Testing Nonlinear Amplification Factors of Ground-Motion Models

2021 ◽  
Author(s):  
Karina Loviknes ◽  
Sreeram Reddy Kotha ◽  
Fabrice Cotton ◽  
Danijel Schorlemmer
Keyword(s):  
Ground Motion ◽  
Nonlinear Models ◽  
Site Response ◽  
Strong Motion ◽  
Site Amplification ◽  
Building Codes ◽  
Linear Amplification ◽  
Ground Acceleration ◽  
Nonlinear Site Response ◽  
The Impact

ABSTRACT We explore nonlinear site effects in the new Japanese ground-motion dataset compiled by Bahrampouri et al. (2020). Following the approach of Seyhan and Stewart (2014), we evaluate the decrease of soil amplification according to the increasing and corresponding ground motion on surface rock (VS30=760  m/s). To better predict the rock ground motion associated with each record, we take into account the between-event variability of the ground motion, and to better evaluate the impact of nonlinearity, we correct observed ground motion on soil by the site-specific linear amplification. Instead of grouping the stations by site-response proxy, we focus on individual stations with several strong-motion records. We develop a framework to test recently published nonlinear site amplification models against a linear site amplification model and compare the results with recent building codes that include nonlinearity. The results show that the site response varies greatly from site to site, indicating that conventional site proxies, such as VS30, are not sufficient to characterize nonlinear site response. Out of all of the Kiban–Kyoshin network stations, 20 stations are selected as having recorded sufficient data to be used in the test. Out of these 20 stations, five stations show signs of nonlinearity, that is, the nonlinear models performed better than the linear-amplification model for all periods T. For most sites, however, the linear site amplification models get the best score. This suggest that, for the range of predicted rock motion considered in this study (peak ground acceleration <0.2g), nonlinearity may not have a sufficiently large impact on soil ground motion to justify the use of nonlinear site terms in ground-motion functional forms and seismic building codes for such moderate-level shaking.

Nonlinear Site Effects from the 30 November 2018 Anchorage, Alaska, Earthquake

2021 ◽  
Author(s):  
John D. Thornley ◽  
Utpal Dutta ◽  
John Douglas ◽  
Zhaohui (Joey) Yang
Keyword(s):  
Site Response ◽  
Strong Motion ◽  
North American Plate ◽  
Peak Ground Velocity ◽  
Reference Station ◽  
Earthquake Hazards ◽  
Ground Acceleration ◽  
Nonlinear Site Response ◽  
Generalized Inversion Technique ◽  
Versus Peak

ABSTRACT Anchorage, Alaska, is a natural laboratory for recording strong ground motions from a variety of earthquake sources. The city is situated in a tectonic region that includes the interface and intraslab earthquakes related to the subducting Pacific plate and crustal earthquakes from the upper North American plate. The generalized inversion technique was used with a local rock reference station to develop site response at >20 strong-motion stations in Anchorage. A database of 94 events recorded at these sites from 2005 to 2019 was also compiled and processed to compare their site response with those in the 2018 Mw 7.1 event (main event). The database is divided into three datasets, including 75 events prior to the main event, the main event, and 19 aftershocks. The stations were subdivided into the site classes defined in the National Earthquake Hazards Reduction Program based on estimated average shear-wave velocity in of the upper 30 m (VS30), and site-response results from the datasets were compared. Nonlinear site response was observed at class D and DE sites (VS30 of 215–300 and 150–215  m/s, respectively) but not at class CD and C sites (VS30 of 300–440 and 440–640  m/s, respectively). The relationship of peak ground acceleration versus peak ground velocity divided by VS30 (shear-strain proxy) was shown to further support the observation that sites with lower VS30 experienced nonlinear site response.

Testing non-linear amplification factors used in ground motion models

2021 ◽  
Author(s):  
Karina Loviknes ◽  
Danijel Schorlemmer ◽  
Fabrice Cotton ◽  
Sreeram Reddy Kotha
Keyword(s):  
Ground Motion ◽  
Site Effects ◽  
Ground Motions ◽  
Site Amplification ◽  
Building Codes ◽  
Linear Amplification ◽  
Motion Models ◽  
Earthquake Predictability ◽  
Non Linear ◽  
Ground Motion Models

