British Institutions Reflection Profiling Syndicate Research Articles

Drummond Hoyle Matthews. 5 February 1931 — 20 July 1997

Drummond (Drum) Matthews was a leader who gave himself selflessly for the good of his students and science. He is best known for his work with Fred Vine (F.R.S. 1974), then his graduate student, on the seafloor spreading hypothesis, which underpinned the plate tectonics revolution, and for the work done under his leadership by the Cambridge marine geophysics group and the British Institutions' Reflection Profiling Syndicate (BIRPS). But perhaps his most enduring scientific legacy lies in his many former students, now in positions of leadership and responsibility around the world, who continue to make significant contributions to the health of science.

Along‐axis variability in crustal accretion at the Mid‐Atlantic Ridge: Results from the OCEAN study

The OCEAN experiment is an integrated geophysical study of a region of the Cape Verde abyssal plain that formed at 140 Ma. Deep seismic reflection and ocean bottom hydrophone (OBH) refraction data were acquired along lines parallel and perpendicular to the paleoridge axis trend identified from a detailed magnetic anomaly survey. The igneous basement is overlain by about 1.3 km of sediment which enables improved imaging of intracrustal structure beyond that possible near the Mid‐Atlantic Ridge axis. We describe the results of a 150‐km long profile oriented parallel to magnetic anomalies M15 and M16, along which deep seismic reflection data collected by the British Institutions Reflection Profiling Syndicate are complemented by refraction data constrained by four OBHs. The line spans an entire spreading segment between two fracture zones; the northern of which has an offset of 40 km and the other (central) has an offset of only 10 km. Away from the fracture zones, the mean igneous crustal thickness is 7.2 km; near both fracture zones, thinning of up to 4 km is observed, giving a mean igneous crustal thickness over the whole segment of approximately 6.5 km. Differences are seen between the two fracture zones in their seismic velocity structure, in the associated basement topography, and in the presence of a strong reflection extending into the mantle beneath the northern fracture zone. The boundary between oceanic layers 2 and 3 correlates with variably coherent normal incidence reflections and a change in the character of the reflectivity. A number of planar reflections up to 10 km in length are present within the middle and lower crust, dipping outward from beneath low‐amplitude basement highs at ∼15°; these appear to be present only within layer 3. The Moho has several expressions in the reflection data, including isolated reflection events, a local increase in reflected amplitudes, and a downward decrease in coherent reflections. At the center of the segment there is a zone at the base of the crust within which both high‐ and low‐velocity materials are present. This zone shows an enhanced level of discontinuous normal incidence reflectivity and may represent an initial fractionation event as melt was emplaced at the spreading ridge.

Broadband receiver response from dual‐streamer data and applications in deep reflection seismology

A method to process dual‐streamer data with under and over configuration is presented. The method combines the results of dephase‐sum and dephase‐subtraction methods. In the dephase methods, the response of one streamer is time shifted so that the primary arrivals on both streamers are aligned, and these responses are then summed or subtracted. The method provides a broad spectral response from dual‐streamer data and increases the signal‐to‐noise ratio by a factor of 1.5. Testing was done on synthetic data and then applied to a real data set collected by the British Institutions Reflection Profiling Syndicate (BIRPS). Its application to a deep seismic reflection data set from the British Isles shows that the reflections from the lower crust contain frequencies up to 80 Hz, suggesting that some of the lower crustal reflectors may have sharp boundaries and could be 20–30 m thick.

Complex structure along a Mesozoic sea-floor spreading ridge: BIRPS deep seismic reflection, Cape Verde abyssal plain

