Dominant Frequency Values Research Articles

Interpretation of Microtremor Data Through Analysis Horizontal to Vertical Spectral Ratio (HVSR) for Microzonation of Seismic Earthquake Hazards in Baubau City

Research has been carried out on seismic hazard microzonation in the city of Bau – bau using microtremor data. The aim of this research is to determine the seismic vulnerability index based on horizontal to vertical spectral ratio (HVSR) analysis and create a dominant frequency microzonation map (F0), dominant period map (T0), amplification factor map (A0), and seismic vulnerability index map (Kg) from microtremor data which can describe the level of vulnerability of an area to seismic hazards. Microtremor measurements were carried out using a portable three-component seismograph (TDS. 303), the data was analyzed with gepsy software via the HVSR method. The research results show that the distribution of dominant frequency values ​​(F0), ranges from 0.4795 Hz to 16.6383 Hz, dominant period values ​​(T0), ranges from 0.0601 seconds to 2.0854 seconds, amplification factor values ​​(A0), ranges from 1.2285 to 4.9043, and the seismic vulnerability index (Kg) value ranges from 0.1043 to 11.0276. The values ​​(F0), (T0), (A0), and (Kg) are interpreted by referring to literature data and surface geological maps of the research area. The results show that the study area has a small portion of sediment layers that are vulnerable to seismic hazards.

Site Characterization and Shallow Shear Velocity through HVSR Measurements around the Hyderabad Metropolitan Region, India

ABSTRACT We investigate the site characterization and shallow shear velocity profiles from the analysis of the Horizontal to Vertical Spectral ratio (HVSR) around the Hyderabad metropolitan region (HMR), which falls under the southern Indian shield. This work uses both the ambient noise and microearthquake data to compute the HVSR, and additionally the Random Decrement technique to compute the HVSR of extracted Rayleigh waves. This study indicates comparable HVSR curves at each station with the three different datasets, from which we obtain the average dominant frequency (f0) and amplification value (A0). They are further used to calculate the seismic vulnerability index value (Kg). We observe that the value of f0 around the HMR is not fixed, but is varying in the range of 3.4 to 18 Hz, whereas the value of A0 is in the range of 1.7 to 12 approximately and Kg in the range of 0.16 to 1.68 approximately, with an exception of ∼ 33 at VKB (Vikarabad) station, which may be due to a local unconsolidated sub-surface structure. Based on the Diffused Field Assumption (DFA), we invert the average HVSR curves and average dispersion curves of Rayleigh waves, and provide the shallow shear velocity profiles up to 300 m, along with an approximate estimate of VS30 (in upper 30 m depth). The estimated VS30 values vary between 911 to 3143 m/s, falling under the classifications A and B (mostly Hard Rock and Rock type) of National Earthquake Hazards Reduction Program (NEHRP) (BSSC, 2001). However, our study shows some stations with shear velocity inversions at shallow depths within 300 m, indicating layers of low velocity, needing further study. In the absence of detailed near-surface findings, these findings are valuable inputs for geotechnical engineering studies and urban-city planning around the HMR, and emphasizes the effectiveness the HVSR method to determine sub-surface topography and/or unknown soil structures as an economical investigation viability.

Seismic vulnerability distribution of the earthquake prone area in Central Aceh

Abstract Central Aceh is known as an earthquake-prone area due to the presence of the Sumatra Fault and secondary fault crossing the area resulting the M 6.1 earthquake in 2013. The objective of the research is to investigate seismic vulnerability of Central Aceh. Microtremor observations were conducted at 25 locations in Central Aceh analysed using the Horizontal to Vertical Spectral Ratio (HVSR). Seismic amplification is represented by the maximum values of H/V. The dominant frequency f0 representing the sediment thickness was obtained when the H/V curve is maximum. The frequency values ranged from 14.9 to 25.9 Hz, and the seismic vulnerability values varied from 0.02 to 3.1. The top soil consists of thin layers of sedimentary material dominated by tertiary rocks. The rocks are classified as Type IV and Class I based on the dominant frequency values. This result is consistent with the geology, consisting of sedimentary and volcanic rocks. Areas with a seismic vulnerability value > 1.0 is considered to have a high risk of earthquake damage because they are likely to experience earthquake amplification. Areas with seismic vulnerability value > 1.0 are found in West Aceh and the Geureudong volcano area.

