Geology topics

Nico Luco

Publications and source records attributed to Nico Luco.

At least 55 records · Page 3Linked to original sources

USGS2019

Updates to USGS national seismic hazard model (NSHM) and design ground motion maps for 2020 NEHRP recommended provisions

This presentation summarizes the proposed updates to earthquake design ground motions for the 2020 edition of the NEHRP Recommended Seismic Provisions, expected to be incorporated into the ASCE 7-22 Standard. The implications of these updates on the values of design ground motions for example locations in both conterminous and nonconterminous U.S. cities are shown and discussed.

Conference Paper↗

USGS2019

Proposed multi-period response spectra and ground motion requirements of the 2020 Recommended Provisions and ASCE 7-22

This paper summarizes a comprehensive set of proposals to the Provisions Update Committee of the Building Seismic Safety Council that would incorporate multi-period response spectra (MPRS) in the 2020 edition of the NEHRP Recommended Seismic Provisions for New Buildings and Other Structures (2020 NEHRP Provisions) and related proposals to the ASCE 7-22 Seismic Subcommittee of the American Society of Civil Engineers for incorporation of MPRS in the ASCE Standard, ASCE/SEI 7-22, Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE 7-22). Ultimately, the intent is that the proposed MPRS and related design requirements of ASCE 7-22 would be adopted, by reference, as part of the 2024 International Building Code.

Conference Paper↗

USGS2019

Seismic design and hazard maps: Before and after

The 1994 Northridge earthquake generated world-record ground motions. At the time, the horizontal peak ground acceleration of 1.8 g measured by a seismometer in Tarzana was the largest ever. The same is true of the peak ground velocity of 148 cm/s measured in Granada Hills. Both measurements were within approximately 15 km of the source of the earthquake; they were also near most of the damage described in other articles of this series. Consequently, the near-source design forces from the seismic zone maps in the Uniform Building Code (UBC) were increased. From the 1994 to 1997 editions, acceleration- and velocity-related near-source factors were introduced. The factors increased the design forces in Zone 4, already the highest seismic zone, by a multiplier as large as 2.0. More enduringly, generational changes were made to the seismic design maps in the NEHRP Recommended Seismic Provisions for New Buildings and Other Structures . The NEHRP maps were – and continue to be – adopted into the International Building Code (IBC), which supplanted the UBC and other model building codes. As described below, the changes to the NEHRP maps took advantage of another post-Northridge change: the modern generation of U.S. Geological Survey (USGS) National Seismic Hazard Maps.

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USGS2018

Science for a risky world—A U.S. Geological Survey plan for risk research and applications

Executive Summary Natural hazards—including earthquakes, tsunamis, volcanic eruptions, landslides, hurricanes, droughts, floods, wildfires, geomagnetic storms, and pandemics—can wreak havoc on human communities, the economy, and natural resources for years following an initial event. Hazards can claim lives and cause billions of dollars in damage to homes and infrastructure as well as lost or compromised economic activity and threats to national security. They also can have adverse environmental, social, economic, and health effects that extend well beyond the immediate area, sometimes with global implications. Changes in population growth, climate, and urbanization may exacerbate hazard impacts. Because of the potential severity of a single hazard event, reducing risk—the potential loss of societally important assets caused by these hazards—is a high priority for everyone, including policy makers, community members, emergency managers, resource managers, utility operators, business owners, and planners. These stakeholders demand usable, user-centric information to support decisions for planning a resilient future and for responding to and recovering from unanticipated events in more adaptable and cost-effective ways. Meeting this demand requires maximizing the use of environmental observations; hazards science; and research on communications, social stressors, and human behavior to deliver risk information in forms that are accessible by decision makers and the public alike. To achieve this, scientists and stakeholders must collaborate to match community needs with actionable insights, research, products, and tools, using advances in technology to improve information discovery and delivery.

Circular↗

USGS2018

Integrate urban‐scale seismic hazard analyses with the U.S. National Seismic Hazard Model

