The nature of crustal boundaries: combined interpretation of wide-angle and normal-incidence seismic data

Long, R. E.; Matthews, Patricia A.; Graham, Daniel P.

doi:10.1016/0040-1951(94)90092-2

Cited by 12 publications

(7 citation statements)

References 13 publications

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“…The high amplitudes observed for some of the crustal phases cannot be explained by sharp, step like velocity contrasts, as these cannot provide large enough reflection coefficients to reproduce the observed amplitudes. Therefore thin layering consisting of high‐ and low‐velocity layers, is required to simulate the high‐amplitude intracrustal reflections [ Long et al , 1994].…”

Section: Velocity Models: Descriptionmentioning

confidence: 99%

Nature of the lithosphere across the Variscan orogen of SW Iberia: Dense wide‐angle seismic reflection data

et al. 2009

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[1] Two wide-angle seismic transects have been acquired across the SW Iberian Massif. They crossed three major geological zones (South Portuguese Zone, Ossa-Morena Zone, and Central Iberian Zone), with their tectonic contacts and the Pyrite Belt being of greatest interest. A total of 690 digital seismic recording instruments (650 Texans and 40 Reftek 3 component units) from the IRIS-PASSCAL Instrument Pool were used. The transects (A and B) are each approximately 300 km long and consist of 3 and 6 shot points, respectively, with an approximately 60-km shot point interval. The charge sizes range from 1000 kg at the edges to 500 kg at the center. These recently acquired experiments were designed to provide velocity constraints on the lithosphere and to complement the previously acquired normal incidence seismic profile IBERSEIS. Both data sets are part of the SW Iberia project, which was developed within the EUROPROBE program and designed to address fundamental questions about the nature and dynamics of the Variscan lithosphere. The acquisition parameters provide closely spaced wide-angle seismic images of the lithosphere beneath SW Iberia. In transect A, the station spacing was on average 400 m, while along transect B, the receiver spacing was approximately 150 m. Because of this close trace spacing, the lateral continuity of the seismic arrivals is greatly improved. Frequency analysis revealed that the recorded events feature relatively low frequencies (6-25 Hz). After processing, the shot records show high-amplitude and well-defined arrivals. The interpreted PmP arrival, located at approximately 11 s (normal incidence traveltime), is characterized by high amplitude and relatively low frequency (6-12 Hz). A well-defined Pn arrival appears at offsets beyond 120 km. At far offsets greater than 180 km, an upper mantle reflection is observed. Furthermore, within the upper crust, the shots records feature a relatively high-velocity arrival, located at 4-5-s normal incidence traveltime. The analysis of this arrival indicates that it probably corresponds to the top of the Iberian Reflective Body identified in the IBERSEIS deep seismic profile. The velocity models obtained by forward modeling show a complex crust, especially in the middle crust. The velocity models are the most detailed ones that have been produced in the area and contain a large amount of new features that are relevant to the understanding of the composition of the crust and upper mantle beneath the zone. The velocity depth functions derived from the velocity models have higher middle crustal velocities than the average in other continental areas. A comparison between laboratory seismic velocity measurements and the velocities of the models was carried out in order to estimate the crustal and the upper mantle composition. Results indicate that the high middle crust velocities correspond to rocks of a mafic composition. The combined data set reveals new aspects related to the lithospheric evolution of this transpressive orogen and allows us to attempt a...

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Section: Velocity Models: Descriptionmentioning

confidence: 99%

Nature of the lithosphere across the Variscan orogen of SW Iberia: Dense wide‐angle seismic reflection data

et al. 2009

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“…Moho reflectivity of similar character has been observed in the adjacent Taranaki Basin (Holt and Stern, 1994) as well as in continental crust at other locations around the World (e.g. Mooney et al, 1987;Long et al, 1994;Cook, 2002 and Clowes, 2010). Both Long et al (1994) and Oueity and Clowes (2010) showed that sequences of reflectivity such as this are best represented by a laterally and vertically heterogeneous crust-mantle transition zone spanning a few kilometers (Fig.…”

