Data Analysis of the Euroseistest Strong Motion Array in Volvi (Greece): Standard and Horizontal-to-Vertical Spectral Ratio Techniques

1998 ◽  
Vol 14 (1) ◽  
pp. 203-224 ◽  
Author(s):  
D. Raptakis ◽  
N. Theodulidis ◽  
K. Pitilakis
Keyword(s):  
Resonant Frequency ◽  
Strong Motion ◽  
Spectral Ratio ◽  
Ratio Method ◽  
Absolute Level ◽  
Data Set ◽  
Alluvial Deposits ◽  
Standard Spectral Ratio ◽  
Strong Motion Station ◽  
Geological Conditions

In this study, the standard spectral ratio and the horizontal-to-vertical spectral ratio techniques are applied in order to study their effectiveness in investigating and quantifying the influence of geological conditions on strong ground motion. For this purpose, an accelerogram data set recorded at the Euroseistest array in the Mygdonia graben (lake Volvi area) near Thessaloniki, Greece, during the period April 1994 to June 1996 is used. Both experimental techniques show similar spectral ratio shapes with comparable fundamental resonant frequencies, which are well correlated with the well known geotechnical-geological conditions. Namely, the resonant frequency at the center of the valley is shifted to lower values, less than 1 Hz, while at the edge it is shifted to higher values, greater than 2 Hz. The horizontal-to-vertical spectral ratio technique is an effective method to estimate some basic characteristics of local site effects using a single accelerograph station. It reveals the fundamental resonant frequency of alluvial deposits by using only a single strong motion station, while the absolute level of the horizontal-to-vertical spectral ratio method tends to underestimate the amplification level compared to the standard spectral ratio technique.

A Comparison of Site Response Techniques Using Weak-Motion Earthquakes and Microtremors

2006 ◽  
Vol 22 (1) ◽  
pp. 169-188 ◽  
Author(s):  
Sheri Molnar ◽  
John F. Cassidy
Keyword(s):  
Site Response ◽  
Strong Motion ◽  
Spectral Ratio ◽  
Ratio Method ◽  
Near Surface ◽  
Fundamental Frequencies ◽  
Standard Spectral Ratio ◽  
Impedance Contrast ◽  
Spectral Ratio Method ◽  
Geologic Setting

The applicability of the microtremor spectral ratio method is examined by comparing microtremor and weak-motion earthquake site responses at seven permanent strong-motion sites in Victoria, British Columbia. For each site, a weak-motion earthquake standard spectral ratio (bedrock reference), the average horizontal-to-vertical spectral ratio of up to five weak-motion earthquakes, and the average microtremor (Nakamura method) spectral ratio are compared. The geologic setting of Victoria is ideal for site response studies with a near-surface high impedance contrast between thin geologic layers of Victoria clay (about 11 m maximum in this study) and Pleistocene till or bedrock. Regardless of excitation source (weak-motion earthquakes or microtremors) and spectral ratio method, similar peak amplitudes and fundamental frequencies were found. Thicker material (>10 m) sites displayed higher peak amplitudes (up to six times amplification) at frequencies of 2–5 Hz compared to sites with a thin lens of material (<3 m) over bedrock that showed peak amplitudes at frequencies of >8 Hz.

Horizontal-to-vertical spectral ratio and geological conditions: The case of Garner Valley Downhole Array in southern California

1996 ◽  
Vol 86 (2) ◽  
pp. 306-319 ◽  
Author(s):  
N. Theodulidis ◽  
P.-Y. Bard ◽  
R. Archuleta ◽  
M. Bouchon
Keyword(s):  
Southern California ◽  
Transfer Functions ◽  
High Sensitivity ◽  
Spectral Ratio ◽  
S Wave ◽  
Absolute Level ◽  
Data Set ◽  
Geological Conditions ◽  
Different Depths ◽  
Downhole Array

Abstract The aim of the present article is to further check the use of the horizontal-to-vertical (h/v) spectral ratio, which has been recently suggested as an indicator of site effects. The data set consists of 110, three-component, high sensitivity accelerograms, recorded at five different depths by the Garner Valley Downhole Array (GVDA), in southern California, with peak ground accelerations 0.0002 g ≦ ag ≦ 0.04 g, magnitudes 3.0 ≦ ML ≦ 4.6, and hypocentral distances 16 km ≦ R ≦ 107 km. First, the stability of the (h/v) spectral ratio is investigated by computing the mean for the whole data set in different depths. The (h/v) spectral ratio on the surface is compared with the surface-to-depth standard spectral ratio, with theoretical S-wave transfer functions derived from the vertical geotechnical profile, as well as with the (h/v) spectral ratio of synthetic accelerograms generated by the discrete wavenumber method. Both theoretical and experimental data show a good stability of the (h/v) spectral ratio shape, which is in good agreement with the local geological structure and is insensitive to the source location and mechanism. However, the absolute level of the (h/v) spectral ratio depends on the wave field and is different from the surface-to-depth spectral ratio. Consequently the (h/v) spectral ratio technique provides only partially the information that can be obtained from a downhole array. But surface-to-depth ratios may also be misleading because they combine effects at surface and at depth.

