Indonesia is one of the most seismically active countries in the world, and its large, vulnerable population makes reliable seismic hazard assessment an urgent priority. In 2016, the Indonesian Ministry of Public Works and Housing established a team of earthquake scientists and engineers tasked with improving the input data available for revising the national seismic hazard map. They compiled results of recent active fault studies using geological, geophysical, and geodetic observations, as well as a new comprehensive earthquake catalog including hypocenters relocated in a three-dimensional velocity model. Seismic hazard analysis was undertaken using recently developed ground motion prediction equations (GMPEs), and logic trees for the inclusion of epistemic uncertainty associated with different choices for GMPEs and earthquake recurrence models. The new seismic hazard maps establish the importance of active faults and intraslab seismicity, as well as the subduction megathrust, in determining the level of seismic hazard, especially in onshore, populated areas. The new Indonesian hazard maps will be used to update national standards for design of earthquake-resilient buildings and infrastructure.

Summary On 28 September 2018, 18:02:44 local time, the Magnitude 7.5 earthquake accompanied by a tsunami and massive liquefaction devastated Palu region in Central Sulawesi, Indonesia. Comprehensive post-disaster surveys have been conducted, including field survey of surface ruptures, LiDAR, multibeam-bathymetry mapping, and seismic-reflection survey. We used these data to map fault ruptures and measure offsets accurately. In contrast to previous remote-sensing studies, suggesting that the earthquake broke an immature, hidden-unknown fault inland, our research shows that it occurred on the mappable, mature geological fault line offshore. The quake ruptured 177-km long multi-fault segments, bypassing two large releasing bends (first offshore and second inland). The rupture onset occurred at a large fault discontinuity underwater in a transition zone from regional extensional to compressional tectonic regimes. Then it propagated southward along the ∼110-km submarine fault line before reaching the west side of Palu City. Hence, its long submarine ruptures might trigger massive underwater landslides and significantly contribute to tsunami generation in Palu Bay. The rupture continued inland for another 67 km, showing predominantly left-lateral strike-slip up to 6-m, accompanied by a 5–10% dip-slip on average. The 7km sizeable releasing bend results in a pull-apart Palu basin. Numerous normal faults occur along the eastern margin. They cut the Quaternary sediments, and some of them ruptured during the 2018 event. Our fault-rupture map on mature straight geological fault lines allows the possible occurrence of early and persistent ‘supershear’, but significant asperities and barriers on segment boundaries may prohibit it.

No abstract

No abstract

A probabilistic seismic hazard assessment that includes the effect of site amplification is undertaken for the island of Sulawesi, Indonesia. High seismic activity rates, both along fast-slipping crustal faults including the major Palu-Koro–Matano Fault System and in regions of distributed deformation, contribute to moderate–high earthquake hazard over all but the SW part of the island. Of particular concern in terms of seismic risk are the numerous cities sited on soft sedimentary basins that have formed due to movement along presently active structures and that can be expected to amplify earthquake ground motions, including the provincial capitals of Palu and Gorontalo.