Cookies

We use cookies to ensure that we give you the best experience on our website. You can change your cookie settings at any time. Otherwise, we'll assume you're OK to continue.

Durham University

Department of Earth Sciences

Profile

Publication details for Professor Christine Peirce

Peirce, C., Sinha, M., Topping, S. & Gill, C. (2007). Morphology and genesis of slow-spreading ridges - seabed scattering and seismic imaging within the oceanic crust. Geophysical Journal International 168(1): 59-89.

Author(s) from Durham

Abstract

A grid of 32 across-axis and five axis-parallel multichannel seismic (MCS) reflection profiles were acquired at an axial volcanic ridge (AVR) segment at 57� 45'N, 32� 35'W on the slow-spreading Reykjanes Ridge, Mid-Atlantic Ridge, to determine the along-axis variation and geometry of the axial magmatic system and to investigate the relationship between magma chamber structure, the along-axis continuity and segmentation of melt supply to the crust, the development of faulting and the thickness of oceanic layer 2A.

Seismic reflection profiles acquired at mid-ocean ridges are prone to being swamped by high amplitude seabed scattered noise which can either mask or be mistaken for intracrustal reflection events. In this paper, we present the results of two approaches to this problem which simulate seabed scatter and which can either be used to remove or simply predict events within processed MCS profiles.

The 37 MCS profiles show clear intracrustal seismic events which are related to the structure of oceanic layer 2, to the axial magmatic system and to the faults which dismember each AVR as it ages through its tectono-magmatic life cycle and which form the median valley walls. The layer 2A event can be mapped around the entirety of the survey area between 0.1 and 0.5 s two-way traveltime below the seabed, being thickest at AVR centres, and thinning both off-axis and along-axis towards AVR tips. Both AVR-parallel and ridge-parallel trends are observed, with the pattern of on-axis layer 2A thickness variation preserved beneath relict AVRs which are rafted off-axis largely intact.

Each active AVR is underlain by a mid-crustal melt lens reflection extending almost along its entire length. Similar reflection events are observed beneath the offset basins between adjacent AVRs. These are interpreted as new AVRs at the start of their life cycle, developing centrally within the median valley. The east�west spacings of relict AVRs and offset basins is 5�7 km, corresponding to a life span of the order of 0.5�0.7 Myr, during which AVRs appear to undergo multiple 20�60 Kyr tectono-magmatic cycles.

