Spectral Inversion for Seismic Site Response in Central Oklahoma: Low-Frequency Resonances from the Great Unconformity

2020 ◽  
Author(s):  
Morgan P. Moschetti ◽  
Stephen H. Hartzell
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Site Response ◽  
Low Frequency ◽  
Precambrian Basement ◽  
Velocity Models ◽  
Seismic Site Response ◽  
Impedance Contrast ◽  
Basement Depth ◽  
The Impact

ABSTRACT We investigate seismic site response by inverting seismic ground-motion spectra for site and source spectral properties, in a region of central Oklahoma, where previous ground-motion studies have indicated discrepancies between observations and ground-motion models (GMMs). The inversion is constrained by a source spectral model, which we computed from regional seismic records, using aftershocks as empirical Green’s functions to deconvolve site and path effects. Site spectra across the region exhibit multiple, strong, low-frequency (f<2  Hz) resonances. Modeling of vertically propagating SH waves reproduces the mean amplitudes and frequencies of the site spectra and requires a deep (∼1–2  km) impedance contrast. Comparison of regional seismic velocity models and geologic profiles indicates that the seismic impedance contrast is, or is in proximity to, the Great Unconformity, which marks the interface between Precambrian basement rocks and overlying Paleozoic sedimentary rocks. Depth to Precambrian basement increases to the southwest across the study region (∼1500–4500  m), and the fundamental frequencies of the site spectra are anticorrelated with basement depth. The first higher-mode resonance also exhibits dependence on basement depth; although modeling suggests that the second higher mode should depend on basement depth, site spectra do not support this. The low-frequency resonances in central Oklahoma are not represented in the GMMs used in current seismic hazard analyses for tectonic earthquakes, though approaches to account for such features are under consideration in other regions of the central and eastern United States. Given the broad spatial extent of the Great Unconformity underlying eastern North America, it is likely that similar effects on seismic site response also occur in other areas. This study highlights the impact of regional geologic structure on earthquake ground motions and reiterates the need for modeling regional effects to improve ground-motion predictions and seismic hazard assessments.

scholarly journals SEISMIC DAMAGE SCENARIOS IN KALAMATA (S. GREECE)

2017 ◽  
Vol 50 (3) ◽  
pp. 1495
Author(s):  
D. Kazantzidou-Firtinidou ◽  
I. Kassaras ◽  
A. Ganas ◽  
C. Tsimi ◽  
N. Sakellariou ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Fragility Curves ◽  
Site Amplification ◽  
Soil Conditions ◽  
Damage Scenarios ◽  
Local Soil ◽  
Protection Strategies ◽  
The Impact ◽  
The City

Damage scenarios are necessary tools for stakeholders, in order to prepare protection strategies and a total emergency post-earthquake plan. To this aim, four seismic hazard models were developed for the city of Kalamata, according to stochastic simulation of the ground motion, using site amplification functions derived from ambient noise HVSR measurements. The structural vulnerability of the city was assessed following an empirical macroseismic model, developed for the European urban environment (EMS-98). The impact of the vulnerability due to the seismic hazard potential is also investigated by means of synthetic response spectral ratios at 108 sites of the city. The expected damage grade per building block, is calculated by combining vulnerability with the respective seismic intensities, derived for the four seismic sources. The importance of the followed methodology for implementing microzonation studies is emphasized, since the expected influence of the ground motion amplification due to local soil conditions has been approximated in detail. Moreover, new fragility curves for the main structural types in Kalamata are proposed for each seismic scenario.

scholarly journals What is the impact of the August 24, 2016 Amatrice earthquake on the seismic hazard assessment in central Italy?

