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.

In order to characterize the subsurface structure of the Jakarta Basin, Indonesia, a dense portable seismic broad-band network was operated by The Australian National University (ANU) and the Indonesian Agency for Meteorology, Climatology and Geophysics (BMKG) between October 2013 and February 2014. Overall 96 locations were sampled through successive deployments of 52 seismic broad-band sensors at different parts of the city. Oceanic and anthropogenic noises were recorded as well as regional and teleseismic earthquakes. We apply regularized deconvolution to the recorded ambient noise of the vertical components of available station pairs, and over 3000 Green's functions were retrieved in total. Waveforms from interstation deconvolutions show clear arrivals of Rayleigh fundamental and higher order modes. The traveltimes that were extracted from group velocity filtering of fundamental mode Rayleigh wave arrivals, are used in a 2-stage Transdimensional Bayesian method to map shear wave structure of subsurface. The images of S wave speed show very low velocities and a thick basin covering most of the city with depths up to 1.5 km. These low seismic velocities and the thick basin beneath the city potentially cause seismic amplification during a subduction megathrust or other large earthquake close to the city of Jakarta.

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Characterizing the interior structure of the Jakarta Basin, Indonesia, is important for the improvement of seismic hazard assessment there. A dense-portable seismic broad-band network, comprising 96 stations, has been operated between October 2013 and February 2014 covering the city of Jakarta. The seismic network sampled broad-band seismic noise mostly originating from ocean waves and anthropogenic activity. We used horizontal-to-vertical spectral ratio (HVSR) measurements of the ambient seismic noise to estimate fundamental-mode Rayleigh wave ellipticity curves, which were used to infer the seismic velocity structure of the Jakarta Basin. By mapping and modelling the spatial variation of low-frequency (0.124-0.249 Hz) HVSR peaks, this study reveals variations in the depth to the Miocene basement. These variations include a sudden change of basement depth from 500 to 1000 m along N-S profile through the centre of the city, with an otherwise gentle increase in basin depth from south to north. Higher frequency (2-4 Hz) HVSR peaks appear to reflect complicated structure in the top 100 m of the soil profile, possibly related to the sediment compaction and transitions among different sedimentary sequences. In order to map these velocity profiles of unknown complexity, we employ a trans-dimensional Bayesian framework for the inversion of HVSR curves for 1-D profiles of velocity and density beneath each station. Results show that very low-velocity sediments (<240 m s −1) up to 100 m in depth cover the city in the northern to central part, where alluvial fan material is deposited. These low seismic velocities and the very thick sediments in the Jakarta Basin will potentially contribute to seismic amplification and basin resonance, especially during giant megathrust earthquakes or large earthquakes with epicentres close to Jakarta. Results have shown good correlation with previous ambient seismic noise tomography and microtremor studies. We use the 1-D profiles to create a pseudo-3-D model of the basin structure which can be used for earthquake hazard analyses of Jakarta, a megacity in which highly variable construction practices may give rise to high vulnerability. The methodology discussed can be applied to any other populated city situated in a thick sedimentary basin.

This paper presents the development of spectral hazard maps for Sumatra and Java islands, Indonesia and microzonation study for Jakarta city. The purpose of this study is to propose a revision of the seismic hazard map in Indonesian Seismic Code SNI 03-1726-2002. Some improvements in seismic hazard analysis were implemented in the analysis by considering the recent seismic activities around Java and Sumatra. The seismic hazard analysis was carried out using 3-dimension (3-D) seismic source models (fault source model) using the latest research works regarding the tectonic setting of Sumatra and Java. Two hazard levels were analysed for representing 10% and 2% probability of exceedance (PE) in 50 years ground motions for Sumatra and Java. Peak ground acceleration contour maps for those two hazard levels and two additional macrozonation maps for 10% PE in 50 years were produced during this research. These two additional maps represent short period (0.2 s) and long-period (1.0 s) spectra values at the bedrock. Microzonation study is performed in order to obtain ground motion parameters such as acceleration, amplification factor and response spectra at the surface of Jakarta. The analyses were carried out using nonlinear approach. The results were used to develop contour of acceleration at the surface of Jakarta. Finally, the design response spectra for structural design purposes are proposed in this study.