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Characterizing the subsurface structure is an important parameter for the improvement of seismic hazard assessment. Due to the tectonic complexity of the earth, some deep fractures do not reach the earth’s surface and are not detectable with visual analysis. Therefore, the lack of knowledge of faults and fractures can result in disasters, especially in urban planning. Many geophysical methods can be used to estimate subsurface structure characterization. However, a more reliable method is required to assess seismic hazards and reduce potential damage in metropolitan areas without destroying buildings and structures. This paper aims to identify hidden faults and structures using shear wave velocity sections. To do this, surface wave dispersion curve was extracted from the vertical component of microtremor array recording using the spatial autocorrelation (SPAC) method in two profiles and 13 array stations (perpendicular to the altitudes) to obtain shear wave velocity structure (Vs) in the west of Mashhad, northeast of Iran. The results of shear wave velocity profiles (Vs) indicate sudden changes in the thickness of sediments. This can be related to the displacement of a normal fault in this area causing the bottom rock to fall and an increase in the alluvial thickness in the central part of the plain. The velocity in the floor rock is 2000 meters per second in this area. According to the surface outcrops and water wells data, its material is slate and Phyllite metamorphic rocks that are exposed in the adjacent heights. Besides, the seismic profile results were well consistent with electrical resistance data and well logs indicating that the tool array method is flexible, non-invasive, relatively fast, and effective for urban areas with satisfactory accuracy.

A comprehensive understanding of the internal structure and construction of a geomechanical formation model play an important role in developing and using geothermal resources. Formation models help in identifying the channel and cycling modes of the heat flow. Due to urban sprawl and development, constructing a formation model of geothermal resources based on data from traditional geophysical methods is challenging. The microtremor survey method (MSM) is adopted to obtain critical information in Jimo, which is famous for rare seawater geothermal resources in China. Three microtremor survey lines are deployed to identify subsurface structures up to 2 km into the ground. Dispersion curves of Rayleigh waves with frequencies from 0.4 to 10 Hz are extracted using the spatial autocorrelation method. An empirical equation is adopted to obtain the apparent shear wave (S-wave) velocity of each survey point and to plot the apparent S-wave velocity sections. The obtained sections reveal the development of two interacting faults, which form a channel for the heat-flow cycle. Two conceptual models are established to depict the formation and cycling modes of seawater geothermal resources in Jimo, based on the results and analysis. Our model will help verify the geothermal system and scientifically guide the development of unique geothermal resources. Moreover, the developed model verifies that MSM is effective and dependable for identifying fracture zones and strata.

Faced with complex engineering geological problems, the application of comprehensive geophysical prospecting technologies allows for various technical achievements to complement each other, verify each other, reduce the ambiguity in geophysical prospecting results, and improve the accuracy of geophysical prospecting interpretations. At present, comprehensive geophysical prospecting is predominantly a simple synthesis of quantification, lacks effective intelligent decision-making methods, and cannot maintain pace with the development direction of future intelligent geophysical prospecting technologies. Therefore, this study proposes a geophysical prospecting selection evaluation method based on comprehensive weights to realize the transformation from empirical to scientific decision-making. In the proposed method, four criteria—specifically, detection accuracy, technical reliability, economic rationality, and data richness level—are first selected to establish an evaluation index system. Then, analytical hierarchy process and entropy weight method are used to combine subjective experience with objective data to form a comprehensive weight for the evaluation of geophysical prospecting selection through the fuzzy evaluation method. The efficacy of the proposed method was evaluated through application to karst exploration in the limestone mining area of the Hepu in Guangxi, for which an optimal geophysical prospecting scheme, composed of electrical resistivity tomography, microtremor survey method, and cross-hole resistivity computed tomography, was obtained. The scheme realizes the asymptotic detection of karst development from coarse to fine and improves the timeliness and economics of disaster management. These results verify the effectiveness and scientific soundness of the proposed method.

