flight line spacing), the new map highlights, in detail, the geometry and setting of the upper crustal features. As Calabria is one of the most seismically active regions in Italy, hit by several high-magnitude earthquakes in recent centuries, the interpretation of this new map will hopefully contribute to new insights into the crustal geological setting, location and dimension of the main seismogenic sources.

New high-resolution aeromagnetic and radiometric surveys in Finnmark and North Troms: linking anomaly patterns to bedrock geology and structure

New high-resolution aeromagnetic and radiometric surveys in Finnmark and North Troms: linking anomaly patterns to bedrock geology and structure

Geoscientific investigation of a remanent anomaly - Teetulpa, South Australia

We investigate a small (100 metre width) 150 nT amplitude magnetic anomaly delineated in a high-resolution aeromagnetic survey in the Teetulpa Goldfield of the southern Flinders Ranges. We believe that the anomaly is due to a kimberlite pipe, part of a field already known in the general region. As is quite common with kimberlites, the magnetization is clearly dominated by remanence. Modelling the anomaly reveals that the source is very shallow, and would have outcropped at some stage. Follow-up ground geophysical, geochemical and biogeochemical investigations are planned to establish a methodology for integrated studies as follow-up to high resolution aeromagnetic surveys.

New data on pre-Mesozoic intraplate magmatism in the East European Platform

This study presents new data on the manifestations of pre-Mesozoic intraplate mafic magmatism beneath the Vendian–Paleozoic and Mesozoic–Cenozoic sedimentary cover of the Russian Plate. The data were obtained from interpretation of high-resolution aeromagnetic and gravity surveys performed over the past two decades. Buried volcanic structures, dike belts, trap fields, and thick mafic intrusions are described. The four phases of magmatism distinguished in this study (Riphean, Vendian, Devonian, and Late Paleozoic) are temporally correlated with the main rifting stages that took place in the East European Platform.

Magnetic Signature Attenuation of an Unmanned Aircraft System for Aeromagnetic Survey

A novel magnetic signature attenuation technique based on reconfiguring the location and orientation of the onboard magnetic sources of an unmanned aircraft system (UAS) is presented in this paper. The UAS, GeoSurv II, is intended for high-resolution aeromagnetic survey which requires the magnetic signature of the aircraft to be very low. Genetic algorithm (GA) is used to find an optimum configuration given multiple objective functions motivated by the application. The magnetic field contribution from a single servomotor onboard GeoSurv II is modeled as a single permanent magnet dipole, which is then used to build the cost function for the GA routine. The optimization/simulation outcome suggests very little alteration in the current configuration of the GeoSurv II servomotors resulting in a substantial improvement of the overall magnetic signature of the UAS. The simulation results are validated by practical experimentation. The experimental results, in addition to the simulation results, further confirm that the GA optimized configuration substantially outperforms the current configuration in terms of magnetic signature of GeoSurv II.

High resolution aeromagnetic anomaly map of Mount Etna volcano, Southern Italy

A high resolution aeromagnetic survey of Mount Etna Volcano was carried out by the Airborne Geophysics Science Team of Istituto Nazionale di Geofisica e Vulcanologia (INGV), aimed at producing the most detailed magnetic anomaly map existing so far for this area. Two datasets of the total intensity of the Earth's Magnetic Field were collected at different altitudes to take into account the huge topographic variations of Etna volcano, that reaches elevations above 3300masl. One level was flown at the altitude of 2200m whereas a second one over the central part, at about 3500m of altitude. Since the region is characterized by a large presence of strongly magnetized volcanic products, the survey was carried out acquiring profile lines only, in order to optimize the resources. From the residual magnetic anomaly analysis we inferred two main trending lineaments (−35°N and 0°N) that are related to regional tectonic stress field and we interpret the main magnetic anomaly as the effect of thickness variation of magnetized volcanic products due to the complex pre-volcanic basement morphology of Etna.

Aeromagnetic constraints on the subsurface structure of Usu Volcano, Hokkaido, Japan

Usu Volcano, Hokkaido, Japan consists mainly of dacitic volcanic rocks underlain by basaltic somma lava and Pliocene–Pleistocene andesitic volcanic rocks, and erupts every 20–30 years. The most recent eruption, in 2000, was the first since 1978. We conducted a helicopter-borne high-resolution aeromagnetic survey almost three months after the start of this eruption. We calculated magnetic anomalies on a smoothed observation surface using a reduction method, assuming equivalent anomalies below the actual observation surface. We conducted three-dimensional (3D) imaging of magnetic anomalies to constrain the subsurface structure. Our model indicates that there are magnetisation highs in the main edifice of Usu Volcano, which may reflect the subsurface distribution of the Usu somma lava. Meanwhile, magnetisation lows lie north-west of the Nishi-Yama Craters Area and on Higashi-Maruyama Cryptodome, where nearby Pliocene and Pleistocene volcanic rocks, respectively, are found. The reverse magnetisation observed at outcrops close to these sites could explain the magnetisation lows.Although the survey improved our understanding of the surface and subsurface distribution of volcanic rocks in the edifice and basement of Usu Volcano, some limitations remain. No information about the magmas intruded during the recent eruptions in 1977–1978 and 2000 was obtained by the survey, though some of these intrusions were revealed by other geophysical data. The small magnetic contrast between the intruded magmas and their host rocks is the most probable reason. Perhaps the intruded magmas (in particular, those of the most recent eruption) had not cooled enough to become strongly magnetised by the time the survey was conducted.

