Probabilistic Hazard Assessment Research Articles

Probabilistic ecological hazard assessment of parabens using Daphnia magna and Pimephales promelas

Parabens are common antimicrobial agents found in thousands of pharmaceuticals and personal care products. Parabens are introduced into aquatic ecosystems from wastewater treatment plant effluents and have been detected in surface waters in the low microgram per liter range. Although these compounds display low toxicity in mammals, paraben toxicity to aquatic organisms has not been investigated. Standardized acute and subchronic endpoints in larval fish (Pimephales promelas) and cladoceran (Daphnia magna) models were examined for seven different parabens (methyl-, ethyl-, isopropyl-, propyl-, isobutyl-, butyl-, benzylparaben), which encompassed a range of log P values. Paraben 48 h median lethal concentration values (LC50) ranged from 4.0 to 24.6 mg/L in D. magna and 3.3 to >160.0 mg/L in fathead minnow. Growth and reproduction in D. magna had lowest-observed-effect concentrations (LOECs) ranging from 0.12 to 9.0 mg/L and 1.5 to 6.0 mg/L, respectively. Fathead minnow growth was adversely affected at levels ranging from 1.0 to 25.0 mg/L. Aquatic toxicity of the parabens was inversely related to lipophilicity, suggesting that responses using standardized endpoints resulted from narcosis. Utilizing toxicity benchmark concentrations (e.g., LC50s, LOECs) for each compound, chemical toxicity distributions, a probabilistic hazard assessment technique, were developed to assess the probabilities of detecting parabens that elicit a response at or below a given concentration. For the responses assessed in the present study, the 5th centile values (the concentration at which 5% of parabens elicit a response) ranged from 15 microg/L to 2.43 mg/L, with D. magna growth eliciting the lowest 5th centile value and acute D. magna mortality eliciting the highest. The distributions demonstrated that at environmentally relevant concentrations in developed countries there is limited acute or subchronic aquatic hazard of parabens to the organisms and responses examined.

Comparison of the sensitivities of common in vitro and in vivo assays of estrogenic activity: Application of chemical toxicity distributions

A number of contaminants in municipal effluent discharges are estrogen agonists to fish. Whereas several in vitro and in vivo techniques have been developed to assess the estrogenic activity of these compounds or ambient environmental samples, previous comparisons of the relative sensitivities of these approaches remain inconclusive. We employed a probabilistic hazard assessment approach using chemical toxicity distributions (CTDs) to perform a novel evaluation of relative sensitivities of six common in vitro and in vivo assays. We predicted that there was an 8.3% (human breast ademocarcinoma cell line, MCF-7, assay), 6.3% (yeast estrogen screen assay), or 1.9% (fish hepatocyte vitellogenin, VTG, assay) probability of detecting a compound in aquatic systems that will elicit an estrogenic response at concentrations at or below 0.1 microg/L, suggesting that the MCF-7 assay was the most sensitive in vitro assay evaluated in this study. The probabilities of eliciting the estrogenic response of VTG induction at a concentration less than 0.1 microg/L in rainbow trout, fathead minnow, and Japanese medaka were determined at 29.9, 26.2, and 18.8%, respectively. Thus, rainbow trout VTG induction was the most sensitive in vivo assay assessed. Subsequently, CTDs may provide a useful technique for hazard assessment of chemical classes for which exposure data are limited and for chemicals with common toxicological mechanisms and modes of action.

Loss estimation in Istanbul based on deterministic earthquake scenarios of the Marmara Sea region (Turkey)

The rapid urban development in Istanbul has lead to an increase in the exposure levels of the urban vulnerability. Due to the steadily increasing population, with improper land-use planning, inappropriate construction techniques and inadequate infrastructure systems, associated with an existing high hazard level, Istanbul is one of the most risky cities in the Mediterranean region. Estimations of casualties and losses, expected for given earthquake scenarios, are necessary to develop sustainable rehabilitation programs and for improving preparedness. Deterministic hazard scenarios and time-dependent probabilistic hazard assessment were used as input to a GIS-based loss estimation model, to evaluate the earthquake risk for Istanbul. The deterministic ground shaking scenarios, used for loss estimation in Istanbul, were defined in terms of acceleration and velocity time series for recognized reference earthquakes caused by different rupture models along extended sources. The ground motions were calculated for the whole metropolitan area extending over a grid system of 25×100 km 2. For the case of Istanbul, the representative scenario was selected by comparing the simulated peak values and response spectra with the empirical ground motion models available for the area. Simulated values are within one standard deviation of the empirical regressions. The availability of wide-ranging building inventory data allowed the application of a GIS-based loss estimation model (KoeriLoss-V2) to evaluate different loss scenarios depending on the ground shaking input, as well as to consider the implications of mitigation actions. It was found that 30% of the buildings in the metropolitan area may be in need of either strengthening or demolition to achieve an adequate degree of life safety.

