Crustal Architecture of the Northwestern and Central Gulf of Mexico from Integrated Geophysical Analysis

The tectonic history of the Gulf of Mexico (GOM) is a subject for ongoing debate. The nature of the crust in the northwestern and central parts of the basin remains poorly understood. Joined interpretation of two 2D seismic cross sections—GUMBO1 and GUMBO2—with potential fields (gravity and magnetics) constrained with available well data allows testing various hypotheses about the subsurface structures and crustal architecture in the study area. In the northwestern GOM, two contradicting hypotheses about the nature of the crust were tested—exhumed mantle versus a thinned and intruded continental crust resulted from magma-rich rifting. The nature of the crust was also investigated in the central GOM, where the disagreement in the location of the ocean-continent boundary (OCB) from various published tectonic models reaches 140 km (87 mi). The results suggest that the crust in the study area is stretched continental with multiple magmatic additions represented by dense and highly magnetic bodies with fast seismic velocities, presumably introduced during the magma-assisted rifting of the GOM. The contact between oceanic and continental domains, i.e., the OCB, is interpreted to be near the Sigsbee Escarpment for both modeled lines. The analysis does not support the presence of thick presalt sediments in the study area. This result questions the currently accepted tectonic reconstructions of the GOM as thick presalt deposits are imaged confidently by various seismic surveys along the western Yucatan margin, which is believed to be a conjugate for the study area. This apparent mismatch in distribution of the presalt sediments requires further investigation

Subsurface Structures along Western Yucatan from Integrated Geophysical Analysis

Integration of seismic, gravity, and magnetic data revealed variations in crustal architecture along the Yucatan passive continental margin. The crust beneath the Yucatan salt basin is ~10 km thick and is primarily a lower continental crust. In contrast, the crust beneath the Campeche salt basin is thicker and comprises both the upper and the lower crustal layers. These variations in crustal architecture explain the strikingly different tectonic histories of these basins outlined by previous authors. The rifting of the Yucatan margin was associated with extensive magmatism expressed as voluminous igneous intrusions in the lower crust, one of which is manifested as the Campeche magnetic anomaly. The zone of extrusive volcanic flows is also interpreted in the northern Yucatan coincident with the Seaward Dipping Reflectors (SDR) in seismic data. Integrated analysis of potential fields and seismic data demands high density and magnetic susceptibility for the rocks of the SDR zone. The presalt sedimentary basin with up to 5 km of sediments overlies the stretched and intruded continental crust adjacent to the Ocean-Continent boundary (OCB). This pre-salt basin is up to 100 km wide and pinches out at the northeastern tip of the Yucatan peninsula. It appears to be compartmentalized with the width of individual segments up to 100 km. All the tectonic elements, namely OCB, SDR, pre-salt sedimentary basin, and magmatic intrusions within the stretched continental crust, have their counterparts in the northeastern Gulf of Mexico and therefore represent important constraints for the prebreakup locations of individual crustal blocks

Comparing Satellite vs Marine Potential Fields Data Over the Bathymetrists Seamounts

The Bathymetrists Seamounts (BSM) are located north of the Sierra Leone Rise (SLR) in the mid-Atlantic Ocean. The seamounts reside on oceanic crust that is 105 to 45 million years old. However, dredging over the Bathymetrists Seamounts dated rocks at ~40 Myr. The general trend of the seamounts contradicts the eastward motion of the African tectonic plate. The origin and tectonic history of the Bathymetrists Seamounts remains debated in literature. Potential fields (gravity and magnetic) data can provide important insight into the formation and evolution of the seamounts. The purpose of this study is to compare available gravity and magnetic data acquired by two different methods, satellite and marine. Satellite gravity and magnetic data over the Bathymetrists Seamounts and Sierra Leone Rise are publicly available for analysis. However, this data has a relatively low resolution. In contrast, recently acquired marine data from the University of Hamburg-Germany is higher resolution, but limited to a number of 2-D profiles. Comparing satellite and marine data revealed that each provide advantages and disadvantages for geological analysis. Marine data is useful for 2-D modeling, while satellite data is better for spatial analysis. Combining both data sets will be beneficial for investigating the origin and history of the Bathymetrists Seamounts

Processing Seismic, Gravity And Magnetic Data Over Diebold Knoll On Juan De Fuca Plate

The Juan de Fuca plate is subducting beneath the North American plate along the Cascadia Subduction Zone. The CSZ is associated with multiple earthquakes, although compared to other subduction zones, it is less active. Many studies suggest that subduction will cause major mega thrust earthquake in near future, while others oppose this view. This project is focused on the Diebold Knoll on the JdF plate Various geophysical methods will be integrated to determine its origin and tectonic history

TESTING A DRONE-BASED MAGNETIC FIELD SURVEYING SYSTEM

Aeromagnetic surveys are conducted by geoscientists to study subsurface geologic structures, such as faults. This type of survey uses a magnetometer mounted upon an airborne vehicle to collect magnetic field data. Magnetic anomalies are caused by variations in subsurface geology, namely in magnetic properties of subsurface rocks. Jacobson and Filina (2019) reported on the development of a new low cost drone, based magnetic field surveying system by the UNL Geophysics Team. This drone-based magnetic system is capable of collecting high resolution data at low speeds and low altitudes. The current study focuses on testing this system by conducting two flights over a known subsurface fault near Venice, NE in fall 2019. 1) FAA part 107 small unmanned aircraft license obtained to operate the drone. 2) The fault is visible from the processed data, but has a different trend with respect to previously published one. 3) Statistical analysis of the magnetic data in 20 crossing points shows an average difference of 2.1 nT. 4) Collected magnetic data generally agreed with the USGS’s published data. There is an average offset of 30 nT

