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At least 109 records · Page 6Linked to original sources
USGS2015

Estimating annualized earthquake losses for the conterminous United States

We make use of the most recent National Seismic Hazard Maps (the years 2008 and 2014 cycles), updated census data on population, and economic exposure estimates of general building stock to quantify annualized earthquake loss (AEL) for the conterminous United States. The AEL analyses were performed using the Federal Emergency Management Agency's (FEMA) Hazus software, which facilitated a systematic comparison of the influence of the 2014 National Seismic Hazard Maps in terms of annualized loss estimates in different parts of the country. The losses from an individual earthquake could easily exceed many tens of billions of dollars, and the long-term averaged value of losses from all earthquakes within the conterminous U.S. has been estimated to be a few billion dollars per year. This study estimated nationwide losses to be approximately $4.5 billion per year (in 2012$), roughly 80% of which can be attributed to the States of California, Oregon and Washington. We document the change in estimated AELs arising solely from the change in the assumed hazard map. The change from the 2008 map to the 2014 map results in a 10 to 20% reduction in AELs for the highly seismic States of the Western United States, whereas the reduction is even more significant for Central and Eastern United States.

Earthquake Spectra↗
USGS2013

Identifying the dynamic characteristics of a dual core-wall and frame building in Chile using aftershocks of the 27 February 2010 (M w =8.8) Maule, Chile, earthquake

Following the 27 February 2010 (M w = 8.8) Offshore Maule, Chile earthquake, a temporary, 16-channel, real-time data streaming array was installed in a recently constructed building in Viña del Mar to capture its responses to aftershocks. The cast-in-place, reinforced concrete building is 16 stories high, with 3 additional basement levels, and has dual system comprising multiple structural walls and perimeter frames. This building was not damaged during the main-shock, but other buildings of similar design in Viña del Mar and other parts of Chile were damaged, although none collapsed. Dynamic characteristics of the building identified from the low-amplitude (PGA of about 2 Gal) response recordings of aftershocks are found to compare well with those determined from modal analyses using a design level FEM model. Distinct “major-axes” translational and torsional fundamental frequencies, as well as frequencies of secondary modes, are identified. Evidence of beating is consistently observed in the response data for each earthquake. Results do not match well with U.S. code formulas.

Talca Province↗
USGS2017

A prototype operational earthquake loss model for California based on UCERF3-ETAS – A first look at valuation

We present a prototype operational loss model based on UCERF3-ETAS, which is the third Uniform California Earthquake Rupture Forecast with an Epidemic Type Aftershock Sequence (ETAS) component. As such, UCERF3-ETAS represents the first earthquake forecast to relax fault segmentation assumptions and to include multi-fault ruptures, elastic-rebound, and spatiotemporal clustering, all of which seem important for generating realistic and useful aftershock statistics. UCERF3-ETAS is nevertheless an approximation of the system, however, so usefulness will vary and potential value needs to be ascertained in the context of each application. We examine this question with respect to statewide loss estimates, exemplifying how risk can be elevated by orders of magnitude due to triggered events following various scenario earthquakes. Two important considerations are the probability gains, relative to loss likelihoods in the absence of main shocks, and the rapid decay of gains with time. Significant uncertainties and model limitations remain, so we hope this paper will inspire similar analyses with respect to other risk metrics to help ascertain whether operationalization of UCERF3-ETAS would be worth the considerable resources required.

Earthquake Spectra↗
USGS2016

Responses of a 58-story RC dual core shear wall and outrigger frame building inferred from two earthquakes

Responses of a dual core shear-wall and outrigger-framed 58-story building recorded during the M w 6.0 Napa earthquake of 24 August 2014 and the M w 3.8 Berkeley earthquake of 20 October 2011 are used to identify its dynamic characteristics and behavior. Fundamental frequencies are 0.28 Hz (NS), 0.25 Hz (EW), and 0.43 Hz (torsional). Rigid body motions due to rocking are not significant. Average drift ratios are small. Outrigger frames do not affect average drift ratios or mode shapes. Local site effects do not affect the response; however, response associated with deeper structure may be substantial. A beating effect is observed from data of both earthquakes but beating periods are not consistent. Low critical damping ratios may have contributed to the beating effect. Torsion is relatively larger above outriggers as indicated by the time-histories of motions at the roof, possibly due to the discontinuity of the stiffer shear walls above level 47.

