Horizontal-to-vertical Spectral Ratio Method Research Articles

The Soft Layer Thickness Estimation using Microtremor Measurement to Identify Landside Potential in Watukumpul, Central Java, Indonesia.

Watukumpul is an area that is prone to landslides, so determining the soft layer thickness is very important to identify the landslide potential. The soft layer thickness can be estimated using microtremor signal measurements which analyzed using the Horizontal to Vertical Spectral Ratio (HVSR). In this study,we measured microtremor signal of 33location around Watukumpul, Pemalang, Central Java area to determine soft layer thickness. Micretremor signal was analyzed based on theHVSR method using Geopsy software and follow the standard of the Sesame Europan Project. The results of the HVSR method are the HVSR curve that fulfills the reliable curve standard. HVSR curve shows that the dominant frequency of soft layer ranges from 1.36 – 7.62 Hz and the amplification values ranges from 9.00 – 41.45. The soft layer thickness value in the study area ranges from 17.58 - 103.60 meters. The high landslide potential area are located at W7, W8, W18, W30 and W32 where has thin soft layer and high soil slope.

Seasonal variations in amplitudes and resonance frequencies of the HVSR amplification peaks linked to groundwater

SUMMARYFollowing the installation of a temporary seismological network in western Greece north of the Gulf of Patras, we determined the quality of the sites of each of the 10 stations in the network. For this, we used the horizontal-to-vertical spectral ratio (HVSR) method and calculated an average curve over randomly selected days between 0 and 10 Hz. The daily HVSR curve is determined by the HVSR 12-hr calculation (1 hr every two) without distinction between seismic ambient noise and earthquake signal. The HVSR curves obtained can be classified in three categories: flat curves without amplification, curves with a amplification peaks covering a large frequency range, and curves with one or more narrow peaks. In this third category C3, one station has one peak, two have two and one has three. On the contrary of what it is commonly assumed, the amplitudes and the resonance frequencies of these narrow peaks are not stable over time in C3. We determined the maximum of the amplitude of each peak with the corresponding central frequency for each day during 2.5 yr. Except for the station with three peaks, which finally appears stable within the uncertainties, the principal peak exhibits a seasonal variation, with a maximum in winter and a minimum in summer, the observations being more dispersed during winter. The second peak, when it exists, varies in the same way except at one station where it varies oppositely. These variations are clearly correlated with the loading and unloading cycle of the underlying aquifers as shown by the comparison with water level and yield measurements from wells located close to the stations. Moreover, they are also correlated with the vertical surface displacements observed at continuously recording GPS stations. The dispersion of the observed maximum amplitude in winter is probably related to the rainfall and the soil moisture modifying the S-wave velocity as revealed by other studies. From this study, we would like to emphasize that the use the HVSR method to constrain the S-wave velocity and the thickness of the sediment layer over the bedrock in the basin, has to be done with caution. Upon further confirmation of its robustness, the HVSR methodology presented here could be a good and easy-to-use tool for a qualitative survey of the aquifer backdrop and its seasonal behaviour, and of the soil moisture conditions.

Ambient noise and earthquake HVSR modelling for site characterization in southern mainland, Gujarat

This study provides the assessment of site characterization and possible shallow shear-velocity structure from the study of the horizontal to vertical spectral ratio (HVSR) measurements using the ambient noise or microtremor (herein called classical HVSR), extracted Rayleigh wave from the ambient noise data (herein called standard HVSR) and earthquake (herein called earthquake HVSR) data at five stations in the Surat district of mainland Gujarat, India. These locations are the hub of many mining and industrial projects like oil and natural gas, which need to function safely within the seismic hazard and ground shaking limits. From the classical and standard HVSR datasets, estimates of the predominant resonant frequency of the soil are obtained, observed to be well matched, from which first order inversions are carried out around the predominant frequency to provide a fair estimate of thickness of the regimented layer over a hard seismic substratum up to a depth of 100 m. In the standard HVSR datasets, the Rayleigh wave ellipticity curves are extracted with time–frequency analysis using continuous wavelet transforms. This is followed by the Rayleigh wave ellipticity inversion approach to derive a first order approximate sedimentary shear velocity structure. We also compute HVSR measurements using earthquakes. The noise and earthquake HVSR curves are well-matched in terms of the predominant frequencies and range from 3.8 to 16.7 Hz and 3.2 to 16.5, respectively. The estimated VS30 values (the average shear wave velocity (VS) for the top 30 m of the soil) vary from 520 to 1350 m/s, matching well with some of the geotechnical studies conducted here. The study emphasizes the effectiveness of the single station HVSR method in determination of hitherto unknown soil structures as economical and non-invasive exploration viability and proving quite useful for critical centres of industrial establishments.

