Horizontal To Vertical Spectral Ratio Research Articles

Seismic microzonation based on microseismic data and damage distribution of 2006 Yogyakarta Earthquake

The 2006 Yogyakarta earthquake caused an extensive damage to various areas of Yogyakarta regions. The damage distribution indicates the role of local site effects during the earthquake as the damage extended from Bantul Regency in Yogyakarta Province to Klaten Regency in Central Java. Microzonation based on the damage distribution is then carried out using Horizontal-to-Vertical Spectral Ratio (HVSR) technique. From this technique, amplification factor and predominant frequency can be obtained and then spatially mapped. Inversion can also be conducted to the HVSR curves to infer the geological condition of the study area.

Ground motion amplification atop the complex sedimentary basin of Haifa Bay (Israel)

The Zevulun Valley (ZV) is a sedimentary basin underlying the heavily populated and industrialized petrochemical hub of Haifa Bay, Israel. With active tectonic faults at close range and a mixture of large population and vulnerable facilities, the seismic risk in the ZV is high. However, until now the national seismic network in Israel only included rock stations with no measurements supporting the expected difference between the ZV and its surroundings. Moreover, a detailed analysis of ground motions atop sedimentary basins using earthquakes data was never conducted in Israel for any basin. In this paper, we present a dataset collected during a 16 months monitoring campaign with a transportable network deployed in the ZV. For the first time in Israel we simultaneously recorded earthquake (3.1 < Mw < 5.5) ground motions at basin- and reference-sites. Spectral ratios reveal amplification factors tangibly higher than those previously reported by horizontal-to-vertical-spectral-ratio (HVSR) techniques and 2-D modeling. In particular, the deeper parts of the valley exhibit ground motion amplification up to a factor of 8 at frequencies lower than 1 Hz. Comparison of the measured spectral ratios with the results of 1-D linear-elastic analysis shows partial correlation reflecting the complexity of the sub-surface structure.

Application of Passive Seismic in Determining Overburden Thickness: North West Zambia

There are several ways to estimate overburden cover thickness. One of the non-invasive and inexpensive ways to rapidly estimate the cover thickness is the Horizontal-to-Vertical Spectral Ratio (HVSR) of the ambient seismic noise method. This approach utilises a broadband three-component sensitive seismometer to record ambient noise (or microtremor) induced by the wind, ocean waves and several anthropogenic activities. These microtremors are mainly composed of Rayleigh Waves which propagate in the surface layer. The Tromino® seismometer, which works on the HVSR principle, is a very light and portable instrument that records seismic noise in the frequency range of 0.1 to 1024 Hz, and is capable of estimating overburden cover up to 100’s of metres depth, depending on the ambient noise strength and geological setting of the survey area. The ratio of the horizontal-to-vertical (H/V) component of the shear wave (Vs) spectrum is used to calculate the peak resonance frequency at a particular survey station, which is used to estimate the overburden thickness by using one or more existing drill holes in the area, 1D modelling, or local geological knowledge about the overburden to get velocity information for calculating depth. This paper discusses different methods used to calculate the overburden thickness, which includes calculations using a hybrid approach and a regression equation. This paper shows the results of a Tromino® HVSR survey in North West Zambia and comparison of estimated overburden thickness using different methods. The results were further compared with those determined from Audio-MagnetoTellurics (AMT) and drilling data. Tromino® successfully estimated the overburden thickness and mapped the bedrock topography with reasonable accuracy.

Application of the passive seismic Horizontal-to-Vertical Spectral Ratio (HVSR) technique for embankment integrity monitoring

Embankments are common features in mine sites necessary for tailings storage, surface water management or general infrastructure such as dewatering ponds. Differing construction methodologies, from loosely placed waste material to engineered embankments with individually compacted lifts, will achieve varying density, strength and permeability. Conventional construction quality assurance is however not always possible without causing significant interruptions to the construction program. Estimating levees’ bulk shear wave velocities via passive seismic HVSR surveying as a proxy for stiffness is a practical, continuous and non-invasive method that can be carried out with limited construction interruption over all types of structures. This also provides a continuous dataset throughout the embankment as opposed to discrete observations using conventional geotechnical methods. Field data acquired over the length of several embankment types demonstrate the very good correlation between estimated shear wave velocities and the levees’ degree of compaction. As a result, alternative construction methodologies can be quantitatively benchmarked against a bulk density spectrum with fully engineered embankments and loose waste dumps as end-members. Collection of repeated measurements over time also discriminates stable embankments from altering ones, and constitutes a cost-effective way to identify possible zones of weakness before hazardous failure.

