[S-EM14] Electric, magnetic and electromagnetic survey technologies and scientific achievements

[SEM14-07] Mesh Design for inversion model resolution of the magmatic system beneath Mount Tongariro, New Zealand

★Invited Papers

*Wiebke Heise¹, Charles Williams¹, Peter McGavin¹, Grant Caldwell¹, Edward Bertrand¹, Stephen C Bannister¹, Yoshiya Usui², Geoff Kilgour³ (1.GNS Science, PO Box 30368, Lower Hutt, New Zealand, 2.Earthquake Research Institute, the University of Tokyo, Tokyo, Japan, 3.GNS Science, Wairakei Research Centre, PB 2000, Taupo, New Zealand)

Keywords:magnetotellurics, mesh design, volcanism

Tongariro Volcanic Centre is a large andesite-dacite stratovolcano complex located at the southern end of the Taupo Volcanic Zone which is located above the subduction of the Pacific plate below the Australian plate in the central North Island of New Zealand. Data from 128 magnetotelluric (MT) measurements have been modelled with a 3-D inversion code which uses an unstructured tetrahedral mesh and can model the pronounced topography of the Tongariro Volcanic Centre.
We test different mesh sizes to investigate the resolution of the MT model at different depths. Main focus was the depth were magma storage is predicted at ~ 5-10km depth. We show the influence of mesh design and smoothing parameter alpha on the 3D-inversion result.
The resulting 3-D resistivity model shows the near surface hydrothermal system and its connection to a deeper magmatic source. Comparison with the seismic tomography shows a good correlation of low Qp and low electrical resistivity values suggesting that the magmatic source at depth extends to the east of the volcanic complex. Together seismicity, electrical resistivity, seismic tomography and petrological data give a coherent picture of the magmatic system of the Tongariro volcanic centre that agrees well with the conceptual geological model.