Investigation of Topographic Site Effects using 3D Waveform Modelling: Amplification, Polarization and Torsional Motions in the Case Study of Arquata del Tronto (Italy)

Abstract The combined effect of topography and near-surface heterogeneities on the seismic response is hardly predictable and may lead to an aggravation of the ground motion. We apply physics-based numerical simulations of 3D seismic wave propagation to highlight these effects in the case study of Arquata del Tronto, a hamlet in the Apennines that suffered irregularly distributed damage during the 2016 seismic sequence in Central Italy. We analyze the linear visco-elastic seismic response for vertically incident plane waves in terms of spectral amplification, polarization and induced torsional motion within the frequency band 1–8 Hz over a 1 km2 square area, with spatial resolution 25 m. To discern the effects of topography from those of the sub-surface structure we iterate the numerical simulations for three different versions of the structural model: one homogeneous, one with a surficial weathering layer and a soil basin and one with a complex internal structure. The numerical results confirm the correlation between topographic curvature and amplification and support a correlation between the induced torsional motion and the topographic slope. On the other hand we find that polarization does not necessarily imply ground motion amplification. In the frequency band above 4 Hz the topography-related effects are mainly aggravated by the presence of the weathering layer, even though they do not exceed the soil-related effects in the flat-topography basin. The structure below the weathering layer plays a recognizable role in the topography-related site response only for frequencies below 4 Hz.

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Investigation of topographic site effects using 3D waveform modelling: amplification, polarization and torsional motions in the case study of Arquata del Tronto (Italy)

Bulletin of Earthquake Engineering ◽

10.1007/s10518-021-01270-2 ◽

2021 ◽

Author(s):

Julie Baron ◽

Ilaria Primofiore ◽

Peter Klin ◽

Giovanna Vessia ◽

Giovanna Laurenzano

Keyword(s):

Numerical Simulations ◽

Seismic Response ◽

Ground Motion ◽

Frequency Band ◽

Site Response ◽

Central Italy ◽

Surface Model ◽

Torsional Motion ◽

Near Surface

AbstractThe combined effect of topography and near-surface heterogeneities on the seismic response is hardly predictable and may lead to an aggravation of the ground motion. We apply physics-based numerical simulations of 3D seismic wave propagation to highlight these effects in the case study of Arquata del Tronto, a municipality in the Apennines that includes a historical village on a hill and a hamlet on the flat terrain of an alluvial basin. The two hamlets suffered different damage during the 2016 seismic sequence in Central Italy. We analyze the linear visco-elastic seismic response for vertically incident plane waves in terms of spectral amplification, polarization and induced torsional motion within the frequency band 1–8 Hz over a 1 km2 square area, with spatial resolution 25 m. To discern the effects of topography from those of the sub-surface structure we iterate the numerical simulations for three different versions of the sub-surface model: one homogeneous, one with a surficial weathering layer and a soil basin and one with a complex internal setting. The numerical results confirm the correlation between topographic curvature and amplification and support a correlation between the induced torsional motion and the topographic slope. On the other hand we find that polarization does not necessarily imply ground motion amplification. In the frequency band above 4 Hz the topography-related effects are mainly aggravated by the presence of the weathering layer, even though they do not exceed the soil-related effects in the flat-topography basin. The geological setting below the weathering layer plays a recognizable role in the topography-related site response only for frequencies below 4 Hz.

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Physical stratigraphy and geotechnical properties controlling the local seismic response in explosive volcanic settings: the Stracciacappa maar (central Italy)

Bulletin of Engineering Geology and the Environment ◽

10.1007/s10064-020-01925-5 ◽

2020 ◽

Vol 80 (1) ◽

pp. 179-199

Author(s):

M. Moscatelli ◽

G. Vignaroli ◽

A. Pagliaroli ◽

R. Razzano ◽

A. Avalle ◽

...

Keyword(s):