Determination of seismic site classification of seismic recording stations in the Himalayan region using HVSR method

An attempt has been made to classify seismic stations installed along the Himalayan belt and in adjoining regions using recorded strong-motion data and different empirical methods. For all recorded data, HVSRs (horizontal-to-vertical spectral ratios) were computed using pseudo-response spectral acceleration (PSA) values. Five empirical techniques based on HVSRs and PSA were used to classify the stations. The first and second methods are based on the predominant period of the site and relationship between VS30 and parameters of HVSR. The third and fourth methods compute the correlation between the HVSR curve of a station and standard HVSR curves. Fifth used the PSA and PGA (peak ground acceleration) to identify the site as rock and soil. Conclusively, the site class which had the highest frequency of occurrence amongst the five methods was determined to be the final class for a given station. The final site class recommended is matched with the existing available site classification and also with available field test results.

Horizontal-to-vertical spectral ratio of S-waves and SH-wave transfer functions at the vertical seismic and strong-motion arrays in the Central United States

Spectral analyses were performed on S-waves of earthquake recordings from two vertical seismic and strong-motion arrays in the central United States to obtain horizontal-to-vertical spectral ratios (HVSR) and transfer functions. Spectral analyses were also performed on ambient noises to obtain HVSRs at both sites. Theoretical SH-wave transfer functions were obtained using Thomson-Haskell propagation matrices and soil profiles at both sites. The results demonstrate that the S-wave HVSR is similar to the observed and theoretical SH-wave transfer functions in terms of peak frequencies up to the fifth mode. In other words, the S-wave HVSR could be used as an empirical SH-wave transfer function and provide in situ constraints on the shear-wave velocity structure of soils at these sites. The results also demonstrate that the ambient-noise HVSR is different from the S-wave HVSR and SH-wave transfer functions of the soils. Thus, the ambient-noise HVSR is not applicable for characterizing earthquake ground-motion site-effect, as well as determining the shear-wave velocity structure.

The relationship between normalised horizontal-to-vertical spectral ratios (HVSRs) of microtremors and the F distribution

The Albarello test is a statistical test proposed in 2001 with the aim of quickly measuring microtremors (e.g. 5 min) to estimate horizontal-to-vertical spectral ratios (HVSRs). This test is used to identify the deviation between the empirical distribution of normalised (amplitude-corrected) HVSRs and the F distribution so as to identify a physically meaningful peak from numerous peaks, including local peaks inevitably generated by chance when a short-time record is analysed. A HVSR peak is regarded to be meaningful when a significant deviation is detected between the two distributions. However, a paper published in 2005 empirically checked the reliability of this test itself and concluded that the test was unreliable. In this study, we investigate the cause of the unreliability and evaluate the applicable condition. First, we show theoretically that the empirical distribution of normalised HVSRs is generally expected to resemble the F distribution. Then, we show that these two distributions are very similar to each other on the basis of both simulated and observed microtremors. This means that we tend to fail to identify the deviation (commit a type II error) when the sample size is not adequate. To be specific, a sample size on the order of 102–104 is required for a Kolmogorov–Smirnov test to avoid a type II error. Such a sample size corresponds to records on the order of 100–102 h in length for a representative parameter set for the spectral analyses. The original purpose of this test cannot be achieved because such long records are required to identify the deviation. It may be useful from a practical perspective to consider that normalised HVSRs can approximate the F distribution when developing methods to evaluate the statistical property of HVSRs.

