Probabilistic Hazard Maps Research Articles

Analysis of non-stationary climate-related extreme events considering climate change scenarios: an application for multi-hazard assessment in the Dar es Salaam region, Tanzania

In this paper we have put forward a Bayesian framework for the analysis and testing of possible non-stationarities in extreme events. We use the extreme value theory to model temperature and precipitation data in the Dar es Salaam region, Tanzania. Temporal trends are modeled writing the location parameter of the generalized extreme value distribution in terms of deterministic functions of explanatory covariates. The analyses are performed using synthetic time series derived from a Regional Climate Model. The simulations, performed in an area around the Dar es Salaam city, Tanzania, take into account two Representative Concentration Pathways scenarios from the Intergovernmental Panel on Climate Change. Our main interest is to analyze extremes with high spatial and temporal resolution and to pursue this requirement we have adopted an individual grid box analysis approach. The approach presented in this paper is composed of the following key elements: (1) an advanced Bayesian method for the estimation of model parameters, (2) a rigorous procedure for model selection, and (3) uncertainty assessment and propagation. The results of our analyses are intended to be used for quantitative hazard and risk assessment and are presented in terms of hazard curves and probabilistic hazard maps. In the case study we found that for both the temperature and precipitation data, a linear trend in the location parameter was the only model performing better than the stationary one in the areas where evidence against the stationary model exists.

Integrating data and compute-intensive workflows for uncertainty quantification in large-scale simulation: application to model-based hazard analysis

Complex inference from simulation ensembles used in uncertainty quantification leads to twin computational challenges of managing large amount of data and performing CPU-intensive computing. While algorithmic innovations using surrogates, localization and parallelization can make the problem feasible, one still has very large data and compute tasks. The problem of dealing with large data gets compounded when data warehousing and data mining are intertwined with computationally expensive tasks. We present here an approach to solving this problem by using a mix of hardware suitable for each task in a carefully orchestrated workflow. The computing environment is essentially an integration of Netezza database and high-performance cluster. It is based on the simple idea of segregating the data-intensive and compute-intensive tasks and assigning the right architecture for them. We present here the layout of the computing model and the new computational scheme adopted to generate probabilistic hazard maps.

Automating Emulator Construction for Geophysical Hazard Maps

This paper describes an efficient and systematic process for using geophysical computer model simulations to guide efforts in probabilistic hazard mapping. The framework being proposed requires the simultaneous construction of many ($10^2$--$10^4$) statistical emulators, e.g., cheap model surrogates. This paper describes an automation process for choosing designs for and fitting these emulators. Throughout the description of this process, several useful modifications to standard emulators are explored. Additionally, this approach enables a fast and flexible uncertainty quantification for multiple sources of aleatory variability (natural randomness) and epistemic uncertainty (uncertainty in geophysical and statistical models) in the context of probabilistic hazard mapping. This process is illustrated through an application to granular volcanic flows.

Long-range hazard assessment of volcanic ash dispersal for a Plinian eruptive scenario at Popocatépetl volcano (Mexico): implications for civil aviation safety

Popocatepetl is one of Mexico’s most active volcanoes threatening a densely populated area that includes Mexico City with more than 20 million inhabitants. The destructive potential of this volcano is demonstrated by its Late Pleistocene–Holocene eruptive activity, which has been characterized by recurrent Plinian eruptions of large magnitude, the last two of which destroyed human settlements in pre-Hispanic times. Popocatepetl’s reawakening in 1994 produced a crisis that culminated with the evacuation of two villages on the northeastern flank of the volcano. Shortly after, a monitoring system and a civil protection contingency plan based on a hazard zone map were implemented. The current volcanic hazards map considers the potential occurrence of different volcanic phenomena, including pyroclastic density currents and lahars. However, no quantitative assessment of the tephra hazard, especially related to atmospheric dispersal, has been performed. The presence of airborne volcanic ash at low and jet-cruise atmospheric levels compromises the safety of aircraft operations and forces re-routing of aircraft to prevent encounters with volcanic ash clouds. Given the high number of important airports in the surroundings of Popocatepetl volcano and considering the potential threat posed to civil aviation in Mexico and adjacent regions in case of a Plinian eruption, a hazard assessment for tephra dispersal is required. In this work, we present the first probabilistic tephra dispersal hazard assessment for Popocatepetl volcano. We compute probabilistic hazard maps for critical thresholds of airborne ash concentrations at different flight levels, corresponding to the situation defined in Europe during 2010, and still under discussion. Tephra dispersal mode is performed using the FALL3D numerical model. Probabilistic hazard maps are built for a Plinian eruptive scenario defined on the basis of geological field data for the “Ochre Pumice” Plinian eruption (4965 14C yr BP). FALL3D model input eruptive parameters are constrained through an inversion method carried out with the semi-analytical HAZMAP model and are varied by sampling them using probability density functions. We analyze the influence of seasonal variations on ash dispersal and estimate the average persistence of critical ash concentrations at relevant locations and airports. This study assesses the impact that a Plinian eruption similar to the Ochre Pumice eruption would have on the main airports of Mexico and adjacent areas. The hazard maps presented here can support long-term planning that would help minimize the impacts of such an eruption on civil aviation.