2016 ◽  
Vol 59 ◽  
Author(s):  
Maura Murru ◽  
Matteo Taroni ◽  
Aybige Akinci ◽  
Giuseppe Falcone
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Hazard Assessment ◽  
Central Italy ◽  
Seismic Hazard Assessment ◽  
Motion Prediction ◽  
Ground Motion Prediction Equations ◽  
Prediction Equations ◽  
Ground Motion Prediction ◽  
The Impact

<p>The recent Amatrice strong event (M<sub>w</sub>6.0) occurred on August 24, 2016 in Central Apennines (Italy) in a seismic gap zone, motivated us to study and provide better understanding of the seismic hazard assessment in the macro area defined as “Central Italy”. The area affected by the sequence is placed between the M<sub>w</sub>6.0 1997 Colfiorito sequence to the north (Umbria-Marche region) the Campotosto area hit by the 2009 L’Aquila sequence M<sub>w</sub>6.3 (Abruzzo region) to the south. The Amatrice earthquake occurred while there was an ongoing effort to update the 2004 seismic hazard map (MPS04) for the Italian territory, requested in 2015 by the Italian Civil Protection Agency to the Center for Seismic Hazard (CPS) of the Istituto Nazionale di Geofisica e Vulcanologia INGV. Therefore, in this study we brought to our attention new earthquake source data and recently developed ground-motion prediction equations (GMPEs). Our aim was to validate whether the seismic hazard assessment in this area has changed with respect to 2004, year in which the MPS04 map was released. In order to understand the impact of the recent earthquakes on the seismic hazard assessment in central Italy we compared the annual seismic rates calculated using a smoothed seismicity approach over two different periods; the Parametric Catalog of the Historical Italian earthquakes (CPTI15) from 1871 to 2003 and the historical and instrumental catalogs from 1871 up to 31 August 2016. Results are presented also in terms of peak ground acceleration (PGA), using the recent ground-motion prediction equations (GMPEs) at Amatrice, interested by the 2016 sequence.</p>

The 2018 update of the US National Seismic Hazard Model: Additional period and site class data

2020 ◽  
pp. 875529302097097
Author(s):  
Allison M Shumway ◽  
Mark D Petersen ◽  
Peter M Powers ◽  
Sanaz Rezaeian ◽  
Kenneth S Rukstales ◽  
...  
Keyword(s):  
United States ◽  
Seismic Hazard ◽  
Ground Motion ◽  
Ground Motions ◽  
Sedimentary Basins ◽  
Hazard Model ◽  
Gridded Data ◽  
Velocity Models ◽  
Hazard Curves ◽  
Site Classes

As part of the update of the 2018 National Seismic Hazard Model (NSHM) for the conterminous United States (CONUS), new ground motion and site effect models for the central and eastern United States were incorporated, as well as basin depths from local seismic velocity models in four western US (WUS) urban areas. These additions allow us, for the first time, to calculate probabilistic seismic hazard curves for an expanded set of spectral periods (0.01 to 10 s) and site classes (VS30 = 150 to 1500 m/s) for the CONUS, as well as account for amplification of long-period ground motions in deep sedimentary basins in the Los Angeles, San Francisco Bay, Seattle, and Salt Lake City areas. Two sets of 2018 NSHM hazard data (hazard curves and uniform-hazard ground motions) are available: (1) 0.05°-latitude-by-0.05°-longitude gridded data for the CONUS and (2) higher resolution 0.01°-latitude-by-0.01°-longitude gridded data for the four WUS basins. Both sets of data contain basin effects in the WUS deep sedimentary basins. Uniform-hazard ground motion data are interpolated for 2, 5, and 10% probability of exceedance in 50 years from the hazard curves. The gridded data for the hazard curves and uniform-hazard ground motions, for all periods and site classes, are available for download at the U.S. Geological Survey ScienceBase Catalog ( https://doi.org/10.5066/P9RQMREV ). The design ground motions derived from the hazard curves have been accepted by the Building Seismic Safety Council for adoption in the 2020 National Earthquake Hazard Reduction Program Recommended Seismic Provisions.

