Azimuthal anisotropy of the Pg-wave velocity in hypocentral volumes of NW Croatia

• Autorzy: Herak M. , Herak D. , Stipčević J.
• Języki publikacji: EN

Abstrakty

EN

Based on a large set of arrival times of the Pg phase reported by local and regional stations, we estimate azimuthal anisotropy of the Pg-wave velocity in focal volumes of the upper crust in NW Croatia. The method is based on analyses of the azimuthal dependence of ratios of cumulative differences of arrival times and travel paths between foci of earthquake pairs, computed for rays propagating within narrow azimuthal windows. The results clearly indicate the presence of anisotropy of 3.3% with the direction of fast velocity (approximately NNE-SSW) coinciding with the direction of the maximum tectonic pressure as revealed by 23 available focal mechanisms and previous geological investigations. Although a large part of observed anisotropy can be explained assuming that focal volumes are pervaded by a system of vertical extensivedilatancy anisotropy (EDA) cracks aligned under the influence of local tectonic stress field, there is indication that - to a smaller extent - some role was also played by alignment of structural features in the region.

Słowa kluczowe

EN

azimuthal velocity anisotropy; extensive-dilatancy anisotropy; Croatia

• Wydawca: Instytut Geofizyki PAN ; Springer
• Czasopismo: Acta Geophysica
• Rocznik: 2009
• Tom: Vol. 57, no. 3
• Strony: 600--615
• Opis fizyczny: Bibliogr. 48 poz.

Twórcy

autor

Herak M.

autor

Herak D.

autor

Stipčević J.

• University of Zagreb, Faculty of Science and Mathematics, Department of Geophysics, Zagreb, Croatia,

