Along-strike variations in the Hikurangi Subduction zone: land-based seismic observations during the 2017-2018 SHIRE seismic onshore-offshore imaging project

Slip along subduction zone slab interfaces exhibit a range of styles, including destructive coseismic earthquakes, slow slip events, tremor, and aseismic creep. These slip processes are influenced by factors such as local stress state, physical properties including friction and elastic properties, presence of fluids, and mineral composition of rocks filling the fault zones where the slip occurs. Estimations of these factors can be made using geophysical and geological methods. The Hikurangi subduction margin at eastern North Island, New Zealand, represents an excellent system to examine these physical processes that govern slip. Significant along-strike variation is present with largely stick-slip (coseismic earthquakes) observed in the southern portion of the system and dominantly aseismic creep (slow slip events) observed to the north. Several other major earthquake and tectonic factors also vary from south to north, either influencing the change in slip behavior or being the result of this lateral change.

The multi-disciplinary, multi-national SHIRE (Seismogenesis at Hikurangi Integrated Research Experiment) project examines these factors that influence slip plus the relationship between this slip and long-term deformation. SHIRE includes research activities in active and passive source seismology, paleoseismology, and geodynamics. SHIRE carried out a large seismic onshore-offshore experiment of the Hikurangi margin during October 2017-February 2018 with international partners from New Zealand, USA, Japan, and UK. This experiment involved (1) the USA R/V Langseth to collect 4046 km of MCS profiles, (2) OBS instruments to acquire airgun refraction/wide angle reflections, and (3) portable short-period land instruments to record the same airgun sources plus four months of local earthquakes. Besides being studied using active-source seismic techniques, the continuous SHIRE land data is being analyzed using earthquakes for structural imaging of the slab and ambient noise for velocity structure and anisotropy. In this poster we describe the land-based field operations and present examples of these data and their early results. Related posters within this session present results of the marine and sea-to-land data collected during this seismic onshore-offshore experiment.