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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering 2 Issues in Earthquake Engineering Research Earthquakes pose inevitable risks to everyone who lives in a seismically active region. Even though the hazard is well recognized, no one knows when an earthquake will strike or how severe it will be. Despite considerable effort over the years to develop the capability to predict earthquakes, it is unclear whether this ever will be achieved. In the face of this uncertainty, NEES offers an unprecedented opportunity to advance knowledge and practice that could ultimately lead to the prevention of earthquake disasters. By disseminating and implementing the cost-effective planning, design, construction, and response measures developed through NEES research, it will be possible to reduce injuries, loss of life, property damage, and the interruption of economic and social activity that have long been associated with strong earthquakes in densely developed regions. Earthquakes will continue to occur, but the disasters that they cause will be a thing of the past. Technology is just one element of earthquake disaster prevention, however. Policy makers and the public they represent must be convinced that the threat is real and that preventing disaster is desirable, economical, and achievable. Action will be taken only when society is convinced that the investment in land planning and zoning, design and construction practices, and emergency response for disaster prevention provides measurable and greater benefits than those afforded by business as usual. Much of the needed knowledge is already available, and more will be forthcoming if the recommendations for research contained in this report are implemented. More importantly, the unique capabilities of NEES-
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering related research, simulation, and simulcast demonstration can be used to generate public support for seismic upgrades, open space zoning near faults and other hazardous areas, and the use of the best current knowledge for all aspects of disaster prevention. Such public awareness and support will hasten the further creation, communication, and application of new information. This chapter discusses seven topical areas—seismology, tsunamis, geotechnical engineering, buildings, lifelines, risk assessment, and public policy—that the committee believes are key to preventing earthquake disasters. The principal problems and challenges presented by each topical area are summarized in Table ES.1. However, these are not stand-alone issues to be resolved on a narrow, discipline-oriented basis. The unique and exciting opportunity presented by NEES is the ability to formulate complex hypotheses regarding seismic excitation, system response, and social interaction at scales that range from individual structures and building components up to regional systems, and then to test these hypotheses using a coupled simulation employing field observations, physical experiments, theoretical analysis, and computer modeling. Figure 2.1 illustrates this multilevel, interdisciplinary concept. The committee’s presentation of the issues follows the logic embodied in Figure 2.1—namely, the fundamental earth science questions to be answered FIGURE 2.1 Nested linkages of activities and disciplines that NEES will bring to the resolution of earthquake engineering problems. SOURCE: G. Deierlein, Stanford University, presentation to the committee, April 25, 2002.
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering in seismology, the direct geologic effects of seismic excitation (tsunamis and ground failure), impacts on the constructed environment of buildings and lifelines, and, finally, risk assessment and public policy. NEES will play a critical role in addressing all these issues but will be more immediately involved in simulating earthquake hazards and their impact on the built environment. It is this knowledge that will inform risk assessments and loss estimates so that public policy options can be developed and evaluated. The research plan presented in Chapter 5 anticipates a high degree of interaction among the NEES equipment sites in creating this knowledge base. This interaction will also include investigators from around the world and will cut across traditional discipline-based research. The connectivity provided by the NEES grid has the ability to make this oft-voiced rhetorical goal a reality. SEISMOLOGY Ground Motion Knowledge of ground motion attributable to earthquakes is crucial for the design of new structures and the retrofit of existing ones, as well as for emergency planning and response. Earthquakes occur as a result of sudden displacements across a fault within the earth. The earthquake releases part of its stored strain energy as seismic waves. These waves propagate outward and along the earth’s surface. It is the motion of the ground as these waves move past that is perceived as an earthquake. With most earthquakes, the direct effects of ground shaking are the principal cause of damage (Holzer, 1994). Fault rupture can create considerable damage but it occurs only near the fault. Indirect shaking effects such as tsunamis, landslides, fire caused by gas-line breaks, and flooding caused by water-line breaks also play a significant role in some cases. Regional tilting and warping across folded strata may result in heavy lifeline damage across entire regions. The factors that influence strong ground motion during earthquakes are traditionally divided into source, path, and site effects. A fundamental challenge for earthquake engineering is predicting the level and variability of strong ground motion from future earthquakes. Enhancing this predictive ability requires better understanding of the earthquake source, the effects of the propagation path on the seismic waves, and basin and near-surface site effects. Seismologists, geologists, and engineers base their understanding on knowledge of the dynamics of earthquake fault rupture, the three-dimensional elastic and energy-dissipation properties (anelastic structure) of the earth’s crust, the modeled nonlinearities that