Spatiotemporal stability of digital twin-guided atrial fibrillation dominant frequency sites and the clinical outcome of catheter ablation

Abstract Background Although the dominant frequency (DF) may localize the reentrant drivers of atrial fibrillation (AF), its meandering nature makes it difficult to localize as an extra-pulmonary vein (extra-PV) target. Purpose We explored and quantified the spatiotemporal stability of DF by sophisticated digital-twin maps and the association with the rhythm outcome of clinical AF catheter ablation (AFCA). Methods We retrospectively examined the DF sites in the digital twin integrated by high-density electroanatomical maps (EAM) of 170 patients previously included in the CUVIA-AF2 trial (male 70.6%, 59.2±11.3 years old, 100% persistent AF). We monitored 34 seconds of virtual AF and analyzed DF sites in 10 different left atrial (LA) regions at 3 consecutive periods (6 seconds each after 16sec induction and blanking periods). The spatiotemporal stability index (STSI) was calculated to quantify mean DF's spatial and temporal variability. During protocol-based rhythm follow-up, we assessed the atrial arrhythmia recurrence rate by dividing patients into two groups based on STSI 0.75. Results During the simulation, 108 out of 170 (63.5%) patients obtained mean DF values in all three consecutive periods. There were 26 (24.1%) patients in the stable DF group (STSI ≥0.75, Stable group) and 82 (75.9%) patients in the unstable DF group (STSI <0.75, Unstable group). Although the proportion of patients with hypertension (73.1 vs. 47.6%, p=0.041) was higher and left ventricular end-diastole diameter (51.3±3.9 vs. 49.0±4.4 mm, p=0.020) was larger in the stable DF group than in the unstable DF group, other parameters, including LA size, LA voltage, or AF ablation targets, did not differ between two groups. During the median 19 [15-22] months follow-up, the atrial arrhythmia recurrence rate of the Stable group is higher than that of the Unstable group (log-rank p=0.031, HR = 2.06, CI [1.06-4.01]) Conclusions We found that the temporally stable DF in EAM-integrated virtual AF, the potential extra-PV AF drivers, is a surrogate marker of the adverse rhythm outcome of AFCA. A prospective clinical trial targeting the spatiotemporally stable DF will be warranted.

Vulnerability Index Assessment for Mapping Ground Movements Using the Microtremor Method as Geological Hazard Mitigation

Various geological disasters, such as landslides and ground movements, occur annually in Srimulyo Village, Malang District, with varying levels of damage. Ground movements can affect structures built above, causing sinking, cracking, and collapse. Research into landslides and ground movements triggered by vibrations is generally conducted using the microtremor method, which has proven effective. This study uses the microtremor method to map the soil condition that is potentially prone to movement or landslides based on the observed soil vulnerability index. Data was collected using a TDL 303s Digital Portable Seismograph instrument; the measurement points were established in the form of a grid distributed across the research area, with a recording duration of approximately 45 minutes at each point. The analysis technique utilizes the Horizontal Vertical Spectrum Ratio (HVSR) based on the Fast Fourier Transform (FFT) principle. The study’s results found that the research location’s seismic vulnerability index varies between 6.5 and 16.5. Areas with high seismic vulnerability index values, specifically those with Kg>11.5, are scattered on the west, south, and southeast sides of the research location. Based on field observations, these areas are dominated by relatively thick sediment layers, leading to lower dominant frequency values and higher amplification values; consequently, the seismic vulnerability index in the southern region is also high. Doi: 10.28991/CEJ-2024-010-05-017 Full Text: PDF

Investigation of Sediment Layer Thickness Estimation at Bengkulu University Hospital Based on Microtremor Data

