Seismic Vulnerability Index Research Articles

Analysis of Earthquake Vulnerability of The Demak Coastal Area based on the HVSR (Horizontal To Vertical Spectral Ratio) Method

<p>Most of the Demak Coastal area, especially on the north coast, has a subsurface structure which is quite thick sediment. The impact of an earthquake will cause damage to subsurface structures and buildings above it, so a method is needed that can determine earthquake vulnerability in an area to take mitigation steps. This research aims to analyze vulnerability to earthquakes based on natural frequency (fo), amplification (Ao) and seismic vulnerability index (SVI). The research was carried out by measuring the microseismic signal response at 89 locations using a 3-component seismograph and data logger. The research results showed that the dominant frequency varied from 0.26 – 5.26 Hz, the amplification factor varied from 0.51 – 3.56 and the seismic susceptibility index varied from 0.14-14.77 micro cm<sup>2</sup>/s. The study area was classified into low SVI (SVI < 5), medium SVI (5 < SVI < 10), and high SVI (SVI > 10). The potential earthquake hazard described by SVI with a value range of 10 < SVI (high classification) is found at observation station 60 (Bedono Hamlet) and observation station 70 (Karangwaru Hamlet Cemetery)</p>

Seismic Vulnerability Indices of Facades of Colonial Houses in the Historic Center of Morelia, México

Evaluating the seismic vulnerability of facades of historic masonry buildings is essential not only for their significant historical and heritage value, but also to evaluate the safety of this type of construction. This work applies a simplified methodology to assess the seismic vulnerability of the facade of masonry buildings in the historic center of Morelia, Michoacán, México. The historic center of Morelia was declared a World Cultural Heritage Site by UNESCO in 1991. On the facades, there is ornamentation with sculptural and vegetal decorative elements. The methodology involved conducting visual inspections to identify the location, type of structure, construction materials, doors, windows, balconies, cornices, ironwork, pediments, niches, and sculptures, among other characteristic elements of colonial architecture. The seismic demands were determined specifically for the city’s historic center based on a recent seismic hazard assessment of Morelia. Based on the methodology and the compiled database, characterized vulnerability indices were defined for the different damage scenarios that buildings may present. Results indicate that earthquakes with intensities greater than VIII on the Modified Mercalli scale risk collapsing heritage masonry buildings’ facades.

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.

Spatial mapping of the seismic vulnerability index in Kathmandu Valley: insight from dominant frequency and amplification factor

Abstract Kathmandu Valley situated in Nepal has experienced several earthquakes in the past. The expanding population of Kathmandu Valley is driving a significant acceleration in building construction reaching record levels and posing risks to both human lives and the economy, despite this surge in development. This study aimed to spatially map the dominant frequency, amplification factor, and vulnerability index map of Kathmandu Valley, Nepal using ArcGIS. This paper presents the nonlinear response analysis of 225 boreholes using the Gorkha earthquake as input motion and DEEPSOIL software for determining the amplification ratio and dominant frequency. The results revealed a range of values for dominant frequency from 0.08 to 7.65 Hz and soil amplification ratio from 0.13 to 8.14. Furthermore, the seismic vulnerability index was derived from the dominant frequency and soil amplification ratio ranging from 0.22 to 21.84. The resulting maps acquired through this study enable the decision-makers and stakeholders, to prioritize resources and implement targeted measures for enhancing seismic resilience in the region.

Identification of Ground Vulnerability Based on Kg, PGA, and GSS Assessment by Single Station Microtremor in Bendosari Hamlet, Kalasan Village, Yogyakarta

