Seismic Hazard Design Issues in the Central United States

The 2012 Seismic Hazard Workshop presented an opportunity to address current issues, resulting in the following two objectives: (1) to educate engineers in the Midwest United States about new seismic design procedures that exist in the international building code (IBC) and the ASCE/SEI 7 Standard and (2) to address potential future issues in the natural hazards arena in the Central United States (CUS) that are often not considered. A good example is the 2011 Tohoku earthquake and tsunami, during which two natural hazard events occurred simultaneously. As a result, event organizers decided to expand the original concept of the workshop to include other aspects of natural hazards. The chapter also provides a brief summary of the papers that were presented in the workshop.

For most construction in the Central and Eastern United States (CEUS), seismic design for new construction did not really start until the 1970s, when the International Conference of Building Officials (ICBO) adopted the 1969 Algermissen seismic hazard map into the 1970 Uniform Building Code (UBC). This chapter describes the four major advances in seismic hazard understanding during the 1990s through 2000s: (1) the development of Project 97, (2) the concept of maximum considered earthquake, (3) the development of the risk-targeted approach, and (4) the high frequency issue. The chapter offers several tentative suggestions for a design and evaluation approach that focuses on protection against loss of life and reduces damage or destruction of infrastructure. The chapter focuses on four violent natural hazards – earthquakes, high-velocity winds and tornados, snow and ice, and floods – with potential for extreme effects peculiar to the CEUS.

The United States lacks a national policy affirming the right to learn in school buildings that are safe from earthquakes. This chapter reviews the status of school seismic safety in five high-seismic-hazard zones identified on the 2008 U.S. Geological Survey (USGS) National Seismic Hazard Maps. These zones include California, Cascadia, Utah, South Carolina, and Missouri. The chapter describes several common themes in these widely disparate regions of the United States suggested by this survey of risk and response. The chapter also proposes a three-part national agenda to make schools safer in high-seismic-hazard regions, centered on a common goal: “unreinforced masonry (URM)-free by 2033.” The discussion emphasizes initiatives in Oregon and Washington; states where the seismic policy environment is less advanced than in California. Principal priorities include identifying and ranking schools at risk, mitigating high-priority schools, and removing URMs from school inventories by 2033.

Striking abruptly, earthquake disasters create destruction, urgency, and confusion, as symbolized by the stopped clock in Hanwang after the May 12, 2008, Wenchuan earthquake in the Sichuan Province of China. The earthquake fit the definition of a “Black Swan” event: nearly unpredictable, having massive impact, and followed by numerous post-disaster explanations. This chapter summarizes different perspectives on the temporal dimensions of decision making for this intraplate earthquake gathered during an October visit by a team comprising members of the Council of Disaster Risk Management (CDRM) and others from ASCE and applies those perspectives to the central and eastern United States (CEUS). It also discusses three sets of building code issues pertaining to importance factors; the seismic intensities used in China's three-level protection, two-level design approach; and practices of quality assurance relating to the designer, contractor, manager, and occupants; and unauthorized modifications.

The central United States has experienced major flooding and periodic catastrophic earthquakes. This chapter explores the effects on central U.S. communities when two Midwest hazards occur near one another. It considers only one to two major effects for each event. The first scenario involves the largest of the historic New Madrid earthquakes and a flood in Shelby County, Tennessee. The second and third scenarios involve major earthquakes and tornados in Cape Girardeau, Missouri and Tuscaloosa, Alabama. The last scenario couples a major earthquake event with the extreme cold that periodically occurs in St. Louis. The usefulness of public education for earthquakes coupled with other hazards may be compromised by the rarity of such events. However, these four scenarios show that despite expected higher levels of damage, preparing for and responding to multiple hazards is fortunately not necessarily beyond the resources of the emergency management and response community.

This chapter highlights the results of recent studies dealing with key seismic geotechnical issues in the Central United States, including (1) the significance of using the conditional mean spectrum (CMS) for seismic design at the periphery of the New Madrid Seismic Zone (NMSZ); (2) site response of deep soil deposits in the Mississippi Embayment; and (3) unique aspects of liquefaction in the Central United States, particularly in the NMSZ. Use of the CMS framework permits the development of ground motions that are consistent with the seismic sources in the area, while maintaining the probabilistic sense of a probabilistic seismic hazard analysis (PSHA). Because the liquefaction features are unique in the NMSZ, site-specific evaluation, including site response analysis, is needed for evaluating liquefaction potential.

The state of the art for development of earthquake response spectra to be used for analysis and design of critical facilities in the central and eastern United States (CEUS) has changed as new earthquakes have provided new data to consider. This chapter addresses the major changes in the earthquake response spectra beginning in the 1960s to 2010 and anticipated changes in the near future. These changes have come about based on experience and knowledge gained from earthquake occurrences and improved analysis techniques. The changes have, in general, increased the earthquake ground motions used for the design of critical facilities. The Electric Power Research Institute (EPRI), Nuclear Regulatory Commission (NRC), and Department of Energy (DOE) are also sponsoring a program to update the next generation of CEUS ground motion attenuation relationships.

Knox County, Tennessee, with its major city Knoxville, represents a county and city that need a seismic code. This chapter talks about Knoxville and Knox County working together to assist the State of Tennessee in adopting seismic codes and the need to stay abreast of continual changes in the area of seismic design. The first seismic code adopted in Knox County and Knoxville, Tennessee, was the 1985 edition of the Southern Building Code (SBC) of the Southern Building Code Congress International (SBCCI). Because unique governmental responsibilities for building codes and permits exist at the federal, state, and local levels, continued education and seminars are required for the future understanding of code requirements for both industry and design professionals.

Adoption and implementation of new seismic safety regulations and design standards have caused serious problems in many communities in the New Madrid region, including western Kentucky. The main reasons for these problems are (1) misunderstanding of the national seismic hazard maps and (2) confusion between seismic hazard and seismic risk. Both are caused by probabilistic seismic hazard analysis (PSHA). The difficulties in the development of design ground motion for National Earthquake Hazards Reduction Program (NEHRP) provisions are caused by the use of the national seismic hazard maps. Deterministic/scenario seismic hazard analysis is an appropriate approach for seismic hazard assessment, seismic risk assessment, and engineering design and other policy considerations. The analysis is also appropriate for engineering design and other policy considerations in the New Madrid and other regions.

Although the most significant area of concern in the central United States is the New Madrid Seismic Zone (NMSZ), which directly affects eight adjoining states, the area in the central United States that could be affected by a major earthquake is much larger. To minimize the impact of a damaging earthquake, community resiliency must be developed. While some measures of resiliency in physical systems can be quantified, resiliency measures for socioeconomic systems are difficult to quantify. Qualitative measures are most appropriate to describe overall community resiliency. This chapter provides a conceptual framework for developing resiliency measures. Overall resiliency of a community comprises resiliency of built environment, resiliency of economic structures, and resiliency of social institutions. The chapter discusses these three components of resiliency considering two determinants: system design and operations.