California↗
USGS2015

Collapse risk of buildings in the Pacific Northwest region due to subduction earthquakes

Subduction earthquakes similar to the 2011 Japan and 2010 Chile events will occur in the future in the Cascadia subduction zone in the Pacific Northwest. In this paper, nonlinear dynamic analyses are carried out on 24 buildings designed according to outdated and modern building codes for the cities of Seattle, Washington, and Portland, Oregon. The results indicate that the median collapse capacity of the ductile (post-1970) buildings is approximately 40% less when subjected to ground motions from subduction, as compared to crustal earthquakes. Buildings are more susceptible to earthquake-induced collapse when shaken by subduction records (as compared to crustal records of the same intensity) because the subduction motions tend to be longer in duration due to their larger magnitude and the greater source-to-site distance. As a result, subduction earthquakes are shown to contribute to the majority of the collapse risk of the buildings analyzed.

Pacific Northwest↗
USGS2016

Comparison of measurement- and proxy-based Vs30 values in California

This study was prompted by the recent availability of a significant amount of openly accessible measured V S 30 values and the desire to investigate the trend of using proxy-based models to predict V S 30 in the absence of measurements. Comparisons between measured and model-based values were performed. The measured data included 503 V S 30 values collected from various projects for 482 seismographic station sites in California. Six proxy-based models—employing geologic mapping, topographic slope, and terrain classification—were also considered. Included was a new terrain class model based on the Yong et al. (2012) approach but recalibrated with updated measured V S 30 values. Using the measured V S 30 data as the metric for performance, the predictive capabilities of the six models were determined to be statistically indistinguishable. This study also found three models that tend to underpredict V S 30 at lower velocities (NEHRP Site Classes D–E) and overpredict at higher velocities (Site Classes B–C).

Earthquake Spectra↗
USGS2017

Study of responses of 64-story Rincon Building to Napa, Fremont, Piedmont, San Ramon earthquakes and ambient motions

We analyze the recorded responses of a 64-story, instrumented, concrete core shear wall building in San Francisco, California, equipped with tuned sloshing liquid dampers (TSDs) and buckling restraining braces (BRBs). Previously, only ambient data from the 72-channel array in the building were studied ( Çelebi et al. 2013 ). Recently, the 24 August 2014 M w 6.0 Napa and three other earthquakes were recorded. The peak accelerations of ambient and the larger Napa earthquake responses at the basement are 0.12 cm/s/s and 5.2 cm/s/s respectively—a factor of ~42. At the 61st level, they are 0.30 cm/s/s (ambient) and 16.8 cm/s/s (Napa), respectively—a factor of ~56. Fundamental frequencies (NS ~ 0.3, EW ~ 0.27 Hz) from earthquake responses vary within an insignificant frequency band of ~0.02–0.03 Hz when compared to those from ambient data. In the absence of soil-structure interaction (SSI), these small and insignificant differences may be attributed to (1) identification errors, (2) any nonlinear behavior, and (3) shaking levels that are not large enough to activate the BRBs and TSDs to make significant shifts in frequencies and increase damping.

California↗
USGS2014

Rocking behavior of an instrumented unique building on the MIT campus identified from ambient shaking data

A state-of-the-art seismic monitoring system comprising 36 accelerometers and a data-logger with real-time capability was recently installed at Building 54 on the Massachusetts Institute of Technology's (MIT) Cambridge, MA, campus. The system is designed to record translational, torsional, and rocking motions, and to facilitate the computation of drift between select pairs of floors. The cast-in-place, reinforced concrete building is rectangular in plan but has vertical irregularities. Heavy equipment is installed asymmetrically on the roof. Spectral analyses and system identification performed on five sets of low-amplitude ambient data reveal distinct and repeatable fundamental translational frequencies in the structural NS and EW directions (0.75 Hz and 0.68 Hz, respectively), a torsional frequency of 1.49 Hz, a rocking frequency of 0.75 Hz, and very low damping. Such results from low-amplitude data serve as a baseline against which to compare the behavior and performance of the building during stronger shaking caused by future earthquakes in the region.

Masachusetts↗
USGS2019

Increases in life-safety risks to building occupants from induced earthquakes in the central United States

Earthquake occurrence rates in some parts of the central United States have been elevated for a number of years; this increase has been widely attributed to deep wastewater injection associated with oil and gas activities. This induced seismicity has caused damage to buildings and infrastructure and substantial public concern. In March 2016, the U.S. Geological Survey (USGS) published its first earthquake ground motion hazard model that accounts for the elevated seismicity, producing a one-year forecast encompassing both induced and natural earthquakes. To assess the potential impacts of the elevated seismicity on buildings and the public, this paper quantifies forecasted risks of a) building collapse and b) falling of nonstructural building components, by combining the 2016 USGS hazard model with fragility curves for generic modern code-compliant buildings. The assessment shows significant increases in both types of risk compared to that due to non-induced earthquakes alone; the magnitudes of the increases vary from a few times to more than a 100 times, depending on location, building period (which is correlated to building height), alternatives for the hazard model, and the type of risk of interest. For exploratory purposes only, we also estimate revised values of the risk-targeted ground motion that are currently used for designing buildings.

