Basin Resonance and Seismic Hazard in Jakarta, Indonesia

Abstract

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 S30 , 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.

Shallow Shear-Wave Velocity Beneath Jakarta, Indonesia Revealed by Body-Wave Polarization Analysis

“…Although the contrast between Holocene and Pleistocene deposits is small and their boundary is not well resolved in our V s ahs map, their deposits obviously fill the Jakarta basin to a depth of at least 150 m. These deposits reach the outer part of the Jakarta administrative margin mostly to the southwest, more than 10 km away. The result is in accordance with Cipta et al [20] who reported the estimation of the basin extension based on extrapolation of the basement depth. The higher V s ahs found in the southern part of the basin may relate to Tertiary volcanic deposits, or even the edges of the basin, which is Tertiary rock.…”

“…In further studies, it might be useful to investigate the frequency-dependence of body-wave polarization in an attempt to reveal further details of the shallow V s profiles. Our estimates of V s ahs reflect the shallow Vs structure obtained within the Jakarta city limits in earlier studies [15,16], but extended this information beyond the city limits of Jakarta to what is thought to be the basin edge [20]. Although the surface geology of the entire study area is composed of quaternary sediments (Figure 1b), we found that on average, V s ahs increases towards the outer edge of the study area ( Figure 6).…”

“…Considering this evidence, they concluded that basin effects in Jakarta are likely to enhance the damaging effects of earthquake-generated seismic waves. This conclusion was also reached by Cipta et al [16,20], who used the same data to invert Horizontal-to-Vertical Spectral Ratio (HVSR) curves to achieve better resolution of the basement architecture. However, neither of these models revealed the basin edges, which extend outside the city of Jakarta beyond the extent of the 2013-2014 seismometer deployment.…”

“…(a) Distribution of earthquakes (yellow circles) observed around the study area (red zone). (b) Map of the seismic deployments and surface geology around Jakarta (modified from[20]). The inverted triangles represent the seismic network deployed between October 2013 and February 2014.…”

Seismic velocity structure of the Jakarta Basin, Indonesia, using trans-dimensional Bayesian inversion of horizontal-to-vertical spectral ratios

“…Cipta et al (2018) have used 2-D waveform modelling along an NS cross-section of the Jakarta Basin model developed here to show that very large amplification of ground motion (up to 1500 per cent PGV) can occur for a large scenario earthquake on the Java Trench, with the thicker sediments in the north experiencing the largest amplification. However, the wedged shape of the basin edge as it shallows to the south also plays an important role in amplifying seismic waves (up to 1200 per cent PGV), particularly for the intraslab earthquake scenario considered by Cipta et al (2018). For both the megathrust and intralsab scenarios, the spectral amplifications were most prominent in the period range 5-7 s, similar to that of the observed f l 0 HVSR peaks.…”