Hazard Deaggregation Research Articles

Impact of seismotectonic source zoning and seismic parameter: Sensitivity study on probabilistic seismic hazard assessment

The demarcation of seismic area source zones plays a pivotal role in probabilistic seismic hazard assessment (PSHA). In this study, we developed five distinct seismotectonic area source models, integrating large and small areas based on geological, tectonic, and seismological data. Logic tree methodology is utilized in FRISK88M for PSHA. Analysis revealed higher hazards in models with larger area sources compared to those with smaller ones. Hazard deaggregation of seismotectonic model-5 (SM5) is examined and sensitivity analysis of various logic tree nodes is investigated in terms of percent deviation w.r.t mean hazard at various spectral and return periods. The findings underscore that recurrence methods fall into "insensitive level" (≤5%), source mechanism and a-value distribution belong to "low sensitive level" (>5–15%), magnitude distribution lies in "medium sensitive level" (>15–25%), b-value distribution belongs to "high sensitive level" (>25–35%), and ground motion prediction equations (GMPEs) and depth distribution falls into "very high sensitive level" (>35%) in relation to seismic hazard.

Deaggregation of probabilistic seismic hazard results for some selected cities in Western Mexico

ABSTRACT Here we present a deaggregation appraisal conducted for 15 selected significant cities in Western Mexico, for four oscillation periods (PGA, SA (0.2 s), SA (1.0 s), and SA (2.0 s)), also considering a different input for the soil condition (for B, B/C and C NEHRP site classes), and for two return periods (475 and 975 years). This study is based on a previous complete recently published seismic hazard evaluation for the region. An area source model consisting of thirty-seven seismic sources has been used alternatively in a logic tree with a spatially smoothed seismicity model for the same region. The obtained hazard deaggregation results prove that for most of the studied cities –those located along the Pacific coast–, nearby seismic sources are contributing most to the seismic hazard at the studied location, especially for lower periods (PGA and SA (0.2 s)). However, for a few cities far from the Middle America Trench, distant large-magnitude earthquakes contribute more to the seismic hazard, especially at larger spectral periods (SA (1.0 s) and SA (2.0 s)). Additionally, this study shows that the differences in the soil conditions for the computed return periods, have a little influence on the obtained deaggregation results.

A Simplified Method for Performing Vector-Valued Probabilistic Seismic Hazard Analysis

ABSTRACT For a seismic risk analysis, the seismic hazard results are usually combined with fragility functions to calculate the probability of seismic losses. Because vector-valued ground-motion intensity measures (IMs) are increasingly used by researchers and practicing engineers to evaluate fragility functions, seismic hazard calculations in terms of vector-valued IMs are required, which are determined by vector-valued probabilistic seismic hazard analysis (PSHA). However, the large computational cost associated with vector-valued PSHAs impedes the application of vector-valued IMs in performing a seismic risk analysis. The study presents a simplified method for conducting vector-valued PSHAs. This simplified method is developed using proposed equivalent earthquakes that are derived from conventional seismic hazard deaggregation. Formulas for performing vector-valued PSHAs using the simplified method are also proposed. Based on a numerical example, this study demonstrates the accuracy and efficiency of the proposed method.

Deaggregation of Wind Speeds for Hurricane Scenarios Used in Risk-Informed Resilience Assessment of Coastal Communities

Coastal cities in the east and southeast regions of the US have seen significant population growth and economic development in the last 2 decades. As a result, urban infrastructure, populations, and economies are becoming increasingly vulnerable to hurricane-driven hazards. Criteria for wind design in national standards are intended specifically for the design and performance assessment of individual buildings and other facilities for life safety. They are not adequate for assessing community resilience because hurricane winds are spatially nonuniform. Although scenario-based approaches to representing hurricane demands are more useful in community performance assessment because the distinct features of various hurricane scenarios and their impact on a community can be captured, they are not tied to a specific hazard level. This study introduces a new method for systematically identifying a set of hurricane scenarios corresponding to a stipulated return period (RP) for resilience assessment of coastal communities using a deaggregation approach, which establishes a connection that has not existed previously between hurricane scenarios and the building regulatory process. A community patterned after Miami, Florida, was used to demonstrate the proposed hazard deaggregation and damage analysis. Hurricane scenario events that are dominant contributors to the stipulated RP events, coupled with fragility models of engineered buildings, were used to identify building damage patterns and form an improved basis for risk-informed decision making.

