Part 3. Present plate boundary and its evolution in the New Zealand region: Detailed structure of North Island seismic zone

Abstract

Fifty four North Island N.Z. intermediate depth earthquakes which had high precision P arrivals at each of the North Island Seismograph stations CNZ, ECZ, GNZ, KRP, MNG, TNZ, WEL*, and whose epicentres lay inside the convex hull of these stations, were relocated using only this P data by the usual least squares method. By restricting the data in this way, the error in location of earthquakes in a small enough geographical group due to errors in the velocity model used should be a constant. Examination of the time residuals of the earthquakes in a group will reveal whether the group is small enough: if at each station the standard deviation of the residuals about the mean residual for that station is very much smaller than the average standard deviation for the group without station means removed, the assumption is valid.