No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
A method for dynamic characteristics estimation of subsurface using microtremor on the ground surfac
Abstract
As methods for dynamic characteristics estimation of surface layers, investigation of boreholes and a method which employs microtremors are well known. Borehole investigation, one of the most accurate methods, is costly and time-consuming and is not available all the time. The method that employs microtremors is handy but has not produced satisfactory results to this day. This paper describes a new processing method that employs microtremor observations yet produces accurate estimates of the characteristics of the ground motion. The method uses a vertical component and horizontal components. As a result, the spectrum ratio of the horizontal components and the vertical component of the microtremors bears a resemblance to the transfer function for the horizontal motion of the surface layers.
... Although [1,2] first applied this technique, Ref. [3] popularized it. Ref. [3] demonstrated the similarities between the spectral ratio of the horizontal and vertical components of a microtremor record, and the transfer function of the surface layers for horizontal movement. ...
... Although [1,2] first applied this technique, Ref. [3] popularized it. Ref. [3] demonstrated the similarities between the spectral ratio of the horizontal and vertical components of a microtremor record, and the transfer function of the surface layers for horizontal movement. The method also offers information on the levels of local amplification and risk of liquefaction of the soils. ...
... This technique utilizes either microtremor records or environmental noise obtained from a tri-axial station to estimate the predominant frequency of sedimentary layers which typically lay over rock substratum. The study uses the concepts introduced by [3] for the study of microtremor spectral ratios. ...
The City of David constitutes one of the most important commercial centers of the Republic of Panama. However, it is located on a coastal plane, close to an area with high seismic activity and has been affected by significant earthquakes (18 July 1934, Mw = 7.4 and 12 March 1962, Mw = 6.7). The goal of this study is to estimate the seismic effects and to classify the soil in the City of David. The experimental work entailed the measurement of environmental noise for H/V spectral ratio (HVSR) analyzed at 22 stations. A series of microtremor refraction studies (ReMi) at six stations distributed from north to south of the city was also performed. The stations were distributed around urban areas of the city, which are characterized by the presence of water supply, sewerage, buildings, roads, etc. The spectral analysis of environmental noise allowed the generation of three different types of maps: First, predominant frequency maps (f0) with zones composed mainly of rigid and semi-rigid soils in the southern end of the city and rigid soils in the central and northern regions. Secondly, maximum H/V amplitude maps (A0) which evidence a low range of HVSR amplitude in the city, ranging from 1.1 to 3.8. Finally, liquefaction vulnerability (Kg) maps, with values less than 2 Hz−1, representative of a low liquefaction risk. Soil classification using ReMi and calculation of the corresponding Vs30 reveal type D soils, which correlate well with results obtained using HVSR analyses. A comparison between HVSR and ReMi shows that HVSR curves that exhibit clear peaks tend to be related to ReMi stations that presented relatively large shear-wave velocity contrasts at some depth. The results from this research are intended to aid the decision-making process related to the future development of the city, as well as government level maintenance and mitigation plans.
... Microtremors are defined as vibrations with periods of 0.05-2 s and amplitudes ranging from 0.01 to 1 microns (Nakamura 1989;Lermo and Chavez-Garcia 1994). Microtremors have been widely used because they show significant changes from point to point according to the soil structure. ...
... Microtremors have been widely used because they show significant changes from point to point according to the soil structure. The microtremor method is used to determine local soil effects (Nakamura 1989;Lermo and Chavez-Garcia 1994;Nakamura 2019). The Nakamura (1989) method is calculated as the ratio of the average of the horizontal component spectra to the vertical component spectrum of the three-component noise recordings (Eq. ...
... The microtremor method is used to determine local soil effects (Nakamura 1989;Lermo and Chavez-Garcia 1994;Nakamura 2019). The Nakamura (1989) method is calculated as the ratio of the average of the horizontal component spectra to the vertical component spectrum of the three-component noise recordings (Eq. 4). ...
The main purpose of this paper is to present the damage features of masonry structures and engineering seismology studies after the 19–22 November 2021 Köprüköy earthquakes (Mw 5.1 and Mw 4.7). The masonry structures damaged near the epicenter have been examined. Damages have been detected that such as vertical cracks in the walls of the masonry structures, out-of-plane bending of the walls, splits in the joints of the walls, and separation of the floors from the elements such as walls and roofs. The fact that the structures in the region do not receive an engineering service and that they are constructed without complying with the relevant earthquake regulations are thought to cause such damage. The damage in Topçu village of Köprüköy district in Erzurum is more than in other settlements. Microtremor measurements have been applied in Topçu Village to investigate dynamic soil features. The soil amplification factor and soil predominant period have been obtained ~ 6.8 and ~ 1.3 s for the first measurement and ~ 9.4 and ~ 1.3 s for second location, respectively. Also, Vs30, bedrock depth, vulnerability index, and shear strain parameters have been calculated using some empirical relations. High bedrock depth and low Vs30 values are obtained for both measurements. The vulnerability index and shear strain values also indicate that the vulnerability of the soil is high. In order to remain in the safe zone for structures in a possible future earthquake, it has been suggested that it should comply with the earthquake-soil-structure relationship and should be designed in accordance with the earthquake regulation standard.
... Vibrations caused by anthropogenic activities are known to affect the frequency range of 2-50 Hz, whereas natural disturbances typically result in changes within the 0.2-2 Hz range (SESAME 2004). The concept of recording ambient vibrations for site effect studies and utilizing the Horizontal to Vertical Spectral Ratio (HVSR) method originated from the efforts of several researchers (Omori 1908;Kanai et al. 1954;Kanai and Tanaka 1961;Nogoshi and Igarashi 1971), but it gained popularity following Nakamura's contributions (Nakamura 1989). Despite receiving critical reviews from various authors (Bindi et al. 2000;Mucciarelli and Gallipoli 2001), this technique has been globally accepted for estimating the fundamental frequency and site amplification, even when using artificially induced vibrations. ...
... Despite receiving critical reviews from various authors (Bindi et al. 2000;Mucciarelli and Gallipoli 2001), this technique has been globally accepted for estimating the fundamental frequency and site amplification, even when using artificially induced vibrations. These vibrations may vary in frequency on a daily or weekly basis, but analyzing the resulting spectra obtained from data collected at different sites yields stable estimates of the fundamental frequency (Nakamura 1989(Nakamura , 2000Mahajan et al. 2011Mahajan et al. , 2021Mahajan et al. , 2022Kumar and Mahajan 2020). The HVSR technique based on Nakamura's method has gained popularity among researchers as an affordable tool for determining sediment thickness in seismic hazard analysis, microzonation studies, and vulnerability assessments of the built environment. ...
... The acquired data was then processed using Grilla software (version 9.7), following the assumptions outlined by various authors and complying with the SESAME criteria (Nakamura 1989;SESAME 2004;Choobbasti et al. 2014). The initial processing step involved the removal of transient noise from the ambient noise record is to prevent its impact on the HVSR curve below 2 Hz (Castellaro and Mulargia 2009;Gosar and Martinec 2009). ...
Active and passive seismic survey was performed in Kangra valley using three different methods i.e. Horizontal-to-Vertical Spectral Ratio (HVSR), Multiple simulations with one receiver (MSOR) and Multichannel analysis of surface waves (MASW) for seismic site characterization. The ambient noise measurements (HVSR) analysis from 200 sites reveals variation in fundamental frequency (f0) and amplification (A0) from 3 to 11 Hz and 2 to 6 respectively. The joint-fit-inversion technique was used to invert HVSR curve with intial information obtained dispersion curves on stiffness parameters using MSOR from same site and derived 1-D shear wave velocity (Vs) profile. Further, MASW survey was performed to get 2-D Vs profile indicating lateral and vertical variation to identify presence of dissolution feautres underneath. The Vs map of the valley suggests the variation in Vs from 200 to 800 m/s and indicated that Kangra valley falls under class ‘C’ and ‘D’ as per NEHRP classification. The 1-D Vs profile derived by inverting HVSR curves is found to be in good agreements with Vs information derived using MASW method. The response analysis for a given magnitude value (mb 6.8) of each site indicated site amplification variation from 0.6 (site 2) to 0.168 (site 50) and natural period of sites vary from 0.10 (site 45) to 0.16 s (site 6). The Standard Spectral Ratio and Floor Spectral Ratio of bulidng having incorporated antiseismic measures were also studied and the results of the analysis reveals low to very low resonance.
... For this purpose, drilling at the site of interest will lead to a better understanding of the response of subsurface layers to seismic vibrations. Exploratory drilling is undoubtedly the most reliable way to understand the dynamic properties of underground layers, but it requires significant expenditure in terms of finance, manpower and time (Nakamura 1989). ...
... These include established techniques such as the traditional spectral ratio technique (Borchardt 1970), the generalized inversion technique (Field and Jacob 1995) and the receiver function method (Langston 1979). Additionally, there are other approaches, such as the Nakamura method, which involves computing the spectral ratio of the horizontal and vertical components of the recorded micro-shocks or ambient noise (Nakamura 1989) and the Coda-wave approach (Phillips and Aoki 1986). ...
... The natural frequency range of each site class is a crucial factor in site classification. Soft surface layers tend to exhibit more prominent horizontal motion compared to vertical motion, while rigid surface layers show similar maximum values and waveforms for both horizontal and vertical motions (Nakamura 2008). H/V spectral ratio curves can reveal the dominant periods of a site, regardless of time, location and season (Nakamura 1989), but the amplification of the site obtained from these curves may not always be consistent. ...