Microtremor HVSR analysis of heterogeneous shallow sedimentary structures at Pohang, South Korea

AbstractWe apply the single-station microtremor horizontal-to-vertical spectral ratio (HVSR) method to image the geometry of Pohang Basin, South Korea, which experienced the greatest earthquake damage in Korea during a series of anthropogenic earthquakes between November 2017 and February 2018. We collected and analysed the ambient seismic noise at 124 temporary stations. The resonance frequencies, which vary significantly across the area (0.35–19.86 Hz), were inverted to constrain the depth of the major impedance contrast, which is interpreted to be the sediment–bedrock interface beneath each station. The sedimentary layer thickness is generally thin in the north and thickens to the southern and central parts of the basin, where the depth to bedrock is up to 340 m. We compare the HVSR results with six borehole observations in the area, whose depth to bedrock ranges from 189 to 359 m. The sediment thicknesses obtained via the direct borehole measurements and HVSR method are comparable with each other. The resultant three-dimensional shape of the sedimentary basin provides crucial information for the microzonation of the Pohang area for seismic risk mitigation. It also provides a realistic initial velocity model for three-dimensional tomographic inversions to elucidate the detailed subsurface structure of the region.

HVSR passive seismic stratigraphy for the investigation of planetary volcanic analogues

This paper presents new results of the application of passive seismic surveys for the stratigraphic investigation of planetary volcanic analogues. We tested HVSR (Horizontal-to-Vertical Spectral Ratio) surveys that seem particularly suitable for planetary subsurface exploration. In order to exploit the potential of these surveys in stratigraphic applications, HVSR surveys were undertaken at the Tinguatón volcanic region (Lanzarote, Canary Islands). Seismic noise measurements were collected during the PANGAEA-X 2018 testing campaign which formed part of the European Space Agency's (ESA) astronaut training program. Single-station, free-field seismic noise data were collected along two orthogonal profiles, one crossing the Tinguatón volcano, the other passing alongside the Tinguatón caldera. Seismic stratigraphic sections obtained from the shear wave velocity constrained inversion of the main H/V peaks provided the main impedance contrasts between layers and a bulk estimate of the shear wave velocity in the layers. Contour maps of the HVSR patterns were used to recognize and identify the main volcanic units, such as scoria deposits and different basaltic lava flows, geological structures, such as a regional fault related to the volcanic vent source, and morphological characteristics, such as the Tinguatón caldera. This study also identified several pitfalls that may limit the accuracy of such investigations. These include the multilayer setting of scoria deposits and, partly, of underlying basalts, as well as the presence of very thin horizons or a very gradual increase in shear wave velocity. Our study also shows the topographic effect due to the volcano's sharp topography along crater rim is significant and results in severe artifacts in the data. From our work, it is clear that HVSR method is an effective method to support the investigation of planetary volcanic terrains on the Moon and Mars with similarly volcanic complex geological settings, even where horizontal layering and the isotropic site response are not fully verified.