On 28th July 2018, a massive landslide occurred in a mountainous area in Northern Thailand. The landslide after ten days of heavy rainfall generated the movement of uphill mountain soil into the populated village. This study presents a comprehensive failure analysis of local rainfall-induced landslides based on topographical and geological information. Rainfall measurement data were gathered from two rainfall stations close to the study area. The rainfall records show that the total monthly rainfalls in 2018 were significantly higher than the average monthly rainfalls over the past decade. Site investigation started with an unmanned aerial photogrammetric survey to generate a digital elevation model. Then, dynamic probing test, microtremor survey, and electrical resistivity survey were carried out along undisturbed soils beside the failed slope to evaluate the thickness of the soft soil cover on top of the rock basement. During the site survey, residual soil samples were collected to determine engineering properties in the laboratory. Finally, a slope stability analysis was performed to assess the landslide hazard based on the results of aerial photogrammetric survey, field exploration, and laboratory tests. The slope stability analysis and rainfall records revealed that the Huay Khab landslide was mainly caused by an increase in the water content of residual soils due to the prolonged rainfall which led to a sharp decrease in the shear strength. This leads to the conclusion that the proposed landslide investigation program could be used to assess the potential of landslide failure due to prolonged rainfall on a local scale.

SUMMARY The applicability of rotational seismology to the general wavefield of microtremors is theoretically demonstrated based on a random process model of a 2-D wavefield. We show the effectiveness of taking the rotations (i.e. spatial differentiation) of microtremor waveforms in separating the Rayleigh and Love waves in a wavefield where waves are simultaneously arriving from various directions with different intensities. This means that a method based on rotational seismology (a rotational method) is capable of separating Rayleigh and Love waves without adopting a specific array geometry or imposing a specific assumption on the microtremor wavefield. This is an important feature of a rotational method because the spatial autocorrelation (SPAC) method, a conventional approach for determining phase velocities in microtremor array surveys, requires either the use of a circular array or the assumption of an isotropic wavefield (i.e. azimuthal averaging of correlations is required). Derivatives of the SPAC method additionally require the assumption that Rayleigh and Love waves are uncorrelated. We also show that it is possible to apply a rotational method to determine the characteristics of Love waves based on a simple three-point microtremor array that consists of translational (i.e. ordinary) three-component sensors. In later sections, we assume realistic data processing for microtremor arrays with translational sensors to construct a theoretical model to evaluate the effects of approximating spatial differentiation via finite differencing (i.e. array-derived rotation, ADR) and the effects of incoherent noise on analysis results. Using this model, it is shown that in a short-wavelength range compared to the distance for finite differencing (e.g. $\lambda < 3h$, where $\lambda $ and $h$ are the wavelength and distance for finite differencing, respectively), the leakage of unwanted wave components can determine the analysis limit. It is also shown that in a long-wavelength range (e.g. $\lambda > 3h$), the signal intensity gradually decreases, and thus the effects of incoherent noise increase (i.e. the signal-to-noise ratio, SNR decreases) and determine the analysis limit. We derive the relation between the SNR and wavelength. Although the analysis results quantitatively depend on the array geometry used for finite differencing, the qualitative understanding supported by mathematical expressions with a physically clear meaning can serve as a guideline for the treatment of data obtained from ADR.

This study conducted microtremor testing along six survey lines that cross three typical earth fissures in the Datong basin to determine the dynamic response characteristics of earth fissure sites with regard to the Fourier amplitude spectrum, response spectrum, and Arias intensity. The results show the following. (1) The predominant frequency of an earth fissure site is mainly affected by the thickness and the shear wave velocity of the soil layer and is minimally effected by the presence of an earth fissure. (2) Earth fissures have a pronounced amplification effect on dynamic response. Fourier amplitude, response acceleration, and Arias intensity are high near an earth fissure and decrease with an increase in distance from the earth fissure, tending toward stability at a distance of 20 m. (3) The area that is seriously affected by this amplification is within 6–8 m of an earth fissure, and the general affected area is farther out than this, to a distance of 25 m. (4) New construction should be avoided in an area affected by the amplification, and existing buildings in general and seriously affected areas need to be reinforced to increase their seismic fortification intensity.

