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A novel approach to construct site-dependent ground-motion prediction equations (GMPEs) was implemented to build a uniform hazard response spectra (UHRS) using a reservoir site in southern Taiwan as an example. This innovation minimizes the GMPE uncertainties to avoid over-estimations in a probabilistic seismic hazard analysis (PSHA). We selected ground-motion records with similar site conditions from the stations within 70 km of the studied site to build a site-dependent ground-motion prediction model for crustal earthquakes in the region. This site-dependent GMPE set obtains a significantly smaller scattering of residuals compared with the existing regional GMPEs from the Taiwan data set. This indicates that a set of site-dependent GMPEs could provide a more accurate and reasonable prediction of ground-motion levels for the design or safety evaluation of important infrastructures.

Many existing earth dams have been designed and built worldwide before the establishment of a seismic code, so that it is of relevant interest to evaluate their seismic performance and post-seismic operational conditions. This requires an accurate geotechnical characterisation of the dam and foundation soils, a proper definition of the seismic scenarios at the site of the dam, the use of simplified procedures for screening-level seismic analyses and advanced non-linear dynamic analyses to study the most critical seismic scenarios. This process has been used for the evaluation of the seismic performance of a zoned earth dam located in a high seismic hazard area of Southern Italy. In this paper the available data of historical seismicity at the site of the dam and the results of a probabilistic seismic hazard analysis are first discussed and input ground motions are selected using compatibility criteria with the energy and frequency content of the expected target motion in a range of vibration period relevant for the non-linear response of the dam. Seismic performance of the dam is then evaluated through procedures based on Newmark-type computations, in which permanent displacements are related to ground motion characteristics and to the seismic resistance of the dam, the latter evaluated detecting the earthquake-induced plastic mechanisms and the corresponding critical accelerations. Also, an original improvement of the well-known Makdisi & Seed procedure, was proposed to better capture the actual influence of non-linear soil behaviour in the evaluation of horizontal acceleration and permanent displacements of the crest of the dam. The analysis results pointed out the relevant role of the earthquake-induced shear strength reduction on the dam permanent displacements.

Southern Peru and northern Chile (17–30°S, 67–74°W) make up a seismically active region due to the convergence of the Nazca Plate and the South American Plate. The region has experienced a number of destructive earthquakes and tsunamis over the past few centuries, which have caused loss of human life and significant damage to infrastructure, highlighting the importance of seismic hazard assessment in the region. In fact, a reliable seismic hazard assessment is critical for developing policies for seismic hazard mitigation and risk reduction. In this study, we performed a probabilistic seismic hazard assessment (PSHA) of the study area based on an earthquake catalog that was very carefully analyzed. In earlier studies, we demonstrated that inappropriate treatment of the earthquake catalog can result in a serious bias in evaluations of seismicity parameters (e.g., a bias of up to 42% in the “b” parameter of the Gutenberg–Richter law). To address this issue, we compiled a homogenous earthquake catalog consisting of 39,977 events during the 1513–2016 period and accounted for site-specific local effects by developing site-specific scaling relationships between different measures of magnitude (e.g., mb, Ms, MD) and moment magnitude (Mw). The study area was subdivided into 15 seismogenic zones, accounting for site-specific seismicity patterns. The parameters “a” and “b” of the Gutenberg–Richter law were estimated for each zone based on independent earthquake events. The PSHA was performed using a standard logic tree approach, which allowed us to systematically take into account the model-based uncertainty and its influence on the estimated ground motion parameters. Uniform hazard spectra for return periods of 475 and 2475 years were estimated for peak ground accelerations and spectral accelerations at 0.2 s and 1.0 s to meet the definitions of seismic hazards provided by the International Building Code (IBC, International Code Council [ICC], 2009). This study is expected to provide a basis for design maps for building codes and emergency planning.

