HR: 0830h
AN: S31E-0794    [PDF]
TI: Local Earthquake Tomography at the Active Tongariro Volcanic Centre, New Zealand
AU: * Rowlands, D P
EM: rowlands@esc.cam.ac.uk
AF: Bullard Laboratories, Dept. Earth Sciences, University of Cambridge, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AU: White, R S
EM: rwhite@esc.cam.ac.uk
AF: Bullard Laboratories, Dept. Earth Sciences, University of Cambridge, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AU: Haines, J
EM: haines@esc.cam.ac.uk
AF: Bullard Laboratories, Dept. Earth Sciences, University of Cambridge, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AB: Back-arc spreading caused by subduction of the Pacific plate beneath the Australian plate ranges from full oceanic spreading north of New Zealand to continental extension in the North Island. The Tongariro Volcanic Centre (TVC) in the North Island of New Zealand marks the southern terminus of continental extension and contains three main active volcanoes -- \emph{Ruapehu}, \emph{Tongariro} and \emph{Ngauruhoe}. Ruapehu last erupted in 1995-96, Ngauruhoe in 1973-75 and Tongariro in 1896. From January-June 2001 twenty-three three-component broadband (0.03--50 Hz) seismometers from the SEIS-UK pool were deployed in and around the TVC. The seismometers recorded continuously at 100 samples/sec throughout the deployment. Additional seismic data were obtained from permanent network seismometers in the surrounding area. We present the results of the project, including an improved 1D velocity model (``\emph{minimum 1D model}'') for standard earthquake location in the area, accurately located local seismicity, and local earthquake tomography results. The TVC is characterised by low-velocity volcanic sediments surrounding the three large, high-velocity andesitic cones. It is flanked to the west, south and east by Tertiary sediments. The western boundary is marked by an active fault scarp along which $\sim$70% of the well-locatable seismicity occurred during the deployment. This seismicity occurs in several clusters concentrated in the depth range 8--15 km. Additional clusters of seismicity are located at 1--4 km depth beneath the Tongariro-Ngauruhoe system, close to sites of persistent geothermal activity. A further cluster of seismicity at shallow depth ($\sim$5 km depth) is located at the north-western edge of Lake Rotoaira. No well-locatable crustal earthquakes are detected beneath Ruapehu. This is most likely due to the typically low magnitude of events beneath Ruapehu and the lack of sufficient nearby stations. The 3D upper-crustal velocity model produced, together with the observed distribution of local seismicity, contribute to our understanding of processes occurring within the active volcanic systems and at the tip of an incipient continental rift system.
DE: 7205 Continental crust (1242)
DE: 7230 Seismicity and seismotectonics
DE: 7280 Volcano seismology (8419)
DE: 8180 Tomography
SC: Seismology [S]
MN: 2003 Fall Meeting