Geophysics of the Taupo Volcanic Zone: A review of recent developments

•The most active part of the TVZ is above strong seismic activity 150–200 km deep.•Seismic mechanisms and fault slip are now consistent with Taupo Volcanic Zone extension.•Magnetotellurics provides resistivity data to a much greater depth than before.•Modelling shows geothermal fields are above localised heat sources.

Since a previous review in 1995, improved geophysical networks and techniques have substantially improved our understanding of the Taupo Volcanic Zone (henceforth TVZ), and particularly why its central portion has such high outputs of magma and heat, much greater than found in similar arc environments elsewhere. Recent studies of the seismicity under New Zealand have revealed a concentration of intermediate-depth (150–220 km) earthquakes immediately under this central portion of the TVZ. A low QP region above these earthquakes is interpreted as a high-temperature region of partial melt, supplying the active area above. The underlying reason for this zone of activity is still a matter of debate.Crustal seismic studies of the TVZ show that from Lake Taupo northwards, the seismicity is largely restricted to the top 8 km of the crust, indicating a brittle–ductile transition at about this level. At the southern end of the zone, somewhat deeper seismicity becomes common. Recent detailed seismic studies covering the area from Taupo to Rotorua show that there are significant variations in seismic properties both across and along the strike of the TVZ.Continuous GPS measurements of deformation in the TVZ show that although the total deformation across the TVZ matches the extension expected from modelling of paleomagnetic data, there are large variations between different sites within the TVZ, with individual GPS sites displaying sudden jumps and periods of faster or slower change superimposed on the long-term trend. Some of these local movements may be due to cooling magma bodies.Magnetotelluric methods and 3-D modelling codes have significantly improved the resolution of deep electrical resistivity measurements. It is now possible to see conductivity anomalies to greater depths, to see the underlying feeding zones of the geothermal fields, as well as the conductivity anomalies in and immediately under the fields.Finally, recent modelling studies of the fluid convection under the geothermal fields of the TVZ indicate that they are driven by hot areas at least as deep as the brittle–ductile depth under the fields, rather than by a uniform heat source with the field spacing controlled by the shape of convection cells.