The role of aeromagnetic data analysis (using 3D Euler deconvolution) in delineating active subsurface structures in the west central Arabian shield and the central Red Sea, Saudi Arabia

In this paper, we present a case study of structural mapping by applying the 3D Euler method to the high-resolution aeromagnetic data that was collected in the west central Arabian Shield region and the coastal region of the central Red Sea in Saudi Arabia. We show the 3D Euler deconvolution algorithm and apply it to magnetic potential field data from the west Central Arabian Shield and the Central Red Sea. The solution obtained with 3D Euler deconvolution gives better-focused depth estimates, which are closer to the real position of sources; the results presented here can be used to constrain depth to active crustal structures (volcanisms) for the study area. The results indicated that the area was affected by sets of fault systems, which primarily trended in the NNW–SSE, NW–SE, EW, and NE–SW directions. Moreover, estimated Euler solution map from aeromagnetic data delineated also the boundaries of shallow, small, and confined magnetic bodies on the offshore section of the study area. These nearly exposed basement intrusions are most likely related to the Red Sea Rift and may be associated with structures higher up in the sedimentary section. These volcanic bodies are extended to the continental part (onshore) of the west central Arabian Shield, particularly beneath both sides of the Ad Damm fault zone. This extension verifies that the fault was largely contemporaneous with a major period during the extension of the Red Sea Basin. Moreover, according to the distribution of circular magmatic-source bodies (circular-shaped ring dikes) that resulted from this study, we can state that the clustering of most earthquakes along this fault may most likely be attributed to the active mantle upwelling (volcanic earthquakes), which are ultimately related to volcanic processes. Furthermore, the oceanic crustal structures near and in the Red Sea offshore regions were also estimated and discussed according to the ophiolite occurrences and further opening of the Red Sea. Our results are largely comparable with studies of previous crustal sections, which were performed along the Red Sea Rift and the Arabian Shield. As a result, the areas above these anomalies are highly recommended for further geothermal study. This example illustrates that high-resolution aeromagnetic surveys can greatly help delineating the subsurface active structures in the west central Arabian Shield and the middle coastal region of the Red Sea of Saudi Arabia.

Analysis of James Ross Island volcanic complex and sedimentary basin based on high-resolution aeromagnetic data

High-resolution aeromagnetic surveys provide a geophysical tool to help image the subsurface structure of volcanoes and their tectonic framework. Here we interpret high-resolution aeromagnetic data and models for James Ross archipelago and surrounding regions to provide a new perspective on Neogene magmatism emplaced along the eastern margin of the Antarctic Peninsula. Based on the analysis and modelling of magnetic anomalies we were able to image the subglacial extent of Miocene to Recent alkaline rocks of the James Ross Island Volcanic Group and map tectonic structures that appear to have exerted important controls on Neogene magmatism. High-amplitude linear anomalies detected over Mount Haddington stratovolcano were modelled as caused by subvertical feeder bodies extending to a depth of at least 3km. These feeder bodies may have been emplaced along a N–S oriented volcano-tectonic rift zone.We also identified several effusive subglacial centres and imaged two concentric magnetic arcs, which we related to Neogene volcanic and subvolcanic lineaments, likely controlled by Mid-Cretaceous strike-slip fault belts and associated deformation zones. The regional magnetic quiet zone that encompasses James Ross Island is caused by the thick sedimentary infill of the Larsen Basin, and a low-amplitude magnetic high within the basin is inferred to reflect a basement push-up structure associated with strike-slip faulting along the eastern edge of the Antarctic Peninsula.In the offshore regions magnetic anomalies southwest of Tabarin Peninsula and west of Vega Island may reflect recent volcanic structures that have yet to emerge from the sea-floor.

Impact of human activities on the geomagnetic field of Antarctica: A high resolution aeromagnetic survey over Mario Zucchelli Station

Environmental protection of Antarctica is a fundamental principle of the Antarctic Treaty. Impact assessment and significance evaluation are due for every human activity on the remote continent. While chemical and biological contaminations are widely studied, very little is known about the electromagnetic pollution levels. In this frame, we have evaluated the significance of the impact of Mario Zucchelli Antarctic Station (Northern Victoria Land) on the local geomagnetic field. We have flown a high resolution aeromagnetic survey in drape mode at 320m over the Station, covering an area of 2km2. The regional and the local field have been separated by a third order polynomial fitting. After the identification of the anthropic magnetic anomaly due to the Station, we have estimated the magnetic field at the ground level by downward continuation with an original inversion scheme regularized by a minimum gradient support functional to avoid high frequency noise effects. The resulting anthropic static magnetic field at ground extends up to 650m far from the Station and reaches a maximum peak to peak value of about 2800nT. This anthropic magnetic anomaly may interact with biological systems, raising the necessity to evaluate the significance of the static magnetic impact of human installations in order to protect the electromagnetic environment and the biota of Antarctica.