The Earthquake Early Warning System Laboratory, Centre of Excellence in Disaster Mitigation & Management, Indian Institute of Technology Roorkee has developed India's first Earthquake Early Warning System (EEWS). For this, Uttarakhand, a Himalayan state of the Republic of India, was selected for setting up the regional EEWS. Seismic sensors have been installed in the central seismic gap region, an area where strong and higher magnitude earthquakes are predicted and likely to occur in the future. A total of 169 sensors have been installed in this seismically active region. The control room has been set up in the Earthquake Early Warning System Laboratory. The data is streamed to the laboratory through dedicated VPNoBB network of BSNL and SWAN. The server does the processing of the data in real time. Warning of the earthquakes that occurred in the instrumented region is issued through two modes. Under first mode, sirens have been installed in the Government-owned buildings of Dehradun, Haldwani, and District Emergency Operation Center in all 13 districts of Uttarakhand. In the second mode, earthquake warning are issued through the mobile app ‘Uttarakhand Bhookamp Alert’, which has now been renamed now as ‘Bhukamp Disaster Early Vigilante (BhuDEV)’. This app was launched to the public on 4th August, 2021 by the honorable Chief Minister of Uttarakhand. In this article, site classification for the instrumented field sites is performed. It is vital for analyzing the seismic hazard of an area and understanding the damage patterns caused by earthquakes. In the present study, 169 sites of the seismic network array of EEWS for Uttarakhand are classified on the basis of geological settlement at the locations of the stations.KeywordsEarthquake early warning systemSite classificationGeological conditionsUttarakhandSeismic gap
... In recent years, the horizontal-to-vertical spectral ratio (HVSR) technique applied to microtremors has acquired increasing importance for the evaluation of the seismic characteristics of a site because the HVSR can aid in identifying areas with similar seismic responses. Theoretical considerations [1] and experimental tests showed that the amplification of horizontal motions between the bottom and the top of a sedimentary cover is related to the ratio between the spectra of the horizontal and vertical components of the ground velocity [1,2]. This ratio is a measure of the ellipticity of Rayleigh wave polarization, overlooking the contribution of Love and body waves. ...
... In recent years, the horizontal-to-vertical spectral ratio (HVSR) technique applied to microtremors has acquired increasing importance for the evaluation of the seismic characteristics of a site because the HVSR can aid in identifying areas with similar seismic responses. Theoretical considerations [1] and experimental tests showed that the amplification of horizontal motions between the bottom and the top of a sedimentary cover is related to the ratio between the spectra of the horizontal and vertical components of the ground velocity [1,2]. This ratio is a measure of the ellipticity of Rayleigh wave polarization, overlooking the contribution of Love and body waves. ...
... The horizontal-to-vertical spectral ratio (HVSR) technique [1,2], applied to ambient seismic noise, is a method widely used to estimate the resonance frequencies of geological structures and is today one of the most applied methods for expedite microzonation studies of large urban areas [26,27]. ...
In the municipality of Enna, 80 HVSR measurements were performed, and some of these were combined with MASW seismic measurements, which made it possible to constrain the data inversion and obtain significant shear wave velocity models. A reconstruction of the depth of the seismic bedrock was performed for the whole territory, showing different depths for the higher and lower areas, as evidenced also by the Vseq parameter map. The frequency peaks identified in the H/V curve were analyzed through a cluster analysis algorithm to evaluate similarities that allow these peaks to be divided according to their stratigraphic origin. A non-hierarchical analysis algorithm modified in such a way as to avoid any a priori choice that could influence the partition has been used. The cluster analysis made it possible to divide the frequency peaks into five groupings, each of which was then associated with a seismic discontinuity, according to the geological contacts expected in the subsoil. Finally, the inversion of the data made it possible to reconstruct the geometries of these geological contact surfaces and to reconstruct a 3D model of the subsoil, which agrees well with the surface geology of the area.
... Microtremors are the varied frequency (~0-25 Hz) noise generated by natural processes as well as human activities [46]. Measuring this ambient/passive noise through the MHVSR test, the f 0 of the subsoil can be estimated using Nakamura's technique [47]. This dynamic parameter, f 0 , is dependent on the stratigraphic layering within the substructure. ...
... Although the concept of microtremors is widely use now, the understanding of the microtremor wavefield is still a matter of contention leading to diverse interpretations of the microtremor data [48,49]. Studies have presented interpretations based on body wave [47,50], surface wave [51] and total wavefield assumptions [52,53]. ...
... Next, the Fourier spectra in each of the three directions were computed by averaging the spectra for each time window. The average of the two horizontal spectra were finally divided by the vertical spectrum [47] to obtain the HVSR curve ( Fig. S2c). ...
Personalised share link:
https://authors.elsevier.com/a/1hZUs_65by2xwE
Extensive geophysical surveys (MHVSR and MASW) conducted for the microzonation of the Kashmir Valley, Himalayas, revealed unexpected dynamic characteristics at certain sites pointing out the weak relationship between fundamental frequency (f0) and time-averaged shear wave velocity over 30 m depth (VS,30). Unusual low-frequency amplification at stiff soil sites and high-frequency amplification at weathered rock sites was obtained. On the contrary, high-frequency amplification was attained at a soft soil site over shallow bedrock. Instances of topographic amplification on slopes, hills, and valleys were encountered. Consequently, the commonly used VS,30-based single-proxy site classification failed to explain these atypical site effects, thus underscoring the caution to be exercised for site classification in geologically complex regions. These findings motivated the documentation of the anomalies and the search for the most suitable site characterisation scheme for the geological deposits of the Kashmir Valley. The coupled MHVSR-VS,30 proxy approach accomplished the best results for the study region.
... One of the most straightforward and accurate techniques for measuring the soil conditions of a region is microtremor measurement technique, often known as the horizontal to vertical spectral ratio (H/V) (HVSR) approach [5]. The ambient noise is used to determine the horizontal and vertical components of the HVSR technique. ...
... The thickness of the sediment layer has an impact on HVSR calculations that determine the amplification and value of the dominant period. Following Nakamura (1989), this approach was widely employed by researchers to examine site effects and ground motion amplification [6,7]. Result of Horizontal to Vertical Spectral ratio before filter applied, D) The application of a series of filtering techniques, including Konno-Ohmachi smoothing, detrending, and bandpass filtering with a cut-off frequency of 1-10 Hz, has been performed on the horizontal to vertical spectral ratio ...
Lake Toba is located on the Sumatra Island, Indonesia. The subduction of the Indo-Australian plate dominates the tectonic setting in this region underneath the Eurasian plate. This area has active seismicity, especially from the subduction process in the West. Most rocks in Lake Toba are tuff sediments. This study’s objective is to map the vulnerability index that can be used to identify high damage areas in the region if an intense event occurs. We use 24 three-component seismometers installed around Lake Toba. We gathered good quality recording data for one day on each station. Next, we divided our data into 1 hour and performed the time to frequency domain using the fast Fourier transform. Lastly, we divided the horizontal and vertical components and extracted some parameters such as dominant frequency value and its amplitude. The dominant frequency value ranged from 0.18 to 27.6 Hz, H/V amplification was found to be between 2.84 and 11.9, and shear wave velocity (Vs30) was found to be between 240 and 760 m/s, and the soil vulnerability index (Kg) was found to be between 0.42-43.4. The study area’s highest vulnerability is in the southeast, whereas the study area’s lowest vulnerability is located in the West and North East.
... Kanai (1957) became the first scientist to introduce the concept of using microtremors to determine the soil's natural frequency of vibration which can evaluate the soil's interaction with earthquake energy. Several subsequent studies were conducted to determine the "soil response" to the earthquake energy and its effects on buildings (Aki, 1957;Kanai and Tanaka, 1961;Kanai, 1962;Nogoshi and Igarashi, 1970;Kagami et al., 1982Kagami et al., & 1986Rogers et al., 1984;Ç elebi et al., 1987;Lermo et al., 1988;ECP, 1993;Nakamura, 1989Nakamura, , 1997Nakamura, & 2000Bour et al., 1998;Diagourtas et al., 2002;Gamal, 2009;Harutoonian et al., 2012;Mahajan et al., 2012;Hunstad et al., 2013;Adib et al., 2015;Akkaya, 2015;Ridwan et al., 2014;Jiang et al., 2016;Singh et al., 2017;Gamal et al., 2019& 2020, Gamal and Maher, 2022. Mucciarelli (1998) excluded some surface sources such as winds or sounds from sources such as winds entering the asphalt layers, making asphaltic waves. ...
... Mucciarelli (1998) considered it as a bad source that may led to bad determination of soil responses. Nakamura (1989) used the little excitation for the soil or the so-called microtremors to study the dynamic properties of the site, such as period and amplitude. Such old studies were mainly based on "low frequency energy", inaudible to human ears (1 -20 Hz). ...
The Earth acts like a low-pass filter to earthquake energy so that frequencies higher than 10 Hz are rapidly attenuated. This intrigues seismologists about the seismic waves in the frequency domain 1–10 Hz, which is crucial to correctly assess the impact of seismic shaking on structures. However, not much attention has been paid to higher frequencies, probably due to its low significance and structural damage. The Earth has high frequency seismic signal (HFSS) in the audible frequency range 20–20,000 Hz and maybe higher (Gamal et al., 2020). These seismic signals result from the transformation of any energy into HFSS energy which is propagated inside the Earth, this energy may be winds, the crustal structure movement, movement due to gravitational force or any mechanical energy transformed into high frequency seismic vibrations. Fifteen different geological environments were tested in Egypt, to monitor the high frequency seismic signals (HFSS) of the subsurface soil. The present study used very high digitising frequency seismographs, not less than 8,000 to 16,000 sample per second, and a set of horizontal and vertical geophones of natural frequencies in the ranges of 4 Hz to 100 Hz. It was found that consolidated rocks have high-pitch that may reach 4,000 Hz, while weak fractured soils sound have a low-pitch, in the frequency range of 20–70 Hz. Speech and audio processing methods have been used to differentiate between these HFSS preserved inside soils and to produce the “unified HFSS map”. The “Soil HFSS map” was considered as avail science could be used in the future to give deep insight on the shallow Earth's interiors.
... An alternative approach to estimate the depth of the seismic bedrock and thickness of surface deposits involves the use of the horizontal-to-vertical spectral ratio (HVSR) methodology [45][46][47], which is also applied to the groundwater exploration and aquifer geometry characterization [12,41,48]. Many authors demonstrated that reliable S-wave-velocity models can be obtained by inverting HVSR data with other stratigraphic and geophysical constraints [47,[49][50][51][52]. ...
... The location of seismic investigations was based on the position of previous investigations, with the aim of integrating the available data mesh (Figure 3). The HVSR (horizontal-to-vertical spectral ratio) methodology [45,98] is a useful technique for the analysis of seismic noise. This methodology consists of calculating the ratio between the horizontal components with respect to the vertical component of the spectrum of seismic ambient noise. ...