From Ergodic to Region- and Site-Specific Probabilistic Seismic Hazard Assessment: Method Development and Application at European and Middle Eastern Sites

2017 ◽  
Vol 33 (4) ◽  
pp. 1433-1453 ◽  
Author(s):  
Sreeram Reddy Kotha ◽  
Dino Bindi ◽  
Fabrice Cotton
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Hazard Assessment ◽  
Method Development ◽  
Site Response ◽  
Seismic Hazard Assessment ◽  
Probabilistic Seismic Hazard Assessment ◽  
Probabilistic Seismic Hazard ◽  
Site Specific ◽  
Aleatory Variability

The increasing numbers of recordings at individual sites allows quantification of empirical linear site-response adjustment factors ( δS2 S s) from the ground motion prediction equation (GMPE) residuals. The δS2 S s are then used to linearly scale the ergodic GMPE predictions to obtain site-specific ground motion predictions in a partially non-ergodic Probabilistic Seismic Hazard Assessment (PSHA). To address key statistical and conceptual issues in the current practice, we introduce a novel empirical region- and site-specific PSHA methodology wherein, (1) site-to-site variability ( φ S2 S) is first estimated as a random-variance in a mixed-effects GMPE regression, (2) δS2 S s at new sites with strong motion are estimated using the a priori φ S2 S, and (3) the GMPE site-specific single-site aleatory variability σ ss,s is replaced with a generic site-corrected aleatory variability σ0. Comparison of region- and site-specific hazard curves from our method against the traditional ergodic estimates at 225 sites in Europe and Middle East shows an approximate 50% difference in predicted ground motions over a range of hazard levels—a strong motivation to increase seismological monitoring of critical facilities and enrich regional ground motion data sets.

Seismic Wave Propagation and Basin Amplification in the Wasatch Front, Utah

2021 ◽  
Author(s):  
Morgan P. Moschetti ◽  
David Churchwell ◽  
Eric M. Thompson ◽  
John M. Rekoske ◽  
Emily Wolin ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Ground Motion ◽  
Seismic Wave ◽  
Seismic Velocity ◽  
Site Response ◽  
Ground Motions ◽  
Seismic Wave Propagation ◽  
Velocity Models ◽  
Ground Motion Variability ◽  
Wasatch Front

Abstract Ground-motion analysis of more than 3000 records from 59 earthquakes, including records from the March 2020 Mw 5.7 Magna earthquake sequence, was carried out to investigate site response and basin amplification in the Wasatch Front, Utah. We compare ground motions with the Bayless and Abrahamson (2019; hereafter, BA18) ground-motion model (GMM) for Fourier amplitude spectra, which was developed on crustal earthquake records from California and other tectonically active regions. The Wasatch Front records show a significantly different near-source rate of distance attenuation than the BA18 model, which we attribute to differences in (apparent) geometric attenuation. Near-source residuals show a period dependence of this effect, with greater attenuation at shorter periods (T&lt;0.5  s) and a correlation between period and the distance over which the discrepancy manifests (∼20–50  km). We adjusted the recorded ground motions for these regional path effects and solved for station site terms using linear mixed-effects regressions, with groupings for events and stations. We analyzed basin amplification by comparing the site terms with the basin geometry and basin depths from two seismic-velocity models for the region. Sites over the deeper parts of the sedimentary basins are amplified by factors of 3–10, relative to sites with thin sedimentary cover, with greater amplification at longer periods (T≳1  s). Average ground-motion variability increases with period, and long-period variability exhibits a slight increase at the basin edges. These results indicate regional seismic wave propagation effects requiring further study, and potentially a regionalized GMM, as well as highlight basin amplification complexities that may be incorporated into seismic hazard assessments.

