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Inferences on active faults at the Southern Alps–Liguria basin junction from accurate analysis of low energy seismicity
Language
English
Obiettivo Specifico
3.2. Tettonica attiva
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
/475(2009)
Publisher
Elsevier
Pages (printed)
470-479
Issued date
2009
Last version
http://dx.doi.org/10.1016/j.tecto.2009.06.007
Abstract
Seismotectonic studies concern themselves with understanding the distribution of earthquakes in space,
time, size and style. Therefore, the better these parameters are known, the most correct the association of any
seismic event with the faulting structure that caused it will result. The use of accurate location methods is
especially required when dealing with very complex areas, where several faulting systems or relatively small
seismogenic structures exist. In fact, even though routinely determined epicentres are capable of revealing
the rough picture of the seismicity, they are not suitable for studies of the fine structure of the causative fault,
as their location uncertainties are often larger than the source dimension itself.
In this work the probabilistic approach of the “Non Linear Localization” has been used to compute precise
locations for earthquakes occurred in the last twenty years nearby the Saorge–Taggia line, a complex fault
system situated in Western Liguria, close to the border between Italy and France. Together with the Breil–
Sospel–Monaco and the Peille–Laghet faults, this line is responsible for the seismic activity of the area.
The seismotectonic study is completed through a local tomographic study and the analysis of the focal
mechanisms computed for an enlarged area. The results show that the seismicity associated with this fault
system is confined within the first 10 km depth. Many clusters of seismic events are identified along the
Saorge–Taggia line. The existence of a not previously mapped branch perpendicular to the Saorge–Taggia line
is also recognized. Although its position may suggest it to be the continuation of the Breil–Sospel–Monaco
fault system towards NE, our finding would rather suggest no association with the fault. The overall results
confirm the complexity of the area; in particular the hypothesis that the Saorge–Taggia system may represent
the eastward limit of a subalpine crustal block comprised within the Nice Arc, the named fault and a thrust
front which is supposed to be located 20 km offshore find a confirm in the shallow depth of the seismic
events. In addition we propose that the western limit of the block, located along the Nice arc, could be instead
shifted where the Peille–Laghet fault lays.
time, size and style. Therefore, the better these parameters are known, the most correct the association of any
seismic event with the faulting structure that caused it will result. The use of accurate location methods is
especially required when dealing with very complex areas, where several faulting systems or relatively small
seismogenic structures exist. In fact, even though routinely determined epicentres are capable of revealing
the rough picture of the seismicity, they are not suitable for studies of the fine structure of the causative fault,
as their location uncertainties are often larger than the source dimension itself.
In this work the probabilistic approach of the “Non Linear Localization” has been used to compute precise
locations for earthquakes occurred in the last twenty years nearby the Saorge–Taggia line, a complex fault
system situated in Western Liguria, close to the border between Italy and France. Together with the Breil–
Sospel–Monaco and the Peille–Laghet faults, this line is responsible for the seismic activity of the area.
The seismotectonic study is completed through a local tomographic study and the analysis of the focal
mechanisms computed for an enlarged area. The results show that the seismicity associated with this fault
system is confined within the first 10 km depth. Many clusters of seismic events are identified along the
Saorge–Taggia line. The existence of a not previously mapped branch perpendicular to the Saorge–Taggia line
is also recognized. Although its position may suggest it to be the continuation of the Breil–Sospel–Monaco
fault system towards NE, our finding would rather suggest no association with the fault. The overall results
confirm the complexity of the area; in particular the hypothesis that the Saorge–Taggia system may represent
the eastward limit of a subalpine crustal block comprised within the Nice Arc, the named fault and a thrust
front which is supposed to be located 20 km offshore find a confirm in the shallow depth of the seismic
events. In addition we propose that the western limit of the block, located along the Nice arc, could be instead
shifted where the Peille–Laghet fault lays.
