Body-Wave Analysis of the 1966 Gisborne, New Zealand, Earthquake

摘要

The M sub L = 6.2 Gisborne earthquake of March 4, 1966 occurred along the East Coast of the North Island. Modeling of P and S body waves shows that the focal mechanism of this event is consistent with northwestward thrusting of the Pacific Plate beneath the North Island (Phi = 249 deg, delta = 25 deg, and lambda = 131 deg). The focal depth is constrained to 18 km, significantly less than the values of 25-30 km computed from local network data. Estimates of the scalar moment, source duration and stress-drop for the event are 4 x 10 to the 24th power dyne-cm, 2-3 s, and 20-120 bar, respectively. Cross-correlation errors of synthetic to observed waveforms were computed for all possible P and T axis locations and slip vector orientations and contoured on a projection of the focal sphere. The error contour at which the synthetic waveforms distinctly diverged from the observed waveforms was established by eye. The procedure shows that the analysis of long-period body waves, at least in this case, provides much better constraint on focal mechanism orientation than does first motion data alone.