The investigation of soil–structure resonance of historical buildings using seismic refraction and ambient vibrations HVSR measurements: a case study from Trabzon in Turkey

In this study, two different historical structures built in Trabzon have been processed by ambient vibrations and seismic refraction measurements. One of the investigated historical structures is the Ataturk Pavilion built in the nineteenth century, and the other one is Hagia Sophia which was built in the thirteenth century. These two buildings are among the most important historical buildings in Trabzon and are very important for the tourism of the city. In order to determine peak/s frequency and amplitude from the horizontal-to-vertical spectral ratios (HVSRs), we have performed several measurements of ambient vibrations both inside (at different floors) and outside (on the ground) of structures. We have also conducted seismic prospecting to evaluate the vertical 1D and 2D profile of longitudinal and shear seismic waves, Vp and Vs, respectively. To this purpose, we have performed seismic refraction tomography and MASW. Ambient vibrations and seismic measurements were compared with each other. The results show that average predominant frequencies and HVSR amplitudes of inside and outside of Ataturk Pavilion are 4.0 Hz, 7.8 Hz and 2.6, 2.3, respectively. The Vp values vary from 300 to 2070 m/s, and the Vs for maximum effective depth is up to 790 m/s in Ataturk Pavilion. On the other hand, average predominant frequencies and HVSR amplitudes of inside and outside of Hagia Sophia and its tower are 4.7, 4.4 and 2.4 Hz and 1.6, 1.8 and 6.9, respectively. Vp values range from 450 to 2200 m/s, and Vs for maximum effective depth is also up to 1000 m/s in Hagia Sophia. The frequency values (F0 = Vs/4 h) calculated from the velocities up to the maximum effective depth for Ataturk Pavilion are in good agreement with the predominant frequency values determined from ambient vibrations. Ataturk Pavilion and Hagia Sophia soils have been classed according to Eurocode 8 by using VS30 values. The class was defined as “B.” Moreover, the bedrock in studied area is basalt. The high Vp and Vs values are also compatible with the lithology. The HVSR curves measured at the Hagia Sophia show the presence of clear peaks when compared to the Ataturk Pavilion. At the same time, there are marked velocity changes in the Vs sections calculated in both areas. As a result, in both areas there are significant impedance contrasts in the subsoil. However, this impedance contrast is more evident in Hagia Sophia. This could be also compatible with a lithological transition. The possible soil–structure interaction was investigated by using all the results and evaluated in terms of resonance risk. It is thought that the probability of resonance risk at Ataturk Pavilion is low according to the ambient vibrations measurements. However, resonance risk should be taken into consideration at Hagia Sophia site since the predominant frequency values are very close to each other. Finally, this site should be investigated in detail and necessary precautions should be taken against the risk of resonance.

Can broad-band earthquake site responses be predicted by the ambient noise spectral ratio? Insight from observations at two sedimentary basins

Site-effect assessments performed through earthquake-based approaches, such as the standard spectral ratio (SSR), require good quality records of numerous earthquakes. In contrast, the use of ambient noise appears to be an attractive solution for ease and rapid computation of site responses with sufficient spatial resolution (microzonation), especially in low seismicity areas. Two main approaches are tested here: the horizontal-to-vertical spectral ratio (HVSR) and the noise-based SSR (SSRn). The HVSR uses the relative amplitude of the horizontal and vertical components of the ambient noise. Instead, the SSRn defines the spectral ratio between the seismic noise recorded simultaneously at a site and at a rock reference station, similar to earthquake-based SSR. While the HVSR is currently used in hundreds of site-specific studies, the SSRn approach has been gradually abandoned since the 1990s. In this study, we compare the results obtain from these two approaches with those of earthquake-based SSR. This comparison is carried out for two sedimentary basins, in Provence (southeastern France) and in Argostoli (western Greece). In agreement with the literature, the HVSR does not provide more than the fundamental resonance frequency of the site (f0). The SSRn leads to overestimation of the SSR amplification factors for frequencies higher than the minimal f0 of the basin (f0min). This discrepancy between SSRn and SSR is discussed, and appears to be mainly dependent on the local geological configuration. We thus introduce the hybrid standard spectral ratio (SSRh) approach, which aims to improve upon the SSRn by adding an intermediate station inside the basin for which the SSR is known. This station is used in turn as a local reference inside the basin for the SSRn computation. The SSRh provides site transfer functions very similar to those of the SSR, in a broad frequency range. Based on these results, the SSRn (or SSRh) should be further tested and should receive renewed attention for microzonation inside sedimentary basins.