The characterization of a groundwater body involves the construction of a conceptual model that constitutes the base knowledge for monitoring programs, hydrogeological risk assessment, and correct management of water resources. In particular, a detailed geological and geophysical approach was applied to define the alluvial Caronia Groundwater Body (CGWB) and to reconstruct a hydrogeological flow model. The analysis of the CGWB, located in north-eastern Sicily, was initially approached through a reanalysis of previous stratigraphic (boreholes) and geophysical (vertical electrical soundings and seismic refraction profiles) data, subsequently integrated by new seismic acquisitions, such as Multichannel Analysis of Surface Waves (MASW) and horizontal-to-vertical seismic ratio (HVSR). The analysis and reinterpretation of geoelectrical data allowed the construction of a preliminary 3D resistivity model. This initial modeling was subsequently integrated by a geophysical data campaign in order to define the depth of the bottom of the shallow CGWB and the thickness of alluvial deposits. Finally, a preliminary mathematical model flow was generated in order to reconstruct the dynamics of underground water. The results show that integration of multidisciplinary data represent an indispensable tool for the characterization of complex physical systems.
... In the late 1960s, Toksoz and Lacoss used a seismic network to sep extract, and analyze the various periodic components of microtremors [43,44] an ported on the components of the different bands of the microtremors and their pos causes. In the 1990s, Nakamura proposed a new microtremor method [45]. This hor tal-to-vertical spectral ratio (H/V) method has gradually become the focus of the ana of site dynamics around the world. ...
... In the late 1960s, Toksoz and Lacoss used a seismic network to separate, extract, and analyze the various periodic components of microtremors [43,44] and reported on the components of the different bands of the microtremors and their possible causes. In the 1990s, Nakamura proposed a new microtremor method [45]. This horizontal-to-vertical spectral ratio (H/V) method has gradually become the focus of the analysis of site dynamics around the world. ...
Earth fissures are widely distributed worldwide, and the Fenwei Basin in China is one of the regions with the most significant number and scale of fissures in the world. The Yuncheng Basin is an important constituent basin of the Fenwei Basin in China, where earth fissures are densely developed and cause severe damage. In particular, the impact of earth fissures on the seismic response of the site is still unknown and is an urgent problem that needs to be solved. Based on microtremor tests, three types of typical earth fissure sites in the Yuncheng Basin were selected for field testing. Through spectrum analysis, the dynamic response characteristics of the earth fissure sites were determined. The results show that the dynamic response of the site is significantly affected by the earth fissures. The dynamic response strength of the site is the largest on both sides of the earth fissures, and it decreases and gradually stabilizes with increasing distance from the fissures. The influence range of the earth fissures on the hanging side is slightly longer than the heading side.
... Se trata de una vibración de origen ambiental producida por actividades humanas, industria o tráfico, que, por lo general, son de alta frecuencia, o ruido natural generado por mareas, vientos o telesismos, generalmente, de baja frecuencia (Ritta et al, 2012). Nakamura (1989) propuso un método de nombre homónimo que permite determinar las características dinámicas del suelo a partir del ruido sísmico y la estimación de la frecuencia fundamental del suelo. La aplicación generalizada del método a lo largo de las últimas décadas, con una validación experimental notoria en diferentes zonas del planeta, convierten la técnica H/V en una herramienta muy atractiva para validar los modelos geológicos a partir de los diferentes tipos de ondas que constituyen el ruido sísmico ambiental. ...
... La profundidad del límite mecánico cobertera-zócalo está directamente relacionado con la frecuencia fundamental obtenida a partir de esta relación de espectros (Nakamura, 1989). Por lo que, dicha profundidad puede ser estimada una vez conocida la frecuencia fundamental del suelo (f0) y la velocidad de las ondas S, de cizalla, (VS), mediante la determinación de un espesor de sedimento (H) (Atakan et al, 2004) a través de la siguiente fórmula: ...
Guadalquivir Basin (GB) is characterised by Neogene and Quaternary sediments which are covering a non-outcropping Paleozoic and Mesozoic basement. This work presents the results of the exploration of the subsoil of the GB obtained from the seismic noise registered in 232 stations, located between the parallels of Cartaya and Rociana del Condado (Huelva). Fundamental frequency was identified and the depth of the mechanical basement was defined in all of them, thanks to the quality of the record. Seismic exploration and characterization was carried out by applying the H/V spectral ratio method from the noise recorded by triaxial seismometers. The emplacement of the stations were located along NW-SE profiles mostly. Data was processed with the software Geopsy and from the formula H = 80.16*fo-1.48 the depth of the mechanical basement was obtained. Deep exploration drills, geological cartographies and the field geological data itself corroborate these data. Five types of response were obtained: a) low frequency and hig amplitude peaks (deep substratum areas); b) high frequency and high amplitude peaks (shallow substratum areas); c) broad peaks which could indicate critical zones (3-2D effects); d) double peaks (marshlands); and e) no peaks (almost outscropping bedrock). The fundamental frequencies obtained vary between 0.2 to 10 Hz. Bedrock depth varies from 1-5 meters to more than 600 meters, from the northwestern zone to the southeast areas, respectively. The slope of transects, which could be approximated to the actual dip, is calculated around 1-2º towards the SE, with a typical deviation of approximately 1º. However, abrupt changes (5-7º) can be seen along narrow bands, with lateral continuity. Such evidence and the singularity of the record (H/Vspectra with broad peaks) suggest that these are fault zones. Geomorphological data would corroborate these interpretations. PALABRAS CLAVE Método del Cociente Espectral H/V, frecuencia fundamental del suelo, fracturación, cuenca del Guadalquivir. INTRODUCCIÓN El ruido sísmico es una señal continua de ondas elásticas cuya génesis responde a diferentes fuentes, tanto de origen natural como antrópico. Se trata de una vibración de origen ambiental producida por actividades humanas, industria o tráfico, que, por lo general, son de alta frecuencia, o ruido natural generado por mareas, vientos o telesismos, generalmente, de baja frecuencia (Ritta et al, 2012). Nakamura (1989) propuso un método de nombre homónimo que permite determinar las características dinámicas del suelo a partir del ruido sísmico y la estimación de la frecuencia fundamental del suelo. La aplicación generalizada
... For both STRs and LTRs, we compute the Fourier spectrum of each pre-processed time series segment by the fast Fourier Transform algorithm and smooth the amplitude spectrum by Konno-Ohmachi method with the bandwidth coefficient of 40 (Konno and Ohmachi, 1998). Then we calculate the HVSRs according to the following equation (Nakamura, 1989;Guo et al., 2014): ...
... Even though the HVSR method is extensively used for site characterization, its theoretical basis is still under debate. Many studies attempted to explain this method in terms of SH waves (Nakamura, 1989;Nakumura, 2008;Nakamura, 2019;Van der Baan, 2009;Oubaiche et al., 2016;Kawase et al., 2019) and Rayleigh waves (Lermo and Chavez-Garcia, 1994;Konno and Ohmachi, 1998;Fäh et al., 2001Fäh et al., , 2003Arai and Tokimatsu, 2005;Tuan et al., 2011), and by considering the effect of Love waves and the role of all waves (Lunedei and Albarello, 2010;Sánchez-Sesma et al., 2011). These studies also reveal that the predominant frequencies obtained by body-wave and surfacewave theories of HVSR method are approximately identical (<10% difference). ...
... However, correspondence of the predominant period from the microtremors, Tp (e.g., 0.2 s > Tp, 0.2 < Tp < 0.6 s, and 0.6 < Tp for hard, medium, and soft sites, respectively), as determined by the zero-crossing method, was subsequently proposed (e.g., Kanai and Tanaka 1961) and has since been implemented in daily building design activities in Japan. After the proposal of Nakamura (1989), together with digital signal processing instead of the zero-crossing method, soil classification for building design in Japan has been primarily based on the predominant period in the microtremor horizontal-tovertical spectral ratio (MHVR) of the Fourier spectra. We should understand that at that time, using the predominant period as a representative value for soil classification in Japan was a direct consequence of the pioneering studies by Sezawa, Kanai, and their colleagues mentioned above. ...
... There have been numerous studies on the use of the MHVR in the past after Nogoshi and Igarashi (1971) and Nakamura (1989), as reviewed by Molnar et al. (2022) as a series of studies on non-invasive methods for velocity exploration . After a long discussion on the optimal use of the MHVR and its theoretical representation, our community finally obtained a complete theoretical solution for MHVR ) and a subsequent inversion code to obtain the velocity structure only from a single-station measurement of microtremors (García-Jerez et al. 2016). ...
Following the 1923 Kanto earthquake in Japan, Japanese researchers noticed the strong effects of surface geology on
seismic motion (ESG) and began to investigate these effects to quantify the site amplification factors (SAFs) associated with soft surface sediments. On the other side of the Pacific Ocean, ESG received limited attention until the 1985
Michoacan, Mexico earthquake revealed significant long-period amplification inside Mexico City that manifested as
the source of devastating damage to high-rise buildings. Since then, seismologists and earthquake engineers have
performed a lot of studies on various ESG issues worldwide. We have not yet reached common conclusions on how
to quantitatively predict SAFs over a broad frequency band of engineering interest, 0.1 to 20 Hz, for moderate to
strong input from different types of earthquakes in different tectonic settings. However, we found here several basic
guidelines useful for successfully modeling ground motions as a common approach to ESG studies. First, in this letter,
we briefly review our history of understanding ESG, which is closely related to the key settings required for reliable
quantifications of SAFs, and then introduce various emerging techniques for broadband quantitative evaluations of
SAFs based on the vast amount of observed ground motions primarily from dense Japanese strong-motion networks.
Based on the findings of our investigation and the physical relationships behind the parameters, the authors would
like to recommend that researchers on ESG and related topics would refer to the five basic guidelines proposed in the
conclusions for the successful implementation of techniques to delineate SAFs in a specific region of interest, such as
the use of Fourier spectra instead of response spectra. We have started applying the proposed techniques to regions
outside Japan. The implementation of the statistical validation exercises will follow.
... These techniques require a single triaxial geophone and simpler equipment, acquisition procedures, and eld operations, which can be very effective for the investigation of large landslide areas with signi cant lateral variations in subsurface properties and challenging logistics. Velocity spectra can be jointly inverted with HVSR curves (Arai and Tokimatsu 2005;Nakamura 1989) to better constrain the velocity models, especially at deeper depths than those investigated by active seismic techniques. ...
... We also record seven passive datasets of ambient noise measurements to determine the HVSR curve (Nakamura 1989). We use the same single 3C geophone used for the acquisition of active single-offset acquisition. ...
