Abstract
Long-period P waveforms have been analyzed to interpret the source mechanism of four intermediate earthquakes with magnitudes of 6.0-6.5 and focal depths between 100 and 200km.
The synthetic seismograms appropriate to each recording station have been constructed, to compare with observed records, on the basis of moving dislocation models with various parameters, including the fault length and width, the amount of dislocation, its time dependence and the fracture velocity, taking into account the combined effects of wave propagation in the earth and of a recording instrument. General features of the observed waveforms do not differ greatly from those for a double-couple point source, but the comparison with synthesized waveforms at a number of stations indicated seismic moment of order of 5-9×1026 dyne·cm, and also probable ranges for some other source parameters on tne assumed source. The bounds of the stress-strain drop, the released strain energy, and of efficiency of seismic wave radiation at the source were also discussed.
