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).

Seismic site response in the greater Vancouver, British Columbia, area: spectral ratios from moderate earthquakes

1999 ◽  
Vol 36 (2) ◽  
pp. 195-209 ◽  
Author(s):  
John F Cassidy ◽  
Garry C Rogers
Keyword(s):  
Site Response ◽  
Strong Motion ◽  
River Delta ◽  
Data Sets ◽  
Fraser River ◽  
Spectral Ratios ◽  
Data Set ◽  
Seismic Site Response ◽  
Fraser River Delta ◽  
S Period

Three-component, digital recordings of two recent moderate earthquakes provide valuable new insight into the response to seismic shaking in the greater Vancouver area, particularly on the Fraser River delta. The 1996 M = 5.1 Duvall, Washington, earthquake (180 km southeast of Vancouver) triggered strong-motion seismographs at seven sites and the 1997 M = 4.3 Georgia Strait earthquake (37 km west of Vancouver) triggered instruments at 13 sites in the greater Vancouver area. The latter data set is especially important because it contains the first three-component recordings made on bedrock in greater Vancouver. Both data sets represent weak ground motion, with peak horizontal accelerations of 0.5-1.5% gravity (g) for the Duvall earthquake, and 0.2-2.4% g for the Georgia Strait earthquake. Using the method of spectral ratios, we estimate the site response for each of the strong-motion instrument soil sites. On the Fraser River delta amplification is observed over a relatively narrow frequency range of 1.5-4 Hz (0.25-0.67 s period), with peak amplification of 4-10 (relative to competent bedrock) for the thick soil delta centre sites, and about 7-11 for the delta edge sites. Relative to firm soil, the peak amplification ranges from 2 to 5 for the thick soil delta centre sites, and 2 to 6 for the delta edge sites. At higher frequencies, little or no amplification, and in many cases slight attenuation, is observed.Key words: seismic site response, Fraser delta, earthquakes.

Regional propagation characteristics and source parameters of earthquakes in northeastern North America

1994 ◽  
Vol 84 (1) ◽  
pp. 1-15 ◽  
Author(s):  
John Boatwright
Keyword(s):  
Site Response ◽  
Source Parameters ◽  
Low Frequency ◽  
Response Spectra ◽  
Spectral Shape ◽  
Propagation Characteristics ◽  
S Wave ◽  
Data Set ◽  
Wave Trains ◽  
Source Site

Abstract The vertical components of the S wave trains recorded on the Eastern Canadian Telemetered Network (ECTN) from 1980 through 1990 have been spectrally analyzed for source, site, and propagation characteristics. The data set comprises some 1033 recordings of 97 earthquakes whose magnitudes range from M ≈ 3 to 6. The epicentral distances range from 15 to 1000 km, with most of the data set recorded at distances from 200 to 800 km. The recorded S wave trains contain the phases S, SmS, Sn, and Lg and are sampled using windows that increase with distance; the acceleration spectra were analyzed from 1.0 to 10 Hz. To separate the source, site, and propagation characteristics, an inversion for the earthquake corner frequencies, low-frequency levels, and average attenuation parameters is alternated with a regression of residuals onto the set of stations and a grid of 14 distances ranging from 25 to 1000 km. The iteration between these two parts of the inversion converges in about 60 steps. The average attenuation parameters obtained from the inversion were Q = 1997 ± 10 and γ = 0.998 ± 0.003. The most pronounced variation from this average attenuation is a marked deamplification of more than a factor of 2 at 63 km and 2 Hz, which shallows with increasing frequency and increasing distance out to 200 km. The site-response spectra obtained for the ECTN stations are generally flat. The source spectral shape assumed in this inversion provides an adequate spectral model for the smaller events (Mo < 3 × 1021 dyne-cm) in the data set, whose Brune stress drops range from 5 to 150 bars. For the five events in the data set with Mo ≧ 1023 dyne-cm, however, the source spectra obtained by regressing the residuals suggest that an ω2 spectrum is an inadequate model for the spectral shape. In particular, the corner frequencies for most of these large events appear to be split, so that the spectra exhibit an intermediate behavior (where |ü(ω)| is roughly proportional to ω).

