BRIDGES OVER TROUBLED WATERS: FROM DISCOVERING TSUNAMI DEPOSITS TO EVALUATING TSUNAMI MITIGATION EFFICACY IN INDONESIA

We have conducted a broad scale, interdisciplinary investigation of tsunami hazards in areas of Indonesia considered most at risk. Our compilation of historical records show that over the past 400 years Indonesia has had an average of 1 tsunami every 4 years. New evidence from our prospecting for paleo-tsunami deposits along the south coasts of Java and the Lesser Sunda islands indicate this rate is persistent, but is punctuated by temporal and spatial clustering. We discovered several candidate sands and other evidence, such as imbricated boulder deposits, of multiple paleo-tsunamis, some of which straddle similar stratigraphic intervals over a distance of 1500 km.

Much growth and development is happening in the inundation zones of these past tsunamis, such as the new Jogjakarta airport and a 3 billion dollar luxury hotel project in Kuta Lombokd. The consequences of this type of development are grave as demonstrated in a 2004 mega-tsunami where Banda Aceh lost 30% of its inhabitants (>170,000). Other large coastal cities in Indonesia at high risk of tsunami hazards are Padang, Pelabuhan Ratu, Cilicap, Denpasar, Mataram and Waingapu. Our tsunami models, which use GEOCLAW and MOST, show that > 3 million people inhabit the tsunami inundation zones of these cities. Major seismic gaps exist in each location with at least 25 meters of potential slip on subduction zone segments from 500-1500 km long.

Surveys we conducted of citizen awareness show many misconceptions persist about tsunamis, how to know one is approaching or how to respond even among those who have already experienced a tsunami. We use a 20-20-20 principle to assist locals to identify natural warning signs: 20 seconds of shaking, 20 minutes to evacuate to 20 meters elevation. We have conducted around 50 evacuation drills at the local level throughout the region from West Java to Sumba. We will also present several cultural practices that both enhance and frustrate mitigation efforts.