New seismic, magnetic, and gravity constraints on the crustal structure of the Lincoln Sea continent–ocean transition

1994 ◽  
Vol 31 (6) ◽  
pp. 905-918 ◽  
Author(s):  
D. A. Forsyth ◽  
M. Argyle ◽  
A. Okulitch ◽  
H. P. Trettin
Keyword(s):  
Crustal Structure ◽  
Velocity Structure ◽  
Seismic Survey ◽  
Moho Depth ◽  
Gravity Gradient ◽  
Volcanic Complex ◽  
Lomonosov Ridge ◽  
The North ◽  
Shelf Slope ◽  
Volcanic Margin

A new seismic model of Canada's northeasternmost margin indicates a complex continent to ocean transition with similarities to both volcanic and nonvolcanic margins. The crustal structure beneath the Lincoln Sea includes: (i) a continental shelf with a uniform 3 km thick cover (velocity = 1.8–3.6 km/s) overlying at least 6 km of synrift(?) basinal strata (velocity = 4.3–4.9 km/s) that terminate near the base of the slope; (ii) a thick unit of oceanic layer 2-type velocity (5.4–5.8 km/s) overlying a velocity structure resembling a volcanic margin; (iii) a high-velocity lower crust (> 7.4 km/s) resembling North Atlantic volcanic margins or the Alpha Ridge but different from the Lomonosov Ridge near the North Pole; (iv) a change in velocity structure 15–25 km seaward of the shelf–slope break that coincides with a distinct short-wavelength, high-amplitude magnetic anomaly and the centre of a steep gravity gradient; and (v) a suggested Moho depth of 23 km beneath the Lincoln Sea margin along 63°W.The velocity structure beneath the Lincoln Sea is transitional from thinned continental crust beneath the shelf to a structure with oceanic affinities to the north. Typical, 10 km thick oceanic crust is not apparent beneath the northern Lincoln Sea. The upper crustal structure resembles a rifted, nonvolcanic margin such as the Goban Spur, while the high lower crustal velocity resembles a volcanic margin like the Hatton Bank or an oceanic complex like the Alpha Ridge. North of the seismic survey, the enigmatic Lincoln Sea plateau may be an intruded Lomonosov Ridge segment or a volcanic complex similar to the Alpha Ridge or the Morris Jesup Plateau.

Structure beneath Queen Charlotte Sound from seismic-refraction and gravity interpretations

1992 ◽  
Vol 29 (7) ◽  
pp. 1509-1529 ◽  
Author(s):  
Tianson Yuan ◽  
G. D. Spence ◽  
R. D. Hyndman
Keyword(s):  
Crustal Structure ◽  
Velocity Structure ◽  
Sedimentary Basin ◽  
Single Channel ◽  
Velocity Variation ◽  
Moho Depth ◽  
High Porosity ◽  
Upper Crust ◽  
Low Velocity ◽  
Data Set

A combined multichannel seismic reflection and refraction survey was carried out in July 1988 to study the Tertiary sedimentary basin architecture and formation and to define the crustal structure and associated plate interactions in the Queen Charlotte Islands region. Simultaneously with the collection of the multichannel reflection data, refractions and wide-angle reflections from the airgun array shots were recorded on single-channel seismographs distributed on land around Hecate Strait and Queen Charlotte Sound. For this paper a subset of the resulting data set was chosen to study the crustal structure in Queen Charlotte Sound and the nearby subduction zone.Two-dimensional ray tracing and synthetic seismogram modelling produced a velocity structure model in Queen Charlotte Sound. On a margin-parallel line, Moho depth was modelled at 27 km off southern Moresby Island but only 23 km north of Vancouver Island. Excluding the approximately 5 km of the Tertiary sediments, the crust in the latter area is only about 18 km thick, suggesting substantial crustal thinning in Queen Charlotte Sound. Such thinning of the crust supports an extensional mechanism for the origin of the sedimentary basin. Deep crustal layers with velocities of more than 7 km/s were interpreted in the southern portion of Queen Charlotte Sound and beneath the continental margin. They could represent high-velocity material emplaced in the crust from earlier subduction episodes or mafic intrusion associated with the Tertiary volcanics.Seismic velocities of both sediment and upper crust layers are lower in the southern part of Queen Charlotte Sound than in the region near Moresby Island. Well velocity logs indicate a similar velocity variation. Gravity modelling along the survey line parallel to the margin provides additional constraints on the structure. The data require lower densities in the sediment and upper crust of southern Queen Charlotte Sound. The low-velocity, low-density sediments in the south correspond to high-porosity marine sediments found in wells in that region and contrast with lower porosity nonmarine sediments in wells farther north.

scholarly journals Southern Chile crustal structure from teleseismic receiver functions: Responses to ridge subduction and terrane assembly of Patagonia

