Scenario‐Dependent Site Effects for the Determination of Unbiased Local Magnitude

2019 ◽  
Vol 109 (6) ◽  
pp. 2658-2673 ◽  
Author(s):  
James Holt ◽  
Benjamin Edwards ◽  
Valerio Poggi
Keyword(s):  
Site Response ◽  
Simulated Data ◽  
Site Amplification ◽  
Local Magnitude ◽  
Near Surface ◽  
Response Information ◽  
Quarter Wavelength ◽  
Site Term ◽  
Dependent Site ◽  
Relative Differences

Abstract We explore the role of scenario‐dependent site amplification on local magnitude (ML) and possible bias it may introduce. ML is strongly influenced by local site response, which is conditioned by unique local geological factors. To isolate the effect of the near‐surface amplification on ML, relative differences between station‐specific ML at the surface and borehole (ΔML,STN) are studied for 34 sites from the KiK‐net network, Japan. We find strong moment magnitude (M) dependent scenario‐specific ΔML,STN trends over the range 3.0<M<6.5. To model these trends, we employ the stochastic method, initially using empirical surface‐to‐borehole (S/B) Fourier spectral ratios for the site term. Simulated data, ΔML,STN(M), based on the available site‐response information are shown to closely match the empirical ΔML,STN trends. Subsequently, the site term is replaced with (a) linear 1D shear‐wave (horizontal) transfer function (1D‐SHTF) amplification, (b) horizontal‐to‐vertical ratios, and (c) quarter wavelength amplification to calculate ΔML,STN(M) in the absence of S/B. We find that ΔML,STN(M) trends are best estimated with S/B as the site term, but in many cases using a linear 1D‐SHTF model is adequate. Furthermore, we discuss how this phenomenon may be related to the observed inequality between M and ML at low magnitudes and how ΔML,STN(M) may be used in the future to compute unbiased ML with greater confidence.

Application of Site Amplification Factors to Determine the Local Magnitude from Borehole Seismic Stations in Taiwan

2020 ◽  
Author(s):  
Tz-Shin Lai ◽  
Yih-Min Wu ◽  
Wei-An Chao
Keyword(s):  
Site Effect ◽  
Site Amplification ◽  
Force Balance ◽  
Earthquake Catalog ◽  
Local Magnitude ◽  
Broadband Seismometer ◽  
Near Surface ◽  
Amplification Factors ◽  
Attenuation Function ◽  
Borehole Seismic

&lt;p&gt;Since the inception of 62 borehole seismic arrays deployed by Central Weather Bureau (CWB) in Taiwan until the end of 2018, a large quantity of strong-motion records have been accumulated from frequently occurring earthquakes around Taiwan, which provide an opportunity to detect micro-seismicity. Each borehole array includes two force balance accelerometers, one at the surface and other at a depth of a few ten-to-hundred (30-492) meters, as well as one broadband seismometer is below the borehole accelerometer. In general, the background seismic noise level are lower at the downhole stations than surface stations. However, the seismograms recorded by the downhole stations are smaller than surface stations due to the near-surface site effect. In Taiwan, the local magnitude (M&lt;sub&gt;L&lt;/sub&gt;) determinations use the attenuation function derived from surface stations. Therefore, the M&lt;sub&gt;L&lt;/sub&gt; will be underestimated by using current attenuation function for downhole stations. In this study, we used 19079 earthquakes to investigate the site amplification at subsurface materials between downhole and surface stations. Results demonstrate the amplification factors ranging from 1.11 to 5.74, provide the site effect parameter at shallow layers and have a strong relationship with Vs30. Further, we apply the amplification factors to revise the station local magnitude for downhole station. The revised M&lt;sub&gt;L&lt;/sub&gt; at downhole stations correlate well with the M&lt;sub&gt;L&lt;/sub&gt; at surface stations. Implement of the downhole station in the M&lt;sub&gt;L&lt;/sub&gt; determination, it enhances the ability to detect the micro-earthquake and makes the earthquake catalog more comprehensive in Taiwan.&lt;/p&gt;

Scenario shakemaps for Montreal

2015 ◽  
Vol 42 (7) ◽  
pp. 463-476 ◽  
Author(s):  
Hadi Ghofrani ◽  
Gail M. Atkinson ◽  
Luc Chouinard ◽  
Philippe Rosset ◽  
Kristy F. Tiampo
Keyword(s):  
Seismic Risk ◽  
Site Response ◽  
Distribution Patterns ◽  
Site Amplification ◽  
Near Surface ◽  
Ground Shaking ◽  
Moderate Seismicity ◽  
Event Location ◽  
Surface Geology ◽  
The Impact

Montreal has significant seismic risk due to the combination of moderate seismicity, high population density, and vulnerable infrastructure. An important tool in damage and risk assessment is a scenario shakemap, which shows the expected ground shaking intensity distribution patterns. In this study, we use regional ground motion and site response evaluations to generate scenario shakemaps for Montreal. The impact of event location on expected ground motions and intensities was tested by considering the occurrence of a scenario (a given magnitude event) at various locations, where the scenarios are defined based on an analysis of the most likely future event locations. Variability in near surface geology plays an important role in earthquake ground shaking; we use microzonation information from Montreal to assess the expected site amplification effects. The results of this study may be used as input to seismic risk studies for Montreal.