<p>Non-linear site effects are mainly expected for strong ground motions and sites with soft soils and more recent ground-motion models (GMM) have started to include such effects. Observations in this range are, however, sparse, and most non-linear site amplification models are therefore partly or fully based on numerical simulations. We develop a framework for testing of non-linear site amplification models using data from the comprehensive Kiban-Kyoshin network in Japan. The test is reproducible, following the vision of the Collaboratory for the Study of Earthquake Predictability (CSEP), and takes advantage of new large datasets to evaluate <span>whether or not</span> non-linear site effects predicted by site-amplification models are supported by empirical data. The site amplification models are tested using residuals between the observations and predictions from a GMM based only on magnitude and distance. When the GMM is derived without any site term, the site-specific variability extracted from the residuals is expected to capture the site response of a site. The non-linear site amplification models are tested against a linear amplification model on individual well-record<span>ing</span> stations. Finally, the result is compared to building codes where non-linearity is included. The test shows that for most of the sites selected as having sufficient records, the non-linear site-amplification models do not score better than the linear amplification model. This suggests that including non-linear site amplification in GMMs and building codes may not yet be justified, at least not in the range of ground motions considered in the test (peak ground acceleration < 0.2 g).</p>

Repeatable Source, Path, and Site Effects from the 2019 M 7.1 Ridgecrest Earthquake Sequence

2020 ◽  
Vol 110 (4) ◽  
pp. 1530-1548 ◽  
Author(s):  
Grace A. Parker ◽  
Annemarie S. Baltay ◽  
John Rekoske ◽  
Eric M. Thompson
Keyword(s):  
Los Angeles ◽  
Ground Motion ◽  
Site Response ◽  
Ground Motions ◽  
Warning System ◽  
Site Amplification ◽  
Earthquake Sequence ◽  
Ground Acceleration ◽  
Small Magnitude ◽  
Earthquake Early Warning System

ABSTRACT We use a large instrumental dataset from the 2019 Ridgecrest earthquake sequence (Rekoske et al., 2019, 2020) to examine repeatable source-, path-, and site-specific ground motions. A mixed-effects analysis is used to partition total residuals relative to the Boore et al. (2014; hereafter, BSSA14) ground-motion model. We calculate the Arias intensity stress drop for the earthquakes and find strong correlation with our event terms, indicating that they are consistent with source processes. We look for physically meaningful trends in the partitioned residuals and test the ability of BSSA14 to capture the behavior we observe in the data. We find that BSSA14 is a good match to the median observations for M>4. However, we find bias for individual events, especially those with small magnitude and hypocentral depth≥7  km, for which peak ground acceleration is underpredicted by a factor of 2.5. Although the site amplification term captures the median site response when all sites are considered together, it does not capture variations at individual stations across a range of site conditions. We find strong basin amplification in the Los Angeles, Ventura, and San Gabriel basins. We find weak amplification in the San Bernardino basin, which is contrary to simulation-based findings showing a channeling effect from an event with a north–south azimuth. This and an additional set of ground motions from earthquakes southwest of Los Angeles suggest that there is an azimuth-dependent southern California basin response related to the orientation of regional structures when ground motion from waves traveling south–north are compared with those in the east–west direction. These findings exhibit the power of large, spatially dense ground-motion datasets and make clear that nonergodic models are a way to reduce bias and uncertainty in ground-motion estimation for applications like the U.S. Geological Survey National Seismic Hazard Model and the ShakeAlert earthquake early warning System.

Site Amplification at Permanent Stations in Northeastern Italy

2021 ◽  
Author(s):  
Peter Klin ◽  
Giovanna Laurenzano ◽  
Carla Barnaba ◽  
Enrico Priolo ◽  
Stefano Parolai
Keyword(s):  
Ground Motion ◽  
Site Response ◽  
Alluvial Soil ◽  
Site Amplification ◽  
Single Step ◽  
Reference Station ◽  
Ground Acceleration ◽  
Amplification Factors ◽  
Generalized Inversion ◽  
Northeastern Italy

ABSTRACT The application of earthquake recordings to the estimation of an event’s magnitude and the construction of rapid-response ground-motion maps requires an adequate classification of the recording stations in terms of their site response. For permanent stations, this information can be obtained from a sufficiently large database of past recordings. In this work, we analyze more than 7300 three-component recordings collected between 1996 and 2017 by 67 permanent stations in northeastern Italy to assess their site amplification. The signals come from 368 earthquakes with a magnitude range of M 3.2–5.8 and a distance range of 10–300 km. We evaluate the frequency-dependent amplification function with respect to a reference station with a flat seismic noise horizontal-to-vertical spectral ratio. The evaluation relies on the decomposition of the S-wave amplitude spectra in terms of source, propagation, and site response. We solve the decomposition with a nonparametric, single-step generalized inversion in the frequency band 0.5–20 Hz. In addition, we compute the amplification factors for peak ground acceleration and velocity with respect to a well-established ground-motion prediction equation. The results highlight that only 11 stations show a relatively flat unitary response with respect to the reference site, whereas the frequency-averaged amplification function at 23 out of 67 stations exhibits a value larger than 2. We classified the sites according to their surface geology and geomorphological scenario and found that amplification affects not only stations installed on the alluvial soil but also several stations installed on what are assumed to be rock sites. Sites in caves and mines exhibit deamplification, whereas the stations with sensors in boreholes exhibit the typical interference pattern. A good correlation between the amplification factors and the frequency-averaged amplification functions suggests the possibility of predicting time-domain peak ground-motion values from amplification functions estimated by generalized inversion.

