Historical tsunamis and present tsunami hazard in eastern Indonesia and the southern Philippines

Eastern Indonesia and the southern Philippines comprise a huge and seismically highly active region that has received less than the deserved attention in tsunami research compared with the surrounding areas exposed to the major subduction zones. In an effort to redress the balance the tsunami hazard in this region is studied by establishing a tsunami event database which, in combination with seismological and tectonic information from the region, has allowed us to define and justify a number of 'credible worst-case' tsunami scenarios. These scenarios have been used in numerical simulations of tsunami generation and propagation to study maximum water level along potentially affected shorelines. The scenarios have in turn been combined to provide regional tsunami hazard maps. In many cases the simulations indicate that the maximum water level may exceed 10 m locally and even reach above 20 m in the vicinity of the source, which is of the same order as what is forecasted along the Sumatra and Java trenches for comparable return periods. For sections of coastlines close to a source, a tsunami may strike only a few minutes after it is generated, providing little time for warning. Moreover, several of the affected areas are highly populated and are therefore also high risk areas. The combination of high maximum water levels, short warning times, dense populations, and relatively short return periods suggests strongly that the tsunami hazard and risk in these regions are alarmingly high.