For more than 20 yrs, damage patterns and instrumental recordings have highlighted the influence of the local 3D geologic structure on earthquake ground motions (e.g., M "> M M 6.7 Northridge, California, Gao et al. , 1996 ; M "> M M 6.9 Kobe, Japan, Kawase, 1996 ; M "> M M 6.8 Nisqually, Washington, Frankel, Carver, and Williams, 2002 ). Although this and other local‐scale features are critical to improving seismic hazard forecasts, historically they have not been explicitly incorporated into the U.S. National Seismic Hazard Model (NSHM, national model and maps), primarily because the necessary basin maps and methodologies were not available at the national scale. Instead, the U.S. Geological Survey (USGS), its partners, and external groups developed urban seismic hazard maps (urban models and maps) that consider detailed site effects in local areas (e.g., Wong et al. , 2002 ; Cramer et al. , 2006 ; Frankel et al. , 2007 ; Graves et al. , 2011 ). The disconnect between the urban and national hazard models, however, means that the national models, which underlie U.S. building codes and other applications, do not make use of all of the scientific results informing earthquake ground‐shaking hazards. We recommend that future U.S. national seismic hazard assessment make use of all available regional information, including that in urban models. In this column, we describe the roles of and differences between the urban and national models, and discuss the obstacles to and benefits of integrating the urban models with the national model. Future progress on this issue will require further coordination and implementation efforts between the USGS and external partners.

Seismological Research Letters↗

USGS2018

Spatial and spectral interpolation of ground-motion intensity measure observations

Following a significant earthquake, ground‐motion observations are available for a limited set of locations and intensity measures (IMs). Typically, however, it is desirable to know the ground motions for additional IMs and at locations where observations are unavailable. Various interpolation methods are available, but because IMs or their logarithms are normally distributed, spatially correlated, and correlated with each other at a given location, it is possible to apply the conditional multivariate normal (MVN) distribution to the problem of estimating unobserved IMs. In this article, we review the MVN and its application to general estimation problems, and then apply the MVN to the specific problem of ground‐motion IM interpolation. In particular, we present (1) a formulation of the MVN for the simultaneous interpolation of IMs across space and IM type (most commonly, spectral response at different oscillator periods) and (2) the inclusion of uncertain observation data in the MVN formulation. These techniques, in combination with modern empirical ground‐motion models and correlation functions, provide a flexible framework for estimating a variety of IMs at arbitrary locations.

Bulletin of the Seismological Society of America↗

USGS2018

Seismic hazard, risk, and design for South America

We calculate seismic hazard, risk, and design criteria across South America using the latest data, models, and methods to support public officials, scientists, and engineers in earthquake risk mitigation efforts. Updated continental scale seismic hazard models are based on a new seismicity catalog, seismicity rate models, evaluation of earthquake sizes, fault geometry and rate parameters, and ground‐motion models. Resulting probabilistic seismic hazard maps show peak ground acceleration, modified Mercalli intensity, and spectral accelerations at 0.2 and 1 s periods for 2%, 10%, and 50% probabilities of exceedance in 50 yrs. Ground shaking soil amplification at each site is calculated by considering uniform soil that is applied in modern building codes or by applying site‐specific factors based on V S 30 "> V S 30 shear‐wave velocities determined through a simple topographic proxy technique. We use these hazard models in conjunction with the Prompt Assessment of Global Earthquakes for Response (PAGER) model to calculate economic and casualty risk. Risk is computed by incorporating the new hazard values amplified by soil, PAGER fragility/vulnerability equations, and LandScan 2012 estimates of population exposure. We also calculate building design values using the guidelines established in the building code provisions. Resulting hazard and associated risk is high along the northern and western coasts of South America, reaching damaging levels of ground shaking in Chile, western Argentina, western Bolivia, Peru, Ecuador, Colombia, Venezuela, and in localized areas distributed across the rest of the continent where historical earthquakes have occurred. Constructing buildings and other structures to account for strong shaking in these regions of high hazard and risk should mitigate losses and reduce casualties from effects of future earthquake strong ground shaking. National models should be developed by scientists and engineers in each country using the best available science.

Bulletin of the Seismological Society of America↗

USGS2018

Preliminary 2018 national seismic hazard model for the conterminous United States

The 2014 U.S. Geological Survey national seismic hazard model for the conterminous U.S. will be updated in 2018 and 2020 to coincide with the Building Seismic Safety Council’s Project 17 timeline for development of new building code design criteria. The two closely timed updates are planned to allow more time for the Provisions Update Committee to analyze the consequences of the hazard model changes in the design criteria. To prepare the 2018 update we held a workshop (March 7-8, 2018) with scientists and engineers to solicit feedback on the model. The 2018 model will be available for public comment during the summer of 2018. The purpose of this paper is to solicit feedback on the modeling choices and results. The 2018 NSHM considers an updated seismicity catalog and certain key changes in the way ground motions are calculated. First, we implemented new Next Generation Attenuation Relationships for the Central and Eastern North America Region and other published models that allow for the calculation of ground motions at additional periods and site classes in the central and eastern U.S. (CEUS). Second, basin depth terms were implemented in the ground motion models in select regions of the western U.S. (WUS) to account for enhanced long-period ground motions at softer soil sites overlying sedimentary basins. Preliminary results indicate higher ground motions for all periods in parts of the CEUS and for long-periods and soft soils in urban areas overlying sedimentary basins in the WUS.

