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Site condition investigation using horizontal to vertical spectral ratios of Iran strong motion data

Eshaghi Attieh, Hassani Behzad, Shahvar Mohammad Pourmohammad, Farzanegan Esmail

Acta Geophysica

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2023

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Vol. 71, no. 5

2049--2064

EN

In this study, horizontal to vertical spectral ratios (HVSR) have been calculated for strong ground motion data recorded by the Iran Strong Motion Network (ISMN). Then, a uniform and specific procedure is applied for selecting the peak amplitude (Apeak) and peak frequency (ƒpeak) of the average HVSR for each station in the database. Based on this procedure, Apeak and ƒpeak values were estimated at 502 stations of ISMN. Also, the relationships between HVSR parameters and time-averaged shear wave velocity in the upper 30 m (VS30) have been investigated and these relationships are presented for Iran. The results and uncertainties of these models are compared with other related studies conducted in Japan, North and Central America, as well as previous studies for Iran. Compared to other datasets, the VS30 model presented for Iran shows the highest VS30 values among all models. The equation developed in this study can be used to estimate VS30 at ISMN stations where there is no other site characteristics available. Therefore, the soil type can be classified according to the Standard No. 2800, which is useful in seismic design codes and other related studies.

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3D subsoil reconstruction of a mud volcano in central Sicily by means of geophysical surveys

Grassi Sabrina, De Guidi Giorgio, Patti Graziano, Brighenti Fabio, Carnemolla Francesco, Imposa Sebastiano

Acta Geophysica

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2022

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Vol. 70, no 3

1083--1102

EN

The upwelling of fluids, subject to overpressure, along with discontinuities in the subsoil, causes the formation of geological structures known as mud volcanoes. These structures, very widespread in the world and in some cases located near inhabited centers, can represent a considerable risk factor for the population, as they can give rise to paroxysmal eruptions, even very violent. The assessment of the characteristics and structure of the subsoil of the areas affected by this phenomenon can prove to be a useful tool for risk mitigation. Non-invasive geophysical surveys were carried out in the area of the active cone of the Santa Barbara mud volcano in order to obtain a 3D characterization of the subsoil. Through the processing and integration of data derived from active and passive seismic surveys was obtained, a 3D model showing the seismostratigraphic subsoil structure. The electrical resistivity tomography surveys provided results comparable to those obtained from seismic surveys and supplied information on the perimetral areas of the mud volcano. The information obtained is useful to study the boundary conditions that influence short-scale activity. Furthermore, this study seeks to evaluate the possibility of using the proposed methodological approach for monitoring the variations that occur over time in the areas affected by mud volcanoes phenomenon.

3

Comparison of site effect values obtained by HVSR and HVSRN methods for single-station measurements in Tarnówek, South-Western Poland

Mendecki M. J., Bieta B., Mateuszów M., Suszka P.

Contemporary Trends in Geoscience

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2016

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Vol. 5, iss. 1

18--27

EN

This study compares the HVSR technique (Horizontal to Vertical Spectral Ratio), based on seismic event records, and the HVSRN technique (Horizontal to Vertical Spectral Ratio of Noise) using seismic noise registrations. Both methods allow us to study the amplification phenomenon of a horizontal component of seismic waves when the waves reach loose sediments in subsurface layers. The seismic data were measured at a three-component single seismic station located in the village of Tarnówek, in the Legnica-Głogów Copper District. The results of the study demonstrate that average HVSRN and HVSR maxima can be distinguished: for periods approximately 3.78 s (H/V = 6.2) and 3.969 s (H/V = 8.98) respectively. The evaluated share of the Rayleigh wave component in the recorded values was β = 0.58 and it can be suggested that the Love wave share in surface motion was insignificant. The Love wave share remains unknown.

4

Study of Site Effect at Seismic Station Located in Undermined Area of Karviná Region (Czech Republic)

Lednicka M., Kalab Z.

Acta Geophysica

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2016

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Vol. 64, no. 5

1715--1730

EN

The Karviná region is well known as an area with an intensive mining induced seismicity. The local geological pattern, especially subsurface sedimentary layers, belongs to one of the most important factors that influence the amplification of seismic effect on the surface. In order to investigate the amplification effect, there are used methods of spectral ratio that enable to analyse records of vibrations. In the present study, two methods, signed as SSR (standard spectral ratio) and HVSR (horizontal to vertical spectral ratio), were used for the site effect evaluation. The analysis was performed in the populated Doubrava locality where high seismic loading on the surface due to mining induced seismicity is documented.