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Abstract
We use earthquake ground motion modelling via Ground Motion Prediction Equations (GMPEs) and numerical simulation of seismic waves to consider the effects of site amplification and basin resonance in Jakarta, the capital city of Indonesia. While spectral accelerations at short periods are sensitive to near-surface conditions (i.e., V S 30 , average shear-wave velocity at topmost 30 m of soil), our results suggest that, for basins as deep as Jakarta’s, available GMPEs cannot be relied on to accurately estimate the effect of basin depth on ground motions at long periods (>3 s). Amplitudes at such long periods are influenced by trapping of seismic waves in the basin, resulting in longer duration of strong ground motion, and interference between incoming and reflected waves as well as focusing at basin edges may amplify seismic waves. In order to simulate such phenomena in detail, a basin model derived from a previous study is used as a computational domain for deterministic earthquake scenario modeling in a 2-dimensional cross-section. A M w 9.0 megathrust, a M w 6.5 crustal thrust and a M w 7.0 intraslab earthquake are chosen as scenario events that pose credible threats to Jakarta, and the interactions with the basin of seismic waves generated by these events were simulated. The highest long-period PGVs amplifications are recorded at sites near the middle of the basin and near its southern edge, with maximum amplifications of PGV in the horizontal component of 726% for the crustal, 1500% for the megathrust and 1125% for the deep intraslab earthquake scenario, respectively. We find that the levels of response spectral acceleration fall below those of the 2012 Indonesian building Codes’s design response spectra for short periods (<1 s), but closely approach or may even exceed these levels for longer periods.
Highlights
Earthquake-induced resonance is a phenomenon that occurs in deep sedimentary basins, as seen in Mexico City (Cruz-Atienza et al [1], Rial et al [2]) and Kathmandu (Galetzka et al [3]) due to the Michoacán and 2015 Nepal earthquakes, respectively
Surface waves are modulated inside the basin and at s, while body waves are attenuated and have faded away outside the basin, surface waves are still reverberating in the basin
We have shown that Ground Motion Prediction Equations (GMPEs) modeling predicts significant influence of near-surface geology, represented by VS30, on short-period (
Summary
Earthquake-induced resonance is a phenomenon that occurs in deep sedimentary basins, as seen in Mexico City (Cruz-Atienza et al [1], Rial et al [2]) and Kathmandu (Galetzka et al [3]) due to the Michoacán and 2015 Nepal earthquakes, respectively. Greater Jakarta (including Jakarta as well as the adjacent cities of Bekasi, Bogor, Depok, Tangerang and Tangerang Selatan) is the world’s 4th largest urban agglomeration with a population of 28.9 million (Brinkhoff [4]), and has experienced destructive earthquakes in 1699 (Nata & Witsen [5]), 1780 (Albini et al [6]) and 1834 (Musson [7]). Basin structure can have a profound influence on seismic ground motion, and various methods have been used to take this into account in seismic hazard studies. These methods can be divided into 2 main approaches. The first approach uses depth ZVS to a reference shear-wave velocity, VS , represent the seismic basement, as a parameter in Ground Motion Prediction
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