| Abstract |
We image the crustal seismic properties beneath a 30 x 50 km area of the Taupo Volcanic Zone (TVZ), New Zealand, encompassing the Wairakei, Mokai, Rotokawa, Ngatamariki, and Ohaaki geothermal fields, as part of a multi-disciplinary research program to investigate the untapped deep geothermal resource in this region. The focus of the study is to resolve seismic properties in the 2-8 km depth range. Our study of seismic properties is complementary to a magnetotelluric study investigating electrical conductivity in the same region (Bertrand et al., 2012a; 2-012b; 2013). Seismic data used for the imaging was recorded using a 38-site broadband seismic array deployed across the region between September 2009 and April 2011 with an average station spacing of ~4-7 km. We supplement this new broadband data with legacy short-period and broadband data recorded by previous research seismic arrays, including the 1995 “TVZ95” array, the 2001 “CNIPSE” array, the “RF2004” array, data recorded by the national GeoNet seismometer network, and with active source data collected in the “NIGHT”-experiment in 2001. The combined dataset is comprised of 1347 well-recorded earthquakes and 9 explosions, recorded at 925 recording stations, providing more than 120,200 differential travel time measurements, calculated using the absolute times from pairs of neighbouring earthquakes. We invert these data to derive the spatial and depth variation of seismic properties Vp, Vs, Vp/Vs, and Q ( 1/attenuation), beneath the area encompassing the geothermal field. The final 3-D Vp, Vp/Vs, Qp and Qs volumes show a high level of heterogeneity at a range of length scales, especially for Q, illustrating that older simplified 2-D models are inappropriate for the region. |