| Title | Geophysical imaging of the Paeroa fault: Insights from a dense nodal seismic array |
|---|---|
| Authors | B. Keats, S. Bannister, C. Massiot, C. Miller, S. Henrys, T. Brakenrig, L. Coup, N. Macdonald, O. Kurimura, L. Werahiko, U. Werahiko-Mita, M. Phillips, C. Jiang |
| Year | 2024 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Seismology, dense nodal seismic array, ambient noise, Paeroa fault |
| Abstract | The Paeroa Fault is one of the longest and most active multistrand faults in the TaupÅ Rift, capable of generating Mw6.8+ ruptures on a millennial timescale. At its northern end the Paeroa Fault splays into the Ngapouri fault and is surrounded by several active geothermal features. Mapping the fault strands and their dip angle is important to understand earthquake hazards, fluid flow pathways and links between faulting, volcanism, and geothermal activity. Over the summer of 2023/24 we deployed a dense nodal seismic array (DNSA) across the northern termination of the Paeroa fault, straddling the deep resistivity boundary along the northern boundary of the Waiotapu and Waimangu geothermal systems. The survey deployed 147 short-period and broadband nodal seismometers recording continuously for a period of ~4 weeks and collected new closely spaced gravity data. In the initial analysis we have cross-correlated and stacked more than 1000 station-station pairs. The derived dispersion spectra for station-station pairs show clean fundamental surface-wave dispersion for Z-Z components for frequencies between 0.3 and 2 Hz. We will apply additional processing approaches to also retrieve higher modes, and to retrieve information for a wider bandwidth. We will then jointly invert the Rayleigh and Love dispersion curves to construct a three-dimensional S-wave velocity model, likely imaging to c. 2 km in depth across the spatial extent of the array for combined interpretation with a new 3D gravity model of the area. We anticipate that our derived 3-D S-wave velocity model will reflect the subsurface heterogeneity across the Paeroa Fault, as well as imaging the northern boundary of the Waimangu and Waiotapu geothermal systems, delineating subsurface faults associated with local seismicity. With this study we aim to show that DNSA surveys are an effective non-invasive geophysical method for imaging shallow faults in the TVZ, for seismic hazard planning and geothermal exploration. |