Seismic Prospecting in the Western Approaches of the English Channel

Abstract

Summary On the basis of the measured seismic velocities, the layering found at 25 seismic stations in the area of the Western Approaches of the English Channel is divided into four classes which are respectively correlated with semi-consolidated Cretaceo-Tertiary sediments, the New Red system, the Palaeozoic system, and a metamorphic basement. The last of these appears to form a long, deep trough. The Palaeozoic floor is depressed in a trough of somewhat variable depth, bounded on the north by an outcrop of the metamorphic basement which is possibly a westward extension of the upthrust Lizard-Start metamorphic belt. Contour maps of the layering are produced.

A Seismic Refraction-Shooting Survey off the North Coast of Cornwall

“…This vertical displacement can be interpreted as an increase in depth of the third layer at this range, and is probably caused by faulting in the vicinity. These displacements of travel-time curves are not unusual and other cases have been reported by Day, Hill, Laughton & Swallow (1956).…”

The Floors of the Oceans

“…Along the east coast of the United States the Coast and Geodetic Survey soundings published by Veatch and Smith (1939) were used for the continental shelf and slope. Other important sources of published soundings include Hill (1956), De Andrade (1937), Dietrich (1939), Wfist (1940a), Emery (1950), and Tolstoy (1951).…”

A Seismic Refraction Line Across the Solent

“…More recently, commercial seismic investigations in the North Sea (Cook, 1965) reveal a congressional wave velocity for the Chalk of approximately 3,650 m/sec. These velocities are appreciably higher than velocities for the Chalk obtained by Bullard et al (1940) in eastern England (1,930-2,520 m/sec), and Day et al (1956) in the English Channel and the Western Approaches (2,290-2,440 m/sec). Stride (1959) suggested that a velocity of 3,000 m/sec observed in refraction surveys over the Dogger Bank may represent the Chalk, but could include Upper Palaeozoic and/or other Mesozoic rocks.…”

“…These velocities are appreciably higher than velocities for the Chalk obtained by Bullard et al (1940) in eastern England (1,930-2,520 m/sec), and Day et al (1956) in the English Channel and the Western Approaches (2,290-2,440 m/sec). Stride (1959) suggested that a velocity of 3,000 m/sec observed in refraction surveys over the Dogger Bank may represent the Chalk, but could include Upper Palaeozoic and/or other Mesozoic rocks.The velocities for the Tertiary sequence within the Solent area compare with the class I velocities (1,700-2,500 m/sec) obtained from seismic refraction studies in the English Channel by King (1953), andDay et al (1956), who identified this velocity interval as Mesozoic and/or Tertiary strata. …”

“…The velocities for the Tertiary sequence within the Solent area compare with the class I velocities (1,700-2,500 m/sec) obtained from seismic refraction studies in the English Channel by King (1953), andDay et al (1956), who identified this velocity interval as Mesozoic and/or Tertiary strata.…”