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering occur in the shallowest parts of the earth’s crust during strong earthquakes, and the complex interactions between structures and the seismic wavefield. Earthquake Sources Understanding the behavior of the earthquake source—the spatial and temporal behavior of slip on the fault or faults that rupture in an earthquake—is central to predicting strong ground motion. A large earthquake starts at the hypocenter and may rupture across several fault segments or even across multiple faults. Using strong ground motion recordings of large earthquakes, seismologists have determined that fault rupture typically propagates at a large fraction—usually about 80 percent—of the shear wave velocity of the ruptured material, although there is evidence that the rupture velocity can locally exceed the shear wave velocity (Bouchon et al., 2001). The slip velocity across the fault is much less well determined but is on the order of several meters per second in a large earthquake (Heaton, 1990). The combination of high rupture velocity and high slip velocity leads to strong directivity in the radiated wavefield—that is, seismic waves emanating from the fault get channeled more strongly in some directions than in others (Somerville et al., 1997). In addition to these constraints, there is ample evidence that slip in earthquakes is a strongly spatial variable (Mai and Beroza, 2002; Somerville et al., 1999; Andrews, 1980). Because the excitation of ground motion by the earthquake source is dependent on the spatial variability of slip, efforts to predict strong ground motion from future earthquakes will probably involve source models that are described stochastically. Owing to the inability, at least for the foreseeable future, to predict the spatial variation of slip on faults, seismologists should opt for multiple realizations of stochastic slip models in describing future earthquake sources. A stochastic description of fault slip for scenario earthquakes should merge naturally with existing probabilistic descriptions of earthquake hazard. Collaboration with the geographic information science community could help to increase understanding of spatial variability in the modeling. Earthquake Simulation To date, most efforts to simulate the earthquake source have been kinematic, in that the rupture characteristics are constructed to be consistent with past earthquakes, with little regard for the physics of the rupture process (Aki and Richards, 1980). Improved simulation of near-fault ground motion will require considering dynamic effects on the earthquake source. Such physically based ground motion simulations could be
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering significantly better than simulations based on kinematic models. Dynamic models differ significantly from kinematic models in their effects on strong ground motion in the near-fault regime because slip amplitude, rise time, the slip velocity, and the rupture velocity are correlated and spatially variable (Guatteri et al., 2003). This means that the directivity effect, for example, will depend not only on the position and the rupture velocity but also on the spatial and temporal evolution of the rupture. Path Effects Path effects—that is, the modification of the seismic wavefield as it propagates through the complex crust of the earth—have a strong, often dominant influence on strong ground motion. As a first approximation, the strongest variation of velocity with position in the earth is an increase in velocity with depth. In the earth’s crust, however, this assumption is often incorrect, particularly in the tectonically active environments in which earthquakes occur, because active tectonics naturally leads to complex geologic structures. Large urban environments are often situated above these structures. To cite a specific example, the Los Angeles metropolitan area is built atop several large sedimentary basins. During earthquakes, seismic waves become trapped and amplified by such basins, resulting in strong ground motion of long duration and strong spatial variation in amplitude, which can substantially increase the seismic forces on structures and lifelines (see, for example, Borcherdt, 1970; Phillips and Aki, 1986; and Trifunac et al., 1994). Moreover, near the edges of such basins, complex interference effects can greatly amplify ground motion relative to what it would have been in the absence of edges and basin effects (Bard and Bouchon, 1985; Aki, 1988). While the three-dimensional structure of the earth’s crust is complex, it is fixed in time for the purposes of predicting strong ground motion. That is, when two different earthquakes occur in the same area, the waves propagate through and are modified by the same structure. Moreover, the mechanics of seismic wave propagation in three-dimensional elastic media is well understood. So, at face value, the problem would seem to be straightforward. The challenges, however, are substantial. The true three-dimensional structure of the earth’s crust is incompletely known, and it is impractical to gather enough data to characterize it completely. Thus, the ability of seismologists to estimate with precision the effects of three-dimensional earth structure on the strong ground motion prescribed in a scenario earthquake currently is limited to frequencies below about 0.5 to 1 Hz and even then only in areas that have been well researched and characterized (Graves, 2002). A sustained effort will be required to map
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering the three-dimensional structure of the earth’s crust in seismic urban regions and to use this information to develop high-fidelity predictions of strong ground motion from scenario earthquakes. Currently, in the absence of such predictions, engineers use historical earthquake records of appropriate magnitude that are rich in the frequency range of interest (i.e., the resonant frequency of the structure under analysis) and apply attenuation relationships to determine peak acceleration values and scale the records to those peak values. This process, while not analytically rigorous, is appropriately conservative and allows engineering design to proceed. A large part of the research in this area will take place outside the NEES research effort. While NEES will play a significant role, effective partnerships with seismological research centers and observational programs such as the Advanced National Seismic System (ANSS) will be essential (for example, ANSS will provide strong motion recordings of future earthquakes that will form the observational foundation for performance-based design.). To model wave propagation at frequencies in excess of 1 Hz, seismologists will likely have to turn to stochastic representations of the heterogeneities within the earth’s crust or to a stochastic representation of the wavefield itself. Ultimately, improved prediction of ground motion based on the physics of the site and wavefield will be coupled with engineering design requirements. This will permit the current conservatism of the design process to be reduced and will result in improved performance at lower cost. Wave Effects Seismic waves are often referred to as elastic waves, but anelastic effects due to energy losses (e.g., interparticle friction), which give rise to the attenuation of seismic waves, cannot be neglected. The effect of attenuation on strong ground motion is profound, because the same soft materials near the earth’s surface that lead to strong amplification of ground motion can also lead to rapid attenuation (Aki and Richards, 1980). The net effect on the level of ground motion is complex because of elastic and anelastic effects. To predict strong ground motion, seismologists and engineers will have to characterize and account for anelastic wave effects in the earth’s crust. Again, research efforts in this area will probably require partnerships between NEES and seismological research centers so that time-series data on an actual earthquake can be recorded as it occurs and made available for NEES experimental and testing purposes.
