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WITHDRAWN Comprehensive Geophysical Analysis of Megathrust and Local Fault Hazards: Microzonation of the Cilegon City Business Area Using Microtremor, MASW and SPAC Methods

Description: 

WITHDRAWN Cilegon City, a vital industrial hub in Banten Province, is located in a seismically active zone influenced by the Sunda Strait megathrust and local fault systems, including the Ujung Kulon Fault and Semangko Graben. This study develops a microzonation map for the city’s business district using quantitative geophysical methods such as Horizontal to Vertical Spectral Ratio (HVSR), Multi-Channel Analysis of Surface Waves (MASW), and Spatial Autocorrelation (SPAC). Key parameters analyzed include Vs30, engineering bedrock depth, seismic vulnerability index (Kg), and soil predominant periods (Tdom).Vs30 values range from 119.1 m/s to 1,119.8 m/s, with hard soil (SC) dominating most areas, while medium soil (SD) is concentrated in the west. HVSR analysis identifies Tdom values between 0.1 and 1.5 seconds, linked to alluvial deposits with high amplification potential. SPAC analysis estimates engineering bedrock depths between 30 and 100 meters, indicated by shear wave velocities exceeding 750 m/s.Kg values highlight zones of varying vulnerability, especially in coastal regions and soft soils prone to amplification, settlement, and deformation. These values correlate with ground shear strain (GSS), where higher Kg reflects greater deformation susceptibility. Shakemap scenarios based on field-observed Vs30 data reveal detailed site effects, especially in soft-soil and coastal regions, showing Modified Mercalli Intensities (MMI) of IV to VI.Field-based shakemaps provide more accurate representations compared to global Vs30 (USGS) models, which rely on generalized slopes and oversimplify site effects. For example, Ujung Kulon Segment A scenarios show stronger ground motion amplification in field-based maps compared to uniform patterns in global models. Local formations such as Banten Tuff and alluvium further amplify seismic waves, highlighting global dataset limitations.

Session: Network Seismology: Recent Developments, Challenges and Lessons Learned [Poster]

Type: Poster

Date: 4/15/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Dadang Permana

Student Presenter: No

Invited Presentation: 

Poster Number: 27

Authors