A Method for Developing Regional Road-Fill Failure Hazard Assessments Using GIS and Virtual Fieldwork

Road-fill failure is a common and potentially catastrophic hazard on mountainous roads. Land managers need methods for assessing road-fill failure hazards that minimize time in the field and that use readily available data. We developed a probabilistic hazard assessment method using virtual fieldwork and LiDAR-derived slope distributions over a 97-km length of the Blue Ridge Parkway in North Carolina. The locations of arc-shaped pavement cracks and previous road-fill failures were mapped using field-verified VisiData video reconnaissance, and the slopes surrounding failed-or-cracked sites were extracted from a digital elevation model and compared to uncracked portions of road. The site-median slopes of the failed-or-cracked sites and uncracked sites are normally distributed and significantly different (P < 0.01) from one another. This observation provides the basis for a probabilistic, hazard assessment model that uses the site-median slope of a 30-m–diameter buffer to categorize currently uncracked sites as either stable or at risk of road-fill failure during future high-intensity rainfall events.

Developing an Event Tree for probabilistic hazard and risk assessment at Vesuvius

Probabilistic characterizations of possible future eruptive scenarios at Vesuvius volcano are elaborated and organized within a risk-based framework. In the EXPLORIS project, a wide variety of topics relating to this basic problem have been pursued: updates of historical data, reinterpretation of previous geological field data and the collection of new fieldwork results, the development of novel numerical modelling codes and of risk assessment techniques have all been completed. To achieve coherence, many diverse strands of evidence had to be unified within a formalised structure, and linked together by expert knowledge. For this purpose, a Vesuvius ‘Event Tree’ (ET) was created to summarise in a numerical-graphical form, at different levels of detail, all the relative likelihoods relating to the genesis and style of eruption, development and nature of volcanic hazards, and the probabilities of occurrence of different volcanic risks in the next eruption crisis. The Event Tree formulation provides a logical pathway connecting generic probabilistic hazard assessment to quantitative risk evaluation. In order to achieve a complete parameterization for this all-inclusive approach, exhaustive hazard and risk models were needed, quantified with comprehensive uncertainty distributions for all factors involved, rather than simple ‘best-estimate’ or nominal values. Thus, a structured expert elicitation procedure was implemented to complement more traditional data analysis and interpretative approaches. The structure of the Vesuvius Event Tree is presented, and some of the data analysis findings and elicitation outcomes that have provided initial indicative probability distributions to be associated with each of its branches are summarized. The Event Tree extends from initiating volcanic eruption events and hazards right through to human impact and infrastructure consequences, with the complete tree and its parameterisation forming a quantitative synoptic framework for comprehensive hazard evaluation and mapping of risk impacts. The organization of the Event Tree allows easy updating, as and when new information becomes available.

Impact of explosive eruption scenarios at Vesuvius

Impact of explosive eruption scenarios at Vesuvius

THE SUMATRAN FAULT ZONE — FROM SOURCE TO HAZARD

The substantial portion of the dextral component of the Sumatran oblique convergence is accommodated by the Sumatran fault. This 1900 km-long active strike-slip fault zone runs along the backbone of Sumatra pose seismic and fault hazards to dense population on and around the fault zones. The Sumatran fault is highly segmented, and consists of 20 major geometrically defined segments, which range in length from about 60 to 200 km. These segment lengths influenced seismic source dimensions and have limited the magnitudes of large historical fault ruptures to between Mw6.5 and about 7.7. Slip rates along the fault increase northwestward, from about 5 mm/yr around the Sunda Strait to 27 mm/yr around Toba Lake. These sliprate values provide a quantitative basis for calculation of average expected recurrence periods for large earthquakes on each segment. Deterministic and probabilistic hazard assessments are constructed based on these active fault data.

