In developing updates to the 2018 NSHM, the USGS makes every reasonable effort to include the best science, data, models, and methods available at the time of publication for these important applications (e.g. Additional figures and supporting information can be found at the USGS ScienceBase Catalog (Rukstales and Petersen, 2019). In past versions of their seismic provisions, the BSSC recommended development of peak horizontal ground acceleration (PGA) as well as 0.2- and 1-s spectral accelerations (SA) that define simplified response spectral shapes with a firm-rock site condition of 760 m/s VS30 (time-averaged shear-wave velocity in the upper 30 m of the crust). | Your California Privacy Rights The 2% probability of exceedance in 50 years ground shaking for 5-s SA at a Seattle site (VS30 = 500 m/s) has a default ground motion of about 0.10 g and a basin-amplified motion of 0.15 g (50% increase). (Source: USGS) The maps represent an assessment of the … | Trademarks. Based on expert recommendations, we reduced the number of seed GMMs from 19 models to 14 models, which we refer to as the Updated Seed GMMs. Table 3. We smoothed the impedance model term and associated uncertainty at 0.1 s via interpolation. This application primarily amplifies ground motions except at soft soil sites where the default basin depth may be deeper than that of the velocity model, resulting in slight deamplification of ground motions over and just below the depth taper range. Geoscience Australia develops the National Seismic Hazard Assessment (NSHA) for Australia. Figure 10. In this update, we are considering, for the first time, seismic velocities and depths of sedimentary basins that can be explicitly used to assess the long-period shaking for four areas that have been characterized at a sufficiently detailed scale: Seattle, San Francisco Bay area, greater Los Angeles region, and areas surrounding Salt Lake City. 0.2 and 1 s) to a more representative spectrum defined at multiple periods. Updated the 2012 BC Hydro GMM (Addo et al., 2012; used in 2014 NSHM) to be consistent with Abrahamson et al. Updates that we are considering for future NSHMs include reevaluation of the acceptance criteria of GMMs based on period and site class and associated weighting schemes for assessing epistemic (Sammon’s map) and fully ergodic and non-ergodic aleatory uncertainties, more complete calculation of uncertainties (fractiles) in the hazard models, assessment of earthquake magnitude-frequency distributions on faults and especially those with unknown or poorly defined slip rate data, regionalization of input models and implementation of non-ergodic inputs, appraisal of time-dependent forecasts of large earthquakes on faults, improvements of fault slip rate information and the associated joint inversion of geologic and geodetic models, development and implementation of physics-based source and ground motion computer simulation models, consideration of alternative decluster models (e.g. For more information view the SAGE Journals Article Sharing page. Following some iteration with the NGA-East Technical Integration (TI) team (Goulet et al., 2017, with addendum), the 17 NGA-East for USGS models ended up being identical to the 17 final NGA-East models for nuclear facilities, which were released after this 2018 NSHM model was completed (Goulet et al., 2018). For example, we carefully reviewed and validated the AIR stochastic catalog for earthquakes with UCERF3 for California by comparing magnitude-rate distribution and hazard calculations at selected locations near Los Angeles and San Francisco, and results are similar. Listen to Dr Matt Gerstenberger talk about the NSHM (2-minute audio clip) on RNZ National. Decreases in seismic hazard are located in the northeast United States (down 12% at New York City, NY), the Eastern Tennessee seismic zone, and across the Intermountain West which are mostly due to catalog changes. We thank the many people who significantly improved the manuscript through reviews and discussions including Jill McCarthy, Bruce Worden, Grace Parker, Bill Stephenson, Gail Atkinson, Jon Ake, Janet Slate, working groups that produced important inputs that are acknowledged within the paper, participants at the 2018 US National Seismic Hazard Model (NSHM) Update workshop, the NSHM Steering Committee, US Geological Survey editors and reviewers, Earthquake Spectra editors and reviewers, and the public who participated in the open comment period. National Seismic Hazard Model Programme This map shows the 2% probability of exceedance of peak ground acceleration (PGA) from earthquake shaking in any 50-year time window. The new building provisions allow for increased seismic safety of buildings in areas of high seismic risk and this is one of the most important applications of these models. I did not want to wait any longer on getting my apartment which is a soft story compliant with our city's earthquake ordinance. National Seismic Retrofit put my concerns at ease with a construction project completed and passing inspections with flying colors. Map showing the chance of minor damaging earthquake shaking in 100 years from the 2018 NSHM. Ground shaking at 5-s SA has increased in four WUS urban areas (Los Angeles, San Francisco Bay area, Seattle, and Salt Lake City) by up to 50% compared to the 2014 NSHM maps that used default basin depths. A general overview of the 2014 USGS National Seismic Hazard Map, indicating the probability of earthquakes throughout the United States. In addition, preliminary findings of recent research using data from southern California basins indicates that deamplification effects in current basin models are mostly from broad, relatively shallow basin structures and not from the edges of deep basins (Nweke et al., 2018). The developers felt that additional research should be conducted if we were to release VS30 of 2000 m/s or greater maps and that in future versions of the models, it may be advantageous to more completely consider the influence of lower kappa values and larger short-period ground shaking for these hard-rock sites (Abrahamson, 2019, written communication). One of the primary improvements to the 2018 model is incorporating new GMMs and site amplification factors that increase the number of period and site classes compared to GMMs applied in earlier NSHMs. NGA-West2 default basin depths (km). Figure 4a shows comparisons of the working group model, updated EPRI and 2018 final models, and demonstrates that the working group model is higher than both the EPRI and 2018 models up to about 1-s period. The final model includes VS30-dependent weighting of site profiles that were more gradual (gradient model) and profiles characterized by sharp velocity contrasts (strong impedance model; Stewart et al., 2020). Seismic hazard analyses show where and how often future earthquakes may occur and the predicted strength of the ground shaking. Their engineers and crew did a great job their work and passed inspection without any problems. Figure 1. We describe published information that was submitted before March 2017 and discussed at our 2018 NSHM Update Workshop. The Z1.0 deep basin definition is based on regression between Z2.5 and Z1.0 depth from the NGA-West2 database (described below). The spectra at Charleston, SC, and Memphis, TN, have similar amplitudes at 0.1 s compared to the sites in the WUS. By continuing to browse In this section, we discuss the shaking hazard and exposure analyses performed using the most recent version of high-resolution LandScan population exposure data set produced by Oak Ridge National Laboratory (LandScan™ Database, 2017).
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