scholarly journals Near-Source Simulation of Strong Ground Motion in Amatrice Downtown Including Site Effects

Geosciences ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 186
Author(s):  
Alessandro Todrani ◽  
Giovanna Cultrera
Keyword(s):  
Ground Motion ◽  
Site Effects ◽  
Central Italy ◽  
Strong Motion ◽  
Seismic Source ◽  
Spectral Ratio ◽  
Intensity Measures ◽  
Standard Spectral Ratio ◽  
Heavy Damage ◽  
Strong Ground

On 24 August 2016, a Mw 6.0 earthquake started a damaging seismic sequence in central Italy. The historical center of Amatrice village reached the XI degree (MCS scale) but the high vulnerability alone could not explain the heavy damage. Unfortunately, at the time of the earthquake only AMT station, 200 m away from the downtown, recorded the mainshock, whereas tens of temporary stations were installed afterwards. We propose a method to simulate the ground motion affecting Amatrice, using the FFT amplitude recorded at AMT, which has been modified by the standard spectral ratio (SSR) computed at 14 seismic stations in downtown. We tested the procedure by comparing simulations and recordings of two later mainshocks (Mw 5.9 and Mw 6.5), underlining advantages and limits of the technique. The strong motion variability of simulations was related to the proximity of the seismic source, accounted for by the ground motion at AMT, and to the peculiar site effects, described by the transfer function at the sites. The largest amplification characterized the stations close to the NE hill edge and produced simulated values of intensity measures clearly above one standard deviation of the GMM expected for Italy, up to 1.6 g for PGA.

Empirical Attenuation Equations for Vertical Ground Motion in Turkey

2004 ◽  
Vol 20 (3) ◽  
pp. 853-882 ◽  
Author(s):  
Erol Kalkan ◽  
Polat Gülkan
Keyword(s):  
Ground Motion ◽  
Strong Ground Motion ◽  
Strong Dependence ◽  
Strong Motion ◽  
Vertical Acceleration ◽  
Data Set ◽  
Attenuation Relationships ◽  
Geological Conditions ◽  
Ground Motion Records ◽  
Strong Ground

In the aftermath of two destructive urban earthquakes in 1999 in Turkey, empirical models of strong motion attenuation relationships that have been previously developed for North American and European earthquakes have been utilized in a number of national seismic hazard studies. However, comparison of empirical evidence and estimates present significant differences. For that reason, a data set created from a suite of 100 vertical strong ground motion records from 47 national earthquakes that occurred between 1976 and 2002 has been used to develop attenuation relationships for strong ground motion in Turkey. A consistent set of empirical attenuation relationships was derived for predicting vertical peak and pseudo-absolute vertical acceleration spectral ordinates in terms of magnitude, source-to-site distance, and local geological conditions. The study manifests the strong dependence of vertical to horizontal (V/H) acceleration ratio on spectral periods and relatively weaker dependence on site geology, magnitude, and distance. The V/H ratio is found to be particularly significant at the higher frequency end of the spectrum, reaching values as high as 0.9 at short distances on soil sites. The largest long-period spectral ratios are observed to occur on rock sites where they can reach values in excess of 0.5. These results raise misgivings concerning the practice of assigning the V/H ratio a standard value of two-thirds. Hence, nonconservatism of this value at short periods and its conservatism at long periods underline the need for its revision, at least for practice in Turkey.

Methodology to identify the reference rock sites in regions of medium-to-high seismicity: an application in Central Italy

2020 ◽  
Vol 222 (3) ◽  
pp. 2053-2067 ◽  
Author(s):  
Giovanni Lanzano ◽  
Chiara Felicetta ◽  
Francesca Pacor ◽  
Daniele Spallarossa ◽  
Paola Traversa
Keyword(s):  
Ground Motion ◽  
Site Effects ◽  
Site Response ◽  
Central Italy ◽  
Large Data ◽  
Spectral Ratio ◽  
Data Set ◽  
Standard Spectral Ratio ◽  
Resonance Frequencies ◽  
The Impact

