El Cerrito, CA, United States
El Cerrito, CA, United States

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Ktenidou O.-J.,University of Greenwich | Ktenidou O.-J.,Helmholtz Center Potsdam | Silva W.J.,Pacific Engineering and Analysis | Darragh R.B.,Pacific Engineering and Analysis | And 2 more authors.
Bulletin of the Seismological Society of America | Year: 2017

The κ parameter (Anderson and Hough, 1984), and namely its sitespecific component (κ0), is important for predicting and simulating high-frequency ground motion. We develop a framework for estimating κ0 and addressing uncertainties under the challenging conditions often imposed in practice: (1) low seismicity (limited, poor-quality, distant records); (2) limited-bandwidth data from the Transportable Array (TA; maximum usable frequency 16 Hz); and (3) low magnitudes (ML 1.2– 3.4) and large uncertainty in stress drop (corner frequency). We cannot resolve stress drop within the bandwidth, so we propose an approach that only requires upper and lower bounds on its regional values to estimate κ0. To address uncertainties, we combine three measurement approaches (acceleration spectrum slope [AS]; displacement spectrum slope [DS]; and broadband spectral fit).We also examine the effect of crustal amplification, and find that neglecting it can affect κ0 by up to 35%. DS estimates greatly exceed AS estimates. We propose a reason behind this bias, related to the residual effect of the corner frequency on κAS and κDS. For our region, we estimate a frequency-independent mean S-wave Q of 900 ± 300 at 9–16 Hz, and an ensemble mean κ0 over all sites of 0:033 ± 0:014 s. This value is similar to the native κ0 of the Next Generation Attenuation-West 2 ground-motion prediction equations, indicating that these do not need to be adjusted for κ0 for use in southern Arizona. We find that stress-drop values in this region may be higher compared to estimates of previous studies, possibly due to trade-offs between stress drop and κ0. For this dataset, the within-approach uncertainty is much larger than the between-approach uncertainty, and it cannot be reduced if the data quality is not improved. The challenges discussed here will be relevant in studies of κ for other regions with bandlimited data; for example, any region where data come primarily from the TA. © 2017, Seismological Society of America. All rights reserved.

Rezaeian S.,U.S. Geological Survey | Bozorgnia Y.,University of California at Berkeley | Idriss I.M.,University of California at Davis | Abrahamson N.,Pacific Gas and Electric Company | And 2 more authors.
Earthquake Spectra | Year: 2014

Ground motion prediction equations (GMPEs) for elastic response spectra are typically developed at a 5% viscous damping ratio. In reality, however, structural and nonstructural systems can have other damping ratios. This paper develops a new model for a damping scaling factor (DSF) that can be used to adjust the 5% damped spectral ordinates predicted by a GMPE for damping ratios between 0.5% to 30%. The model is developed based on empirical data from worldwide shallow crustal earthquakes in active tectonic regions. Dependencies of the DSF on potential predictor variables, such as the damping ratio, spectral period, ground motion duration, moment magnitude, source-to-site distance, and site conditions, are examined. The strong influence of duration is captured by the inclusion of both magnitude and distance in the DSF model. Site conditions show weak influence on the DSF. The proposed damping scaling model provides functional forms for the median and logarithmic standard deviation of DSF, and is developed for both RotD50 and GMRotI50 horizontal components. A follow-up paper develops a DSF model for vertical ground motion.© 2014, Earthquake Engineering Research Institute.

Gregor N.,Bechtel Corporation | Abrahamson N.A.,PG and E | Atkinson G.M.,University of Western Ontario | Boore D.M.,U.S. Geological Survey | And 7 more authors.
Earthquake Spectra | Year: 2014

A presentation of the model parameters and comparison of the median ground-motion values from the NGA-West2 GMPEs is presented for a suite of deterministic cases. In general, the median ground motions are similar, within a factor of about 1.5-2.0 for 5 < M < 7 and distances between 10-100 km. Differences increase (on the order of 2-3) for large-magnitude (M > 8) earthquakes at large distances (R > 100-200 km) and for close distances (R < 10 km). A similar increase is observed for hanging-wall sites, and slightly larger differences are observed for soil sites as opposed to rock sites. Regionalization of four of the GMPEs yields similar attenuation rate adjustments based on the different regional data sets. All five GMPE aleatory variability models are a function of magnitude with higher overall standard deviations values for the smaller magnitudes when compared to the large-magnitude events. © 2014, Earthquake Engineering Research Institute.

