Seismic refraction - Sverdrup Basin

Shallow and deep crustal structure of the western Sverdrup Basin, arctic Canada

Canadian Journal of Earth Sciences ◽

10.1139/e84-096 ◽

1984 ◽

Vol 21 (8) ◽

pp. 902-919 ◽

Cited By ~ 11

Author(s):

L. W. Sobczak ◽

A. Overton

Keyword(s):

Gravity Data ◽

Seismic Refraction ◽

Sediment Accumulation ◽

Density Control ◽

Gravity Effects ◽

Sverdrup Basin ◽

Deep Crustal Structure ◽

Crystalline Crust ◽

Free Air Anomaly ◽

Drill Holes

An analysis of gravity data along two detailed profiles over the western Sverdrup Basin in the Canadian Arctic supports a seismic refraction model. Drill holes as deep as 5.4 km near the profiles provide excellent density control. Mean densities in the thickest part of the basin exceed those in the thinner parts by an average of 0.13 Mg/m3.Bouguer anomalies corrected for the effect of water, sedimentary, and crystalline layers indicate significant anomalies that vary in width from 20 to 275 km and in amplitude from 3 to 46 mGal (30 to 460 μm s−2). These can all be explained by density structures within the sedimentary column. Sedimentary thickness along the profiles varies from 9 to 17.4 km, crystalline thickness varies from 18 to 33 km, and the total crustal thickness varies from 34 to 42 km. The analysis also shows: (1) negative gravity effects of about 60 to 120 mGal (600 to 1200 μm s−2) due to the mass deficiency of the water and sediments are offset by positive gravity effects of similar magnitude due to crustal thinning; (2) isostatic compensation of water and sediments by a mantle antiroot is evident from a regional free-air anomaly near zero and the apparent inverse variation of sedimentary thickness with the thickness of the crystalline crust; (3) in the thickest part of the basin, undulations at the sedimentary–crystalline boundary are in phase with and smaller in amplitude than undulations at the crust–mantle boundary; conversely, in the thinnest part of the basin, these undulations are out of phase and larger in amplitude.These effects may be explained by stretching of a crystalline crust and a general decrease in crustal rigidity with depth during sediment accumulation and subsequent orogenic events.

Download Full-text

Seismic Refraction-Sverdrup Basin

10.4095/104353 ◽

1975 ◽

Author(s):

G D Hobson ◽

A Overton

Keyword(s):

Seismic Refraction ◽

Sverdrup Basin

Download Full-text

DEEP SEISMIC REFRACTION INVESTIGATION IN THE CANADIAN ARCTIC ARCHIPELAGO

Geophysics ◽

10.1190/1.1439548 ◽

1965 ◽

Vol 30 (1) ◽

pp. 87-96 ◽

Cited By ~ 20

Author(s):

G. W. Sander ◽

A. Overton

Keyword(s):

Seismic Refraction ◽

Canadian Arctic ◽

The Arctic ◽

Seismic Profiles ◽

Seismic Surveys ◽

Refraction Seismic ◽

Sverdrup Basin ◽

Basic Portion ◽

The Government ◽

Government Of Canada

During 1962 and 1963, the Dominion Observatory conducted refraction seismic surveys in the islands north of the Canadian mainland. These surveys are part of a project of the Government of Canada to explore the Polar Continental Shelf. The operation consisted of three stationary recording units and a shooting party which traversed the frozen sea in a tractor train. Three refraction‐seismic profiles form a continous section from the Canadian Shield through the Franklinian Geosyncline and the Sverdrup Basin to the Arctic Ocean. Post Devonian sediments in the Sverdrup Basin were found to be 10 km thick. The lower, basic portion of the crust is indicated by a velocity of 7.3 km/sec at a depth of 24 km and the base of the crust at 38 km.

Download Full-text

Seismic Refraction-Sverdrup Basin

10.4095/103215 ◽

1974 ◽

Author(s):

G D Hobson

Keyword(s):

Seismic Refraction ◽

Sverdrup Basin

Download Full-text

Integration of Multi-geophysical Approaches to Identify Potential Pathways of Heavy Metals Contamination - A Case Study in Zeida, Morocco

Journal of Environmental and Engineering Geophysics ◽

10.32389/jeeg9-067 ◽

2020 ◽

Vol 25 (3) ◽

pp. 415-423

Author(s):

Ahmed Lachhab ◽

El Mehdi Benyassine ◽

Mohamed Rouai ◽

Abdelilah Dekayir ◽

Jean C. Parisot ◽

...

Keyword(s):

Heavy Metals ◽

Seismic Velocity ◽

Seismic Refraction ◽

Geophysical Methods ◽

Low Frequency ◽

Electrical Current ◽

P Wave ◽

Low Resistivity ◽

Refraction Tomography ◽

Geophysical Surveys

The tailings of Zeida's abandoned mine are found near the city of Midelt, in the middle of the high Moulouya watershed between the Middle and the High Atlas of Morocco. The tailings occupy an area of about 100 ha and are stored either in large mining pit lakes with clay-marl substratum or directly on a heavily fractured granite bedrock. The high contents of lead and arsenic in these tailings have transformed them into sources of pollution that disperse by wind, runoff, and seepage to the aquifer through faults and fractures. In this work, the main goal is to identify the pathways of contaminated water with heavy metals and arsenic to the local aquifers, water ponds, and Moulouya River. For this reason, geophysical surveys including electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and very low-frequency electromagnetic (VLF-EM) methods were carried out over the tailings, and directly on the substratum outside the tailings. The result obtained from combining these methods has shown that pollutants were funneled through fractures, faults, and subsurface paleochannels and contaminated the hydrological system connecting groundwater, ponds, and the river. The ERT profiles have successfully shown the location of fractures, some of which extend throughout the upper formation to depths reaching the granite. The ERT was not successful in identifying fractures directly beneath the tailings due to their low resistivity which inhibits electrical current from propagating deeper. The seismic refraction surveys have provided valuable details on the local geology, and clearly identified the thickness of the tailings and explicitly marked the boundary between the Triassic formation and the granite. It also aided in the identification of paleochannels. The tailings materials were easily identified by both their low resistivity and low P-wave velocity values. Also, both resistivity and seismic velocity values rapidly increased beneath the tailings due to the compaction of the material and lack of moisture and have proven to be effective in identifying the upper limit of the granite. Faults were found to lie along the bottom of paleochannels, which suggest that the locations of these channels were caused by these same faults. The VLF-EM surveys have shown tilt angle anomalies over fractured areas which were also evinced by low resistivity area in ERT profiles. Finally, this study showed that the three geophysical methods were complementary and in good agreement in revealing the pathways of contamination from the tailings to the local aquifer, nearby ponds and Moulouya River.

Download Full-text