Impressive and large-scale slow-moving landslides with a long-term evolutionary history of activity and dormancy are a common landform in the southern Apennines mountain belt. The spatial and temporal evolution of a multi-stage complex landslide located in a catchment of the frontal sector of the southern Apennine chain was reconstructed by multitemporal geomorphological analysis, near-surface seismic survey, and DEM comparison. The Tolve landslide shows a multi-decadal evolution characterized by intermittent periods of activity and dormancy. Geomorphological evidences suggest that the initial failure of the large-scale landslide has a multi-millennial age and can be related to a roto-translational movement that evolved in an earthflow. Recent evolution is associated with a major reactivation event in the middle and lower sectors of the larger complex landslide, which probably is related to a heavy rainfall event occurred in January 1972. Recent evolution is mainly associated with minor movements in the source area, toe advancements, and widespread shallow landslides along the flank of the earthflow. Our results demonstrate the need to integrate traditional geomorphological analysis with multi-source data to reconstruct the evolution of slow-moving landslides and to identify their main predisposing and triggering factors.
... However, it is often non economically feasible to perform tests at all location. In parallel, it is possible to estimate the natural frequency of the deposit using indirect approaches such as the HVSR method [19] a strong correlation exists between and indirect surface measurements [20]. ...
... The HVSR or H/V is a passive measurement method developed by Nakamura [19]. The HVSR is defined as the ratio of the Fourier amplitude between the horizontal and vertical motions recorded by a sensor on the free surface. ...
Defining a reference shear wave velocity profile () is crucial for seismic-hazard assessment and seismic response analysis. However, selecting a reference velocity profile is not straightforward, mainly because of the high variability of shear wave velocity in complex formations. This study considered 26 shear wave profiles from downhole tests carried out in the Laga Basin (Gran Sasso, Central Apennines), where the soil can be categorised as complex owing to the chaotic succession of turbidite and Quaternary continental deposits. Downhole tests and stratigraphy were used to (i) develop a probabilistic model for predicting the shear wave profiles calibrated on the collected test data and (ii) propose an outlier detection method for estimating the first fundamental frequency of the deposit from horizontal-to-vertical spectral ratio (HVSR) analyses. Specifically, the stochastic shear wave model provides the uncertainty of the first fundamental frequency estimated from downhole tests based on a simplified mechanics-based formulation. The defined bounds have been used to define the criteria for outlier detection in HVSR frequency assessments, given an approximate estimate of the equivalent depth.
... The horizontal-to-vertical spectral ratio (HVSR) technique, also known as the Nakamura method, was first introduced by Nogoshi and Igarashi (1971) [35] and spread widely by Nakamura (1989) [36]. This method uses a single station comprising a three-component seismometer that records ambient vibrations. ...
... The horizontal-to-vertical spectral ratio (HVSR) technique, also known as the Nakamura method, was first introduced by Nogoshi and Igarashi (1971) [35] and spread widely by Nakamura (1989) [36]. This method uses a single station comprising a three-component seismometer that records ambient vibrations. ...
Conventional geophysical methods are suitable for estimating the thicknesses of subsoil layers. By combining several geophysical methods, the uncertainties can be assessed. Hence, the reliability of the results increases with a more accurate engineering solution. To estimate the base of an abandoned landfill, we collected data using classical approaches: high-resolution seismic reflection and refraction, with more modern methods including passive surface wave analysis and horizontal-to-vertical spectral ratio (HVSR) measurements. To evaluate the thickness of the landfill, three different datasets were acquired along each of the two seismic lines, and five different processing methods were applied for each of the two arrays. The results of all the classical methods indicate very consistent correlations and mostly converge to clear outcomes. However, since the shear wave velocity of the landfill is relatively low (<150 (m/s)), the uncertainty of the HVSR results is significant. All these methods are engineering-oriented, environmentally friendly, and relatively low-cost. They may be jointly interpreted to better assess uncertainties and therefore enable an efficient solution for environmental or engineering purposes.
... A complexa estrutura dos ambientes geológicos, aliada à elevada ocupação urbana dificulta a cartografia geológica, caracterização geotécnica e realização de ensaios geofísicos à superfície. Atualmente, é reconhecido como uma mais-valia o uso de técnicas não invasivas, simples e de baixo custo com base em registos de vibrações ambientais, como a técnica HVSR (Horizontal-to-Vertical Spectral Ratio) (Nakamura, 1989), ou ondas superficiais, como a técnica MASW (Multichannel Analysis of Surface Waves) (Park et al., 1999). A sua compatibilidade e complementaridade com outras informações (p.e., sondagens e características geológicas) permite uma caracterização mais robusta e com maior fiabilidade, contribuindo para melhorar a compreensão dos efeitos de sítio e a qualidade dos estudos de microzonagem sísmica. ...
... A técnica baseada na razão espectral entre as componentes horizontal e vertical (método HVSR) do ruído sísmico ambiente registado à superfície é amplamente utilizada para estimar a frequência fundamental do terreno, f0 (Nakamura, 1989 ...
As condições locais podem alterar de forma significativa as características do movimento sísmico à superfície, pelo que é fundamental caracterizar adequadamente os diferentes tipos de terreno de modo a estimar as propriedades do movimento sísmico à superfície para um dado cenário sísmico. Atualmente é reconhecida a necessidade de integrar diferentes técnicas e parâmetros para uma caracterização mais robusta e com maior fiabilidade. Com base num conjunto de dados multidisciplinar que inclui (i) dados geotécnicos (p.e., sondagens, resultados de SPT), (ii) ensaios geofísicos (p.e., perfis sísmicos, registos de vibrações ambientais) e (iii) características geológicas, foi desenvolvida uma abordagem integrada para apoiar uma caracterização robusta de ambientes geológico-geotécnicos complexos, como é o caso de Lisboa. A partir das medidas de vibrações ambientais foi avaliada a distribuição da frequência fundamental dos terrenos e propostas três zonas com base no seu padrão de variação na cidade. É também apresentada uma estimativa da profundidade dos contrastes de impedância calculada através de dois processos, considerando os resultados anteriores: (i) a profundidade do contraste mais superficial foi avaliada através da variação acentuada dos valores de NSPT disponíveis, e (ii) a profundidade do contraste mais profundo foi estimada com base em dados geológicos e informação de sondagens profundas.
... It offers accurate data concerning the dynamic characteristic of the soil layer. Since lots of boring are needed for the wide area, in high intensity, it is not feasible considering high demand for manpower, substantial time as well as tremendous cost (Nakamura 1989). Kanai (1957) introduced the microtremor method for site effect study and later improved by Nakamura (1989) and it becomes widespread method as a low cost and effective tool to estimate the fundamental resonant frequency of sediments by measuring at a single station (Paudyal et al. 2013). ...
... Since lots of boring are needed for the wide area, in high intensity, it is not feasible considering high demand for manpower, substantial time as well as tremendous cost (Nakamura 1989). Kanai (1957) introduced the microtremor method for site effect study and later improved by Nakamura (1989) and it becomes widespread method as a low cost and effective tool to estimate the fundamental resonant frequency of sediments by measuring at a single station (Paudyal et al. 2013). ...
Recent, 2015 Gorkha earthquake created the havoc situation in Bhaktapur municipality, smallest municipality of Nepal. This earthquake had shown the variation in the destruction pattern within the Bhaktapur municipality, showing the need for the site-specific ground response analysis of the area. Among the various methods available for the site response analysis, here in this study, Microtremor survey of the area is done. Microtremor is a low amplitude ambient vibration of the ground caused by natural or man-made disturbances. Study of the ambient vibration of the ground helps to understand the predominant frequency of the ground. In this study, Bhaktapur Municipality is divided into a number of grids; each grid of 200m by 200m. As study area is very densely populated and each node of the grid as a reference point. In total, observation and measurement of 50 nodes are made. Obtained time domain data is then transformed into the frequency domain by using Fourier transformation. The results after the analysis show the fundamental frequency varies from 0.4Hz to 3.8Hz. The central and western part has lower frequency than the eastern part of Bhaktapur. At central region, Sakotha area, has the lowest of frequency 0.42 Hz.
... The concept of the microtremor was introduced by Omori in 1908 and later further developed by Kanai andTanaka in 1961. In 1970, Nogoshi and Igarashi introduced a technique using the horizontal to vertical spectral ratio of microtremor (HVSR), which was later used by Nakamura (1989) to estimate resonance frequency and local geologic amplification factors. The horizontal-to-vertical spectral ratio (HVSR) is defined as follows: ...
A microtremor survey based on ground surface data acquisition was used to identify and characterize the karst area of Cerme Cave, Yogyakarta, Indonesia, from the entrance to the exit of the cave. The entrance and exit of the cave are used as tie-in points because the characteristics of the two locations can be directly observed. Parameters used in this study include ground vibration amplification, shear wave velocity, and Poisson’s ratio. The presence of cavities can be characterized by a relatively strong contrast between these physical parameters and their surroundings. The exit of the cave, which can be considered as a sinkhole, has a dominant frequency of 3.2 to 4.6 Hz, which is relatively higher than that of the surrounding area. At the entrance of Cerme Cave, which has a large cavity, a small ground vibration amplification was detected, less than 0.1. The entrance and exit of the cave also exhibit a low shear wave propagation velocity of less than 350 m/s. The presence of a subsurface fluvial channel in Cerme Cave can be characterized by a high Poisson’s ratio of 0.4–0.5, a gain value of less than 0.1, and a shear wave velocity of less than 350 m/s.
... Nakamura (1989) menyatakan bahwa perbandingan spektrum H/V sebagai fungsi frekuensi berhubungan erat dengan fungsi site transfer untuk gelombang S. Perbandingan H/V pada mikrotremor adalah perbandingan kedua komponen yang secara teoritis menghasilkan suatu nilai. Periode dominan suatu lokasi secara dasar dapat diperkirakan dari periode puncak perbandingan H/V microtremor [9] . Analisis HVSR pada spektrum mikrotremor akan Kanai. ...