A Ground-Motion Prediction Model for Shallow Crustal Earthquakes in Greece

2020 ◽  
Author(s):  
David M. Boore ◽  
Jonathan P. Stewart ◽  
Andreas A. Skarlatoudis ◽  
Emel Seyhan ◽  
Basil Margaris ◽  
...  
Keyword(s):  
Prediction Model ◽  
Ground Motion ◽  
Site Response ◽  
Epistemic Uncertainty ◽  
Peak Ground Velocity ◽  
Motion Prediction ◽  
Ground Motion Prediction ◽  
Ground Acceleration ◽  
Magnitude Scaling ◽  
Nonlinear Site Response

ABSTRACT Using a recently completed database of uniformly processed strong-motion data recorded in Greece, we derive a ground-motion prediction model (GMPM) for horizontal-component peak ground velocity, peak ground acceleration, and 5% damped pseudoacceleration response spectra, at 105 periods ranging from 0.01 to 10 s. The equations were developed by modifying a global GMPM, to account for more rapid attenuation and weaker magnitude scaling in the Greek ground motions than in the global GMPM. Our GMPM is calibrated using the Greek data for distances up to 300 km, magnitudes from 4.0 to 7.0, and time-averaged 30 m shear-wave velocities from 150 to 1200  m/s. The GMPM has important attributes for hazard applications including magnitude scaling that extends the range of applicability to M 8.0 and nonlinear site response. These features are possible because they are well constrained by data in the global GMPM from which our model is derived. An interesting feature of the Greek data, also observed previously in studies of mid-magnitude events (6.1–6.5) in Italy, is that they are substantially overpredicted by the global GMPM, which may be a repeatable regional feature, but may also be influenced by soil–structure interaction. This bias is an important source of epistemic uncertainty that should be considered in hazard analysis.

scholarly journals Prediction and evaluation of nonlinear site response with potentially liquefiable layers in the area of Nafplion (Peloponnesus, Greece) for a repeat of historical earthquakes

2010 ◽  
Vol 10 (11) ◽  
pp. 2281-2304 ◽  
Author(s):  
V. K. Karastathis ◽  
G. A. Papadopoulos ◽  
T. Novikova ◽  
Z. Roumelioti ◽  
P. Karmis ◽  
...  
Keyword(s):  
Ground Motion ◽  
Strong Ground Motion ◽  
Site Response ◽  
Soft Soil ◽  
Soil Layer ◽  
Ground Acceleration ◽  
Nonlinear Site Response ◽  
Strong Ground Motion Simulation ◽  
Scenario Earthquakes ◽  
Strong Ground

Abstract. We examine the possible non-linear behaviour of potentially liquefiable layers at selected sites located within the expansion area of the town of Nafplion, East Peloponnese, Greece. Input motion is computed for three scenario earthquakes, selected on the basis of historical seismicity data, using a stochastic strong ground motion simulation technique, which takes into account the finite dimensions of the earthquake sources. Site-specific ground acceleration synthetics and soil profiles are then used to evaluate the liquefaction potential at the sites of interest. The activation scenario of the Iria fault, which is the closest one to Nafplion (M=6.4), is found to be the most hazardous in terms of liquefaction initiation. In this scenario almost all the examined sites exhibit liquefaction features at depths of 6–12 m. For scenario earthquakes at two more distant seismic sources (Epidaurus fault – M6.3; Xylokastro fault – M6.7) strong ground motion amplification phenomena by the shallow soft soil layer are expected to be observed.