Hazard assessment of far-range volcanic ash dispersal from a violent Strombolian eruption at Somma-Vesuvius volcano, Naples, Italy: implications on civil aviation

Long-range dispersal of volcanic ash can disrupt civil aviation over large areas, as occurred during the 2010 eruption of Eyjafjallajokull volcano in Iceland. Here we assess the hazard for civil aviation posed by volcanic ash from a potential violent Strombolian eruption of Somma-Vesuvius, the most likely scenario if eruptive activity resumed at this volcano. A Somma-Vesuvius eruption is of concern for two main reasons: (1) there is a high probability (38 %) that the eruption will be violent Strombolian, as this activity has been common in the most recent period of activity (between AD 1631 and 1944); and (2) violent Strombolian eruptions typically last longer than higher-magnitude events (from 3 to 7 days for the climactic phases) and, consequently, are likely to cause prolonged air traffic disruption (even at large distances if a substantial amount of fine ash is produced such as is typical during Vesuvius eruptions). We compute probabilistic hazard maps for airborne ash concentration at relevant flight levels using the FALL3D ash dispersal model and a statistically representative set of meteorological conditions. Probabilistic hazard maps are computed for two different ash concentration thresholds, 2 and 0.2 mg/m3, which correspond, respectively, to the no-fly and enhanced procedure conditions defined in Europe during the Eyjafjallajokull eruption. The seasonal influence of ash dispersal is also analysed by computing seasonal maps. We define the persistence of ash in the atmosphere as the time that a concentration threshold is exceeded divided by the total duration of the eruption (here the eruption phase producing a sustained eruption column). The maps of averaged persistence give additional information on the expected duration of the conditions leading to flight disruption at a given location. We assess the impact that a violent Strombolian eruption would have on the main airports and aerial corridors of the Central Mediterranean area, and this assessment can help those who devise procedures to minimise the impact of these long-lasting low-intensity volcanic events on civil aviation.

Digital elevation model uncertainty and hazard analysis using a geophysical flow model

This paper describes a new methodology to quantify the variation in the output of a computational fluid dynamics model for block and ash flows, when the digital elevation model (DEM) of the terrain and other inputs are given as a range of possible values with a prescribed uncertainty. Integrating these variations in the possible flows as a function of input uncertainties provides well-defined hazard probabilities at specific locations, i.e. a hazard map. Earlier work provided a methodology for assessing hazards based on variations in flow initiation and friction parameters. This paper extends this approach to include the effect of terrain error and uncertainty. The results are based on potential flows at Mammoth Mountain, CA, and Galeras Volcano, Colombia. The analysis establishes the soundness of the approach and the effect of including the uncertainty in DEMs in the construction of probabilistic hazard maps.

Modelling of Strong Ground Motions from 1991 Uttarkashi, India, Earthquake Using a Hybrid Technique

We present a simple and efficient hybrid technique for simulating earthquake strong ground motion. This procedure is the combination of the techniques of envelope function (Midorikawaet al. Tectonophysics 218:287–295, 1993) and composite source model (Zenget al. Geophys Res Lett 21:725–728, 1994). The first step of the technique is based on the construction of the envelope function of the large earthquake by superposition of envelope functions for smaller earthquakes. The smaller earthquakes (sub-events) of varying sizes are distributed randomly, instead of uniform distribution of same size sub-events, on the fault plane. The accelerogram of large event is then obtained by combining the envelope function with a band-limited white noise. The low-cut frequency of the band-limited white noise is chosen to correspond to the corner frequency for the target earthquake magnitude and the high-cut to the Boore’s fmax or a desired frequency for the simulation. Below the low-cut frequency, the fall-off slope is 2 in accordance with the ω2 earthquake source model. The technique requires the parameters such as fault area, orientation of the fault, hypocenter, size of the sub-events, stress drop, rupture velocity, duration, source–site distance and attenuation parameter. The fidelity of the technique has been demonstrated by successful modeling of the 1991 Uttarkashi, Himalaya earthquake (Ms 7). The acceptable locations of the sub-events on the fault plane have been determined using a genetic algorithm. The main characteristics of the simulated accelerograms, comprised of the duration of strong ground shaking, peak ground acceleration and Fourier and response spectra, are, in general, in good agreement with those observed at most of the sites. At some of the sites the simulated accelerograms differ from observed ones by a factor of 2–3. The local site geology and topography may cause such a difference, as these effects have not been considered in the present technique. The advantage of the technique lies in the fact that detailed parameters such as velocity-Q structures and empirical Green’s functions are not required or the records of the actual time history from the past earthquakes are not available. This method may find its application in preparing a wide range of scenarios based on simulation. This provides information that is complementary to the information available in probabilistic hazard maps.

