Options
Estimation of an optimum velocity model in the Calabro-Peloritan mountains – Assessment of the variance of model parameters and variability of earthquake locations
Author(s)
Language
English
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
3/170(2007)
Publisher
Blackwell
Pages (printed)
1151-1164
Issued date
September 2007
Abstract
Accurate earthquake locations are of primary importance when studying the seismicity of a given area, they allow important inferences on the ongoing seismo-tectonics. Both, for standard, as well as for earthquake relative location techniques, the velocity parameters are kept fixed to a-priori values, that are assumed to be correct, and the observed traveltime residuals are minimised by adjusting the hypocentral parameters. However, the use of an unsuitable velocity model, can introduce systematic errors in the hypocentre location. Precise hypocentre locations and error estimate, therefore, require the simultaneous solution of both velocity and hypocentral parameters.
We perform a simultaneous inversion of both the velocity structure and the hypocentre location in NE-Sicily and SW-Calabria (Italy). Since the density of the network is not sufficient for the identification of the 3D structure with a resolution of interest here, we restrict ourselves to a 1D inversion using the well-known code VELEST. A main goal of the paper is the analysis of the stability of the inverted model parameters. For this purpose we carry out a series of tests concerning the initial guesses of the velocity structure and locations used in the inversion. We further assess the uncertainties which originate from the finiteness of the available datasets carrying out resampling experiments. From these tests we conclude that the data catalogue is sufficient to constrain the inversion. We note that the uncertainties of the inverted velocities increases with depth. On the other hand the inverted velocity structure depends decisively on the initial guess as they tend to maintain the overall shape of the starting model. In order to derive an improved starting model we derive a guess for the probable depth of the MOHO. For this purpose we exploit considerations of the depth distribution of earthquake foci and of the shear strength of rock depending on its rheological behaviour at depth. In a second step we derived a smooth starting model and repeated the inversion. Strong discontinuities tend to attract hypocentre locations which may introduce biases to the earthquake location. Using the smooth starting model we obtained again a rather smooth model as final solution which gave the best travel-time residuals among all models discussed in this paper. This poses severe questions as to the significance of velocity discontinuities inferred from rather vague a-priori information. Besides this, the use of those smooth models widely avoids the problems of hypocentre locations being affected by sudden velocity jumps, an effect which can be extremely disturbing in relative location procedures. The differences of the velocity structure obtained with different starting models is larger than those encountered during the bootstrap test. This underscores the importance of the choice of the initial guess. Fortunately the effects of the uncertainties discussed here on the final locations turned out as limited, i. e., less than 1 km for the horizontal coordinates and less than 2 km for the depth.
We perform a simultaneous inversion of both the velocity structure and the hypocentre location in NE-Sicily and SW-Calabria (Italy). Since the density of the network is not sufficient for the identification of the 3D structure with a resolution of interest here, we restrict ourselves to a 1D inversion using the well-known code VELEST. A main goal of the paper is the analysis of the stability of the inverted model parameters. For this purpose we carry out a series of tests concerning the initial guesses of the velocity structure and locations used in the inversion. We further assess the uncertainties which originate from the finiteness of the available datasets carrying out resampling experiments. From these tests we conclude that the data catalogue is sufficient to constrain the inversion. We note that the uncertainties of the inverted velocities increases with depth. On the other hand the inverted velocity structure depends decisively on the initial guess as they tend to maintain the overall shape of the starting model. In order to derive an improved starting model we derive a guess for the probable depth of the MOHO. For this purpose we exploit considerations of the depth distribution of earthquake foci and of the shear strength of rock depending on its rheological behaviour at depth. In a second step we derived a smooth starting model and repeated the inversion. Strong discontinuities tend to attract hypocentre locations which may introduce biases to the earthquake location. Using the smooth starting model we obtained again a rather smooth model as final solution which gave the best travel-time residuals among all models discussed in this paper. This poses severe questions as to the significance of velocity discontinuities inferred from rather vague a-priori information. Besides this, the use of those smooth models widely avoids the problems of hypocentre locations being affected by sudden velocity jumps, an effect which can be extremely disturbing in relative location procedures. The differences of the velocity structure obtained with different starting models is larger than those encountered during the bootstrap test. This underscores the importance of the choice of the initial guess. Fortunately the effects of the uncertainties discussed here on the final locations turned out as limited, i. e., less than 1 km for the horizontal coordinates and less than 2 km for the depth.
References
Barberi, G., Cosentino, M.T., Gervasi, A., Guerra, I., Neri, G. & Orecchio, B., 2004. Crustal seismic tomography in the Calabrian Arc, Phys. Earth Planet. Int., 147, 297-314.