Shaking hazard compatible methodology for probabilistic assessment of permanent ground displacement across earthquake faults

A methodology for probabilistic hazard assessment of permanent displacement across faults caused by earthquake rupture is presented, compatible with region specific models for ground shaking hazard in California, developed earlier by the authors and coworkers. Assessment of permanent dislocations across faults is important for the design and retrofit of highway bridges and tunnels crossing faults, as well as for other lifelines crossing faults, such as aqueducts, water and gas lines, etc. The methodology is illustrated for two strike-slip faults (prototypes of Class A and Class B faults in California), for 50 years exposure. The illustrations show that, for given seismic moment rate, the hazard estimates are quite sensitive to how the seismic moment is distributed over earthquake magnitudes. They also show that the hazard is small even for very small levels of displacement, in contrast to ground shaking hazard, which is due to the fact that only one fault contributes to the hazard and not every event on that fault necessarily affects the site.

An inverse cascade explanation for the power-law frequency-area statistics of earthquakes, landslides and wildfires

Abstract Frequency-magnitude statistics for natural hazards can greatly help in probabilistic hazard assessments. An example is the case of earthquakes, where the generality of a power-law (fractal) frequency-rupture area correlation is a major feature in seismic risk mapping. Other examples of this power-law frequency-size behaviour are landslides and wildfires. In previous studies, authors have made the potential association of the hazard statistics with a simple cellular-automata model that also has robust power-law statistics: earthquakes with slider-block models, landslides with sandpile models, and wildfires with forest-fire models. A potential explanation for the robust power-law behaviour of both the models and natural hazards can be made in terms of an inverse-cascade of metastable regions. A metastable region is the region over which an ‘avalanche’ spreads once triggered. Clusters grow primarily by coalescence. Growth dominates over losses except for the very largest clusters. The cascade of cluster growth is self-similar and the frequency of cluster areas exhibits power-law scaling. We show how the power-law exponent of the frequency-area distribution of clusters is related to the fractal dimension of cluster shapes.

Earthquake forecasting and its verification

Abstract. No proven method is currently available for the reliable short time prediction of earthquakes (minutes to months). However, it is possible to make probabilistic hazard assessments for earthquake risk. In this paper we discuss a new approach to earthquake forecasting based on a pattern informatics (PI) method which quantifies temporal variations in seismicity. The output, which is based on an association of small earthquakes with future large earthquakes, is a map of areas in a seismogenic region ("hotspots'') where earthquakes are forecast to occur in a future 10-year time span. This approach has been successfully applied to California, to Japan, and on a worldwide basis. Because a sharp decision threshold is used, these forecasts are binary--an earthquake is forecast either to occur or to not occur. The standard approach to the evaluation of a binary forecast is the use of the relative (or receiver) operating characteristic (ROC) diagram, which is a more restrictive test and less subject to bias than maximum likelihood tests. To test our PI method, we made two types of retrospective forecasts for California. The first is the PI method and the second is a relative intensity (RI) forecast based on the hypothesis that future large earthquakes will occur where most smaller earthquakes have occurred in the recent past. While both retrospective forecasts are for the ten year period 1 January 2000 to 31 December 2009, we performed an interim analysis 5 years into the forecast. The PI method out performs the RI method under most circumstances.

Probabilistic risk characterization: An example with di(2-ethylhexyl) phthalate

While probabilistic methods gain attention in hazard characterization and are increasingly used in exposure assessment, full use of the available probabilistic information in risk characterization is still uncommon. Usually, after probabilistic hazard characterization and/or exposure assessment, percentiles from the obtained distributions are used as point estimates in risk characterization. In this way, all information on variability and uncertainty is lost, while these aspects are crucial in any risk assessment. In this paper, we present a method to integrate the entire distributions from probabilistic hazard characterization and exposure assessment into one risk characterization plot. This method is illustrated using di(2-ethylhexyl) phthalate as an example. The final result of this probabilistic risk assessment is summarized in a single plot, containing two pieces of information: the confidence we may have in concluding there is no risk, and the fraction of the population this conclusion applies to. This information leads to a better informed conclusion on the risk of a substance, and may be very useful to define the necessary measures for risk reduction.