Texas, Oklahoma↗
USGS2015

Updates to building-code maps for the 2015 NEHRP recommended seismic provisions

With the 2014 update of the U.S. Geological Survey (USGS) National Seismic Hazard Model (NSHM) as a basis, the Building Seismic Safety Council (BSSC) has updated the earthquake ground motion maps in the National Earthquake Hazards Reduction Program (NEHRP) Recommended Seismic Provisions for New Buildings and Other Structures , with partial funding from the Federal Emergency Management Agency. Anticipated adoption of the updated maps into the American Society of Civil Engineers Minimum Design Loads for Building and Other Structures and the International Building and Residential Codes is underway. Relative to the ground motions in the prior edition of each of these documents, most of the updated values are within a ±20% change. The larger changes are, in most cases, due to the USGS NSHM updates, reasons for which are given in companion publications. In some cases, the larger changes are partly due to a BSSC update of the slope of the fragility curve that is used to calculate the risk-targeted ground motions, and/or the introduction by BSSC of a quantitative definition of “active faults” used to calculate deterministic ground motions.

Earthquake Spectra↗
USGS2016

Responses of a tall building in Los Angeles, California as inferred from local and distant earthquakes

Increasing inventory of tall buildings in the United States and elsewhere may be subjected to motions generated by near and far seismic sources that cause long-period effects. Multiple sets of records that exhibited such effects were retrieved from tall buildings in Tokyo and Osaka ~ 350 km and 770 km from the epicenter of the 2011 Tohoku earthquake. In California, very few tall buildings have been instrumented. An instrumented 52-story building in downtown Los Angeles recorded seven local and distant earthquakes. Spectral and system identification methods exhibit significant low frequencies of interest (~0.17 Hz, 0.56 Hz and 1.05 Hz). These frequencies compare well with those computed by transfer functions; however, small variations are observed between the significant low frequencies for each of the seven earthquakes. The torsional and translational frequencies are very close and are coupled. Beating effect is observed in at least two of the seven earthquake data.

Earthquake Spectra↗
USGS2016

Responses of a tall building with U.S. code-type instrumentation in Tokyo, Japan, to events before, during and after the Tohoku earthquake of 11 March 2011

The 11 March 2011 M 9.0 Tohoku earthquake generated long-duration shaking that propagated hundreds of kilometers from the epicenter and affected tall buildings in urban areas several hundred kilometers from the epicenter of the main shock. Recorded responses show that tall buildings were affected by long-period motions. This study presents the behavior and performance of a 37-story building in the Tsukuda area of Tokyo, Japan, as inferred from modal analyses of records retrieved for a time interval covering a few days before, during, and for several months after the main shock. The U.S. “code-type” array comprises three triaxial accelerometers deployed at three levels in the superstructure. Such a sparse array in a tall structure limits a reliable assessment, because its performance must be based on only the average drift ratios. Based on the inferred values of this parameter, the subject building was not structurally damaged.

Toyko↗
USGS2014

Implementation of NGA-West2 ground motion models in the 2014 U.S. National Seismic Hazard Maps

The U.S. National Seismic Hazard Maps (NSHMs) have been an important component of seismic design regulations in the United States for the past several decades. These maps present earthquake ground shaking intensities at specified probabilities of being exceeded over a 50-year time period. The previous version of the NSHMs was developed in 2008; during 2012 and 2013, scientists at the U.S. Geological Survey have been updating the maps based on their assessment of the “best available science,” resulting in the 2014 NSHMs. The update includes modifications to the seismic source models and the ground motion models (GMMs) for sites across the conterminous United States. This paper focuses on updates in the Western United States (WUS) due to the use of new GMMs for shallow crustal earthquakes in active tectonic regions developed by the Next Generation Attenuation (NGA-West2) project. Individual GMMs, their weighted combination, and their impact on the hazard maps relative to 2008 are discussed. In general, the combined effects of lower medians and increased standard deviations in the new GMMs have caused only small changes, within 5–20%, in the probabilistic ground motions for most sites across the WUS compared to the 2008 NSHMs.