Bengkulu is the capital of Bengkulu Province and is located in the subduction zone between the Eurasian and Indo-Australian plates. Bengkulu is also close to the major faults of Sumatra, namely the Musi fault, the Ketahun fault, and the Manna fault. Therefore, regional planning and infrastructure development for earthquake mitigation is necessary. The purpose of this study is to estimate the thickness of the sedimentary layers in the construction zone of Bengkulu Hospital during the earthquake attenuation phase. This study is conducted by surface geological analysis using the HVSR method; data analysis using microtremor data. The microtremor data were analyzed using the HVSR method to obtain the amplification value (A0) and the dominant frequency (f0). HVSR analysis gave dominant frequency (f0) values from 5.1 to 5.8 Hz, amplification (A0) from 1.64 to 5.91 times, and dominant period (T0) from 1.49 to 2.81 seconds. The values of A0, f0, T0 are interpreted with reference to the literature and surface geology as a moderate risk of seismic vulnerability, characterized by moderate to weak sedimentation and moderate amplification values.

Investigation of sediment thickness in the rammang-rammang maros karst area using microtremor method

The aims of this study were to analyze the value of dominant frequency and amplification, estimate the thickness of the sediment, and to evaluate the seismic vulnerability of the Rammang-Rammang Maros Karst Area. This work was carried out at the Rammang-Rammang Maros Karst Area, Salenrang and Bontolempangan Village, Bontoa District, Maros Regency, South Sulawesi. Microtremor data were analyzed using the Horizontal to Vertical Spectra Ratio (HVSR) method to obtain the H/V curve representing the dominant frequency and amplification values. The dominant frequency values were obtained in the range from 1.389 to 6.251 Hz. The amplification values were in the range from 0.455 to 3.944. The sediment thickness was obtained in the range from 18.521 to 88.029 m, and the seismic vulnerability was in the range from 0.040 to 5.761. High values of sediment thickness were obtained in riverbank areas, which indicated that the weathering that occurred was caused by weathering of limestone and sedimentation by rivers. Meanwhile, low sediment thickness values were obtained in karst hill areas, indicating that the weathering occurred due to the limestone dissolution process. Based on the seismic vulnerability and amplification, the Rammang-Rammang Maros Karst Area is in a relatively safe zone.

Site classification Based on Shear Wave Velocity Inversion in The Jlantah Dam Construction Project using the HVSR (Horizontal to Vertical Spectral Ratio) Analysis Method

This research was conducted with the aim to test whether the results of the inversion of the HVSR curve can be used as complementary data for N-SPT values in classifying areas according to site classification. The inversion result in the form of shear wave velocity (VS ) is then compared directly with the N-SPT data in several boreholes. Ellipticity curve method is used for inversion. The data generated in this study are dominant frequency, Amplitude Peak, and H/V curve as a result of the HVSR analysis performed on microtremor data. Furthermore, an inversion was carried out on the H/V curve by taking into account secondary data in the form of borehole, shear wave velocity, density and poisson ratio for each type of lithology. The dominant frequency value obtained has a value range of 0.33 to 17.15 Hz. The Amplitude Peak obtained in the study area has a value range of 1.81 – 11.4. The inversion (VS ) value has a range of 110.5 m/s – 400 m/s, so it is included in the classification of Soft Soil, Medium Soil, and Hard Soil and Soft Rock. The correlation of and N-SPT show that inversion method with HVSR analysis of microtremor data is quite reliable as supporting data for N-SPT. Considering cons of drilling, the method used in this study can be a new alternative for use in construction projects because it can be carried out at a relatively low cost, and is quite simple in terms of data acquisition and processing.