Conference Paper↗

USGS2018

The science, engineering applications, and policy implications of simulation-based PSHA

We summarize scientific methods for developing probabilistic seismic hazard assessments from 3-D earthquake ground motion simulations, describe current use of simulated ground motions for engineering applications, and discuss on-going efforts to incorporate these effects in the U.S. national seismic hazard model. The 3-D simulations provide important, additional information about earthquake ground-shaking, which is critical to proper characterization of potential ground motions. Example uses of these simulations for engineering applications provide alternative approaches to introducing the effects of deep basins on long-period ground motions into design requirements. In Seattle, Washington tall building design includes requirements for accounting for the effect of the Seattle basin, and one method for including this effect relies upon local 3-D simulations. In Los Angeles, California a working group of scientists and engineers is advancing the use of local 3-D simulations for local building codes. In light of the benefit to ground motion characterization from the use of 3-D simulations, similar efforts are underway for national-scale seismic hazard analyses, which seek to make use of the extensive work applied from local efforts; current methods for incorporating these effects on a national-scale are presented.

Conference Paper↗

USGS2018

Damage accumulation for a two-story wood-frame building in sequences of induced earthquakes

In this study, a nonlinear model of a two-story multifamily wood-frame residential structure is subjected to recordings of sequences of induced earthquakes in order to quantify changes in fragility and accumulation of damage throughout multiple earthquake loadings. Initial efforts consisting of ground motion selection, building design, numerical modeling, and preliminary results are presented. Damage is quantified through a seismic loss estimation procedure that accounts for damage to nonstructural and structural components of the building. Examining damage accumulation from sequential earthquake shaking enables us to explore how the occurrence of damage in an earthquake, even to relatively small levels, may increase a structure’s susceptibility to collapse or damage in subsequent ground shaking. Ultimately, the goal is to compare damage fragilities and seismic losses as a function of the building’s initial damage state.

Kansas, Oklahoma↗

USGS2018

Opportunities to enhance seismic demand parameters for future editions of the AS1170.4

Geoscience Australia has recently released its 2018 National Seismic Hazard Assessment (NSHA18). Results from the NSHA18 indicate significantly lower seismic hazard across almost all Australian localities at the 1/500 annual exceedance probability level relative to the factors adopted for the current Australian Standard AS1170.4–2007 (R2018). These new hazard estimates, coupled with larger probability factors (kp) for long return periods, have challenged notions of seismic hazard in Australia in terms of the recurrence of damaging ground motions. As a consequence, the new hazard estimates have raised questions over the appropriateness of the prescribed National Construction Code probability level as used in the AS1170.4 to determine appropriate seismic demands for the design of ordinary-use structures. Therefore, it is suggested that the ground-motion exceedance probability used in the current AS1170.4 be reviewed in light of the recent hazard assessment and the expected performance of modern buildings for rarer ground motions. Whilst adjusting the AS1170.4 exceedance probability level would be a major departure from previous earthquake loading standards, it would bring it into line with other international building codes in similar tectonic environments. Additionally, it would offer opportunities to further modernise how seismic demands are considered in Australian building design. In particular, the authors highlight the following additional opportunities: 1) the use of uniform hazard spectra to replace and simplify the spectral shape factors, which do not deliver uniform hazard across all natural periods; 2) updated site amplification factors to ensure continuity with modern ground-motion models, and; 3) the potential to define design ground motions in terms of uniform collapse risk rather than uniform hazard. Estimation of seismic hazard at any location is an uncertain science. However, as our knowledge improves, our estimates of the hazard will converge more closely to the actual – but unknowable – (time independent) hazard. It is therefore prudent to regularly update the estimates of the seismic demands in our building codes using the best available evidence-based methods and models.

Conference Paper↗

USGS2017

U.S. Geological Survey National Strong-Motion Project strategic plan, 2017–22

The mission of the National Strong-Motion Project is to provide measurements of how the ground and built environment behave during earthquake shaking to the earthquake engineering community, the scientific community, emergency managers, public agencies, industry, media, and other users for the following purposes: Improving engineering evaluations and design methods for facilities and systems; Providing timely information for earthquake early warning, damage assessment, and emergency response action; and Contributing to a greater understanding of the mechanics of earthquake rupture, groundmotion characteristics, and earthquake effects.