Seismic Response ◽

Ground Motion ◽

Central Italy ◽

Volcanic Event ◽

Ground Motion Amplification ◽

Local Seismic Response ◽

Single Station ◽

Seismic Scenarios ◽

Physical Stratigraphy ◽

Subsoil Model

AbstractNowadays, policies addressed to prevention and mitigation of seismic risk need a consolidated methodology finalised to the assessment of local seismic response in explosive volcanic settings. The quantitative reconstruction of the subsoil model provides a key instrument to understand how the geometry and the internal architecture of outcropping and buried geological units have influence on the propagation of seismic waves. On this regard, we present a multidisciplinary approach in the test area of the Stracciacappa maar (Sabatini Volcanic District, central Italy), with the aim to reconstruct its physical stratigraphy and to discuss how subsoil heterogeneities control the 1D and 2D local seismic response in such a volcanic setting. We first introduce a new multidisciplinary dataset, including geological (fieldwork and log from a 45-m-thick continuous coring borehole), geophysical (electrical resistivity tomographies, single station noise measurements, and 2D passive seismic arrays), and geotechnical (simple shear tests performed on undisturbed samples) approaches. Then, we reconstruct the subsoil model for the Stracciacappa maar in terms of vertical setting and distribution of its mechanical lithotypes, which we investigate for 1D and 2D finite element site response analyses through the application of two different seismic scenarios: a volcanic event and a tectonic event. The numerical modelling documents a significant ground motion amplification (in the 1–1.5 Hz range) revealed for both seismic scenarios, with a maximum within the centre of the maar. The ground motion amplification is related to both 1D and 2D phenomena including lithological heterogeneity within the upper part of the maar section and interaction of direct S-waves with Rayleigh waves generated at edges of the most superficial lithotypes. Finally, we use these insights to associate the expected distribution of ground motion amplification with the physical stratigraphy of an explosive volcanic setting, with insights for seismic microzonation studies and local seismic response assessment in populated environments.

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Regional-Scale 3D Ground-Motion Simulations of Mw 7 Earthquakes on the Hayward Fault, Northern California Resolving Frequencies 0–10 Hz and Including Site-Response Corrections

Bulletin of the Seismological Society of America ◽

10.1785/0120200147 ◽

2020 ◽

Vol 110 (6) ◽

pp. 2862-2881

Author(s):

Arthur J. Rodgers ◽

Arben Pitarka ◽

Ramesh Pankajakshan ◽

Bjorn Sjögreen ◽

N. Anders Petersson

Keyword(s):

Ground Motion ◽

Site Response ◽

Regional Scale ◽

Frequency Resolution ◽

Earthquake Ground Motion ◽

Northern California ◽

Soft Soils ◽

Near Surface ◽

Ground Motion Simulations ◽

Scenario Earthquakes

ABSTRACT Large earthquake ground-motion simulations in 3D Earth models provide constraints on site-specific shaking intensities but have suffered from limited frequency resolution and ignored site response in soft soils. We report new regional-scale 3D simulations for moment magnitude 7.0 scenario earthquakes on the Hayward Fault, northern California with SW4. Simulations resolved significantly broader band frequencies (0–10 Hz) than previous studies and represent the highest resolution simulations for any such earthquake to date. Seismic waves were excited by a kinematic rupture following Graves and Pitarka (2016) and obeyed wave propagation in a 3D Earth model with topography from the U.S. Geological Survey (USGS) assuming a minimum shear wavespeed, VSmin, of 500 m/s. We corrected motions for linear and nonlinear site response for the shear wavespeed, VS, from the USGS 3D model, using a recently developed ground-motion model (GMM) for Fourier amplitude spectra (Bayless and Abrahamson, 2018, 2019a). At soft soil locations subjected to strong shaking, the site-corrected intensities reflect the competing effects of linear amplification by low VS material, reduction of stiffness during nonlinear deformation, and damping of high frequencies. Sites with near-surface VS of 500 m/s or greater require no linear site correction but can experience amplitude reduction due to nonlinear response. Averaged over all sites, we obtained reasonable agreement with empirical ergodic median GMMs currently used for seismic hazard and design ground motions (epsilon less than 1), with marked improvement at soft sedimentary sites. At specific locations, the simulated shaking intensities show systematic differences from the GMMs that reveal path and site effects not captured in these ergodic models. Results suggest how next generation regional-scale earthquake simulations can provide higher spatial and frequency resolution while including effects of soft soils that are commonly ignored in scenario earthquake ground-motion simulations.

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Seismic response of RC buildings during the Mw 6.0 August 24, 2016 Central Italy earthquake: the Amatrice case study

Bulletin of Earthquake Engineering ◽

10.1007/s10518-017-0277-5 ◽

2017 ◽

Vol 17 (10) ◽

pp. 5631-5654 ◽

Cited By ~ 24

Author(s):

A. Masi ◽

L. Chiauzzi ◽

G. Santarsiero ◽

V. Manfredi ◽

S. Biondi ◽

...

