IDENTIFICATION OF WEATHERED LAYERS USING HVSR-PSO INVERSION AT ITERA
DOI:
https://doi.org/10.23960/jge.v12i2.537Keywords:
HVSR, Microtremor, PSO Inversion, Shear wave velocity, Weathered LayerAbstract
The Sumatra Institute of Technology (ITERA) is located in area dominated by volcanic tuff that is highly susceptible to weathering, resulting in heterogeneous subsurface conditions that may influence geotechnical characteristics and infrastructure development. This study aims to identify the distribution of weathered layers based on shear-wave velocity (Vs) using the Horizontal-to-Vertical Spectral Ratio (HVSR) microtremor method combined with Particle Swarm Optimization (PSO) inversion. Microtremor data were acquired along three survey lines with 10 m spacing between observation points. HVSR analysis was conducted to obtain H/V spectral curves, predominant frequencies, and amplification factors, while PSO inversion was applied to estimate the subsurface Vs model and generate two-dimensional cross-sections. The results show that relatively low Vs values of approximately 100–500 m/s are associated with relatively soft and less consolidated subsurface materials, which may correspond to weathered tuff or unconsolidated volcanic materials. Higher Vs values are associated with denser and more competent subsurface materials. The relatively low- Vs zones are mainly distributed from the surface to depths of approximately 20–30 m, with variations in thickness among the survey lines. These results provide a preliminary geophysical characterization of low-Vs zones associated with relatively soft and less-consolidated subsurface materials in the ITERA area. Because low Vs does not uniquely indicate weathering, the interpretation of weathered layers requires further geological validation. However, because low Vs values do not uniquely represent weathering zones, these findings should be considered a geophysical interpretation that requires direct geological control, such as borehole or core data, for definitive geotechnical investigations.
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