Bendosari Hamlet, Kalasan, Yogyakarta is a research area that is one of the areas affected by the earthquake that occurred on May 27, 2006. The earthquake with a magnitude of 6.4 caused quite severe damage to buildings around the research area. Based on the phenomenon of earthquakes that have occurred, there needs to be further study related to vulnerable areas in the event of another earthquake. Research data is primary data taken using a single statiun microtremor tool with an overall acquisition point of 50 measurement points. This study aims to find out the value of seismic vulnerability index (Kg), Peak Ground Acceleration (PGA), and Ground Shear Strain (GSS). Using the Horizontal to Vertical Spectral Ratio (HVSR) method, the dominant frequency result (f0) and amplification factor value (A0) from data that has been recorded through the microtremor tool. Based on research that has been done, the results are obtained in the f0rm of seismic vulnerability index values that are in the range of 0.49 - 30.18, the value of the acceleration of ground movement is in the range of 0.21 - 0.61 Gal, and the ground shear strain value is in the range of 4 x 10-6 to 38 x 10-5. Point K26 which is the original documentation of buildings affected by the earthquake, analyzed that the value of Vs of 858.112 m / s on the vs ground profile indicates that there is hard soil at a depth after 27.2 m. This shows that the thickness of subsurface sedimentary rocks at point K26 is quite thick. Keywords: Bendosari Hamlet; Mikrotremor; GSS; HVSR; PGA; Seismic Vulnerability

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

Assessing road vulnerability in seismic conditions: a comprehensive study

Road infrastructure is indispensable for societal functionality, yet it is highly susceptible to the devastating impacts of seismic events. This paper focuses on enhancing the resilience of road systems by systematically identifying, quantifying, and assessing factors contributing to their vulnerability during earthquakes. The core objective of this study is to develop and validate a seismic vulnerability index for road sections, which aims to evaluate and classify the susceptibility of road infrastructure to earthquake-induced damage comprehensively. This systematic approach is pivotal for guiding effective mitigation strategies and prioritization efforts. To fulfill this objective, the study employs the Analytic Hierarchy Process (AHP) to introduce a novel methodology for calculating the seismic vulnerability index, incorporating various factors that influence road vulnerability. This method allows for the accurate classification of road sections into distinct levels of susceptibility, providing a solid foundation for implementing targeted interventions and enhancing road resilience. Further, the paper validates the theoretical model through several case studies, demonstrating the practical applicability and effectiveness of the seismic vulnerability index in real-world scenarios. Additionally, the use of Geographic Information System (GIS) technology to simulate earthquake scenarios within an urban road network offers valuable insights into the potential seismic behavior of roads. These simulations are crucial for identifying critical areas that require intervention and for planning resilience-building efforts more effectively. By proposing a comprehensive framework that combines rigorous analysis, empirical validation, and advanced simulation techniques, this paper seeks to make a significant contribution to the field of infrastructure resilience. It aims to advance the understanding of road vulnerability in seismic conditions and supports the development of strategic approaches for enhancing the resilience of road infrastructure against earthquakes. Through the development and validation of a seismic vulnerability index, this study meets its primary objective, providing a valuable resource for researchers, policymakers, and practitioners in disaster management and infrastructure planning.

Distribusi Kerentanan Seismik di Wilayah Pusat Kota Surabaya

Surabaya is the second major city of Indonesia and the economic capital of eastern Indonesia. The city’s central area is the governmental center of East Java Province. This area is traversed by the Surabaya section of the Kendeng Fault which could potentially generate a maximum M6.5 earthquake. The East Java megathrust zone also threatens this area with a potential maximum magnitude of M8.9 earthquake. The rock geology of this region is dominated by soft alluvial soil which could amplify earthquake shaking. This study aims to identify the distribution of seismic vulnerability index in Surabaya’s central area. Therefore, microtremor measurements were carried out at 61 points in this area. The results were then analyzed using the Horizontal to Vertical Spectral Ratio (HVSR) method to determine the amplification factor values and seismic vulnerability index. The results of the HVSR analysis show that the amplification factor value and seismic vulnerability index are in the low to medium category ranging from 0.8370 - 3.8298 and 0.6041 - 14.6268, respectively. The distribution of the results shows that the northern area is more vulnerable than the southern part. This is verified by the geological conditions of the northern part which is dominated by alluvial soil.

