Naser Meqbel

Observatório Nacional · Coordination of Geophysics - COGE

The relationship between deep crustal structure and the deformation in the overlying sedimentary wedge in Santos basin, Brazil is not well understood, and the origin and evolution of the salt‐related “Albian Gap (AG)” remain a topic of debate. We investigate the deep structure using three‐dimensional inversion of full tensor marine magnetotelluric...

ABSTRACT The Neogene-Quaternary volcanism in central Anatolia is characterized by ignimbrite sequences, and associated calderas have been partly dismantled and buried as a result of tectonic, volcanic, erosional and depositional processes, hindering the identification of these structures from surface expressions. To search the location of a concea...

The central Anatolian Volcanic Province encompasses many volcanoes elongated in a northeast-southwest direction. Karadağ is one of the dormant Quaternary stratovolcanoes of the region at the southern end of the province. We acquired broadband magnetotelluric (MT) data in the period range 0.0001–251 s at 124 locations to obtain a three-dimensional e...

The 100 km wide Mérida Andes extend from the Colombian/Venezuelan border to the Coastal Cordillera. The mountain chain and its associated major strike-slip fault systems in western Venezuela formed due to oblique convergence of the Caribbean with the South American Plates and the north-eastwards expulsion of the North Andean Block. Due to the limit...

The central Anatolian Volcanic Province encompasses many volcanoes elongated in a northeast-southwest direction. Karadag is one of the dormant Quaternary stratovolcanoes of the region at the southern end of the province. We acquired broadband magnetotelluric (MT) data in the period range 0.0001-251 s at 124 locations to obtain a three-dimensional e...

Long-period magnetotelluric (MT) sites, covering much of the continental United States (US) have been collected through the EarthScope USArray MT Transportable Array (TA) project. Previous regional studies using subsets of these data suggest large-scale variations in deep (sub-lithospheric) resistivity, often of significant amplitude. Here, we pres...

Abstract 3D inversions of magnetotelluric data are now almost standard, with computational power now allowing an inversion to be performed in a matter of days (or hours) rather than weeks. However, when compared to 2D inversions, these are still very computationally demanding. As a result, 3D inversions are generally not subjected to as rigorous te...

Abstract The Lorca earthquake (May 11th, 2011, Mw 5.2) stands as the most destructive one in Spain over the last 50 years, interpreted as having occurred in an intersegment zone of the strike–slip Alhama de Murcia Fault (AMF) (Eastern Betics, Spain). Magnetotelluric data were acquired along a profile to the SW of Lorca (La Torrecilla profile), to c...

Hoggar, as part of the Tuareg shield, is a key area in the assembly of Western Gondwana during the Neoproterozoic. To better understand the tectonic process, 61 broadband magnetotelluric (MT) stations were acquired in Central/Western Hoggar to image the underlying lithosphere. We performed 2-D and 3-D inversions of the impedance tensor and the vert...

In the Garhwal Himalayan Corridor (GHC), we recorded the magnetotelluric (MT) data at 40 sites, in three phases. Out of these 40 sites, useful tipper or vertical magnetic field transfer function (VTF) data was available only at 19 sites. The resistivity model, obtained from 3D inversion of the MT data, is used to investigate the existence of transv...

A magnetotelluric survey has been conducted in the Cappadocia region of central Turkey in order to find new geothermal resources. The survey area has formerly been postulated as the location of a buried caldera that was one of the main eruptive centres of Cappadocian Volcanic Province. Three-dimensional non-linear conjugate gradient inversion of ma...

The current study in the Menderes Massif geothermal province aims to assert a crustal-scale geoelectrical evidence showing the role of extensional tectonics on the flow of geothermal fluids through both high-angle and low-angle normal (detachment) faults and on the heat transport mechanism in the convection dominatedamagmatic geothermal play systems,...

We present a model of the electrical resistivity structure of the lithosphere in the Central Andes between 20° and 24°S from 3‐D inversion of 56 long‐period magnetotelluric sites. Our model shows a complex resistivity structure with significant variability parallel and perpendicular to the trench direction. The continental forearc is characterized...

