Geology topics

C. B. Crouse

Publications and source records attributed to C. B. Crouse.

4 recordsLinked to original sources

USGS2026

Development of liquefaction-targeted design basis in U.S. seismic provisions

Seismic design criteria for new buildings in the United States have historically focused on life safety performance objectives through minimizing the potential for structural collapse. Development of design criteria to meet this performance objective has evolved over time, leading to the current, risk-targeted maximum considered earthquake (MCE R ) design basis. Corresponding MCE R seismic design loads incorporate the full range of probabilistic ground motion hazard information available from U.S. Geological Survey National Seismic Hazard Models, as well as a representation of the uncertainty in structural collapse capacity. Despite these considerable advances in structural design criteria, guidelines for geotechnical hazards such as liquefaction-induced damage, which continue to be based on uniform ground-shaking hazard (i.e., MCE ground motions), are not well-connected with risk-based, collapse prevention performance objectives. This study, undertaken as part of Building Seismic Safety Council efforts to update recommended seismic provisions through the National Earthquake Hazards Reduction Program, presents probabilistic, liquefaction-targeted design objectives and corresponding ground motion parameters, with a focus on improving consistency in first-level screening criteria for liquefaction hazard assessment. This study identifies a potential maximum acceptable annualized probability of liquefaction triggering ( P L,max ) of 2.5% in 50 years, above which liquefaction consequences and potential mitigation measures would be considered. The P L,max -based design basis is calibrated to effective probabilistic liquefaction hazard levels obtained in practice using current MCE peak ground accelerations, and could be implemented via a new liquefaction-targeted maximum considered earthquake (MCE L ) peak ground acceleration ( PGA L ). The proposed PGA L is derived from probabilistic liquefaction hazard curves and includes uncertainties inherent to liquefaction hazard modeling. The potential design effects of the proposed PGA L are demonstrated via comparison with current MCE PGA levels, effects on first-level liquefaction screening analyses, and improvements in the consistency of P L,max levels across the United States, and for a wide range of site conditions.

conterminous United States↗

USGS2020

Risk-targeted alternatives to deterministic ground motion caps in U.S. seismic provisions

Since their inception over 20 years ago, the maximum considered earthquake ground motion maps in U.S. building codes have capped probabilistic values with deterministic ground motions from characteristic earthquakes on known active faults. This practice has increasingly been called into question both because of spatially non-uniform risk levels that are produced (risk being higher mainly in coastal California) and practical difficulties in defining characteristic earthquakes from recent earthquake rupture forecast models. We describe two proposals developed to enable phase-out of deterministic caps. One approach modestly increases collapse risk targets nationwide based on recent information on return periods of characteristic earthquakes on major central and eastern U.S. seismic sources; adoption of this approach would remove the perceived need for caps in California. The second approach uses geographically varying collapse risk targets, being higher near the highly active faults in California and unchanged elsewhere. Neither approach was adopted for the 2020 National Earthquake Hazards Reduction Program recommended seismic Provisions for new building structures, but they are described in a Part 3 document to accompany the Provisions and Commentary .

Earthquake Spectra↗

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

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.

Report↗