Billi, A., Barberi, G., Faccenna, C., Neri, G., Pepe, F. & Sulli, A., 2006. Tectonics and Seismicity of the Tindari Fault System, southern Italy: Crustal Deformations at the transition between ongoing contractional and extensional domains located above the edge of a subducting slab, Tectonics, 25, TC2006, doi: 10.1029/2004TC001763.
Caltabiano, T., Condarelli, D., Gresta, S., Patanè, D. & Patanè, G., 1986. Analisi preliminare dei dati della stazione sismica di Serra Pizzuta Calvarina, CNR-IIV Open File Report 10/86.
Cernobori, L., Hirn, A., McBride, J.H., Nicolich, R., Petronio, L. & Romanelli, M., 1996. Crustal image of the Ionian basin and its Calabrian margins, Tectonophysics, 264, 175-189.
D’Agostino, N. & Selvaggi, G., 2004. Crustal motion along the Eurasia-Nubia plate boundary in the Calabrian Arc and Sicily and active extension in the Messina Straits from GPS measurements, J. Geophys. Res., 109, B11402, doi:10.1029/2004JB002998.
De Luca, G., Filippi, L., Caccamo, D., Neri, G. & Scarpa, R., 1997. Crustal structure and seismicity of southern Tyrrenian basin, Phys. Earth Planet. Int., 103, 117-133.
Dezes, P. & Ziegler, P. A., 2001. European Map of the Mohorovicic discontinuity. 2nd EUCOR-URGENT Workshop (Upper Rhine Graben Evolution and Neotectonics). Mt. St. Odile, France.
Dziewonski, A. M., Ekström, G., Franzen, J. E. & Woodhouse, J. H., 1987. Global seismicity of 1978: centroid-moment tensor solutions for 512 earthquakes, Phys. Earth Planet. Int., 46, 316-342.
Eberhart – Phillips D. & Michael, A.J., 1993. Three-dimensional velocity structure, seismicity, and fault structure in the Parkfield region, central California, J. Geophys. Res., 98, 737-758.
Efron, B., 1982. The Jackknife, the Bootstrap, and Other Resampling Plans, Society of Industrial and Applied Mathematics, Philadelphia, CBMS-NSF Monographs, pp. 38.
Finetti, I. & Del Ben, A., 1986. Geophysical study of the Tyrrhenian opening, Boll. Geof. Teor. Appl., 110, 75-155.
Frémont, M. J. & Malone, S. D., 1987. High precision relative locations of earthquakes at Mt. St. Helens, Washington, J. Geophys. Res., 92, 10223-10236.
Gasparini, C., Iannaccone, G. & Scarpa, R., 1985. Fault plane solutions and seismicity of the Italian peninsula, Tectonophysics, 117, 59-78.
Goetze, C., 1978. The mechanisms of creep in olivine. Phil. Trans. Roy. Soc. London, 288, 99-119.
Hastie, T., Tibshirani, R. & Friedman, J., 2002. The Elements of Statistical Learning, Springer-Verlag, Berlin, pp. 533.
Hesterberg, T., Monaghan, S., Moore, D. S., Clipson, A. & Epstein, R., 2003. Bootstrap and permutation tests – Companion chapter 18 to the “Practice of Business Statistics”, in: the Practice of Business Statistics, eds. Freeman, W.H. and Company, New York.
Husen, S., Kissling, E., Flueh, E. & Asch, G., 1999. Accurate hypocenter determination in the seismogenic zone of the subducting Nazca plate in north Chile using a combined on-/offshore network, Geophys. J. Int., 138, 687-701.
Kissling, E., Ellsworth, W.L., Eberhart-Phillips, D. & Kradolfer, U., 1994. Initial reference models in local earthquake tomography, J. Geophys. Res., 99, 19,635-19,646.
Kissling, E., 1995. Velest User’s Guide. Internal Report, Institute of Geophysics, ETH, Zurich, pp. 26.
Laigle, M., 1998. Images sismiques de l’Etna à diverses èchelles: Nouveaux éléments sur son comportement et le cadre règional, PhD. thesis, University of Paris 7, Paris, pp. 288.
Lentini, F., Catalano, S. & Carbone, S., 2000. Carta geologica della provincia di Messina, Provincia Regionale di Messina. Assessorato Territorio–Servizio geologico, SELCA, Firenze.
Michelini, A. & Lomax, A., 2004. The effect of velocity structure errors on double-difference earthquake location, Geoph. Res. Lett., 31, L099602, doi: 10.1029/2004GL019682.
Monaco, C. & Tortorici, L., 2000. Active faulting in the Calabrian Arc and eastern Sicily, Journal of Geodynamics, 29, 407-424.