Micro-Zonation of hot spring manifestation site at Umbul Niti, South Lampung based on microtremor

In 2021, an intriguing event unfolded at Umbul Niti village when a resident’s well drilling endeavor unexpectedly yielded to a hot spring, thus transforming the site into a small local tourist attraction that captivates visitors and enhances local economies. However, it is crucial to prioritize the safety of visitors and infrastructure, considering the geological implications of hot springs are related to unstable weak zones that would be severely damaged when an earthquake strikes. Weak zones often exhibit heightened susceptibility to seismic events. Using Horizontal to Vertical Spectral Ratio (HVSR) analysis of micro-tremor data that was recorded for 40 minutes at 25 locations, the Amplification (A 0) and Natural Frequency (f 0) were obtained; then the Seismic Vulnerability Index (Kg ) were calculated. The study area has a dominant frequency of around 4.74 - 9.7 Hz indicating the dominance of hard Tertiary Type I soil from Lampung Formation (QTI). Kg value ranges from 0.08 - 3.57 interpreted as mostly low hazard level. However, in the NW - SE direction the value indicates a high Kg value which means a relatively high hazard level, passing through the hot spring location. Thus, the area at the NW-SE zone might require more specific treatment.

Machine learning predictions of code-based seismic vulnerability for reinforced concrete and masonry buildings: Insights from a 300-building database

This paper proposes a data-driven model for predicting the code-based seismic vulnerability index calibrated on a dataset comprising almost 300 buildings. The vulnerability index, estimated following the Italian Seismic Code, involved rigorous investigations, including geometric surveys, experimental tests, and numerical modelling. Leveraging data from these investigations, encompassing approximately 15 categorical and numerical explanatory variables, the authors developed several regression and classification predictive models, such as Logistic Regression and Artificial Neural Networks (ANN). The optimal models perform binary classification to determine the categorization into two macro-classes, defined by an arbitrary vulnerability threshold. The ANN model stands out as the best performer. When adjusting the vulnerability threshold to obtain a balanced dataset, such a model achieves an accuracy higher than 85%. The paper also discusses the importance of each feature by calculating the SHapley Additive exPlanations (SHAP) values. The proposed model can aid decision-makers in allocating resources effectively to mitigate seismic risks of built environments.

MICROZONATION ANALYSIS IN MANNA CITY & PASAR MANNA SUBDISTRICTS UTILIZING MICROTREMOR DATA, SOUTH BENGKULU REGENCY

South Bengkulu is prone to earthquakes because it is located on the Great Sumatran Fault. Apart from that, it is also influenced by the activity of the Musi and Manna segments, so that besides being influenced by the two active tectonic plates it is also influenced by the local segment. This research is located in Manna City and Manna Market, which is mostly inhabited by people and is the capital of South Bengkulu. In connection with infrastructure development, it is necessary to know the condition of the soil layers to minimize the risk of building damage due to earthquakes. This research aims to analyze earthquake-prone areas based on dominant frequency parameters, soil amplification, seismic vulnerability index and sediment layer thickness (h). Research data comes from microtremor measurements at 60 measuring station points in Manna City and Manna Market. The tool used is a Short Period Portable Seismometer Model Gemini 2 SN-1405. This microtremor data is processed using the Horizontal to Vertical Spectral Ratio (HVSR) method. The results of data processing show that the research area has the lowest dominant frequency of 3.95 Hz and the highest of 49.71 Hz. The ground vibration amplification value is classified as small to medium, the lowest is 1.3 and the highest is 5.19. The lowest earthquake vulnerability index was 0.18 cm2/s and the highest was 2.24 cm2/s. The smallest sediment thickness was 3.77 meters and the thickest was 47.48 meters. From the results of the calculation of the seismic vulnerability index in Kota Manna and Pasar Manna Districts, the seismic vulnerability index value is relatively small, in accordance with the amplification factor and the thickness of the sediment layer. Based on this research, although Manna City and Manna Market are often shaken by earthquakes, the earthquake vibrations experience small amplification.