The electrical resistivity tomography (ERT) method provides moderately good constraints for both conductive and resistive structures, while the radio-magnetotelluric (RMT) method is well suited to constrain conductive structures. Additionally, RMT and ERT data may have different target coverage and are differently affected by various types of noise...

This talk presented the latest results of AusLAMP within South Australia, the long-period magnetotelluric array that will eventually cover Australia at 0.5 degree intervals. This talk, and all others from the Geological Survey of South Australia’s annual conference can be found here: http://minerals.dpc.sa.gov.au/knowledge_centre/events/geological_...

We report on a study to explore the deep electrical conductivity structure of the Dead Sea Basin (DSB) using magnetotelluric (MT) data collected along a transect across the DSBwhere the left lateral strike-slip Dead Sea transform (DST) fault splits into two fault strands forming one of the largest pull-apart basins of theworld. Avery pronounced fea...

As a consequence of measuring time variations of the electric and the magnetic field, which are related to current flow and charge distribution, magnetotelluric (MT) data in two dimensional (2-D) and three dimensional (3-D) environments are not only sensitive to the geoelectrical structures below the measuring points but also to any lateral anomali...

The Namibian continental margin marks the starting point of the Tristan da Cunha hotspot trail, the Walvis Ridge. This section of the volcanic southwestern African margin is therefore ideal to study the interaction of hotspot volcanism and rifting, which occurred in the late Jurassic/early Cretaceous. Offshore magnetotelluric data image electromagn...

Egbert, G., N. Meqbel, and K. Strack, 2013, Cabled marine magnetotellurics: Denser data at lower cost and higher information content. SEG Technical Program Expanded Abstracts 2013 (poster): pp. 840-844.

SUMMARY A long period magnetotelluric (MT) survey, comprising 39 sites over an area of 270 by 150 km, has identified partial melt within the thinned lithosphere of Quaternary Newer Volcanics Province (NVP) in southeast Australia. MT inversion models reveal several important tectonic features and unravel critical information about the tectonics of t...

We present a deep electrical resistivity image from the passive continental margin in Namibia. The approximately 700 km long magnetotelluric profile follows the Walvis Ridge offshore, continues onshore across the Kaoko Mobile Belt and reaches onto the Congo Craton. Two-dimensional inversion reveals moderately resistive material offshore, atypically...

Electromagnetic methods are routinely applied to image the subsurface from shallow to regional structures. Individual electromagnetic methods differ in their sensitivities towards resistive and conductive structures and in their exploration depths. If a good balance between different electromagnetic data can be be found, joint 3D inversion of multi...

NOTE: The electric resistivity model file can be found at: URL：(https://ds.iris.edu/ds/products/emc-mcrmtyang-etal2015resistivity/) We present initial results from three-dimensional inversion of long period EarthScope magnetotelluric (MT) transportable array data from 232 sites covering the north-central US. The study area covers the 1.1 Ga Mid-Co...

Electromagnetic (EM) methods are routinely applied to image the subsurface from shallow to regional structures. EM methods differ in their sensitivities towards resistive and conductive structures as well as in their exploration depths. Joint 3D inversion of multiple EM data result in significantly better resolution of subsurface structures than th...

We describe implementation of a modular system of computer codes for inversion of electromagnetic geophysical data, referred to as ModEM. The system is constructed with a fine level of modular granularity, with basic components of the inversion ─ forward modeling, sensitivity computations, inversion search algorithms, model parametrization and regu...

Combining different electromagnetic (EM) methods in joint inversion approaches can enhance the overall resolution power. Every method is associated with a particular sensitivity pattern. By assembling complementary patterns, subsurface imaging becomes more complete and reliable. We describe different paths to obtain multi-EM inversions. First, a jo...

With the increasing success of marine electromagnetics, the trend is to go to similar acquisition density as with seismic data. Cabled marine controlled source electromagnetic (CSEM) systems under development will make acquisition of dense CSEM datasets for seafloor exploration practical. Natural source EM data, which may also be collected by such...

Oblique shear directions along the left lateral strike-slip Dead Sea transform (DST) fault caused the formation of the Dead Sea Basin (DSB), one of the world's largest pull-apart basins. The Dead Sea, which covers the northern part of the basin, is one of the most saline lakes in world. To understand interaction of saline water from the Dead Sea wi...