SUMMARY As part of an intensive study of a small area of oceanic lithosphere, the British Institutions Reflection Profiling Syndicate (BIRPS) acquired closely spaced deepseismic-reflection profiles over the Early Cretaceous crust of the Cape Verde abyssal plain off West Africa. The survey consisted of profiles spaced at 4 km arranged into strike lines parallel to the old sea-floor spreading axis (‘isochron’ profiles) and orthogonal dip lines oriented in the original direction of spreading (‘flow’ profiles). A large-capacity, well-tuned airgun source and very quiet shooting conditions ensured a high signal-to-noise ratio for deep reflection. Devising a strategy for mitigating contamination from ‘wrap-around’ multiples arriving from previous shots enabled us to use the minimum possible shot-point interval (50 m) allowed for collecting long (18 s) records. Data processing was oriented towards a medium with low root-mean-square velocity, steeply dipping structure, and pervasive low apparent velocity noise from diffraction at the top of the igneous crust. The contrast between the isochron and flow profiles is striking. Isochron profiles are typically highly reflective throughout the igneous crust, consisting of bright, bidirectionally dipping reflection sets that extend in places from the top of the igneous basement down to the interpreted Moho reflection. These reflections do not offset intracrustal or top-basement structure and thus are not interpreted as faults: an igneous intrusive origin seems more likely. Flow profiles are more sparsely reflective but show individual steeply dipping reflections best developed in the upper igneous crust, continuing down in places to the Moho. Dipping reflections on the flow profiles are interpreted as major normal faults since they are clearly associated with offsets of the top of the basement as well as truncation of horizontal reflections within the igneous crust. The dominant dip of these reflections is to the west towards the spreading ridge axis. Reflections from the vicinity of the Moho, while well developed in some places, are not particularly prominent across the survey area. Moho reflections appear to show a different structural relation to crustal features on the isochron and flow profiles: on isochron profiles, dipping reflections occasionally flatten out into, and may merge with, the Moho reflection; on flow profiles, as dipping crustal reflections approach the Moho reflection, they are usually abruptly cut off by it without extending deeper. This survey shows how oceanic crustal structure can vary rapidly over relatively small areas, provides convincing evidence that a structurally complex fabric dominates oceanic igneous crust, and gives a conclusive observation of faults that penetrate the entire oceanic crust.

Seismic reflection profiling to expand knowledge of U.K. shelf

In 1993, two experiments in waters outside the United Kingdom used seismic reflection profiling to investigate the U.K.'s deep structure and adjacent areas of continental shelf.The experiments were conducted by the British Institutions Reflection Profiling Syndicate (BIRPS), which was established in 1981. These experiments, covering portions of Denmark, Germany, and Ireland, reflect BIRPS' recently broadened mission—to conduct experiments over oceanic crust and overseas that contribute to an understanding of U.K. geology and problems related to deep crustal reflectivity.

Separation and enhancement of split S‐waves on multicomponent shot records from the BIRPS WISPA experiment

Instantaneous rotations are combined with f-k filtering to extract coherent S‐wave events from multicomponent shot records recorded by British Institutions Reflection Profiling Syndicate (BIRPS) Weardale Integrated S‐wave and P‐wave analysis (WISPA) experiment. This experiment was an attempt to measure the Poisson’s ratio of the lower crest by measuring P‐wave and S‐wave velocities. The multihole explosive source technique did generate S‐waves although not of opposite polarization. Attempts to produce stacks of the S‐wave data are unsuccessful because S‐wave splitting in the near surface produced random polarizations from receiver group to receiver group. The delay between the split wavelets varies but is commonly between 20 to 40 ms for 10 Hz wavelets. Dix hyperbola are produced on shot records after instantaneous rotations are followed by f-k filtering. To extract the instantaneous polarization, the traces are shifted back by the length of a moving window over which the calculation is performed. The instantaneous polarization direction is computed from the shifted data using the maximum eigenvector of the covariance matrix over the computation window. Split S‐waves are separated by the instantaneous rotation of the unshifted traces to the directions of the maximum eigenvectors determined for each position of the moving window. F-K filtering is required because of the presence of mode converted S‐waves and S‐waves produced by the explosive source near the time of detonation. Examples from synthetic data show that the method of instantaneous rotations will completely separate split S‐waves if the length of the moving window over which the calculation is performed is the length of the combined split wavelets. Separation may be achieved on synthetic data for wavelet delays as small as two sample intervals.

Some problems in velocity analysis for marine deep seismic profiles

The petroleum industry has identified deep seismic profiling as an additional means to assess frontier exploration areas. Those of us working within the British Institutions Reflection Profiling Syndicate (BIRPS) have recognized velocity analysis to be one of the most crucial steps in the data processing stream for deep seismie data. Although also true for conventional processing for sedimentary basins, the drastic differences in the depth, seismic velocity, and structural complexity of the target in the crust and upper mantIe force one to change the relative emphasis placed on the various aspects of velocity analysis.

Deep seismic surveys in the Mediterranean Sea

As part of a European multinational collaboration, 1104 km of deep seismic reflection data were collected in the Mediterranean Sea during February and March 1992 under the technical supervision of the British Institutions Reflection Profiling Syndicate (BIRPS), based at the University of Cambridge. The surveys were centered over the southern Ionian Sea between Italy and Greece and over the Valencia trough and Balearic ridge offshore Spain (Figure 1).Principal funding for data acquisition was provided by the European Economic Community under the auspices of Project STREAMERS and by the Consejo Superior de Investigaciones Cientificas (CSIC) in Barcelona, respectively. The STREAMERS Project, coordinated by Alfred Hirn at the Institut de Physique du Globe de Paris, is based on a collaboration between the Institut Physique du Globe de Paris, Istituto di Miniere e Geofisica Applicata Universita' Degli Studi Trieste, Public Petroleum Corporation of Greece, the University of Athens, the University of Lisbon, the CSIC, and the BIRPS team (Universities of Cambridge, College Wales, East Anglia, Leicester, and London).