Local site effects and seismic microzonation around Suban Area, Curup Rejang Lebong, Bengkulu deduced by ambient noise measurements

BackgroundThe Suban area of Curup Rejang Lebong is a tourist region in Bengkulu Province, Indonesia, close to the active Ketaun and Musi faults, which are segments of the Sumatra Fault System (SFS). However, no studies have been conducted in this area to assess how geological structures affect seismic ground motions and contribute to seismic hazard and risk assessment.MethodsThe first study of seismic microzonation in the Suban area of Curup City by ambient noise measurements was conducted at 100 sites, spaced ~ 1 km apart, with 60 min of data acquisition for each site. All microseismic data were processed using the Horizontal to Vertical Spectral Ratios (HVSR) method.ResultsThe HVSR method revealed the amplification factors (A0) ranging from 1.23 to 8.26 times, corresponding to natural frequency (f0) variations between 1.24 and 9.67 Hz. About 13% and 55% of the sites show high (6 ≤ A0 ≤ 9) and medium (3 ≤ A0 ≤ 6) amplifications, respectively, predominantly in the western parts of the study area, consistent with a high seismic vulnerability index (Kg). Furthermore, we also estimated the ground shear strain (GSS) of the region using the Kanai method with two large historical earthquakes at the Ketahun segment in 1943 (Mw 7.4) and the Musi segment in 1979 (Mw 6.0). The Kg value is consistent with the GSS values and indicates areas of severe damage during the historic earthquakes.ConclusionsThus, the western parts of the Suban region are vulnerable to severe damage from an earthquake. These findings could provide valuable insights for future planning and risk management efforts aimed at minimizing the impact of earthquakes in the Suban region.

ZONATION OF SEISMIC VULNERABILITY LEVELS IN SOUTH BENGKULU REGENCY, INDONESIA FOR DISASTER-BASED REGIONAL PLANNING

The accurate prediction and prevention of earthquakes remains challenging. Consequently, the primary approach to mitigate the impact of earthquakes is through disaster risk reduction efforts. One significant strategy involves conducting seismic vulnerability analyses based on disaster scenarios. This study aims to identify and map areas with varying levels of seismic vulnerability, analyzing the factors contributing to vulnerability in the South Bengkulu Regency. Secondary data, including peak ground acceleration (PGA) values, were collected, along with microtremor data obtained through the Horizontal to Vertical Spectral Ratio (HVSR) method. The recorded microtremor data serve as input parameters for PGA, Modified Mercalli Intensity (MMI), Seismic Vulnerability Index (Kg), shear wave velocity (Vs), and the time-averaged shear wave velocity for the first 30 m depths (Vs30) values. The findings reveal that, overall, seismic vulnerability in the South Bengkulu Regency can be categorized as low. However, specific areas, particularly in the southwestern and northeastern zones, exhibit relatively higher levels of vulnerability. The heightened vulnerability in these areas is attributed to elevated PGA values, despite the region's generally high soil density, which acts as a mitigating factor against earthquake threats.

Development of a seismic vulnerability and risk model for typical bridges considering innovative intensity measures

Seismic intensity measures are one of the core parameters for estimating regional bridges’ seismic risk and vulnerability. Using macroscopic seismic intensity indicators to predict and assess the seismic vulnerability of bridges can contribute positively to establishing urban and rural earthquake risk models. However, the developed vulnerability model rarely considers the contribution of instrument intensity to its quantification results and ignores the influence of nondamage bridge samples on the development of bridge risk models and the membership relationship between seismic vulnerability levels, which makes the developed model somewhat localized and uncertain. This study proposes a quantitative method and innovative model considering composite seismic intensity (instrumental and macroseismic intensity) indicators. The model was updated and validated using 300,000 acceleration records monitored by ten seismic stations during the Luding earthquake on September 5, 2022, in China, and the features of seismic motion parameters were analysed. The established empirical vulnerability dataset of bridges during the 2008 Wenchuan earthquake in China was updated and optimized using the developed models and methods. The traditional vulnerability level of bridges has been expanded by adding and refining actual samples (2317 bridges) from different seismic intensity zones. A vulnerability prediction model based on an updated extended bridge database was developed using nonlinear regression methods. A fragility membership index calculation model for estimating the correlation features of bridge vulnerability levels is proposed by combining the probability risk and fuzzy membership correlation algorithm. The traditional method for calculating the seismic vulnerability index has been improved, and a multiparameter bridge vulnerability model validation and rationality analysis have been conducted using the newly developed bridge sample dataset.

