Physical Society of Indonesia Articles Journal of the Physical Society of Indonesia 2.
, 34-46 .
https://doi.
org/10.
35895/jpsi.
Seismic Microzonation of Toba Lake Region Using Microtremor Analysis Fauzan Surya Nanda1*.
Furqon Raharjo2.
Suaidi Ahadi2 1 Department of Physics.
Universitas Andalas.
Padang 25163.
Indonesia 2 Agency of Meteorology.
Climatology, and Geophysics, 10720.
Indonesia (Received October 21, 2026.
revised February 09, 2026.
accepted February 12, 2026.
published online April 18, 2.
The Toba Lake region, characterized by complex volcanic and tectonic history, represents a significant seismic hazard zone due to its proximity to the active Sumatra Fault System and heterogeneous geological conditions.
This study applies the Horizontal to Vertical Spectral Ratio (HVSR) method using microtremor data to assess seismic vulnerability across the region.
Three-component microtremor recordings from 29 stations were analyzed to derive key seismic parameters including predominant frequency .
ce0 ), amplification factor .
a0 ), dominant period .
cN0 ), and seismic vulnerability index .
ayci ).
The results reveal significant spatial variations in seismic hazard parameters, with high vulnerability zones concentrated in the central and southern areas, characterized by low predominant frequencies .
2 H.
, high amplification factors .
p to 12.
, long dominant periods .
1 second.
, and elevated vulnerability indices (Kg > 8.
These zones correspond to Quaternary alluvial deposits with soft, unconsolidated sediments.
Conversely, northern and northwestern regions exhibit lower vulnerability with high predominant frequencies (>2.
0 H.
, low amplification factors (<4.
, short dominant periods (<0.
6 second.
, and reduced vulnerability indices (Kg < 3.
, correlating with consolidated Miocene volcanic rocks.
Critical high-risk areas include measurement points LT34.
LT14.
LT17.
LT21, and LT49, while point LT20 in Tarutung, located along the Sumatra Fault Zone, demonstrates the compound effect of active tectonics and soft geological conditions.
The resulting microzonation maps provide a regional-scale framework for seismic hazard identification and disaster risk mitigation planning, and can serve as a reference for prioritizing areas requiring more detailed, site-specific investigations.
Keywords: Seismic Vulnerability Index.
HVSR.
Microtremor This is an open access article under the CC BY-NC license.
Copyright A 2026 by Author.
Published by Physical Society of Indonesia
INTRODUCTION
The Toba Caldera, formed by a supervolcanic eruption approximately 74,000 years ago.
This caldera now constitutes the world's largest volcanic lake and preserves complex geological history with high natural hazard potential (Aldiss & Ghazali, 1.
Beyond its scientific value, the region holds strategic socio-economic importance as a center for tourism activities and transportation for North Sumatra communities (Arrasyid et al.
, 2.
Infrastructure development, population density, and tourism sector growth render this area vulnerable to geological disaster impacts (Grutas et al.
, 2.
Consequently, this region requires comprehensive disaster mitigation studies based on geological and geophysical data (Wibowo et al.
, 2.
Tectonically, the Lake Toba area lies within the influence of the active Sumatra Fault System, creating high potential for seismic events (Asnawi et al.
, 2.
Additionally, volcanic sediment deposits from past eruptions generate heterogeneous surface geological conditions that potentially caduse local seismic wave amplification (Darmawan et al.
, 2.
Thick sediment layers can resonate with natural building frequencies, increasing damage risk during earthquakes (Z.
Chen et al.
, 2.
This phenomenon was observed in the 2018 Palu and 2006 Yogyakarta earthquakes, where damage was more influenced by local soil conditions than distance from earthquake sources (Eka Setiawan et al.
, 2.
*Contact Author: fauzansuryananda@gmail.
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Understanding local soil characteristics becomes crucial for earthquake disaster mitigation efforts (Hakim, 2.
The microtremor method with Horizontal to Vertical Spectral Ratio (HVSR) is widely utilized as it is non-destructive, efficient, and applicable in densely populated areas (Yulianto & Yuliyanto, 2.
In Indonesia, the method has been successfully applied for site response analysis along active fault zones such as the Kaligarang Fault.
HVSR enables identification of important parameters including soil predominant frequency .
, dominant period .
, seismic vulnerability index .
ayci ),and amplification factor .
a0 ) earthquakes (Z.
Chen et al.
, 2.
Previous research has demonstrated HVSR method effectiveness across various geological and seismotectonic contexts (Akkaya, 2.