Long period (10-20,000 s) magnetotelluric (MT) data are being acquired in a series of temporary arrays deployed across the continental United States through the EMScope component of EarthScope. MT deployments in 2006-2011 have acquired data at 325 sites on an approximately regular grid, with the same nominal spacing as the USArray broadband seismic...

We have performed a set of three dimensional inversions of magnetotelluric data in the Snake River Plain and Yellowstone areas. We used a total of 73 sites from Earthscope MT Transportable Array (Idaho, Montana and Wyoming areas) and a subset of 19 sites from an earlier long-period MT survey in the Snake River Plain (SRP). Data for 14 periods from...

We have developed a modular system of computer codes for inversion of electromagnetic (EM) geophysical data (ModEM). ModEM allows for rapid adaptation of inversion algorithms developed for one purpose (e.g., three-dimensional magnetotellurics (MT)) to other EM problems (e.g., controlled source EM). The modular approach can also simplify maintenance...

Long period (10-20,000 s) magnetotelluric (MT) data are being acquired in a series of temporary arrays deployed across the continental United States through EMScope, a component of EarthScope, a multidisciplinary decade-long project to study the structure and evolution of the North American Continent. MT deployments in 2006-2010 have so far acquire...

A comparison of error and resolution properties of 2-D models of electrical resistivity from single and joint inversions of direct-current resistivity DCR and radiomagnetotelluric RMT data is presented. Linearized model resolution and error estimates are computed from the Jacobian and its smoothnessconstrained generalized inverse. As a novelty, lin...

For the first time, a comparative analysis of the resolution and variance properties of 2-D models of electrical resistivity derived from single and joint inversions of dc resistivity (DCR) and radiomagnetotelluric (RMT) measurements is presented. DCR and RMT data are inverted with a smoothness-constrained 2-D scheme. Model resolution, model varian...

Fault zones are the locations where motion of tectonic plates, often associated with earthquakes, is accommodated. Despite a rapid increase in the understanding of faults in thelast decades, our knowledge of their geometry, petrophysical properties, and controlling processes remains incomplete. The central questions addressed here in our study of t...

Since the advent of plate-tectonics the Dead Sea Transform (DST) has been considered a prime site to examine geodynamic processes. It has accommodated a total of 105 km of left-lateral transform motion between the African and Arabian plates since early Miocene (~20 My). Large historical earthquakes on the DST with magnitudes up to 7 and the 1995 Nu...

Fault zones are the locations where motion of tectonic plates, often associated with earthquakes, is accommodated. Despite a rapid increase in the understanding of faults in the last decades, our knowledge of their geometry, petrophysical properties, and controlling processes remains incomplete. The central questions addressed here in our study of...

The left-lateral Dead Sea transform (DST) is a major transform fault separating the Arabian plate in the east from the African and Sinai plates in the west. It extends from the Red Sea rift to the Taurus collision zone in eastern Turkey, with a total length of more than 1000 km. During its evolution, the DST formed several deep sedimentary (pull-ap...

Within the Dead-Sea-Rift-Transec-(DESERT)-project seismic, seismological, electromagnetic, gravity, magnetic, geodynamic and geological studies were done at the Dead Sea Rift/Dead Sea Transform (DST) to give answers to the questions: "How do shear zones work and what controls them?". Among large scale insights of the DST structure which were derive...

Within the Dead-Sea-Rift-Transect-(DESERT)-project seismic, seismological, electromagnetic, gravity, magnetic, geodynamic and geological studies were done at the Dead Sea Rift/Dead Sea Transform (DST) to give answers to the question: How do shear zones work and what controls them?. Most of the small scale experiments were located at the Araba fault...

We have performed a set of three dimensional inversions of magnetotelluric data in the Snake River Plain and Yellowstone areas. We used a total of 73 sites from USArray MT Transportable Array (Idaho, Montana and Wyoming areas) and a subset of 19 sites from an earlier long-period MT survey in the Snake River Plain (SRP). Data for 14 periods from 7.3...