Penelitian regangan geser tanah untuk gempa bumi dengan magnitudo M 6,00 SR dengan melibatkan data mikrotremor telah dilakukan untuk wilayah Kota Jayapura. Tujuan dari penelitian ini adalah untuk memperkirakan dan memetakan nilai regangan geser tanah akibat kejadian gempa bumi dengan skala magnitudo M≥6.0 SR. Metode penelitian yang digunakan adalah metode pengukuran lapangan dan analisis geofisika lanjutan. Spektrum mikrotremor diukur menggunakan alat perekam seismograf. Data mikrotremor dianalisis menggunakan metode HVSR (Horizontal to Vertical Spectral Ratio) untuk mengetahui frekuensi dan periode tanah dominan, dimana nilai tersebut digunakan untuk menghitung nilai regangan geser tanah. Daerah penelitian meliputi wilayah Kota Jayapura dengan koordinat 2.0 – 4.0 Selatan dan 139,0 – 141,5 Timur. Pengukuran mikrotremor dilakukan pada 50 titik pengukuran. Gempa kontrol yang digunakan adalah 10 kejadian terpilih pada periode 1964 – 2021. Hasil penelitian menunjukkan bahwa nilai regangan geser tanah untuk terjadinya 3 gempa dengan magnitudo M≥6.00 SR memberikan hasil yang bervariasi. Gempa bumi 16 Desember 2018, pukul 09:42:37,200 GMT memberikan ukuran 4,5811 x 10-4 – 1,2990 x 10-2. Gempa 17 September 2016, pukul 01:20:17.940 GMT memberikan ukuran 1,8740 x 10-3 – 4,6295 x 10-2. Gempa 18 Januari 2020, pukul 16:38:14,301 GMT memberikan ukuran 4,4302 x 10-4 – 1,1713 x 10-2. Nilai regangan geser tanah tertinggi terjadi di Kecamatan Abepura bagian utara, sekitar Kabupaten Heram bagian tengah dan utara, serta Kecamatan Muara Tami bagian tengah. Fenomena yang mungkin terjadi berupa getaran, gelombang, subsidensi dan pemadatan tanah serta longsor.
... Lebih rinci kajian mikrotermor telah banyak digunakan untuk memperkirakan kerusakan yang timbul akibat bencana gempabumi. Kajian ini sangat tepat dan baik dalam memperkirakan tingkat resiko yang disebabkan oleh aktivitas seismik dengan kondisi geologi setempat (Nakamura, 1989). ...
Tujuan penelitian ini yaitu untuk menentukan nilai amplifikasi getaran tanah dalam kaitannya dengan frekuensi dominan tanah di Distrik Jayapura Utara, Kota Jayapura dan Menentukan nilai periode dominan tanah di Distrik Jayapura Utara, Kota Jayapura. Metode penelitian yang digunakan adalah Metode Survei Lapangan, dimana dilakukan pengukuran langsung di lapangan dengan mengunakan alat perekaman mikrotremor. Nilai frekuensi dominan, periode dominan, dan amplifikasi, akan ditentukan berdasarkan analisis rekaman sinyal mikrotremor dengan metode HVSR. Nilai frekuensi dominan, periode dominan, dan amplifikasi dengan metode HVSR akan dihitung dengan bantuan software Geopsy versi 2.0.9. Nilai amplifikasi getaran tanah maksimum 17,976800 dengan nilai frekuensi dominan tanah 0,573656 Hz berlokasi di titik JU02 (Halaman Masjid AURI Angkasapura) dan nilai frekuensi dominan amplifikasi getaran tanah minimum 1,410200 dengan frekuensi dominan 0,681167 Hz berlokasi di titik pengukuran JU17. Lokasi disekitar titik JU02 (Halaman Masjid AURI Angkasapura) lebih rawan terhadap gempabumi relatif terhadap yang lain dan lokasi di sekitar titik pengukuran JU17 (Halaman Kantor Pos Jayapura) lebih aman terhadap gempabumi relatif dibandingkan dengan lokasi yang lain. Nilai Periode dominan tanah maksimum 1,847194 s berlokasi di titik pengukuran JU12 (Bayangkara) dan periode dominan tanah Minimum 0,090822 s berlokasi disekitar titik JU02 (Bayangkara) lebih rawan terhadap gempabumi relatif terhadap yang lain dan lokasi disekitar titik pengukuran JU09 (Angkasa Lembah Sunyi) lebih aman terhadap gempabumi relatif dibandingkan dengan lokasi yang lain.
... Soil investigation campaigns carried out in Beirut and part of it suburbs in the framework of the ANR-LIBRIS project investigated 827 sites using seismic noise recordings (Brax et al., 2018;Salameh et al., 2017;Salloum et al., 2014). The soil fundamental resonance frequency (fsoil) was obtained from these recordings using the HVSR (horizontal to vertical spectral ratio) approach (Nakamura, 1989). From these measurements, interpolated maps of both the fsoil and A0HV were derived for the surveyed area ( Fig. 16 (a) and (b) respectively). ...
The estimation of seismic damages and debris at the urban scale-at a building-by-building level-is challenging for several reasons. First, commonly used methodologies for seismic damage estimation rarely take into account the local site effects, precisely at the building-level. Second, the available methods for debris estimation fail to estimate at the same time the quantity of debris generated per building according to its damage level and the distribution of the debris (extent and height) around buildings. Finally, the lack of comprehensive data on the building stock and the relevant building properties and their taxonomy further increases the complexity of assessing possible earthquake consequences at an urban scale. This paper addresses these challenges and proposes improvements to the assessment of seismic damages and debris from building-level simulations, along with the development of a 3D building model based on satellite images and heterogeneous data. These developments, 2 applied to the city of Beirut, Lebanon, highlight the control of the site effects on the seismic damage's spatial distribution throughout the city and the large volume and extent of debris to be expected in the city for a strong earthquake. Acknowledgements- We would like to thank the two anonymous reviewers for taking the necessary time and effort to review the manuscript. We also would like to thank the Centre National d'Etudes Spatiales (CNES) that kindly provided the set of very high-resolution Pleiades 1-B satellite images covering Beirut through the DINAMIS project. We also would like to thank Kamel Allaw for his contribution in the satellite images treatment.
... Finally, we also observe a reasonable agreement between predicted and measured single-site, within-event variability (φ SS ; compare vertical and horizontal error bars in Fig. 10b-e; see also Table 2). The second validation comparison was performed with local (city-scale) ground motion amplification models, available for the Swiss cities of Basel (Michel et al. 2017 here on the juxtaposition with the Basel model, which represents the soil response in terms of PSA, hence it is directly comparable with our Swiss national amplification model On the other hand, the soil response layers for Lucerne, Sion and Visp represent the amplification in the Fourier domain, so the quantitative comparison is inevitably less rigorous, and it is described in the Online Resource 3. The Basel site amplification layer (Michel et al. 2017) was obtained by cross-referencing ESM ) amplification functions at local seismic stations, validated with site-to-reference spectral ratio method (Borcherdt 1970), with a set of geophysical surveys of the subsurface and about 2200 single-station microtremor measurements processed in terms of horizontal-to-vertical spectral ratio (Nakamura 1989). The Basel model is therefore based on extensive, locally acquired geophysical datasets and it is therefore considered more reliable than the global national model issued by this study; besides, it generally achieves a higher spatial resolution. ...
The spatial estimation of the soil response is one of the key ingredients for the modelling of earthquake risk. We present a ground motion amplification model for Switzerland, developed as part of a national-scale earthquake risk model. The amplification model is based on local estimates of soil response derived for about 240 instrumented sites in Switzerland using regional seismicity data by means of empirical spectral modelling techniques. These local measures are then correlated to continuous layers of topographic and geological soil condition indicators (multi-scale topographic slopes, a lithological classification of the soil, a national geological model of bedrock depth) and finally mapped at the national scale resorting to regression kriging as geostatistical interpolation technique. The obtained model includes amplification maps for PGV (peak ground velocity), PSA (pseudo-spectral acceleration) at periods of 1.0, 0.6 and 0.3 s; the modelled amplification represents the linear soil response, relative to a reference rock profile with VS30 (time-averaged shear-wave velocity in the uppermost 30 m of soil column) = 1105 m/s. Each of these amplification maps is accompanied by two layers quantifying its site-to-site and single-site, within event variabilities, respectively (epistemic and aleatory uncertainties). The PGV, PSA(1.0 s) and PSA(0.3 s) maps are additionally translated to macroseismic intensity aggravation layers. The national-scale amplification model is validated by comparing it with empirical measurements of soil response at stations not included in the calibration dataset, with existing city-scale amplification models and with macroseismic intensity observations from historical earthquakes. The model is also included in the Swiss ShakeMap workflow.
... However, it is important to recognize that this approach falls within in a spectrum of possible analyses that support subsurface characterization efforts and have their respective merits and drawbacks. Here, we highlight five complementary, non-destructive seismic approaches able to provide subsurface constraints on the S-wave velocity profile: (1) horizontal-vertical spectral ratio (HVSR) [48]; (2) spectral analysis of surface waves (SASW) [49]; (3) multichannel analysis of surface waves (MASW) [50]; (4) SH-wave seismic refraction tomography (SH-SRT) [51]; and (5) SRT+E-FWI presented herein. ...
Seismic characterization of landslides offers the potential for developing high-resolution models on subsurface shear-wave velocity profile. However, seismic methods based on reflection processing are challenging to apply in such scenarios as a consequence of the disturbance to the often well-defined structural and stratigraphic layering by the landslide process itself. We evaluate the use of alternative seismic characterization methods based on elastic full waveform inversion (E-FWI) to probe the subsurface of a landslide complex in Majes, southern Peru, where recent agricultural development and irrigation activities have altered the hydrology and groundwater table and are thought to have contributed to increased regional landslide activities that present continuing sustainability community development challenges. We apply E-FWI to a 2D near-surface seismic data set for the purpose of better understanding the subsurface in the vicinity of a recent landslide location. We use seismic first-arrival travel-time tomography to generate the inputs required for E-FWI to generate the final high-resolution 2D compressional- and shear-wave (P- and S-wave) velocity models. At distances greater than 140 m from the cliff, the inverted models show a predominantly vertically stratified velocity structure with a low-velocity near-surface layer between 5–15 m depth. At distances closer than 140 m from the cliff, though, the models exhibit significantly reduced shear-wave velocities, stronger heterogeneity, and localized shorter wavelength structure in the top 20 m. These observations are consistent with those expected for a recent landslide complex; however, follow-on geotechnical analysis is required to confirm these assertions. Overall, the E-FWI seismic approach may be helpful for future landslide characterization projects and, when augmented with additional geophysical and geotechnical analyses, may allow for improved understanding of the hydrogeophysical properties associated with suspected ground-water-driven landslide activity.