Marine seismic sources used for deep seismic reflection profiling

With the continuing interest shown by the oil industry in the ability of deep seismic profiling to image structure throughout the entire crust, it seems appropriate to summarize what BIRPS (British Institutions Reflection Profiling Syndicate) has learnt about acquisition parameters from a decade of first pioneering and then developing deep seismic profiling at sea. Though this paper will concentrate on the seismic source, the influences of the streamer and of recording filters are also discussed.

Oceanic crust deep seismic survey

In September 1991, the British Institutions Reflection Profiling Syndicate (BIRPS) collected 578 km of deep seismic reflection profiles over the oceanic crust beneath the Cape Verde abssyal plain in approximately 4900 m of water (Fig. 1). The survey, under the direction of J. H. McBride, was undertaken in response to a proposal made by R. S. White at the 1990 BIRPS open syndicate meeting in Birmingham, England, and was acquired using GECO‐PRAKLA'S M/V Bin Hai 511. The survey consisted of two strike lines parallel to magnetic sea‐floor lineations and nine orthogonal crossing lines oriented parallel to the spreading direction (Fig. 2). Adjacent lines are spaced at 4 km. For the first time, this provides the ability to map oceanic crust in “3D,” since the line spacing is less than or equal to the Fresnel‐zone diameter for the lower crust.

Crustal structure of the central and southern North Sea from BIRPS deep seismic reflection profiling

Through the generous gift of shiptime on M/V Mobil Search in June 1987, BIRPS (British Institutions Reflection Profiling Syndicate) was able to acquire nearly 1500 km of deep seismic profiles recorded to 16s TWT in a regional survey across the central and southern North Sea. Reflective lower crust beneath the southern North Sea basin gives way laterally to a zone of mid-crustal reflections within the London–Brabant platform. These mid-crustal reflectors are interpreted as due to crustal shearing, although whether related to stretching during basin formation or to some earlier event remains enigmatic. Sub-crustal, SW-dipping reflections are observed at the edge of the London–Brabant platform. Across the mid-North Sea High, N–S profiles show distinctive patterns of lower-crustal reflectivity that indicate lateral variability in structure and character on a scale of 30–50 km. These are interpreted as crustal units relating to the Iapetus suture developed during the Caledonian orogeny. They may have been modified, however, during Carboniferous basin development, or subsequently. The absence of any distinctive sub-crustal reflectors associated with the Iapetus Suture, where a Caledonian subduction zone should have existed, tends to suggest that sub-crustal reflections observed elsewhere around Britian are not subduction related but are more likely to be from younger faults or shear zones relating to lithosphere extension and basin formation. Onshore wide-angle recording in northern England of the marine seismic source produced good quality data. The high resolution obtained has revealed details of mid-crust (PcP) and Moho (PmP) reflections, from around 18 and 30 km depth respectively, not observed before in this area. Both reflectors show events of laterally variable reflectivity that appear as bands of discontinuous reflection segments.

Reflection‐diffraction seismic pattern at crustal suture zones

Seismic reflection profiling across strong dip (more than 25°) suture zones between different crustal terranes or provinces reveals a distinct seismic reflectivity pattern of dipping reflections and associated diffractions. Suture zones in areas dominated by thin‐skinned tectonics do not show this pattern. Profiles from southern Germany (Deutsches Kontinentales Reflexionsseismisches Programm), Great Britain (British Institutions Reflection Profiling Syndicate) and North America (Consortium for Continental Reflection Profiling and U.S. Geological Survey) crossing major sutures are examined with respect to dipping reflections in the upper crust and accompanying diffractions in the lower crust. The strong resemblance of seismic patterns suggests a similar origin for these structures.

