The 2004 Sumatra tsunami was clearly recorded by two UK bottom pressure gauges, DPN and DPS, deployed in Drake Passage between South America and Antarctica. These open-ocean records were examined to estimate characteristics of the tsunami waves and to compare the results of numerical simulations with the observations. Maximum wave heights measured at these gauges were 4.9 cm at DPN and 7.4 cm at DPS; the travel times from the source area were 19 h 46 min and 19 h 39 min respectively, consistent with the times obtained from the nearby coastal tide gauges. The numerical model described well the frequency content, amplitudes and general structure of the observed waves, with only small time shifts probably related to wave dispersion effects. The shifts were 15 min for DPN and 10 min for DPS, with the modeled waves leading the observations in each case. Further inspection of the simulated and observed records revealed that the identified tsunami waves are related to the second (main) train of waves propagating by the energy conserving route along the mid-ocean ridges, while the first train of waves travelling by the fastest route across the ocean remained unrecognizable in the observed DPS and DPN records and undetectable in the records of coastal tide gauges because of their insignificant amplitudes compared to the background variabilit
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