... tremors, a few minutes of seismic background noise must be recorded. For a single station, the researchers calculate the spectral ratio of the horizontal and vertical components of the microtremor measurement. The generated curves identify a frequency that is thought to fit remarkably with the place under study's S-wave resonance frequency. Later, Nakamura. (1989) improved this method, arguing that due to the main body wave character of the noise, this HVSR is a trustworthy evaluation of the site transfer function for S-waves with regard to bedrock. Numerous studies conducted in recent years have demonstrated that the H/V ratio of a microtremor is much more stable than the raw noise spectrum and ...
Many people are killed by landslides due to earthquakes or severe rain, and structures and facilities built on or near slopes sustain significant damage. Such landslides on naturally occurring slopes can be large enough to utterly destroy towns or communities. Based on remote sensing and microtremor data, the area around Al Taif has been evaluated for its susceptibility to landslides. Digital elevation model (DEM), slope angle, and slope aspect thematic layers were used to depict remote sensing data. The landslide susceptibility was extracted from remote sensing thematic data. The elevations of the Al Taif area, which range from 832 to 2,594 m amsl, were identified based on the DEM. Al Taif’s slope angles range from 0° to 67.3° degrees. Nearly flat (0° to 4.75°), moderate (4.75° to 11.1°), steep (11.2° to 29.1°), and very steep slope (≤29.1°) are the different classifications for the slope. Additionally, measurements of the microtremor have been taken at 42 locations throughout the region. The horizontal-to-vertical spectral ratio (HVSR) approach was used to process and analyze microtremor data in order to determine the resonance frequency and H/V amplification factor. The findings show that, while the amplification factor varies from 1.17 to 9.28, the dominant frequency values fall between 0.3 and 12.75 Hz. To determine the frequency, amplitude, and azimuthal site response, 11 sites were eventually chosen. Furthermore, the direction of the site response in the sliding areas was parallel to the landslide directional response, indicating that the site response direction tracked the landslide direction. Practical approval of the study’s findings has been given at a number of locations by field measurements at some of the Taif urban area’s most recent landslide occurrence areas. These findings show that the integration between remote sensing and microtremor measurements is a useful tool for pinpointing landslide-prone areas, which helps to lessen the danger to people’s lives and property. This susceptibility zonation applied to the Al Taif area has produced a good match between the distribution of the reported landslides and the zones of high susceptibility. To define the general trend and geographic distribution of potentially unstable slopes and landslide potential zones, this study’s findings must be used as a guide.
... Also, the single-station approach, which involves estimating site-response from S waves recorded on the horizontal component and on the vertical component at a single site, has been used with success in some locations (e.g., Lermo and Chávez-García, 1993). Use of this technique, popularized by Nakamura (1989) who used recordings of microtremors, involves calculating the ratio of horizontal-to vertical-component amplitude spectra (HVSR) and assumes the vertical-component approximates reference-site horizontal ground motions. ...
Earthquake S waves can become trapped, or resonate, between the free surface and high-impedance basal layers, strongly contributing to site response at specific frequencies. Strong S-wave resonances have been observed in the central and eastern U.S., where many sites sit on unlithified sediments underlain by stiff bedrock. To evaluate S-wave resonances in this region, we calculated 1D linear site-responses at 89 seismic stations with developed S-wave velocity profiles into bedrock. We found that S-wave resonances at the fundamental and strongest (peak) modes occur across large ranges of frequencies, each spanning more than two orders of magnitude — 0.21–54.0 Hz and 0.29–71.5 Hz, respectively. Amplifications of ∼5 and ∼6 are common at the fundamental frequency and peak modes, respectively; the largest amplification calculated was 13.2. Using simple regression analyses, we evaluated the skills of six proxies derived from the S-wave velocity profiles to predict the frequencies and corresponding amplifications of the fundamental and peak modes. We found that the depths to the 1.0 km/s and 2.5 km/s horizons, consistent with other studies, and to the maximum impedance contrasts strongly correlate with the resonance frequencies and that the fundamental-mode and peak amplifications correlate with the maximum impedance ratios. Correlations improved for data subsets based on the number and magnitude of impedance ratios underlying the sites and are the strongest at sites underlain by a single impedance ratio of 3.0 or greater. Finally, we calculated the S-wave horizontal-to-vertical spectral ratios (HVSR) at each possible seismic station and found, consistent with other studies, that the first peak can be used to estimate fundamental-mode frequencies and the corresponding amplifications. Thus, S-wave HVSR, can provide useful estimates of the fundamental-mode linear site response parameters at sites lacking S-wave velocity profiles. Furthermore, S-wave HVSR curves appear to be useful to broadly categorize impedance-ratio profiles.
... The dominant frequency value of the soil and the amplification factor is used to make a vulnerability map. The HVSR method was first described by Nogoshi and Igarashi (Nogoshi & Igarashi, 1971), and was widely introduced by Nakamura (Nakamura, 1989), so this method is commonly known as Nakamura's technique : ...
... Another approach to estimating the site characteristics is the horizontal-to-vertical spectral ratio computed from ASF, also known as the H/V method (Nakamura 1989 ). Subsurface elastic property contrasts along depth can have a significant impact on the resonant frequency (represented by the H/V peak frequency), making H/V anal ysis highl y sensiti ve to identifying the depth of the impedance contrasts. ...
The Granada Basin in southeast Spain is an area of moderate seismicity. Yet, it hosts some of the highest seismic hazards in the Iberian Peninsula due to the presence of shallow soft sediments amplifying local ground motion. In urban areas, seismic measurements often suffer from sparse instrumentation. An enticing alternative to conventional seismometers is the Distributed Acoustic Sensing (DAS) technology that can convert fiber-optic telecommunication cables into dense arrays of seismic sensors. In this study, we perform a shallow structure analysis using the ambient seismic field interferometry method. We conduct a DAS array field test in the city of Granada on the August 26th and 27th, 2020, using a telecommunication fiber. In addition to the existing limitations of using DAS with unknown fiber-ground coupling conditions, the complex geometry of the fiber and limited data recording duration further challenge the extraction of surface-wave information from the ambient seismic field in such an urban environment. Therefore, we develop a processing scheme that incorporates a frequency-wavenumber (f − k) filter to enhance the quality of the virtual shot gathers and related multi-mode dispersion images. We are able to employ this dataset to generate several shear-wave velocity (VS) profiles for different sections of the cable. The shallow VS structure shows a good agreement with different geological conditions of soil deposits. This study demonstrates that DAS could provide insights into soil characterization and seismic microzonation in urban areas. In addition, the results contribute to a better understanding of local site response to ground motion.
... Rayleigh waves will propagate most effectively in which frequency range is defined as the dominant frequency (fo) [8]. This technique, have been extensively studied by many researchers to measure the site effects such as amplification, ambient noise produced by soft ground layers in certain frequency bands [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Soil behavior analysis depends not only on the geomorphology and properties of the subterranean soil layers, but also on the bedrock type and location. ...
It is very important and necessary to know the depth of the bedrock in determining the soil behavior. However, determining the depth of bedrock spatially is a very difficult and costly process. The depth of the bedrock can be obtained by using the dominant vibration frequency obtained by the microtremor data. The bedrock depth map was created with the correlation produced from the dominant vibration frequencies obtained from microtremor measurements made in Antakya (Turkey). In bedrock calculations at low frequencies, the value range shows scattering. In the vulnerability analysis for Antakya soils, a low level of vulnerability (Kg = 6) was obtained in the east and northeast of the area. It has been observed that the S-wave velocity (Vs) in this area is lower than 406 ms-1. In this case, this value has been accepted as the vulnerability threshold value in Antakya soils. Peak Ground Acceleration (PGA) and Peak Ground Velocity (PGV) were obtained for each location by using earthquake ground motion levels with 2%, 10%, 50%, and 68% probability of exceedance in 50-year periods. The PGA values in the region range from 0.43 to 0.47 g for earthquakes with a return period of 475 years.
... The is the ratio of the of horizontal ground motion [ ] to that of vertical ground motion [ ] recorded at the same location (Eq. 9), which can be used to estimate site effects (Borcherdt, 1970;Nakamura, 1989 there is no site ampli cation for vertical ground motions. Thus, the HVSR was most applicable for sites located on rock and rm soil sites because the site ampli cation on these sites was small. ...
In low to moderate seismic regions such as the Korean peninsula, it is difficult to perform seismic hazard analyses to construct hazard maps and curves because only a limited number of strong ground motion records is available. In this study, to solve such obstacles, ground motions were simulated using a model with a GIT-based spectral decomposition algorithm. The algorithm was adopted to determine the constituent parameters (source effect, path effect, site effect) of the Fourier amplitude spectrum ( FAS ) while considering Korea’s seismological characteristics. The accuracy of the GIT-based spectral decomposition algorithm for FAS and the ground motion simulation (GMS) model with the calculated FAS values was verified.
... The Horizontal to Vertical Spectral Ratio method is used to estimate the resonant frequency of soft sediments on top of the bedrock. The method was originally proposed by Nogoshi and Igarashi (1971), and further developed by Nakamura (1989). It consists of estimating the ratio between the Fourier amplitude spectra of the horizontal (H) and vertical (V) components of the ambient seismic noise vibrations recorded by one single seismometer (e.g., Lermo and Chavez-Garcia, 1993;Lunedei and Malischewsky, 2015;Sánchez-Sesma, 2017). ...
In order to estimate well-constrained seismic hazard and risk on local scales, the knowledge of site amplification factors is one of several important requirements. Seismic hazard studies on national or regional scales generally provide the level of earthquake shaking only at bedrock conditions, thereby avoiding the difficulties that are caused through local site effects. Oftentimes, local site conditions are not well understood or even non-existent. In this study we investigate an efficient and non-invasive methodology to derive the local average shear wave velocity in the uppermost 30 m of the ground (Vs30). The Vs30 value is a useful parameter to define soil classes and soil amplification used in seismic hazard assessment and to extend the knowledge of the site to include the depth to basement rock. At the level of the municipality of Oslo, there is currently no map available that describes the Vs30, and as such any seismic risk study is lacking potentially critical information on local site amplification. The new proposed methodology includes the use of existing well databases (with knowledge on minimum basement depth), topographic slope derived from Digital Elevation Models (as a proxy for both depth to basement and Vs30, integrated with geological maps) and near-surface Quaternary geological maps. The Horizontal to Vertical Spectral Ratio (HVSR) method and a statistics-based geological mapping tool (COHIBA) are used to integrate the various sources of data estimates. Finally, we demonstrate our new methodology and workflow with data from three different regions within the Oslo municipality and propose an approach to conduct cost-efficient mapping for seismic site amplification on a general municipality scale.
