German Indonesian Tsunami Early Warning System

Kurzfassung

Tsunami Early-Warning has become a major issue of concern for the geoscience community in the aftermath of Boxing Day 2004 tsunami. The problem has received a huge amount of attention and funding mainly because critical aspects of the problem still remain unsolved: between 2005 and 2007, five false tsunami alarms were issued worldwide. Such alarms have negative societal and economic effects. Conventional tsunami warning systems rely on estimates of an earthquake's magnitude to determine whether a large tsunami will be generated. Earthquake magnitude is not always a reliable indicator of tsunami potential, however. The 2004 Indian Ocean quake generated a huge tsunami, while the 2005 Nias (Indonesia) quake did not, even though both had almost the same magnitude from initial estimates. However, the Indonesian Government requires a warning to be issued within 5 minutes from the initial quake. Also, when developing new concepts, it is important to consider which other sensors and technologies are already out there, in order to design a concept providing complementary and not redundant information. In this perspective, tsunami models are expected to progress sensibly in the next few years, thanks to bathymetric and topographic surveys and to better determination of the tsunami source from GPS technologies. Coupled to tide gauges, which are reliable, cheap and widespread sensors, and ever-increasing computing power, these ground-based technologies constitute a low-cost network that will soon solve the problem of far-field tsunami early warning. Robustness will also be improved by GPS detection of ionospheric tsunami signatures in the ionosphere, which have been recently characterized by accurate models. Near-field tsunami early warning is, on the other hand, an open problem. False alarms are being issued because of the time gap between the seismometric detection of a potentially tsunamigenic quake and the first direct measurement. Whatever the sensor, tide gauges, off-shore buoys or ionospheric signatures, the first actual measurement comes with a delay ranging from 30 minutes to 1 hr. In this time lapse, tsunami watches must anyway be issued, since the tsunami wave can reach coastlines in the near field within 15-20 minutes. The concepts proposed in this report put forth possible solutions to the problem.