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering Site Effects Site effects are, in a sense, a specific example of path effects; they refer to the effects on ground motion when seismic waves interact with the complex geological environment in the shallowest 100 or so meters of the earth’s crust. The low seismic velocities and impedances in shallow sediments can lead to extremely large and locally varying amplitudes during strong ground motion (Seed and Idriss, 1982; Rosenblueth and Meli, 1986). Moreover, in this domain, wave propagation during strong ground motion is often nonlinear, with large-scale damage to geologic materials themselves, which in turn can lead to (for example) strong, amplitude-dependent attenuation effects (Finn, 1988; Field et al., 1997). In saturated, cohesionless soils, the change in excess pore water pressure during earthquakes can approach or equal the effective vertical stress, causing liquefaction, which in turn can lead to large and sudden changes in the behavior of surficial soils (Seed and Idriss, 1982; Youd and Garris, 1995), including excessive deformation, which could threaten the integrity of structures built on these soils. Even in the absence of liquefaction, transient increases in pore pressure can lead to profound changes in strong ground motion. The NEES geotechnical facilities will be essential for studying the response of typical near-surface materials to strong ground motion inputs and developing soil-improvement techniques to mitigate this phenomenon. Soil-Foundation-Structure Interaction Earthquake ground motion varies considerably, both in amplitude and duration, from one location to another within a seismic region. This variation is due to the complexity of the source, the propagation path, and site effects. Improved understanding of such effects through observation and simulation can contribute greatly to the elucidation of important issues raised by recent earthquakes—for example, Why do similar buildings in a region have such different amounts of damage, even when they are sometimes located at nearby sites? How do directivity of the seismic waves, permanent displacements, and other near-fault phenomena affect different structures? How do the damaging features of blind faults differ from those of faults with surface rupture? How does the structural vibration affect the free-field ground motion? These issues would benefit from having seismic zones and microzones for an urban region that allow predicting regional impacts. One manifestation of the interaction that takes place between a structure, its foundation, and the surrounding soil is the fact that a vibrating structure can generate its own seismic waves, which in turn affect the
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering free-field ground motion. In fact, several well-known aspects of soil-structure interaction, including the two interactions described in what follows, are of primary importance to earthquake engineering and engineering seismology. First, the response to earthquake motion of a structure founded on a deformable soil can be significantly different from the response of the same structure on a rigid foundation (rock), mainly through an increase in natural periods, a change in the amount of system damping due to wave radiation and damping in the soil, and modification of the effective seismic excitation (see, for example, Jennings and Bielak, 1973; Veletsos and Meek, 1974). In certain cases, for large or elongated structures like dams, buildings with large dimensions, and bridges, it may be desirable to know the spatial distribution of the ground motion rather than the motion at a single location. However, the benefits of such geographically precise data must be weighed against the cost of obtaining them. Second, the motion recorded at the base of a structure or in its vicinity can be different in important details from the motion that would have been recorded if there were no building. This effect can be significantly magnified if there are a number of structures in the same general vicinity, in which case the recorded motion can be affected by the presence of the structures—it might, for example, exhibit an elongated duration and increased or decreased amplitude due to diffracted surface waves generated by the structures (Borcherdt, 1970; Wirgin and Bard, 1996). The amplitude of this diffraction and of soil-structure-foundation interaction in general can be pronounced when stiff structures rest on soft soils. Forced-vibration tests of a nine-story structure in the Greater Los Angeles Basin showed that this diffracted wavefield could be significant up to large distances, even for stiff soils (Jennings, 1970). Despite this evidence and the practical importance for earthquake engineering, little work has been done to explain this effect or to quantify it predictably. To model with greater reliability soil-foundation-structure interaction effects during strong earthquakes, integrated models that incorporate the structure, the surrounding soil, and more realistic, spatially distributed seismic excitation must be developed. This effort will require close collaboration between engineers and seismologists. The participation of NEES in this area will be particularly advantageous. Ground Motion Prediction The prediction of strong ground motion in future earthquakes is currently carried out primarily by applying attenuation laws, or parametric scaling relations (e.g., Abrahamson and Silva, 1997). These relations link parameters describing the seismic source, such as the magnitude, and the