Ancheta T.D.,Risk Management Solutions | Darragh R.B.,Pacific Engineering and Analysis | Stewart J.P.,University of California at Los Angeles | Seyhan E.,University of California at Los Angeles | And 7 more authors.
Earthquake Spectra | Year: 2014

The NGA-West2 project database expands on its predecessor to include worldwide ground motion data recorded from shallow crustal earthquakes in active tectonic regimes post-2000 and a set of small-to-moderate-magnitude earthquakes in California between 1998 and 2011. The database includes 21,336 (mostly) three-component records from 599 events. The parameter space covered by the database is M 3.0 to M 7.9, closest distance of 0.05 to 1,533 km, and site time-averaged shear-wave velocity in the top 30 m of VS30= 94 m/s to 2,100 m/s (although data becomes sparse for distances >400 km and VS30> 1,200 m/s or <150 m/s). The database includes uniformly processed time series and response spectral ordinates for 111 periods ranging from 0.01 s to 20 s at 11 damping ratios. Ground motions and metadata for source, path, and site conditions were subject to quality checks by ground motion prediction equation developers and topical working groups. © 2014, Earthquake Engineering Research Institute.

Abrahamson N.A.,Pacific Gas and Electric Company | Silva W.J.,Pacific Engineering and Analysis | Kamai R.,Ben - Gurion University of the Negev
Earthquake Spectra | Year: 2014

Empirical ground motion models for the average horizontal component from shallow crustal earthquakes in active tectonic regions are derived using the PEER NGA-West2 database. The model is applicable to magnitudes 3.0-8.5, distances 0-300 km, and spectral periods of 0-10 s. The model input parameters are the same as those used by Abrahamson and Silva (2008), with the following exceptions: the loading level for nonlinear effects is based on the spectral acceleration at the period of interest rather than the PGA; and the distance scaling for hanging wall (HW) effects off the ends of the rupture includes a dependence on the source-to-site azimuth. Regional differences in large-distance attenuation and VS30scaling between California, Japan, China, and Taiwan are included. The scaling for the HW effect is improved using constraints from numerical simulations. The standard deviation is magnitude-dependent, with smaller magnitudes leading to larger standard deviations at short periods, but smaller standard deviations at long periods. Directivity effects are not included through explicit parameters, but are captured through the variability of the empirical data. © 2014, Earthquake Engineering Research Institute.

Hashash Y.M.A.,University of Illinois at Urbana - Champaign | Kottke A.R.,Bechtel Corporation | Stewart J.P.,University of California at Los Angeles | Campbell K.W.,EQECAT Inc. | And 5 more authors.
Bulletin of the Seismological Society of America | Year: 2014

The reference rock site condition has two important applications for ground-motion prediction in the stable continental region of central and eastern North America (CENA). (1) It represents the site condition for which ground motions are computed using semiempirical ground-motion prediction equations. In addition, (2) it represents the site condition to which site amplification factors, which are used to modify ground-motion intensity measures for softer site condition, are referenced (i.e., site amplification is unity for reference rock).We define reference rock by its shear (S)- and compression (P)-wave velocities, as well as a site attenuation parameter (κ0), which is used in stochastic ground-motion simulation methods. Prior definitions of reference rock conditions in CENAwere based mostly on indirect large-scale crustal velocity inversions and judgment. We compile and interpret a unique database of direct velocity measurements to develop criteria for assessing the presence of reference rock site condition based on measured seismic velocities and their gradient with respect to depth. We apply the criteria to available profiles and perform rigorous statistical analysis from which we recommend S- and P-wave velocities of 3000 and 5500 m=s, respectively, for the reference rock condition.We recommend that, for practical applications, use ranges of reference S- and P-wave velocities of 2700-3300 m/s and 5000-6100 m/s, respectively. The ranges are based on a ±5% change in amplification using quarterwavelength theory. We do not find evidence for regional dependence of the reference velocities, which are derived principally from three general geographic regions: (1) Atlantic coast, (2) continental interior, and (3) Appalachian Mountains. Our data do not provide reference velocities for the Gulf Coast region. The recommended velocity-compatible reference rock site kappa is 0.006 s.© 2014 by the Seismological Society of America.