The effect site analysis based on microtremor data using the Horizontal to Vertical Spectral Ratio (HVSR) method in the Bandar Lampung City

Bandar Lampung is the capital of Lampung Province which is crossed by faults, one of the faults that crosses Bandar Lampung namely the Panjang Fault or commonly called the Tarahan Fault, it is making the Bandar Lampung to be a potential earthquake area. Over the past 20 years many large earthquakes have rocked Indonesia, especially in the western part of Indonesia, such as Aceh, Nias, Padang, Bengkulu, Tasikmalaya, and Ciamis. Lampung Province is located near the subduction boundary of the Indo-Australian Plate against the Eurasian Plate, and also there is another fault, the Semangko Fault. Therefore, Lampung Province and especially Bandar Lampung have greater potential to the earthquake effect. The potential of this earthquake needs to be carried out by disaster mitigation activities to minimize the consequences that occur due to earthquakes, namely by classifying soil vulnerability by characterizing site effects. This study aims to determine the site effect based on dominant frequency parameters. The study was used 135 microtremor measurement points by using the Ref-Tek 130-SMHR strong motion accelerograph type (3 components). Microtremor data was analyzed using the Horizontal to Vertical Spectral Ratio (HVSR) method in Geopsy software. Based on the HVSR method, the Bandar Lampung City is dominated by soft soil types with a dominant frequency of f0 <1.33 Hz. It’s shows that Bandar Lampung City has a high vulnerability to earthquakes. Moreover, based on map analysis of the dominant frequency, the areas that have the highest risk are Kecamatan Panjang, Bumiwaras, Telukbetung Utara, Teluk Betung Selatan, Telukbetung Timur, Tanjungkarang Pusat, Tanjungkarang Barat, Rajabasa, Enggal, Langkapura, Kedamaian, Wayhalim, and Kedaton.

PENGOLAHAN DATA MIKROTREMOR BERDASARKAN METODE HVSR DENGAN MENGGUNAKAN MATLAB

The research has conducted to get the result of Matlab program for microtremor data processing. The purpose of this research is to apply Matlab software into microtremor data processing. The microtremor is the ground motion to identify earthquake vulnerability by using HVSR (Horizontal to Vertical Spectral Ratio) method. The HVSR method for comparing both of horizontal component and vertical component on microtremor wave to obtain the result dominant frequency(f0) based on the high spectrum H/V value from the analysis of HVSR curve. Based on this research which concludes that microtremor data processing has processed using Matlab software. The result of this data processing gives similar value from the geopsy software. The value of dominant frequency by Matlab software and geopsy software calculation are classified on the site class type II which is dominantly alluvium. Whereas, the result of dominant period by geopsy and Matlab are classified on the site class type I which shows as the bedrock.

ANALISIS TINGKAT RESIKO DAMPAK GEMPABUMI DI KABUPATEN CILACAP MENGGUNAKAN METODE DSHA DAN DATA MIKROTREMOR

Soil mechanical research has been done in Cilacap Regency using DSHA method and microtremor data. This study aims to analyze the local land response to earthquakes based on the dominant frequency parameters (f0), amplification factor (A0), wave velocity VS30 and seismic hazard analysis through deterministic approach. This research uses 193 microtremor measurement points using a short period TDS-303 type (3 component) seismometer. Microtremor data were analyzed using the Horizontal to Vertical Spectral Ratio (HVSR) method in geopsy software. DSHA analysis refers to the source of the Lembang Fault earthquake and Java Subduction zone for deterministic calculations. Based on the analysis of HVSR method, Cilacap Regency is located on land type 1 (frequency 0-1.33 Hz) and soil type 2 (frequency 1,33-5 Hz) according to Kanai Classification (1983), dominated amplification value 1,104 to 8,171 times, then Dominated by soil class E (VS30 value 183 m / s) and soil class D (183 m / s VS30 366 m / s) according to NEHRP Classification (2000). This indicates that Cilacap Regency has high vulnerability to earthquake disaster. Based on the estimated value of PGA calculation method of DSHA, from the calculation of earthquake source Subduction obtained Java PGA bedrock 0,045 g - 0,0671 g and PGA surface rock 0,1926 g - 0,4855 g and calculation of Lembang Fault obtained PGA bedrock 0, 09 g - 0.025 g and PGA surface rocks 0.017 g - 0.089 g. Based on risk map analysis (combination of dominant frequency analysis, amplification, susceptibility factor and ability factor), the highest risk areas are Kec. Adipala, Kasugihan, Binangun, Nusawungun, Cil. Middle, Cil. South, Cil. North, allegedly the soil layer constituent area is a layer of thick and soft sediments. While the low risk of Kec. Majenang and Dayeuh Luhur.

