Abstract
A layeredP- andS-wave velocity model is obtained for the Friuli seismic area using the arrival time data ofP- andS-waves from local earthquakes. A damped least-squares method is applied in the inversion.
The data used are 994P-wave arrival times for 177 events which have epicenters in the region covered by the Friuli seismic network operated by Osservatorio Geofisico sperimentale (OGS) di Trieste, which are jointly inverted for the earthquake hypocenters andP-wave velocity model. TheS-wave velocity model is estimated on the basis of 978S-wave arrival times and the hypocenters obtained from theP-wave arrival time inversion. We also applied an approach thatP- andS-wave arrival time data are jointly used in the inversion (Roecker, 1982). The results show thatS-wave velocity structures obtained from the two methods are quite consistent, butP-wave velocity structures have obvious differences. This is apparent becauseP-waves are more sensitive to the hypocentral location thanS-waves, and the reading errors ofS-wave arrival times, which are much larger than those ofP-waves, bring large location errors in the joint inversion ofP- andS-wave arrival time. The synthetic data tests indicated that when the reading errors ofS-wave arrivals are larger than four times that ofP-wave arrivals, the method proposed in this paper seems more valid thanP- andS-wave data joint inversion. Most of the relocated events occurred in the depth range between 7 and 11 km, just above the biggest jump in velocity. This jump might be related to the detachment line hypothesized byCarulli et al. (1982). From the invertedP- andS-wave velocities, we obtain an average value 1.82 forV p /V s in the first 16 km depth.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Aki, K., andLee, W. H. K. (1976),Determination of Three-dimensional Velocity Anomalies under a Seismic Array Using First P arrival Times from Local Earthquakes. Part I. A Homogenous Initial Model. J. Geophys. Res.81, 4381–4399.
Aki, K., andRichards, P.,Methods of Quantitative Seismology (Freeman, San Francisco 1980).
Amato, A., Barnaba, P. F., Finetti, I., Groppi, G., Martinis, B., andMuzzin, A. (1976).Geodynamic Outline and Seismicity of Friuli-Venezia Giulia Region, Boll. Geof. Teor. Appl.,19, 217–256.
Anderson, H., andJackson, J. (1987),Active Tectonics of the Adriatic Region, Geophys. J. R. Astr. Soc.91, 937–983.
Backus, G. E., andGilbert, J. F. (1967),Numerical Applications of a Formalism for Geophysical Inverse Problems, Geophys. J. R. Astr. Soc.13, 247–279.
Backus, G. E., andGilbert, J. F. (1968),The Resolving Power of Gross Earth Data, Geophys. J. R. Astr. Soc.16, 169–205.
Backus, G. E., andGilbert, J. F. (1970),Uniqueness in the Inversion of Inaccurate Gross Earth Data, Phil. Trans. Roy. Soc.A266, 123–192.
Bernardis, G., Giorgetti, F., Nieto, D., Russi, M., andSuhadolc, P. (1976),Seismicity of the Friuli-Venezia Giulia Region, Boll. Geof. Teor. Appl.19, 365–376.
Bollettino della Rete Sismometrica dell'Italia Nord Orientale (Osservatorio Geofisico Sperimentale, Trieste 1977).
Carulli, G. B., Giorgetti, F., Nicolich, R., andSlejko, D.,Friuli zona sismica: sintesi di dati sismologici, strutturali e geofisici. InGuida alla geologia del sudalpino centro-orientale, Guide geol. reg. G.G.I. (eds. Castellarin, A., and Vai, G. B.) (Tecnoprint, Bologna 1982) pp. 361–370.
Crosson, R. S. (1976a),Crustal Structure Modeling of Earthquake Data. Part 1. Simultaneous Least Squares Estimation of Hypocenter and Velocity Parameters, J. Geophys. Res.81, 3036–3046.
Crosson, R. S. (1976b),Crustal Structure Modeling of Earthquake Data. Part 2. Velocity Structures of the Puget Sound Region, Washington, J. Geophys. Res.81, 3047–3053.
Franklin, J. N. (1970),Well Posed Stochastic Extensions of Ill Posed Linear Problems. J. Math. Anal. Applic.31, 682–716.
Lee, W. H. K., andLahr, J. C. (1975),HYPO71 (revised): A Computer Program for Determining Hypocenter, Magnitude, and First Motion Pattern of Local Earthquakes, Geol. Surv. Open-File Rep. (U.S.) 75–311, 116 pp.
Lee, W. H. K., andStewart, S. W.,Principles and Applications of Microearthquake Networks, Adv. Geophys. Suppl. 2 (Academic Press, New York 1981).
Leonard, M. A., andJohnson, L. R. (1987),Velocity Structure of Silent Canyon Caldera, Nevada Test Site, Bull. Seismol. Soc. Am.77, 597–613.
Levenberg, K. (1944),A Method for the Solution of Certain Nonlinear Problems in Least Squares, Quant. Appl. Math.2, 164–168.
Mao, W. J. (1989),Deformazione crostale ed inversione dei dati sismici nello studio dell' area sismica del Friuli, Ph.D. thesis, University of Triests, Italy.
Marquardt, D. W. (1963),An Algorithm for Least-squares Estimation of Nonlinear Parameters, J. Soc. Ind. Appl. Math.11, 431–441.
Menke, W.,Geophysical Data Analysis: Discrete Inverse Theory (Academic Press, San Diego 1984).
Pavlis, G. L., andBooker, J. R. (1980),The Mixed Discrete Continuous Inverse Problem: Application to the Simultaneous Determination of Earthquake Hypocenters and Velocity Structure, J. Geophys. Res.85, 4801–4810.
Roecker, S. W. (1982),Velocity Structure of the Pamir-Hindu Kush Region: Possible Evidence of Subducted Crust. J. Geophys. Res.87, 945–959.
Rogers, T. H., andCluff, L. S. (1979),The May 1976 Friuli Earthquake (Northeastern Italy) and Interpretations of Past and Future Seismicity, Tectonophys.52, 521–532.
Spencer, C., andGubbins, D. (1980),Travel-time Inversion for Simultaneous Earthquake Location and Velocity Structure Determination in Laterally Varying Media, Geophys. J. R. Astr. Soc.63, 95–116.
Thurber, C. H., andAki, K. (1987),Three-dimensional Seismic Imaging, Ann. Rev. Earth Planet. Sci.15, 115–139.
Wiggins, R. A. (1972),The General Linear Inverse Problem: Implication of Surface Waves and Free Oscillations for Earth Structure, Rev. Geophys. Space Phys.10, 251–285.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Mao, W.J., Suhadolc, P. Simultaneous inversion of velocity structures and hypocentral locations: Application to the Friuli seismic area NE Italy. PAGEOPH 138, 267–285 (1992). https://doi.org/10.1007/BF00878899
Received:
Revised:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00878899