The uncertainty assessment for the development of the new seismic hazard maps of Spain is explained in this work. A detailed description of how uncertainties are considered in the different phases followed for the probabilistic seismic hazard assessment study is presented. Special emphasis is given to the characterization of the uncertainty of earthquake size parameters contained in the catalog, and their propagation to subsequent phases of the analysis such as catalog homogenization, completeness and declustering. Aleatory and epistemic uncertainties are examined and assessed using Monte Carlo simulations and a logic tree, respectively. The final impact of uncertainty in hazard estimates is evaluated through coefficient of variation maps, showing the areas where larger and lower variability is obtained. The hazard maps developed in this work are intended to be the basis for the future revision of the Spanish seismic code.

Financiado por el Grupo de Investigacion "Peligrosidad Sismica y Microzonificacion" de la Junta de Andalucia (RNM-0217) y por el proyecto de la CICYT (RIES-CTIDIB/2002/177).

Deterministic seismic hazard analysis (DSHA) and probabilistic seismic hazard analysis (PSHA) are incompatible methods. DSHA is based on geology and is attuned to physical reality in nature; PSHA is based on earthquake statistics and theory-guided numerical calculations. PSHA is less reliable than DSHA because PSHA is full of grave uncertainties that are created by the method itself; DSHA is more reliable because it deals principally with observed geological facts and is logical and transparent. DSHA and PSHA can be combined to advantage if one accepts that they are not equally valid. To combine them, one must recognize the weaknesses in PSHA and not use PSHA for design of critical structures. Only DSHA is suitable for that purpose. However, PSHA can be used for (1) preliminary evaluations, (2) for an operating basis earthquake (OBE), (3) for risk analysis when unrelated to design decisions for a critical project, and (4) for design of non-critical construction. Probabilistic methods that should never be used are (1) multiple expert opinion, (2) logic trees, and (3) deaggregation. No unrepentant seismic probabilist will agree to this diminishment of PSHA. Consequently, DSHA and PSHA will remain irreconcilable. The solution is for policymakers in regulatory agencies and owners of major engineering projects to determine which of the methods to use or in what combination. They need to (1) engage open-minded advisors, (2) ask hard questions, and (3) choose wisely. Meanwhile, Krinitzsky [Eng. Geol. 65 (2002) 1] provides procedures to obtain earthquake ground motions for engineering design that combine DSHA and PSHA according to the above criteria.

Earthquake hazards can be communicated with both probabilistic seismic hazard maps and “deterministic” maps showing estimated ground motions expected from a subset of the possible earthquakes. This paper describes the latter class of maps as “scenario” ground motion maps. The principle behind the scenario maps is to portray a median estimate of ground motions from events that are reasonable, and regionally the most significant. The intent is that the scenario map answers the common question: “If the fault ruptures, what do you expect?” This paper proposes rules for construction of scenario maps, argues that a parallel map (a scenario probability map) should be constructed giving estimates of the annual recurrence rates of the scenario ground motions, and compares probabilistic and scenario ground motions for areas with high and moderate seismic hazards. Uses for scenario maps include educating the public about the earthquake hazards, some engineering applications and hazard response planning.

Individual faults within a region cannot have a Gutenberg-Richter recurrence if the total of earthquakes within the region follow a Gutenberg-Richter recurrence. Few faults have produced and adequate number of earthquakes to establish the nature of recurrence on them. Broad seismic regions, however, for which there is a statistically viable earthquake data set, have been shown to obey a Gutenberg-Richter recurrence with a slope of about 1. A Gutenberg-Richter recurrence is often assumed for faults in probabilistic seismic hazard analyses. The requirement that individual faults cannot produce earthquakes with this recurrence casts doubt on the validity of such probabilistic methods. Errors in probabilistic seismic hazard analysis tend to be amplified in the calculation of rare earthquake probabilities and it is these rare earthquakes for which critical facilities must be designed. Therefore, sole use of probabilistic seismic hazard analysis for critical facilities is not recommended.

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.

Probabilistic seismic hazard analysis (PSHA) is beginning to be seen as unreliable. The problem with PSHA is that its data are inadequate and its logic is defective. Much more reliable, and more scientific, are deterministic procedures, especially when coupled with engineering judgment.

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.