Hard as a rock? Looking for typical and atypical reference sites in the Greek network

2021 ◽  
Author(s):  
Olga-Joan Ktenidou ◽  
Faidra Gkika ◽  
Erion-Vasilis Pikoulis ◽  
Christos Evangelidis
Keyword(s):  
Ground Motion ◽  
Site Response ◽  
Time Budget ◽  
Strong Motion ◽  
General Rule ◽  
Spectral Ratio ◽  
Reference Sites ◽  
Motion Models ◽  
Ground Motion Variability

<p>Although it is nowadays desirable and even typical to characterise site conditions in detail at modern recording stations, this is not yet a general rule in Greece, due to the large number and geographical dispersion of stations. Indeed, most of them are still characterised merely through geological descriptions or proxy-based parameters, rather than through in-situ measurements. Considering: 1. the progress made in recent years with sophisticated ground motion models and the need to define region-specific rock conditions based on data, 2. the move towards large open-access strong-motion databases that require detailed site metadata, and 3. that Greek-provenance recordings represent a significant portion of European seismic data, there are many reasons to improve our understanding of site response at these stations. Moreover, it has been shown recently in several regions that even sites considered as rock can exhibit amplification and ground motion variability, which has given rise to more scientific research into the definition of reference sites. For Greece, in-situ-characterisation campaigns for the entire network would impose unattainable time/budget constraints; so, instead, we implement alternative empirical approaches using the recordings themselves, such as the horizontal-to-vertical spectral ratio technique and its variability. We present examples of 'well-behaved', typical rock sites, and others whose response diverges from what is assumed for their class.</p><p> </p>

A site effect study in Acapulco, Guerrero, Mexico: Comparison of results from strong-motion and microtremor data

1992 ◽  
Vol 82 (2) ◽  
pp. 642-659 ◽  
Author(s):  
Carlos Gutierrez ◽  
Shri Krishna Singh
Keyword(s):  
Seismic Waves ◽  
Site Response ◽  
Nonlinear Behavior ◽  
Strong Motion ◽  
Site Effect ◽  
Seismic Gap ◽  
S Wave ◽  
Data Set ◽  
S Waves ◽  
The City

Abstract The city of Acapulco is located near or above the mature seismic gap of Guerrero along the Mexican subduction zone. With the purpose of studying the character of strong ground motion on soft sites, four digital accelerographs have been installed in the city on such sites. These instruments have been in operation since 1988. Two additional instruments, part of the Guerrero Accelerograph Array, are located on hard sites in the area. One of these, VNTA, has been in operation since 1985 and the other, ACAN, since 1989. These stations have recorded several earthquakes. We use data from eight events (4.2 ≤ M ≤ 6.9) to study spectral amplification of seismic waves at the soft sites with respect to VNTA. The S waves are amplified by a factor of 6 to 25 at the soft sites in a fairly broad range of frequencies; both the amplification and the frequency band over which it occurs depend upon the site. Although the largest earthquake in our data set (M = 6.9) gave rise to a peak horizontal acceleration exceeding 0.3 g at one of the soft sites, no clear evidence of nonlinear behavior of the subsoil is found. Spectral amplifications of S-wave coda are very similar to those of S waves. We also measured microtremors at the strong-motion sites. The microtremor spectra were interpreted, using reasonable assumptions, to test the feasibility of this technique in reproducing the spectral amplifications observed during earthquakes. Our results show that only a rough estimate of site response can be obtained from this technique, at least in Acapulco; caution is warranted in its use elsewhere.

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.