Studies have shown that younger geological formations tend to be more susceptible to seismic wave amplification, with areas containing thick sediment layers (>15 .
and low fCA values (<1 H.
exhibiting high Kg values and significant amplification potential.
However, limited research has specifically mapped seismic vulnerability using HVSR methods in the Lake Toba region (Eka Setiawan et al.
, 2.
despite its complex geological characteristics and high anthropogenic activity, particularly in densely populated zones such as Balige.
Parapat, and Haranggaol (Grutas et al.
This study aims to apply HVSR methodology to obtain maps of predominant frequency .
, dominant period .
cN0 ), and seismic vulnerability index .
ayci ),) as foundation for identifying earthquakeprone zones in the Lake Toba region (Chen et al.
, 2.
The findings are expected to contribute to more adaptive development planning and earthquake disaster risk mitigation based on geophysical data (Wibowo et al.
, 2.
Figure 1 Map of the study area showing the locations of microtremor measurement points.
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DATA AND METHOD
1 Data This study utilized secondary data consisting of three-component microtremor recordings obtained from GEOFON and European Integrated Data Archive (EIDA) open repositories.
A total of 29 stations were analyzed, with data collected during September 2008.
The use of this dataset is considered appropriate because ambient seismic noise is dominated by natural sources and is assumed to be stationary over long time periods, particularly for regional-scale site response assessment.
The measurement sites are mostly located in areas with limited anthropogenic activity, minimizing the influence of non-seismic noise.
The microtremor recordings include vertical (Z), north-south (N), and east-west (E) components, which are essential for HVSR analysis.
Data processing was conducted in accordance with the SESAME .
guidelines for H/V spectral ratio analysis.
The time-series records were detrended, corrected for baseline offsets, and divided into stationary time windows.
Windows affected by transient noise were excluded prior to spectral analysis.
This procedure ensures the reliability of the estimated predominant frequency .
ce0 ) and prevents artificial overestimation of the amplification factor .
a0 ) and seismic vulnerability index .
ayci ).
Area of Study The research area is geographically located in the Lake Toba region.
North Sumatra.
Indonesia, as shown in Figure 1 Map of Research Area Around Lake Toba.
It extends from approximately 1A48'N to 3A00'N latitude and 98A12'E to 99A12'E longitude, covering both the western and eastern margins of the Toba Caldera.
The distribution of microtremor measurement points across the caldera and its surroundings was designed to capture these spatial variations and to provide a regional-scale characterization of site Consequently, the study area offers an appropriate setting for seismic microzonation based on ambient vibration analysis, particularly for identifying zones with potentially higher seismic vulnerability (Nakamura, 1.
Figure 2 Seismicity map showing earthquake events around Lake Toba from January 2020 to April 2025.
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Seismicity and Tectonics The The seismic and tectonic characteristics of the Lake Toba region, which reflect a complex interplay between volcanic and tectonic processes, are illustrated in Figure 2.
This map integrates earthquake distribution data with regional geological structures, highlighting seismic events (M > .
recorded between January 2020 and April 2025.
These data, sourced from BMKG, are plotted alongside the Sumatra Fault System and regional seismic stations.
This visual framework is crucial for understanding how active tectonic features, such as the Sumatra Fault and surrounding crustal fractures, influence the spatial distribution of seismicity in northern Sumatra.
The tectonic and volcanic complexity of Lake Toba is illustrated in the Earthquake Events map, which plots seismicity (M> .
from 2020 to 2025 using BMKG data.
The earthquake distribution aligns closely with major fault systems like the Sumatra Fault and Renun Fault, indicating active tectonic Lake Toba lies above the subducting Indo-Australian plate and is affected by the oblique convergence with the Eurasian plate.
Hutchings and Mooney .
noted that most earthquakes in this region are shallow (O70 k.
, but intermediate and deep events trace the subduction geometry.
Meanwhile.
Simanjuntak et al.
identified a slab gap beneath Toba, formed due to the oblique subduction of the Investigator Fracture Zone (IFZ).
This fracture zone, though not seen on the surface, generates complex seismic patterns and may involve a possible slab tear.
Hypocenter relocation confirms that seismic events cluster along a dipping structure consistent with the IFZ trajectory, reinforcing the idea of segmented slab subduction.
This unique tectonic configuration contributes to Toba's persistent seismicity and underscores the region's geological hazards.
Figure 3 Geological map around Lake Toba.