Preliminary approach to assess the seismic hazard on a lunar site

The passive seismic network deployed on the Moon during the Apollo missions operated for eight years and allowed the observation of seismic activity. More than 12500 seismic events were registered, where 28 were classified as shallow moonquakes with moment magnitudes up to 4.1. Seismic events of this nature pose a significant risk to future long-term lunar habitats; thus, these events must be carefully studied and considered in the seismic design of these structures. This paper proposes a preliminary seismic hazard assessment imposed by shallow moonquakes. The hazard assessment is performed using the Probabilistic Seismic Hazard Analysis (PSHA) methodology, considering previous studies and theories regarding the seismic environment of the Moon. The study zone covers ∼860 km2 of the Taurus-Littrow Valley, containing the Apollo 17 landing site and the Lee-Lincoln lobate scarp as the considered seismic source. The seismic hazard is quantified in terms of peak ground acceleration (PGA) and spectral acceleration (5% damped pseudo-acceleration, PSA). Seismic hazard deaggregation scenarios, Uniform Hazard Spectra (UHS) for different hazard levels, and a Conditional Mean Spectrum (CMS) for a target period of 0.2 s are obtained to quantify the seismic hazard on a specific site on the Moon. The developed seismic hazard assessment provides a preliminary approach for realistic scenarios to conduct structural designs that ensure the seismic performance of fully operational long-term lunar structures.

Regional tsunami hazard from splay faults in the Gulf of Oman

The present study evaluates the tsunami hazard from splay thrust and normal faults in the western Makran, Gulf of Oman for the first time. We interpret splay thrust and normal faults in the Gulf of Oman using reflection seismic data and analyze the implied regional deterministic and probabilistic tsunami hazards. The tsunami hazards associated with splay thrust and more specifically normal faults in Makran have not been well understood before. Our results indicate the need to pay much more attention to hazards from splay thrust and normal faults in the Makran subduction zone. The highest tsunami waves impact Jask and Muscat. The results of inundation modeling show the high power of generated tsunami waves to penetrate inland. Our tsunami hazard deaggregation analysis indicates an unusual large contribution from normal faults to the local tsunami hazard. We find out that the probability that tsunami wave height exceeds 1m and 3m in 250 years reach 1 and 0.8 in the Gulf of Oman Basin.

Seismic probabilistic risk assessment of weir structures considering the earthquake hazard in the Korean Peninsula

Seismic safety evaluation of weir structure is significant considering the catastrophic economical consequence of operational disruption. In recent years, the seismic probabilistic risk assessment (SPRA) has been issued as a key area of research for the hydraulic system to mitigate and manage the risk. The aim of this paper is to assess the seismic probabilistic risk of weir structures employing the seismic hazard and the structural fragility in Korea. At the first stage, probabilistic seismic hazard analysis (PSHA) approach is performed to extract the hazard curve at the weir site using the seismic and geological data. Thereafter, the seismic fragility that defines the probability of structural collapse is evaluated by using the incremental dynamic analysis (IDA) method in accordance with the four different design limit states as failure identification criteria. Consequently, by combining the seismic hazard and fragility results, the seismic risk curves are developed that contain helpful information for risk management of hydraulic structures. The tensile stress of the mass concrete is found to be more vulnerable than other design criteria. The hazard deaggregation illustrates that moderate size and far source earthquakes are the most likely scenario for the site. In addition, the annual loss curves for two different hazard source models corresponding to design limit states are extracted.

Probabilistic Seismic Hazard Assessment for United Arab Emirates, Qatar and Bahrain

A probabilistic seismic hazard assessment in terms of peak ground acceleration (PGA) and spectral acceleration (SA) values, for both 10% and 5% probability of exceedance in 50 years, has been performed for the United Arab Emirates, Qatar, and Bahrain. To do that, an updated, unified, and Poissonian earthquake catalog (since 685 to 2019) was prepared for this work. Three alternative seismic source models were considered in a designed logic-tree framework. The discrimination between the shallow and intermediate depth seismicity along the Zagros and the Makran regions was also considered in this assessment. Three alternative ground-motion attenuation models for crustal earthquakes and one additional for intermediate-depth ones have been selected and applied in this study, considering the predominant stress regime computed previously for each defined source. This assessment highlights that the maximum obtained hazard values are observed in the northeastern part of the studied region, specifically at Ras Al-Khaimah, Umm Al-Quwain, and Fujaira, being characterized by mean PGA and SA (0.2 s) pair values equal to (0.13 g, 0.30 g), (0.12 g, 0.29 g), and (0.13 g, 0.28 g), respectively, for a 475-year return period and for B/C National Earthquake Hazards Reduction Program (NEHRP) boundary site conditions. Seismic hazard deaggregation in terms of magnitude and distance was also computed for a return period of 475 years, for ten emirates and cities, and for four different spectral periods.

