Effects of the March 2011 Japanese Tsunami in Bays and Estuaries of SE Australia
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Pure and Applied Geophysics
Effects of the March 2011 Japanese Tsunami in Bays and Estuaries of SE Australia JON B. HINWOOD1 and ERROL J. MCLEAN2 Abstract—On 11 March 2011 a subsea earthquake off the north-eastern coast of Honshu Island, Japan generated a huge tsunami which was felt throughout the Pacific. At the opposite end of the Pacific Ocean, on the south-east coast of Australia, multiple reflections, scatterings and alternate pathways lead to a prolonged and complicated response. This response was largely unaltered in crossing the continental shelf but was then transformed by bay resonances and admittances. These effects are described using data from tide recorders sparsely spread over 1,000 km of the coast. Some new adaptations and applications of time-series analysis are applied to separate tsunami waves that have followed different pathways but contain the same spectral components. The possible types of harbour response are classified and illustrated. Despite its small height in this region, the tsunami put several swimmers at serious risk and generated strong harbour oscillations, which should be considered when generating future warnings. Key words: Tsunami, Japan, harbour oscillations, tide gauge record, correlation, spectra, timeseries.
1. Background 1.1. The Tsunami in Japan The earthquake occurred at 05:46 UTC or 16:46 AEDT on 11 March (USGS, 2011a, b) (AEDT, Australian Eastern Daylight Time, which will be used here). It had a magnitude of 9.0 on the Richter scale making it the 4th largest ever recorded and comparable to the earthquake which generated the 2004 Boxing Day Tsunami in the Indian Ocean. The epicenter was located 130 km offshore at a depth of 32 km (USGS, 2011a), in deep ocean waters. The sea bed in the vicinity of the epicenter was reported to
1 Department of Mechanical and Aerospace Engineering, Monash University, Melbourne, VIC 3800, Australia. E-mail: [email protected] 2 School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW, Australia.
have risen by up to 2.4 m along a 400 km line along the strike direction, which was S19E (USGS, 2011a). This uplift generated a positive (upwards) displacement of the water surface which propagated outwards as a positive tsunami wave (NOAA, 2011), most strongly to the east and west. The wave broke in the relatively shallow water on the continental shelf of Japan and formed a surge, which struck the eastern coast of Honshu, with heights at the shoreline up to 10 m. The wave ran inland along stream courses and overland, typically for 2–4 km with maximum run-up height onshore of about 40 m above sea level. Loss of life and catastrophic damage to buildings and infrastructure were caused by impact of the surge, by scouring of soil and foundations, and by the effects of inundation. This paper describes the nature of the tsunami after its 12,000 km journey to south-eastern Australia and its effects there. In Sect. 2 we outline the chronology of the tsunami on the SE coast of Australia, primarily from model simulations as th
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