Simulation of strong-motion displacements using surface-wave modal superposition

Synthetic seisomograms constructed by addition of surface-wave modes in a layered half-space are compared to Cagniard-de Hoop calculations of Heaton and Helmberger (1977, 1978) and to ground displacement recordings near El Centro, California to examine the applicability of modal superposition as a means of simulating ground motion of possible engineering interest. Modal solutions of flat earth problems are desirable because of the modest cost involved and the versatility of the method in simulating extended sources and anelastic damping. P-SV and SH motions can be computed with almost equal ease. The comparisons show that in sedimentary structures surface waves can dominate ground displacement motion at epicentral distances of only a few source depths. Superposition of the higher modes often approximates quite well impulsive arrivals with analogies to refracted and reflected rays. Ground displacement recordings of El Centro from the 1968 Borrego Mountain earthquake are modeled using a multi-layered geological structure and a source model based on independent studies. The gross character of the records appears to be insensitive to the details of the source. Both point sources and propagating sources with horizontal dimensions larger than half the epicentral distance give'reasonable fits to the observed transverse motion. This insensitivity appears to be due to a complex interaction between rupture propagation and the surface-wave dispersion. By using the integrated El Centro accelerogram, which may have more reliable amplitude information than the Carder displacement record used in other studies, the moment is estimated to be 12 x 102s dyne-cm. This is similar to values found from studies of teleseismic data.

[1]  Ari Ben-Menahem,et al.  Radiation of seismic surface-waves from finite moving sources , 1961 .

[2]  C. R. Allen,et al.  Geophysical Framework of Northern End of Gulf of California Structural Province , 1964 .

[3]  David G. Harkrider,et al.  Surface waves in multilayered elastic media. I. Rayleigh and Love waves from buried sources in a multilayered elastic half-space , 1964 .

[4]  The Anelasticity of the Earth. , 1964 .

[5]  THEORETICAL INVESTIGATION OF MODAL SEISMOGRAMS FOR A LAYER OVER A HALF‐SPACE , 1965 .

[6]  R. Hamilton Time-term analysis of explosion data from the vicinity of the Borrego Mountain, California, earthquake of 9 April 1968 , 1970 .

[7]  David G. Harkrider,et al.  Surface waves in multilayered elastic media. Part II. Higher mode spectra and spectral ratios from point sources in plane layered Earth models , 1970, Bulletin of the Seismological Society of America.

[8]  Mihailo D. Trifunac,et al.  A method for synthesizing realistic strong ground motion , 1971, Bulletin of the Seismological Society of America.

[9]  M. Wyss,et al.  Source Parameters of the Borrego Mountain Earthquake , 1972 .

[10]  C. R. Allen,et al.  Foreshock, Main Shock, and Larger Aftershocks of the Borrego Mountain Earthquake , 1972 .

[11]  J. Brune,et al.  Surface waves and crustal structure in the Gulf of California region , 1973 .

[12]  V. W. Lee,et al.  A note on the accuracy of computed ground displacements from strong-motion accelerograms , 1974, Bulletin of the Seismological Society of America.

[13]  W. B. Joyner,et al.  Calculation of nonlinear ground response in earthquakes , 1975 .

[14]  D. Helmberger,et al.  Modeling local earthquakes as shear dislocations in a layered half space , 1975 .

[15]  Thomas C. Hanks,et al.  Strong ground motion of the San Fernando, California, earthquake: Ground displacements , 1975, Bulletin of the Seismological Society of America.

[16]  R. Herrmann,et al.  Ground-motion modelling at regional distances for earthquakes in a continental interior, I. Theory and observations , 1975 .

[17]  R. Herrmann,et al.  Ground‐motion modelling at regional distances for earthquakes in a continental interior, II. Effect of focal depth, azimuth and attenuation , 1975 .

[18]  G. Mellman,et al.  Inversion of the body waves from the Borrego Mountain earthquake to the source mechanism , 1976, Bulletin of the Seismological Society of America.

[19]  T. Heaton,et al.  A study of the strong ground motion of the Borrego Mountain, California, earthquake , 1977, Bulletin of the Seismological Society of America.

[20]  I. Kawasaki THE NEAR-FIELD LOVE WAVES BY THE EXACT RAY METHOD , 1978 .

[21]  T. Heaton,et al.  PREDICTABILITY OF STRONG GROUND MOTION IN THE IMPERIAL VALLEY: MODELING THE M4.9, NOVEMBER 4, 1976 BRAWLEY EARTHQUAKE , 1978 .

[22]  W. B. Joyner,et al.  THE INFLUENCE OF RUPTURE INCOHERENCE ON SEISMIC DIRECTIVITY , 1978 .