Open-File Report↗

USGS2017

Considerations in comparing the U.S. Geological Survey one‐year induced‐seismicity hazard models with “Did You Feel It?” and instrumental data

The recent steep increase in seismicity rates in Oklahoma, southern Kansas, and other parts of the central United States led the U.S. Geological Survey (USGS) to develop, for the first time, a probabilistic seismic hazard forecast for one year (2016) that incorporates induced seismicity. In this study, we explore a process to ground‐truth the hazard model by comparing it with two databases of observations: modified Mercalli intensity (MMI) data from the “Did You Feel It?” (DYFI) system and peak ground acceleration (PGA) values from instrumental data. Because the 2016 hazard model was heavily based on earthquake catalogs from 2014 to 2015, this initial comparison utilized observations from these years. Annualized exceedance rates were calculated with the DYFI and instrumental data for direct comparison with the model. These comparisons required assessment of the options for converting hazard model results and instrumental data from PGA to MMI for comparison with the DYFI data. In addition, to account for known differences that affect the comparisons, the instrumental PGA and DYFI data were declustered, and the hazard model was adjusted for local site conditions. With these adjustments, examples at sites with the most data show reasonable agreement in the exceedance rates. However, the comparisons were complicated by the spatial and temporal completeness of the instrumental and DYFI observations. Furthermore, most of the DYFI responses are in the MMI II–IV range, whereas the hazard model is oriented toward forecasts at higher ground‐motion intensities, usually above about MMI IV. Nevertheless, the study demonstrates some of the issues that arise in making these comparisons, thereby informing future efforts to ground‐truth and improve hazard modeling for induced‐seismicity applications.

Kansas, Oklahoma↗

USGS2017

Development and utilization of USGS ShakeCast for rapid post-earthquake assessment of critical facilities and infrastructure

The ShakeCast system is an openly available, near real-time post-earthquake information management system. ShakeCast is widely used by public and private emergency planners and responders, lifeline utility operators and transportation engineers to automatically receive and process ShakeMap products for situational awareness, inspection priority, or damage assessment of their own infrastructure or building portfolios. The success of ShakeCast to date and its broad, critical-user base mandates improved software usability and functionality, including improved engineering-based damage and loss functions. In order to make the software more accessible to novice users—while still utilizing advanced users’ technical and engineering background—we have developed a “ShakeCast Workbook”, a well documented, Excel spreadsheet-based user interface that allows users to input notification and inventory data and export XML files requisite for operating the ShakeCast system. Users will be able to select structure based on a minimum set of user-specified facility (building location, size, height, use, construction age, etc.). “Expert” users will be able to import user-modified structural response properties into facility inventory associated with the HAZUS Advanced Engineering Building Modules (AEBM). The goal of the ShakeCast system is to provide simplified real-time potential impact and inspection metrics (i.e., green, yellow, orange and red priority ratings) to allow users to institute customized earthquake response protocols. Previously, fragilities were approximated using individual ShakeMap intensity measures (IMs, specifically PGA and 0.3 and 1s spectral accelerations) for each facility but we are now performing capacity-spectrum damage state calculations using a more robust characterization of spectral deamnd.We are also developing methods for the direct import of ShakeMap’s multi-period spectra in lieu of the assumed three-domain design spectrum (at 0.3s for constant acceleration; 1s or 3s for constant velocity and constant displacement at very long response periods). As part of ongoing ShakeCast research and development, we will also explore the use of ShakeMap IM uncertainty estimates and evaluate the assumption of employing multiple response spectral damping values rather than the single 5%-damped value currently employed. Developing and incorporating advanced fragility assignments into the ShakeCast Workbook requires related software modifications and database improvements; these enhancements are part of an extensive rewrite of the ShakeCast application.

Conference Paper↗

USGS2017

Development of the next generation of seismic design value maps for the 2020 NEHRP Provisions