Bibliografia

• BCIS (1972), Tables des temps des ondes séismiques. Hodochrones pour la region des Balkans (Manuel d’utilisation), Strasbourg.
• Babuška, V., and M. Cara (1991), Seismic Anisotropy in the Earth, Kluwer Academic Publishers, Dordrecht.
• Babuška, V., J. Plomerová, L. Vecsey, M. Granet, and U. Achauer (2002), Seismic anisotropy of the French Massif Central and predisposition of Cenozoic rifting and volcanism by Variscan suture hidden in the mantle lithosphere, Tectonics 21, 4, 1029.
• Backus, G.E. (1965), Possible forms of seismic anisotropy of the uppermost mantle under oceans, J. Geophys. Res. 70, 14, 3429-3439.
• Bada, G. (1999), Cenozoic stress field evolution in the Pannonian basin and surrounding orogens. Inferences from kinematic indicators and finite element stress modelling, Ph.D. Thesis, Vrije Universiteit, Amsterdam, 204 pp.
• Crampin, S. (1978), Seismic wave propagation through a cracked solid: Polarization as a possible dilatancy diagnostic, Geophys. J. Roy. Astron. Soc. 53, 467- 496.
• Crampin, S. (1981), A review of wave motion in anisotropic and cracked elastic media, Wave Motion 3, 4, 343-391.
• Crampin, S. (1984), Anisotropy in exploration seismics, First Break 2, 19-21.
• Crampin, S. (1987), Geological and industrial implications of extensive-dilatancy anisotropy, Nature 328, 6130, 491-496.
• Crampin, S. (1989), Suggestions for a consistent terminology for seismic anisotropy. Geophys. Prosp. 37, 7, 753-770.
• Crampin, S. (1991), Wave propagation through fluid-filled inclusions of various shapes: interpretation of extensive-dilatancy anisotropy, Geophys. J. Int. 104, 3, 611-623.
• Crampin, S. (1993), A review of the effects of crack geometry on wave propagation through aligned cracks, Canad. J. Exploration Geophys. 29, 3-17.
• Crampin, S. (2003), Aligned cracks not LPO as the cause of mantle anisotropy, Geophys. Res. Abstr. 5, 00205.
• Crampin, S., and J.H. Lovell (1991), A decade of shear-wave splitting in the Earth’s crust: what does it mean? what use can we make of it? and what should we do next? Geophys. J. Int. 107, 387-407.
• Crampin, S., and S. Peacock (2008), A review of the current understanding of seismic shear-wave splitting in the Earth’s crust and common fallacies in interpretation, Wave Motion 45, 6, 675-722.
• Crampin, S., R. McGonigle, and D. Bamford (1980), Estimating crack parameters from observations of P-wave velocity anisotropy, Geophysics 45, 345-360.
• Crampin, S., R. McGonigle, and M. Ando (1986), Extensive-dilatancy anisotropy beneath Mount Hood, Oregon, and the effect of aspect ratio on seismic velocities through aligned cracks, J. Geophys. Res. 91, B12, 12703-12710.
• Estey, L.H., and B.J. Douglas (1986), Upper mantle anisotropy: A preliminary model, J. Geophys. Res. 91, B11, 11,393-11,406.
• Garbin, H.D., and L. Knopoff (1973), The compressional modulus of a material permeated by a random distribution of free circular cracks, Q. Appl. Math. 30, 453-464.
• Garbin, H.D., and L. Knopoff (1975a), The shear modulus of a material permeated by a random distribution of free circular cracks, Q. Appl. Math. 33, 296-300.
• Garbin, H.D., and L. Knopoff (1975b), Elastic moduli of a medium with liquid-filled cracks, Q. Appl. Math. 33, 301-303.
• Herak, M. (1989), HYPOSEARCH – An earthquake location program, Comput. Geosci. 15, 7, 1157-1162.
• Herak, D., and M. Herak (1995), Body-wave velocities in the circum-Adriatic region, Tectonophysics 241, 1-2, 121-141.
• Herak, M., M. Živčić, and D. Herak (2003), Azimuthal anisotropy of the P-wave velocity in the hypocentral volume of the Krn Mt. (Slovenia) earthquake sequence, J. Appl. Geophys. 54, 3-4, 257-264
• Herak, D., M. Herak, and B. Tomljenović (2009), Seismicity and earthquake ocal mechanisms in North-Western Croatia, Tectonophysics 465, 1-4, 212-220.
• Hudson, J.A., E. Liu, and S. Crampin (1996), The mechanical properties of materials with interconnected cracks and pores, Geophys. J. Int. 124, 1, 105-112.
• Hudson, J.A., T. Pointer, and E. Liu (2001), Effective-medium theories for fluidsaturated materials with aligned cracks, Geophys. Prosp. 49, 5, 509-522.