Site Response in the Oklahoma Region from Seismic Recordings of the 2011 Mw 5.7 Prague Earthquake

2019 ◽  
Author(s):  
Carlos Mendoza ◽  
Stephen Hartzell
Keyword(s):  
Transfer Functions ◽  
Site Response ◽  
Site Amplification ◽  
Waveform Analysis ◽  
Resonant Peak ◽  
Corner Frequency ◽  
Inversion Method ◽  
S Wave ◽  
Near Surface ◽  
Spectral Peaks

ABSTRACT We invert the shear‐wave displacement spectra obtained from 30 three‐component, broadband waveforms recorded within 300 km of the 6 November 2011 Mw 5.7 Prague, Oklahoma, earthquake to recover the site‐response contribution using an inversion method that simultaneously inverts for source, path, and site effects. Site‐response functions identify resonant frequencies within a range of 0.1–10 Hz that generally coincide with spectral peaks in horizontal‐to‐vertical ratio curves derived from the recorded waveforms. S‐wave velocity profiles available for several sites were also used to calculate theoretical SH transfer functions that predict the site amplification due to the near‐surface soil structure down to depths of 30–50 m. The transfer functions do not provide resonance information below about 5–8 Hz, indicating that the spectral peaks in the site response obtained from the waveform analysis result from deeper velocity variations. A 0.3 Hz spectral peak observed at several stations, for example, coincides with the strong, surface‐wave amplitudes observed at 3 s periods for induced M≥3 earthquakes in Oklahoma and Kansas, suggesting that this resonant peak may be due to surface waves trapped in the upper ∼2  km sedimentary layer of the crust. Both shallow and deep contributions to the site response are important for the characterization of ground motion from central and eastern North America (CENA) earthquakes. We obtain a corner frequency of 0.229, consistent with independent observations of the size of the event. A frequency‐dependent attenuation relation of Q(f)=1107f0.398 consistent with prior CENA path measurements is also derived.

Ground motion and site effect observations in the wellington region from the 2016 Mw7.8 Kaikōura, New Zealand earthquake

2017 ◽  
Vol 50 (2) ◽  
pp. 94-105 ◽  
Author(s):  
Brendon A. Bradley ◽  
Liam M. Wotherspoon ◽  
Anna E. Kaiser
Keyword(s):  
Ground Motion ◽  
Site Response ◽  
Ground Motions ◽  
Site Effect ◽  
Site Amplification ◽  
Design Standards ◽  
Site Class ◽  
Near Surface ◽  
Long Period ◽  
Basin Edge

This paper presents ground motion and site effect observations in the greater Wellington region from the 14 November 2016 Mw7.8 Kaikōura earthquake. The region was the principal urban area to be affected by the earthquake-induced ground motions from this event. Despite being approximately 60km from the northern extent of the causative earthquake rupture, the ground motions in Wellington exhibited long period (specifically T = 1 - 3s) ground motion amplitudes that were similar to, and in some locations exceeded, the current 500 year return period design ground motion levels. Several ground motion observations on rock provide significant constraint to understand the role of surficial site effects in the recorded ground motions. The largest long period ground motions were observed in the Thorndon and Te Aro basins in Wellington City, inferred as a result of 1D impedance contrasts and also basin-edge-generated waves. Observed site amplifications, based on response spectral ratios with reference rock sites, are seen to significantly exceed the site class factors in NZS1170.5:2004 for site class C, D, and E sites at approximately T=0.3-3.0s. The 5-95% Significant Duration, Ds595, of ground motions was on the order of 30 seconds, consistent with empirical models for this earthquake magnitude and source-to-site distance. Such durations are slightly longer than the corresponding Ds595 = 10s and 25s in central Christchurch during the 22 February 2011 Mw6.2 and 4 September 2010 Mw7.1 earthquakes, but significantly shorter than what might be expected for large subduction zone earthquakes that pose a hazard to the region. In summary, the observations highlight the need to better understand and quantify basin and near-surface site response effects through more comprehensive models, and better account for such effects through site amplification factors in design standards.

