Source investigation of a small event using empirical Green's functions and simulated annealing

We propose a two-step inversion of three-component seismograms that (1) recovers the far-field source time function at each station and (2) estimates the distribution of co-seismic slip on the fault plane for small earthquakes (magnitude 3 to 4). The empirical Green's function (EGF) method consists of finding a small earthquake located near the one we wish to study and then performing a deconvolution to remove the path, site, and instrumental effects from the main-event signal. The deconvolution between the two earthquakes is an unstable procedure: we have therefore developed a simulated annealing technique to recover a stable and positive source time function (STF) in the time domain at each station with an estimation of uncertainties. Given a good azimuthal coverage, we can obtain information on the directivity effect as well as on the rupture process. We propose an inversion method by simulated annealing using the STF to recover the distribution of slip on the fault plane with a constant rupture-velocity model. This method permits estimation of physical quantities on the fault plane, as well as possible identification of the real fault plane. We apply this two-step procedure for an event of magnitude 3 recorded in the Gulf of Corinth in August 1991. A nearby event of magnitude 2 provides us with empirical Green's functions for each station. We estimate an active fault area of 0.02 to 0.15 km2 and deduce a stress-drop value of 1 to 30 bar and an average slip of 0.1 to 1.6 cm. The selected fault of the main event is in good agreement with the existence of a detachment surface inferred from the tectonics of this half-graben.

[1]  Donald V. Helmberger,et al.  Upper mantle structure of the western United States , 1971 .

[2]  A. Zollo,et al.  How does an asperity break? New elements from the waveform inversion of accelerograms for the 2319 UT, October 15, 1979, Imperial Valley Aftershock , 1991 .

[3]  Alexis Rigo.  Etude sismotectonique et géodésique du Golfe de Corinthe (Grèce) , 1994 .

[4]  N. Metropolis,et al.  Equation of State Calculations by Fast Computing Machines , 1953, Resonance.

[5]  M. Briscoe,et al.  Global Ocean Observing System gains momentum , 1994 .

[6]  A. Tarantola.  Inverse problem theory : methods for data fitting and model parameter estimation , 1987 .

[7]  Aaron A. Velasco,et al.  Empirical Green function deconvolution of broadband surface waves: rupture directivity of the 1992 Landers, California (Mw = 7.3), earthquake , 1994 .

[8]  Jean Virieux,et al.  On the use of simulated annealing method and cross-validation theory for deconvolution of seismograms , 1996, Bulletin of the Seismological Society of America.

[9]  Charles S. Mueller,et al.  Source pulse enhancement by deconvolution of an empirical Green's function , 1985 .

[10]  B. Feignier.  How geology can influence scaling relations , 1991 .

[11]  D. L. Anderson,et al.  Theoretical Basis of Some Empirical Relations in Seismology by Hiroo Kanamori And , 1975 .

[12]  R. Sibson.  Fault zone models, heat flow, and the depth distribution of earthquakes in the continental crust of the United States , 1982 .

[13]  A. Frankel,et al.  Reply to K. Aki's “Comment on ‘microearthquake spectra from the Anza, California seismic network: Site response and source scaling’” , 1989, Bulletin of the Seismological Society of America.

[14]  C. D. Gelatt,et al.  Optimization by Simulated Annealing , 1983, Science.

[15]  Jean Virieux,et al.  Electromagnetic Imaging and Simulated Annealing , 1991 .

[16]  Daniel H. Rothman,et al.  Automatic estimation of large residual statics corrections , 1986 .

[17]  Aldo Zollo,et al.  Use of small earthquake records to determine the source time functions of larger earthquakes: an alternative method and an application , 1995 .

[18]  S. Hartzell.  Earthquake aftershocks as Green's functions , 1978 .

[19]  X. Pichon,et al.  The hellenic arc and trench system: A key to the neotectonic evolution of the eastern mediterranean area , 1979 .

[20]  Paul G. Richards,et al.  Quantitative Seismology: Theory and Methods , 1980 .

[21]  Jim Mori,et al.  Source inversion of the 1988 Upland, California, earthquake: Determination of a fault plane for a small event , 1990, Bulletin of the Seismological Society of America.

[22]  S. Hough,et al.  Empirical Green's function analysis of Loma Prieta aftershocks , 1991 .

[23]  N. Voulgaris,et al.  Subcrustal microearthquake seismicity and fault plane solutions beneath the Hellenic Arc , 1993 .

[24]  V. Cerný.  Thermodynamical approach to the traveling salesman problem: An efficient simulation algorithm , 1985 .

[25]  G. Ori.  Geologic history of the extensional basin of the Gulf of Corinth (?Miocene-Pleistocene), Greece , 1989 .

[26]  Huang,et al.  AN EFFICIENT GENERAL COOLING SCHEDULE FOR SIMULATED ANNEALING , 1986 .

[27]  J. Boatwright,et al.  A spectral theory for circular seismic sources; simple estimates of source dimension, dynamic stress drop, and radiated seismic energy , 1980 .

[28]  J. Mori.  Fault plane determinations for three small earthquakes along the San Jacinto Fault, California: Search for cross faults , 1993 .

[29]  Thomas H. Heaton,et al.  Initial investigation of the Landers, California, Earthquake of 28 June 1992 using TERRAscope , 1992 .

[30]  C. Lawson,et al.  Solving least squares problems , 1976, Classics in applied mathematics.

[31]  Michael Creutz,et al.  Monte Carlo Study of Quantized SU(2) Gauge Theory , 1980 .

[32]  K. Irikura,et al.  Rupture process of the 1983 Japan Sea (Akita-Oki) earthquake using a waveform inversion method , 1986 .

[33]  Christopher H. Scholz,et al.  Scaling laws for large earthquakes: Consequences for physical models , 1982 .

[34]  Thomas C. Hanks,et al.  Source parameters of southern California earthquakes , 1973 .

[35]  Aaron A. Velasco,et al.  Rapid estimation of rupture directivity: Application to the 1992 Landers (MS = 7.4) and Cape Mendocino (MS = 7.2), California earthquakes , 1993 .

[36]  Stephen H. Hartzell,et al.  Comparison of seismic waveform inversion results for the rupture history of a finite fault: Application to the 1986 North Palm Springs, California, earthquake , 1989 .

[37]  P. Bernard,et al.  A new asymptotic method for the modeling of near-field accelerograms , 1984 .

[38]  James Jackson,et al.  The relationship between plate motions and seismic moment tensors, and the rates of active deformation in the Mediterranean and Middle East , 1988 .

[39]  L. Neil Frazer,et al.  Use of ray theory to calculate high-frequency radiation from earthquake sources having spatially variable rupture velocity and stress drop , 1984 .

[40]  Jean Virieux,et al.  Seismicity, normal faulting, and the geomorphological development of the Gulf of Corinth (Greece): the Corinth earthquakes of February and March 1981 , 1982 .