Reply to comment by J. Trampert

Books Reviewed in this Article:
Seismic tomography and mantle circulation Eds O'Nions, R. K. & Parsons, B., Royal Society of London Special Publication , 1989, ISBN 0854 033823.     

Reply to comment by J. R. Murphy on 'Q for short-period P waves: is it frequency dependent?' by A. Douglas

Using network averaged spectra Murphy (1989) demonstrates that if it is assumed that the source functions of explosions at Pahute Mesa, Nevada Test Site (NTS) are as predicted by the Mueller-Murphy (M-M) source model then the average t * at around 1 Hz for P waves radiated from the test site must be about 0.75 s. With this value of t * Murphy (1989) estimates the best fitting M-M spectrum for each explosion studied, by adjusting A, t _o & c ; A & t _o being the amplitude and delay time of pP relative to P and c the wave speed for the material in which the explosion was fired. The absolute amplitudes of the theoretical spectra are obtained using a calibration factor estimated from the data. Murphy (1993) extends the analysis to explosions in granite at the Nevada, French Sahara and E. Kazakh test sites. For the French Sahara explosion t * is assumed to be 0.75 s (Murphy's estimate for NTS explosions), and for the E. Kazakh explosion a t * of 0.55 s is used. For the French Sahara and E. Kazakh explosions Murphy (1993) shows that by using the same calibration factor as for the NTS it is possible by varying A & t _o to fit the estimated average network spectra using the M-M granite source. Murphy (1993) states that the amplitudes and spectra for the largest NTS explosion in granite (PILE DRIVER) can also be predicted using the M-M model but these results are not shown.     

Reply to comment by A. Douglas on 'Systematic determination of earthquake rupture directivity and fault planes from analysis of long-period P-wave spectra'

We respond to the comments by Douglas regarding our earlier paper by emphasizing that our automated method was intended to distinguish between the primary and auxiliary fault planes in earthquake focal mechanisms and does not always produce reliable results for rupture velocity and rupture length.