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering location of a site with respect to that source, to ground motion data sets characterized by a simple measure of ground motion severity, such as the spectral acceleration at a given period and damping. The current scarcity of strong motion data at short distances from the epicenters of large earthquakes means that there are not enough data to represent the near-field hazard from the most dangerous events. Computer simulation provides a way to fill this gap in the data. To fulfill the expectation of performance-based engineering, structural engineers will probably require full time histories of ground motion. This requirement suggests that a simple extrapolation of attenuation relations to larger-magnitude earthquakes will not suffice and that a combination of improved observations and large-scale simulation will be important for making progress in this area. TSUNAMIS Tsunami Generation Tsunamis are generated by seismic fault displacements of the seafloor, landslides triggered by earthquakes, volcanic eruptions, or explosions. All of these generation mechanisms involve a displacement of the ocean boundary, either at the seafloor, at the shoreline, or at the water surface. Since at the present time seismic data alone cannot define the important wave generation characteristics of these various tsunami sources, real-time deep water tsunami data are essential to forecasting tsunami impacts and providing critical boundary conditions for numerical models of their coastal effects. The generation sites include oceans, harbors, lakes, reservoirs, and rivers. The run-up and inundation associated with tsunamis cause loss of life, destruction, and economic losses. (“Run-up” as used herein is defined as the maximum vertical excursion of the tsunami above mean sea level when the tsunami has propagated the farthest inland.) Historical Impacts Since 1992, 16 lethal tsunamis have occurred in the Pacific, resulting in more than 4,000 fatalities (NOAA, 2003). The tsunamis in all of these events struck land near their source, so little warning time was available. Of course, losses from offshore earthquakes occurring near the coast are not limited to the coast closest to the source. For example, the Chilean tsunami of 1960 caused loss of life and damage not only near the source in Chile but also thousands of kilometers away in Hawaii and Japan. Thus, ironically and unfortunately, scenic coastal areas that are preferred resi-
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering FIGURE 2.2 A view of damage in Aonae, a small town on Okushiri, an island in the Sea of Japan, from the 1993 Hokkaido tsunami and related fire. Photo courtesy of Commander Dennis J. Sigrist, acting director of the International Tsunami Information Center. dential sites have been frequent and vulnerable targets for seismically generated sea waves from near and distant sources. Between 1992 and 1994, the Nicaraguan tsunami, the Flores Island tsunami (Indonesia), and the Hokkaido tsunami (Japan) caused devastating property damage and many deaths. The measured run-up from several of these events was about 30 meters. In 1994 alone, four additional tsunamis occurred: at East Java (Indonesia), Shikotan Island (Russia/Japan), Mindoro (Philippines), and Skagway (Alaska). In the latter half of the 1990s, there were several more large tsunamis: the Peruvian tsunami in 1996, the Papua New Guinea tsunami in 1998, the Vanuatu and Turkey tsunamis in 1999, and the tsunami in Peru in 2001. Figure 2.2 shows the damage inflicted by the 1993 Hokkaido tsunami on Aonae, a small town on Okushiri, an island in the Sea of Japan. Although the majority of the tsunamis during the 1990s were caused by seafloor displacements, at least three—the Skagway, the Turkey, and the Papua New Guinea tsunamis—are suspected (or known) to have been caused by land subsidence and/or landslides. The Papua New Guinea tsunami killed more than 2,000 people and completely destroyed three
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering villages. Primarily because of these tsunamis, in recent years research on the modeling of landslide-generated sea waves has been intensified. Similar landslide-generated waves can occur in bays, estuaries, rivers, lakes, and reservoirs. An example of an impulsively generated wave that occurred some distance inland from the sea is the one that resulted from a subaerial landslide—that is, a slide above the still water level—in the reservoir of the Vaiont Dam located in the Dolomite region of northern Italy in October 1963. The slide generated a wave that overtopped Vaiont Dam and killed 2,000 people downstream. The wave generation mechanism was a slope failure without an earthquake. Thus, the investigation of the tsunamis generated by subaerial and submarine earthquake-induced landslides has wide application for engineering design and hazard management planners. Although most of the tsunamis during the 1990s described above occurred at locations along the Pacific Rim and did not affect our nation’s coast, the United States is certainly not immune to distant or nearshore events. For example, the Alaska earthquake and tsunami of 1964 and the Chilean earthquake and tsunami in 1960 caused damage and loss of life along the Pacific west coast from Alaska to California as well as in Hawaii. Approximately 120 people lost their lives in the Alaska tsunami of 1964, and the estimated damage from that event along the West Coast and in Hawaii was about $600 million in current dollars. Tsunamis in Waiting It is well known that the Cascadia subduction zone off the Washington-Oregon-northern-California coast is a potential source of giant earthquakes and tsunamis. Indeed, past land subsidence and landward sand deposits postulated as being due to tsunamis provide geological evidence for Cascadia subduction zone events (e.g., Atwater, 1987). In addition, Satake et al. (1996) reported that several historic Japanese documents described coastal flooding on the east coast of Japan in 1700; they suggested that this flooding was caused by a tsunami generated by a Cascadia earthquake of magnitude 9. It is interesting that the size of this tsunami was consistent with a Native American legend of an earthquake and large wave striking and flooding the Washington coastal area (see, e.g., Heaton and Snavely, 1985). A major rupture at this subduction zone would create havoc in coastal cities along the West Coast of the United States. McCarthy et al. (1993) suggested that landslides in the sediment stored at the heads of the numerous submarine canyons along the California coast in close proximity to the shoreline could generate tsunamis in the event of an earthquake. These nearshore canyons just seaward of relatively densely populated areas—for example, offshore of Port Hueneme,
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering FIGURE 2.8 Failure of a span of the Nishinomiya Bridge during the 1995 Kobe, Japan, earthquake. Reproduced courtesy of the National Information Service for Earthquake Engineering, University of California, Berkeley. FIGURE 2.9 Lateral highway offset of 2.5 meters as a result of the 2002 Denali, Alaska, Earthquake. SOURCE: Alaska Department of Natural Resources. Photo by Patty Craw, Division of Geological and Geophysical Surveys.