References

Anderson, R.N. et al., 1982. DSDP hole 504B, the first reference section
over 1 km through layer 2 of the oceanic crust, Nature, 300, 589�
594.
Applegate,B.&Shor, A.N., 1994. The northern Mid-Atlantic and Reykjanes
Ridges: Spreading centre morphology between 55◦ 50N and 63◦ 00N,
J. geophys. Res., 99, 17 935�17 956.
Auzende, J.-M. et al., 1996. Recent tectonic, magmatic and hydrothermal
activity on the East Pacific Rise between 17◦S and 19◦S: submersible
observations, J. geophys. Res., 101, 17 995�18 010.
Barclay, A.H., Toomey, D.R. & Solomon, S.C., 1998. Seismic structure and
crustal magmatism at the Mid-Atlantic Ridge, 35◦N, J. geophys. Res., 103,
17 827�17 844.
Barclay, A.H., Toomey,D.R.&Solomon, S.C., 2001. Microearthquake characteristics
and crustal V p/V s structure at the Mid-Atlantic Ridge, 35◦N,
J. geophys. Res., 103, 17 827�17 844.
Bazin, S. et al., 2001. Three-dimensional shallowcrustal emplacement at the
9◦03�overlapping spreading centre on the East Pacific Rise: correlations
between magnetization and tomographic images, J. geophys. Res., 106,
16 101�16 117.
Becker, K. et al., 1989. Drilling deep into young oceanic crust, Hole 504B,
Costa Rica Rift, Rev. Geophys., 27, 79�102.
Blacic, T.M., Ito, G., Canales, J.P., Detrick, R.S. & Sinton, J., 2004.
Constructing the crust along the Galapagos spreading centre 91.3◦�
95.5◦W: correlation of seismic layer 2A with axail magma lens
and topographic characteristics, J. geophys. Res., 109, B10310,
doi:10.1029/2004JB003066.
Burnett, M.S., Caress, D.W. & Orcutt, J.A., 1989. Tomographic image of
the magma chamber at 12◦50N on the East Pacific Rise, Nature, 339,
206�208.
Calvert, A.J., 1995. Seismic evidence for a magma chamber beneath the
slow-spreading Mid-Atlantic Ridge, Nature, 377, 410�414.
Calvert, A.J., 1997. Backscattered coherent noise and seismic reflection
imaging of the oceanic crust: an example from the rift valley of the Mid-
Atlantic Ridge at 23◦N, J. geophys. Res., 102, 5119�5133.
Canales, J.P. & Detrick, R.S., 1998. Segment-scale crustal structure variations
within the rift mountains of the Mid-Atlantic Ridge (35◦N), Ann.
Geophys., 16(1), 292.
Cao, S.H. & Kennett, B.L.N., 1989. Reflection seismograms in a 3-D elastic
model: an isochronal approach, Geophys. J. Int., 99(1), 63�80.
Carbotte, S.M.&Macdonald, K.C., 1990. Causes of variation in fault-facing
direction on the ocean floor, Geology, 18, 749�752.
Carbotte, S.M., Mutter, J.C. & Xu, L., 1997. Contribution of volcanism and
tectonism to axial flank morphology of the southern East Pacific Rise, 17◦
10�17◦ 40S, from a study of layer 2A geometry, J. geophys. Res., 102,
10 165�10 184.
Caress, D.W., Burnett, M.S. & Orcutt, J.A., 1992. Tomographic image of the
axial low-velocity zone at 12◦50N on the East Pacific Rise, J. geophys.
Res., 97, 9243�9263.
Christeson, G.L., Purdy, G.M.&Fryer, G.J., 1992. Structure of young upper
crust at the East Pacific Rise at 930◦N, Geophys. Res. Lett., 19, 1045�
1048.
Christeson, G.L., Kent, G.M., Purdy, G.M. & Detrick, R.S., 1996. Extrusive
thickness variability at the East Pacific Rise, 9◦�10◦N: constraints from
seismic techniques, J. geophys. Res., 101, 2859�2973.
Collier, J.S. & Sinha, M.C., 1990. Seismic images of a magma chamber
beneath the Lau Basin back-arc spreading centre, Nature, 346, 646�648.
Collier, J.S.&Sinha, M.C., 1992a. TheValu Fa Ridge: the pattern of volcanic
activity at a back-arc spreading centre, Marine Geology, 104, 243�263.
Collier, J.S. & Sinha, M.C., 1992b. Seismic mapping of a magma chamber
beneath theValu Fa Ridge, Lau Basin, J. geophys. Res., 97, 14 031�14 053.
Collins, J.A., Brocher, T.M. & Purdy, G.M., 1998. Seismic reflection structure
of the upper oceanic crust: implications from DSDP/ODP hole 504B,
Panama Basin, Proceedings of the Ocean Drilling Programme, Scientific