Padang is the capital of West Sumatra Province, close to three earthquake sources such as the Megathrust Zone, the Mentawai Fault, and the Great Sumatra Fault on the mainland. Due to the fact that the impact of the earthquake can create a tsunami event in the future, the government needs to prepare shelters for vertical evacuation. About 65 existing buildings have been selected as vertical evacuation buildings, but there is no clear information on their seismic performance. This research proposes a complete assessment of the existing RC building by considering soil characteristics such as the predominant period and Vs30 from microtremor observations. A selected 3 stories of a school building located in the earthquake red zone (Vs30 1.5s), less than 1 Km far from the shoreline, was considered in this paper. Based on the seismic index evaluation of the building, the X direction is smaller than the seismic demand (0.8) for the first and second floors (unsatisfactory). For the first, second and third floor, the Y direction has a larger seismic index than the seismic demand. Therefore, the performance is satisfactory for the first to the third story. Based on the required inspection, the building is unsatisfactory for the X-direction. Therefore, it needs to be strengthened. We propose a re-size of the RC for the building column to improve the ductility. The proposed size for the column is 50 x 60 cm. From the re-seismic evaluation, a satisfactory seismic index for the X and Y direction can be obtained.

Single-station microtremor measurements were conducted to investigate earthquake and soil behaviour for the first time in Nicosia, Cyprus. Cyprus is located in a tectonically complex area in the Eastern Mediterranean where three plates meet. The study area was chosen to cover the areas to be opened for new development. Nicosia, the capital of Cyprus, is also the island's most important cultural, industrial, commercial, and transportation centre. The study creates base maps for the soil to assess earthquake resistance crucial for construction. Microtremor Method was applied at 100 stations and the Multi-Channel Analysis of Surface Waves (MASW) method was used at 52 stations. Also, RefractionMicrotremor (Re-Mi) and L-Shaped Spatial Autocorrelation (L-SPAC) methods were carried out at 17 stations to substantiate the research. The results of the microtremor method indicate that the predominant soil period values have an average of 1 second and pre-dominant peak period values are generally found between 0.1 to 5 s at the study area. Peak amplitude values are observed between 1 and 2.4. The Vulnerability Index Parameter (Kg) exceeded 20 at the central and the southern stations, and Kg values change between 7 and 54 units. The Kg values were found to be higher than 20 in soils where shear wave velocity is lower than 760 m/s. At the same time, the values of the predominant peak period were greater than 1 second. Cyprus is located in the Alpine Himalayan earthquake zone. The Cyprus Arc is known as the main seismic source of the island, It constitutes the tectonic border among African and Eurasian lithospheric plates in the region. During an earthquake in Nicosia, seismic waves will be amplified by an average of 1.5 times and soil deformation will occur due to the exceeding elastic limits. The results provided important insight into soil behaviour and indicated its reactions in a potential earthquake., Mjerenja mikroseizmičkog nemira provedena su po prvi puta u Nikoziji na Cipru radi istraživanja ponašanja tla tijekom potresa. Cipar se nalazi u tektonski složenom području na istočnom Mediteranu gdje se susreću tri tektonske ploče. Istraživano područje odabrano je tako da uključi prostor planiran za novu gradnju. Nikozija je glavni grad Cipra, ujedno i najvažnije otočno kulturno, industrijsko, trgovačko i prometno središte. Za okrug Nikozija cilj je izračunati i objaviti osnovne karte tala da bi se procijenila potresna otpornost kako postojećih tako i novih zgrada. Mjerenja mikroseizmičkoga nemira obavljena su na 100 lokacija, a metoda višekanalne analize površinskih valova (MASW) na 52 lo-kacije. Također, na 17 lokacija provedene su metode refrakcijskog mikrotremora (Re-Mi) i L-Shaped Spatial Autocorrelation (L-SPAC) kako bi se povećala dubina istraživanja. Rezultati dobiveni analizom mikroseizmičkog nemira pokazuju da su prevladavajuće vrijednosti vlastitoga perioda tla oko jedne sekunde, a prevladavajuće vrijednosti perioda s najvećom amplifikacijom uglavnom su između 0.1 i 5 s. Vrijednosti vršne amplitude uglavnom su između 1 i 2,4. Parametar indeksa povredljivosti (Kg) prelazi 20 na središnjim i južnim lokacijama, a vrijednosti Kg općenito variraju između 7 i 54 jedinice. Vrijednosti brzine posmičnog vala u prvih 30 m dubine na mjestima gdje su vrijednosti indeksa Kgveće od 20, manje su od 760 m/s. Istodobno su predominantni periodi bili veći od 1 sekunde. Cipar se nalazi u alpskom himalajskom području potresa. Ciparski luk poznat je kao glavni seizmički izvor otoka. On čini tektonsku granicu između afričkih i euroazijskih litosferskih ploča u regiji. Tijekom potresa u Nikoziji, seizmički valovi pojačat će se u prosjeku 1,5 puta i doći će do deformacije tla zbog nadmašenih granica njegove elastičnosti. Rezultati su pružili važan uvid u ponašanje tla tijekom mogućih potresa.