• Kohler, W.M., J.H. Healy, and S.S. Wegener (1982), Upper crustal structure of the Mount Hood, Oregon, region as revealed by time term analysis, J. Geophys. Res. 87, B1, 339-355.
• Lenkey, L., P. Dövényi, P. Horváth, and S.A.P.L. Cloetingh (2002), Geothermics of the Pannonian basin and its bearing on the neotectonics. In: S. Cloetingh et al. (eds.), Neotectonics and Surface Processes: the Pannonian Basin and Alpine/Carpathian system, Copernicus GmbH, Katlenburg-Lindau, EGU Stephan Mueller Special Publ. Ser. 3, 29-40.
• Lokmer, I., and M. Herak (1999), Anisotropy of P-wave velocity in the upper crust of the central External Dinarides, Stud. Geophys. Geod. 43, 4, 345-356.
• Mele, G. (1998), Pn anisotropy in the northern Apennine chain (Italy), Pure Appl. Geophys. 151, 2-4, 495-502.
• Mele, G., A. Rovelli, D. Seber, T.M. Hearn, and M. Barazangi (1998), Compressional velocity structure and anisotropy in the uppermost mantle beneath. Italy and surrounding regions, J. Geophys. Res. 103, B6, 12,529-12,543.
• Mohorovičić, A. (1910), Das beben vom 8. X. 1909, Jahrbuch des meteorologischen Observatoriums in Zagreb (Agram) fuer das Jahr 1909. 9/4, 63 pp.
• Peacock, S., and J.A. Hudson (1990), Seismic properties of rocks with distributions of small cracks, Geophys. J. Int. 102, 2, 471-484.
• Piccardi, L., L. Toth, E. Vittori, S. Aliaj, G. Cello, W.D. Cunningham, G. Drakatos, A. Gosar, D. Herak, M. Herak, S. Sebela, E. Sulstarova, G. Windhoffer, B. Glavatović, A. Kiratzi, A. Ganas, M. Omerbashich, S. Pavlides, L. Petro, G. Sijarić, B. Tomljenović, and E. Tondi (2007), A first attempt at compiling a map of active faults of the Adria region, Geophys. Res. Abstracts 9, 09228.
• Plomerová, J., L. Margheriti, J. Park, V. Babuška, S. Pondrelli, L. Vecsey, D. Piccinini, V. Levin, P. Baccheschi, and S. Salimbeni (2006), Seismic anisotropy beneath the Northern Apennines (Italy): Mantle flow or lithosphere fabric?, Earth Planet. Sc. Lett. 247, 1-2, 157-170.
• Pointer, T., E. Liu, and J.A. Hudson (2000), Seismic wave propagation in cracked porous media, Geophys. J. Int. 142, 1, 199-231.
• Pondrelli, S., S. Salimbeni, G. Ekström, A. Morelli, P. Gasperini, and G. Vannucci (2006), The Italian CMT dataset from 1977 to the present, Phys. Earth Planet. Int. 159, 3-4, 286-303.
• Prelogović, E., B. Saftić, V. Kuk, J. Velić, M. Dragaš, and D. Lučić (1998), Tectonic activity in the Croatian part of the Pannonian basin, Tectonophysics 297, 1- 4, 283-293.
• Růžek, B., V. Vavryčuk, P. Hrubcová, J. Zedník, and the CELEBRATION Working Group (2003), Crustal anisotropy in the Bohemian Massif, Czech Republic: Observations based on Central European Lithospheric Experiment Based on Refraction (CELEBRATION) 2000, J. Geophys. Res. 108, B8, 2392.
• Smith, G.P., and G. Ekström (1999), A global study of Pn anisotropy beneath continents, J. Geophys. Res. 104, B1, 963-980.
• Środa, P. (2006), Seismic anisotropy of the upper crust in southeastern Poland – effect of the compressional deformation at the EEC margin: Results of CELEBRATION 2000 seismic data inversion, Geophys. Res. Lett. 33, L22302.
• Thomsen, L. (1995), Elastic anisotropy due to aligned cracks in porous rock, Geophys. Prosp. 43, 6, 805-829.
• Tomljenović, B., and L. Csontos (2001), Neogene-Quaternary structures in the border zone between Alps, Dinarides and Pannonian Basin (Hrvatsko Zagorje and Karlovac Basins, Croatia), Int. J. Earth Sci. 90, 3, 560-578.
• Vavryčuk, V. (2004), Inversion for anisotropy from non-double-couple components of moment tensors, J. Geophys. Res. 109, B07306.
• Vavryčuk, V., P. Hrubcová, M. Brož, J. Málek, and The ALP 2002 Working Group (2004), Azimuthal variation of Pg velocity in the Moldanubian, Czech Republic: observations based on a multi-azimuthal common-shot experiment, Tectonophysics 387, 1-4, 189-203.
• Vavryčuk, V., M. Bohnhoff, Z. Jechumtálová, P. Kolář, and J. Šílený (2008), Nondouble- couple mechanisms of microearthquakes induced during the 2000 injection experiment at the KTB site, Germany: A result of tensile faulting or anisotropy of a rock?, Tectonophysics 456, 1-2, 74-93.
• Wolfe, C.J., and S.C. Solomon (1998), Shear-Wave Splitting and Implications for Mantle Flow Beneath the MELT Region of the East Pacific Rise, Science 280, 5367, 1230-1232.