Geosphere ◽  
2019 ◽  
Vol 16 (1) ◽  
pp. 378-391 ◽  
Author(s):  
E.E. Rodriguez ◽  
R.M. Russo
Keyword(s):  
Crustal Structure ◽  
Triple Junction ◽  
Oceanic Lithosphere ◽  
Receiver Functions ◽  
Moho Depth ◽  
The South ◽  
Ridge Subduction ◽  
The North ◽  
Tectonic Processes ◽  
Chile Triple Junction

Abstract Continental crustal structure is the product of those processes that operate typically during a long tectonic history. For the Patagonia composite terrane, these tectonic processes include its early Paleozoic accretion to the South America portion of Gondwana, Triassic rifting of Gondwana, and overriding of Pacific Basin oceanic lithosphere since the Mesozoic. To assess the crustal structure and glean insight into how these tectonic processes affected Patagonia, we combined data from two temporary seismic networks situated inboard of the Chile triple junction, with a combined total of 80 broadband seismic stations. Events suitable for analysis yielded 995 teleseismic receiver functions. We estimated crustal thicknesses using two methods, the H-k stacking method and common conversion point stacking. Crustal thicknesses vary between 30 and 55 km. The South American Moho lies at 28–35 km depth in forearc regions that have experienced ridge subduction, in contrast to crustal thicknesses ranging from 34 to 55 km beneath regions north of the Chile triple junction. Inboard, the prevailing Moho depth of ∼35 km shallows to ∼30 km along an E-W trend between 46.5°S and 47°S; we relate this structure to Paleozoic thrust emplacement of the Proterozoic Deseado Massif terrane above the thicker crust of the North Patagonian/Somún Cura terrane along a major south-dipping fault.

scholarly journals Deep crustal structure of the North-West African margin from combined wide-angle and reflection seismic data (MIRROR seismic survey)

2015 ◽  
Vol 656 ◽  
pp. 154-174 ◽  
Author(s):  
Y. Biari ◽  
F. Klingelhoefer ◽  
M. Sahabi ◽  
D. Aslanian ◽  
P. Schnurle ◽  
...  
Keyword(s):  
Crustal Structure ◽  
Seismic Data ◽  
West African ◽  
Seismic Survey ◽  
Wide Angle ◽  
North West ◽  
Reflection Seismic ◽  
The North ◽  
Deep Crustal Structure

scholarly journals The crustal structure of the Northeast Greenland continental shelf across the extension of the West Jan Mayen Fracture Zone

2020 ◽  
Author(s):  
Thomas Funck ◽  
Andreas Skifter Madsen ◽  
Christian Berndt ◽  
Anke Dannowski ◽  
Dieter Franke ◽  
...  
Keyword(s):  
Continental Margin ◽  
Crustal Structure ◽  
Fracture Zone ◽  
Seismic Refraction ◽  
Moho Depth ◽  
Gravity Modeling ◽  
The South ◽  
The West ◽  
The North ◽  
Lower Crustal

<p>Between August and October 2017, the German research vessel Maria S. Merian acquired geophysical data along the Northeast Greenland continental margin during its cruise MSM-67. This included seismic reflection and wide-angle/refraction data as well as potential field data. In comparison to the conjugate mid-Norwegian margins, the Northeast Greenland continental margin is less well studied. Hence, one of the key objectives of the expedition was to improve the understanding of the opening of the Northeast Atlantic Ocean and the evolution of the conjugate margin pair. One particular goal of the experiment was the mapping of the lateral extent of magmatism associated with the opening and how this relates to margin segmentation.</p><p>Seismic refraction line BGR17-2R2 runs on the shelf and parallel to the coast of NE Greenland. It crosses the landward extension of the West Jan Mayen Fracture Zone that separates the seafloor spreading along the Mohn’s Ridge in the north from the Kolbeinsey Ridge in the south. A total of 29 ocean bottom seismometers (OBS) equipped with a hydrophone and three-component geophones were deployed along the 235-km-long line. The seismic source was a G-gun array with a total volume of 4840 cubic inches (79.3 L) fired every 60 s. In the central and northern part of the line, two older seismic refraction profiles are crossed (lines AWI2003-500 and 400, respectively), which run perpendicular to the margin and can be used for lateral correlation of the crustal structure.</p><p>For the initial analysis, a velocity model was developed by forward and inverse modeling of travel times using the program RAYINVR. Later, a travel time tomography was carried out employing the code Tomo2D and performing a Monte Carlo analysis with 100 inversions from which an average model was calculated. The models show a 1-to 3-km-thick sedimentary column with velocities ranging from 1.6 to 4.0 km/s. In the central and northern part, a 1-km-thick layer with velocities around 4.6 km/s is underlying the sediments and is interpreted to consist of volcanic material. Below and extending along the entire length of the line, velocities of 5.6 km/s are observed in a layer that is ~2 km thick. The crystalline basement has a depth around 5 km with higher velocities in the north (6.5 km/s) than in the south (6.3 km/s). High lower crustal velocities (>7.2 km/s) are observed along the entire line and either indicate magmatic underplating or lower crustal sill intrusions. The Moho depth is seismically constrained along the central part of the line where it is 30 km. Gravity modeling suggest a depth of 35 and 27 km at the southern and northern limit of the profile, respectively. Within the zone of the landward extension of the West Jan Mayen Fracture Zone, a decrease in mid-crustal velocities by 0.2 km/s is observed. Slightly to the north of the fracture zone, a 50-km-wide zone with increased mid-and lower crustal velocities may indicate an igneous center in an area where the upper volcanic layer is shallowest.</p>

scholarly journals Transboundary geophysical mapping of geological elements and salinity distribution critical for the assessment of future sea water intrusion in response to sea level rise