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering isolation bearings to mitigate the effects of near-field motion, the performance of reinforced-concrete bridge piers, and the prediction and characterization of liquefaction-induced ground movement at abutments. For subway tunnels in soft ground, there may be need to develop innovative, cost-effective techniques to anchor tunnels against liquefaction-induced flotation in loose marine deposits. There is also a need to develop designs for ground transportation systems that can withstand permanent ground displacements along faults. Ports and Air Transportation Systems Ports and air transportation systems move people, commodities, and products by sea, inland waterways, and air. Port facilities are located throughout the United States in seismically active areas and are typically susceptible to structural damage resulting from foundation failure, such as liquefaction-induced ground settlement or lateral spread and tsunami run-up and impact. The Kobe, Japan, earthquake of 1995 damaged numerous waterfront facilities, mainly through liquefaction of loosely placed fill materials. Airports and air traffic control facilities are vulnerable to earthquakes in much the same way that various types of buildings and industrial facilities are. The principal research needs for ports and harbors relate to assessing liquefaction potential, predicting lateral spread and settlement, including the effects on earth retaining structures and foundations of berthing structures and docks, and tsunami mitigation methods. Electric Power Transmission and Distribution Systems Electric power systems consist of power generation stations, transmission and distribution substations, transmission and distribution lines, and communications and control systems. Control systems are unique in that they must be able to respond almost instantaneously to system changes in order to maintain operation (Schiff and Tang, 1995). With respect to the extent and duration of power outages, the overall performance of power systems in past California earthquakes has been good. In the most heavily damaged areas, power was restored more slowly, but considering that it would be unsafe to restore power quickly to areas that might have gas leaks, the standard of service has been generally acceptable. There has been damage to high-voltage substations (220 kV and greater), most of it from the breakage of porcelain components such as insulators. The size, and hence the fragility, of porcelain insulators increases with voltage, so the level of damage generally increases with voltage as well. The most important research needs for electric power transmission
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering and distribution systems relate to the vulnerability of porcelain insulators and rigid bus bars. Research directed at developing components with improved seismic performance is ongoing. Communications Communications systems comprise two types of communication networks: the public switched network and wireless networks. Both types consist of switching, transmission, and signaling (Schiff and Tang, 1995). Damage to communications equipment in past earthquakes was generally light, but there have been instances of circuit card packs becoming disconnected, emergency power generators malfunctioning when commercial power was lost, and damage to battery racks, heating, ventilation, and air conditioning (HVAC) systems, and computer floors. Buildings that housed the communications were severely damaged, but typically the equipment inside performed well. Most of the disruptions to communications came from the high volume of calls following earthquakes, a problem that must be addressed by system control software. The telecommunications industry has addressed earthquake hazards by developing vibration and anchorage standards for equipment. Other concerns relate to seismic design and the strengthening of buildings, which are identical to the concerns discussed for buildings elsewhere in this report. (In light of the effects on wireless communications of the collapse of the World Trade Center towers on September 11, 2001, this issue may deserve additional attention.) Gas and Liquid-Fuel Systems Gas and liquid-fuel lifelines are the infrastructure for the transportation and distribution of crude oil, natural gas, and refined products. Seismic damage to gas and liquid-fuel lines can cause environmental damage and interrupt energy supply to the local area as well as to distant delivery points. Gas and liquid-fuel systems consist of pipelines, pump stations, compressor stations, communications and control systems and support facilities, storage tanks, process equipment, and sometimes marine terminals. The principal earthquake hazards include ground failure due to liquefaction or landslides, settlement, ground-shaking effects on aboveground facilities and equipment, and the surface rupture of faults. The principal research needs unique to gas and liquid-fuel systems relate to soil restraint and/or loading on buried pipelines; the determination of compressive, postbuckling strain limit states; and the study of strain localization associated with pipe wrinkling under high compressive loads. Only a limited number of test facilities worldwide have the
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering capability to conduct such test programs, and most are located outside the United States. Water and Sewage Systems Water and sewage systems provide critical services to our society. Water is essential for public health and well-being, firefighting, business and industry, and agriculture. Sewage systems are needed to provide sanitary disposal and maintain public health. Water and sewage systems consist of pipelines, pump stations, compressor stations, storage tanks and reservoirs, control systems, and water purification systems. The principal earthquake hazards include ground failure due to liquefaction or landslides, settlement, ground-shaking effects on aboveground facilities and equipment, and surface rupture of faults. Water and sewage systems have been damaged by earthquakes. Most of the damage was to transmission and distribution pipelines in areas that experienced ground deformation as a result of liquefaction or fault rupture. Pipelines fabricated of brittle materials such as asbestos, cement, or concrete have experienced more failures than welded, ductile steel pipelines. Water treatment facilities also experienced damage, but much less than the damage to pipelines. The potential for the release of chlorine gas can be a significant safety concern at water treatment plants. Water systems are especially important when earthquakes occur, because large quantities of water may be needed for firefighting in damaged localities. For example, both the San Francisco earthquake of 1906 and the Loma Prieta earthquake of 1989 damaged the municipal water system, impairing firefighting efforts. The fire that devastated San Francisco in 1906 in the aftermath of the earthquake is well chronicled. Fortunately, there was no wind on the evening of the Loma Prieta earthquake in 1989, and fires were more easily contained (Schiff, 1998). One of the more important knowledge gaps for water and sewage systems is the response of large-diameter, thin-wall pipe to seismic wave propagation. Methods for improved characterization of soil-pipe interaction are also needed along with validation by full-scale testing. Industrial Systems For the purpose of this discussion, industrial systems encompass various commercial processes such as refining, manufacturing, fabrication and assembly, and material handling and cover a broad range of products such as chemicals, fuels, electronics, mechanical equipment, and commodities—essentially everything that is produced or consumed in the United States. Industrial systems consist of process equipment, buildings,