Study on Differences in Floor Response Spectra due to the Seismic Input Approach

2016 ◽  
Author(s):  
Jana Sue Bochert ◽  
Henry Schau ◽  
Timo Schmitt
Keyword(s):  
Wave Propagation ◽  
Site Response ◽  
Response Spectra ◽  
Response Analysis ◽  
Ground Response ◽  
Soil Layers ◽  
Seismic Input ◽  
Floor Response Spectra ◽  
Propagation Analysis ◽  
Different Depths

In this paper the differences of floor response spectra (FRS) resulting from different ground response spectra are discussed. These spectra include the site effects which are quantified via site response analysis. This response is generated by wave propagation from the base rock through the overlying soil layers to the surface. The influences of the different layers and the corresponding dynamic soil properties are considered by using wave propagation analysis. The paper then discusses the results obtained from seismic input at different depths conditions. Similar results might be expected, because the depth of the input spectra is adjusted for each layer. However, in comparing the floor response spectra of these calculations, significant differences are observed and therefore interpreted. The paper is completed with the explanation of these significant differences and also with comparable floor response spectra.

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.

Methodology for Site Classification Estimation Using Strong Ground Motion Data from the Chi-Chi, Taiwan, Earthquake

2006 ◽  
Vol 22 (2) ◽  
pp. 511-531 ◽  
Author(s):  
Vietanh Phung ◽  
Gail M. Atkinson ◽  
David T. Lau
Keyword(s):  
Ground Motion ◽  
Strong Motion ◽  
Spectral Ratio ◽  
Response Spectra ◽  
Site Classification ◽  
Site Conditions ◽  
Site Condition ◽  
Borehole Data ◽  
Lower Accuracy ◽  
Taiwan Earthquake

The ground motions of the Chi-Chi, Taiwan, earthquake ( Mw=7.6) were recorded at 420 strong-motion stations, including 69 near-fault sites. However, the site conditions of many stations are not available. Among 420 strong-motion stations, the site conditions are known for only 87 stations, which were classified into four groups ( S1, S2, S3, and S4) by using borehole data and some surface geology. This paper presents a methodology to estimate the missing site condition information at strong-motion stations in Taiwan. The method is based on the shape of the 5% damped pseudo-acceleration spectrum of the horizontal ground motion component normalized with respect to average PGA, where the classification scheme is developed using the data from the 87 stations for which the site conditions are known. Possible effects of soil nonlinearity, and distance to the fault on the classification are investigated. The results obtained from the proposed methodology are well correlated with the available known site classification information data. The methodology is then applied to estimate the site condition for the other 333 stations without known site classification. Our results are compared to previous results obtained based on interpretation of geologic maps and geomorphologic data. We find that the two approaches agree in 71% of the cases. We also tested the horizontal-to-vertical spectral ratio technique to estimate the site classification of other 333 strong-motion stations. However, this technique resulted in lower accuracy than does the proposed technique based on the spectral shape of normalized response spectra.

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 The web portal of the EUROSEISTEST strong ground motion database.

2016 ◽  
Vol 47 (3) ◽  
pp. 1221
Author(s):  
K. Pitilakis ◽  
Z. Roumelioti ◽  
M. Manakou ◽  
D. Raptakis ◽  
K. Liakakis ◽  
...  
Keyword(s):  
Strong Motion ◽  
Response Spectra ◽  
Great Effort ◽  
Web Database ◽  
Web Portal ◽  
Northern Greece ◽  
Strong Motion Data ◽  
Motion Data ◽  
Graphical Environment ◽  
The Web

Strong motion data that have been recorded during the 20-years of operation of the permanent network of EUROSEISTEST (Mygdonia basin, Northern Greece) have been homogenized and organized in an easily accessible, via the web, database. The EUROSEISTEST web portal and the application server running underneath are based solely on free and open source software (F/OSS; MySQL v5.5; RubyOnRails,SAC, Gnuplot and numerous GNU supporting utilities). Its interface allows the user to easily search strong motion data from approximately 200 events and 26 strong motion stations using event-related, record-related or station-related criteria. Further investigation of the data is possible in a graphical environment which includesplots of processed and unprocessed acceleration waveforms, velocity and displacement time histories, amplitude Fourier and response spectra and spectrograms. A great effort was directed toward the inclusion of accurate and most updated earthquake metadata, as well as a wealth of stations related information such as geotechnicaland geophysical site characterization measurements, subsoil structure and site effects. Acceleration data can be easily downloaded in either SAC or ASCII format, while all stations metadata are also available to download. 

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