References
References
Bigot-Cormier, F., Sage, F., Sosson, M., Deverchere, J., Ferrandini, M., Guennoc, P., Popoff,
M., Stephan, J.F., 2004. Deformations pliocenes de la marge nord-Ligure (France):
les consequences d'un chevauchement crustal sud-alpin. Bull. Soc. Geol. Fr. 175 (2),
197–211.
Calais, E., Nocquet, J.M., Jouanne, F., Tardy, M., 2002. Current extension in the central
part of the western Alps from continuous GPS measurements, 1996–2001. Geology
30 (7), 651–654.
Camprendon, R., Franco, M., Giannerini, G., Gigot, P., Irr, F., Lanteaume, M., Spini, H.,
Tapoul, J.F., 1977. Les deformation de conglomerats pliocenes de l'arc de Nice. C.R.
Somm. Soc. Geol. Fr. 2, 75–77.
Cosani, L., 1997. Neotectonique et heritege sructural entre massif du Mercatour et marge
ligure: le secteur de Saorge–Taggia. Geol. Alp. 128–134.
Courboulex, F., Deschamps, A., Cattaneo, M., Costi, F., Deverchere, J., Virieux, J., Augliera,
P., Lanza, V., Spallarossa, D.,1998. Source study and tectonic implications of the 1995
Ventimiglia (border of Italy and France) earthquake (Ml=4.7). Tectonophysics 290,
245–257.
Courboulex, F., Larroque, C., Deschamps, A., Gelis, C., Charreau, J., Stephan, J.F., 2003. An
unknown active fault revealed by microseismicity in the south-east of France.
Geophys. Res. Lett. 30 (15). doi:10.1029/2003GL017171.
Courboulex, F., Larroque, C., Deschamps, A., Kohrs-Sansorny, C., Gelis, C., Got, J.L.,
Charreau, J., Stephan, J.F., Bethoux, N., Virieux, J., Brunel, D., Maron, C., Duval, A.M.,
Perez, L., Mondielli, P., 2007. Seismic hazard on the French Riviera: observations,
interpretations and simulations. Geophys. J. Int. 170 (1), 387–400.
Ellsworth, W.L., 1977. Three dimensional structure of the crust and mantle beneath the
island of Hawaii. Ph.D. thesis, 327 pp.
Eva, E., Solarino, S., 1998. Variations of stress directions in the western Alpine arc.
Geophys. J. Int. 135, 438–448.
Eva, E., Solarino, S., Spallarossa, D., 2001. Seismicity and crustal structure beneath the
western Ligurian Sea derived from local earthquake tomography. Tectonophysics
339 (3–4), 495–510.
Font, Y., Kao, H., Lallemand, S., Liu, C.-S., Chiao, L.-Y., 2004. Hypocentral determination
offshore EasternTaiwain using theMaximumIntersectionmethod. Geophys. J. Int.158,
655–675.
Gentile, G.F., Bressan, G., Burlini, L., De Franco, R., 2000. Three-dimensional Vp and Vp/Vs
models of the upper crust in the Friuli area (northeastern Italy). Geophys. J. Int. 141,
457–478.
Guallini, L., 2004. Rilevamento geologico “finesta tettonica di Ceriana” (alta Valle
Armea-Provincia di Imperia): controllo dell'asseto strutturale sui fenomeni di
dissesto idrogeologico dell'autunno 2000. Tesi di Laurea, Univ. di Genova.
Guardia, P., Ivaldi, J.P., Dubar, M., Guglielmi, Y., Perez, J.L., 1996. Paleotectonique
lineamentarie et tectonique active des Alpes maritimes franco-italiennes: une
synshese. Geol. France 1, 43–55.
Hoang-Trong, P., Haessler, H., Holl, J.M., Legros, Y.,1987. L'essain sismique (oct. 83–jan. 84)
de lamoyenne vallee de laRoya (AlpesMeritimes): active recente d'un ancien systeme
de failles conjuguees? C.R. Acad. Sci. Paris 304, 419–424.
Husen, S., Smith, R.B., 2004. robabilistic earthquake relocation in three-dimensional
velocity models for the Yellowstone National Park Region, Wyoming. Bull. Seismol.