Results, 111, 117�191.
Cudrack, C.F. & Clowes, R.M., 1993. Crustal structure of Endeavour Ridge
Segment, Juan de Fuca Ridge, from detailed seismic refraction survey,
J. geophys. Res., 98, 6329�6349.
Day, A.J., Peirce, C. & Sinha, M.C., 2001. Three-dimensional crustal structure
and magma chamber geometry at the intermediate-spreading, backarc
Valu Fa Ridge, Lau Basin � results of a wide-angle seismic tomographic
inversion, Geophys. J. Int., 146, 31�52.
Detrick, R.S., Buhl, P., Vera, E.E., Mutter, J.A., Orcutt, J.A., Madsen, J.
& Brocher, T., 1987. Multichannel seismic imaging of a crustal magma
chamber along the East Pacific Rise, Nature, 326, 35�41.
Detrick, R.S., Mutter, J.C., Buhl, P. & Kim, I.I., 1990. No evidence from
multichannel reflection data for a crustal magma chamber in the MARK
area on the Mid-Atlantic Ridge, Nature, 347, 61�64.
Detrick, R.S., Harding, A.J., Kent, G.M., Orcutt, J.A., Mutter, J.C. & Buhl,
P., 1993. Seismic structure of the southern East Pacific Rise, Science, 259,
499�503.
Detrick, R.S., Collins, J., Stephen, R. & Swift, S., 1994. In situ evidence for
the nature of the seismic layer 2/3 boundary in oceanic crust, Nature, 370,
288�290.
Detrick, R.S. et al., 1997. Mid-Atlantic Ridge bullseye experiment: a seismic
investigation of segment-scale crustal heterogeneity at a slow-spreading
ridge, InterRidge News, 6(1), 27�32.
Dunn, R.A., Toomey, D.R. & Solomon, S.C., 2000. Three-dimensional seismic
structure and physical properties of the crust and shallow mantle
beneath the East Pacific Rise at 9◦ 30N, J. geophys. Res., 105, 23 537�
23 555.
Dunn, R.A., Leki�c, V., Detrick, R.S. & Toomey, D.R., 2005. Threedimensional
seismic structure of the Mid-Atlantic Ridge (35◦N): evidence
for focused melt supply and lower crustal dyke injection, J. geophys. Res.,
110, doi:10.1029/2004JB003473.
Escartin, J. & Lin, J., 1995. Ridge offsets, normal faulting, and gravity
anomalies of slow spreading ridges, J. geophys. Res., 100, 6163�
6177.
Escartin, J.,Cowie, P.A., Searle, R.C., Allerton, S., Mitchell,N.C., MacLeod,
C.J.&Slootweg, A.P., 1999. Quantifying tectonic strain and magmatic accretion
at a slowspreading ridge segment, Mid-Atlantic Ridge, 29 degrees
N, J. geophys. Res., 104, 10 421�10 437.
Francheteau, J., Armijo, R., Chemin�ee, J.L., H�ekinian, R., Lonsdale, P. &
Blum, N., 1992. Dyke complex of the East Pacific Rise exposed in the
walls of the Hess Deep and the structure of the upper oceanic crust, Earth
planet. Sci. Lett., 111, 109�121.
Fuchs, K. & M�uller, G., 1971. Computation of synthetic seismograms with
the reflectivity method and comparison with observations, Geophys. J. R.
astr. Soc., 23, 417�433.
Gardiner, A.B., 2003. Segmentation and cycles of crustal accretion at midocean
ridges: a study of the Reykjanes Ridge, unpublished PhD thesis,
University of Durham, p. 177.
Greer, A., Sinha, M.C. & MacGregor, L.M., 2002. Joint effective medium
modelling for co-incident seismic and electromagnetic data, its application
to studies of porosity structure at mid-ocean ridge crests, Lithos Science
Report, 4, 103�120.
Grevemeyer, I., Kaul, N., Villinger, H. & Weigel, W., 1997. Hydrothermal
circulation and the seismic structure of upper oceanic crust: results from
the EXCO cruise, InterRidge News, 6, 27�30.
Harding, A.J., Orcutt, J.A., Kappus, M.E., Vera, E.E., Mutter, J.C., Buhl, P.,
Detrick, R.S. & Brocher, T., 1989. The structure of young oceanic crust at
13◦N on the East Pacific Rise from expanding spread profiles, J. geophys.
Res., 94, 12 163�12 196.
Harding, A.J., Kent, G.M. & Orcutt, J.A., 1993. A multichannel seismic
investigation of upper crustal structure at 9◦N on the East Pacific Rise:
implications for crustal accretion, J. geophys. Res., 98, 13 925�13 944.
Heinson, G.S., Constable, S.C. & White, A., 2000. Episodic melt transport