EARTHQUAKE MICROZONATION STUDY ON BATUBESI DAM OF NUHA, EAST LUWU, SOUTH SULAWESI, INDONESIA

A study entitled to Earthquake Microzonation on Batubesi Dam of Nuha, East Luwu, SouthSulawesi, Indonesia has been conducted. The study was conducted to obtain a map of peak groundacceleration (PGA) based on the historical seismicity in Sorowako and surrounding area, as well seismicvulnerability index (Kg) based on the measurement of local microtremor on site. The study was conducted ata location between 2.71428 degree - 2.70585 degree South Latitude and 121.3013 degree - 121.3117 degreesEast Longitude. This research is expected to obtain the spatial distribution of the amplification factor (Ao),resonant frequency (Fo), PGA, and Kg to estimate the earthquake hazards potential on location. Themaximum ground acceleration value or PGA obtained by microtremor wave analysis based on Kanai formula.As for determining the Kg used Nakamura or Horizontal to Vertical Spectral Ratio (HVSR) method. Basedon the results of data processing obtained the value of PGAmin is 0.079 Gal. at the point of MSBB25,PGAmax is 0.381Gal at the point of MASBB21, and PGAavg is 0.18 Gal. As for the Kg obtained value ofKgmin is 0.28 at the point of MSBB22, Kgmax is 43.42 at the point of MSBB10, and Kgavg is 9.81. Whilebased on the interpretation by means of the PGA value has been estimated that the MMI intensity is in therange of VII-IX with seismic risk level at a medium range of III until great of III. By means of the dominantfrequency (fo) and dominant period (To) was estimated that soil classification for Kanai in the range of IIuntil IV and the range of B - C for Omote-Nakajima.

Seismic velocity structure of the Jakarta Basin, Indonesia, using trans-dimensional Bayesian inversion of horizontal-to-vertical spectral ratios

Characterizing the interior structure of the Jakarta Basin, Indonesia, is important for the improvement of seismic hazard assessment there. A dense-portable seismic broad-band network, comprising 96 stations, has been operated between October 2013 and February 2014 covering the city of Jakarta. The seismic network sampled broad-band seismic noise mostly originating from ocean waves and anthropogenic activity. We used horizontal-to-vertical spectral ratio (HVSR) measurements of the ambient seismic noise to estimate fundamental-mode Rayleigh wave ellipticity curves, which were used to infer the seismic velocity structure of the Jakarta Basin. By mapping and modelling the spatial variation of low-frequency (0.124–0.249 Hz) HVSR peaks, this study reveals variations in the depth to the Miocene basement. These variations include a sudden change of basement depth from 500 to 1000 m along N–S profile through the centre of the city, with an otherwise gentle increase in basin depth from south to north. Higher frequency (2–4 Hz) HVSR peaks appear to reflect complicated structure in the top 100 m of the soil profile, possibly related to the sediment compaction and transitions among different sedimentary sequences. In order to map these velocity profiles of unknown complexity, we employ a trans-dimensional Bayesian framework for the inversion of HVSR curves for 1-D profiles of velocity and density beneath each station. Results show that very low-velocity sediments (<240 m s−1) up to 100 m in depth cover the city in the northern to central part, where alluvial fan material is deposited. These low seismic velocities and the very thick sediments in the Jakarta Basin will potentially contribute to seismic amplification and basin resonance, especially during giant megathrust earthquakes or large earthquakes with epicentres close to Jakarta. Results have shown good correlation with previous ambient seismic noise tomography and microtremor studies. We use the 1-D profiles to create a pseudo-3-D model of the basin structure which can be used for earthquake hazard analyses of Jakarta, a megacity in which highly variable construction practices may give rise to high vulnerability. The methodology discussed can be applied to any other populated city situated in a thick sedimentary basin.