Geology The geological conditions of Lake Toba, which reflect its complex volcanic and tectonic history, are illustrated in Figure 3 This geological map provides a comprehensive overview of the lithological units and structural features that have shaped the region, including remnants of the Toba Caldera, volcanic deposits, and fault systems associated with the active Sumatra Fault Zone.
Understanding these ISSN: 2685- 3841 (Onlin.
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geological characteristics is essential for interpreting subsurface conditions, assessing geohazards, and supporting further geophysical analyses in the area.
The geological conditions of the Lake Toba area can be further detailed by examining the specific geological units mapped in the region (Aldiss & Ghazali, 1.
Key units that compose the Lake Toba area and its surroundings include Qa (Alluviu.
, representing unconsolidated sediments transported and deposited by water, indicating ongoing modern sedimentary processes.
The presence of Qv (Andesite.
Toba Rhyodacitic Tuf.
signifies volcanic rocks directly linked to the Toba volcanic activity, highlighting the dominant volcanic nature of the area.
Additionally.
Tmv (Andesite Lava.
Dacite, partly Basalt.
Crystal Tuf.
, consisting of a variety of igneous volcanic rocks, points to a complex and diverse history of volcanism.
Qs (Swamp Deposit.
refers to marshy area deposits, suggesting the existence of past or present wetlands around Lake Toba.
Furthermore.
Tomsm (Oligocene-Miocene Intermontane Sediment.
indicates sedimentary basins formed between mountainous topographies during the Oligocene to Miocene epochs.
Lastly.
Tms (Miocene Shallow Marine Sediment.
suggests that parts of the area were characterized by a shallow marine environment during the Miocene before undergoing uplift and subsequent geological process (Gafoer et al, 1.
Horizontal to Spectral Vertical Ration (HVSR) HVSR, pioneered by Nakamura .
, is a widely used seismic microzonation technique for evaluating the influence of local soil conditions on earthquake ground motion amplification and supporting urban-scale seismic microzonation studies (Gosar, 2.
The method involves calculating the spectral amplitude ratio between the average horizontal components and the vertical component of microtremor signals (Konno & Ohmachi, 1.
The resulting HVSR curve provides the ground's resonance behavior, where the peak frequency corresponds to the site's dominant frequency .
The HVSR ratio is formally expressed as yaycOycIycI = Oo .
cAOeycI) .
))2 .
cOOey.
))2 .
cO) .
) .
where ya.
cAOeycI) and ya.
cOOey.
are the amplitude spectra of the North-South and West-East horizontal components, and ya.
cO) is the amplitude spectrum of the vertical component.
This approach is highly reliable for identifying soft sediment layers and their thickness (Nugroho et al.
, 2.
6 Seismic Hazard Parameter 1 Natural Frequency The natural frequency, commonly denoted as the peak frequency of the HVSR curve, is a key parameter in characterizing local site conditions.
It represents the fundamental frequency at which ground layers resonate due to incoming seismic energy, particularly in soft sedimentary basins overlaying bedrock (Alonso-Pandavenes et al.
, 2.
Determining this frequency is essential for assessing potential resonance with structures during seismic events.
To calculate the natural frequency, the following equation is used :
yce0 = ycOyc 4Ea where yce0 denotes the natural frequency (H.
, ycOyc represents the average shear wave velocity of the sediment layer .
, and h is the thickness of the soft sediment layer .
This relation assumes a twolayer system, where surface soft sediments overlay a stiffer substratum.
Table 1 .
Definition of site classification for this project (Grajales-Saavedra et al, 2.
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Site Class Predominant Frequency (H.
rock/stiff soil rigid soil semi-rigid soil soft soil yce0 > 5 5 < yce0 O5 6 < yce0 O 2.
yce0 O 1.
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Amplification factor The amplification factor reflects the extent to which seismic waves are intensified due to local soil conditions.
It is derived from the HVSR curve as the maximum ratio of horizontal to vertical spectral amplitudes (Asnawi et al.
, 2.
The amplification factor can be calculated using the following yayca ya0 = .
ya yc with ya0 representing the amplification factor, yayca denoting the shear wave velocity .
cOy.
in the basement layer .
, and yayc indicating the shear wave velocity .
cOy.
in the weathered layer .
The dominant period is the inverse of the natural frequency and indicates the time at which the soil profile oscillates most significantly during ground shaking.
It is particularly relevant in assessing the resonance risk between site conditions and building structures (Grutas et al.
, 2.