Testing claims about volcanic disruption of a potential geologic repository at Yucca Mountain, Nevada

Yucca Mountain is a potential repository site for high‐level radioactive waste. We examine claims that the frequency of future basaltic dike intersection could be 1 × 10−6/yr or higher (i.e., on average, one penetration every million yrs). These claims fail simple tests at four time scales. Spatial‐temporal models that predict intrusion frequencies &gt;2 × 10−7/yr are overly pessimistic because no dikes have been found in the 13 Myr‐old potential repository footprint. More realistic models are developed by considering this non‐detection of dikes and by applying probabilistic hazard assessments based on known patterns of Pleistocene volcanism. Using a hazard assessment code, we estimate the frequency of dike intersection at 5.4 × 10−8/yr with an upper 95% confidence bound of 9.8 × 10−8/yr.

Probabilistic hazard assessment of environmentally occurring pharmaceuticals toxicity to fish, daphnids and algae by ECOSAR screening

The risks associated with occurrence of pharmaceuticals in water resources are mostly unknown. In the absence of extensive toxicological data, we scanned all the compounds observed in the environment for toxicological properties by (Quantitative) Structure Activity Relationship ((Q)SAR). The results of the probabilistic distribution of environmental and effect concentrations and hazard quotients (HQs) do not indicate significant acute risks prior to application of assessment factors. Compared with measured effect concentrations SAR predictions were more “sensitive” 80% of the time. The long-term effects of subtle and chronic changes, additive or synergistic effects and effects on other endpoints e.g. reproduction, behavior, metabolism, bacterial resistance etc. are still uncertain. (Q)SAR's can be important prioritization tools for subsequent experimental risk assessment of pharmaceuticals in surface waters, due to the prevalent lack of ecotoxicological data.

The potential for earthquake early warning in southern California.

Earthquake mitigation efforts in the United States currently use long-term probabilistic hazard assessments and rapid post-earthquake notification to reduce the potential damage of earthquakes. Here we present the seismological design for and demonstrate the feasibility of a short-term hazard warning system. Using data from past earthquakes, we show that our Earthquake Alarm System (ElarmS) could, with current TriNet instrumentation, issue a warning a few to tens of seconds ahead of damaging ground motion. The system uses the frequency content of the P-wave arrival to determine earthquake magnitude, an approach that allows magnitude determination before any damaging ground motion occurs.

Seismic Hazard Assessment: Simultaneous Effect of Earthquakes at Close and Distant Sites

A modified version of seismic hazard assessment, directed toward planning of emergency relief efforts, is proposed. The method begins with a probabilistic hazard assessment to determine a reference peak ground acceleration (PGA) at a near site, rather than using a reference earthquake of a given magnitude. The reference PGA then serves as a basis for a probabilistic assessment of PGA at more distant sites. The ideas are illustrated by studying seismic hazard for Northern Israel from earthquakes on the northern section of the Dead Sea Rift (DSR). The reference PGA at a site 10 km from the DSR is taken to be 0.3 g, which has a return period estimated to be 320 years. Given an event with PGA of 0.3 g at 10 km, the subsequent analysis for distant sites shows that there is less than a 31% probability of PGA above 0.1 g at 30 km and an 8% probability that the PGA at 50 km will exceed 0.1 g.

Past Earthquake-Induced Rapid Subsidence along the Northern San Andreas Fault: A Paleoseismological Method for Investigating Strike-Slip Faults