Ambient noise analysis for characterizing sub-surface dynamic parameters

Ambient noise analysis of horizontal to vertical spectral ratio (HVSR) method has been used widely to provide reliable estimates of the site fundamental frequency and to constrain the inversion of near-surface shear wave velocity. The present paper focuses on the site measurement using the aforementioned analysis by means of the HVSR method for characterizing sub-surface dynamic parameters in the City of Banda Aceh, Indonesia. A Guralp CMG-6TD broadband seismometer was used in this study to cover a wide frequency range from 0.033 Hz to 50 Hz in standard operation. The instrument was deployed at two different sites (i.e. Location#1 of Blang Padang and Location#2 of Stadion Dirmutala) in the City of Banda Aceh for at least 2 hours for ambient noise recording. This continuous of 2 hours’ microtremor time series was separated into 30 minutes record from which the site fundamental frequency and shear wave velocity of the measured site were deduced. The later sub-surface dynamic parameter was validated using another technique of reflection seismic. This investigation suggests the fundamental frequency of 0.45 Hz at Location#1 and of 0.65 Hz at Location#2. The estimated shear wave velocity of the top 30 m, Vs,30 of this investigation is 165 m/s at Location#1 and 156 m/s at Location#2. Both the site fundamental frequency and shear wave velocity are important for infrastructure design in the high seismic region of Banda Aceh, Indonesia.

Shallow Structure of the Longmen Shan Fault Zone from a High-Density, Short-Period Seismic Array

ABSTRACTThe Longmen Shan fault zone that was shocked by the 12 May 2008 M 8.0 Wenchuan earthquake acts as the boundary between the western edge of the Sichuan basin and the steep eastern margin of the Songpan-Ganze block. In this study, continuous seismic data recorded by 176 temporary short-period seismic stations between 22 October and 20 November 2017 are used to study the shallow crustal structure of the Longmen Shan fault zone by applying ambient-noise tomography and horizontal-to-vertical spectral ratio (HVSR) analysis. From ambient-noise analysis, fundamental-mode Rayleigh-wave dispersion curves between 0.25 and 1 Hz are extracted. Then, the direct surface-wave tomographic method is used to invert surface-wave dispersion data for the 3D shallow shear-wave velocity structure. Our results show that low shear-wave velocities are mainly distributed around the surface rupture trace of the Wenchuan earthquake at least down to 2 km. From the HVSR method, the sites are sorted into two types according to the pattern of HVSR curves with single peak or double peak. By converting frequency to depth, the results show that the sediments are thicker near the surface rupture. The low-velocity zone based on ambient-noise tomography agrees well with the distribution of sedimentary cover estimated from HVSR, which are generally consistent with geological information. Our results provide high-resolution shallow crustal velocity structure for future detailed studies of the Longmen Shan fault.

Passive seismic horizontal to vertical spectral ratio (HVSR) surveying to help define bedrock depth, structure and layering in shallow coal basins

SummaryTrial passive seismic HVSR survey lines were carried out in the north-western part of the Wilga sedimentary basin in Western Australia, which is a small and shallow isolated sub-basin to the Perth Basin, sitting above rifted Archaean granite-gneiss basement rocks. The HVSR survey method was trialled to determine if it could resolve subsurface basin features quickly and cheaply. This trial HVSR survey was carried out as a series of transects along open walking tracks. It was very successful for mapping the general basin architecture by resolving bedrock depth to a maximum depth of close to 200 m along the survey transects, and defining a half-graben structure that forms the faulted eastern boundary of the basin, with the basin depth gently deepening toward the west. The HVSR data are also interpreted to have detected subtle layering within the basin sedimentary sequence to possibly map Permian black shale beds, coal measures and splits sitting below an unconformity of Cretaceous sedimentary cover. The passive seismic HVSR method has potential to be a robust survey method for defining basin architecture in shallow coal basins with poorly indurated basin fill deposits, especially in remote parts of the world with difficult access and limited exploration funds to carry out active seismic surveys.

