Rahmania Sofyana Ulya Rahmania Sofyana Ulya, Mochamad Aryono Adhi, Nugroho Budi Wibowo, Desi Mustami Limayukha Desi Mustami Limayukha, Elsa Fadlika Widyantari Elsa Fadlika Widyantari, Billqis El Farsiyyi Bilqis El Farsiyyi, Ilqia Rahma Ilqia Rahma

Site Effect Analysis in Prambanan District and Surroundings Using Shear Wave Velocity and Ellipticity Curve Method from Microtremor Data

Introduction

Site effect analysis in prambanan district and surroundings using shear wave velocity and ellipticity curve method from microtremor data. Prambanan seismic site effect analysis using Vs30 & microtremor data. Classifies subsurface layers & earthquake amplification potential for regional planning & disaster mitigation.

Abstract

The shear wave velocity (Vs) is a crucial parameter for determining subsurface layers by averaging the Vs value to a depth of 30 meters, known as Vs30. This study aims to analyze the subsurface soil layers, calculate the Vs30 value, and assess the potential seismic site classifications in Kapanewon Prambanan and its surrounding areas. The research utilizes secondary microtremor data from 27 observation points in the form of MSD files. The microtremor data was processed using Geopsy software with the HVSR method to generate an H/V curve. This curve was further analyzed with the Ellipticity Curve method via Dinver software to obtain the Vs profile at various depths. The findings suggest that the subsurface layers in Kapanewon Prambanan are predominantly composed of hard, very dense soil, soft rocks, and solid rocks, based on the Vs30 values. The Vs30 distribution across the region ranges from 267.857 m/s to 1675.977 m/s, classified into site categories A, B, C, and D. However, the majority of the area falls under site classes B and C. These classifications indicate that the regions under B and C have a relatively lower potential for significant earthquake wave amplification. Nonetheless, attention should still be given to areas categorized under sites D and E, particularly for earthquake disaster mitigation efforts. This detailed Vs30 analysis provides critical insights for seismic assessments, regional planning, and mitigation strategies in Kapanewon Prambanan.

Review

This study presents a crucial site effect analysis for the Kapanewon Prambanan district, utilizing shear wave velocity (Vs) and the ellipticity curve method from microtremor data. The authors clearly outline their objective to characterize subsurface soil layers, compute Vs30 values, and establish seismic site classifications, which are fundamental parameters for seismic hazard assessment. The methodology, involving the processing of secondary microtremor data through Geopsy for HVSR analysis and subsequent application of the Ellipticity Curve method using Dinver software to derive Vs profiles, is standard and appropriate for this type of regional investigation. The relevance of this work for understanding local ground response and informing earthquake disaster mitigation strategies is well-established. The findings offer valuable insights into the geological characteristics of the study area, revealing subsurface layers primarily composed of hard to very dense soil, soft rocks, and solid rocks. The derived Vs30 values, ranging from 267.857 m/s to 1675.977 m/s, enabled the classification of sites into categories A, B, C, and D, with a notable predominance of B and C classifications. This suggests that a substantial portion of the region may experience relatively lower seismic wave amplification compared to areas with softer soils. Crucially, the identification of regions falling under site classes D and E underscores areas warranting specific attention for earthquake disaster mitigation, providing a granular understanding of varying seismic risk potential across the district. While the study provides a solid foundation for seismic risk assessment, a few areas could enhance its scientific depth and applicability. A brief discussion on the provenance and quality assurance of the "secondary microtremor data" would add confidence in the input datasets. Furthermore, although Vs30 classification is a key output, elaborating on the "site effect analysis" implied in the title by explicitly presenting or discussing amplification factors, perhaps derived directly from the H/V curves or Vs profiles, would offer a more direct measure of ground response beyond classification alone. Incorporating an analysis of the uncertainties associated with the Vs profiles and Vs30 values, along with a brief acknowledgment of potential limitations of the microtremor method (e.g., 1D assumption, depth limitations), would also strengthen the robustness of the conclusions. Despite these suggestions, the research offers critical data for informed regional planning and is a significant contribution to seismic assessment in Kapanewon Prambanan.

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