Evaluation of stratigraphic effects on seismic site response over large areas: the case study of Italy

2021 ◽  
Author(s):  
Gaetano Falcone ◽  
Gianluca Acunzo ◽  
Amerigo Mendicelli ◽  
Federico Mori ◽  
Giuseppe Naso ◽  
...  
Keyword(s):  
Ground Motion ◽  
Site Effects ◽  
Risk Mitigation ◽  
Site Response ◽  
Free Field ◽  
Response Spectra ◽  
Seismic Intensity ◽  
Site Condition ◽  
Ground Shaking ◽  
Seismic Site Response

&lt;p&gt;Estimation of site effects over large areas is a key-issue for land management and emergency system planning in a risk mitigation perspective. In general, site-conditions are retrieved from available global datasets and the ground-shaking estimation is based on ground motion prediction equations.&lt;/p&gt;&lt;p&gt;An advanced procedure to estimate site effects over large areas is here proposed with reference to the Italian territory. Site-condition were defined for homogenous morpho-geological areas in accordance to the borehole logs and the geophysical data archived in the Italian database for seismic microzonation (https://www.webms.it/). Ground motion modifications were determined by means of about 30 milion of one-dimensional numerical simulations of local seismic site response. Correlations between amplification factors (i.e. the ratio between free-field and outcrop response spectra), AF, and site-condition (i.e. harmonic mean of the shear wave velocity in the upper 30&amp;#160;m of the deposit, V&lt;sub&gt;S30&lt;/sub&gt;) were determined for each morpho-geological homogeneous area depending on the reference seismic intensity (i.e. referred to the outcropping stiff rock characterised by V&lt;sub&gt;S30&lt;/sub&gt;&amp;#160;&amp;#8805;&amp;#160;800&amp;#160;m/s). The AF-V&lt;sub&gt;S30&lt;/sub&gt; correlations were proved to satisfactory forecast the site effects when compared with the results of site specific estimation of local seismic site response.&lt;/p&gt;

scholarly journals A review on the multi-criteria seismic hazard analysis of Ethiopia: with implications of infrastructural development

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Alemayehu Ayele ◽  
Kifle Woldearegay ◽  
Matebie Meten
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Active Fault ◽  
Site Response ◽  
Seismic Hazard Assessment ◽  
Earthquake Ground Motion ◽  
Response Analysis ◽  
Ethiopian Rift ◽  
Rift System ◽  
Main Ethiopian Rift

AbstractEarthquake is a sudden release of energy due to faults. Natural calamities like earthquakes can neither be predicted nor prevented. However, the severity of the damages can be minimized by development of proper infrastructure which includes microzonation studies, appropriate construction procedures and earthquake resistant designs. The earthquake damaging effect depends on the source, path and site conditions. The earthquake ground motion is affected by topography (slope, hill, valley, canyon, ridge and basin effects), groundwater and surface hydrology. The seismic hazard damages are ground shaking, structural damage, retaining structure failures and lifeline hazards. The medium to large earthquake magnitude (< 6) reported in Ethiopia are controlled by the main Ethiopian rift System. The spatial and temporal variation of earthquake ground motion should be addressed using the following systematic methodology. The general approaches used to analyze damage of earthquake ground motions are probabilistic seismic hazard assessment (PSHA), deterministic seismic hazard assessment (DSHA) and dynamic site response analysis. PSHA considers all the scenarios of magnitude, distance and site conditions to estimate the intensity of ground motion distribution. Conversely, DSHA taken into account the worst case scenarios or maximum credible earthquake to estimate the intensity of seismic ground motion distribution. Furthermore, to design critical infrastructures, DSHA is more valuable than PSHA. The DSHA and PSHA ground motion distributions are estimated as a function of earthquake magnitude and distance using ground motion prediction equations (GMPEs) at top of the bedrock. Site response analysis performed to estimate the ground motion distributions at ground surface using dynamic properties of the soils such as shear wave velocity, density, modulus reduction, and material damping curves. Seismic hazard evaluation of Ethiopia shown that (i) amplification is occurred in the main Ethiopian Rift due to thick soil, (ii) the probability of earthquake recurrence due to active fault sources. The situation of active fault is oriented in the N-S direction. Ethiopia is involved in huge infrastructural development (including roads, industrial parks and railways), increasing population and agricultural activity in the main Ethiopian Rift system. In this activity, socio-economic development, earthquake and earthquake-generated ground failures need to be given attention in order to reduce losses from seismic hazards and create safe geo-environment.

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.

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