Identification of Subsurface Water Pipe Based on Horizontal to Vertical Spectral Ratio (HVSR)

Disruption of water distribution through underground pipe is a frequent case. As a handling, a method that can detect disturbances from subsurface pipe is needed. Microtremor is one of the geophysical methods that can provide an overview of the subsurface. Processing is done with the HVSR method with input in the form of seismic waves in the time domain which is then processed using Geopsy software to get output in the form of dominant frequency values, amplification, and H/V spectrum. The data used in this study are primary data obtained from data acquisition with a total of 60 measurement points. The distance between points is given 5 dm with a measurement time of 10 minutes for each point. The study was conducted on pipe with empty, partially filled with water, and fully filled with water with a pipe diameter of 0,9 dm. The pattern in each pipe condition from the modeling results appears at a frequency of 0-10 Hz. The difference in the range of amplification values in pipe anomalies is due to different levels of water content which can be concluded that pipe filled with water have higher amplification than empty pipe and be showed in 3D modelling.

Application of HVSR Method on Microtremor Data for Analysis of Earthquake Potential in Candipuro District, Lumajang, Indonesia

The Earthquake of 6.1 magnitude occurred on April 10, 2021, in Lumajang district. One affected area suffered building losses, road damage, and casualties in Candipuro District, Lumajang Regency, East Java. Then the research was conducted to determine the strength of the soil against the potential earthquake by micro zoning the area in Candipuro District. This research uses the microtremor method with HVSR (Horizontal to Vertical Spectral Ratio) analysis. Analysis of earthquake potential includes parameters of Ground Amplification (A0), Dominant Frequency (f0), Ground Vulnerability Index (Kg), and Ground Shear Strain (GSS). The acquisition was completed with 16 measurement points in Supiturang Village with 500 meters between points using the Portable Seismograph TDS - 303. The results obtained in Supiturang Village have the results of the amplification value factor which is classified as medium-high (2.7 - 8.7), low dominant frequency value (0.5 - 1.4 Hz), medium-high soil susceptibility index (10 - 90), VS30 value which includes medium - hard soil (187.81 - 548.38) m/s, and GSS value which shows the response of cracks and soil subsidence to shaking (2 x 10-5 - 2 x 10-4).

Mapping of Soil Dynamic Response of Palu City Based on Horizontal to Vertical Spectral Ratio (HVSR) Method

Palu is one of the earthquake prone coastal cities in Indonesia. The 28 September 2018 earthquake (Mw 7.5) destroyed buildings in Palu due to ground shaking amplification, liquefaction, and tsunami. This phenomenon implies the importance of soil dynamic properties knowledge as a basis for proper building design to reduce such an earthquake. This paper presents the results of microtremor measurements conducted at 110 locations in Palu to estimate the dynamic properties of alluvial and marine deposits for earthquake mitigation. The microtremor data were processed using the HVSR method to estimate dominant frequency and amplification factors. Based on these two parameters, the seismic vulnerability index value can be used to estimate the dynamic characteristic variations of the area. The results show that alluvial and marine sediments in Palu have dominant frequency values from 0.54 to 11.72 Hz, amplification from 1.64 to 6.15, and seismic vulnerability index of 1.49 to 56. Sediments with low dominant frequency and high amplification factors are mostly found in the western and eastern Palu and Mantikulore districts, which are associated with thick sediment layers. The areas with the highest amplification factor and seismic vulnerability index are Petobo and Balaroa, which experienced severe damage during the 2018 earthquake.

Preliminary Result: Analysis of Dominant Frequency in Western Part of Java, Indonesia using Hilbert-Huang Transform-HVSR Method

The western part of Java is situated near various geological formations stemming from the collision between the Indo-Australian and Eurasian tectonic plates. These formations include the Java Trench, Sunda Strait, and several active onshore faults, rendering the area susceptible to seismic activity. The dynamic response of the soil to seismic shaking in this region warrants thorough investigation, particularly due to the prevalence of alluvium deposits in certain areas, which have the potential to amplify ground motion. In this research endeavor, seismic data recorded by 81 temporary seismic stations in West Java were utilized. The analysis employed the Hilbert-Huang Transform technique in conjunction with the Horizontal to Vertical Spectral Ratio (HVSR) method to derive the Horizontal-to-Vertical (H/V) spectral response curve for each measurement point. The implementation of the Hilbert-Huang Transform served the purpose of mitigating non-stationary transient noise commonly encountered in urban measurements, thereby enhancing the accuracy of the HVSR curve in portraying the dominant frequency characteristics of the measurement area. The findings of this study reveal that within the western part of Java, the dominant frequency values fall within the range of 0.9 to 7 Hz. Areas exhibiting lower dominant frequencies are indicative of a greater sediment thickness, predominantly observed in the northern region of the western part of Java, the Bandung Basin, some areas surrounding active volcanoes as well as various locales within the province of Banten.