Site amplification within the Mississippi embayment of the central United States: Investigation of possible differences among various phases of seismic waves and presence of basin waves

The impact of unconsolidated sedimentary basins on ground motion amplification is of particular interest for earthquake engineers and seismologists. The Mississippi embayment (ME) of the New Madrid seismic zone, located in the central United States, is covered with a thick layer of unconsolidated soil deposits. Thus, the estimation of site response in this region is vital to simulate site-specific ground motions and to conduct site-specific probabilistic seismic hazard analysis. We evaluated site amplification at 11 stations within the ME, employing the horizontal-to-vertical spectral ratio (HVSR) technique.Regarding the results obtained from this study, weak ground motions recorded by stations on the unconsolidated ME sediments are amplified 3–7 times for frequencies less than 5 Hz compared to stations located on bedrock. The fundamental resonant frequencies vary from 0.2 to 0.4 Hz within the ME. We investigated differences between the HVSRs obtained from P-waves, S-waves, coda, and pre-event noise. All fundamental frequencies obtained from different seismic phases are in good agreement with a less than 10% difference. The fundamental frequencies of the P-wave and S-wave are relatively higher due to higher velocity of the P-wave and S-wave compared to other phases since the velocity of seismic waves and fundamental frequencies are proportional. There is a good correlation between the HVSR of the S-wave, coda, and pre-event noise portions for frequencies more than 4 Hz. For the frequencies less than 4 Hz, the HVSR of the S-wave is higher than the HVSR of coda by a factor of 3. Reflections of S-waves from the edges of the unconsolidated sedimentary basin of the ME produce surface waves. The presence of basin-induced surface waves in the coda portion for frequencies less than 3 Hz results in increased amplitude of coda, and as a result, slower decay rate with time implying higher Q values. These basin-induced surface waves have a period of 0.5–4.0 s.

ANALYSIS OF SURFACE WAVES RECORDED AT A MASS MOVEMENT IN BRASÍLIA, BRAZIL: AN IMPLICATION IN HAZARD MITIGATION

Ever increasing urbanization over the thick and less cohesive soil of the Federal District (DF), Brazil has increased area's vulnerability to natural hazards, especially the soil erosion and mass movement. This preliminarily study applied noise based geophysical techniques like power spectral density (PSD), horizontal to vertical spectral ratio (HVSR), multichannel analysis of surface waves (MASW) and noise interferometry to a mass movement in Brasilia for the understating of geodynamic processes working in the background of these hazards. Here obtained results show a uniform stratigraphic peak at 2 Hz observed on all HVSR curves, a four layered shear wave section was obtained by MASW. Dispersion curve (frequency vs phase velocity) shows first and second fundamental modes at frequencies of 5 and 25 Hz, respectively. Noise correlograms show time delay larger than +- 0.5 sec on the waveforms of ZR (vertical-radial) component, mainly in acausal part. Relative velocity changes calculated by stretching technique show anomalous trends in response to rainfall events. Follow research will focus on the detection of possible changes in noise records within mass movement mainly related to natural triggering factors (rainfall and river erosion) under more controlled data conditions.

Regional Landslide Potential Mapping in Earthquake-Prone Areas of Kepahiang Regency, Bengkulu Province, Indonesia

Kepahiang regency is an area above the Musi segment of the Sumatran fault system. This condition makes the study area prone to natural disasters such as landslides in the slope area caused by earthquakes due to tectonic plate movement. The objective of this study was to locate potential landslide areas in earthquake-prone areas of Kepahiang regency, Bengkulu province, Indonesia. We performed horizontal to vertical spectral ratio (HVSR) analysis and simple additive weighting (SAW) methods to accomplish the goal. The acquisition of field data involved a broad band seismometer PASI Gemini-2 (triaxial geophone). The microtremor data recorded in the field were then analyzed by the wave spectrum. The results showed that the landslide potential in the study area could be divided into three categories, i.e., low, medium, and high potential. Areas with high potential should be more aware of the threat of landslides, especially in population-dense areas. The greatest threat in the study area is an earthquake along Sumatra’s active fault. An earthquake that occurs in a very steep, landslide-prone area can increase risk and trigger a landslide.