Earthquake Spectra↗
USGS2014

NGA-West 2 Equations for predicting PGA, PGV, and 5%-Damped PSA for shallow crustal earthquakes

We provide ground-motion prediction equations for computing medians and standard deviations of average horizontal component intensity measures (IMs) for shallow crustal earthquakes in active tectonic regions. The equations were derived from a global database with M 3.0–7.9 events. We derived equations for the primary M- and distance-dependence of the IMs after fixing the V S30 -based nonlinear site term from a parallel NGA-West 2 study. We then evaluated additional effects using mixed effects residuals analysis, which revealed no trends with source depth over the M range of interest, indistinct Class 1 and 2 event IMs, and basin depth effects that increase and decrease long-period IMs for depths larger and smaller, respectively, than means from regional V S30 -depth relations. Our aleatory variability model captures decreasing between-event variability with M, as well as within-event variability that increases or decreases with M depending on period, increases with distance, and decreases for soft sites.

Earthquake Spectra↗
USGS2017

Effects of deep basins on structural collapse during large subduction earthquakes

Deep sedimentary basins are known to increase the intensity of ground motions, but this effect is implicitly considered in seismic hazard maps used in U.S. building codes. The basin amplification of ground motions from subduction earthquakes is particularly important in the Pacific Northwest, where the hazard at long periods is dominated by such earthquakes. This paper evaluates the effects of basins on spectral accelerations, ground-motion duration, spectral shape, and structural collapse using subduction earthquake recordings from basins in Japan that have similar depths as the Puget Lowland basin. For three of the Japanese basins and the Puget Lowland basin, the spectral accelerations were amplified by a factor of 2 to 4 for periods above 2.0 s. The long-duration subduction earthquakes and the effects of basins on spectral shape combined, lower the spectral accelerations at collapse for a set of building archetypes relative to other ground motions. For the hypothetical case in which these motions represent the entire hazard, the archetypes would need to increase up to 3.3 times its strength to compensate for these effects.

Earthquake Spectra↗
USGS2016

NGA-West2 equations for predicting vertical-component PGA, PGV, and 5%-damped PSA from shallow crustal earthquakes

We present ground motion prediction equations (GMPEs) for computing natural log means and standard deviations of vertical-component intensity measures (IMs) for shallow crustal earthquakes in active tectonic regions. The equations were derived from a global database with M 3.0–7.9 events. The functions are similar to those for our horizontal GMPEs. We derive equations for the primary M - and distance-dependence of peak acceleration, peak velocity, and 5%-damped pseudo-spectral accelerations at oscillator periods between 0.01–10 s. We observe pronounced M -dependent geometric spreading and region-dependent anelastic attenuation for high-frequency IMs. We do not observe significant region-dependence in site amplification. Aleatory uncertainty is found to decrease with increasing magnitude; within-event variability is independent of distance. Compared to our horizontal-component GMPEs, attenuation rates are broadly comparable (somewhat slower geometric spreading, faster apparent anelastic attenuation), V S 30 -scaling is reduced, nonlinear site response is much weaker, within-event variability is comparable, and between-event variability is greater.

Earthquake Spectra↗
USGS2016

An investigation of soil-structure interaction effects observed at the MIT Green Building

The soil-foundation impedance function of the MIT Green Building is identified from its response signals recorded during an earthquake. Estimation of foundation impedance functions from seismic response signals is a challenging task, because: (1) the foundation input motions (FIMs) are not directly measurable, (2) the as-built properties of the super-structure are only approximately known, and (3) the soil-foundation impedance functions are inherently frequency-dependent. In the present study, aforementioned difficulties are circumvented by using, in succession, a blind modal identification (BMID) method, a simplified Timoshenko beam model (TBM), and a parametric updating of transfer functions (TFs). First, the flexible-base modal properties of the building are identified from response signals using the BMID method. Then, a flexible-base TBM is updated using the identified modal data. Finally, the frequency-dependent soil-foundation impedance function is estimated by minimizing the discrepancy between TFs (of pairs instrumented floors) that are (1) obtained experimentally from earthquake data and (2) analytically from the updated TBM. Using the fully identified flexible-base TBM, the FIMs as well as building responses at locations without instruments can be predicted, as demonstrated in the present study.

Massachussets↗
USGS2014

Comparison of NGA-West2 directivity models

Five directivity models have been developed based on data from the NGA-West2 database and based on numerical simulations of large strike-slip and reverse-slip earthquakes. All models avoid the use of normalized rupture dimension, enabling them to scale up to the largest earthquakes in a physically reasonable way. Four of the five models are explicitly “narrow-band” (in which the effect of directivity is maximum at a specific period that is a function of earthquake magnitude). Several strategies for determining the zero-level for directivity have been developed. We show comparisons of maps of the directivity amplification. This comparison suggests that the predicted geographic distributions of directivity amplification are dominated by effects of the models' assumptions, and more than one model should be used for ruptures dipping less than about 65 degrees.

Earthquake Spectra↗