The dominant period is calculated using the following equation:
ycN0 = .
yce where ycN0 is the dominant period .
and yce0 is the natural frequency (H.
This simple yet important relationship allows for the identification of potentially vulnerable buildings whose natural periods are close to that of the ground, increasing the risk of resonance during earthquakes (Asnawi et al.
, 2.
Table 2 .
Definition of site classification for this project (Savaadra, 2.
Site Class Dominant Period .
SC I SC II SC i SC IV T < 0.
2 O T < 0.
4 O T < 0.
T Ou 0.
Seismic Vulnerability Index The Seismic Vulnerability Index .
ayci ) is a composite indicator that integrates the amplification factor and natural frequency to assess site susceptibility to seismic damage.
It has been increasingly used in urban seismic microzonation and disaster risk mitigation efforts (Wibowo et al.
, 2.
To compute the vulnerability index, the calculated using the following equation:
yayci = ya2 In this expression, yayci is the vulnerability index, ya0 is the amplification factor, and yce0 is the natural A higher yayci value indicates greater seismic vulnerability, often associated with soft, thick sediment layers exhibiting both high amplification and low frequency (Arrasyid et al.
, 2.
RESULTS AND DISCUSSION
Horizontal to Spectral Vertical Ration (HVSR) The H/V spectral ratio (HVSR) curves obtained from ambient noise recordings at selected measurement points around Lake Toba are presented in Figure 4 These curves illustrate the frequencydependent behavior of seismic wave amplification at each site and serve as the basis for identifying predominant frequencies, amplification factors (Z.
Chen et al.
, 2.
The curve shown in Figure 4 exhibits a sharp and distinct peak, indicating a strong impedance contrast between two subsurface layers.
The measured predominant frequency .
reflects the depth of the reflection interface, typically representing the boundary between sedimentary layers and the underlying bedrock.
A lower yce0 value .
onger perio.
suggests a deeper boundary, indicating thicker sedimentary deposits.
Conversely, a higher fCA value implies a shallower boundary, associated with thinner sediment layers.
In addition, the amplification factor (ACA) on the HVSR curve indicates the extent to which surface waves are amplified by subsurface structures.
Higher ACA values correspond to greater impedance contrasts between layers, which are influenced by differences in density and seismic wave velocity across each layer.
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A curve featuring two distinct peaks .
ouble pea.
suggests the presence of impedance contrasts at multiple depths, meaning that surface waves are traversing several layers with differing physical For instance, the surface layer may consist of loose or unconsolidated sediments, followed by a denser sediment layer, and finally, a relatively rigid bedrock at greater depth.
Meanwhile, a broad peak curve is typically associated with inclined bedrock morphologyAisuch as in concave valley structuresAior lateral variations in the sediment-bedrock interface.
This type of topology reflects the geological complexity of the subsurface structure, both vertically and laterally.
Figure 4 The H/V curve around Lake Toba.
2 Seismic Hazard Parameter 1 Natural Frequency The microzonation map of predominant frequency around Lake Toba as shown in Figure 5 reveals significant spatial variations, with observed frequencies generally ranging from approximately 6 Hz .
luish color.
to over 2.
1 Hz .
ed color.
The predominant frequency .
is a key parameter that reflects the natural frequency at which soil layers resonate most strongly with seismic waves.
Based on the analysis results, areas with low predominant frequency .
ndicated by bluish to yellow color.
are prominently observed in the central and southern parts of the study area, particularly around the immediate vicinity of Lake Toba and extending southwards.
These areas likely correspond to thicker sediment basins or soft, unconsolidated For instance, points LT34.
LT14.
LT17.
LT21, and LT49 show lower predominant frequencies.
According to Table 1, these low frequencies typically indicate soft to medium soil conditions.
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Conversely, areas with high predominant frequency .
ndicated by orange to dark red color.
tend to be situated in locations with stiffer soil layers or shallow bedrock, such as the regions to the northwest .
LT10.
LT.
and isolated spots like LT44 and LT36.
These higher frequencies, as per Table 1, are indicative of stiff soil or rock sites.
Figure 5 The microzonation of Predominant Frequency around Lake Toba.
Notably, the highest predominant frequency was observed at point LT39, located in the Parapat area on the northwestern margin of Lake Toba.
When correlated with the geological map, this point corresponds to the Tmv unit, which represents Miocene volcanic rocks.
These rocks are characterized by andesitic and dacitic lava flows, partly basaltic, along with breccia, agglomerate, lapilli, and volcaniclastic sediments.