Keyword(s):

Seismic Response ◽

Central Italy ◽

Rc Buildings ◽

Central Italy Earthquake

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An approach to construct a Netherlands-wide ground-motion amplification model

10.5194/egusphere-egu21-1657 ◽

2021 ◽

Author(s):

Janneke van Ginkel ◽

Elmer Ruigrok ◽

Rien Herber

Keyword(s):

The Netherlands ◽

Ground Motion ◽

Seismic Wave ◽

Transfer Functions ◽

Site Response ◽

Data Availability ◽

Earthquake Ground Motion ◽

Sediment Layer ◽

Small Magnitude ◽

Near Surface

Local site conditions can strongly influence the level of amplification of ground-motion at the surface during an earthquake. Especially near-surface low velocity sediments overlying stiffer seismic bedrock modify earthquake ground motions in terms of amplitudes and frequency content, the so-called site response. Earthquake ground-motion site response is of great concern because it can lead to amplified surface shaking resulting in significant damage on structures despite small magnitude events. The Netherlands has tectonically related seismic activity in the southern region with magnitudes up to 5.8 measured so far. In addition, gas extraction in the Groningen field in the northern part of the Netherlands, is regularly causing shallow (3 km), low magnitude (Mw max= 3.6), induced earthquakes. The shallow geology of the Netherlands consists of a very heterogeneous soft sediment cover, which has a strong effect on seismic wave propagation and in particular on the amplitude of ground shaking.&#160;The ambient seismic field and local earthquakes recorded over 69 borehole stations in Groningen are used to define relationships between the subsurface lithological composition, measured shear-wave velocity profiles, horizontal-to-vertical spectral ratios (HVSR) and empirical transfer functions (ETF). For the Groningen region we show that the HVSR matches the ETF well and conclude that the HVSR can be used as a first proxy for earthquake site-response. In addition, based on the ETFs we observe that most of the seismic wave amplification occurs in the top 50 m of the much thicker sediment layer. Here, a velocity contrast is present between the very soft Holocene clays and peat on top of the stiffer Pleistocene sands.&#160;Based on the learnings from Groningen we first constructed sediment type classes for the Dutch subsurface, each class representing a level of expected amplification. Secondly, the HVSR curves are estimated for all surface seismometers in the Netherlands seismic network and a sediment class is assigned to each location. Highest HVSR peak amplitudes are measured at sites with the highest level of amplification of the sediment classification. Based on this correlation and the presence of a detailed shallow geological model at most sites in the Netherlands, a simplistic approach is presented to predict amplification at any location with sufficient lithologic information. With this approach based on the shallow sediment composition, we can obtain constraints on the seismic hazard in areas that have limited data availability but have potential risk of seismicity, for example due to geothermal energy extraction.

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The basin effect and liquefaction in the catastrophe models: Case study – Vancouver region, Canada

10.5194/egusphere-egu2020-21355 ◽

2020 ◽

Author(s):

Svetlana Stripajova ◽

Peter Pazak ◽

Jan Vodicka ◽

Goran Trendafiloski

Keyword(s):

Ground Motion ◽

Sedimentary Basin ◽

Water Saturation ◽

Site Response ◽

Earthquake Ground Motion ◽

Soil Conditions ◽

Liquefaction Hazard ◽

Geological Conditions ◽

Catastrophe Models

The presence of thick soft alluvial sediment-filled basins, like in river&#8217;s deltas, can significantly amplify and prolongate the earthquake ground motion. Moreover, the high-water saturation of such soft sediments and cyclic earthquake loading can lead to liquefaction. The basin and liquefaction effect can contribute to substantial modification of the seismic motion and increase of the potential losses at a particular location. Well-known examples of such high financial losses during earthquakes for basin effect is Mw 8.1 Mexico City 1985 and for liquefaction is Darfield and Christchurch earthquakes series in 2010 and 2011. Thus, the quantification of these effects is particularly important for the current underwriting products and the industry requires their further detailed consideration in the catastrophe models and pricing approaches. Impact Forecasting, Aon&#8217;s catastrophe model development center of excellence, has been committed to help (re)insurers on that matter.This paper presents case study of the quantification of the basin effect and liquefaction for Vancouver region, Canada for specific scenario Mw 7.5 Strait of Georgia crustal earthquake. The southern part of the Vancouver region is located on a deep sedimentary basin created in the Fraser River delta. In case of deep Vancouver sedimentary basin considering amplification only due to shallow site response Vs30-dependent site term is not sufficient. Therefore, we derived (de)amplification function for different periods to quantify basin effect. We used NGA &#8211; West 2 ground motion prediction equations (GMPEs) for crustal events which include basin depth term. Amplification function was derived with respect to standard GMPEs for crustal events in western Canada. Amplification, considering site response including Vs30 and basin depth term at period 0.5 s can reach values as high as 3 at the softest and deepest sediments. The liquefaction potential was based on HAZUS and Zhu et al. (2017) methodologies calibrated to better reflect local geological conditions and liquefaction observations (Monahan et al. 2010, Clague 2002). We used USGS Vs30 data, enhanced by local seismic and geologic measurements, to characterize soil conditions, and topographical data and IF proprietary flow accumulation data to characterize water saturation. Liquefaction hazard is calculated in terms of probability of liquefaction occurrence and permanent ground deformation. For the chosen scenario the potential contribution to mean loss due to basin effect could be in the range 15% - 30% and 35% - 75% due to liquefaction depending on structural types of the buildings.