Determinatioan Of Sediment Thickness By Using Microtremor Data In Kadia Sub-District, Kendari City

This study aims to determine the value of the distribution of sediment layer thickness. This research was conducted in the Kadia District area, Kendari City, with data collection carried out at 16 measurement points with intervals for each point varying from 400 to 600 meters with a sampling frequency of 100 Hz. The data obtained from this study is in the form of ground vibration data which is then downloaded software DataPro.exe East-Westhorizontal component, the North-South vertical component Up-Down. The downloaded microtremor data is then processed using a device software Geopsy 4.3.2 to obtain the H/V curve. The dominant frequency value (f0) is obtained from the H/V curve with a dominant frequency range of 1.247 Hz to 4.955 Hz and the shear (VS30) is obtained from the website www.USGS.gov with a VS30 of 276 m/s up to 301 m/s. Based on the data that has been obtained, the distribution value of the sediment layer thickness (h) will be determined. The value of the thickness of the sediment layer (h) in the study area ranged from 13,016 meters to 59,473 meters.

Correlational fractal characteristics and damage progression of granite with different grain sizes based on acoustic emission monitoring

Mineral grain size caused by the geological diagenetic process is one of the fundamental reasons leading to the differences in rock mechanical behaviors, which brings challenges to the stability of underground engineering, especially in rock masses with continuous grain size changes. This study conducted uniaxial compression tests on granite samples obtained from the same invaded anticline with different grain sizes. During the tests, the acoustic emission (AE) signals were acquired synchronously. The correlation between damage evolution and AE data was then studied by frequency-spectrum analysis, fractal theory methods, and G-P algorithms. The mechanism of grain size effect on granite failure evolution was discussed. The results reveal that as the grain size increases, the strength and the elastic modulus decrease while the plastic deformation characteristic is enhanced. Grain size also affects the frequency distribution of AE signals and its time-varying characteristics. With the increase in grain size, the proportion of high-frequency signals declines during loading. The fractal dimension value of dominant frequency during loading fluctuates within the range from 0.5 to 2.25 and generally shows an overall ‘rise-fall-rise-fall’ mode. In addition, as the grain size increases from fine-grained to medium-grained, the fractal dimension changes from an increasing to a decreasing trend earlier in the compaction and elastic stages. Especially in coarse-grained samples, after a brief increase, the fractal dimension decreases continuously until approaching the overall failure. The frequency domain characteristics and correlation fractal variation of granites reflect the damage and crack evolution inside the rock sample. More scattered and unordered micro-cracks generated in samples with finer grains facilitate the dispersion of applied stress and the reduction of local stress concentration, resulting in higher strength and stiffness of the sample.

Study on the flow mechanism and frequency characteristics of rales in lower respiratory tract.

