Abstract
The studies of Azores seismicity generally show shocks with either normal faulting or right-lateral strike-slip along the ESE direction, compatible with a eastward relative motion of the Eurasian (EU) relative to the African (AF) plate. However, the 1 January 1980 earthquake was interpreted as a clear left-lateral strike-slip shock along the N150E direction. This pattern is difficult to explain in terms of the relative motion between the EU, AF and North American (NA) plates: all available models for the present day movement of this triple junction fail to explain the regional variability in the stress conditions of the area. Here we present data from a 34-day long Ocean Bottom Seismograph array deployment. We show that the seismicity is distributed along a band aligned with the island chain itself, and is concentrated along several faults with an approximate N150E strike, cutting the Azores plateau in all the area covered by the OBS network. The combination of these new results with other geophysical data permits us to conclude that the tectonic setting of the Azores plateau is characterised by the existence of two sets of faults, in the N120E and N150E directions, defining several crustal blocks, whose relative motion accommodates the interaction of the three megaplates. The deformation of these tectonic blocks is probably driven by the shear between the EU and AF plates. This model explains well the spatial variability of the stress conditions in the Azores domain, the combination of dextral and sinistral strike slip mechanisms and the observed seismotectonics of the Azores islands.
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References
Asada, T., Kanasawa, T. and Shimamura, H., 1979, A pop-up type ocean bottom seismometer, Prog. Abstr. Seis. Soc. Japan 2: 114 (in Japanese).
Brillinger, D., Udias, A. and Bolt, B. A., 1980, A probability model for regional focal mechanism solutions, Bull. Seism. Soc. Am. 70: 149–170.
Bryan, W. B., Juteau, T., et al., 1988, Proc. ODP Initial Reports, (Pt A), 109, College Station, TX (ODP).
Buforn, E., Udias, A. and Colombas, M. A., 1988, Seismicity, source mechanisms and tectonics of the Azores-Gibraltar plate boundary, Tectonophysics 152: 89–118.
DeMets, C., Gordon, R. G., Argus, D. F. and Stein S., 1990, Current Plate Motions, Geophys. J. Int. 101: 425–478.
Féraud, G., Kaneoka, I. and Allègre, J. C., 1980, K/Ar ages and stress pattern in the Azores: Geodynamic implications. Earth Planet. Sci. Lett. 46: 275–286.
Fowler, C. M. R., 1976, Crustal Structure of the Mid-Atlantic Ridge crest at 37° N. Geophys. J. Roy. Astron. Soc 47: 459–491.
Grimison, N. L. and Chen, W. P., 1986, The Azores-Gibraltar plate boundary: focal mechanism, depths of earthquakes and their tectonic implications. J. Geophys. Res. 91(B2): 2029–2047.
Grimison, N. L. and Chen, W. P., 1988, Source mechanisms of four recent earthquakes along the Azores-Gibraltar plate boundary. Geophys. J. Int. 92: 391–401.
Hirata N. and Matsu'ura, M., 1987, Maximum likelihood estimation of hypocenter with origin time eliminated using nonlinear inversion techniques, Phys. Earth Planet. Int. 47: 50–61.
Hirn, A., Haessler, H., Hoang Tronc, P., Wittlinger, G. and Mendes Victor, L. A., 1980, Aftershock sequence of the January 1, 1980, earthquake and present-day tectonics in the Azores. Geophys. Res. Lett. 7: 501–504.
Kanasawa, T. and Shiobara, H., 1994, New Ocean Bottom Seismometer System for a Dense Survey, Abstr. Japan Earth Planet. Sci. Joint Mtg I11–P82: 341 (in Japanese).
Krause, D. C. and Watkins, N. D., 1970, North Atlantic crustal genesis in the vicinity of Azores. Geophys. J. Roy. Astron. Soc. 19: 261–283.
Laughton, A. S. and Whitmarsh, R. B., 1974, The Azores Gibraltar plate boundary, 'Geodynamics of Iceland and North Atlantic Area': L. Kristjansson, Ed. (Reidel, Dordrecht), 63–81.
Luis, J., Miranda, J. M., Patriat, Ph., Galdeano, A., Rossignol. J. C. and Mendes Victor, L. A., 1994, Açores Triple Junction Evolution in the last 10 Ma from a new aeromagnetic survey, Earth Planet. Sci. Lett. 125: 439–459.
Matsu'ura, M., 1984, Bayesian estimation of hypocenter with otigin time eliminated, J. Phys. Earth 32: 469–483.
McKenzie, D. P., 1972, Active tectonics of the Mediterranean region. Geophys. J. R. Astron. Soc. 30: 109–185.
Miranda, J. M., Freire Luis, J., Abreu, I., Mendes Victor, L. A., Galdeano, A. and Rossignol, J. C., 1991, Tectonic framework of the Azores triple junction. Geophys. Res. Lett. 18: 1421–1424.
Nunes, J. C. R., 1991, Microssismos e Neotectónica, contribuição para o seu estudo nos Açores, Universidade dos Açores.
Patriat, Ph., 1987, Reconstitution de l'évolution du systeme de dorsales de l'Océan Indien par la méthode de la Cinématique des Plaques, Territoire des Terres Australes et Antartiques Françaises: 308 pp. Paris.
Purdy, G. M. and Detrick, R. S., 1986, Crustal Structure of the Mid-Atlantic Ridge at 23° N from Seismic Refraction Studies, J. Geophys. Res. 91(83): 3739–3762.
Searle, R. C., 1980, Tectonic pattern of the Azores spreading center and triple junction, Earth Planet. Sci. Lett. 51: 415–434.
Udias, A., Lopez Arroyo, A. and Mezcua, J., 1976, Seismotectonic of the Azores Alboran region, Tectonophysics 31: 259–289.
Urabe T. and Hirata, N., 1984, A playback system for long-term analog tape recordings of Ocean Bottom Seismographs, Zisin 37: 633–645.
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Miranda, J., Mendes Victor, L., Simões, J. et al. Tectonic setting of the Azores Plateau deduced from a OBS survey. Marine Geophysical Researches 20, 171–182 (1998). https://doi.org/10.1023/A:1004622825210
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DOI: https://doi.org/10.1023/A:1004622825210