Simulation-based site amplification model for shallow bedrock sites in Korea

2021 ◽  
pp. 875529302098198
Author(s):  
Muhammad Aaqib ◽  
Duhee Park ◽  
Muhammad Bilal Adeel ◽  
Youssef M A Hashash ◽  
Okan Ilhan
Keyword(s):  
Linear Models ◽  
Site Response ◽  
Site Amplification ◽  
One Dimensional ◽  
Nonlinear Component ◽  
Nonlinear Site Response ◽  
Simulation Based ◽  
Linear And Nonlinear ◽  
Input Motion ◽  
Nonlinear Components

A new simulation-based site amplification model for shallow sites with thickness less than 30 m in Korea is developed. The site amplification model consists of linear and nonlinear components that are developed from one-dimensional linear and nonlinear site response analyses. A suite of measured shear wave velocity profiles is used to develop corresponding randomized profiles. A VS30 scaled linear amplification model and a model dependent on both VS30 and site period are developed. The proposed linear models compare well with the amplification equations developed for the western United States (WUS) at short periods but show a distinct curved bump between 0.1 and 0.5 s that corresponds to the range of site natural periods of shallow sites. The response at periods longer than 0.5 s is demonstrated to be lower than those of the WUS models. The functional form widely used in both WUS and central and eastern North America (CENA), for the nonlinear component of the site amplification model, is employed in this study. The slope of the proposed nonlinear component with respect to the input motion intensity is demonstrated to be higher than those of both the WUS and CENA models, particularly for soft sites with VS30 < 300 m/s and at periods shorter than 0.2 s. The nonlinear component deviates from the models for generic sites even at low ground motion intensities. The comparisons highlight the uniqueness of the amplification characteristics of shallow sites that a generic site amplification model is unable to capture.

scholarly journals MAX-DOAS observations of aerosols, formaldehyde and nitrogen dioxide in the Beijing area: comparison of two profile retrieval approaches

2015 ◽  
Vol 8 (2) ◽  
pp. 941-963 ◽  
Author(s):  
T. Vlemmix ◽  
F. Hendrick ◽  
G. Pinardi ◽  
I. De Smedt ◽  
C. Fayt ◽  
...  
Keyword(s):  
Standard Deviation ◽  
A Priori ◽  
Systematic Bias ◽  
Aerosol Extinction ◽  
Data Set ◽  
Near Surface ◽  
Beijing Area ◽  
Least Squares Fit ◽  
Relative Differences ◽  
Good Agreement

Abstract. A 4-year data set of MAX-DOAS observations in the Beijing area (2008–2012) is analysed with a focus on NO2, HCHO and aerosols. Two very different retrieval methods are applied. Method A describes the tropospheric profile with 13 layers and makes use of the optimal estimation method. Method B uses 2–4 parameters to describe the tropospheric profile and an inversion based on a least-squares fit. For each constituent (NO2, HCHO and aerosols) the retrieval outcomes are compared in terms of tropospheric column densities, surface concentrations and "characteristic profile heights" (i.e. the height below which 75% of the vertically integrated tropospheric column density resides). We find best agreement between the two methods for tropospheric NO2 column densities, with a standard deviation of relative differences below 10%, a correlation of 0.99 and a linear regression with a slope of 1.03. For tropospheric HCHO column densities we find a similar slope, but also a systematic bias of almost 10% which is likely related to differences in profile height. Aerosol optical depths (AODs) retrieved with method B are 20% high compared to method A. They are more in agreement with AERONET measurements, which are on average only 5% lower, however with considerable relative differences (standard deviation ~ 25%). With respect to near-surface volume mixing ratios and aerosol extinction we find considerably larger relative differences: 10 ± 30, −23 ± 28 and −8 ± 33% for aerosols, HCHO and NO2 respectively. The frequency distributions of these near-surface concentrations show however a quite good agreement, and this indicates that near-surface concentrations derived from MAX-DOAS are certainly useful in a climatological sense. A major difference between the two methods is the dynamic range of retrieved characteristic profile heights which is larger for method B than for method A. This effect is most pronounced for HCHO, where retrieved profile shapes with method A are very close to the a priori, and moderate for NO2 and aerosol extinction which on average show quite good agreement for characteristic profile heights below 1.5 km. One of the main advantages of method A is the stability, even under suboptimal conditions (e.g. in the presence of clouds). Method B is generally more unstable and this explains probably a substantial part of the quite large relative differences between the two methods. However, despite a relatively low precision for individual profile retrievals it appears as if seasonally averaged profile heights retrieved with method B are less biased towards a priori assumptions than those retrieved with method A. This gives confidence in the result obtained with method B, namely that aerosol extinction profiles tend on average to be higher than NO2 profiles in spring and summer, whereas they seem on average to be of the same height in winter, a result which is especially relevant in relation to the validation of satellite retrievals.