SUMMARY To evaluate the site response using both empirical approaches (e.g. standard spectral ratio, ground motion models (GMMs), generalized inversion techniques, etc.) and numerical 1-D/2-D analyses, the definition of the reference motion, that is the ground motion recorded at stations unaffected by site-effects due to topographic, stratigraphic or basin effects, is needed. The main objective of this work is to define a robust strategy to identify the seismic stations that can be considered as reference rock sites, using six proxies for the site response: three proxies are related to the analysis of geophysical and seismological data (the repeatable site term from the residual analysis, the resonance frequencies from horizontal-to-vertical spectral ratios on noise or earthquake signals, the average shear wave velocity in the first 30 m); the remaining ones concern geomorphological and installation features (outcropping rocks or stiff soils, flat topography and absence of interaction with structures). We introduce a weighting scheme to take into account the availability and the quality of the site information, as well as the fulfillment of the criterion associated to each proxy. We also introduce a hierarchical index, to take into account the relevance of the proposed proxies in the description of the site effects, and an acceptance threshold for reference rock sites identification. The procedure is applied on a very large data set, composed by accelerometric and velocimetric waveforms, recorded in Central Italy in the period 2008–2018. This data set is composed by more than 30 000 waveforms relative to 450 earthquakes in the magnitude range 3.2–6.5 and recorded by more than 450 stations. A total of 36 out of 133 candidate stations are identified as reference sites: the majority of them are installed on rock with flat topography, but this condition is not sufficient to guarantee the absence of amplifications, especially at high frequencies. Seismological analyses are necessary to exclude stations affected by resonances. We test the impact of using these sites by calibrating a GMMs. The results show that for reference rock sites the median predictions are reduced down to about 45 per cent at short periods in comparison to the generic rock motions.

scholarly journals A Novel Method for Predicting Local Site Amplification Factors Using 1-D Convolutional Neural Networks

2021 ◽  
Vol 11 (24) ◽  
pp. 11650
Author(s):  
Xiaomei Yang ◽  
Yongshan Chen ◽  
Shuai Teng ◽  
Gongfa Chen
Keyword(s):  
Ground Motion ◽  
Earthquake Engineering ◽  
Spectral Ratio ◽  
Ratio Method ◽  
Observation Data ◽  
Prediction Ability ◽  
Amplification Factors ◽  
Standard Spectral Ratio ◽  
Local Site ◽  
Spectral Ratio Method

The analysis of site seismic amplification characteristics is one of the important tasks of seismic safety evaluation. Owing to the high computational cost and complex implementation of numerical simulations, significant differences exist in the prediction of seismic ground motion amplification in engineering problems. In this paper, a novel prediction method for the amplification characteristics of local sites was proposed, using a state-of-the-art convolutional neural network (CNN) combined with real-time seismic signals. The amplification factors were computed by the standard spectral ratio method according to the observed records of seven stations in the Lower Hutt Valley, New Zealand. Based on the geological exploration data from the seven stations and the geological hazard information of the Lower Hutt Valley, eight parameters related to the seismic information were presumed to influence the amplification characteristics of the local site. The CNN method was used to establish the relationship between the amplification factors of local sites and the eight parameters, and the training samples and testing samples were generated through the observed and geological data other than the estimated values. To analyze the CNN prediction ability for amplification factors on unrecorded domains, two CNN models were established for comparison. One CNN model used about 80% of the data from 44 seismic events of the seven stations for training and the remaining data for testing. The other CNN model used the data of six stations to train and the remaining station’s data to test the CNN. The results showed that the CNN method based on the observation data can provide a powerful tool for predicting the amplification factors of local sites both for recorded positions and for unrecorded positions, while the traditional standard spectral ratio method only predicts the amplification factors for recorded positions. The comparison of the two CNN models showed that both can effectively predict the amplification factors of local ground motion without records, and the accuracy and stability of predictions can meet the requirements. With increasing seismic records, the CNN method becomes practical and effective for prediction purposes in earthquake engineering.

EURO-SEISTEST strong-motion array near Thessaloniki, Northern Greece: A study of site effects

1998 ◽  
Vol 88 (3) ◽  
pp. 862-873
Author(s):  
P. P. Dimitriu ◽  
Ch. A. Papaioannou ◽  
N. P. Theodulidis
Keyword(s):  
Wave Propagation ◽  
Time Window ◽  
Site Response ◽  
Strong Motion ◽  
Spectral Ratio ◽  
Response Spectra ◽  
Response Assessment ◽  
Northern Greece ◽  
Data Set ◽  
Propagation Models

Abstract The effects of local geology on the characteristics of strong ground motion have been, and continue to be, a field of active research. Despite the considerable efforts made so far, there are still several unresolved and controversial issues remaining. In particular, debates still continue over the limits of applicability of one-dimensional (1D) wave-propagation models. There are also unresolved questions related to the implementation and reliability of site-response estimation techniques such as the standard spectral ratio (SSR) and the horizontal-to-vertical spectral ratio (HVSR). This study addresses these issues on the basis of data from the EURO-SEISTEST strong-motion array at Volvi, near Thessaloniki, Greece. The data set used consists of accelerograms of 32 earthquakes, almost exclusively local, covering a magnitude range from ML 2.0 to 6.1. The range of recorded accelerations is 0.001 − 0.042 g. We implement two 1D wave-propagation models (the Haskell-Thompson matrix method and Kennett's reflectivity-coefficient method) and the HVSR site-response assessment technique. We test the applicability of the 1D models in a basin environment. We use both Fourier-amplitude and response spectra to compute HVSR and investigate how HVSR is influenced by the choice of the time window and smoothing procedure. We found the HVSR technique and 1D SH-wave modeling to perform reasonably well in a sediment-valley environment (the modeling was performed for a site in the center of the valley).

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