Earthquake triggering in the Hawke's Bay, New Zealand, region from 1931 to1934 as inferred from elastic dislocation and static stress modeling

During the 1930s the Hawke's Bay region of New Zealand experienced four lar ge earthquakes, Napier (M-W 7.6) and Hawke Bay (M-W 7.3) in 1931, Wairoa (M -W 6.9) in 1932, and Pahiatua (M-W 7.4) in 1934. We address the question of whether these comprise a triggered sequence of events. There are significa nt difficulties in dealing with earthquakes that were recorded 70 years ago as fault parameters are difficult to obtain. With the exception of the Pah iatua earthquake, no primary surface fault ruptures were identified, and lo cations for the other three events may be in error by tens of kilometers. H owever, geodetic data were collected before and after the Napier and Wairoa earthquakes, and regions of uplift and subsidence from the former have bee n mapped from low-order leveling data. This information helps to constrain the fault parameters for the first of these events through elastostatic mod eling. Results from recent teleseismic body wave modeling have been used to determine fault parameters for the Hawke Bay event. Our analysis of the in duced static stresses with the Coulomb failure criterion shows that the Nap ier earthquake triggered both the Hawke Bay and Wairoa earthquakes but that the Hawke Bay earthquake probably delayed the Wairoa earthquake. We also c onclude that these three events did not trigger the Pahiatua earthquake.