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering tanks, vessels, piping, switchgear, motor control centers, instrumentation and control systems, material-handling systems, emergency power systems, fabrication and assembly systems, material storage facilities—the list is nearly endless. Industrial systems are a source of employment and/or of vital products for a region and are vital to its economic health. In addition, certain industrial facilities might transport, handle, or produce hazardous materials that could be released as a result of earthquake damage. As with buildings, the principal earthquake hazard affecting industrial systems is ground shaking. Proper attention to building design, equipment anchorage, and seismic qualification of essential systems usually allows them to withstand seismic shaking with minimal damage or interruption in operation. Performance-based design approaches require the selection of appropriate design parameters that will achieve the desired result. Liquefaction or landslides may also affect industrial facilities, but these hazards normally can be handled on a site-specific basis through prudent location or foundation improvement. In general, the principal research needs for industrial systems mimic those for buildings, with the addition of performance-based design criteria for operating systems within industrial facilities, similar to such criteria for critical equipment within some of the other lifeline areas—electric power, communications, and gas and liquid-fuel lifelines. RISK ASSESSMENT The challenge in risk assessment is to provide decision makers with accurate and understandable information on risk exposure and risk mitigation alternatives and with the tools that will enable them to make prudent decisions based on that information. The major obstacle to developing convincing risk assessments is the lack of good data regarding performance of the natural and built environment—this information must come from tests and field observations, which can then be archived and available via the NEES grid. More specifically, it is necessary to do the following: Develop methods for risk assessment that are comprehensive, based on sound scientific and engineering principles, and usable by a variety of stakeholders. Develop the foundation and tools for rational decision making that leads to risk reduction. Formulate a framework for risk-mitigation and risk-reduction policies that can be implemented by the public and private sectors. Establish adequate incentives for incorporating risk-mitigation
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering measures that will lead to reduced earthquake risk and mechanisms for incorporating these incentives in practice. Although damaging earthquakes are infrequent events, their consequences can be profound. Decision makers are often complacent with respect to the earthquake hazard because a damaging earthquake may not have occurred during their lifetimes or where they live. They may neglect earthquake risks in city planning, building design, and lifeline design and operation. However, a strong earthquake can kill thousands, destroy buildings and infrastructure, interrupt the nation’s production of critical products and services for a long period, cause national economic collapse, and interfere with national security. It is only through the application of prudent and persistent risk-assessment and risk-mitigation actions that these problems can be addressed adequately. Risk assessment requires knowledge of the following types of problems: The likelihood of earthquake events, their size and location, ground shaking and ground failures throughout their influence area, and the likelihood of their causing tsunamis or seiches. Physical damage, with its direct consequences in terms of death, injury, loss of operational functionality, and destruction of property. Social and economic consequences of the direct physical damage, including losses from damage to buildings, lifelines, and other critical structures; homelessness; unemployment; collateral losses resulting from damage to critical facilities, such as the spread of chemical and bacteriological agents from industrial plants; losses from business interruptions, large-scale business failures such as in the property loss insurance industry, and losses of markets to international trade competitors; and impairment of national security capabilities. Improved loss estimation models that support cost-effective earthquake mitigation measures will be a critically important output of NEES. These models will need to couple with practical decision tools that can be used by policy makers, regulators, and building owners to select appropriate mitigation strategies. The social and policy sciences will have a major role to play in shaping this aspect of NEES activities. PUBLIC POLICY A major challenge for the earthquake community, and one of the most important measures of NEES success, will be to have earthquake hazard mitigation placed on public, municipal, and legislative agendas.
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering Although the findings from research discussed in this report will advance the state of practice over time, the revolutionary changes that NEES is seeking will be achieved only through the aggressive development and implementation of policy. The adoption of policy measures, supported by state-of-the-art technology, will significantly increase our nation’s ability to prevent major disasters and thus reduce their devastating economic and social consequences. There is a strong case to be made for a holistic technical-social-economic approach to implementing earthquake mitigation measures. Petak notes that mitigation technology has advanced considerably over the years but deployment has not kept pace, even in earthquake-prone California (Petak, 2003). He believes one of the principal reasons for the lag in deployment is that many view earthquake risk reduction as a technical problem with a technical solution. However, even once a technology has been proven, it requires institutions and people to implement workable solutions. Figure 2.10 illustrates how the elements of such a system work together for effective decision making. FIGURE 2.10 A sociotechnical system view for decision making. SOURCE: Linstone (1984).
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering One of the major difficulties in reducing the economic and social consequences of earthquakes is that policies for disaster mitigation and preparedness are generally inadequate to meet the challenge that disasters pose to a community. The many areas that must be addressed on the road to formulating and implementing disaster policy include the timeliness of the relevant policy; the education of decision makers; the education of stakeholders to obtain their support for introducing legislation; the identification of appropriate alternatives that are consistent with the risk exposure and the ability of a community to implement these policies; and the development of strategies for the implementing legislation. Issues of public policy that NEES activities can help advance are discussed below. Getting on the agenda. After any disaster, there is a clearing of the agenda of those directly involved, and it is in this “teachable moment” that long-term policy change is possible. The need is to be prepared to extend and take advantage of this teachable moment. Understanding and addressing risks. A community at risk needs to understand its risks in order to determine how to mitigate them and how to respond to emergency situations. The technical basis comes from integration of all the geologic, structural, and sociological data to plan for a realistic potential disaster. Knowledge from NEES and other NEHRP programs can define the earthquake hazard and simulate the vulnerability of community infrastructures. These simulations would provide a rational and understandable basis for public and private policy decisions on mitigation and preparedness. Justifying the policies. In formulating public policy, it is often necessary to undertake a cost-benefit analysis of the proposed policy or regulation. For a policy maker to advocate a potentially unpopular (or expensive) new hazard-mitigation policy requires a level of proof that is convincing to the policy maker and understandable to his or her constituency. Defining alternatives. Policy decisions on earthquake mitigation need to be informed by the best science and engineering available but ultimately will be shaped by community values. Better ways of integrating new technical knowledge with the decision-making process will require the collaboration of NEES researchers with the social and policy sciences. The decision tools thus developed would allow policy makers to differentiate among and evaluate alternatives. Educating the public. Most often, public policy is developed in response to public demand. The public is capable of making and influencing controversial (i.e., expensive) policy decisions, but only if people are sufficiently knowledgeable about the underlying issues and the alternative solutions and their implications.