Analysis of Influencing Factors and Numerical Simulation of Horizontal-to-Vertical Spectral Ratio Method

To improve the calculation accuracy of the horizontal-to-vertical spectral ratio (HVSR) method, this study theoretically analyzed the influencing factors of Rayleigh wave polarizability. The phase difference of the horizontal component and the phase difference of the vertical component are found to play a key role in calculating the polarizability. The influence mechanism of the superposition of body waves and different Rayleigh waves on the polarizability of the Rayleigh wave is derived. The effects of the body wave, amplitude, frequency and Rayleigh wave superposition of different sources on the polarizability are verified by numerical simulation. The results show that the body wave significantly interferes with the polarizability of the Rayleigh wave. When a signal contains more than one set of Rayleigh waves, the superposition of the same-source Rayleigh waves does not affect the ratio. However, the superposition of Rayleigh waves from different sources significantly interferes with the calculation of the polarizability. This provides a technical method and a theoretical basis for accurately extracting the Rayleigh wave polarizability dispersion curve from a seismic record signal. This would help improve the detection accuracy of the HVSR method for ground pulse signals.

IDENTIFIKASI KELAYAKAN JEMBATAN BATANGHARI II KOTA JAMBI MENGGUNAKAN MIKROTREMOR DENGAN METODE HORIZONTAL TO VERTICAL SPECTRAL RATIO (HVSR)

The feasibility study of Batanghari II Bridge with the value of natural frequency of Bridge using microtremor has been done. The purpose of this research is to know the bridge's natural frequency value using Horizontal to Vertical Spectral Ratio (HVSR) method and to know the relative damage to Bridge. In this study Bridge as an object because, Bridge is an alternative way that connects one place with another place separated by a river or ditch which is often used by society for activity. To get the bridge's natural frequency value using Microtremor sensor which is directly placed bridged with geopsy software to process its data and using HVSR method. The result of this research is the natural bridge frequency value of 7.40441 Hz. To determine the feasibility of the bridge compared with the standard value of the bridge frequency of 7,675 Hz and stated the state of the Batanghari II bridge is still intact from the structural and the natural frequency value of the soil on the bridge buffer of 12.7489 Hz and 13.6343 Hz that the soil type is older soil. Can be said the foundation of the bridge last long.

Determining Soft Layer Thickness Using Ambient Seismic Noise Record Analysis in Kota Baru, South Lampung

The local site effect of an earthquake can be calculated through an analysis of short period ambient noise, known as microtremors. The fundamental frequency and amplification factors can be identified by analyzing microtremors using the Horizontal to Vertical Spectral Ratio ( HVSR) method. This information can then be used to determine the thickness of the soft layers of sediment. This study analyzed microtremor recordings made in Kota Baru, South Lampung. The amplification factor range according to the HVSR method was 2.3 to 6.17, and the fundamental frequency range was 0.56 Hz to 1.46 Hz. Some spectrums exhibit two peaks with f 0 > f 1 . We suggest that these locations have two layers with significant impedance contrast, which aligns with the geological conditions. The center of the Kota Baru area, especially the region around T11 and T15, has a thicker soft layer than the outskirts; in the central area, the soft layer is approximately 85 to 102 meters thick. The western part of the analyzed area has a shallower soft layer of about 32 to 46 meters. The analysis indicates that the western part has less amplification because it is shallower than the other parts of the analyzed region.