Regional probabilistic tsunami hazard assessment associated with active faults along the eastern margin of the Sea of Japan

We analyze the regional tsunami hazard along the Sea of Japan coast associated with 60 active faults beneath the eastern margin of the Sea of Japan. We generate stochastic slip distribution using a Monte Carlo approach at each fault, and the total number of required earthquake samples is determined based on convergence analysis of maximum coastal tsunami heights. The earthquake recurrence interval on each fault is estimated from observed seismicity. The variance parameter representing aleatory uncertainty for probabilistic tsunami hazard analysis is determined from comparison with the four historical tsunamis, and a logic-tree is used for the choice of the values. Using nearshore tsunami heights at the 50 m isobath and an amplification factor by the Green’s law, hazard curves are constructed at 154 locations for coastal municipalities along the Sea of Japan coast. The highest maximum coastal tsunamis are expected to be approximately 3.7, 7.7, and 11.5 m for the return periods of 100-, 400-, and 1000-year, respectively. The results indicate that the hazard level generally increases from southwest to northeast, which is consistent with the number and type of the identified fault systems. Furthermore, the deaggregation of hazard suggests that tsunamis in the northeast are predominated by local sources, while the southwest parts are likely affected by several regional sources.

Hazard-Consistent Earthquake Scenario Selection for Seismic Slope Stability Assessment

Design ground shaking intensity, based on probabilistic seismic hazard analysis (PSHA) maps, is most commonly used as a triggering condition to analyze slope stability under seismic loading. Uncertainties that are associated with expected ground motion levels are often ignored. This study considers an improved, fully probabilistic approach for earthquake scenario selection. The given method suggests the determination of the occurrence probability of various ground motion levels and the probability of landsliding for these ground motion parameters, giving the total probability of slope failure under seismic loading in a certain time interval. The occurrence hazard deaggregation technique is proposed for the selection of the ground shaking level, as well as the magnitude and source-to-site distance of a design earthquake, as these factors most probably trigger slope failure within the time interval of interest. An example application of the approach is provided for a slope near the highway in the south of Sakhalin Island (Russia). The total probability of earthquake-induced slope failure in the next 50 years was computed to be in the order of 16%. The scenario peak ground acceleration value estimated from the disaggregated earthquake-induced landslide hazard is 0.15g, while the 475-year seismic hazard curve predicts 0.3g. The case study highlights the significant difference between ground shaking scenario levels in terms of the 475-year seismic hazard map and the considered fully probabilistic approach.

Illustrative Analysis of Probabilistic Sea Level Rise Hazard

AbstractSea level rise results from several contributing physical processes, including ocean thermal expansion and glacier and ice sheet mass loss. Future projections of sea level remain highly uncertain due to several sources of aleatory and epistemic uncertainty. Quantifying different sources of sea level rise involves considering possible pathways of future radiative forcing and integrating models of different sea level rise processes. The probabilistic hazard analysis strategy has been proposed for combining sea level rise prediction models and climate forcing scenarios to examine sea level rise prediction uncertainty and the sources of this uncertainty. In this study we carry out an illustrative probabilistic sea level rise hazard analysis using ensembles of sea level rise predictions and emissions scenarios from the literature. This illustrative analysis allows us to estimate the probability that sea level rise will exceed a specified threshold at a given location and time and highlights how sea level rise uncertainty is sensitive to scenario inputs and sea level rise projection modeling choices. Probabilistic hazard is depicted for Earth using sea level rise hazard maps. We also demonstrate how hazard deaggregation can help us quantify the relative contributions of sea level rise sources, prediction models, and climate forcing scenarios to sea level rise hazard. The ice sheet contribution to sea level rise has a large impact on probabilistic projection of sea level rise due to the disagreements between current ice sheet models related to differences in modeling ice sheet instability.

APPLICATION OF DEAGGREGATION OF SPATIAL PROBABILISTIC SEISMIC HAZARD FOR DISASTER PREPAREDNESS

For regional disaster prevention, it is important to understand the area of occurrence of strong ground motion and its occurrence probability. The spatial probabilistic seismic hazard analysis (SPSHA) proposed by the authors can provide this information. In SPSHA, the results are expressed as a relation between the area where a given seismic intensity is generated and the exceedance probability. Results obtained from such a probabilistic approach include the effects of various seismic sources. Therefore, to efficiently describe an earthquake scenario for regional earthquake countermeasures, it is necessary to understand the impact of each earthquake source. In this study, we propose a seismic hazard deaggregation for SPSHA, and present a method for quantitatively understanding the earthquakes that affect the target region. As a practical application, SPSHA is conducted for Kanagawa prefecture in Japan. We conducted seismic hazard deaggregation for whole and sub-area, and discussed the differences in dominant earthquakes among areas and the use of such information in disaster prevention.