This study aims to explain the potential of liquefaction in Padang Lekat Village and Pasar Ujung Village Kepahiang District, explaining the feasibility of developed learning packages, and explaining students' critical thinking skills after learning the wave material through the learning package "Strain Liquidity Learning". The type of study used was research and development which aims to develop digital-based physics learning packages that are integrated with disaster mitigation education on the basic competencies of waves in high school education units. This research was conducted using ADDIE development research procedures. The results of research on the analysis of liquefaction potential based on microtremor data using the Ground Shear Strain method, zoning indication of liquefaction potential due to geological conditions and seismic potential, generally Padang Lekat Village and Pasar Ujung Kepahiang Village are areas that have no potential to experience liquefaction. However, there are a number of locations indicated by potential liquefaction, although not significantly. Learning Package Book "Learning Liquid Strain" compiled based on the analysis of liquefaction potential based on expert validation is appropriate to be used as a learning medium for seismic and liquefaction waves. In its application with distance learning, the compiled learning package book has been able to improve critical thinking skills in students even though the N-gain improvement obtained is still in the low and medium categories.

We attempted a comprehensive site response study of Garhwal-Kumaun Himalaya in the Central seismic Gap (CSG) using the data collected from 97 strong motion, microtremor and broadband stations. Site...

The geotechnical industry has widely adopted the refraction microtremor shear-wave velocity measurement technique, which is accepted by building authorities for evaluation of seismic site class around the world. Clark County and the City of Henderson, Nevada, populated their Earthquake Parcel Map with over 10,000 site measurements for building code enforcement, made over a 3-year period. 2D refraction microtremor analysis now allows engineers to image lateral shear-wave velocity variations and do passive subsurface imaging. Along with experience at a basic level, the ability to identify the “no energy area” and the “minimum-velocity envelope” on the slowness-frequency (p-f) image helps practitioners to assess the quality of their ReMi data and analysis. Guides for grading (p-f) image quality, and for estimating depth sensitivity, velocity-depth tradeoffs, and depth and velocity resolution also assist practitioners in deciding whether their refraction microtremor data will meet their investigation objectives. Commercial refraction microtremor surveys use linear arrays, and a new criterion of 2.2% minimum microtremor energy in the array direction allows users to assess the likelihood of correct results. Unfortunately, any useful and popular measurement technique can be abused. Practitioners must follow correct data collection, analysis, interpretation, and measurement procedures, or the results cannot be labeled “refraction microtremor” or “ReMi” results. We present some of the common mistakes and provide solutions with the objective of establishing a “best practices” template for getting consistent, reliable models from refraction microtremor measurements.