Neri, G., Barberi, G., Orecchio, B. & Aloisi, M., 2002. Seismotomography of the crust in the transition zone between the southern Tyrrhenian and Sicilian tectonic domains, Geophys. Res. Lett., 29, (23), 2135, doi: 10.1029/2002GL015562.
Neri, G., Barberi, G., Orecchio, B. & Mostaccio, A., 2003. Seismic strain and seismogenic stress regimes in the crust of the southern Tyrrhenian region, Earth and Planetary Science Letters, 213, 97-112.
Neri, G., Barberi, G., Oliva, G. & Orecchio B., 2005. Spatial variations of seismogenic stress orientations in Siciliy, South Italy, Phys. Earth Planet. Int., 148, 175-191.
Nicolich, R., Laigle, M., Hirn, A., Cernobori, L. & Gallart, J., 2000. Crustal structure of the Ionian margin of Sicily: Etna volcano in the frame of regional evolution, Tectonophysics, 329, 121-139.
Scarfì, L., Langer, H. & Scaltrito, A., 2005. Relocation of microearthquake swarms in the Peloritani mountains – implications on the interpretation of seismotectonic patterns in NE Sicily, Italy, Geophys. J. Int., 163, 225-237, doi: 10.1111/j.1365-246X.2005.02720.x.
Sgroi, T., Braun, T., Dahm T. & Frugoni F., 2006. An improved seismicity picture of the Southern Tyrrhenian area by the use of OBS and land-based networks: the TYDE experiment, Annals of Geophysics, 49, 2/3, 801 - 817.
Stüwe, K., 2002. Geodynamics of the Lithosphere, Springer-Verlag Berlin Heidelberg, pp. 449.
Thurber, C.H., 1992. Hypocentre–velocity structure coupling in local earthquake tomography, Phys. Earth Planet. Int., 75, 55-62.
Waldhauser, F. & Ellsworth, W. L., 2000. A double-difference earthquake location algorithm: Method and application to North Hayward Fault, California, Bull. Seism. Soc. Am., 90, 1353-1368.
Wells, D. L. & Coppersmith, J., 1994. New Empirical Relationships among Magnitude, Rupture Length, Rupture Width, Rupture Area and Surface Displacement, Bull. Seism. Soc. Am., 84, 974-
1002.
Billi, A., Barberi, G., Faccenna, C., Neri, G., Pepe, F. & Sulli, A., 2006. Tectonics and Seismicity of the Tindari Fault System, southern Italy: Crustal Deformations at the transition between ongoing contractional and extensional domains located above the edge of a subducting slab, Tectonics, 25, TC2006, doi: 10.1029/2004TC001763.
Caltabiano, T., Condarelli, D., Gresta, S., Patanè, D. & Patanè, G., 1986. Analisi preliminare dei dati della stazione sismica di Serra Pizzuta Calvarina, CNR-IIV Open File Report 10/86.
Cernobori, L., Hirn, A., McBride, J.H., Nicolich, R., Petronio, L. & Romanelli, M., 1996. Crustal image of the Ionian basin and its Calabrian margins, Tectonophysics, 264, 175-189.
D’Agostino, N. & Selvaggi, G., 2004. Crustal motion along the Eurasia-Nubia plate boundary in the Calabrian Arc and Sicily and active extension in the Messina Straits from GPS measurements, J. Geophys. Res., 109, B11402, doi:10.1029/2004JB002998.
De Luca, G., Filippi, L., Caccamo, D., Neri, G. & Scarpa, R., 1997. Crustal structure and seismicity of southern Tyrrenian basin, Phys. Earth Planet. Int., 103, 117-133.
Dezes, P. & Ziegler, P. A., 2001. European Map of the Mohorovicic discontinuity. 2nd EUCOR-URGENT Workshop (Upper Rhine Graben Evolution and Neotectonics). Mt. St. Odile, France.
Dziewonski, A. M., Ekström, G., Franzen, J. E. & Woodhouse, J. H., 1987. Global seismicity of 1978: centroid-moment tensor solutions for 512 earthquakes, Phys. Earth Planet. Int., 46, 316-342.
Eberhart – Phillips D. & Michael, A.J., 1993. Three-dimensional velocity structure, seismicity, and fault structure in the Parkfield region, central California, J. Geophys. Res., 98, 737-758.
Efron, B., 1982. The Jackknife, the Bootstrap, and Other Resampling Plans, Society of Industrial and Applied Mathematics, Philadelphia, CBMS-NSF Monographs, pp. 38.
Finetti, I. & Del Ben, A., 1986. Geophysical study of the Tyrrhenian opening, Boll. Geof. Teor. Appl., 110, 75-155.
Frémont, M. J. & Malone, S. D., 1987. High precision relative locations of earthquakes at Mt. St. Helens, Washington, J. Geophys. Res., 92, 10223-10236.