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Case Study: Effect of Soil-Structure Interaction and Ground Motion Incoherency on Nuclear Power Plant Structures

Volume 8: Seismic Engineering ◽

10.1115/pvp2009-77323 ◽

2009 ◽

Author(s):

Jim Xu ◽

Sujit Samaddar

Keyword(s):

Power Plant ◽

Nuclear Power Plant ◽

Seismic Response ◽

Ground Motion ◽

Nuclear Power ◽

Soil Structure ◽

Soil Structure Interaction ◽

Soil Conditions ◽

Structure Interaction

The soil-structure interaction (SSI) has a significant impact on nuclear power plant (NPP) structures, especially for massive and rigid structures founded on soils, such as containments. The U.S. Nuclear Regulatory Commission’s (NRC) Standard Review Plan (SRP) provides the requirement and acceptance criteria for incorporating the SSI effect in the seismic design and analyses of NPP structures. The NRC staff uses the SRP for safety review of license applications. Recent studies have indicated that ground motions in recorded real earthquake events have exhibited spatial incoherency in high-frequency contents. Several techniques have been developed to incorporate the incoherency effect in the seismic response analyses. Section 3.7.2 of Revision 3 of the SRP also provided guidance for use in the safety evaluation of seismic analyses considering ground motion spatial incoherency effect. This paper describes a case study of the SSI and incoherency effects on seismic response analyses of NPP structures. The study selected a typical containment structure. The SSI model is generated based on the typical industry practice for SSI computation of containment structures. Specifically, a commercial version of SASSI was used for the study, which considered a surface-founded structure. The SSI model includes the foundation, represented with brick elements, and the superstructure, represented using lumped mass and beams. The study considered various soil conditions and ground motion coherency functions to investigate the effect of the range of soil stiffness and the ground motion incoherency effect on SSI in determining the seismic response of the structures. This paper describes the SSI model development and presents the analysis results as well as insights into the manner in which the SSI and incoherency effects are related to different soil conditions.

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

Geophysical Journal International ◽

10.1093/gji/ggaa261 ◽

2020 ◽

Vol 222 (3) ◽

pp. 2053-2067 ◽

Cited By ~ 2

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.

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Methodology for Validation of Simulated Ground Motions for Seismic Response Assessment: Application to CyberShake Source-Based Ground Motions

Bulletin of the Seismological Society of America ◽

10.1785/0120200240 ◽

2020 ◽

Author(s):

Jawad Fayaz ◽

Sarah Azar ◽

Mayssa Dabaghi ◽

Farzin Zareian

Keyword(s):

Seismic Response ◽

Ground Motion ◽

Site Response ◽

Ground Motions ◽

Engineering Application ◽

Response Assessment ◽

Simulation Method ◽

Earthquake Scenarios ◽

Structural Responses ◽

Simulated Ground Motions

ABSTRACT A comprehensive methodology for the validation of simulated ground motions is presented. The suggested methodology can be geared toward any ground-motion simulation method and seismic response assessment, in a target engineering application. The methodology is founded on the comparison between conforming groups of ground-motion waveforms from recordings and simulations and their effect on a representative collection of structures that represent the engineering application. The comparison considers the statistics of earthquake scenarios at the level of the event and site parameters, the resulting waveform characteristics, and the subsequent structural responses. Regression models are developed at three levels (between structural responses and waveform characteristics, structural responses and event and site parameters, and waveform characteristics and event and site parameters). Similarities between the models from groups of recorded and simulated ground motions guide the validation process. The validation methodology is applied to CyberShake (v.15.12) simulations and for the estimation of the column drift ratio of a bridge structure. It is shown that CyberShake (v.15.12) can be used to assess the median seismic response of the used bridge. Some discrepancies between simulations and recordings are observed, which could be attributed to the basin and site-response models used for simulations. Further implementation and refinement of the suggested methodology are recommended to make broader conclusions.

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