Using Large Strong Motion Datasets to Model Regional Site Response in Seismic Risk Assessment: Examples from Japan and Europe

2020 ◽  
Author(s):  
Graeme Weatherill ◽  
Fabrice Cotton ◽  
Sreeram Reddy Kotha
Keyword(s):  
Risk Analysis ◽  
Ground Motion ◽  
Seismic Risk ◽  
Site Response ◽  
Epistemic Uncertainty ◽  
Spatial Scales ◽  
Strong Motion ◽  
Site Amplification ◽  
Seismic Risk Analysis ◽  
Data Set

<p>Characterisation of seismic risk within a probabilistic framework is dependent upon well-constrained models of the seismic source, the ground motion scaling and the local site response, in addition to both their aleatory variability and epistemic uncertainty. When assessing risk as a large geographical scale such as that of a country or continent, however, complex models of site response that require detailed parameterization of the site conditions are seldom feasible to constrain. Instead, the use of simpler proxies, such as the well-known topographically inferred 30 m averaged shear-wave velocity (V<sub>S30</sub>), have become widely adopted for this purpose. In practice, the inference of V<sub>S30</sub> from topographic and/or geological proxies have substantial limitations in terms of both the geological environments for which they are appropriate and the increased uncertainty in the prediction of site response; limitations that are not always accounted for in existing seismic risk models.</p><p>The volume of data reported by both new and well-established stations is increasing at an exponential rate, with hundreds of thousands of strong motion records now available from thousands of stations. Through this enormous and ever-expanding data set it is possible to constrain thousands of station-specific amplifications and utilize this dataset to calibrate the site amplification directly upon regionally mappable parameters, which can be applied across large spatial scales needed for regional seismic risk analysis. In doing so, it is possible not only to adapt the model of site amplification to different geological environments, but also to adjust the uncertainty in the ground motion characterization to ensure that this is captured appropriately in the seismic risk analysis when using the mappable site proxies. Applications of this approach have been made for two case study regions: i) Japan, where detailed station metadata are available and the relative increase in uncertainty from using regionally-mappable parameters instead of well-constrained site properties can be constrained, and ii) Europe, where station metadata more limited but a large number of stations with repeated observations are available. The implications for the estimates of seismic losses when adopting this new approach in place of the existing methodology are illustrated using examples from the 2020 European Seismic Risk model.</p>

Ground Motion Site Amplification Factors for Sites Located within the Mississippi Embayment with Consideration of Deep Soil Deposits

2015 ◽  
Vol 31 (2) ◽  
pp. 699-722 ◽  
Author(s):  
Mojtaba Malekmohammadi ◽  
Shahram Pezeshk
Keyword(s):  
Ground Motion ◽  
Site Response ◽  
Site Amplification ◽  
Sediment Depth ◽  
Deep Soil ◽  
Mississippi Embayment ◽  
Soil Response ◽  
Amplification Factors ◽  
Nonlinear Site Response ◽  
Soil Deposits

In this study, site amplification factors for the deep soil deposits of the Mississippi embayment are computed using a nonlinear site response analysis program first to develop a model for nonlinear soil response for possible use by ground motion developers and second to address site amplification estimation. The effects of geology, sediment depth, and average shear wave velocity at the upper 30 m of soil ranging 180–800 m/s, as well as the effect of peak ground acceleration at the bedrock on nonlinear ground motion amplification for the upper embayment, are investigated. The site response computations cover various site conditions, sediment depth of 70–750 m, and peak acceleration of input rock motions of 0.01–0.90 g. The amplification (or de-amplification) at various frequencies implied by the sediment depth is greater than that implied just by site classification of the top 30 m of soil.

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 Investigating the influence of topographic irregularities and two-dimensional effects on surface ground motion intensity with one- and two-dimensional analyses

2014 ◽  
Vol 14 (7) ◽  
pp. 1773-1788 ◽  
Author(s):  
G. Ç. İnce ◽  
L. Yılmazoğlu
Keyword(s):  
Ground Motion ◽  
Site Response ◽  
Soil Conditions ◽  
Response Analysis ◽  
Two Dimensional ◽  
Ground Acceleration ◽  
Equivalent Linear ◽  
Local Soil ◽  
Different Depths ◽  
Earthquake Response Analysis

Abstract. In this work, the surface ground motion that occurs during an earthquake in ground sections having different topographic forms has been examined with one and two dynamic site response analyses. One-dimensional analyses were undertaken using the Equivalent-Linear Earthquake Response Analysis (EERA) program based on the equivalent linear analysis principle and the Deepsoil program which is able to make both equivalent linear and nonlinear analyses and two-dimensional analyses using the Plaxis 8.2 software. The viscous damping parameters used in the dynamic site response analyses undertaken with the Plaxis 8.2 software were obtained using the DeepSoil program. In the dynamic site response analyses, the synthetic acceleration over a 475-year return period representing the earthquakes in Istanbul was used as the basis of the bedrock ground motion. The peak ground acceleration obtained different depths of soils and acceleration spectrum values have been compared. The surface topography and layer boundaries in the 5-5' cross section which cuts across the study area west to east were selected in order to examine the effect of the land topography and layer boundaries on the analysis results, and were flattened and compared with the actual status. The analysis results showed that the characteristics of the surface ground motion change in relation to the varying local soil conditions and land topography.

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