Geodesy and Geodynamics (Nov 2020)
A new empirical equation of shear wave velocity to predict the different peak surface accelerations for Jakarta city
Abstract
Site condition and bedrock depth play important roles in the determination of peak surface acceleration (PSA) values by earthquake motions. The soil parameters of shear wave velocity (Vs) and standard penetration test-number (N) value for Jakarta city are available up to 100 m below the Earth's surface even though the typical depths to bedrock are in excess of 100 m. This study referred to the base motion peak ground acceleration (PGA) values of 0.100 g, 0.218 g and 0.378 g to predict the PSA values using the Nonlinear Earthquake site Response Analysis (NERA) to analyse a simulated dataset for the bedrock depths of 100 m, 200 m, 300 m, 400 m and 500 m with conditioned by clayey and sandy soils. A new empirical equation of Vs = 102.48 N0.297 (m/s) was proposed to calculate the values of Vs used as an input parameter in the NERA programme for the prediction of seismic wave propagation.The results showed that the PSA values are dependent on the amplitude of seismic waves, depths of bedrock and the local site conditions. Changes in the PSA values from 41.0% to 51.5% and from 46.1% to 79.8% for the bedrocks overlain by sand, from 20.0% to 42.1% and from 45.9% to 58.8% for the bedrocks overlain by clay with increasing of bedrock depths from 200 m to 300 m and from 400 m to 500 m, respectively, were predicted for a 2500-year return period earthquake. Decreases in the PSA values by 41.0%, 51.5%, 46.1%, 79.8% for the bedrocks overlain by sand and by 20.0%, 42.1%, 45.9%, 58.8% for the bedrocks overlain by clay were predicted for a 2500-year return period earthquake due to the bedrock depth changes of 200 m, 300 m, 400 m, 500 m.Large-magnitude earthquake of Jakarta city has a significant effect on an increase or a decrease of the PSA value with depth of bedrock and may cause the vibration damage to buildings and other constructions on the ground. The analysis of the PSA value and PSA ratio influenced by the PGA value, bedrock depth and local soil conditions will make a contribution to the design of earthquake-safe building for Jakarta city in the future.