at a mid-ocean ridge inferred from magnetotelluric sounding, Geophys.
Res. Letts., 27(15), 2317�2320.
Hilterman, F.J., 1970. Three-dimensional seismic modelling, Geophysics,
35(6), 1020�1037.
Hobbs, R.W., Tong, C.H. & Pye, J.W., 2003. Modelling and processing of
3-D seismic data collected over the overlapping spreading centre on the
East Pacific Rise at 903N, Special Publication of the Geological Society
of London, 212, 251�259.
Hooft, E.E.E., Schouten, H. & Detrick, R.S., 1996. Constraining crustal
emplacement processes from the variation in seismic layer 2A thickness
at the East Pacific Rise, Earth planet. Sci. Lett., 142, 289�309.
Hooft, E.E.E., Detrick, R.S.&Kent, G.M., 1997. Seismic structure and indicators
of magma budget along the southern East Pacific Rise, J. geophys.
Res., 102, 27 319�27 340.
Hussenoeder, S.A., Collins, J.A., Kent, G.M.&Detrick, R.S., 1996. Seismic
analysis of the axial magma chamber reflector along the southern East
Pacific Rise from conventional reflection profiling, J. geophys. Res., 101,
22 087�22 105.
Hussenoeder, S.A., Detrick, R.S., Kent, G.M., Schouten, H. & Harding,
A.J., 2002a. Fine-scale seismic structure of young upper crust at
17◦20S on the fast spreading East Pacific Rise, J. geophys. Res., 107,
doi:10.1029/2001JB001688, EPM 2.
Hussenoeder, S.A., Kent, G.M. & Detrick, R.S., 2002b. Upper crustal
seismic structure of the slow spreading Mid-Atlantic Ridge, 35◦N:
constraints on volcanic emplacement processes, J. geophys. Res., 107,
doi:10.1029/2001JB001691, EPM 1.
Kappus, M.E., Harding, A.J. & Orcutt, J.A., 1995. A baseline for upper
crustal velocity variations along the East Pacific Rise at 13◦N, J. geophys.
Res., 100, 6143�6161.
Keeton, J.A., Searle, R.C., Parsons, B., White, R.S., Murton, B.J., Parson,
L.M., Peirce, C.&Sinha, M.C., 1997. Bathymetry of the Reykjanes Ridge,
Marine geophys. Res., 19, 55�64.
Kent, G.M., Harding, A.J. & Orcutt, J.A., 1990. Evidence for a smaller
magma chamber beneath the East Pacific Rise at 9◦30N, Nature, 344,
650�653.
Kent, G.M., Harding, A.J. & Orcutt, J.A., 1993a. Distribution of magma
beneath the East Pacific Rise between the Clipperton transform and
the 9◦17N deval from forward modelling of common depth point data,
J. geophys. Res., 98, 13 945�13 969.
Kent, G.M., Harding, A.J. & Orcutt, J.A., 1993b. Distribution of magma
beneath the East Pacific Rise near the 9◦03Noverlapping spreading centre
from forward modelling of common depth point data, J. geophys. Res.,
98, 13 971�13 996.
Kent, G.M., Harding, A.J., Orcutt, J.A., Detrick, R.S., Mutter, J.C. & Buhl,
P., 1994. Uniform accretion of oceanic crust south of the Garrett transform
at 14◦ 15S on the East Pacific Rise, J. geophys. Res., 99, 9097�
9116.
Kent, G.M., Kim, I.I., Harding, A.J., Detrick, R.S., Orcutt, J.A., 1996. Suppression
of seafloor scattered energy using a dip move-out approach �
application to the mid-ocean ridge environment, Geophysics, 61(3), 821�
834.
Kent, G.M. et al., 2000. Evidence from three-dimensional seismic reflectivity
images for enhanced melt supply beneath mid-ocean ridge discontinuities,
Nature, 406, 614�618.
Kong, L.S.L., Solomon, S.C. & Purdy, G.M., 1992. Microearthquake characteristics
of a mid-ocean ridge along axis high, J. geophys. Res., 97,
1659�1685.
Langmuir, C.H., Bender, J.F. & Batiza, R., 1986. Petrological and tectonic
segmentation of the East Pacific Rise 5◦30N�14◦30N, Nature, 322, 422�
429.
Lee, S.-M. & Searle, R.C., 2000. Crustal magnetisation of the Reykjanes
Ridge and implications for its along-axis variability and the formation of
axial volcanic ridges, J. geophys. Res., 105, 5907�5930.
Macdonald, K.C., 1982. Mid-ocean ridges: fine-scale tectonic, volcanic and
hydrothermal processes within the plate boundary zone, Ann. Rev. Earth
