NEOTECTONIC EVALUATION OF SEISMIC HAZARD ALONG THE RUATANIWHA FAULT, DANNEVIRKE REGION, NEW ZEALAND

The Ruataniwha Fault lies within the Hawke’s Bay region of New Zealand’s North Island. A diverse spectrum of methods and results aim to characterize earthquake activity along this reverse fault to better inform local bodies of the seismic risk posed by the fault. Interpretation of LiDAR results, orthophotographs, and ground topography enabled the creation of a detailed map of fault location for ~50 kilometers of its trace. An RTK GPS surveyed vertical offsets across late Quaternary terraces along the fault providing detailed amounts of vertical offset up to ~21 meters. Correlation of terrace stratigraphy to other previously dated late Quaternary surfaces within the region determined age constraints for the offset Q1, to Q6 surfaces. Reinterpretation of seismic profiles collected within the Ruataniwha-Dannevirke Basin constrained fault dips in select locations between 51 and 63 degrees to the NW. Data on offset amount, age constraint, and dip angle calculated slip rate along the fault, increasing from zero at the margins to a maximum of 0.64 mm/yr in the central section. Larger scale tectonic interpretations of a 8 km wide anticline (cored by the fault) identified tighter interlimb fold angles in sections of more active surface faulting. Using the regional tectonic similarities, the nearby and geometrically similar Tukituki fault served as a proxy for periodicity estimates of the Ruataniwha Fault. As well, untested methods identifying "kinks" in the slope of the fault scarp determined periodicity directly along the fault. These findings calculated maximum recurrence intervals ranging from ~4,450 yr to ~9,000 yr. and classified New Zealand seismic hazards of class III and class IV for sections of the fault. These classifications give a quantifiable assessment of risk along the Ruataniwha Fault for the benefit of residents and municipalities near this seismic hazard. Additionally, this study aids in an overall effort to characterize the surface faulting hazard of reverse faults in the Hawke's Bay region and provides a basis for understanding strain release across the onshore segment of the Hikurangi subduction margin.