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering Property rights. In the United States, individual property rights are a fundamental constant in all zoning and land use decisions. It is difficult to deprive individuals (or companies) of their right to develop their property, even if it might be hazardous for them to do so. Overcoming this problem has been a challenge for planning agencies, the courts, and concerned citizens on both sides of the issue. However, if a community can be unified behind a decision to improve public safety through land use planning, the community can effect needed changes. REFERENCES Abrahamson, N.A., and W.J. Silva. 1997. Empirical response spectral attenuation relations for shallow crustal earthquakes. Seismological Research Letters 68(1):94-127. Aki, K. 1988. Local site effects on strong ground motion. Pp. 103-155 in Earthquake Engineering and Soil Dynamics II: Recent Advances in Ground-Motion Evaluation, J.L. Von Thun, ed. Geotechnical Special Publication No. 20. Reston, Va.: American Society of Civil Engineers. Aki, K., and P.G. Richards. 1980. Quantitative Seismology, Theory and Methods. New York: W.H. Freeman Company. Andrews, D.J. 1980. A stochastic fault model: I. Static case. Journal of Geophysical Research 85(2):3867-3877. Atwater, B.F. 1987. Evidence of great holocene earthquakes along the outer coast of Washington state. Science 236:942-944. Bard, P.Y., and M. Bouchon. 1985. The two-dimensional resonance of sediment-filled valleys. Bulletin of the Seismological Society of America 75:519-541. Borcherdt, R.D. 1970. Effects of local geology on ground motion near San Francisco Bay. Bulletin of the Seismological Society of America 60:29-61. Borrero, J. 2002. Analysis of the tsunami hazard for southern California, Ph.D. dissertation. Los Angeles: University of Southern California. Bouchon, M., M.P. Bouin, H. Karabulut, M.N. Toksoz, and M. Dietrich. 2001. How fast does rupture propagate during an earthquake? New insights from the 1999 Turkey earthquakes. Geophysical Research Letters 28:2723-2726. EQE. 1989. The October 17, 1989 Loma Prieta Earthquake. EQE Report, October 1989. Houston, Tex.: ABS Consulting (was EQE International, Inc.). Available online at <http://www.eqe.com/publications/lomaprie/lomaprie.htm> [November 19, 2002]. FEMA (Federal Emergency Management Agency). 1987. Abatement of Seismic Hazards to Lifelines, FEMA-142. Washington, D.C.: FEMA. Field, E.H., P.A. Johnson, I.A. Beresnev, and Y. Zeng. 1997. Nonlinear sediment amplification during the 1994 Northridge earthquake. Nature 390:599-602. Finn, W.D.L. 1988. Dynamic analysis in geotechnical engineering. Pp. 523-591 in Earthquake Engineering and Soil Dynamics II: Recent Advances in Ground Motion Evaluation, J.L. Von Thun, ed. Geotechnical Special Publication 20. Reston, Va.: American Society of Civil Engineers. Graves, R.W. 2002. The seismic response of the San Bernardino basin region. Eos Trans. AGU 83(47). Guatteri, M., P.M. Mai, G.C. Beroza, and J. Boatwright. 2003. Strong ground motion prediction from stochastic-dynamic source models. Bulletin of the Seismological Society of America 93(1):301-313.
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering Hausler, E.A., and M. Koelling. 2003. Performance of improved ground during the 2001 Nisqually, Washington earthquake. Proceedings, Fifth International Conference on Case Histories in Geotechnical Engineering, April 13-17, 2003, New York. Hausler, E.A., and N. Sitar. 2001. Performance of soil improvement techniques in earthquakes. Paper 10.15 in Fourth International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, March 26-31. Heaton, T.H. 1990. Evidence for and implications of self-healing pulses of slip in earthquake rupture. Phys. Earth and Planet. Int. 64:1-20. Heaton, T.H., and P.D. Snavely, Jr. 1985. Possible tsunami along the northwest coast of the U.S. inferred from Indian tradition. Bulletin of the Seismological Society of America 75(5):1455-1460. Holzer, T.L. 1994. Loma Prieta damage largely attributed to enhanced ground shaking. Transactions, American Geophysical Union 75-26:299-301. Idriss, I.M. 2002. How well have we learned from recent earthquakes? 2002 Distinguished Geotechnical Lecture, March 18, Virginia Polytechnic Institute and State University, Blacksburg, Va. Jennings, P.C. 1970. Distant motions from a building vibration test. Bulletin of the Seismological Society of America 60:2037-2043. Jennings, P.C., and J. Bielak. 1973. Dynamics of building-soil interaction. Bulletin of the Seismological Society of America 63:9-48. Jibson, R.W., E.L. Harp, E. Schneider, R.A. Hajjeh, and R.A. Spiegel. 1998. An outbreak of Coccidioidomycosis (Valley Fever) caused by landslides triggered by the 1994 Northridge, California earthquake. A Paradox of Power: Voices of Warning and Reason in the Geosciences: Reviews in Engineering Geology, C.W. Welby and M.E. Gowan, eds. Boulder, Colo.: Geological Society of America. Lepelletier, T.G., and F. Raichlen. 