The frequency characteristics of lung sounds have great significance for noninvasive diagnosis of respiratory diseases. The rales in the lower respiratory tract region that can provide rich information about symptoms of respiratory diseases are not clear. In this paper, a three-dimensional idealized bifurcated lower respiratory tract geometric model, which contains 3rd to 13th generation (G3-G13) bronchi is constructed, where , and then the large eddy simulation and volume of fluid are used to study the fluid flow characteristics. Ffowcs Williams and Hawkings model are subsequently used to study the frequency characteristics of rale of different generations of bronchi. The results showed that bronchial blockage and sputum movement will enhance the turbulence intensity and vortex shedding intensity of flow. The dominant frequency and highest value of sound pressure level (SPL) of rhonchi/moist crackles decrease with the increase of bronchial generation. The change rates of dominant frequency of rhonchi/moist crackles in adjacent generations were 5.0 ± 0.1~9.1 ± 0.2% and 3.1 ± 0.1~11.9 ± 0.3%, respectively, which is concentrated in 290~420Hz and 200~300Hz, respectively. The change rates of SPL of rhonchi/moist crackles were 8.8 ± 0.1~15.7 ± 0.1% and 7.1 ± 0.1~19.5 ± 0.2%, respectively, which is concentrated in 28~50dB and 16~32dB, respectively. In the same generation of bronchus (e.g., G8, G9) with the same degree of initial blockage, the dominant frequency and SPL of moist crackles can be 3.7 ± 0.2% and 4.5 ± 0.3% slightly higher than that of rhonchi, respectively. This research is conducive to the establishment of a rapid and accurate noninvasive diagnosis system for respiratory diseases.

Landslide susceptibility mapping of Al Taif urban area, Saudi Arabia, using remote sensing data and microtremor measurements: integrated approach

Many people are killed by landslides due to earthquakes or severe rain, and structures and facilities built on or near slopes sustain significant damage. Such landslides on naturally occurring slopes can be large enough to utterly destroy towns or communities. Based on remote sensing and microtremor data, the area around Al Taif has been evaluated for its susceptibility to landslides. Digital elevation model (DEM), slope angle, and slope aspect thematic layers were used to depict remote sensing data. The landslide susceptibility was extracted from remote sensing thematic data. The elevations of the Al Taif area, which range from 832 to 2,594 m amsl, were identified based on the DEM. Al Taif’s slope angles range from 0° to 67.3° degrees. Nearly flat (0° to 4.75°), moderate (4.75° to 11.1°), steep (11.2° to 29.1°), and very steep slope (≤29.1°) are the different classifications for the slope. Additionally, measurements of the microtremor have been taken at 42 locations throughout the region. The horizontal-to-vertical spectral ratio (HVSR) approach was used to process and analyze microtremor data in order to determine the resonance frequency and H/V amplification factor. The findings show that, while the amplification factor varies from 1.17 to 9.28, the dominant frequency values fall between 0.3 and 12.75 Hz. To determine the frequency, amplitude, and azimuthal site response, 11 sites were eventually chosen. Furthermore, the direction of the site response in the sliding areas was parallel to the landslide directional response, indicating that the site response direction tracked the landslide direction. Practical approval of the study’s findings has been given at a number of locations by field measurements at some of the Taif urban area’s most recent landslide occurrence areas. These findings show that the integration between remote sensing and microtremor measurements is a useful tool for pinpointing landslide-prone areas, which helps to lessen the danger to people’s lives and property. This susceptibility zonation applied to the Al Taif area has produced a good match between the distribution of the reported landslides and the zones of high susceptibility. To define the general trend and geographic distribution of potentially unstable slopes and landslide potential zones, this study’s findings must be used as a guide.

Discontinuity Detection System in Marble: Analysis of the Time-Frequency Characteristics of Ultrasonic P-waves

Abstract This study attempted to determine both the presence and the appearance of the surface of a crack artificially created in a marble block without axial loading or compression by FFT analysis of ultrasonic longitudinal sound waves by scanning the surface. In such respect, the study differs from other studies in the literature. The aim of the study was to minimize marble waste by determining the most appropriate slab cut direction based on the orientation of the fracture or discontinuity within the marble block. During location-controlled scanning of the marble surface, mean longitudinal wave velocity, Young modulus, Poisson ratio and longitudinal wave velocity variation data were obtained using a V-Meter Mark IV™ ultrasonic test device. For each location, longitudinal ultrasonic velocity data was taken at 250 kHz sampling rate and 256 data points were created. Data from the computer environment were subsequently reorganized using the MATLAB software and FFT conversions for such velocity data were obtained for each location. Then, the peaks of the FFT transformation components were determined by using the “Findpeaks” function in MATLAB‘s signal processing toolbox. The number of peaks in the 50-60 kHz range was determined for each location. A single difference was determined between the peak numbers at the locations within the cracked and uncracked regions. By examining the FFT graphs, it was determined that such additional peak occurring in the cracked regions appeared as a second frequency component near the dominant frequency values. Points with secondary frequency were recorded as 1, while all other points were recorded as 0 in a new matrix. Such data matrices created for each sample were examined by visualization in the form of surface graphics. Using these graphics, the orientations of discontinuities within the marble block may be determined according to the scanning surface.