Seismic images of continental lithosphere

Seismic reflection profiles in USA and West Germany over thirty years ago showed strong reflections from the lower crust but technical advances through the 1970s were needed for the method to image the continental lithosphere. The British Institutions Reflection Profiling Syndicate, BIRPS, found advantage in working offshore and has obtained over 12,000 km of profiles around Britain during the past decade, giving the densest regional coverage anywhere. Reflections are observed from strata in sedimentary basins, from low angle faults that can be followed from surface to mid-crust, from a laterally variable reflective zone in the lower crust, from the Moho and from fault-like features in the upper mantle. There is evidence around Britain that faults bounding sedimentary basins are older structures which have been reactivated. It is argued that lower crustal reflectivity around Britain is mainly due to anastomosing ductile shears which accommodate extension in the lower crust commensurate with extension in the upper crust by faulting and block rotation. There is also evidence of reflections preserved from older orogenic features, so that reflections interpreted as extensional ductile shears in the lower crust may also derive from older features that have been reactivated. Most reflections in the lower crust arise from rocks that have been highly strained. Evidence of lateral variability in the reflective character of the Moho suggests that the Moho has been actively involved in the structural evolution of the lithosphere. Upper mantle reflections are interpreted as shear zones which transfer crustal deformation through the lithosphere.

Reflections from mantle fault zones around the British Isles

Research Article| June 01, 1990 Reflections from mantle fault zones around the British Isles Catherine A. Flack; Catherine A. Flack 1British Institutions Reflection Profiling Syndicate (BIRPS), Bullard Laboratories, Madingley Road, Cambridge CB3 0EZ, England Search for other works by this author on: GSW Google Scholar Simon L. Klemperer; Simon L. Klemperer 1British Institutions Reflection Profiling Syndicate (BIRPS), Bullard Laboratories, Madingley Road, Cambridge CB3 0EZ, England Search for other works by this author on: GSW Google Scholar Susan E. McGeary; Susan E. McGeary 1British Institutions Reflection Profiling Syndicate (BIRPS), Bullard Laboratories, Madingley Road, Cambridge CB3 0EZ, England Search for other works by this author on: GSW Google Scholar David B. Snyder; David B. Snyder 1British Institutions Reflection Profiling Syndicate (BIRPS), Bullard Laboratories, Madingley Road, Cambridge CB3 0EZ, England Search for other works by this author on: GSW Google Scholar Mike R. Warner Mike R. Warner 1British Institutions Reflection Profiling Syndicate (BIRPS), Bullard Laboratories, Madingley Road, Cambridge CB3 0EZ, England Search for other works by this author on: GSW Google Scholar Geology (1990) 18 (6): 528–532. https://doi.org/10.1130/0091-7613(1990)018<0528:RFMFZA>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Catherine A. Flack, Simon L. Klemperer, Susan E. McGeary, David B. Snyder, Mike R. Warner; Reflections from mantle fault zones around the British Isles. Geology 1990;; 18 (6): 528–532. doi: https://doi.org/10.1130/0091-7613(1990)018<0528:RFMFZA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract British Institutions Reflection Profiling Syndicate (BIRPS) deep seismic reflection surveys show that the upper mantle around the British Isles is reflective, exhibiting discrete, isolated reflecting zones within an otherwise seismically transparent mantle. There are 20 known occurrences of reflectors within the upper mantle across the continental shelf of the British Isles, many delimited by intersecting or closely spaced profiles. Most of the mantle reflectors have similar reflection characteristics: they dip 10° to 30° and are thin (∼0.5 s [∼2 km]) and discrete. The geologic history of the continental shelf around the British Isles (an area 1000 x 1000 km) is complex, and the tectonic settings of these reflectors vary. Each mantle reflector is associated with a major zone of deformation in the crust. This association, the dips of the reflectors, and their high reflectivity all indicate a structural origin. The BIRPS mantle reflectors include probable early Paleozoic thrusts and Mesozoic normal faults. In contrast to BIRPS data, deep reflection profiles in other areas of the world, in a variety of geologic settings, have only rarely image reflectors within the upper mantle This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Short Paper: Seismic reflection evidence for the location of the Iapetus suture west of Ireland

A new deep seismic profile recorded west of Ireland by the British Institutions’ Reflection Profiling Syndicate (BIRPS) images prominent north-dipping reflectors west of the Shannon estuary. Qualitatively similar north-dipping reflectors have been imaged on previous BIRPS profiles recorded across the Solway Line both east and west of Britain, and have there been interpreted as structures related to the Iapetus suture. By analogy with these other north-dipping reflectors, and because the newly discovered reflectors lie close to previously hypothesized locations of the Iapetus suture, the structures seen on the new BIRPS profile are here interpreted as representing part of the Iapetus suture zone.