Planet. Sci., 10, 155�190.
Macdonald, K.C., Sempere, J. & Fox, P.J., 1984. East Pacific Rise from
Siqueiros to Orinoco FZ: along strike continuity of axial neovolcanic zone
and structure and evolution of overlapping spreading centres, J. geophys.
Res., 87, 6049�6069.
Macdonald, K.C. et al., 1988. A new view of the mid-ocean ridge from the
behaviour of ridge-axis discontinuities, Nature, 335, 217�225.
MacGregor, L.M., 1997. Electromagnetic investigation of the Reykjanes
Ridge near 58◦N, unpublished PhD thesis, University of Cambridge,
p. 264.
MacGregor, L.M., Constable, S. & Sinha, M.C., 1998. The RAMESSES
experiment III: Controlled-source electromagnetic sounding of the Reykjanes
Ridge at 57◦ 45N, Geophys. J. Int., 135, 772�789.
Minshull, T.A., White, R.S., Mutter, J.C., Buhl, P., Detrick, R.S., Williams,
C.A.&Morris, E., 1991. Crustal structure at the Blake Spur Fracture zone
from expanding spread profiles, J. geophys. Res., 96, 9955�9984.
Murton, B.J. & Parson, L.M., 1993. Segmentation, volcanism and deformation
of oblique spreading centres: a qualitative study of the Reykjanes
Ridge, Tectonophysics, 222, 237�257.
Mutter, J.C. et al., 1995. Seismic images of active magma systems beneath
the East Pacific Rise between 17◦ 05 and 17◦ 35S, Science, 268, 391�
395.
Navin, D.A., 1996. Seismic investigation of crustal accretion at the slow
spreading Mid-Atlantic Ridge � the Reykjanes Ridge at 57◦45N, unpublished
PhD thesis, University of Durham, pp. 309.
Navin, D.A., Peirce, C. & Sinha, M.C., 1998. The RAMESSES experiment
� II. Evidence for accumulated melt beneath slow spreading ridge from
wide-angle refraction and multichannel reflection seismic profiles, Geophys.
J. Int., 135, 746�772.
Parmentier, E.M. & Phipps Morgan, J., 1990. Spreading rate dependence of
3-dimensional structure in oceanic spreading centres, Nature, 348, 325�
328.
Parson, L.M. et al., 1993. En echelon axial volcanic ridges at the Reykjanes
Ridge: a life cycle of volcanism and tectonics, Earth planet. Sci. Lett.,
117, 73�87.
Peirce, C. & Navin, D.A., 2002. The RAMESSES experiment � V. Crustal
accretion at axial volcanic segments � a gravity study at 57◦45N on the
slow-spreading Reykjanes Ridge, Geophys. J. Int., 148, 1�19.
Peirce, C. & Sinha, M.C., 1998. RAMESSES II � Reykjanes Ridge axial
melt experiment: structural synthesis from electromagnetics and seismic,
RRS Discovery 235c Cruise Report, unpublished, p. 38.
Peirce, C., Turner, I.M. & Sinha, M.C., 2001. Crustal structure, accretionary
processes and rift propagation: a gravity study of the intermediatespreading
Valu Fa Ridge, Lau Basin, Geophys. J. Int., 146, 53�
73.
Peirce, C., Gardiner, A. & Sinha, M.C., 2005. Temporal and spatial cyclicity
of accretion at slow-spreading ridges � evidence from the Reykjanes
Ridge, Geophys. J. Int., 163, 56�78.
Reston, T.J., Ranero, C.R., Ruoff, O., Perez-Gussinye,M. & Da�nobeitia, J.J.,
2004. Geometry of extensional faults developed at slow-spreading centres
from pre-stack depth migration of seismic reflection data in the Central
Atlantic (Canary Basin), Geophys. J. Int., 159, 591�606.
Rohr, K.M.M., Milkereit, B. & Yorath, C.J., 1988. Asymmetric deep
crustal structure across the Juan de Fuca Ridge, Geology, 16, 533�
537.
Sandwell, D.T. & Smith, W.H.F., 1997. Marine gravity anomaly from
Geosat and ERS-1 satellite Altimetry, J. geophys. Res., 102, 10 039�
10 054.
Searle, R.C., Field, P.R. & Owens, R.B., 1994. Segmentation and a nontransform
ridge offset on the Reykjanes Ridge near 58◦N, J. geophys.
Res., 99, 24 159�24 172.
Searle, R.C., Keeton, J.A., Owens, R.B., White, R.S., Mecklenburgh, R.,
Parsons, B. & Lee, S.-M., 1998. The Reykjanes Ridge: Structure and
tectonics of a hot-spot influenced, slow-spreading ridge, from multibeam
bathymetry, gravity and magnetic investigations, Earth planet. Sci. Lett.,