Soc. Am. 94, 880–896.
Kissling, E., 1988. Geotomography with local earthquake data. Rev. Geophys. 26, 598–659.
Lahr, J.C., 1989. HYPOELLIPSE/Version 2.0: a computer program for determining local
earthquake hypocentral parameters, magnitude and first motion pattern. U.S. Geol.
Surv., Open File Rep., vol. 79–431, p. 230.
Larroque, C., Bethoux, N., Calais, E., Caourboulex, F., Deschamps, A., Deverchere, J.,
Stephan, J.F., Ritz, J.F., Gilli, E., 2001. Active and recent deformation at the Southern
Alps–Ligurian basin junction. Netherlands J. Geosci./Geol. en Mijnbouw 80 (3–4),
255–272.
Lemoine, M., Tricart, P., Boillot, G.,1987. Ultramafic and gabbroic ocean floor of the Ligurian
Tethys (Alps, Corsica, Apennines): in search of a genetic imodel. Geology 15, 622–625.
Lippitsch, R., White, R.S., Soosalu, H., 2005. Precise hypocentre relocation of
microearthquakes in a high-temperature geothermal field: the Torfajökull central
volcano, Iceland. Geophys. J. Int. 160 (1), 371–388.
Lomax, A., Curtis, A., 2001. Fast, probabilistic earthquake location in 3D models using
oct-tree importance sampling. Geophys. Res. Abstr. 3, 955.
Lomax, A., Virieux, J., Volant, P., Berge, C., 2000. Probabilistic earthquake location in 3D
and layered models: introduction of a Metropolis–Gibbs method and comparison
with linear locations. In: Thurber, C.H., Rabinowitz, N. (Eds.), Advances in Seismic
Event Location. Kluwer, Amsterdam, pp. 101–134.
Lomax, A., Zollo, A., Capuano, P., Virieux, J., 2001. Precise, absolute earthquake location
under Somma–Vesuvius volcano using a new 3D velocità model. Geophys. J. Int. 146,
313–331.
Nicolas, M., Bethoux, N., Madeddu, B., 1998. Instrumental seismicity of the Western
Alps: a revised catalogue. Pure Appl. Geophys. 152, 707–731.
Moser, T.J., van Ech, T., Nolet, G., 1992. Hypocenter determination in strongly
heterogeneous earth models using the shortest path method. J. Geophys. Res. 97,
6536–6572.
Podvin, P., Lecomte, L., 1991. Finite difference computation of traveltimes in very
contrasted velocity models: a massively parallel approach and its associated tools.
Geophys. J. Int. 105, 271–284.
Reasemberg, P., Oppenheimer, D.H., 1985. FPFIT, Fortran computer program for
calculating and displaying earthquake fault-plane solutions. USGS Open file Rept.,
pp. 85–739.
Scafidi, D., Solarino, S., Eva, C., 2009. P wave seismic velocity and Vp/Vs ratio beneath
the Italian peninsula from local earthquake tomography. Tectonophysics 465, 1–23.
doi:10.1016/j.tecto.2008.07.013.
Spallarossa, D., Ferretti, G., Augliera, P., Bindi, D., Cattaneo, M., 2001. Reliability of
earthquake location procedures in heterogeneous areas: synthetic tests in the
South Western Alps, Italy. Phys. Earth Planet. Inter. 123, 247–266.
Tarantola, A., Vallette, B., 1982. Inverse problems = quest for information. J. Geophys. 50,
159–170.
Thurber, C.H.,1983. Earthquake locations and three-dimensional crustal structure in the
Coyote Lake area, central California. J. Geophys. Res. 88, 8226.
Wessel, C.H., Smith, W.H.F., 1991. Free software helps map and display data. Eos. Trans.
AGU 72 441, 445-44.
Wittlinger, G., Herquel, G., Nakache, T., 1993. Earthquake location in strongly
heterogeneous media. Geophys. J. Int. 115, 759–777.
