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

2020 ◽  
Vol 17 (5) ◽  
pp. 861-869 ◽  
Author(s):  
Su Young Kang ◽  
Kwang-Hee Kim ◽  
Jer-Ming Chiu ◽  
Lanbo Liu
Keyword(s):  
South Korea ◽  
Risk Mitigation ◽  
Three Dimensional ◽  
Spectral Ratio ◽  
Velocity Model ◽  
The North ◽  
Impedance Contrast ◽  
Resonance Frequencies ◽  
Single Station ◽  
Hvsr Method

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

Estimation of Site Dynamic Characteristics from Ambient Noise Measurements Using HVSR Method in Microzonation Study: Senggarang, Batu Pahat, Malaysia

2014 ◽  
Vol 931-932 ◽  
pp. 803-807 ◽  
Author(s):  
Ahmad Fahmy Kamarudin ◽  
Mohd Effendi Daud ◽  
Zainah Ibrahim ◽  
Ibrahim Azmi ◽  
Mohamad Khairani Yub ◽  
...  
Keyword(s):  
Dynamic Characteristics ◽  
Ambient Noise ◽  
Hazard Analysis ◽  
Resonance Effect ◽  
Spectral Ratio ◽  
Boundary Area ◽  
Contour Maps ◽  
The North ◽  
Hvsr Method ◽  
Noise Measurements

Site dynamic characteristics evaluation of fundamental ground frequency, Fo and amplification factor, Ao in Senggarang region were presented in 2D and 3D contour maps (microzonation maps) based on the ambient noise measurements carried out using Lennartz 1 Hz tri-axial seismometer sensors. Reliability of Fo and Ao determined from the ambient noise technique has become the main key components in seismic hazard analysis, resonance effect assessment, predictions of sedimentary layer and shear wave velocity, through cheaper, non-destructive and quick methodology. 73 points of ambient noise records were analyzed using Horizontal-to-Vertical Spectral Ratio (HVSR) method in the boundary area of 800 m x 800 m with the grid spacing of 100 m x 100 m. Significant peaks of mean HVSR curves were checked against the criterions proposed by the SESAME guideline. Slight difference of the Fo contours pattern between the North-South (NS) and the East-West (EW) directions was observed, but vice versa to the Ao contours between both directions. Significant peaks of Fo values were distributed from 1.61 to 6.35 Hz, whereas the Ao values were found from 3.18 to 9.39. Wide gap between the ranges of Fo and Ao in respective direction have shown to the variation of sediment thicknesses. Meanwhile, dominance shape of significant peak from the HVSR curves may indicate to a large velocity contrast presence underneath the ground surfaces.

scholarly journals Study on the applicability of microtremor HVSR method to support seismic microzonation in the town of Idrija (W Slovenia)

2017 ◽  
Author(s):  
Andrej Gosar
Keyword(s):  
Seismic Hazard ◽  
Resonance Frequency ◽  
Complex Geometry ◽  
Free Field ◽  
Seismic Refraction ◽  
Spectral Ratio ◽  
Seismic Microzonation ◽  
Clear Correlation ◽  
Resonance Frequencies ◽  
Hvsr Method

Abstract. The Idrija town is located in area with increased seismic hazard in W Slovenia and is partly built on alluvial sediments or artificial mining and smelting deposits which can amplify seismic ground motion. There is a need to prepare a comprehensive seismic microzonation in the near future to support seismic hazard and risk assessment. To study the applicability of microtremor Horizontal-to-Vertical Spectral Ratio (HVSR) method for this purpose, 70 free-field microtremor measurements were performed in 0.8 km2 large town area with 50–200 m spacing between points. HVSR analysis has shown that it is possible to derive sediments resonance frequency at 48 point, whereas at remaining one third of measurements nearly flat HVSR curves were obtained indicating small or no impedance contrast with the seismological bedrock. Iso-frequency (range 2.5–19.5 Hz) and HVSR peak amplitude (range 3–6, with few larger values) maps were prepared by using natural neighbour interpolation algorithm and compared with the geological map and map of artificial deposits. Surprisingly no clear correlation was found between distribution of resonance frequencies or peak amplitudes and the known extent of supposed soft sediments or deposits. This can be explained by relatively well compacted and rather stiff deposits and complex geometry of sedimentary bodies. However, at several individual locations it was possible to correlate the shape and amplitude of the HVSR curve with the known geological structure and prominent site effects were established in different places. On the other hand, in given conditions (very limited free space and high level of noise) it would be difficult to perform active seismic refraction or MASW measurements to investigate the S-waves velocity profiles and thickness of sediments in details, which would be representative enough for microzonation purposes. The importance of microtremor method is therefore even greater, because it enables direct estimation of the resonance frequency without knowing the internal structure and physical properties of the shallow subsurface. The results of this study can be used directly in analyses of possible occurrence of soil-structure resonance of individual buildings, including important cultural heritage mining and other structures protected by UNESCO. Second application of the derived free-field iso-frequency map is to support soil classification according to the recent trends in building codes.