INDUCED DRAFT FAN DOMINANT FREQUENCY DETECTION USING SHORT-TIME FOURIER TRANSFORM METHOD

Weak suction and large vibrations indicate an Induced Draft Fan (IDF) problem. The Fast Fourier Transform (FFT) method cannot be applied to non-stationary vibration signals. Therefore, this study aims to analyze non-stationary vibration signals for IDF vibration signals at start-up so that the source of damage to the IDF can be found. The research process begins with a brief measurement of both bearing locations with horizontal and axial axes. Processing of the vibration signal from the measurement using the FFT method and the Short Time Fourier Transform (STFT). Based on the STFT spectrogram graph for measurements on the horizontal and axial axes, the dominant frequency values are the same. The frequency with the largest amplitude value is at one RPM IDF or 25 Hz. High vibration at 1 RPM is a big indication that the IDF is experiencing unbalance.

Early Analysis of Vulnerability Study in Lake Toba

Lake Toba is located on the Sumatra Island, Indonesia. The subduction of the Indo-Australian plate dominates the tectonic setting in this region underneath the Eurasian plate. This area has active seismicity, especially from the subduction process in the West. Most rocks in Lake Toba are tuff sediments. This study’s objective is to map the vulnerability index that can be used to identify high damage areas in the region if an intense event occurs. We use 24 three-component seismometers installed around Lake Toba. We gathered good quality recording data for one day on each station. Next, we divided our data into 1 hour and performed the time to frequency domain using the fast Fourier transform. Lastly, we divided the horizontal and vertical components and extracted some parameters such as dominant frequency value and its amplitude. The dominant frequency value ranged from 0.18 to 27.6 Hz, H/V amplification was found to be between 2.84 and 11.9, and shear wave velocity (Vs30) was found to be between 240 and 760 m/s, and the soil vulnerability index (Kg) was found to be between 0.42-43.4. The study area’s highest vulnerability is in the southeast, whereas the study area’s lowest vulnerability is located in the West and North East.

Seismic Vulnerability Analysis Using the Horizontal to Vertical Spectral Ratio (HVSR) Method on the West Palu Bay Coastline

This research was carried out to make a map of the dominant frequency (f0), amplification factor (A0), seismic susceptibility index (Kg), Vs30, Sediment Layer Thickness (H) and Peak ground acceleration (PGA). Microtremor measurements were carried out with a three-component seismometer of the TDL-303S type as many as 27 measurement points. The data was analyzed by the Horizontal to Vertical Spectral Ratio (HVSR) method. The PGA calculation was carried out using the Kanai equation with a reference to the Palu-Donggala earthquake on September 28, 2018. The results showed that the distribution of the dominant frequency value (f0) ranged from 0.4149 Hz-0.8869 Hz, the soil amplification factor (A0) ranged from 2,199–4,884, the seismic vulnerability index (Kg) ranged from 8.79 s2/cm-41.41 s2/cm, the shear wave velocity to a depth of 30 meters ( Vs30) ranged from Vs30 197.7 m/s-320.2 m/s , the thickness of the sedimentary layer ranges from 260.3 m-291.1 m and the peak ground acceleration (PGA) of Kanai ranges from 137.3 gal – 234.2 gal by using Mw 7.4 earthquakes with an intensity scale (MMI) VI to VII. The coastal area of West Palu bay has an intermediate seismic vulnerability II to a high seismic vulnerability IV so that it will be vulnerable in the event of an earthquake disaster. Areas that have a very high vulnerability index are in the upper western and easternmost regions while those with a lower level tend to have a lower vulnerability index value.