Bigot-Cormier, F., Sage, F., Sosson, M., Deverchere, J., Ferrandini, M., Guennoc, P., Popoff,
M., Stephan, J.F., 2004. Deformations pliocenes de la marge nord-Ligure (France):
les consequences d'un chevauchement crustal sud-alpin. Bull. Soc. Geol. Fr. 175 (2),
197–211.
Calais, E., Nocquet, J.M., Jouanne, F., Tardy, M., 2002. Current extension in the central
part of the western Alps from continuous GPS measurements, 1996–2001. Geology
30 (7), 651–654.
Camprendon, R., Franco, M., Giannerini, G., Gigot, P., Irr, F., Lanteaume, M., Spini, H.,
Tapoul, J.F., 1977. Les deformation de conglomerats pliocenes de l'arc de Nice. C.R.
Somm. Soc. Geol. Fr. 2, 75–77.
Cosani, L., 1997. Neotectonique et heritege sructural entre massif du Mercatour et marge
ligure: le secteur de Saorge–Taggia. Geol. Alp. 128–134.
Courboulex, F., Deschamps, A., Cattaneo, M., Costi, F., Deverchere, J., Virieux, J., Augliera,
P., Lanza, V., Spallarossa, D.,1998. Source study and tectonic implications of the 1995
Ventimiglia (border of Italy and France) earthquake (Ml=4.7). Tectonophysics 290,
245–257.
Courboulex, F., Larroque, C., Deschamps, A., Gelis, C., Charreau, J., Stephan, J.F., 2003. An
unknown active fault revealed by microseismicity in the south-east of France.
Geophys. Res. Lett. 30 (15). doi:10.1029/2003GL017171.
Courboulex, F., Larroque, C., Deschamps, A., Kohrs-Sansorny, C., Gelis, C., Got, J.L.,
Charreau, J., Stephan, J.F., Bethoux, N., Virieux, J., Brunel, D., Maron, C., Duval, A.M.,
Perez, L., Mondielli, P., 2007. Seismic hazard on the French Riviera: observations,
interpretations and simulations. Geophys. J. Int. 170 (1), 387–400.
Ellsworth, W.L., 1977. Three dimensional structure of the crust and mantle beneath the
island of Hawaii. Ph.D. thesis, 327 pp.
Eva, E., Solarino, S., 1998. Variations of stress directions in the western Alpine arc.
Geophys. J. Int. 135, 438–448.
Eva, E., Solarino, S., Spallarossa, D., 2001. Seismicity and crustal structure beneath the
western Ligurian Sea derived from local earthquake tomography. Tectonophysics
339 (3–4), 495–510.
Font, Y., Kao, H., Lallemand, S., Liu, C.-S., Chiao, L.-Y., 2004. Hypocentral determination
offshore EasternTaiwain using theMaximumIntersectionmethod. Geophys. J. Int.158,
655–675.
Gentile, G.F., Bressan, G., Burlini, L., De Franco, R., 2000. Three-dimensional Vp and Vp/Vs
models of the upper crust in the Friuli area (northeastern Italy). Geophys. J. Int. 141,
457–478.
Guallini, L., 2004. Rilevamento geologico “finesta tettonica di Ceriana” (alta Valle
Armea-Provincia di Imperia): controllo dell'asseto strutturale sui fenomeni di
dissesto idrogeologico dell'autunno 2000. Tesi di Laurea, Univ. di Genova.
Guardia, P., Ivaldi, J.P., Dubar, M., Guglielmi, Y., Perez, J.L., 1996. Paleotectonique
lineamentarie et tectonique active des Alpes maritimes franco-italiennes: une
synshese. Geol. France 1, 43–55.
Hoang-Trong, P., Haessler, H., Holl, J.M., Legros, Y.,1987. L'essain sismique (oct. 83–jan. 84)
de lamoyenne vallee de laRoya (AlpesMeritimes): active recente d'un ancien systeme
de failles conjuguees? C.R. Acad. Sci. Paris 304, 419–424.
Husen, S., Smith, R.B., 2004. robabilistic earthquake relocation in three-dimensional
velocity models for the Yellowstone National Park Region, Wyoming. Bull. Seismol.
