Source parameters of small events using constrained deconvolution with empirical Green’s functions

Summary An iterative and constrained deconvolution technique, called projected Landweber deconvolution (PLD), is applied to a local earthquake data set recorded in the southwestern Alps (NW Italy) in order to estimate the relative source time function (RSTF) of the events. The magnitude range analysed is 1.4<ML<4.3. The smallest events (ML<2.0) are used as empirical Green’s functions (EGF) to deconvolve the larger earthquakes. The crucial choice of appropriate EGF is tackled using high-precision relative locations. Results demonstrate that PLD successfully overcomes the instability effects of the deconvolution process and provides stable and reliable RSTFs. Moreover, this method allows us to obtain an objective determination of the duration of the RSTF, which is essential to estimate correctly the source size. Combining the information inferred from both RSTFs and displacement spectra, source parameters are computed for all the events. We obtain seismic moments ranging from 2.9 × 1011 to 3.1 × 1014 N m and source radii between 70 and 700 m. Taking the instrumental limits into account, no breakdown in constant stress drop scaling is seen in our estimates.

[1]  Frank L. Vernon,et al.  Rupture characteristics and tomographic source imaging of ML ∼ 3 earthquakes near Anza, southern California , 1986 .

[2]  M. Granet,et al.  Some medium properties at friuli (Italy) from amplitude spectrum analysis: A possible change in time or in space , 1980 .

[3]  Susan E. Hough,et al.  Earthquake and Its Aftershocks: Empirical Green's Function Analysis of GEOS and TERRAscope Data , 1995 .

[4]  Source parameters and scaling relationships of small earthquakes in the northeastern Caribbean , 1981 .

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

[6]  Robert M. Nadeau,et al.  Seismological studies at Parkfield VI: Moment release rates and estimates of source parameters for small repeating earthquakes , 1998, Bulletin of the Seismological Society of America.

[7]  C. Doll,et al.  Source characterization and fault plane determination for MbLg = 1.2 to 4.4 earthquakes in the Charlevoix Seismic Zone, Quebec, Canada , 1995, Bulletin of the Seismological Society of America.

[8]  Mario Bertero,et al.  Application of the projected Landweber method to the estimation of the source time function in seismology , 1997 .

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

[10]  Rachel E. Abercrombie,et al.  Earthquake source scaling relationships from −1 to 5 ML using seismograms recorded at 2.5‐km depth , 1995 .

[11]  Bertolt Eicke.  Iteration methods for convexly constrained ill-posed problems in hilbert space , 1992 .

[12]  Pulse-shape distortion introduced by broadband deconvolution , 1992, Bulletin of the Seismological Society of America.

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

[14]  Jean Virieux,et al.  Source investigation of a small event using empirical Green's functions and simulated annealing , 1996 .

[15]  M. Popa,et al.  Scaling of source parameters for Vrancea (Romania) intermediate depth earthquakes , 1996 .

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

[17]  S. J. Gibowicz,et al.  Source parameters of seismic events at the Underground Research Laboratory in Manitoba, Canada: Scaling relations for events with moment magnitude smaller than −2 , 1991 .

[18]  Shamita Das.  Three‐dimensional spontaneous rupture propagation and implications for the earthquake source mechanism , 1981 .

[19]  David M. Boore,et al.  Moment‐magnitude relations in theory and practice , 1984 .

[20]  N. Deichmann.  Far-field pulse shapes from circular sources with variable rupture velocities , 1997, Bulletin of the Seismological Society of America.

[21]  Frank Scherbaum,et al.  Source parameters and scaling laws of the 1978 Swabian Jura (southwest Germany) aftershocks , 1983 .

[22]  W. Bakun,et al.  Seismic moments, local magnitudes, and coda-duration magnitudes for earthquakes in central California , 1984 .

[23]  R. Madariaga.  Dynamics of an expanding circular fault , 1976, Bulletin of the Seismological Society of America.

[24]  William H. Press,et al.  Numerical recipes , 1990 .

[25]  Heinz W. Engl,et al.  Inverse and Ill-Posed Problems , 1987 .

[26]  Charles S. Mueller,et al.  Source parameters of the 1980 Mammoth Lakes, California, earthquake sequence , 1982 .

[27]  Jim Mori,et al.  Source parameters for small events associated with the 1986 North Palm Springs, California, earthquake determined using empirical Green functions , 1990 .

[28]  Hiroo Kanamori,et al.  Determination of rupture duration and stress drop for earthquakes in southern California , 1983 .

[29]  Jon B. Fletcher,et al.  A general inversion scheme for source, site, and propagation characteristics using multiply recorded sets of moderate-sized earthquakes , 1991 .

[30]  Tamao Sato,et al.  Seismic radiation from circular cracks growing at variable rupture velocity , 1994, Bulletin of the Seismological Society of America.

[31]  Marco Cattaneo,et al.  Reconstruction of seismogenetic structures by multiplet analysis: An example of Western Liguria, Italy , 1997, Bulletin of the Seismological Society of America.

[32]  J. Brune.  Tectonic stress and the spectra of seismic shear waves from earthquakes , 1970 .

[33]  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 .

[34]  Thomas C. Hanks,et al.  Source parameters for aftershocks of the Oroville, California, earthquake , 1984 .

[35]  M. Nafi Toksöz,et al.  Study of the source process of the 1992 Colombia Ms=7.3 earthquake with the empirical Green's Function Method , 1993 .