... This has been indirectly considered a random Frontiers in Earth Science frontiersin.org 06 variable by using the following relationship proposed in Nakamura (1989): ...
At certain depths, the elastic properties of the ground are not affected by seismic waves. However, as they reach the surface, the soil density decreases and so does its elastic limit. This means that the expected ground motion acting at the foundation of a structure cannot be adequately described without considering the inelastic response of the soil near the surface. Therefore, one of the key elements in characterizing the seismic response of civil structures is the site effect. These depend mainly on the parameters of the soil beneath the structure and the features of the ground motion acting at the depth, where non-linear effects are negligible. Therefore, the main objective of this paper is to find an intensity measure that incorporates the information provided by the soil profile under the structure and the ground motion acting at the bedrock level. Due to the random nature of both elements, a probabilistic framework using Monte Carlo simulation has been developed to analyze this problem. For this purpose, random soil profiles have been generated to obtain a representative sample of likely scenarios of the study area. A large database of Colombian ground motion records has been used to model the seismic hazard. Finally, power functions capable of relating the input variables to the dynamic response of a large set of reinforced concrete structures have been derived by considering multi-regression analysis. It has been observed that, in several cases, intensity measures extracted from the displacement spectrum appear in the mathematical arrangements. These functions could be used to improve the efficiency of seismic risk prediction at the urban level.
... A utilização de técnicas não invasivas, simples e de baixo custo é a abordagem atualmente adotada na caracterização dos terrenos e estudos de microzonagem sísmica. Estas técnicas baseiam-se no registo de ondas superficiais, como o método MASW (Multichannel Analysis of Surface Waves) (Park et al., 1999) e ReMi (Refraction Microtremor) (Louie, 2001), ou registo de vibrações ambientais, como a técnica HVSR (Horizontal-to-Vertical Spectral Ratio) (Nakamura, 1989). A compatibilidade dessas técnicas e a complementaridade com outras informações dão robustez à avaliação dos efeitos de sítio e a caracterização dos terrenos. ...
Para uma caracterização adequada dos terrenos é fundamental a realização de ensaios sísmicos, que permitem estimar as propriedades dinâmicas das camadas superficiais, nomeadamente a velocidade das ondas de corte (VS). Associando a variação de VS em profundidade às características litoestratigráficas do local, é possível caracterizar o perfil de terreno e o VS associado a cada formação geológica. De forma a colmatar a falta de informação devido aos poucos ensaios geofísicos disponíveis na cidade, foram realizados ensaios sísmicos de superfície em áreas-chave. Foi criada uma base de dados geofísicos onde foram compilados todos os resultados de ensaios sísmicos realizados em Lisboa, efetuando-se uma análise exaustiva da variação de VS em profundidade. Foi feita uma análise de regressão linear e definida uma expressão que descreve a variação de VS em profundidade para cada formação geológica da cidade. Esta análise baseia-se no agrupamento por formação geológica dos valores pontuais de velocidade da onda S, considerando as informações litoestratigráficas de sondagens geotécnicas próximas dos ensaios sísmicos. Também foi realizada uma análise estatística para avaliar a fiabilidade de cada regressão linear. A aplicação a Lisboa da abordagem descrita leva à caracterização das formações geológicas da cidade em termos de VS e visa contribuir para a nova classificação dos terrenos do EC8 baseada nos parâmetros VS,H, f0 e H800.
... A geophysical campaign based on the HVSR technique (Horizontal to Vertical Spectral Ratio, Nakamura, 1989) was carried out to detect the boundary between marine and continental deposits (IMO-AEI limit in Fig. 2) and support the stratigraphic analysis. HVSR measurements provide an estimate of site resonant frequencies that are a function of subsurface geology (Castellaro and Mulargia, 2009;Choobbasti et al., 2013;Moisidi et al., 2015;Martorana et al., 2017;Akkaya and Ö zvan, 2019). ...
... Among the available surface wave methods, the microtremor horizontal-tovertical spectral ratio (HVSR) technique has gained popularity due to its ease of use in field measurements. The spectral ratio can be calculated from horizontal and vertical components of microtremor records at a single station for site amplification [13]. The possibility of utilizing the microtremor HVSR to estimate S-wave velocity profiles was first investigated by Nogoshi and Igarashi [14] based on the similarity between the HVSR and the ellipticity of the fundamental mode Rayleigh wave. ...
We propose a simple method for 1D S-wave velocity (Vs) profile estimation using a measured surface S-wave velocity (V1) and peak frequency of the observed microtremor horizontal-to-vertical spectral ratio (HVSR). In this method, the S-wave velocity profile is presented as linear velocity increase with depth in sediments over a bedrock layer that has a given constant S-wave velocity. Thus, the profile can be parameterized with the measured surface S-wave velocity and the velocity gradient. The gradient can be estimated based on the agreement of the peak frequencies of the observed microtremor HVSR and the theoretical ellipticity of the fundamental mode of the Rayleigh wave. We examined the applicability of the proposed method using numerical tests as well as application to actual data at five sites in the Bandung Basin, Indonesia, where observed Rayleigh wave phase velocities from microtremor array surveys were available. The applicability was confirmed in numerical tests using sample models of soil profiles in the basin. Actual application indicated the appropriateness of the estimated S-wave velocity profiles due to the similarity of their theoretical Rayleigh wave phase velocities with the observed Rayleigh wave phase velocities. Since the proposed method needs prior confirmation of the linear increase of the S-wave velocity, it is suitable for use in spatial interpolation of shallow S-wave velocity profiles with simple data acquisition.
... In the first one, the peaks of amplitude spectra can be considered as the peaks of the vertically propagating, horizontally polarized shear-wave (SH wave) transfer function. For the simple case of an isotropic layer over an isotropic half-space, these peaks occur at resonance frequencies ( f n ) of the SH wave transfer function Nakamura (1989Nakamura ( , 2000 f n = (2n + 1) V S H 4h , (n = 0, 1, 2, . . . ) ...
In this study, non-principal waves propagating in an isotropic elastic half-space covered by an orthotropic layer are examined. The main objective is to establish a formula for the SH transfer function induced by an vertically incident SH wave and a formula for the H/V ratio of surface waves. The peak frequencies of both the SH transfer function and the H/V ratio curve are examined for models with low to high impedance contrasts to verify the applicability of the quarter wave-length rule for both SH body waves and surface waves. It is numerically shown that the quarter wave-length rule applies well for non-principal SH body wave. Non principal surface waves are shown to be a composition of Love and Rayleigh waves, and their peaks follow the quarter wave-length rule only in the case of high impedance contrast. For medium or low impedance contrasts, the peak frequencies of surface waves could differ from the peak frequencies of SH body wave with relative differences up to 50%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$50\%$$\end{document}.
... The concept of utilizing HVSR for medium structure inversion was originally presented by Boore et al. (1969), which is a viable approach for field measurements. Nakamura (1989) proposed and promoted HVSR based on the vector characteristics of microtremor. After numerous investigations, the feasibility of using HVSR method for site measurements has been verified (e.g., Mark et al., 1975;Sexton et al., 1977;Lermo et al., 1994;Tanimoto and Alvizuri, 2006;Ferreira et al., 2007). ...
In recent years, engineering examples have shown that traditional surface-wave detection methods are easily limited in areas with small space and heavy traffic. The horizontal-to-vertical spectral ratio survey method has become increasingly prevalent in site measurements and is favored by geophysicists for its ability to detect near-surface velocity structures with greater sensitivity than phase velocities. Based on the phase difference method and polarization filtering, we proposed a passive seismic ellipticity method. The objective of this method is to extract the Rayleigh waves from ambient noise recordings and the analysis of ellipticity dispersion characteristic. This method was applied to an actual case study. Specifically, the velocity dispersion profile of the site is obtained using the active-source surface-wave method. Then, we compared the results obtained by the passive seismic ellipticity method with those obtained by the active-source surface-wave method and the field data, to evaluate the accuracy of results. The results demonstrate that the proposed method can effectively detect the location of subsurface shield tunnels and has the characteristics of simple data processing steps, less interference, and high stability of results. This demonstrates the necessity of using the phase difference method to select segments dominated by Rayleigh waves in ambient noise recordings and applying polarization filtering before calculating ellipticity. The paper provides an actual case study for the application and promotion of the passive seismic ellipticity method and has significant practical value and reference significance.
Laterite weathering profile (LWP) thicknesses are functions of precipitation rate and time, but their exact dependence on them is uncertain. We investigate LWP development on ground surfaces in Hawai'i that are neither aggrading nor eroding across substrates from 0.01 to 4 Ma and rainfall rates of <250 to >3000 mm/a. The Hawaiian Islands provide an excellent opportunity for LWP studies across climates and over millions of years on a single rock type, basalt. LWP weathering rates are usually determined by geochemical approaches. We present a geophysical method once bedrock ages and precipitation rates are known. We employed multichannel analysis of surface waves and horizontal‐to‐vertical spectral ratio methods. Results indicate that >70% of the variability in LWP thickness is due to precipitation and bedrock age. The remainder is attributed to measurement uncertainty and heterogeneity in the permeability of basalt. LWPs develop by two paths. Dry (<1000 mm/a) areas have a negative water balance with evapotranspiration exceeding rainfall. LWPs thicken until they reach a steady state where the storage capacity of the saprolite precludes the percolation of water into subjacent lava. In wetter areas, downslope interflow produces thick laterite wedges near coastlines that migrate upslope over ~1 Ma. Subsequently, they thicken and reach a steady state where precipitation cannot deliver water through the vadose zone. LWPs' thickness ( T ) increases as a function of time ( t ) and precipitation ( P ) according to the expression (95% confidence): . The first partial derivative, or weathering rate, is . Weathering rates decrease with time and are strong functions of t and P . These expressions add considerable insight into the rates and processes driving weathering at large scales and can also be solved for t , giving a rough estimate of the time of landscape formation of eroded surfaces.
An important application of the multichannel surface wave (MASW) method is seismic safety assessment. The key parameters in the calculation of increments in the input of seismic microzoning are the thickness and average velocity of the soil mass lying on the base of more rigid rocks. To determine these parameters, we propose a new method for constructing horizontally layered models of the upper part of the geological section using the features (positions of extrema of the second derivative) of the dispersion curves of phase velocities of the Rayleigh surface wave, which, as shown by numerical experiments, are associated with the position of contrasting boundaries in the medium under study. (e.g., the boundary between soils and rocks). This approach is much simpler than the problem of recovering a horizontally layered model traditionally solved in the MASW method from a set of phase velocities for a sequence of frequencies and does not require an initial approximation and/or any restrictions on the possible values of the model parameters. In the case of two-layer and three-layer media, our approach is reduced to a simple and fast application of explicit formulas.