The estimation of the impact of earthquakes on buildings and mega structures in large urban areas is of extremely importance. That is why it always gets attentions from construction planners and policy makers who are concerned about construction rules. When earthquake occurs, the vibration is transferred to sites. Although the vibration intensity is at first not too strong, the motion probably becomes stronger and lasts longer under special conditions of the local site. Two famous examples for these effects occurred in Mexico City in 1985 and in Taiwan in 1999. There are a number of approaches to this problem, such as evaluations based on seismic field observations, the microtremor method, the method using the weak motion data, the method using the strong motion data, the one-dimensional wave propagation method or the three dimensional wave propagation method with simulation etc. In this paper, we will give an overview and discuss about the advantages and the disadvantages of the methods that have been commonly applied in the world. We also present the application of these methods in studies carried out in Vietnam in general and in particular, in Hanoi city. We found that the studies for Hanoi city were mainly carried out in the western areas of Hanoi and a few positions in the urban districts. In addition, the authors only gave comments about and assessments of the shear wave velocity, and classified the ground type without a detailed map of local site effects for the entire area of Hanoi. In order to obtain a full site effects evaluation for Hanoi city, future studies should focus on the application of 1D analysis for the central area of Hanoi city and combining 1D analysis with 2D or 3D to give a better picture about the impact of local site effects. This hybrid approach is necessary in order to compare and verify the data obtained by the empirical and the analytical methods. On the other hand, many problems need to be addressed, for instance, the construction of a detailed 3D geological model for Hanoi, the calculation of the dominant periods and the amplification of the local soil conditions for the urban areas.

Underground space utilization is becoming increasingly essential for modern metropolitan cities such as Singapore. Mapping a soil/rock interface using traditional borehole investigation methods is expensive and difficult, owing to the numerous physical constraints within a built-up city. Boreholes are often far apart, resulting in many unforeseen ground conditions during subsequent excavation. Geophysical methods are sometimes employed as possible alternatives for fast, economical, and efficient bedrock surveys. The goal of this study is to investigate the practical details of applying microtremor array measurement (MAM) as a non-invasive surface wave survey for mapping soil/rock interfaces in Singapore. Critical configurations in field data acquisition are examined, and practical recommendations for array construction are provided. In addition, 30 in situ MAM tests are carried out for two major geological formations in Singapore. From the results, a standard shear wave velocity (Vs) of 500 m/s is found to be suitable for interpreting the soil/rock interface, for the Bukit Timah Granite and Jurong formations. However, the method does not predict well when soft Kallang formation deposits are present. Other limitations are also discussed in the later parts of this paper. Conclusions and practical recommendations are discussed, providing constructive guidance to the industry. The proposed Vs-based method and associated guidelines and limitations can be used to create a digital geological database and are especially useful for rock profiling in an urban environment.

Bu çalışmada, deprem nedeniyle hasar oluşma tehlikesi bulunan yapılar üzerinde oluşabilecek titreşim kaynaklı zararların belirlenebilmesi amacıyla mikrotremor ölçümleri alınarak değerlendirilmiştir. Bu kapsamda, hem karayolu hem de hafif raylı sistem trafiğinin yoğun olduğu İzmir İli, Bornova İlçesinde bulunan Bornova viyadüğü boyunca viyadük ayaklarında 13 farklı noktada ölçümler alınmıştır. Veriler, trafiğin yoğun olduğu gündüz saatlerinde ve sakin olduğu gece saatlerinde iki kez kaydedilmiştir. Alınan ölçümler değerlendirilerek, trafik kaynaklı titreşimlerin hem frekans spektrumu hem de H/V yöntemi ile gündüz ve gece ölçümleri arasındaki farklar incelenmiştir. Viyadükle aynı zemin özelliklerine sahip olan Ege Üniversitesi Merkez Yerleşkesi içinde çeşitli noktalarda alınan mikrotremor ölçümleri kullanılarak, zemin etkisi giderilmiş ve sadece yapının etkisi ortaya konmuştur. Ayrıca belirlenen baskın frekansların çevre binalar üzerindeki olası etkisi de belirlenmiştir. Trafiğin yoğun olması ve bölgede bulunan metro hattının aktif olması nedeniyle gündüz ölçümlerinden elde edilen frekansların, gece ölçümlerinden elde edilen frekanslara göre daha düşük olduğu tespit edilmiştir., In this study, microtremor measurements were performed and analysed in order to determine the vibration-induced damages that may occur on structures by carrying risk of damage due to earthquakes. In this context, 13 measurements were taken at different points of the viaduct feet along the Bornova viaduct located in Bornova district of Izmir province, where both dense highway and light rail system traffic is observable. Data were recorded twice during the daytime hours when the traffic was heavy and at night when it was calm. By evaluating the measurements taken, the differences between the frequency spectrum of traffic-induced vibrations and the H/V method between day and night measurements were examined. By using microtremor measurements taken at various points in the Central Campus of Ege University, which has the same ground characteristics as the viaduct, the ground effect was eliminated and only the effect of the structure was revealed. In addition, the possible effects of the dominant frequencies based on the surrounding buildings were also determined. It has been determined that the frequencies obtained from daytime measurements are lower than the frequencies obtained from nighttime measurements due to the heavy traffic and the active metro line in the region.

