The amplification of seismic waves in sedimentary basins is an important aspect of seismic hazard that is often poorly understood. This is particularly important in Indonesia, where most major cities are built on basins filled with young alluvial sediments and/or volcanic tuff. The architecture of these basins, and their ability to amplify seismic waves, is poorly unknown. We are collaboration with universities and government technical agencies of Indonesia to deploy dense, temporary networks of seismometers in selected urban areas: Jakarta an Bandung in Java, and Palu in Sulawesi. The objective of these experiments is to determine the 3D structure of the basin well enough to enable the deterministic simulation of earthquake waves with periods as short as 1 sec. Such simulations can improve our understanding of the effects seismic waves may have on large buildings and infrastructure, and can be combined with stochastic simulations to include shorter periods that may affect residential structures. By helping to accurately forecast the damaging effects of earthquake waves, the project will inform mitigation efforts towards reducing earthquake fatalities.