2012 ◽  
Vol 16 (7) ◽  
pp. 1845-1862 ◽  
Author(s):  
F. Jørgensen ◽  
W. Scheer ◽  
S. Thomsen ◽  
T. O. Sonnenborg ◽  
K. Hinsby ◽  
...  
Keyword(s):  
Groundwater Flow ◽  
Sea Level Rise ◽  
Sea Level ◽  
Preferential Flow ◽  
Sea Water ◽  
Saline Water ◽  
Seismic Survey ◽  
Salinity Distribution ◽  
Geological Structures ◽  
The North

Abstract. Geophysical techniques are increasingly being used as tools for characterising the subsurface, and they are generally required to develop subsurface models that properly delineate the distribution of aquifers and aquitards, salt/freshwater interfaces, and geological structures that affect groundwater flow. In a study area covering 730 km2 across the border between Germany and Denmark, a combination of an airborne electromagnetic survey (performed with the SkyTEM system), a high-resolution seismic survey and borehole logging has been used in an integrated mapping of important geological, physical and chemical features of the subsurface. The spacing between flight lines is 200–250 m which gives a total of about 3200 line km. About 38 km of seismic lines have been collected. Faults bordering a graben structure, buried tunnel valleys, glaciotectonic thrust complexes, marine clay units, and sand aquifers are all examples of geological structures mapped by the geophysical data that control groundwater flow and to some extent hydrochemistry. Additionally, the data provide an excellent picture of the salinity distribution in the area and thus provide important information on the salt/freshwater boundary and the chemical status of groundwater. Although the westernmost part of the study area along the North Sea coast is saturated with saline water and the TEM data therefore are strongly influenced by the increased electrical conductivity there, buried valleys and other geological elements are still revealed. The mapped salinity distribution indicates preferential flow paths through and along specific geological structures within the area. The effects of a future sea level rise on the groundwater system and groundwater chemistry are discussed with special emphasis on the importance of knowing the existence, distribution and geometry of the mapped geological elements, and their control on the groundwater salinity distribution is assessed.

Detailed crustal structure of the North China and its implication for seismicity

2014 ◽  
Vol 81 ◽  
pp. 53-64 ◽  
Author(s):  
Wenliang Jiang ◽  
Xin Wang ◽  
Tian Tian ◽  
Jingfa Zhang ◽  
Donglei Wang
Keyword(s):  
Crustal Structure ◽  
North China ◽  
The North

Sediment Thickness and Moho Depth Beneath Western Indonesian Region From Teleseismic Receiver Function

2021 ◽  
Author(s):  
Syaiful Bahri ◽  
Wiwit Suryanto ◽  
Drajat Ngadmanto
Keyword(s):  
Shear Wave ◽  
Shear Wave Velocity ◽  
Receiver Function ◽  
Velocity Model ◽  
Moho Depth ◽  
Sediment Layer ◽  
The North ◽  
East Kalimantan ◽  
Crust Layer ◽  
Teleseismic Receiver Function

Abstract The Earth's crust layer and sediment in Western Indonesia has been studied using the inversion of teleseismic receiver function from BMKG’s seismic network. Earthquake events were analyzed in this study with a moment magnitude greater than 6.0 with epicentral distances of 30° to 90°. A total of 60 earthquake events were observed and recorded by 91 stations around the study area. Furthermore, an inversion process was carried out using the initial velocity model from the modification of the AK135f velocity model to obtain the shear wave velocity structure below each stations. The velocity model from the azimuthally stacked vertical receiver function showed that the sediment layer had a relatively medium shear wave velocity value with an average of 2.1 km/s, while the crust layer had 4.60 km/s. The sedimentary layer thickness in this region also varies between 2 km to 10 km. A relatively thick sediment layer of about 8 km to 10 km was observed in two locations, in East Kalimantan associated with the Kutai Basin and Northern part of Sumatera in the North Sumatera Basin, a two major oil producer basinal area in Indonesia. The Moho discontinuity was also found at depths that vary between 16 km to 50 km. In addition, the most shallow Moho depth is 16 km below the North Kalimantan and North part of West Java, while the deeper Moho depth of 50 km is located below East Kalimantan, Central Kalimantan, North Sumatera and South Sumatera.

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