Ellis L. Krinitzsky

How to obtain earthquake ground motions for engineering design

Abstract The earthquake ground motions that ultimately are selected for engineering design depend chiefly on the criticality of a site or structure and the engineering analyses that are to be performed. Several key steps are necessary in this selection process: They are (1) a reconnaissance to understand the hazards and obtain preliminary earthquake ground motions; (2) decisions on the application of deterministic or probabilistic methods; (3) selection of appropriate motions for requirements in design; (4) consideration of thresholds at which motions become significant for engineering; and (5) decisions on specifying appropriate earthquake ground motions for sizes of earthquakes, distances from sources, the structures, sites, and testing to be done. This paper presents five tables that show steps for evaluating these factors and for enabling the investigator to specify earthquake ground motions appropriate for engineering design.

Earthquake probability in engineering—Part 2: Earthquake recurrence and limitations of Gutenberg-Richter b-values for the engineering of critical structures: The third Richard H. Jahns distinguished lecture in engineering geology

Abstract Ellis L. Krinitzsky, 1993. Earthquake probability in engineering—Part 2: Earthquake recurrence and limitations of Gutenberg-Richter b-values for the engineering of critical structuresEng. Geol., 36: 000-000. Gutenberg-Richter b-values are dysfunctional for site-specific applications in the engineering of critical structures. Their dysfunction results from differences in the mechanism of faulting and nonuniformity in the occurrences of earthquakes over time and space. The mechanisms of faulting include stick slip, various categories of controlled slip, and a multitude of thermodynamic slip processes which range from rock melting to stress releases by hydrothermal and other fluids at or near lithostatic pressures. These processes cause accelerated fault movements and chaotic earthquake occurrences, while asperities and barriers along faults contribute to temporary clustering effects that develop characteristic earthquakes but do not give them continuity through time. B-line projections must incorporate these complexities, but they can do so only when they are inclusive for large, seismically active areas such as southern California, the Aleutian arc, etc. Within the relatively small earthquake source areas that determine damaging earthquake ground motions at individual engineering sites, b-values become dysfunctional atM ≥ 5.0. Because b-values are the determinants of probabilistic seismic hazard analyses, there are severe restraints on the usefulness of probabilistic methods to assign earthquake ground motions for the engineering of critical structures. The latter include major dams, nuclear power plants, liquefied petroleum gas installations, repositories for dangerous wastes, military command centers, sensitive industrial and defense installations, fire stations, schools, and hospitals.

Earthquake probability in engineering — Part 1: The use and misuse of expert opinion. The Third Richard H. Jahns Distinguished Lecture in Engineering Geology

Abstract The Lawrence Livermore National Laboratory and the Electric Power Research Institute have developed procedures that statistically merge multiple expert opinions to get probabilistic seismic hazard evaluations. Such methods are intrinsically defective and should not be used for design applications in engineering.

Deterministic versus probabilistic seismic hazard analysis for critical structures

Abstract Probabilistic seismic hazard analysis has been practically unchallenged since its inception three decades ago. However, information has been accumulating which shows convincingly that PSHA is a defective procedure. Its greatest weakness is the dependence of the probability theory on the Gutenberg-Richter magnitude and a recurrence relation which can no longer be regarded as a power law. Remedies that rely on incorporating paleoseismic information and characteristic earthquakes into the probability calculation introduce other errors resulting from fragmentary data and the known non-uniformity of earthquake occurrence in space and time. The worst corrective for probability is the method developed by the Electric Power Research Institute and the Lawrence Livermore National Laboratory that averages multiple expert opinions. Expert opinions cannot be averaged meaningfully because the criteria for different models are nonequivalent. On the other hand, the deterministic procedure for earthquake hazard evaluation avoids the above defects by eliminating the falsely precise time element in the probabilistic estimation. Geologic time for recurrence is used, according to accepted criteria such as a single movement in the past 12,000 years or multiple movements in 500,000 years. For a critical project, where the consequences of failure are intolerable and protection is needed against the worst that can be reasonably expected to occur (the maximum credible earthquake), the deterministic method is strongly recommended.

The Bhuj, India, earthquake: lessons learned for earthquake safety of dams on alluvium

Abstract The Bhuj, India, earthquake of 26 January 2001, M s 7.9, caused dams built on alluvium to sustain damage ranging from cosmetic to severe. Major damage was caused almost entirely by soil liquefaction in the alluvium. The critical factor was the level of earthquake ground motion. The Bhuj earthquake showed that peak horizontal accelerations (PHAs)≤0.2 g were generally safe. PHAs>0.2 g were hazardous, when unconsolidated granular foundation soils were water saturated. N values of 0.2 g, must be evaluated over the full area beneath a new dam and all soils deemed susceptible to liquefaction must be either removed or treated. For remediating an old dam, reliable options are removal and replacement of liquefiable alluvium beneath upstream and downstream portions of the dam, combined with building berms designed to provide stability for the dam should there be a strength loss in soils beneath the dam.

Problems with logic trees in earthquake hazard evaluation

Abstract Logic trees make sense when used in earthquake risk analysis where costs are compared for specific outcomes. However logic trees fail in earthquake hazard analysis when they are used to develop earthquake ground motions for applications in engineering. The failure stems from a misguided attempt to assign numbers for degrees of belief which are personal and indefinable, almost like love or taste, and for which there are neither tests nor measurements. The result is a complicated jumble of egocentric impressions. In contrast, the need in engineering is to have values that are based as much as possible on evidence.

Earthquake safety evaluation of sanitary landfills

Abstract Earthquake ground motions at municipal solid waste landfills must be specified according to the level of hazard or criticality of the site along with the type of engineering analysis that is to be performed. Todays landfills, when built to regulatory standards, are unlikely to be critical, but older landfills can be seriously hazardous. Consequently, the hazards are graded as: (1) none to negligible; (2) low; (3) moderate; and (4) great. For non-critical sites, motions may be obtained from a probabilistic map but a deterministic map, if available, is preferred as part of a non-sites-pecific investigation; however, for critical sites, a deterministic, site-specific evaluation should be made. Motions must be specified appropriately for the type of analysis, whether it is for foundation liquefaction, stability of slopes, integrity of barriers, earth pressures, or the design of appurtenant structures.

A new and defective regulation in California for protecting critical buildings from earthquakes

Abstract The California Geological Survey issued a new regulatory directive specifying that critical buildings be designed for 50- and 100-year earthquakes obtained by probabilistic seismic hazard analysis (PSHA). PSHA incorporates serious uncertainties. Chiefly, they are: (1) PSHA smears earthquakes together to produce motions that are unrealistic for any specific earthquake-generating fault source, (2) PSHA assumes there is an essentially log–linear predictability through time for both the sizes of earthquakes and their motions, although earthquake experiences deny this assumption, and (3) PSHA derives design values from an almost total lack of data on the recurrences that it claims to represent. Error bands for probabilistic motions, if honestly applied, would be so enormously broad that probabilistic values would be seen to be too uncertain as a rational basis for critical designs. Worse yet, the directive of the California Geological Survey has forced a de facto elimination of deterministic seismic hazard analysis (DSHA) from consideration. Yet, DSHA provides more logical, more transparent, more peer reviewable, and more dependable solutions than does PSHA. In summary, the new regulatory directive fails to provide the public in California with a necessary level of seismic safety.