160, 463�478.
Shaw, P.R. & Lin, J., 1993. Causes and consequences of variations in
faulting style at the Mid-Atlantic Ridge, J. geophys. Res., 98, 21 839�
21 851.
Sinha, M.C., Peirce, C. & Constable, S., 1994. An integrated geophysical
investigation of the axial volcanic region of the Reykjanes
Ridge at 57◦45N, RRS Charles Darwin 81 Cruise report, unpublished,
p. 39.
Sinha, M.C., Navin,D.A., MacGregor, L.M., Constable, S., Peirce, C., White,
A., Heinson, G. & Inglis, M.A., 1997. Evidence for accumulated melt beneath
the slow-spreading Mid-Atlantic Ridge, Phil. Trans. R. Soc. Lond.,
A, 355, 233�253.
Sinha, M.C., Constable, S., Peirce, C., White, A., Heinson, G., MacGregor,
L.M. & Navin, D.A., 1998. Magmatic processes at slow spreading ridges:
implications of the RAMESSES experiment, Mid-Atlantic Ridge at 57◦N,
Geophys. J. Int., 135, 731�745.
Sinton, J.M., Smaglik, S.M., Mahoney, J.J. & Macdonald, K.C., 1991. Magmatic
processes at superfast spreading mid-ocean ridges: glass compositional
variations along the East Pacific Rise 13◦�23◦S, J. geophys. Res.,
96, 6133�6155.
Smallwood, J.R. & White, R.S., 1998. Crustal accretion at the Reykjanes
Ridge, 61◦�62◦N, J. geophys. Res., 103, 5185�5201.
Sohn, R.A., Webb, S.C. & Hildebrand, J.A., 2004. Fine-scale seismic structure
of the shallow volcanic crust on the East Pacific Rise at 9◦50N, J.
geophys. Res., 109, B12104, doi:10.1029/2004JB003152.
Taylor, R.N., Murton, B.J. & Thirwall, M.F., 1995. Petrographic and geochemical
variation along the Reykjanes Ridge, 57◦N�59◦N, J. geol. Soc.
Lond., 152, 1031�1037.
Tong, C.H. et al., 2002. Asymmetric melt sills and upper crustal construction
beneath overlapping ridge segments: implications for the development of
melt sills and ridge crests, Geology, 30(1), 83�86.
Toomey, D.R., Purdy, G.M., Solomon, S.C. & Wilcock, W.S.D., 1990. The
three-dimensional seismic velocity structure of the East Pacific Rise near
latitude 9◦30N, Nature, 347, 639�645.
Toomey, D.R., Solomon, S.C. & Purdy, G.M., 1994. Tomographic imaging
of the shallow crustal structure of the East Pacific Rise at 9◦30N, J.
geophys. Res., 99, 24 135�24 157.
Topping, S., 2002. RAMESSES II: seismic reflections at the Mid-Atlantic
Ridge from analysis of real and synthetic data, unpublished PhD thesis,
University of Cambridge, p. 196.
Trorey, A.W., 1970. A simple theory for seismic diffractions, Geophysics,
35(5), 762�784.
Turner, I.M., Peirce, C. & Sinha, M.C., 1999. Seismic imaging of the axial
region of the Valu Fa Ridge, Lau Basin � the accretionary processes of an
intermediate back-arc spreading ridge, Geophys. J. Int., 138, 495�519.
Vera, E.E. & Diebold, J.B., 1994. Seismic imaging of oceanic layer 2A
between 9◦30N and 10◦N on the East Pacific Rise from two-ship wideaperture
profiles, J. geophys. Res., 99, 3031�3041.
Vera, E.E., Mutter, J.C., Buhl, P., Orcutt, J.A., Harding, A.J., Kappus, M.E.,
Detrick, R.S. & Brocher, T.M., 1990. The structure of 0 to 0.2 Ma old
oceanic crust at 9◦N on the East Pacific Rise from expanded spread profiles,
J. geophys. Res., 95, 15 529�15 556.
Wessel, P. & Smith, W.H.F., 1995. New version of the Generic Mapping
Tools released, EOS, Trans. Am. geophys. Un., 76, 329.
White, D.J. & Clowes, R.M., 1990. Shallow crustal structure beneath the
Juan de Fuca Ridge from 2-D seismic refraction tomography, Geophys. J.
Int., 100, 349�367.
Wilcock, W.S.D., Solomon, S.C., Toomey, D.R. & Purdy, G.M., 1992. The
seismic attenuation structure of a fast spreading mid-ocean ridge, Science,
258, 1470�1473.
Wild, A.J. & Hudson, J.A., 1998. A geometrical approach to the elastic
complex screen, J. geophys. Res., 103, 707�725.
Wild, A.J., Hobbs, R.W. & Frenje, L., 2000. Modelling complex media: an
introduction to the phase-screen method, Phys. Earth planet Inter., 120,
219�225.