Seismic vulnerability assessment of historical minarets in Cairo

IntroductionMasonry minarets in Old Cairo are highly susceptible to earthquake damage, particularly those not designed or updated to withstand seismic loads. Therefore, regular monitoring is necessary to ensure their safety and detect any deterioration or reduction in seismic performance. The direct loss of a minaret can lead to the collapse or severe damage to the structure itself. The cascading impacts of partial or complete minaret failure can have significant consequences for the immediate vicinity and the broader community. By studying the effects of earthquakes on minarets and developing mitigation strategies, countries can take proactive measures to protect these structures and ensure the safety of people.ObjectiveThis study focuses on a specific type of Islamic architecture: the historic minarets in Cairo. The research aims to evaluate the seismic vulnerability of eight cultural heritage minarets in Cairo, identifying the parameters influencing their seismic behaviour and susceptibility to earthquake damage.MethodsThe research utilizes empirical seismic vulnerability methods and ambient vibration measurements on eight minarets. An empirical approach compatible with the nature and style of the minarets is employed to evaluate their vulnerability using index values and curves. The method's validity is assessed, and areas of conformity and limitations are identified. Ambient vibration tests (AVTs) are also conducted using a temporary seismic network installed at various heights inside each minaret to determine their dynamic characteristics.ResultsThe seismic vulnerability Index (I_V) is calculated for the selected minarets based on the state of each vulnerability parameter. The contribution of each parameter to the final I_V values of the minarets are presented. Vulnerability curves are developed for each minaret, interpreting the conventional vulnerability indexes in terms of mean damage grades for seismic events with varying intensity on the EMS-98 scale. These mean damage grades can also indicate the expected damage levels of structural and non-structural minaret elements for events with different seismic intensity levels. AVTs are conducted at various heights on the selected minarets, and the dynamic characteristics are extracted from the recorded data. Variations in these characteristics are considered significant for structural health monitoring analysis. The peak-picking method is employed to directly extract each minaret's natural frequencies and mode shapes, as changes in dynamic characteristics are relevant to health monitoring analyses.ConclusionsThe recent study examined the seismic vulnerability assessment of eight masonry minarets in the historic Old Cairo district. The assessment revealed vulnerability index values ranging from 10.3 to 26.1, indicating a concerning susceptibility to seismic events among these structures. Vulnerability curves were constructed for each minaret, visually representing potential damage scenarios across different levels of the EMS-98 intensity scale. These outcomes are significant as they facilitate prioritizing interventions to safeguard the most vulnerable minarets. Additionally, a novel empirical period equation was introduced to estimate the fundamental period of minarets in Old Cairo based on their heights. The equation was validated against field measurements and data from the literature. The study is limited by its focus on a specific category of minarets, specifically the historical masonry minarets in Old Cairo. Furthermore, limitations arise from the need for detailed finite element models to capture these minarets' dynamic responses accurately. Therefore, ongoing research involves the development of detailed finite element models and calibrating fundamental periods for the selected minarets. The anticipated results hold the potential to enhance our understanding of the structural dynamics of historical minarets, ultimately guiding the formulation of tailored seismic retrofitting and preservation strategies. These strategies, aimed at preserving these cherished cultural heritage assets, represent our collective commitment to ensure the endurance of these timeless landmarks for future generations.

Soil characterization of Babol City using single-station ambient seismic noise method