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

2021 ◽  
Vol 226 (1) ◽  
pp. 1-13
Author(s):  
Alexis Rigo ◽  
Efthimios Sokos ◽  
Valentine Lefils ◽  
Pierre Briole
Keyword(s):  
Soil Moisture ◽  
Wave Velocity ◽  
Maximum Amplitude ◽  
Spectral Ratio ◽  
Vertical Surface ◽  
Sediment Layer ◽  
S Wave ◽  
Surface Displacements ◽  
Resonance Frequencies ◽  
Hvsr Method

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

Detecting 1-D and 2-D ground resonances with a single-station approach

2020 ◽  
Vol 223 (1) ◽  
pp. 471-487
Author(s):  
Giulia Sgattoni ◽  
Silvia Castellaro
Keyword(s):  
Site Response ◽  
Spectral Ratio ◽  
Response Assessment ◽  
Sediment Layer ◽  
Resonance Frequencies ◽  
Single Station ◽  
Bedrock Depth ◽  
Lateral Width ◽  
A Site ◽  
Resonance Nature

SUMMARY The vibration modes of the ground have been described both in the 1-D and 2-D case. The 1-D resonance is found on geological structures whose aspect ratio is low, that is on layers with a lateral width much larger than their thickness. A typical example is that of a horizontal soft sediment layer overlying hard bedrock. In this case, the 1-D resonance frequency, traditionally detected by means of the microtremor H/V (horizontal to vertical spectral ratio) technique, depends on the bedrock depth and on the shear wave velocity of the resonating cover layer. The H/V technique is thus used both to map the resonance frequencies in seismic microzonation studies and for stratigraphic imaging. When 2-D resonance occurs, generally on deep and narrow valleys, the whole sedimentary infill vibrates at the same frequency and stratigraphic imaging can no longer be performed by means of the 1-D resonance equation. Understanding the 1-D or 2-D resonance nature of a site is therefore mandatory to avoid wrong stratigraphic and dynamic interpretations, which is in turn extremely relevant for seismic site response assessment. In this paper, we suggest a procedure to address this issue using single-station approaches, which are much more common compared to the multistation synchronized approach presented by research teams in earlier descriptions of the 2-D resonances. We apply the procedure to the Bolzano sedimentary basin in Northern Italy, which lies at the junction of three valleys, for which we observed respectively 1-D-only, 1-D and 2-D, and 2-D-only resonances. We conclude by proposing a workflow scheme to conduct experimental measurements and data analysis in order to assess the 1-D or 2-D resonance nature of a site using a single-station approach.

scholarly journals A Shear-Wave Velocity Model in the City of Oued-Fodda (Northern Algeria) from Rayleigh Wave Ellipticity Inversion

2020 ◽  
Vol 10 (5) ◽  
pp. 1717
Author(s):  
Abdelouahab Issaadi ◽  
Fethi Semmane ◽  
Abdelkrim Yelles-Chaouche ◽  
Juan José Galiana-Merino ◽  
Khalissa Layadi
Keyword(s):  
Rayleigh Wave ◽  
Cross Sections ◽  
High Frequency ◽  
Spectral Ratio ◽  
Velocity Model ◽  
Soil Characteristics ◽  
North Central ◽  
Fundamental Frequencies ◽  
Hvsr Method ◽  
The City