Evidence for shear zones in the lower crust offshore Britain

Lower crustal reflections seen on British Institutions Reflection Profiling Syndicate (BIRPS) deep seismic reflection data, recorded offshore the United Kingdom, are commonly short, convex‐up, and crosscutting. Consequently, the lower crust should not be described as layered, as much of the reflecting structure is not fully resolved and may be quite complex. Moreover, the lower crustal reflective zone (LCRZ) is not a uniformly reflective layer, but contains reflective bands that wrap around nonreflective (“transparent”) zones. Because transparent zones probably correspond to a lack of a reflecting fabric, understanding why these features are unreflective may help constrain the cause of the reflectivity of the lower crust. Although transparent zones may have a variety of explanations (e.g., large shear pods or frozen magma bodies), the geometry of reflective bands and transparent zones is perhaps best explained by the geometry of shear zones and low‐strain lozenges predicted both by combining theoretical lithospheric strength profiles with slip‐line field theory and by drawing analogies with structures developed in highly tectonised high‐grade metamorphic terrains. This interpretation implies that lower crustal reflections may be from shear zones and also has implications for the way the lower crust deforms. In particular, extension may be accommodated by the relative movement of low‐strain lozenges along intervening zones of simple shear. The lower crust may be stretched during extension, but it must also transfer deformation between the upper crust and the mantle. The observation on BIRPS data of mantle reflections, interpreted as mantle shear zones, implies that deformation in the mantle is localised. However, the manue reflections are never colinear with faults in the upper crust, requiring, at least locally, a component of sub‐horizontal bulk strain within the lower crust, which may greatly increase the amount of shearing therein and hence perhaps may increase the reflectivity of the LCRZ.

The Continental Crust: A Geophysical Approach

Nearly 80 years ago, Yugoslavian seismologist Andrija Mohorovicic recognized, while studying a Balkan earthquake, that velocities of seismic waves increase abruptly at a few tens of kilometers depth , giving rise to the seismological definition of the crust. Since that discovery, many studies concerned with the nature of both the continental and oceanic crusts have appeared in the geophysical literature.Recently, interest in the continental crust has cascaded. This is largely because of an infusion of new data obtained from major reflection programs such as the Consortium for Continental Reflection Profiling (COCORP) and British Institutions Reflection Profiling Syndicate (BIRPS) and increased resolution of refraction studies. In addition, deep continental drilling programs are n ow in fashion. The Continental Crust: A Geophysical Approach is a summary of present knowledge of the continental crust. Meissner has succeeded in writing a book suited to many different readers, from the interested undergraduate to the professional. The book is well documented , with pertinent figures and a complete and up‐to‐date reference list.

BIRPS seeks deep geological proposals

The Deep Geology Committee of the National Environment Research Council (NERC) is inviting interested scientists to submit proposals for research to complement the data being gathered by the British Institutions Reflection Profiling Syndicate (BIRPS).BIRPS was established at Cambridge University (Cambridge, U.K.) in 1981 by NERC to study the lower crust and upper mantle. So far it has collected more than 10,000 km of reflection profiles on the continental shelf near the United Kingdom, using 15‐s two‐way travel times that measure to a depth of about 50 km.

Iapetus suture located beneath the North Sea by BIRPS deep seismic reflection profiling

The Iapetus suture, one of the more fundamental geologic boundaries of the British Isles, has been located beneath the North Sea by deep seismic reflection profiling carried out by the British Institutions Reflection Profiling Syndicate (BIRPS). Reflection profiling and magnetotelluric sounding have previously been used to infer the position of the Iapetus suture beneath the Irish Sea and the Southern Uplands, but the present study provides the first direct evidence for the location of the Iapetus suture east of Britain. A comparison of the seismic reflection profiles over the Iapetus suture east and west of Britain shows variations in the dip of the suture, which steepens to the northeast beneath the North Sea. The comparison also reveals unexpected changes in lower crustal reflectivity along the strike of the suture and suggests that there may be no straightforward relation in this area between the crustal reflectivity and the crustal age.

Seismic profiling the continental lithosphere

Deep seismic-reflection profiling is successfully being used worldwide to study the structure of the continental crust1–7. The MOIST8 profile recorded by BIRPS (British Institutions Reflection Profiling Syndicate) was the first to show that the structure of the upper mantle could also be imaged given a powerful source and long recording times. BIRPS has recently acquired an ultra-deep seismic reflection line, DRUM (Deep Reflections from the Upper Mantle). The DRUM line was designed specifically to investigate the reflectivity of the lower continental lithosphere and was therefore recorded to a two-way-time (TWT) of 30 s, giving a depth of penetration into the lithosphere of ∼ 110 km. This profile has now revealed strong reflections which are unequivocally from the lower lithosphere, well below the base of the crust, and which are, as far as we are aware, the deepest and most continuous structures imaged in the upper mantle by multi-channel seismic-reflection profiling.