Estimation of Site Amplification from Geotechnical Array Data Using Neural Networks

2021 ◽  
Author(s):  
Daniel Roten ◽  
Kim B. Olsen
Keyword(s):  
Neural Network ◽  
Neural Networks ◽  
Site Response ◽  
Site Amplification ◽  
Data Driven ◽  
Vertical Array ◽  
The Neural Network ◽  
Simplifying Assumptions ◽  
The Mean ◽  
Fully Connected

ABSTRACT We use deep learning to predict surface-to-borehole Fourier amplification functions (AFs) from discretized shear-wave velocity profiles. Specifically, we train a fully connected neural network and a convolutional neural network using mean AFs observed at ∼600 KiK-net vertical array sites. Compared with predictions based on theoretical SH 1D amplifications, the neural network (NN) results in up to 50% reduction of the mean squared log error between predictions and observations at sites not used for training. In the future, NNs may lead to a purely data-driven prediction of site response that is independent of proxies or simplifying assumptions.

Correspondence between Site Amplification and Topographical, Geological Parameters: Collation of Data from Swiss and Japanese Stations, and Neural Networks-Based Prediction of Local Response

2021 ◽  
Author(s):  
Paolo Bergamo ◽  
Conny Hammer ◽  
Donat Fäh
Keyword(s):  
Frequency Response ◽  
Large Scale ◽  
Site Response ◽  
Low Frequency ◽  
Field Measurements ◽  
Site Amplification ◽  
Local Response ◽  
Regional Variability ◽  
Individual Site ◽  
Digital Elevation

ABSTRACT We address the relation between seismic local amplification and topographical and geological indicators describing the site morphology. We focus on parameters that can be derived from layers of diffuse information (e.g., digital elevation models, geological maps) and do not require in situ surveys; we term these parameters as “indirect” proxies, as opposed to “direct” indicators (e.g., f0, VS30) derived from field measurements. We first compiled an extensive database of indirect parameters covering 142 and 637 instrumented sites in Switzerland and Japan, respectively; we collected topographical indicators at various spatial extents and focused on shared features in the geological descriptions of the two countries. We paired this proxy database with a companion dataset of site amplification factors at 10 frequencies within 0.5–20 Hz, empirically measured at the same Swiss and Japanese stations. We then assessed the robustness of the correlation between individual site-condition indicators and local response by means of statistical analyses; we also compared the proxy-site amplification relations at Swiss versus Japanese sites. Finally, we tested the prediction of site amplification by feeding ensembles of indirect parameters to a neural network (NN) structure. The main results are: (1) indirect indicators show higher correlation with site amplification in the low-frequency range (0.5–3.33 Hz); (2) topographical parameters primarily relate to local response not because of topographical amplification effects but because topographical features correspond to the properties of the subsurface, hence to stratigraphic amplification; (3) large-scale topographical indicators relate to low-frequency response, smaller-scale to higher-frequency response; (4) site amplification versus indirect proxy relations show a more marked regional variability when compared with direct indicators; and (5) the NN-based prediction of site response is the best achieved in the 1.67–5 Hz band, with both geological and topographical proxies provided as input; topographical indicators alone perform better than geological parameters.

Significance of site natural period effects for linear site amplification in central and eastern North America: Empirical and simulation-based models

2020 ◽  
Vol 36 (1) ◽  
pp. 87-110 ◽  
Author(s):  
Youssef M. A. Hashash ◽  
Okan Ilhan ◽  
Behzad Hassani ◽  
Gail M. Atkinson ◽  
Joseph Harmon ◽  
...  
Keyword(s):  
North America ◽  
Site Response ◽  
Reference Conditions ◽  
Site Amplification ◽  
Empirical Models ◽  
Response Analysis ◽  
Eastern North America ◽  
Natural Period ◽  
Motion Models ◽  
Simulation Based

This article evaluates linear simulation-based and empirical site amplification models including site natural period dependency parameters to account for the distinctive amplification behavior near site fundamental frequencies resulting from the sharp impedance contrast between soil and underlying hard bedrock in central and eastern North America (CENA). The simulation-based amplification models are developed using 581,685 frequency-domain linear analyses generated from a parametric study and include VS30-scaling and site natural period ( Tnat) parameters. The empirical models are derived from residuals analyses of ground-motion models for two reference conditions: B/C boundary ( VS30 = 760 m/s) and CENA hard-rock condition ( VS = 3000 m/s). The simulation-based and empirical models are compared for 8 site profiles in CENA to measured horizontal-to-vertical (H/V) component response spectral (RS) ratios, the mean of linear simulations for similar sites, and one-dimensional (1D) linear site response analysis for four of these sites. Comparisons between observed and estimated site amplification behaviors highlight model dependency on Tnat in CENA. Model consistencies and differences related to the distinct linear amplification features near site fundamental frequency are discussed.

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