Seismic Site Effect along Bukit Tinggi Fault Line from Microtremor Analysis

In the shallow subsurface analysis, the potential hazard is identified and evaluated through the site investigation studies which can be determined either by conducting standard penetration test, cone penetration test, and multichannel analysis of surface wave (MASW). While the three methods stated are widely established and highly reliable, the result produced is sometimes unconvincing and lack of details. In this study, the horizontal to vertical spectral ratio (HVSR) analysis method is proposed instead of the more established methods. HVSR is a technique that based on the spectral analyses of recorded ambient noise in order to estimate the site effect parameters such as fundamental frequency and the amplification factor of local soil. The HVSR method was implemented in Bukit Tinggi, Pahang, Malaysia, which known to experience several small earthquakes between 2007 to 2009. Since the earthquake in central Peninsular Malaysia is uncommon, the tremor has caused panic and requires a thorough investigation of the soil effect in the region. The work conducted is motivated by this after effects with focus on the potential fault line investigation using the spectral ratio method (HVSR). The ambient noise signal measurements were performed at 20 sites along the probable fault line in order to calculate the HVSR. Receiver array arrangement and dimensions are chosen based on the prior information about the earthquake location as experienced by the local resident. At the end of the work, the amplification spectra for the soil column is evaluated at each site location, and the nominal frequency obtained, and maximum amplitudes are contoured showing the corresponding value trends in the region.

Inversion of shallow subsurface structure from Rayleigh ellipticity beneath a station in Tangerang, Indonesia

Horizontal to vertical spectral ratio (HVSR) method has been widely used for estimating site effects and soil properties beneath a station. Recent studies have shown that it is possible to extract Rayleigh wave ellipticity from the record of seismic noise or vibration. In this study, we applied HVSR method to obtain frequency resonance and site amplification beneath a seismic station in Tangerang, Indonesia. We applied time frequency analysis (HVTFA) using a continuous wavelet transform to extract Rayleigh ellipticity. We carried out inversion from the computed Rayleigh ellipticity to estimate shallow subsurface structure. We applied non linear inversion using two layers as initial model to obtain the best fit subsurface structure. We obtained that the layer boundary between two layer model is found at depth of about 100 m.

Efficiency of ambient vibration HVSR investigations in soil engineering studies: backfill study in the Algiers (Algeria) harbor container terminal

This paper deals with the contribution of the ambient vibration horizontal-to-vertical spectral ratio (HVSR) method in soil engineering studies, particularly in backfill compactness assessment. The study is based on 60 ambient vibration recordings performed in 2015 at the container terminal of Algiers harbor, subjected a year before to a geotechnical study based on 23 boreholes and 13 cone penetration tests (CPT) for backfill improvement. To highlight the contribution of the HVSR method, the results of the geotechnical and HVSR studies are first analyzed separately and then in combination. The HVSR method provides a compactness zonation map based on peak amplitude variation. Both methods define the same pattern: a southern section where the backfill is more compact, and a northern section where the backfill is less compact. This shows that the HVSR peak amplitudes are sensitive to compactness variations, which may be sufficient for qualitative zonation. In addition, with the combination of the two methods, rough estimations of shear-wave velocity and thickness of the backfill can be retrieved. This study shows that the HVSR method can be a very useful investigative tool in soil engineering studies. When the HVSR method is deployed before any conventional technique, a geotechnical investigation campaign can be significantly optimized. Moreover the combined interpretation brings complementary quantitative soil information.

Shallow structure of the Tangshan fault zone unveiled by dense seismic array and horizontal-to-vertical spectral ratio method