Site term from single-station sigma analysis of S-waves in western Turkey

The main aim of this study is to obtain site terms from single-station sigma analysis and to compare them with the site functions resulting from different techniques. The dataset consists of 1764 records from 322 micro- and moderate-size local earthquakes recorded by 29 stations in western Turkey. Median models were derived from S-wave Fourier amplitude spectra for selected 22 frequencies, by utilizing the MLR procedure which performs the maximum likelihood (ML) estimation of mixed models where the fixed effects are treated as random (R) effects with infinite variance. At this stage, b (geometrical spreading coefficient) and Q (quality factor) values were decomposed, simultaneously. The residuals of the median models were examined by utilizing the single-station sigma analysis to obtain the site terms of 29 stations. Sigma for the median models is about 0.422 log10 units and decreases to about 0.308, when the site terms from the single-station sigma analysis were considered (27% reduction). The event-corrected within-event standard deviations for each frequency are rather stable, in the range 0.19–0.23 log10 units with an average value of 0.20 (± 0.01). The site terms from single-station sigma analysis were compared with the site function estimates from the horizontal-to-vertical-spectral-ratio (HVSR) and generalized inversion (INV) techniques by Akyol et al. (2013) and Kurtulmus and Akyol (2015), respectively. Consistency was observed between the single-station sigma site terms and the INV site transfer functions. The results imply that the single-station sigma analysis could separate the site terms with respect to the median models.

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.

Natural Frequencies Evaluation on Partially Damaged Building using Ambient Vibration Technique

Severe damages observed on the school blocks, roads, retaining walls and drainage within the compound of SMK Kundasang Sabah possibly due to the ground movements triggered by the Ranau earthquake in 1991. Ambient vibration measurements were carried on the remaining demolished 3-storey building which partially damaged in order to measure the predominant building frequencies using tri-axial 1 Hz seismometer sensors. Popular methods of Horizontal-to-vertical spectral ratios (HVSR) and Fourier amplitude spectra (FAS) were used to compute the ambient vibration wave fields of each building axes (Transverse or North-South (NS), Longitudinal or East-West (EW) and vertical) into Fourier spectra. Two main modes of translation and torsion were observed from the peaks frequencies obtained at 2.99 to 3.10 Hz (1st mode), 4.85 Hz (2nd mode) and 5.63 to 5.85 Hz (3rd mode). The building experiencing translation modes of bending and shear in the NS and EW directions. It could be seen when the amplitudes tends to increase when the floor are increased. Meanwhile, the torsional bending mode is expected to occur when the deformation amplitudes are found to be increasing horizontally, when moving into partially structural damaged section located on the East wing of building.

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.

Local site effect of soil slope based on microtremor measurement in Samigaluh, Kulon Progo Yogyakarta

This paper investigated soil slope-local site effect of earthquake inducing landslide by using microtremor Horizontal to Vertical Spectral Ratio (HVSR) method. Microtremor measurements of 15 sites which were recorded for 45 minutes at each site were carried out in Ngargosari village, Samigaluh, Kulon Progo-Indonesia. Microtremor analysis using HVSR method was performed using Geopsy software. HVSR method resulted in predominant frequency values that ranges between 2,77 to 13,82 Hz and amplification factors varied from 0,46 to 5,70. The predominant frequency is associated with the depth of bedrock and the amplification factor reflects the geological condition of soil (sedimentary layer). The soil vulnerability index (Kg) varied from 0,08 to 5,77 and the higher value (Kg>3,4) in the south of the research area was identified as the weak zone of earthquake inducing landslide.