Stewart J.P.,University of California at Los Angeles | Lanzo G.,University of Rome La Sapienza | Pagliaroli A.,CNR Institute of Environmental Geology and Geoengineering | Scasserra G.,University of Rome La Sapienza | And 4 more authors.
Earthquake Spectra | Year: 2012

The 2009 L'Aquila earthquake sequence includes the April 6 M w 6.3 main shock and triggered events on April 7 and 9, each recorded on a digital network having five stations on the hanging wall of the main shock fault. We describe a geometric source model drawing upon inversions by others. We describe record-specific ground motion data processing that includes the incorporation of static displacements of up to 13 cm (downdrop of hanging wall). The resulting database includes 47, 38, and 31 corrected triaxial recordings from the April 6, 7, and 9 events, respectively. We present site conditions for recording stations, including recent surface wave and borehole geophysics. We demonstrate that the high-frequency data are weaker than expected for normal fault earthquakes of these magnitudes and that the data attenuate with distance at rates generally consistent with modified next generation attenuation (NGA) equations for Italy that were available prior to the event. © 2012, Earthquake Engineering Research Institute.

Kamai R.,Ben - Gurion University of the Negev | Abrahamson N.A.,Pacific Gas and Electric Company | Silva W.J.,Pacific Engineering and Analysis
Earthquake Spectra | Year: 2014

The nonlinear soil amplification models developed by Walling et al. (2008) are revisited for three main reasons: (a) the simulation database on which the models were developed has been updated and extended, (b) two alternatives for the input shaking parameter - (PGA and Sa(T)) - are explored, and (c) a constraint on the nonlinearity at long periods is removed. The model is based on site amplification factors, relative to a VS30= 1;180 m/s site. Simulations included a wide range of soil profiles, shaking amplitudes and soil properties, from which only a subset was used herein. Finally, four models for the nonlinear site amplification are developed using two nonlinear material property models (peninsular range and EPRI) and two input-shaking parameters (PGA1180and Sa1180(T)). These results are intended for use by the NGA-West2 developers to constrain the nonlinear scaling of the site response for the horizontal ground motion models. © 2014, Earthquake Engineering Research Institute.

Seyhan E.,University of California at Los Angeles | Stewart J.P.,University of California at Los Angeles | Ancheta T.D.,Risk Management Solutions | Darragh R.B.,Pacific Engineering and Analysis | Graves R.W.,U.S. Geological Survey
Earthquake Spectra | Year: 2014

The NGA-West2 site database (SDB) contains information on site condition and instrument housing for 4,147 strong-motion stations with recordings in the project flatfile. The stations are from active tectonic regions, mainly in California, Japan, Taiwan, China, and the Mediterranean area. The principal site parameter is the time-averaged shear wave velocity in the upper 30 m (VS30), which we characterize using measurements where available (2,013 stations) and proxy-based relationships otherwise. We also provide basin depths from published models for 2,761 sites mostly in California and Japan. We improved the documentation and consistency of site descriptors used as proxies for VS30estimation (surface geology, ground slope, and geotechnical or geomorphic categories) and analyzed proxy performance relative to VS30values from measurements. We present protocols for VS30estimation from proxies that emphasize methods minimizing bias and dispersion relative to data. For each site, we provide the preferred VS30and its dispersion. © 2014, Earthquake Engineering Research Institute.

Darragh R.B.,Pacific Engineering and Analysis | Silva W.J.,Pacific Engineering and Analysis | Addo K.O.,BC Hydro
NCEE 2014 - 10th U.S. National Conference on Earthquake Engineering: Frontiers of Earthquake Engineering | Year: 2014

Probabilistic Seismic Hazard Analysis (PSHA) reflecting an outcropping reference firm rock site condition (Vs30=760 m/sec) was performed at two BC Hydro dam (hard rock) sites. This reference firm rock condition is consistent with assumptions made in the development of the most recent ground motion prediction equations (GMPEs) for these locations as part of a SSHAC Level 3 project. The next step is the development of frequency and amplitude dependent relative amplification factors (for 5% damped response spectra) between the hard rock dam sites and the firm rock reference site. These factors accommodate potential linear or nonlinear site response using equivalent-linear analysis in a frequency domain random vibration theory methodology. The uncertainty in parameters (e.g. near-surface velocity and dynamic properties) is accounted for when developing the site specific hazard curves. Third, site-specific motions are computed by scaling the reference firm rock site motions with the amplification factors. Probabilistic methods have been developed that accurately preserve the reference site hazard level and result in site-specific hazard curves. These fully probabilistic approaches represent a viable and preferred mechanism to properly incorporate the site-specific aleatory (randomness) and epistemic (uncertainty) variability of the site properties to achieve desired hazard levels. A parallel analysis develops V/H ratios for the calculation of the vertical hazard using the site-specific horizontal motions scaled by empirical and analytical V/H ratios. The site response analyses at two BC Hydro dam sites produced site-specific hazard curves as well as horizontal and vertical response spectra which reflect the desired exceedance frequencies.

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