Seismogenic stress conditions in central New Zealand

Abstract

Analysis of head-wave first-motions in the geographical domain elucidates areas of well organised and poorly organised stress and indicates the orientation of the stress tensor in well organised areas. Using some 2,000 first-motions, recorded at five central New Zealand seismograph stations since 1964, the study region was found to consist of three areas, each with a different stress regime. In the south the stress tensor is oriented in accordance with the known faulting whilst in the north it is not. In between lies an area of indeterminate stress. These differences may be attributed to stress changes associated with the occurrence of large crustal earthquakes.