Microtremor Horizontal to Vertical spectral ratio technique, also known as the Nakamura’s method is growing in status for site response analysis. 500 locations in RAJUK area (1530 km2) have been selected for microtremor observations. Microtremor data have been compiled and studied to estimate the predominant resonance frequency and H/V peak amplitude following the SESAME (2004) guideline. Finally, seismic vulnerability index of site soil using Nakamura’s technique has been determined from predominant resonance frequency and H/V peak amplitude parameter. The calculated seismic vulnerability index for the studied 500 locations varies between 0.16 and 7.28. The low seismic vulnerability index (Kg) value means that the areas are relatively stiff and underlain by substantial deposit of sediments. The relatively higher Kg values are spread in the soft alluvial deposit areas. The areas with high Kg values are considered as fragile zones that may initiate significant damage to infrastructure situated in those areas during an earthquake.

Lombok Island is an active seismic area in Indonesia potentially hit by an earthquake due to located between two earthquake generators from the south and the North. Several large earthquakes rocked Lombok, an earthquake with a magnitude of 6.4 on July 29, 2018, and 7.0 on August 5, 2018. This study aims to determine the characteristics of the local site effect based on the dominant frequency value ( ), soil amplification ( ), sediment layer thickness (d), , dominant period (T 0 ), and seismic vulnerability index ( ) and to comprehend the soil class (site class) based on the thickness of the sediment layer (d), and in the North Lombok region. The data used is secondary data from microtremor signal recordings in North Lombok Regency in 2018. Data processing used Geopsy software, and microtremor data were analyzed using the HVSR method. From processing the HVSR data, the dominant frequency value about (0.8 - 18) Hz, amplification value (1.7 – 9.7), dominant period value (0.05 – 1.2) seconds, seismic vulnerability index value (0.4 – 71) , and the value of in the study area (20.05 – 287.04) m/s. Based on microtremor analysis, the local site effect indicates that alluvium rocks caused stronger earthquake vibrations and more damage. Whereas the Kalibabak and Lekopiko formations caused fewer earthquake vibrations and less wear. Based on the dominant period and , area study classify as Site Class IV class E and Site Class III class D Copyright © 2021 IPR . All rights reserved.

This research proposes a relationship between two methods such as a numerical approach by conducting a microtremor array observation and field survey by using the seismic cone penetration test unit (SCPTu). A database of shear-wave velocity (Vs) measurements was established using the microtremor array technique and seismic cone penetration test unit (SCPTu) on high-quality samples of rock and soft soil in Padang city, Indonesia. The study also demonstrates that the Vs values obtained from the different methods are consistent with the microtremor array technique. This technique may thus be deemed a valuable tool, as it can be used in engineering practice with confidence. Comparison of the Vs for different soils at the first layer between the microtremor array observation results and the SCPTu results exhibited the microtremor array method is unable to determine the Vs at the layer where its Vs changes dramatically, such as at the same layer as station UNP at 2 to 3.5m deep.