Section: Comparison To Multi-channel-seismic Datasupporting

confidence: 68%

“…Mooney et al, 1987;Long et al, 1994;Cook, 2002 and Clowes, 2010). Both Long et al (1994) and Oueity and Clowes (2010) showed that sequences of reflectivity such as this are best represented by a laterally and vertically heterogeneous crust-mantle transition zone spanning a few kilometers (Fig. 4.18).…”

Section: Comparison To Multi-channel-seismic Datamentioning

confidence: 99%

Crustal Structure of Wanganui Basin: Implications for Back-Arc Basin Formation

Tozer¹

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Onshore-offshore and onshore wide-angle reflection and refraction seismic data are analysed in order to constrain the crustal P-wave velocity structure within Wanganui Basin and the southern Hikurangi margin, western North Island, New Zealand. Two, two-dimensional, P-wave velocity models are constructed using reflection and refraction phase travel-times based on forty-four onshore-offshore receiver gathers, twelve onshore shot gathers and two marine multi-channel-seismic reflection profiles collected along two transects within Wanganui Basin. The profiles are orientated both sub-parallel and perpendicular to the strike of the Hikurangi margin.

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“…The conventional refraction studies with long spacing of sources suggest the Moho as a first-order discontinuity. Contrarily, high-resolution refraction studies with 50-to 100-m shot spacing and high-frequency sources suggest that the wide-angle reflections from the Moho arise from short discontinuous reflectors instead of a sharp first-order discontinuity/boundary similar to vertical reflection studies (Long et al, 1994). These laterally discontinuous bright lower-crustal reflections are modeled as a lamellar structure with a stack of thin layers (1-to 5-km long and 100-to 500-m thick) of alternating high and low velocities (Krishna & Vijaya Rao, 2011;Sandmeier & Wenzel, 1986).…”

Section: Lower Crust and Reflection Mohomentioning

confidence: 80%

Common Reflection Surface Stack Imaging of the Proterozoic Chambal Valley Vindhyan Basin and Its Boundary Fault in the Northwest India: Constraints on Crustal Evolution and Basin Formation

et al. 2018

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The Vindhyan basin of northwestern and central India is one of the largest undeformed Meso-Neoproterozoic basins in the world with likely potential of hydrocarbons. Crustal seismic reflection data along a 165-km long Chandli-Bundi-Kota-Kunjer profile of the Chambal Valley Vindhyan basin processed using common reflection surface stack method brought out new crustal features, which were missing in earlier images. A gently dipping structure of the basin is imaged with a maximum of 7.5-km thick Proterozoic sediments, 1.5-km thick volcanic sequence, and the granitic basement at 9.0-km depth. The Great Boundary Thrust, a NW dipping crustal-scale regional tectonic feature outcropping at Bundi, and a new NW dipping reflection band from 9-to 30-km depth, named here as the Chambal thrust, are imaged beneath Bundi-Kota segment. Subduction and collision are responsible for evolution of these thrusts implying horizontal crustal growth. Seismic images of compression on one side and extension on another side along with differences in the Moho characteristics and other constraints from geophysical data around Kota indicate the presence of a new tectonic boundary with a strong lateral discontinuity and strike-slip features. The Moho topography is delineated for the first time revealing a crustal thickness ranging from 40 to 44 km. A 9-to 12-km thick mafic underplating at the lower crust suggests an important postcollisional process indicating vertical crustal growth. Based on the images from the present reflection study, a geodynamic model of the region is suggested in a plate tectonic framework, which may apply to similar Paleoproterozoic collisional areas and associated basin formation.

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The nature of crustal boundaries: combined interpretation of wide-angle and normal-incidence seismic data

Cited by 12 publications

References 13 publications

Nature of the lithosphere across the Variscan orogen of SW Iberia: Dense wide‐angle seismic reflection data

Nature of the lithosphere across the Variscan orogen of SW Iberia: Dense wide‐angle seismic reflection data

Crustal Structure of Wanganui Basin: Implications for Back-Arc Basin Formation

Common Reflection Surface Stack Imaging of the Proterozoic Chambal Valley Vindhyan Basin and Its Boundary Fault in the Northwest India: Constraints on Crustal Evolution and Basin Formation

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