Abstract :
Following the recent reports by YUAN et al. (2005) of recordings of the 2004 Sumatra
tsunami on the horizontal components of coastal seismometers in the Indian Ocean basin, we build a much
enhanced dataset extending into the Atlantic and Pacific Oceans, as far away as Bermuda and Hawaii, and
also expanded to five additional events in the years 1995–2006. In order to interpret these records
quantitatively, we propose that the instruments are responding to the combination of horizontal
displacement, tilt and perturbation in gravity described by GILBERT (1980), and induced by the passage of
the progressive tsunami wave over the ocean basin. In this crude approximation, we simply ignore the
island or continent structure, and assume that the seismometer functions de facto as an ocean-bottom
instrument. The records can then be interpreted in the framework of tsunami normal mode theory,and lead
to acceptable estimates of the seismic moment of the parent earthquakes. We further demonstrate the
feasibility of deconvolving the response of the ocean floor in order to reconstruct the time series of the
tsunami wave height at the surface of the ocean, suggesting that island or coastal continental seismometers
could complement the function of tsunameters.