1987. Harbor oscillations induced by nonlinear transient long waves. Journal of Waterway, Port, Coastal, and Ocean Engineering 113(4):381-400. Linstone, H., 1984. Multiple Perspectives for Decision Making: Bridging the Gap Between Analysis and Action. New York, N.Y.: Elsevier-Science Publications. Mahin, S.A. 1998. Lessons from Steel Buildings Damaged by the Northridge Earthquake. National Information Service for Earthquake Engineering, University of California, Berkeley. Available online at <http://nisee.berkeley.edu/northridge/mahin.html> [April 9, 2003]. Mai, P.M., and G.C. Beroza. 2002. A spatial random-field model to characterize complexity in earthquake slip. Journal of Geophysical Research 107(11):2308. Marcuson, W.F., W.D. Finn, and R.H. Ledbetter. 1996. Geotechnical engineering practice in North America: The last 40 years. Thirty-second Henry M. Shaw Lecture in Civil Engineering, March, North Carolina State University, Raleigh, N.C. McCarthy, R.J., E.N. Bernard, and M.R. Legg. 1993. The Cape Mendocino earthquake: A local tsunami wakeup call? Proceedings of the 8th Symposium on Coastal and Ocean Management 3:2812-2828. Mitchell, J.K., and J.R. Martin. 2000. Performance of improved ground and earth structures. Chapter 9 in 1999 Kocaeli, Turkey, Earthquake Reconnaissance Report, Supplement A to Volume 16, Earthquake Spectra, December, pp. 191-225. Oakland, Calif.: EERI Publications. NOAA (National Oceanic and Atmospheric Administration). 2003. Tsunami Event Database Search. Available online at <http://www.ngdc.noaa.gov/seg/hazard/tsevsrch_idb.shtml> [July 20, 2003]. Petak, W.J. 2003. Earthquake mitigation implementation: A sociotechnical system approach. 2003 Distinguished Lecture, 55th Annual Meeting of the Earthquake Engineering Research Institute, February 5-8, 2003, Portland, Ore.
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Preventing Earthquake Disasters: The Grand Challenge in Earthquake Engineering Phillips, W.S., and K. Aki. 1986. Site amplification of coda waves from local earthquakes in central California. Bulletin of the Seismological Society of America 76:627-648. Pierepiekarz, M. 2001. Seattle earthquake gets insurers’ attention. Claims Magazine. Available online at <http://www.claimsmag.com/Issues/May01/seattle.asp> [April 9, 2003]. Rogers, S.R., and C.C. Mei. 1977. Nonlinear resonant excitation of a long and narrow bay. Journal of Fluid Mechanics 88:161-180. Rosenblueth, E., and R. Meli. 1986. The earthquake of 19 September 1985: Effects in Mexico City. Concrete International 8:23-34. Satake, K., K. Shimazaki, Y. Tsuiji, and K. Ueda. 1996. Time and size of a giant earthquake in Cascadia inferred from Japanese tsunami records of January 1700. Nature 379(6562):246-259. Scawthorn, C., et al. 1995. The January 17, 1995 Kobe Earthquake. An EQE Summary Report. Available online at <http://www.eqe.com/publications/kobe/kobe.htm> [April 9, 2003]. Schiff, A.J., ed. 1998. The Loma Prieta, California, Earthquake of October 17, 1989—Lifelines. U.S. Geological Survey (USGS) Professional Paper 1552-A. Reston, Va.: USGS. Schiff, A.J., and A. Tang. 1995. Policy and general technical issues related to mitigating seismic effects on electric power and communication systems. Critical Issues and State of the Art in Lifeline Earthquake Engineering, Monograph No. 7. Reston, Va.: American Society of Civil Engineers. Seed, H.B., and I.M. Idriss. 1982. Ground motions and soil liquefaction during earthquakes. Earthquake Engineering Research Institute (EERI) Monograph Series. Berkeley, Calif.: EERI. Seed, H.B., I.M. Idriss, and H. Dezfulian. 1970. Relationships between soil conditions and building damage in the Caracas earthquake of July 29, 1967. Report No. UCB/EERC-70/2. February. University of California, Berkeley: Earthquake Engineering Research Center. Somerville, P.G., K. Irikura, R. Grave, S. Sawada, D.J. Wald, N. Abrahamson, Y. Iwasaki, T. Kagawa, N. Smith, and A. Kowada. 1999. Characterizing crustal earthquake slip models for the prediction of strong ground motion. Seismological Research Letters 70(1):59-80. Somerville, P., N. Smith, R. Graves, and N. Abrahamson. 1997. Modification of empirical strong ground motion attenuation results to include the amplitude and duration effects of rupture directivity. Seismological Research Letters 68(1):199-222. Trifunac, M.D., M.I. Todorovska, and S.S. Ivanovic. 1994. A note on distribution of uncorrected peak ground accelerations during the Northridge, California, earthquake of 17 January 1994. Soil Dynamics and Earthquake Engineering 13(3):187-196. USGS (United States Geological Survey). 2003. The National Landslides Hazard Program. Available online at <http://landslides.usgs.gov/html_files/landslides/program.html> [July 15, 2003]. Veletsos, A.S., and J.W. Meek. 1974. Dynamic behavior of building-foundation systems. Journal of Earthquake Engineering Structural Dynamics 3(2):121-138. Wirgin, A., and P.Y. Bard. 1996. Effects of buildings on the duration and amplitude of ground motion in Mexico City. Bulletin of the Seismological Society of America 86:914-920. Youd, T.L., and C.T. Garris. 1995. Liquefaction-induced ground surface disruption. Journal of Geotechnical Engineering 121(11):805-809. Zelt, J.A., and F. Raichlen. 1990. A Lagrangian model for wave induced harbor oscillations. Journal of Fluid Mechanics 213:203-225.
Representative terms from entire chapter: