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


Publication details for Prof Roger Clive Searle

Searle, R. C., Francheteau, J. & Armijo, R. (2006). Compressional deformation north of the Easter microplate: a manned submersible and seafloor gravity investigation. Geophysical Journal International 164(2): 359-369.

Author(s) from Durham


We have investigated an E-W compressional ridge in 0.9 Ma lithosphere of the Nazca Plate, just north of the Easter microplate on the East Pacific Rise, using a combination of visual observation and seabed gravity measurements from four manned submersible dives. Three of the dives made a 26 km long traverse across the ridge during which 14 gravity measurements were made. The observations confirm the presence of active thrust faulting on the 1.1 km high south face of the ridge. However, the gravity precludes the existence of a simple low angle thrust, and is only compatible with significant crustal shortening and thickening if the block to the south of the thrust has a lower density than the overriding block. Visual and sonar observations of pervasive fine-scale tectonism in this area lend some support to this idea. Alternatively there could be oblique thrusting on a high-angle fault with relatively little crustal shortening. In addition, a small degree of crustal shortening may take place in the form of buckling of an elastic or plastic lithosphere, though this cannot explain the strong asymmetry of the ridge, which we believe must imply faulting.


Anderson, R.N., Forsyth, D.W., Molnar, P. & Mammerickx, J., 1974. Fault plane solutions on the Nazca plate boundaries and the Easter plate, Earth planet. Sci. Lett., 24, 188–202.
Ballard, R.D. & Moore, J.E., 1997. Photographic Atlas of the Mid-Atlantic Ridge Rift Valley, 114 pp., Springer-Verlag, Heidelberg.
Bergeron, A. & Bonnin, J., 1991. The deep structure of Gorringe bank (NE
Atlantic) and its surrounding area, Geophys. J. Int., 105, 491–502.
Bird, R.T., Naar,D.F., Larson, R.L., Searle, R.C.&Scotese, C.R., 1998.
Plate tectonic reconstructions of the Juan Fernandez microplate:
transformation from internal shear to rigid rotation, J. geophys. Res., 103, 7049–7067.
Bull, J.M. & Scrutton, R.A., 1992. Seismic reflection images of intraplate deformation, central Indian Ocean, and their tectonic significance, J.
Soc. Lond., 149, 955–966.
Bull, J.M.,Martinod, J.&Davy, P., 1992. Buckling of the oceanic lithosphere from geophysical data and experiments, Tectonics, 11, 537–548.
Chamot-Rooke, N., Jestin, F., de Voogd, B. & the PHEDRE team, 1993.
Intraplate shortening in the central Indian Ocean from a 2100 km long north-south deep seismic reflection profile, Geology, 21, 1043–1046.
Cogn´e, J.P., et al., 1995. Large rotation of the Easter microplate as evidenced by oriented paleomagnetic samples from the ocean floor, Earth planet. Sci. Lett., 136, 213–222.
Delouis, B., Nicolas, A., Ildefonse, B. & Philip, H., 1998. Earthquake focal mechanism and oceanic thrust in Easter microplate analogy with Oman ophiolite, Geophys. Res. Lett., 25, 1443–1446.
Dziewonski, A.M., Chou, T.-A. &Woodhouse, J.H., 1981. Determination of earthquake source parameters from waveform data for studies of global and regional seismicity, J. geophys. Res., 86, 2825–2852.
Engeln, J.F. & Stein, S., 1984. Tectonics of the Easter plate, Earth planet. Sci. Lett., 68, 259–270.
Francheteau, J. et al., 1988. Pito and Orongo fracture zones: the northern and southern boundaries of the Easter microplate (southeast Pacific), Earth planet. Sci. Lett., 89, 363–374.
Francheteau, J. et al., 1994. Black smoker discovered, Pito Seamount near Easter microplate propagator tip, EOS, Trans. Am. geophys. Un., 75, 322.
Galindo-Zald´ıvar, J., Maldonado, A. & Schreider, A.A., 2003. Gorringe Ridge gravity and magnetic anomalies are compatible with thrusting at a crustal scale, Geophys. J. Int., 153, 586–594.
Girardeau, J. et al., 1998. Extensional tectonics in the Gorringe Bank rocks, eastern Atlantic Ocean: evidence of an oceanic ultra-low mantellic accreting centre, TerraNova, 10, 330–336.
Gordon, R.G., DeMets, C. & Argus, D.F., 1990. Kinematic constraints on distributed deformation in the equatorial Indian Ocean from present motion between the Australian and Indian plates, Tectonics, 9, 409–422.
Handschumacher, D.W., Pilger, R.H., Foreman, J.A. & Campbell, J.F., 1981.
Structure and evolution of the Easter plate, Memoir of the Geological Society of America, 154, 63–76.
Hayward, N.,Watts, A.B.,Westbrook, G.K. & Collier, J.S., 1999. A seismic reflection and GLORIA study of compressional deformation in the Gorringe Bank region, eastern North Atlantic, Geophys. J. Int., 138, 831–850.
Herron, E.M., 1972. Two small crustal plates in the South Pacific near Easter Island, Nature Physical Science, 240, 35–37.
Hey, R.N., Naar, D.F., Kleinrock, M.C., Phipps Morgan, W.J., Morales, E. & Schilling, J.-G., 1985. Microplate tectonics along a superfast seafloor spreading system near Easter Island, Nature, 317, 320–325.
Hey, R.N. et al., 2002. Preliminary attempt to characterize the rotation of seafloor in the Pito Deep area of the Easter microplate using a submersible magnetometer, Marine Geophysical Researches, 23, 1–12.
Larson, R.L. et al., 1992. Roller-bearing tectonic evolution of the Juan Fernandez microplate, Nature, 356, 571–576.
Luyendyk, B.P., 1984. On-bottom gravity profile across the East Pacific Rise crest at 21◦n, Geophysics, 49, 2166–2177.
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.
Marching, V. et al., 1992. Abschussbericht Geometsp 5 (So62), 565pp., Bundesanstalt f¨ur Gewissenschaften und Rohstoffe, Hanover.
Martinod, J. & Davy, P., 1992. Periodic instabilities during compression or extension of the lithosphere: 1, deformation modes from an analytical perturbation method, J. geophys. Res., 97, 1999–2014.
Masson, D.G., Cacchione, D.A. & Drake, D., 1989. Tectonic evolution of Gorda Ridge inferred from sidescan sonar images, Marine Geophysical Researches, 10, 191–204.
McAdoo, D.C. & Sandwell, D.T., 1985. Folding of the oceanic lithosphere, J. geophys. Res., 90, 8563–8569.
Morel, J. & Meghraoui, M., 1996. Gorringe-Alboran-Tell tectonic zone – a transpression system along the Africa-Eurasia plate boundary, Geology, 24, 755–758.
Naar, D.F. & Hey, R.N., 1989. Recent Pacific-Easter-Nazca plate motions, in Evolution of Mid Ocean ridges, pp. 9–30, ed. Sinton, J.M., American Geophysical Union, Washington, DC.
Naar, D.F. & Hey, R.N., 1991. Tectonic evolution of the Easter microplate, J. geophys. Res., 96, 7961–7973.
Naar, D.F. et al., 2004. Hydrothermal venting at Pito Seamount near Easter Island, in Mid-ocean ridges: hydrothermal interactions between the lithosphere and oceans: Geophysical Monongraph 148, eds German, C., Lin, J. & Parson, L., American Geophysical Union, Washington, DC.
Nettleton, L.L., 1939. Determination of density for reduction of gravimeter observations, Geophysics, 4, 176–183.
Neves, M.C., Searle, R.C.&Bott, M.H.P., 2003. Easter microplate dynamics, J. geophys. Res., 108, ETG14, doi:10.1029/2001JB000908, citation no.
Perram, L.J., Macdonald, K.C. & Miller, S.P., 1990. Deep-tow magnetics near 20◦s on the East Pacific Rise: a study of short wavelength anomalies at a very fast spreading center, Marine Geophysical Researches, 12, 235–245.
Purdy, G.M., 1975. The eastern end of the Azores-Gibraltar plate boundary, Geophys. J. R. astr. Soc., 43, 973–1000.
Rusby, R.I., 1992. Tectonic Pattern and history of the Easter Microplate, based on GLORIA and other geophysical data, PhD thesis, University of Durham.
Rusby, R.I. & Searle, R.C., 1993. Intraplate thrusting near the Easter microplate, Geology, 21, 311–314.
Rusby, R.I. & Searle, R.C., 1995. A history of the Easter microplate, 5.25 ma to present, J. geophys. Res., 100, 12 617–12 640.
Sartori, R., Torelli, L., Zitellini, N., Peis, D.&Lodolo, E., 1994.
Eastern segment of the Azores-Gibraltar plate boundary (central-eastern
Atlantic): an
oceanic plate boundary with diffuse compressional deformation, Geology, 22, 555–558.
Schouten, H., Klitgord, K.D. & Gallo, D.G., 1993. Edge-driven microplate kinematics, J. geophys. Res., 98, 6689–6701.
Searle, R.C., Rusby, R.I., Engeln, J., Zukin, J., Hunter, P.M., LeBas, T.P., Hoffman, H.-J. & Livermore, R., 1989. Comprehensive sonar imaging of the Easter microplate, Nature, 341, 701–705.
Searle, R.C., Bird, R.T., Rusby, R.I. & Naar, D.F., 1993. The development of two oceanic microplates: Easter and Juan Fernandez microplates, east pacific rise, J. geol. Soc. Lond., 150, 965–976.
Searle, R.C., Armijo, R. & Francheteau, J., 2003. Manned submersible and seafloor gravity investigation of a compressional ridge in young oceanic lithosphere near the Easter microplate, Geophysical Research Abstracts, 5, 06724.
Silver, 1971. Tectonics of the Mendocino triple junction, Geological Society of America Bulletin, 82, 2965–2978.
Talwani, M. & Heirtzler, J.R., 1964. Computation of magnetic anomalies caused by two-dimensional structures of arbitrary shape, Computers in the Mineral Industries1, Stanford University Publications in the Geological Sciences, 9, 464–480.
Tortella, D., Torne, M.&P´erez-Easta´un, 1997. Geodynamic evolution of the eastern segment of the Azores-Gibraltar zone: The Gorringe Bank and the Gulf of Cadiz region, Marine Geophysical Researches, 19, 211–230.
van Orman, J., Cochran, J.R.,Weissel, J.K.&Jestin, F., 1995. Distribution of shortening between the Indian and Australian plates in the central Indian Ocean, Earth planet. Sci. Lett., 133, 35–46.
Wallace, M.H. & Melosh, H.J., 1994. Buckling of a pervasively faulted lithosphere, Pure appl. Geophys., 142, 239–261.
Wang, X. & Cochran, J.R., 1993. Gravity anomalies, isostasy, and mantle flow at the East Pacific Rise crest, J. geophys. Res., 98, 19 505–519 532.
Weissel, J.K., Anderson, R.N. & Geller, C.A., 1980. Deformation of the Indo-Australian plate, Nature, 287, 284–291.
Wilson, D.S., 1989. Deformation of the so-called Gorda plate, J. geophys.
Res., 94, 3065–3075.
Zukin, J.H.&Francheteau, J., 1990. A tectonic test of instantaneous kinematics of the Easter microplate, Oceanologica Acta, special vol. 10, 183–198.