Lombok Island and its surrounding is an area that has a high seismicitys level because it is located in the Eastern Sunda Arc. Tectonically, Lombok Island located between the Indo-Australia plate collision zone with Eurasia in the south and the fult of the backarc Bali-Flores in the north. This research’s purposed to determine the distribution of vulnerability index and peak ground acceleration value are used to determine the GSS value, so mapping of potential damage areas could be done. The microtremor data taken on 32 observation points distributed in Lombok Island. Microtremor data is analysed using Horizontal to Vertical Spectral Ratio (HVSR) method to get seismic vulnerability index (Kg) and dominant period. Determination of Peak Ground Acceleration (PGA) value using data from the MASE Stasion measurement results based on earthquake events on August 5, 2018. Seismic vulnerability index and peak ground acceleration value are used to determine the GSS value. Determination of potential damage area using analysis of the dominant period, seismic vulnerability indexs and Ground Shear Strain values. The results of this research showed that seismic vulneribility index value in research area is about 0,029 sekon to 1,360 sekon, seismic vulneribility index value is about 0,56 to 189,92 and GSS value is about 2,52 x 10-5 to 8,46 x 10-3. The results show that the light damage dominated in East Lombok Districts, the moderate damage is on Mataram City and it dominated in West Lombok Districts. The heavy damage present in the most parts of West Lombok Districts.

Microtremor measurements are used for preliminary site effect of the Quaternary sediments of Varanasi in Indo-Gangatic plain, which is being planned as a Smart City of India. We evaluated site effects using single and arrays Microtremor measurements at various sites in the Varanasi City, Uttar Pradesh, India. At City, H/V spectral ratios using microtremor measurements indicate fundamental frequency range 0.37–0.63 Hz, corresponds amplification 5 to 14 times. This indicates that the deep thickness of the upper soft soil at about several hundreds of meters. Such huge amount of sediments deposition sources could be associated with fluvial rivers system in the area and sediment drain from Himalaya. The average peak frequency (~0.5) may reflect the Quaternary-Tertiary boundary. Microtremor array measurements at two sites were taken using circular arrays (30 and 60 m) which consists of three recording stations on the circumference of circle and one in the centre of circle. The Phase velocity dispersion of Rayleigh wave is calculated from array using SPAC method, and a 1-D shear wave velocity structure is determined by means of inversion processes. The top layers up to 50 m show shear velocities between 280 and 320 m/s and the velocities of underneath layer vary between 1500 and 1600 m/s till 100 m of depth. These results from the present study would be useful for future planning purposes as well as risk management and to reduce severity of earthquake effects in the study area.

Provinsi Nusa Tenggara Barat (NTB) merupakan daerah dengan aktivitas kegempaan yang tinggi. Fenomena ini disebabkan oleh adanya aktivitas tektonik sebagai akibat pertemuan Lempeng Eurasia-Australia (zona subduksi) di bagian selatan dan Sesar Flores di bagian utara serta adanya keberadaan sesar-sesar lokal. Terkait dengan rencana pengembangan kawasan Samota di Pulau Sumbawa, NTB, perlu dilakukan suatu kajian kegempaan. Tujuan penelitian ini adalah memetakan indeks kerentanan seismik (Kg) melalui pengukuran mikrotremor dengan analisis menggunakan metode Horizontal to Vertical Spectral Ratio (HVSR). Hasil penelitian berupa peta kerentanan seismik daerah Plampang yang menunjukkan bahwa sisi utara lokasi penelitian memiliki indeks kerentanan seismik rendah yang ditandai dengan nilai amplifikasi kurang dari tiga jika dibandingkan daerah lainnya. Geologi sisi utara lokasi penelitian tersusun oleh batuan gunung api dengan karakteristik batuan keras, ketebalan sedimen sangat tipis, dan tersusun atas batuan Tersier atau lebih tua. Peta kerentanan seismik berguna sebagai acuan dalam mitigasi gempa bumi untuk mengurangi risiko yang ditimbulkan. ABSTRACT Nusa Tenggara Barat (NTB) Province is an area with intense seismic activity. This phenomenon is caused by tectonic activity as the result of the convergency of the Eurasia-Australia Plates (subduction zone) in the south and the Flores Fault in the north as well as the presence of local faults. Regarding the plan to develop the Samota area in Sumbawa Island, NTB, a study concerning earthquakes should be done. The purpose of this study is to map the seismic vulnerability index (Kg) through microtremor measurement by using the Horizontal to Vertical Spectral Ratio (HVSR) analysis method. The result of the study is a seismic vulnerability map of the Plampang area which its northern part has a low seismic vulnerability index indicated by the amplification factor value of less than three compared to other areas. The geology of the northern part of the Plampang area consists of volcanic rocks which has hard rock characteristic, very thin sediment thickness, and composed of Tertiary or older rocks. Seismic vulnerability maps can be useful as a reference for earthquake mitigation to reduce its risks.