The unit exhibits porphyritic and dacitic composition in its upper layers, suggesting a highly consolidated and competent geological formation.
The high value of predominant frequency at LT39 is thus consistent with the presence of shallow, stiff volcanic bedrock, which tends to resonate at higher frequencies due to its rigidity and lower thickness of unconsolidated cover (Gafoer et al, 1.
Amplification factor The amplification factor .
a0 ) map around Lake Toba (Figure .
illustrates the extent to which seismic waves can be amplified by local soil conditions, with values generally ranging from 0 .
luish color.
to over 12.
ark red color.
High amplification factors .
ndicated by bluish color.
are notably concentrated in the central and southern areas, largely overlapping with the low predominant frequency zones.
Specific measurement points like LT34.
LT14.
LT17.
LT21, and LT49 exhibit significantly high amplification values, suggesting a substantial increase in ground motion in these regions during an earthquake.
These areas are generally associated with thick alluvial deposits, soft soils, or unconsolidated geological formations, which have the ability to amplify seismic wave energy.
Conversely, areas with low amplification factors .
ndicated by dark red color.
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northwestern parts, for example, near LT10.
LT11.
LT44, and LT36, which typically represent locations with shallow bedrock or denser soils, and thus tend not to amplify seismic waves significantly.
The highest amplification factors were recorded at point LT24, located in the Pakkat area.
LT25 in the Sitandoek area, and LT28 in Parlitan.
These locations are characterized by elevated amplification values, suggesting significant ground motion enhancement during seismic events, likely due to the presence of soft, unconsolidated surface materials.
Interestingly, point LT20, situated in the Tarutung area, also shows a notably high amplification factor.
This location is particularly important as it lies directly along the Sumatra Fault Zone (SFZ)Aia major active strike-slip fault system in the region.
When correlated with geological data, the Tarutung area is found to be underlain by Quaternary alluvial deposits, consisting of soft, loose sediments with poor compaction.
These geological conditions, combined with tectonic activity from the SFZ, contribute to significant site effects and a heightened potential for ground shaking amplification (Gafoer et al, 1.
Figure 6 The microzonation of amplification factor around Lake Toba.
Dominant Period The dominant period .
map around Lake Toba as shown in Figure 7 reveals periods generally ranging from approximately 0.
6 seconds .
luish color.
to over 2.
1 seconds .
ark red color.
The dominant period is particularly relevant for assessing the potential resonance with structures of varying The dominant period is the inverse of the predominant frequency (Equation .
and represents the most significant oscillation time of the soil profile during shaking.
Areas with long dominant periods .
isplayed in dark red color.
are conspicuously present in the central and southern parts of the study area, precisely mirroring the regions with low predominant frequencies and high amplification factors .
LT34.
LT14.
LT17.
LT21.
LT.
According to Table 2 (Classification Table for Dominant Perio.
, these long periods typically indicate soft to very soft soil conditions.
These zones indicate the presence of thick and soft sediment layers that will oscillate more slowly, typically for periods ranging 2 to 2.
1 seconds or higher.
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buildings that have similar natural periods, increasing the risk of structural damage.
Conversely, areas with short dominant periods .
isplayed in bluish color.
, such as the northwestern and scattered northern locations .
LT10.
LT11.
LT44.
LT.
, indicate stiffer soil layers or shallow bedrock, which tend to resonate with low-rise buildings .
eriods typically below 0.
6 second.
Based on Table 2, these shorter periods are characteristic of stiff soil or rock sites.
Figure 7 The microzonation of dominant period around Lake Toba A notable example is point LT39 in the Parapat area, which exhibits the shortest dominant period across the study area.
When correlated with the geological map, this point lies within the Tmv unit, representing Miocene volcanic rocks composed of andesitic to dacitic lavas, basalt, breccia, agglomerate, and volcaniclastic deposits.
These volcanic rocks are known for their high rigidity and shallow depth, resulting in a stiff response to seismic waves and hence, a very short dominant period.
This correlation confirms that consolidated and coherent lithologies, such as those in the Tmv unit, contribute to rapid ground response during shaking.
In contrast, the longest dominant periods were observed in the central part of Samosir Island and are also widespread along the southern shoreline of Lake Toba.
These zones are underlain by the Qa unit (Quaternary alluviu.
, which consists of soft, unconsolidated deposits such as clay, silt, sand, and gravel (Gafoer et al, 1.
The thick and lowdensity nature of these sediments causes them to resonate at longer periods.
