Development of an engineering bedrock map beneath Jakarta based on microtremor array measurements
M. Ridwan, S. Widiyantoro, M. Irsyam, Afnimar, H. Yamanaka, 2017. "Development of an engineering bedrock map beneath Jakarta based on microtremor array measurements", Geohazards in Indonesia: Earth Science for Disaster Risk Reduction, P. R. Cummins, I. Meilano
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Jakarta has been selected as a study area for seismic microzonation by considering its population and its infrastructure growth, seismicity and geological setting. One of the important factors in seismic hazard analysis is the characteristics of the ground overlying bedrock, and, as yet, this has not been studied for Jakarta. This study was intended to estimate the depth to bedrock by applying microtremor array exploration. The phase velocity of microtremors was estimated by the spatial autocorrelation (SPAC) method, whereas the S-wave velocity profile was estimated by inversion using a genetic algorithm. Microtremor array analysis has been conducted at 55 sites that covered the whole of Jakarta. The result of one-dimensional (1D) S-wave velocity profile estimation indicates that the engineering bedrock depth has pronounced differences between northern (>700 m) and southern Jakarta (about 300 m). A 3D S-wave velocity model was constructed from 1D profiles resulting from a second inversion in which the depth of constant-velocity layers, with velocities of 500, 700 and 900 m s−1, was determined. The constructed 3D velocity structures show a bedrock morphology that has a depth range of 350–725 m, with depths increasing towards northern Jakarta. The implication of differences in bedrock depth is that estimated seismic amplification for the thicker sediment will be higher.
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With dense urban populations located in one of the most active tectonic belts in the world, Indonesia is a hotspot for natural hazard risk. During the twentieth century, Indonesia had limited means to keep natural disaster fatalities from rising commensurately with the explosive growth in population. This situation is changing rapidly, however, with major political and economic advances over the past two decades having led to substantial investments in seismic and geodetic infrastructure. The potential for advances in Earth science to reduce natural disaster fatalities in Indonesia has never been greater.
This Special Publication documents some of the recent advances made by Earth scientists that contribute towards a better understanding of geological hazards in Indonesia.