The interrelation between the local site conditions and the severity of destruction during earthquakes has increased the necessity for more investigations on soil characterization in recent years. In residential areas, where active seismic methods are problematic for defining soil properties, passive seismic methods have attracted considerable attention due to their cost-effective and non-invasive features. Therefore, we have utilized 35 single-station ambient seismic noise recordings in the seismically vulnerable city of Babol, Iran, to evaluate the site response (including azimuthal variation and resonance frequency), estimate the seismic vulnerability index (Kg), and classify the soil based on the Vs30 of the region. To address the aim, we extract Rayleigh wave ellipticities from ambient seismic noise using their polarization features and employ them to define the azimuthal variations, resonance frequencies, and Kg values of the region. In each station, the ellipticity curve is inverted with the support of supplementary geotechnical information to obtain a shear velocity profile. The inversion results have good consistency with borehole and downhole test information.The study identifies a low resonance frequency of 0.9 Hz with a NE directivity for the majority of the city and a Vs30 range of 180 m/s to 350 m/s. Moreover, the seismic bedrock of Babol City is represented by a 3D Vs model at a depth of 60 m. Our results reveal that the city is vulnerable to seismic hazards due to the thick and low-velocity deposits responsible for high amplification affecting the study region, which combines with a high seismic vulnerability index, particularly in the southern part. This work has applications for future structural design, urban development, and seismic hazard reduction.

Contribution of HVSR, MASW, and geotechnical investigations in seismic microzonation for safe urban extension: A case study in Ghabt Admin (Agadir), western Morocco

Ghabt Admin, located in western Morocco, is prone to seismic activity and site effects due to its position within an alluvial basin situated between two faulted mountain belts. The region has experienced several devastating earthquakes, including the 1960 Agadir earthquake that resulted in the loss of 12,000 lives and the destruction of over 75% of the city. Moreover, the area has recently undergone rapid urbanization, necessitating the implementation of seismic studies to make informed decisions regarding land use. This study aims to conduct the first seismic microzonation and site characterization studies by using HVSR, 1D-MASW, and geotechnical investigations. The datasets consist of 80 microtremors, 15 1D-MASW profiles, detailed geological observations, boreholes, and soil/rock identification tests. Due to challenges related to anthropogenic sources and soil heterogeneities, only 31 H/V measurements met the SESAME criteria. The HVSR results indicate the following: (i) the predominant peak frequency (f0) ranges from 1.4 to 15.7 Hz, with lower values (1.4–3 Hz) observed in the Oued Issen alluvial fans and the sand dune area, while moderate to high values (4–15.7 Hz) are found in the lacustrine limestone and Tagragra’s dome. (ii) The amplitude peak frequency (A0) ranges from 2 to 7.7, with higher values observed in the southwestern zone and certain parts of the glacis-fans zone, particularly in the Oued Issen zone. (iii) The seismic vulnerability index (Kg) ranges from 0.28 to 39.5. The Oued Issen area, which is composed of recent unconsolidated deposits and affected by the Oued Issen fault, exhibits high Kg values. Analysis of HVSR curve typology reveals complex geology. The VS30 map shows VS values ranging from 179 m/s to 830 m/s, classifying the study area into soil classes A, B, and C according to Eurocode 8. Furthermore, the 1D-MASW results are compatible with the HVSR results and the distribution of the geological units.

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.

Analysis of the Effect of Local Magnitude on Peak Ground Acceleration and Seismic Vulnerability Index for Geothermal Field Monitoring Using Microearthquake

Intensive exploitation of geothermal injection and production can trigger microearthquakes which it signals come from dynamic fractures. The purpose of this study is to decide the impact of local magnitude on mitigation in geothermal fields based on soil acceleration and vulnerability of seismic in geothermal fields. This study uses seismic wave recording data and the geology of the research area. It is focable on calculating local magnitude, ground acceleration and seismic susceptibility index to earthquakes based on ground acceleration and seismic susceptibility index in geothermal fields. The maximum amplitude value represent that the medium classification class (3<A0<6) is associated with a moderate degree of deformation. Natural frequency value are found with a moderate classification (4<f0<10) around the area of injection wells and production wells, indicating that the research area has a moderate level of soil hardness structure. The peak ground acceleration in the study area is classified as moderate (0.25<PGA<0.7) which means that the area has a moderate level of risk. Vulnerability of seismic in the study area is included in the low classification (Kg<10). The local magnitude impact on soil acceleration and vulnerability of seismic in this study has a moderate risk and can be categorised as safe. In the future, this research serves as a basis for proper decision-making in geothermal energy operations, monitoring, and infrastructure development