The Tangshan fault zone has been considered to be a potential seismogenic fault from the devastating 1976 Ms 7.8 Tangshan earthquake. Based on the dense seismic array with interstation distance of ∼1 km and length of ∼40 km, HVSR (horizontal-to-vertical spectral ratio) curves at 37 stations are obtained with the micro-tremor seismic waveforms, and the two-dimensional Quaternary sedimentary structures cross the Tangshan fault zone are imaged by frequency-to-depth conversion. Results suggest that two significant seismic impedance interfaces at ∼100 m and 300–800 m depth are clearly revealed, respectively. The interface at ∼100 m depth can be attributed to the strong contrasts between the unconsolidated sand-clay and semi-consolidated silt, which suggests very small variations and is well consistent with the seismic reflection interface from shallow seismic reflection exploration. While the deeper interface at 300–800 m depth can be attributed to the Quaternary sedimentary basement, which increases from 300 to 800 m from the west to the east, and is also consistent with the results in previous studies. Rapid variations (∼200 m) of the Quaternary sedimentary basement depth just beneath the fault zone well agrees with spatial characteristics of the fault revealed by deep seismic reflection profiling. Our work suggests that the Tangshan fault zone has been significantly ruptured and modified by strong earthquake activities since Quaternary. This study also suggests that the HVSR method with dense seismic array is an efficient, effective, non-invasive and low-cost method for investigating active faults in shallow sediments. It is useful for probing the active faults buried by thick sediments in the densely populated urban settings where seismic investigation with explosive sources are too hazardous to carry out.

Influence of Traffic Vehicles Against Ground Fundamental Frequency Prediction using Ambient Vibration Technique

Ambient vibration (AV) technique is widely used nowadays for ground fundamental frequency prediction. This technique is easy, quick, non-destructive, less operator required and reliable result. The input motions of ambient vibration are originally collected from surrounding natural and artificial excitations. But, careful data acquisition controlled must be implemented to reduce the intrusion of short period noise that could imply the quality of frequency prediction of an investigated site. In this study, investigation on the primary noise intrusion under peak (morning, afternoon and evening) and off peak (early morning) traffic flows (only 8 meter from sensor to road shoulder) against the stability and quality of ground fundamental frequency prediction were carried out. None of specific standard is available for AV data acquisition and processing. Thus, some field and processing parameters recommended by previous studies and guideline were considered. Two units of 1 Hz tri-axial seismometer sensor were closely positioned in front of the main entrance Universiti Tun Hussein Onn Malaysia. 15 minutes of recording length were taken during peak and off peak periods of traffic flows. All passing vehicles were counted and grouped into four classes. Three components of ambient vibration time series recorded in the North-South: NS, East-West: EW and vertical: UD directions were automatically computed into Horizontal to Vertical Spectral Ratio (HVSR), by using open source software of GEOPSY for fundamental ground frequency, Fo determination. Single sharp peak pattern of HVSR curves have been obtained at peak frequencies between 1.33 to 1.38 Hz which classified under soft to dense soil classification. Even identical HVSR curves pattern with close frequencies prediction were obtained under both periods of AV measurement, however the total numbers of stable and quality windows selected for HVSR computation were significantly different but both have satisfied the requirement given by SESAME (2004) guideline. Besides, the second peak frequencies from the early morning HVSR curve was clearly indicated between 8.23 to 8.55 Hz at very low amplitude (Ao < 2), but it should be neglected according to the similar guideline criteria. In conclusion, the ground fundamental frequency using HVSR method was successfully determined by 1 Hz seismometer instrument with recommended to specific parameters consideration on field as well as data processing, without disruption from the nearest traffic excitations.

Application of Microtremor Horizontal-to-Vertical Spectral Ratio (MHVSR) Analysis for Site Characterization: State of the Art

Nakamura (Q Rep Railway Tech Res Inst 30:25–33, 1989) popularized the application of the horizontal-to-vertical spectral ratio (HVSR) analysis of microtremor (seismic noise or ambient vibration) recordings to estimate the predominant frequency and amplification factor of earthquake shaking. During the following quarter century, popularity in the microtremor HVSR (MHVSR) method grew; studies have verified the stability of a site’s MHVSR response over time and validated the MHVSR response with that of earthquake HVSR response. Today, MHVSR analysis is a popular reconnaissance tool used worldwide for seismic microzonation and earthquake site characterization in numerous regions, specifically, in the mapping of site period or fundamental frequency and inverted for shear-wave velocity depth profiles, respectively. However, the ubiquity of MHVSR analysis is predominantly a consequence of its ease in application rather than our full understanding of its theory. We present the state of the art in MHVSR analyses in terms of the development of its theoretical basis, current state of practice, and we comment on its future for applications in earthquake site characterization.