Aeromagnetic anomalies over faulted strata

High-resolution aeromagnetic surveys are now an industry standard and they commonly detect anomalies that are attributed to faults within sedimentary basins. However, detailed studies identifying geologic sources of magnetic anomalies in sedimentary environments are rare in the literature. Opportunities to study these sources have come from well-exposed sedimentary basins of the Rio Grande rift in New Mexico and Colorado. High-resolution aeromagnetic data from these areas reveal numerous, curvilinear, low-amplitude (2–15 nT at 100-m terrain clearance) anomalies that consistently correspond to intrasedimentary normal faults (Figure 1). Detailed geophysical and rock-property studies provide evidence for the magnetic sources at several exposures of these faults in the central Rio Grande rift (summarized in Grauch and Hudson, 2007, and Hudson et al., 2008). A key result is that the aeromagnetic anomalies arise from the juxtaposition of magnetically differing strata at the faults as opposed to chemical processes acting at the fault zone. The studies also provide (1) guidelines for understanding and estimating the geophysical parameters controlling aeromagnetic anomalies at faulted strata (Grauch and Hudson), and (2) observations on key geologic factors that are favorable for developing similar sedimentary sources of aeromagnetic anomalies elsewhere (Hudson et al.).

Connecting the Yakima fold and thrust belt to active faults in the Puget Lowland, Washington

[1] High-resolution aeromagnetic surveys of the Cascade Range and Yakima fold and thrust belt (YFTB), Washington, provide insights on tectonic connections between forearc and back-arc regions of the Cascadia convergent margin. Magnetic surveys were measured at a nominal altitude of 250 m above terrain and along flight lines spaced 400 m apart. Upper crustal rocks in this region have diverse magnetic properties, ranging from highly magnetic rocks of the Miocene Columbia River Basalt Group to weakly magnetic sedimentary rocks of various ages. These distinctive magnetic properties permit mapping of important faults and folds from exposures to covered areas. Magnetic lineaments correspond with mapped Quaternary faults and with scarps identified in lidar (light detection and ranging) topographic data and aerial photography. A two-dimensional model of the northwest striking Umtanum Ridge fault zone, based on magnetic and gravity data and constrained by geologic mapping and three deep wells, suggests that thrust faults extend through the Tertiary section and into underlying pre-Tertiary basement. Excavation of two trenches across a prominent scarp at the base of Umtanum Ridge uncovered evidence for bending moment faulting possibly caused by a blind thrust. Using aeromagnetic, gravity, and paleoseismic evidence, we postulate possible tectonic connections between the YFTB in eastern Washington and active faults of the Puget Lowland. We suggest that faults and folds of Umtanum Ridge extend northwestward through the Cascade Range and merge with the Southern Whidbey Island and Seattle faults near Snoqualmie Pass 35 km east of Seattle. Recent earthquakes (MW ≤ 5.3) suggest that this confluence of faults may be seismically active today.

New evidence about the structure and growth of ocean island volcanoes from aeromagnetic data: The case of Tenerife, Canary Islands

[1] We present 3-D magnetic models of Tenerife based on a high-resolution aeromagnetic survey carried out in 2006. Two different inverse modeling techniques have been applied: (1) a linear method aimed at imaging lateral magnetization contacts and (2) a nonlinear method aimed at obtaining a 3-D description of deep intrusive bodies, in which a constant magnetization value characterizes the main sources. Magnetic models show that deep intrusive structures are located beneath the northern part of the island and aligned along the E-W direction. This arrangement of intrusive bodies does not support the hypothesis of a three-armed rift system that has been present since the early formation of the island. The shallow portion of the intrusive structures shows a round geometry that agrees with the previously proposed location of some of the landslide headwalls, suggesting that collapse scars have acted as preferential sites for magma upwelling. Our magnetic model probably provides the first geophysical evidence of the location of the headwall of the Icod landslide beneath the Teide-Pico Viejo complex, thus supporting the vertical collapse hypothesis for the origin of the Cañadas caldera. The largest intrusive complex is located to the northwest of Teide and Pico Viejo, revealing the presence of a very high dike density in this area. This complex probably resulted from the intrusion of magma over the span of millions of years, beginning with the early phases of basaltic shield volcanism in central Tenerife and lasting until the building of Teide and Pico Viejo stratovolcanoes.

Magnetic expression of salt diapir–related structures in the Nordkapp Basin, western Barents Sea

High-resolution aeromagnetic surveys in the Nordkapp Basin, western Barents Sea, demonstrate the capability of modern, high-resolution aeromagnetic surveys to provide an efficient and promising tool for mapping features related to salt diapirism. Salt diapirs are clearly visible by a small, low-amplitude negative round to ellipsoidal magnetic pattern. This pattern coincides with shallow sedimentary layers deformed by the rising salt during active and passive diapirism. The dimensions of these features coincide in shape and size with those interpreted on gravity and seismic surveys.