Soc. Am. 94, 880–896.
Kissling, E., 1988. Geotomography with local earthquake data. Rev. Geophys. 26, 598–659.
Lahr, J.C., 1989. HYPOELLIPSE/Version 2.0: a computer program for determining local
earthquake hypocentral parameters, magnitude and first motion pattern. U.S. Geol.
Surv., Open File Rep., vol. 79–431, p. 230.
Larroque, C., Bethoux, N., Calais, E., Caourboulex, F., Deschamps, A., Deverchere, J.,
Stephan, J.F., Ritz, J.F., Gilli, E., 2001. Active and recent deformation at the Southern
Alps–Ligurian basin junction. Netherlands J. Geosci./Geol. en Mijnbouw 80 (3–4),
255–272.
Lemoine, M., Tricart, P., Boillot, G.,1987. Ultramafic and gabbroic ocean floor of the Ligurian
Tethys (Alps, Corsica, Apennines): in search of a genetic imodel. Geology 15, 622–625.
Lippitsch, R., White, R.S., Soosalu, H., 2005. Precise hypocentre relocation of
microearthquakes in a high-temperature geothermal field: the Torfajökull central
volcano, Iceland. Geophys. J. Int. 160 (1), 371–388.
Lomax, A., Curtis, A., 2001. Fast, probabilistic earthquake location in 3D models using
oct-tree importance sampling. Geophys. Res. Abstr. 3, 955.
Lomax, A., Virieux, J., Volant, P., Berge, C., 2000. Probabilistic earthquake location in 3D
and layered models: introduction of a Metropolis–Gibbs method and comparison
with linear locations. In: Thurber, C.H., Rabinowitz, N. (Eds.), Advances in Seismic
Event Location. Kluwer, Amsterdam, pp. 101–134.
Lomax, A., Zollo, A., Capuano, P., Virieux, J., 2001. Precise, absolute earthquake location
under Somma–Vesuvius volcano using a new 3D velocità model. Geophys. J. Int. 146,
313–331.
Nicolas, M., Bethoux, N., Madeddu, B., 1998. Instrumental seismicity of the Western
Alps: a revised catalogue. Pure Appl. Geophys. 152, 707–731.
Moser, T.J., van Ech, T., Nolet, G., 1992. Hypocenter determination in strongly
heterogeneous earth models using the shortest path method. J. Geophys. Res. 97,
6536–6572.
Podvin, P., Lecomte, L., 1991. Finite difference computation of traveltimes in very
contrasted velocity models: a massively parallel approach and its associated tools.
Geophys. J. Int. 105, 271–284.
Reasemberg, P., Oppenheimer, D.H., 1985. FPFIT, Fortran computer program for
calculating and displaying earthquake fault-plane solutions. USGS Open file Rept.,
pp. 85–739.
Scafidi, D., Solarino, S., Eva, C., 2009. P wave seismic velocity and Vp/Vs ratio beneath
the Italian peninsula from local earthquake tomography. Tectonophysics 465, 1–23.
doi:10.1016/j.tecto.2008.07.013.
Spallarossa, D., Ferretti, G., Augliera, P., Bindi, D., Cattaneo, M., 2001. Reliability of
earthquake location procedures in heterogeneous areas: synthetic tests in the
South Western Alps, Italy. Phys. Earth Planet. Inter. 123, 247–266.
Tarantola, A., Vallette, B., 1982. Inverse problems = quest for information. J. Geophys. 50,
159–170.
Thurber, C.H.,1983. Earthquake locations and three-dimensional crustal structure in the
Coyote Lake area, central California. J. Geophys. Res. 88, 8226.
Wessel, C.H., Smith, W.H.F., 1991. Free software helps map and display data. Eos. Trans.
AGU 72 441, 445-44.
Wittlinger, G., Herquel, G., Nakache, T., 1993. Earthquake location in strongly
heterogeneous media. Geophys. J. Int. 115, 759–777.
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