Evidence of rapid relative sea level changes preserved in sediment of coastal estuaries along the north coast segment of the San Andreas fault provides information on the dates of past earthquakes. This approach, although successfully used to document large subduction zone earthquakes, has not been used previously to constrain the dates of San Andreas fault or other strike-slip fault earthquakes. Data on prehistoric San Andreas fault earthquakes is needed for development of robust probabilistic hazard assessments in northern California and the San Francisco Bay area. Evidence of earthquake-induced subsidence is preserved in marshes at the northern margin of Bolinas Lagoon and the southeastern margin of Bodega Harbor. These sites occupy structural basins or troughs along the northern San Andreas fault. Radiocarbon dating and identification of the first occurrence of nonnative pollen near abrupt sedimentological changes in cores are used to constrain the dates of San Andreas fault earthquakes over about the last 800 years. Estuarine sediment from northern Bolinas Lagoon preserves evidence of an earthquake that occurred about 750 years ago. Evidence for this earthquake includes a marsh soil that was abruptly buried by tidal flat mud or coarse, poorly sorted deltaic deposits containing a mixture of terrestrial sediment and marine mud. Evaluation of diatom assemblages from above and below the buried soil horizon provides evidence of at least several decimeters of sustained relative sea level rise. Three buried soils in a marsh at the southern end of Bodega Harbor are likely a result of coseismic subsidence. All three buried marsh soils have abrupt upper contacts, although diatom evidence for decimeters of sustained subsidence is not as strong as it is for the buried soil in Bolinas Lagoon. Existing paleoseismic data on the northern San Andreas fault is compared with results of this study in order to evaluate the dates of prehistoric large earthquakes and length of past ruptures. These data indicate that an earthquake occurred about 400 years ago and another earthquake occurred about 700 years ago. The data allow for 1906-type ruptures of the fault from the Santa Cruz Mountains to at least Point Arena. However, a sequence of closely timed, smaller earthquakes would produce a similar set of paleoseismic data.

Earthquake hazard and risk assessment study for the Canterbury region, South Island, New Zealand

In recognition of the earthquake threat to Canterbury, and its statutory responsibilities, Environment Canterbury initiated a comprehensive, staged multi-year earthquake hazard and risk assessment study programme in 1997. In this paper the general framework and philosophy behind Environment Canterbury's Earthquake Hazard and Risk Assessment Programme is outlined. The results of the stage 1A earthquake source characterisation, and stage 1B probabilistic seismic hazard assessment for the Canterbury region are presented in companion papers in this volume. The programme participants have ongoing earthquake hazard research projects, and also are involved as practitioners in land-use planning and development of relevance to the Canterbury region. The coordinated programme is primarily designed to facilitate the integration of a diverse range of independent studies, so making relevant earthquake hazard and risk information readily available to a wide range of end-users, including other professionals (engineers and scientists), planners, civil defence and emergency management staff, utility operators, and developers. In addition the programme provides up to date, relevant information for public education and awareness purposes. The first stage of the programme has been completed, and includes identification and characterisation of earthquake sources, probabilistic hazard assessment, and formulation of earthquake scenarios. The long-term staged study programme will address the earthquake hazard, the risks posed, possible mitigation options and mitigation implementation methods available.

Cellular-automata models applied to natural hazards

The concept of self-organized criticality evolved from studies of three simple cellular automata models: the forest-fire, slider-block, and sandpile models. Each model is associated with natural hazards which have frequency-size statistics that are well approximated by power law distributions. These distributions have important implications for probabilistic hazard assessments.

A probabilistic seismic hazard map of India and adjoining regions

This paper presents the results of an exercise carried out under GSHAP, over India and adjoining regions bound by 0°N-40°N and 65°E-100°E. A working catalogue of main shocks was prepared by merging the local catalogues with the NOAA catalogue, and removing duplicates, aftershocks and earthquakes without any magnitude. Eighty six potential seismic source zones were delineated based on the major tectonic features and seismicity trends. Using the probabilistic hazard assessment approach of McGuire, adopted by GSHAP, the Peak Ground Accelerations (PGA) were computed for 10% probability of exceedance in 50 years, at locations defined by a grid of 0.5° x 0.5°. Since no reliable estimates of attenuation values are available for the Indian region, the attenuation relation of Joyner and Boore (1981) was used. The PGA values over the grid points were contoured to obtain a seismic hazard map. The hazard map depicts that a majority of the Northern Indian plate boundary region and the Tibetan plateau region have hazard level of the order of 0.25 g with prominent highs of the order of 0.35-0.4 g in the seismically more active zones like the Burmese arc, Northeastern India and Hindukush region. In the Indian shield, the regional seismic hazard, covering a major area, is of the order of 0.05-0.1 g whereas some areas like Koyna depict hazard to the level of 0.2 g. The present map can be converted into a conventional seismic zoning map having four zones with zone factors of 0.1 g, 0.2 g, 0.3 g and 0.4 g respectively.

Probabilistic risk and hazard assessment

Probabilistic risk and hazard assessment