[HDS10-P04] Volcanic Tsunami Earthquakes on the Kermadec Ridge, North of New Zealand
Keywords:tsunami earthquake, tsunami simulation, crustal deformation, caldera, volcanic earthquake
On 8 Dec 2017 (UTC), another volcanic tsunami earthquake occurred near Curtis and Cheeseman Islands on the Kermadec Ridge, north of New Zealand (Fig). Tsunamis with the maximum amplitude of ~40 cm were recorded by tide gauges on Raoul Island and the North Island of New Zealand. In the past, another volcanic tsunami earthquake occurred on 17 Feb 2009, which also accompanied tsunami waves in tide gauge records. The two earthquakes are remarkably similar in seismic magnitudes (M~6.0), focal mechanisms (dominant NDC components), centroid location (distance of ~10 km) and observed tsunami waveforms (Fig).
In this study, we preliminary located its source region by numerical tsunami simulations, in order to investigate the geophysical condition of the source region. For initial conditions, Gaussian-shaped uplift models on sea surface were assumed at 9 locations in an area of ~100 km2 around the seismic epicenters. The linear Boussinesq equations including the Coriolis force were solved with the simulation code JAGURS [Baba et al., 2015, PAGEOPH]. Bathymetry data are created from GEBCO_2014 [Weatherall et al., 2015] and New Zealand Regional Bathymetry 2016 [NIWA, 2016].
The uplift model around Curtis and Cheeseman Islands yields synthetic waveforms similar to observed tsunami waveforms at the tide gauges, while other uplift models distant from the islands showed poor agreements. Therefore, the tsunami earthquakes probably occurred at the submarine volcano below the islands and accompanied large seafloor uplift.
To explore the geophysical condition of the source region, topographic structures and crustal deformations characteristic of caldera edifices has been found; (1) From bathymetric view, there exists a circular bathymetric depression around Curtis and Cheeseman Islands, which is a common structure in collapsed caldera edifice[s3] [e.g. Cole et al., 2005, Ear. Sci. Rev]. (2) Large regional uplifts were reported on the islands during 1929 and 1964 [Doyle et al., 1979, J. Roy. Soc. New Zealand], which may be explained as a "resurgence," or uplift associated mainly with subsurface magmatic pressure, which is often observed on seafloor at collapsed calderas [e.g. Lipman, 2000, Academic Press]. These might imply that Curtis and Cheeseman Islands are portions of a resurgent dome on a collapsed caldera on seafloor, and that the volcanic tsunami earthquakes are related to some activity at a submarine collapsed caldera, similar to the Torishima earthquakes.