The city of Oued-Fodda is located in north-central Algeria on the margins of the Middle-Cheliff Basin. This region has suffered several destructive earthquakes. The strongest was the 1980 El-Asnam earthquake (Ms7.3), whose causative fault was located about 1 km north of the city of Oued-Fodda. Therefore, a good knowledge of the soil characteristics in this city may allow a better evaluation of the seismic risk and help to minimize damages in the future. With this objective, a detailed microzonation study of Oued-Fodda has been carried out in this study. For that, the horizontal-to-vertical spectral ratio (HVSR) method has been applied on 102 sites along the city, estimating the soil fundamental frequencies and their corresponding amplitudes. Besides, the Rayleigh wave ellipticity inversion has been accomplished in order to estimate the corresponding Vs profiles and provide two cross-sections of the geology under the city. In the central part of the city, high-frequency peaks are observed, between 12.5 and 15 Hz, which correspond to impedance contrasts at shallow depth (<20 m). In the surrounding plain, two clear peaks are identified in the ranges 1.8–3.5 Hz (fundamental frequencies) and 6.5–15 Hz (secondary peaks).

A Pseudo-3D Vs Velocity Model of Ischia Island (Italy) by HVSR spectral ratio inversion

2021 ◽  
Author(s):  
Roberto Manzo ◽  
Lucia Nardone ◽  
Guido Gaudiosi ◽  
Claudio Martino ◽  
Danilo Galluzzo ◽  
...  
Keyword(s):  
Spectral Ratio ◽  
Velocity Model ◽  
Inversion Process ◽  
Good Correspondence ◽  
Good Convergence ◽  
Velocity Models ◽  
High Impedance ◽  
Impedance Contrast ◽  
3D Velocity Model ◽  
Ischia Island

&lt;p&gt;Following the M&lt;sub&gt;D&lt;/sub&gt;4.0 (Mw3.9) earthquake of August 21 2017 which occurred on the Ischia island (Naples, southern Italy), the local monitoring seismic network was significantly improved in terms of both number of stations and instrumentation performance. Due to the considerable amount of collected data, in particular of seismic noise recorded at broadband stations, some efforts have been addressed in particular to the definition of a 1D average velocity model effective for the whole island. This is an important scientific step because, in complex volcanic areas, the use of reliable velocity models is essential for an accurate localization of local earthquakes. In this work, the main target is to retrieve a pseudo-3D velocity model of the Ischia island. Specifically, we inverted H/V curves and frequency peaks evaluated at about twenty sites to obtain a velocity profile for each of the investigated measurement points. Taking into account that the H/V frequency peak depends on both velocity and thickness of layers, for each site we applied an inversion process fixing the velocities and modifying the thicknesses in order to obtain the corresponding 1D velocity models. We are quite enough confident about the robustness of models, since during the inversion process, we achieved a good convergence towards the best-fit solutions. Then, a pseudo-3D velocity model was obtained by contouring the 1D models of each station site to highlight possible lateral variations of the layer thicknesses and to reconstruct the morphology of the deeper interface characterized by a high impedance contrast. A good correspondence between the pseudo-3D model and the geological features of the island was observed, especially in the northern sector where most of the stations is installed. In particular, the top of the high-impedance contrast interface appears deeper in the northern coastal areas and shallower in the central sector. This is in agreement with the structural setting of the island likely due to the resurgence of Mount Epomeo.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals Determination of the resonance frequency – thickness relation based on the ambient seismic noise records from Upper Silesia Coal Basin

2014 ◽  
Vol 3 (1) ◽  
pp. 41-51 ◽  
Author(s):  
Maciej Jan Mendecki ◽  
Barbara Bieta ◽  
Mateusz Mycka
Keyword(s):  
Resonance Frequency ◽  
Seismic Data ◽  
Seismic Noise ◽  
Spectral Ratio ◽  
Seismic Survey ◽  
Coal Basin ◽  
Upper Silesia ◽  
Resonance Frequencies ◽  
Hvsr Method

Abstract In this paper the Horizontal-to-Vertical Spectral Ratio (HVSR) method and seismic data were applied to evaluate the resonance frequency - thickness relation. The HVSR method was used to estimate the parameters of site effects: amplification and resonance frequency from seismic noise records. The seismic noise was generated by artificial source occurring in Upper Silesia Coal Basin (UBSC), Poland, such as: traffic, industry, coal plants etc. The survey points were located near the Faculty of Earth Sciences in Sosnowiec, Bytom and Chorzow. Based on Albarello’s statistical test the observed H/V maxima was confirmed or rejected. Resonance frequencies were compared with available thicknesses of soft layer obtained by seismic survey (Mendecki 2012). Finally, the estimated resonance frequency - thickness relation for UBSC area showed quite similar power function coefficients as those obtained by other authors

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