Gasparini, C., Iannaccone, G. & Scarpa, R., 1985. Fault plane solutions and seismicity of the Italian peninsula, Tectonophysics, 117, 59-78.
Goetze, C., 1978. The mechanisms of creep in olivine. Phil. Trans. Roy. Soc. London, 288, 99-119.
Hastie, T., Tibshirani, R. & Friedman, J., 2002. The Elements of Statistical Learning, Springer-Verlag, Berlin, pp. 533.
Hesterberg, T., Monaghan, S., Moore, D. S., Clipson, A. & Epstein, R., 2003. Bootstrap and permutation tests – Companion chapter 18 to the “Practice of Business Statistics”, in: the Practice of Business Statistics, eds. Freeman, W.H. and Company, New York.
Husen, S., Kissling, E., Flueh, E. & Asch, G., 1999. Accurate hypocenter determination in the seismogenic zone of the subducting Nazca plate in north Chile using a combined on-/offshore network, Geophys. J. Int., 138, 687-701.
Kissling, E., Ellsworth, W.L., Eberhart-Phillips, D. & Kradolfer, U., 1994. Initial reference models in local earthquake tomography, J. Geophys. Res., 99, 19,635-19,646.
Kissling, E., 1995. Velest User’s Guide. Internal Report, Institute of Geophysics, ETH, Zurich, pp. 26.
Laigle, M., 1998. Images sismiques de l’Etna à diverses èchelles: Nouveaux éléments sur son comportement et le cadre règional, PhD. thesis, University of Paris 7, Paris, pp. 288.
Lentini, F., Catalano, S. & Carbone, S., 2000. Carta geologica della provincia di Messina, Provincia Regionale di Messina. Assessorato Territorio–Servizio geologico, SELCA, Firenze.
Michelini, A. & Lomax, A., 2004. The effect of velocity structure errors on double-difference earthquake location, Geoph. Res. Lett., 31, L099602, doi: 10.1029/2004GL019682.
Monaco, C. & Tortorici, L., 2000. Active faulting in the Calabrian Arc and eastern Sicily, Journal of Geodynamics, 29, 407-424.
Neri, G., Barberi, G., Orecchio, B. & Aloisi, M., 2002. Seismotomography of the crust in the transition zone between the southern Tyrrhenian and Sicilian tectonic domains, Geophys. Res. Lett., 29, (23), 2135, doi: 10.1029/2002GL015562.
Neri, G., Barberi, G., Orecchio, B. & Mostaccio, A., 2003. Seismic strain and seismogenic stress regimes in the crust of the southern Tyrrhenian region, Earth and Planetary Science Letters, 213, 97-112.
Neri, G., Barberi, G., Oliva, G. & Orecchio B., 2005. Spatial variations of seismogenic stress orientations in Siciliy, South Italy, Phys. Earth Planet. Int., 148, 175-191.
Nicolich, R., Laigle, M., Hirn, A., Cernobori, L. & Gallart, J., 2000. Crustal structure of the Ionian margin of Sicily: Etna volcano in the frame of regional evolution, Tectonophysics, 329, 121-139.
Scarfì, L., Langer, H. & Scaltrito, A., 2005. Relocation of microearthquake swarms in the Peloritani mountains – implications on the interpretation of seismotectonic patterns in NE Sicily, Italy, Geophys. J. Int., 163, 225-237, doi: 10.1111/j.1365-246X.2005.02720.x.
Sgroi, T., Braun, T., Dahm T. & Frugoni F., 2006. An improved seismicity picture of the Southern Tyrrhenian area by the use of OBS and land-based networks: the TYDE experiment, Annals of Geophysics, 49, 2/3, 801 - 817.
Stüwe, K., 2002. Geodynamics of the Lithosphere, Springer-Verlag Berlin Heidelberg, pp. 449.
Thurber, C.H., 1992. Hypocentre–velocity structure coupling in local earthquake tomography, Phys. Earth Planet. Int., 75, 55-62.
Waldhauser, F. & Ellsworth, W. L., 2000. A double-difference earthquake location algorithm: Method and application to North Hayward Fault, California, Bull. Seism. Soc. Am., 90, 1353-1368.
Wells, D. L. & Coppersmith, J., 1994. New Empirical Relationships among Magnitude, Rupture Length, Rupture Width, Rupture Area and Surface Displacement, Bull. Seism. Soc. Am., 84, 974-
1002.
Type
article
File(s)
Loading...
Name
Langer et al_GJI07.pdf
Description
Published paper
Size
850.39 KB
Format
Adobe PDF
Checksum (MD5)
5e6511349e96cc09577e2b2471ccde54