Vs30 of Coastal Cities in Eastern Indonesia in the Context of Earthquake Phenomenology

Shear wave velocity measurements to 30 m depth (Vs30) using Multichannel Analysis of Surface Waves (MASW) indicate high seismic risk to the built environment in coastal cities adjacent to the Sunda and Banda subduction zones in Eastern Indonesia. These measurements were taken at 58 sites in the cities of Pacitan (southern Java), Lombok, Ambon, and the Banda Islands. Comparing Vs30 estimates with local geologic maps show low velocities associated mostly with unconsolidated alluvium on coastal plains where most of the built environment resides. Due to recent destructive earthquakes in two of the sites (2018 Lombok and 2019 Ambon) we were able to directly compare damage using the MMI scale to Vs30. In most cases the heavy damage was experienced in sites with low Vs30 values. The least damage was experienced near sites with high Vs30 values, which are in foothills underlain by shallow volcanic units. These data provide a way to quantify earthquake hazards in densely populated and rapidly developing regions of eastern Indonesia and provide foundational constraints for studies of resonance frequency.