Evidence of Ridge Propagation in the Eastern Gulf of Mexico from Integrated Analysis of Potential Fields and Seismic Data

Integrated analysis of gravity, magnetic, and seismic data reveals two phases of spreading in the eastern Gulf of Mexico (GOM) including two distinct spreading centers, suggesting a major ridge reorganization during the opening of the eastern part of the GOM. Ridge propagation between the two spreading episodes explains the following observations: (1) the drastic asymmetry in the oceanic domain of northeastern GOM, (2) the presence of two distinct crustal zones with dramatically different thickness and physical properties, and (3) the observed seismicity within the oceanic domain that is not aligned with any known tectonic structure. The initial Late Jurassic spreading center (~160 Ma) resulted in a thin (~5 km) and uniform oceanic crust with a fast compressional velocity (7 km/s). Based on our analysis, the estimated full spreading rate of this older spreading event is less than 1 cm/yr. The spreading regime changed in Early Cretaceous around 150 Ma, resulting in a propagation (i.e., jump) of the spreading center. The new spreading episode was characterized by a change in spreading direction and increased magma supply as it produced thicker (up to 9 km) oceanic crust with a typical two-layered structure. Despite the increase in magmatic material, the full rate of this younger spreading event estimated from our analysis is only slightly faster (1.1 cm/yr assuming that spreading ceased at 137 Ma). The later conclusion is consistent with the morphology of the spreading centers mapped by seismic data. Our analysis shows that recent deep crustal earthquakes in the middle of the Gulf of Mexico are aligned with the boundary between the two identified distinct oceanic zones, referred to here as a pseudofault

Seismicity in Nebraska and adjacent states: The historical perspective and current trends

A sudden spike in earthquake events has been observed in central Nebraska. Since April 2018, 26 earthquakes with equivalent moment magnitudes from 2.7 to 4.1 occurred, clustered tightly in Custer County. A similar cluster of 24 earthquakes with equivalent moment magnitudes from 2.6 to 3.7 occurred in Jewell County in northern Kansas in 2017. We have compiled an earthquake database for Nebraska and parts of adjacent states from different sources to determine whether these recent earthquake spikes are consistent with historic seismicity. We identified two historic earthquake clusters occurring in our study area. The first contained 32 events and was active in Red Willow County in southwestern Nebraska from 1977 to 1982. As it coincides spatially with the Sleepy Hollow oil field, it may be related to enhanced oil recovery from that field, although it is also located at the edge of the Chadron-Cambridge Arch. The second historical earthquake cluster is located in Pawnee and Richardson counties in southwestern Nebraska and includes eight earthquakes with equivalent moment magnitudes of 2.3 to 2.8 that occurred in a period from 1982 to 1989 over the Nemaha uplift and appear to be related to the Humboldt fault. We note an increase in both maximum magnitude, as well as in the cumulative seismic moment per cluster with time. We have also used gravity and magnetic fields to map potential basement faults in the study area. Our analysis shows that the two recent earthquake spikes are aligned with the proposed basement faults. Despite this correlation, the cause of this sudden spike in seismicity is not well understood, as the stresses that might reactivate these basement faults are unknown. In addition, both recent clusters are distant from oil and gas operations. More seismic stations are necessary in central Nebraska in order to better detect focal depths and faulting style in the ongoing cluster of earthquakes and investigate possible causes

Introduction to Special Section: Integrated Geophysical Imaging

This special section illustrates the value of integration with nonseismic geophysical methods, namely potential fields (gravity and magnetics) and electric and electromagnetic techniques. The primary objective is to overcome the overall underappreciation of these methods as exploration tools. We provide their brief overview and present nine case studies illustrating how the integrative approach to geophysical data analysis influences the overall result and reduces the uncertainty of the derived solution

Integrated Imaging: A Powerful but Undervalued Tool

Following the 2018 SEG Annual Meeting, the Gravity and Magnetics Committee held a postconvention workshop titled “Integrated Imaging.” The half-day workshop attracted nearly 50 participants from various backgrounds. Three primary objectives of the workshop were to explore the nonseismic toolbox, highlight real examples of integrated projects that benefited (or did not benefit) from nonseismic data, and provide geoscientists from all backgrounds a learning opportunity to see how they might optimize the value of their imaging projects via integration with relatively low-cost nonseismic methods. The workshop had a highly interactive format that differed from traditional presentation-based settings. After eight brief case studies were presented, three concurrent guided discussions ensued. Participants were divided into three groups, and each group focused on one discussion topic at a time. The groups rotated, allowing everyone to discuss all three topics. The first discussion was centered on two general questions: what is integrated imaging and what tools are available for it? The second discussion provided an opportunity to examine the relationships between different physical properties that must be managed during integrated multiphysics analysis. The third discussion focused on the costs and benefits of a multiparameter data acquisition. According to feedback from participants, these discussions were the most valuable part of the workshop. The participants agreed that an integrated approach in geophysical data analysis is a powerful but currently undervalued tool. Also noted were the value of integration with nonseismic methods illustrated in the case studies and the need for the integrated approach in data analysis to be taught in schools in addition to the classic overview of individual geophysical methods

Peculiarities of local blood microcirculation in patients with psoriasis

Local hemodynamic parameters were studied by means of laser Doppler flowmetry in 15 patients with psoriasis in the stationary stage, who have plaques on the inner surface of the forearm. LDF signals recorded at the site of psoriatic lesions of the tissue as well as in the intact tissue at a distance of 1-2 cm from the affected area were analysed. LDF signals were postprocessed by continuous wavelet transform using the Morlet wavelet