Evaluation of SCEC CyberShake Ground Motions for Engineering Practice

This paper evaluates CyberShake (version 15.12) ground motions for potential application to high-rise building design in the Los Angeles region by comparing them against recordings from past earthquakes as well as empirical models. We consider two selected sites in the Los Angeles region with different underlying soil conditions and select comparable suites of ground motion records from CyberShake and the NGA-West2 database according to the ASCE 7-16 requirements. Major observations include (1) selected ground motions from CyberShake and NGA-West2 share similar features, in terms of response spectra and polarization; (2) when selecting records from Cyber-Shake, it is easy to select motions with sources that match the hazard deaggregation; (3) CyberShake durations on soil are consistent with the empirical models considered, whereas durations on rock are slightly shorter; (4) occasional excessive polarization in ground motion is produced by San Andreas fault ruptures, though those records are usually excluded after the ground motion selection. Results from this study suggest that CyberShake ground motions are a suitable and promising source of ground motions for engineering evaluations.

Seismic risk assessment of intake tower in Korea using updated fragility by Bayesian inference

This research aims to assess the tight seismic risk curve of the intake tower at Geumgwang reservoir by considering the recorded historical earthquake data in the Korean Peninsula. The seismic fragility, a significant part of risk assessment, is updated by using Bayesian inference to consider the uncertainties and computational efficiency. The reservoir is one of the largest reservoirs in Korea for the supply of agricultural water. The intake tower controls the release of water from the reservoir. The seismic risk assessment of the intake tower plays an important role in the risk management of the reservoir. Site-specific seismic hazard is computed based on the four different seismic source maps of Korea. Probabilistic Seismic Hazard Analysis (PSHA) method is used to estimate the annual exceedance rate of hazard for corresponding Peak Ground Acceleration (PGA). Hazard deaggregation is shown at two customary hazard levels. Multiple dynamic analyses and a nonlinear static pushover analysis are performed for deriving fragility parameters. Thereafter, Bayesian inference with Markov Chain Monte Carlo (MCMC) is used to update the fragility parameters by integrating the results of the analyses. This study proves to reduce the uncertainties associated with fragility and risk curve, and to increase significant statistical and computational efficiency. The range of seismic risk curve of the intake tower is extracted for the reservoir site by considering four different source models and updated fragility function, which can be effectively used for the risk management and mitigation of reservoir.

Computation of Vector Hazard Using Salient Features of Seismic Hazard Deaggregation

Deaggregation is one of the products of probabilistic seismic hazard analysis (PSHA) suitable for identifying the relative contributions of various magnitude-distance bins to a hazard or intensity measure (IM) level. In this paper, we elucidate some interesting features of deaggregations, such as: their monotonically decreasing nature with IM; their invariance to any minimum IM level; and the pertinence of their bins to a complementary cumulative distribution function (CCDF). We use these features of hazard deaggregation along with copula functions in a simplified method for computing vector deaggregation and vector hazard given the scalar counterparts. We validate our simplified procedure at a hypothetical site surrounded by multiple fault sources where seismic hazard is calculated using a logic tree. We also demonstrate the application of our approach to a real site in Los Angeles, CA. Finally, we explore whether the invariance property of deaggregations can be used to compute scalar hazard curves using new ground motion prediction models/IMs, and find that for low to moderate levels of IM, a reasonable approximation is obtained.

Introduction of conditional mean spectrum and conditional spectrum in the practice of seismic safety evaluation in China

This paper aims at implementing and introducing the use of conditional mean spectrum (CMS) and conditional spectrum (CS) as the main input parameters in the practice of seismic safety evaluation (SSE) in China, instead of the currently used uniform hazard spectrum (UHS). For this purpose, a procedure for M-R-epsilon seismic hazard deaggregation in China was first developed. For illustration purposes, two different typical sites in China, with one to two dominant seismic zones, were considered as examples to carry out seismic hazard deaggregation and illustrate the construction of CMS/CS. Two types of correlation coefficients were used to generate CMS and the results were compared over a vibration period range of interest. Ground motion records were selected from the NSMONS (2007–2015) and PEER NGA-West2 databases to correspond to the target CMS and CS. Hazard consistency of the spectral accelerations of the selected ground motion records was evaluated and validated by computing the annual exceedance probability rate of the response spectra and comparing the results to the hazard curve corresponding to each site of concern at different periods. The tools developed in this work and their illustrative application to specific case studies in China are a first step towards the adoption of CMS and CS into the practice of seismic safety evaluation in this country.

