|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
DEPARTMENT OF EARTH AND ATMOSPHERIC SCIENCES SAINT LOUIS UNIVERSITY, P.O. BOX 8099, LACLEDE STATION, ST. LOUIS, MISSOURI 63156
Abstract
The objective of this study is to determine the focal mechanisms of small earthquakes at very near epicentral distances and use them to predict the observed waveforms. To achieve our objectives, the following steps were adopted before attempting to match the entire waveform: (a) obtain an appropriate velocity model; (b) calculate the Green's functions and predict ground motions due to an earthquake specified by dip (
), slip (
), and strike (
) of a fault; (c) select all mechanisms which satisfy the first-motion polarity at all stations; (d) select a subset of focal mechanisms from those obtained in step (c) which produce P and S amplitudes and P/SV and SV/SH amplitude ratios correctly; and (e) use focal mechanisms of step (d) to match waveforms. As an alternative approach, a least-squares inversion for the moment-tensor elements was performed and decomposition of moment tensor matrix to two double couples (major and minor) was performed. Green's functions were computed using the Cagniard-de-Hoop theory (Helmberger and Harkrider, 1978).
We applied the above approaches to four aftershocks (mbLg 
3.5) of the New Brunswick earthquake of 9 January 1982 and succeeded in obtaining focal mechanisms and producing synthetic waveforms very similar to the observed waveforms. Two groups of focal mechanisms are found. Two of the earthquakes are found to have reverse fault geometry similar to that of the main event of 9 January 1982 (mb = 5.7), while the other two have significant components of strike-slip motion on a dipping plane. The results obtained from the least-squares analysis support the results of the search method. The fault geometries determined by the search method correspond well to the results of the major double couple of the least-square inversion.
For completeness of the source characteristics investigation, spectral analysis of the seismograms was performed to determine the source parameters: corner frequencies, fc, seismic moments, source dimensions, and stress drops.
This article has been cited by other articles:
|
|
 |
|
  Y. Tan and D. Helmberger A New Method for Determining Small Earthquake Source Parameters Using Short-Period P Waves Bulletin of the Seismological Society of America, August 1, 2007; 97(4): 1176 - 1195. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. BERNARD and A. ZOLLO Inversion of near-source S polarization for parameters of double-couple point sources Bulletin of the Seismological Society of America, December 1, 1989; 79(6): 1779 - 1809. [Abstract] [PDF]
|
|
|
|
|
|
P. S. DYSART, J. A. SNOKE, and I. S. SACKS Source parameters and scaling relations for small earthquakes in the Matsushiro region, southwest Honshu, Japan Bulletin of the Seismological Society of America, April 1, 1988; 78(2): 571 - 589. [Abstract] [PDF]
|
|
|
|
|
|
T.-C. SHIN and R. B. HERRMANN Lg attenuation and source studies using 1982 Miramichi data Bulletin of the Seismological Society of America, April 1, 1987; 77(2): 384 - 397. [Abstract] [PDF]
|
|
|
|
|
|
C. K. SAIKIA and R. B. HERRMANN Moment-tensor solutions for three 1982 Arkansas swarm earthquakes by waveform modeling Bulletin of the Seismological Society of America, June 1, 1986; 76(3): 709 - 723. [Abstract] [PDF]
|
|
|
|
|
|
C. K. SAIKIA Waveform modeling of two earthquakes (M {approx} 1.1) of July 1983 from the Miramichi aftershock zone Bulletin of the Seismological Society of America, June 1, 1986; 76(3): 725 - 732. [Abstract] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