The measurement of site amplification of microtremors is an important tool for evaluating seismic hazard at local and regional level. The H/V spectral ratio (HVSR) method is applied to estimate the amplification of ground motion at resonance frequency. The fundamental resonance frequency is estimated at 8 different sites in study region and shows the maximum vulnerability of the site to the earthquakes. This frequency ranges between a minimum of 2.8 Hz to a maximum of 9.3 Hz. The thickness of the sediments below the surface of recording sites is calculated using the empirical relationship that comes out to be in a particular range of 9.5 m–33.1 m above the bed rock. The sedimentary thickness and the resonance frequency clearly matched with geological setting of the study area. The observation shows a slow reduction in the thickness of the sediments and increase in the resonance frequency from South-western part to North-eastern part of the study region. The results show that most of the sites are highly vulnerable to seismic risks with high amplification of seismic waves in the area. Thus, current study provides a deep insight in to the seismic hazard of the Sikkim region with a clear emphasis on the site amplification and the sedimentary cover for the region.

Landslides with a shallow and complex bedrock layer, where bedrock topography affects the stability of the slide, are a widespread phenomenon. The current methods for evaluating such landslides include conventional in situ methods and array-based geophysical methods. However, these methods are not capable of characterizing the complete spatial extent of the bedrock layer cost-effectively and are difficult to conduct for steep slopes. Therefore, in this study, microtremor horizontal to vertical spectral ratio (MHVSR) is proposed as an effective tool when used in conjunction with other methods to improve our understanding of the landslide. In this study, the method is used to make a tight grid of MHVSR measurements within the landslide. Using this method, a 3D image of bedrock topography can be created over a larger spatial extent to reveal the potential critical landslide zones. This method is employed for two active landslides that have recently experienced considerable movements. Using the MHVSR, several bowl-shaped features were detected in the bedrock layer, which were not detected using conventional invasive in situ methods. These features play a key role in landslide behavior as they can trap water and create a fully saturated soft zone within the critical slide. Missing such key features in the geologic model of the landslide can lead to errors in the slope stability models and cost overruns in rehabilitation efforts. The grid pattern MHVSR method used in this study offers a simple, rapid, and cost-effective tool for landslide site characterization for sites with shallow and complex bedrock topography.

Recently, the passive seismic techniques based on the microtremor measurements have emerged as an alternative to conventional seismic and geotechnical methods used in engineering seismology and earthquake engineering, especially in the local site effect investigations. These methods are basically based on the recording of seismic ambient noise and analysis of its spectral features. Although these techniques are more practical than traditional seismic methods, the commercial instruments designed for recording the seismic ambient noise are quite expensive. Furthermore, most of these instruments require an external computer for recording and monitoring the data. In this sense, this article intends to present a low-cost and Raspberry Pi single-board microcomputer aided seismic ambient noise recording and monitoring system (RaspMI) as an alternative to the computer aided commercial seismic noise measurement systems. RaspMI is an open-source hardware and software system that is controlled by a graphical user interface developed by using the MonoDevelop cross-platform and C# programming language. This system has many features such as 72 dB dynamic range, 100 Hz sampling frequency, timer recording mode, text and SAC data file format, and latitude, longitude, date and time support with GPS module. RaspMI has subjected to the various tests in terms of the reliability and sensitivity. The obtained results have shown that RaspMI can be used as an alternative instrument for seismic ambient noise measurements.