A Methodology of Determination of Scenario Tsunami for Fragility Assessment Based on Hazard Deaggregation

A Methodology of Determination of Scenario Tsunami for Fragility Assessment Based on Hazard Deaggregation

Probabilistic seismic hazard analysis using a synthetic earthquake catalog: comparison of the Gyeongju City Hall site with the Seoul City Hall site in Korea

Probabilistic seismic hazard analysis (PSHA) generally requires the identification of line sources (active faults) and area sources where seismicity parameters must be determined. It is not easy to identify seismic sources and to estimate seismicity parameters for sources in the intraplate region. We perform an alternative PSHA with a synthetic earthquake catalog, which does not require the delineation of seismic sources. A synthetic catalog of the Korean Peninsula for 500,000 years is constructed by simulating earthquakes using the Monte Carlo method in such a way that an earthquake is randomly selected from the observed earthquake catalog, its epicenter is perturbed by a normally distributed random number, and a magnitude is assigned to the simulated event with a random value generated based on the Gutenberg-Richter magnitude-frequency relation with specified minimum and maximum magnitudes. The seismicity of the Korean Peninsula is thoroughly investigated for estimation of parameters required for synthesizing the catalog. The SMSIM computer program is used to simulate ground motions at sites instead of estimating the ground motion prediction equation. Two sites are chosen for PSHA; the one is the Seoul City Hall site (Seoul site), a densely populated metropolitan site, and the other is the Gyeongju City Hall site (Gyeongju site) close to the epicenter of the M L 5.8 earthquake on 12 September 2016. Seismic hazard curve, uniform hazard spectra (UHSs), and deaggregation of hazard for two sites are presented. The mean return periods for 0.1, 0.2, and 0.3 g at the Seoul site appears to be 1640, 6170, and 17650 years, respectively while those at the Gyeongju site appears to be 327, 1197, and 3548 years, respectively. The mean return periods for the Seoul site are around five times longer than those for the Gyeongju site, and this fact implies that the seismic hazard level of the Gyeongju site is considerably higher than that of the Seoul site. UHSs for 10% and 2% probabilities of exceedance over 50 years are constructed at both sites. The spectra show peak amplifications around the 0.05-s period.

An Applied Method for General Regional Seismic Loss Assessment—With A Case Study in Los Angeles County

ABSTRACTWe describe the formulation and application of an integrated general regional seismic loss assessment (RSLA) method for buildings in seismic regions. An efficient method for RSLA is valuable for engineers involved in city planning, risk management, and insurance dealings. In contrast to previously reported methods, the framework presented herein is hazard-based and utilizes a regional rapid seismic hazard deaggregation tool that allows regional assessment to be conducted more efficiently. The proposed technique is implemented as an example to assess general regional seismic loss in Los Angeles County for a ground motion hazard with 10% probability of exceedance in 50 years.

Probabilistic Seismic Hazard Deaggregation for Selected Egyptian Cities

A probabilistic seismic hazard analysis in terms of peak ground acceleration (PGA) and spectral acceleration (SA) values has been performed for the Egyptian territory. Eighty-eight potential seismic sources (for shallow- and intermediate-depth seismicity) in and around Egypt were identified and characterized based on an updated and unified earthquake catalog spanning the time period from 2200 B.C. until 2013 A.D. A logic-tree approach was followed, after a sensitivity analysis, to consider the epistemic uncertainty in the different input parameters, including the selected ground-motion attenuation models to predict the ground motion for the different tectonic environments. Then the seismic hazard deaggregation results, in terms of distance and magnitude, for the most important cities in Egypt have been computed to help understanding the relative contributions of the different seismic sources. Seismic hazard deaggregation, in particular, was computed for PGA and SA at periods of 0.2, 1.0 and 2.0 s for rock-site conditions, and for 10% probability of exceedance in 50 years. In general, the results at most of the cities indicate that the distance to the seismic sources which mostly contribute to the seismic hazard is mainly controlled by the nearby seismic sources (especially for PGA). However, distant events contribute more to the hazard for larger spectral periods (for 1.0 and 2.0 s). A significant result of this type of work is that seismic hazard deaggregation provides useful data on the distance and magnitude of the contributing seismic sources to the hazard in a certain place, which can be applied to generate scenario earthquakes and select acceleration records for seismic design.