Their widespread presence, especially in the southern basin and coastal margins of the lake, highlights a broader zone of potential seismic hazard due to extended shaking durations and greater likelihood of resonance with taller buildings (Gafoer et al1.
Seismic Vulnerability Index The seismic vulnerability index (K.
map around Lake Toba (Figure .
, values typically range from approximately 3.
luish color.
to over 12.
ark red color.
High seismic vulnerability index values .
ndicated by bluish color.
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shores and extending towards the south, encompassing points like LT34.
LT14.
LT17.
LT21, and LT49.
These zones are identified as most susceptible to earthquake damage.
These areas typically have a critical combination of high amplification and low predominant frequency .
r long dominant perio.
, indicating soft, thick soil layers with a high potential for ground motion amplification.
The Kg values in these regions can reach up to 12.
0 or higher.
Conversely, areas with low seismic vulnerability index .
ndicated by red color.
are primarily located in the northern and northwestern regions .
LT10,
LT11.
LT44.
LT.
, indicating more stable soil conditions and less susceptibility to seismic amplification, with Kg values generally below 3.
From a geological perspective, low Kg values, generally below 1.
0, are found in the northern and northwestern regions .
LT10.
LT11.
LT44,
LT.
, where soils are stiffer and bedrock is shallower.
These areas correlate with the Tmv unit (Miocene volcanic rock.
, comprising andesite, dacite, and brecciaAilithologies that produce lower amplification and shorter response periods (Gafoer et al, 1.
Figure 8 The microzonation of seismic vulnerability index around Lake Toba Distribution of H/V Spectral Ratio To assess variability of subsurface conditions, the results of the H/V spectral ratio analysis for each measurement station are summarized in Table 3.
Key parameters derived from the analysis include the predominant frequency of the subsoil, the corresponding period .
ominant perio.
, the peak amplitude of the H/V curve, and the seismic vulnerability index.
Results obtained in the H/V spectral ratio analysis for each station are presented in Table 3.
It should be noted that the seismic microzonation maps presented in this study are derived from 29 microtremor measurement stations distributed across the Lake Toba region.
Given the large spatial extent and geological complexity of the study area, the relatively low station density may introduce spatial aliasing effects, particularly in areas characterized by strong lateral variations in lithology and sediment thickness.
Consequently, the interpolated microzonation patterns should be interpreted as firstorder regional trends rather than detailed representations of local site conditions.
Despite this limitation.
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the observed spatial consistency between low predominant frequency, high amplification factor, elevated seismic vulnerability index, and Quaternary alluvial deposits suggests that the HVSR results capture the dominant regional site response characteristics.
The maps therefore provide a useful framework for identifying zones of relatively higher and lower seismic hazard at a regional scale, while acknowledging that finer-scale variations may not be fully resolved without higher station density.
Table 3 .
Value of the Predominant frequency .
ce0 ), amplification factor .
a0 ), dominant period .
cN0 ), and seismic vulnerability index( yayci ) obtained in each of the 29 stations Station yeNya (H.
LT01
LT02
LT04
LT05
LT06
LT09
LT10
LT11
LT13
LT14
LT16
LT17
LT19
LT20
LT21
LT24
LT25
LT27
LT28
LT34
LT36
LT39
LT40
LT41
LT44
LT48
LT49
LT50
CONCLUSION
This study applied the HVSR method to identify regional-scale variations in seismic site response across the Lake Toba region using microtremor data from 29 measurement stations.
The resulting microzonation maps of predominant frequency .
CA), amplification factor (ACA), dominant period (TCA), and seismic vulnerability index (KCO) highlight zones with relatively higher and lower seismic susceptibility, particularly in relation to Quaternary alluvial deposits and consolidated volcanic Vs30 estimation and H/V inversion for shear-wave velocity (V.
profiles were not conducted in this study due to the lack of independent subsurface constraints, such as borehole or active seismic data, which are required to reduce the non-uniqueness of HVSR inversion results.
Therefore, the analysis focuses on robust HVSR-derived parameters .
CA.
ACA.
TCA, and KCO) for regional-scale seismic hazard Future studies integrating HVSR with complementary geophysical data are recommended for reliable Vs30-based site classification.
Given the limited station density and the extensive spatial coverage of the study area, the results should be interpreted as a regional seismic hazard identification rather than a basis for site-specific engineering design or building regulations.
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as a reference for prioritizing areas where more detailed geophysical investigations and higherresolution microzonation studies are required.
REFERENCE