During the period January 2015 through August 2018, a joint committee of U.S. Geological Survey (USGS) representatives and National Institute of Building Sciences Building Seismic Safety Council (BSSC) volunteers and staff formed a committee to conduct Project 17. The purpose of Project 17 was to formulate recommendations for the rules by which next-generation seismic design value maps, derived from USGS national seismic hazard models, will be developed for adoption by the 2020 National Earthquake Hazard Reduction Program Recommended Provisions for Seismic Regulations of New Buildings and Other Structures (NEHRP Provisions), ASCE 7-22 and the 2024 International Building Code. Two similar projects, Project 97 and Project 07, had been conducted in the past. Each of these projects established, for a period of approximately ten years, the rules by which design ground motion values referenced by the building codes would be developed both by USGS and by private consultants engaged in site-specific studies. Project 17 was originally commissioned in response to issues identified in adopting the 2014 edition of the USGS national seismic hazard model and the design procedures that reference them for use, including the NEHRP Provisions, building codes and referenced standards. Specific issues included: the engineering profession’s discontent with the fluctuating design values portrayed by successive map editions; discovery that the standard spectral shape referenced by the design provisions did not adequately represent ground motion amplitude and spectral character on some sites; and a change in seismologic characterization of the possible size of earthquakes originating on various faults and source zones. Project 17 was funded by the Federal Emergency Management Agency (FEMA), and supported by the USGS with some collaborating experts. An initial planning committee met throughout calendar year 2015 to identify key issues to be considered and to develop a work plan for addressing these as part of the 2020 NEHRP Provisions update cycle. The planning committee recommended an effort of approximately 30-months duration during which the USGS would develop draft design maps based on the rules proposed, to allow evaluation and refinement of the recommendations. A Project 17 Committee (P17C) was empaneled and four task subcommittees were formed, each charged with evaluating one of the key issues identified in the planning effort: Stabilizing mapped values; Definition of Acceptable Risk; Development of multi-period spectral parameter data; and, Definition of procedures for computing deterministic caps, should it be necessary to continue use of such caps in development of the maps. A fifth task subcommittee was formed in 2017 to look at ways to stabilize the seismic design category as an extended effort to stabilize mapped values. The P17C met three times per year throughout 2016, 2017 and 2018 to resolve these issues and develop recommendations for an updated technical basis and procedures to be followed in preparing next-generation seismic design value maps for inclusion in the NEHRP Provisions. The P17C documented these in the form of draft proposals for revision of the NEHRP Provisions. In August 2018, the P17C passed these recommendations to the Provisions Update Committee (PUC) for completion, development of consensus and adoption as appropriate.

Report↗

USGS2016

Get your science used—Six guidelines to improve your products

Introduction Natural scientists, like many other experts, face challenges when communicating to people outside their fields of expertise. This is especially true when they try to communicate to those whose background, knowledge, and experience are far distant from that field of expertise. At a recent workshop, experts in risk communication offered insights into the communication challenges of probabilistic hazard products, suggested tips, and shared their strategies for making products that a targeted audience can understand and use. Although the workshop was held to broaden the understanding and use of the U.S. Geological Survey (USGS) National Seismic Hazard Maps (NSHM), the workshop outcomes presented in this report can benefit anyone who develops products based on technical information. On the basis of research and practice into how people think, use tools, make decisions, and understand scientific/technical information, the social and behavioral scientists, marketers, and social-impact designers at the NSHM workshop provided remarkably consistent guidelines to develop successful science products, such as text, maps, and other products. In this report the guidelines are numbered for clarity, but they can be applied repeatedly, piecemeal, or out of order to fit each project and your resources.

Circular↗

USGS2016

Earthquake probabilities for the Wasatch front region in Utah, Idaho, and Wyoming

In a letter to The Salt Lake Daily Tribune in September 1883, U.S. Geological Survey (USGS) geologist G.K. Gilbert warned local residents about the implications of observable fault scarps along the western base of the Wasatch Range. The scarps were evidence that large surface-rupturing earthquakes had occurred in the past and more would likely occur in the future. The main actor in this drama is the 350-km-long Wasatch fault zone (WFZ), which extends from central Utah to southernmost Idaho. The modern Wasatch Front urban corridor, which follows the valleys on the WFZ’s hanging wall between Brigham City and Nephi, is home to nearly 80% of Utah’s population of 3 million. Adding to this circumstance of “lots of eggs in one basket,” more than 75% of Utah’s economy is concentrated along the Wasatch Front in Utah’s four largest counties, literally astride the five central and most active segments of the WFZ.

Utah, Idaho, Wyoming↗

USGS2016

Earthquake ground motion

Most of the effort in seismic design of buildings and other structures is focused on structural design. This chapter addresses another key aspect of the design process—characterization of earthquake ground motion into parameters for use in design. Section 3.1 describes the basis of the earthquake ground motion maps in the Provisions and in ASCE 7 (the Standard). Section 3.2 has examples for the determination of ground motion parameters and spectra for use in design. Section 3.3 describes site-specific ground motion requirements and provides example site-specific design and MCER response spectra and example values of site-specific ground motion parameters. Section 3.4 discusses and provides an example for the selection and scaling of ground motion records for use in various types of response history analysis permitted in the Standard.

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