We investigate the effects of site response on source parameter estimates using earthquakes recorded by the LArge‐n Seismic Survey in Oklahoma (LASSO). While it is well known that near‐surface unconsolidated sediments can cause an apparent breakdown of earthquake self‐similarity, the influence of laterally varying site conditions remains unclear. We analyze site conditions across the 1825‐station array on a river plain within an area of 40 km by 23 km using vertical ground motions from 14 regional earthquakes. While the source radiation pattern controls P‐wave ground motions below 8 Hz, the surface geology correlates with P‐wave ground motions above 8 Hz and S‐wave ground motions at 2 – 21 Hz. Stations installed in alluvial sediments have vertical ground motions that can exceed three times the array median. We use the variation of ground motion of regional earthquakes across the array as a proxy for site effects. The corner frequencies and stress drops of local earthquakes ( M L = 0.01 – 3) estimated using a standard single‐spectra approach show negative correlations with the site‐effect proxy, while the seismic moments show positive correlations. In contrast, the spectral‐ratio approach effectively shows no correlation. The overall bias is small as expected for this relatively homogeneous structure; accurate estimation of site‐related biases requires at least 30 stations. Correcting for site‐related biases reduces the standard deviations of the source parameters by less than 13% of the total variations. Remaining variations are partially associated with source directivity and model misfits— as small earthquakes can have complex ruptures.
This article is protected by copyright. All rights reserved.
Seismic hazard assessment is a process that involves extensive geological, geophysical and geotechnical studies of a region where such studies are required. In such an endeavour, we need to model three main contributing factors, source, path and site effects. The passive geophysical techniques play a significant role in providing important inputs for modelling source, path and site effects. The main advantages of geophysical techniques are that they are mostly non-destructive, efficient, cost-effective and well-proven in the last 50 years. Geophysical techniques such as Gravity and Magnetotelluric (MT) contribute largely to the detection and characterization of possible local seismic faults, both, exposed and blind, in other words, characterization of the source. It is found that near surface shear-wave velocity helps in estimating the local site effect. Mostly, shallow geophysical surveys like multi-channel analysis of surface waves (MASW) or down-hole/up-hole/cross-hole surveys constrain the shear-wave velocity. Time-domain electromagnetic (TDEM), resistivity imaging and microtremor techniques are becoming popular in constraining structures up to few hundred of metres. The MASW surveys are implemented for obtaining 1D and 2D models of shear-wave velocities at a site in microzonation and site-specific studies. The microtremor is another geophysical technique that was earlier used to map predominant periods of a site under investigation, is now actively used to obtain 1D and 2D structures up to a few hundred metres by modelling horizontal-to-vertical ratio (HVSR) curves. The use of geophysical methods in resolving the dips of major active faults and segregation of major lithological units in the Kachchh rift is provided as case study. The integrated geophysical approach is also discussed in resolving the depth of engineering bed layer in Ahmedabad.KeywordsSeismic microzonationMulti-channel analysis of surface wavesMicrotremorTime-domain electromagneticMagnetotelluric
Near‐surface seismic structure, particularly the shear wave velocity ( V s ), can strongly affect local site response, and should be accurately estimated for ground motion prediction during seismic hazard assessment. The Imperial Valley (California), occupying the southern end of the Salton Trough, is a seismically active basin with thick surficial lacustrine sedimentary deposits. In this study, we utilize ambient noise records and local earthquake events for high‐resolution near‐surface characterization and site effect estimation with an unlit fiber‐optic telecommunication infrastructure (dark fiber) in Imperial Valley by using the distributed acoustic sensing (DAS) technique. We apply ambient noise interferometry to retrieve coherent surface waves from DAS records, and evaluate performances of three different surface wave methods on DAS ambient noise dispersion imaging. We develop a quality control workflow to improve the dispersion measurement of noisy portions of the DAS dataset by using a data selection strategy. Using the joint inversion of both the fundamental mode and higher overtones of Rayleigh waves, a high resolution two‐dimensional (2D) V s structure down to 70 m depth is obtained. We successfully achieve an improved V s 30 (the time‐averaged shear‐wave velocity in the top 30 m) model with higher spatial‐resolution and reliability compared to the existing community model for the area. We also explore the potential for utilizing DAS earthquake events for site amplification estimation. The preliminary results reveal a clear anti‐correlation between the approximated site response and the V s 30 profile. Our results indicate the potential utility of DAS deployed on dark fiber for near‐surface characterization in appropriate contexts.
Kappa (the high-frequency spectral decay slope at near-source distances; often referred to as κ0) is determined at 25 seismograph stations in Eastern Canada using broadband ground-motion modeling approaches. The database comprises Fourier spectra (effective amplitude spectrum for the horizontal component and the vertical component, 0.8–40 Hz) computed from 3318 earthquakes of moment magnitude M 1.5–5 recorded on stations within 150 km. Average kappa values for bedrock sites, having shear-wave velocities from 850 to 2400 m/s, are highly variable, ranging from −29 to +21 ms (horizontal) and −28 to +11 ms (vertical), but appear on average to be near-zero. The values obtained are sensitive to methodology, especially the necessary adjustments to the spectra to account for site amplification effects. Kappa values do not appear to correlate well with site parameters such as rock shear-wave velocity, average shear-wave velocity in the upper 30 m, primary wave velocity, site class, type and age of rock, or instrument housing. This lack of correlation may reflect the noted sensitivities to methodological factors. We conclude that kappa values in rock environments are not reliably estimated from such proxies and should be determined from recorded ground motions at a given location. On average, there is little evidence of significant high-frequency attenuation on rock sites beyond that already accounted for in ground-motion modeling by the empirical parameterization of regional Q-related path effects.
Human activities cause seismic noise over 1 Hz (cultural noise), and the recent articles have reported that the curtailing of socioeconomic activities during the novel coronavirus (COVID-19) pandemic in 2020 appeared to reduce high-frequency seismic noise amplitudes in cities. The Tokyo metropolitan area in Japan, where seismic stations are densely distributed and various anthropogenic activities have been closely monitored, is an ideal study area to investigate the effect of human activity on high-frequency seismic noise during the pandemic. We demonstrated that the magnitude of seismic data traffic (SDT), indexed by the packet size of continuous seismic data in WIN32 format, is a good indicator for monitoring time-dependent changes in high-frequency noise levels. The SDT of 169 Metropolitan Seismic Observation network (MeSO-net) stations—a continuous accelerometer network that is mostly located at schools in the Tokyo metropolitan area—decreased by approximately 1%–3% from March to June 2020, when a state of emergency in Japan was first declared, compared with that in the previous year. We revealed that the SDT decrease was prominent only at stations near school buildings, and the SDT trend was uncorrelated with the temporal changes in the population and vehicular traffic volume near the seismic stations. We also found strong correlations between the SDT reduction and school size (classified by the number of students enrolled), implying that the noise decrease at the MeSO-net stations during the pandemic was strongly influenced by school-based activities. Thus, the noise reduction observed at MeSO-net stations during the COVID-19 pandemic in 2020 did not provide strong evidence of quieting in the Tokyo metropolitan area.
Bengkulu City in Indonesia is one of the areas prone to earthquakes, yet it has developed increasingly in the last five years. One of the prospective areas in Bengkulu City, called Singaran Pati, is located close to the Dendam Tak Sudah Lake, a natural tropical lake. This research aims to interpret geological characteristics for the spatial plan development in the study area. Microtremor measurement and site investigation are implemented to observe the geophysical and geological characteristics of the study site. Inversion analysis using Monte Carlo simulated annealing is conducted to generate a shear wave velocity profile. Based on the shear wave velocity, the identified bedrock surface is illustrated in a 3D geological model. A simple analysis of the natural period to estimate allowable structural building storeys is also performed. Results show that the depth of the bedrock surface is around 4.5–147 m. The study area is dominantly categorised as Site Classes C and D. Low- to medium-rise buildings are appropriate to construct based on the geophysical and geotechnical information. The findings can provide preliminary guidelines on geotechnical and geological information for the seismic site conditions in the study area in Bengkulu City.
In the present study, 1991 Uttarkashi (M 7) and 1999 Chamoli (M 6.6) earthquakes that occurred on October 19, 1991, at 21:23:14 h and March 28, 1999, at 19:05:11 h, respectively, have been simulated using the modified hybrid technique. Hybrid technique is the combination of two existing techniques, i.e., envelope technique and composite source model technique. In the present modified technique, site amplification functions and kappa factor have also been incorporated. The simulated waveforms and their corresponding response and Fourier spectra for each site have been generated. In this study, simulation has been done at 11 and 9 recorded stations of Uttarkashi and Chamoli earthquakes, respectively. Important frequency- and time-domain parameters, i.e., Fourier spectra, response spectra, peak ground acceleration (PGA) and duration at stations, have been estimated and compared with the observed accelerograms. It has been observed that the simulated PGA (231 cm/s2) at the closest distance Bhatwari (22 km) matched with the observed one (248 cm/s2) for the Uttarkashi earthquake. The same has been observed at the nearest most station Gopeshwar (19 km) of the Chamoli earthquake. The simulated PGA (347 cm/s2) for this station has been found well matched with the observed PGA value (352 cm/s2). Similar matching has been observed for other stations also. The present technique is independent of velocity-Q structure of earth’s layered model and past events data of small earthquakes. This study brings light on the site effect and high-frequency decay parameter. This study can be very helpful in the estimation of seismic hazard in a specific region and designing earthquake-resistant buildings.
The main objective of this research is to investigate the use of horizontal-to-vertical spectral ratio (HVSR) measured from ambient vibrations for predicting site response using artificial
neural networks (ANNs). The entire spectrum (amplitudes of all frequencies) of HVSR is used as a predictor variable in the model. Artificial neural network models are developed and then
optimized through hyperparameter tuning. The developed models have been assessed based on the standard deviation of the residual terms and how these residuals compare with the
corresponding values in ground motion models based on traditional regression approaches. It has been observed that the ANN models improve the prediction of site response as evidenced by the reduction in the uncertainty (about 10% at short periods) in the site-to-site variability.
ResearchGate has not been able to resolve any references for this publication.