Probabilistic seismic hazard assessment in Greece – Part 2: Acceleration response spectra and elastic input energy spectra

Abstract. This second part of the study, deals with the evaluation of the earthquake hazard in Greece in terms of the response spectral acceleration and the elastic input energy equivalent velocity. Four sets of predictive equations were selected, two for each type of spectra. Probabilistic hazard maps were created by determining the seismic hazard at grid points covering the region of interest. The maps are presented for the dominant periods of 0.2 s and 1.0 s for each spectrum. Uniform hazard response spectra (UHRS) for six cities located in the regions of highest estimated hazard are also presented. The comparison with elastic design spectra proposed by the latest national building code, has shown that the UHRS values exceed the design values at almost all periods.

PROBABILISTIC FLOOD HAZARD MAPPING FOR EMBANKMENT BREACHING

ABSTRACT The study proposes a methodology for producing probabilistic flood hazard maps based on an ensemble of 2-D hydrodynamic model and frequency analysis of discharge data. With available floodplain topography and limited river bathymetric data, a 2-D hydrodynamic model has been set-up to predict flood inundation area for recently breaching location of the embankment of the river Brahmaputra for a given flood hydrograph. Frequency analysis of the flood waves in nearby gauged records has been conducted and the flood inundation at the breaching location for flood waves of different return period and average monsoonal condition (dry, normal and wet) has been simulated. After that, spatial analysis of the simulated flood inundation depth and maximum velocity is conducted to categorize flood hazard zones. The methodology was applied over a 600 km2 of flood prone area, close to the northern bank of a 64 km reach of the river Brahmaputra (Assam, India). In this study, probabilistic flood hazard mapping approach for embankment breaching at Matamara, Lakhimpur district, Assam was evaluated with the flood inundation obtained from satellite imagery. The spatial variation of simulated flood inundation of 20 years return period closely matches with the observed inundation. The most vulnerable zone within the floodplain area is identified considering random breaching locations. This study demonstrates that probabilistic flood hazard maps in a river valley can be prepared by this approach with limited topographic dataset.

Statistical Comparison of National Probabilistic Seismic Hazard Maps and Frequency of Recorded JMA Seismic Intensities from the K-NET Strong-motion Observation Network in Japan during 1997-2006

National seismic hazard maps for Japan with meshes of 1×1 km2 were published by the Earthquake Research Committee of Japan in March 2005. They are updated annually to reflect time passage of event recurrence (NIED 2005). Since the probabilistic seismic hazard maps focus on estimates for 30 and even 50 years, strict validation of the maps requires probabilistic and statistical approaches with future data. Nevertheless, in this study, as the first step in verifying the validity of the maps, we compared the Japan Meteorological Agency (JMA) instrumental intensities from strong-motion records for the 10-year period ending 31 December 2006 with the corresponding values on the probabilistic hazard maps. The JMA instrumental intensity is a cumulative strong motion indicator, which was adjusted to match the scale previously used to measure seismic intensity, which was based on human response and an index of damage. The JMA intensity scale has 10 grades from 0 to 7 (5 and 6 were divided in lower and higher) and is described at http://www.jma.go.jp/jma/kishou/know/shindo/shindokai.html. Explanations of individual intensities can be found at http://www.jma.go.jp/jma/kishou/know/shindo/explane.html. Although corresponding peak ground acceleration could not precisely be adapted to the intensity scale, relative peak ground acceleration is indicated in http://en.wikipedia.org/wiki/Japan\_Meteorological\_Agency\_seismic\_intensity_scale. JMA has promptly reported this intensity since April 1996 (http://www.jma.go.jp/en/quake/). Verification was done using all of K-NET's strong-motion records for the period 1 January 1997 through 31 December 2006. K-NET is an observation network that uniformly covers all of Japan with stations in polygonal configurations that cover areas about 25 kilometers in size. Network operations began in 1997 with 1,000 stations. New observation sites—many of them in the Kanto metropolitan area—have been added since then. The number of observation sites peaked at 1,035, but by the end of 2006 the number had dropped to 1,028 stations, including …

Probabilistic seismic hazard assessment of the Pyrenean region

A unified probabilistic seismic hazard assessment (PSHA) for the Pyrenean region has been performed by an international team composed of experts from Spain and France during the Interreg IIIA ISARD project. It is motivated by incoherencies between the seismic hazard zonations of the design codes of France and Spain and by the need for input data to be used to define earthquake scenarios. A great effort was invested in the homogenisation of the input data. All existing seismic data are collected in a database and lead to a unified catalogue using a local magnitude scale. PSHA has been performed using logic trees combined with Monte Carlo simulations to account for both epistemic and aleatory uncertainties. As an alternative to hazard calculation based on seismic sources zone models, a zoneless method is also used to produce a hazard map less dependant on zone boundaries. Two seismogenic source models were defined to take into account the different interpretations existing among specialists. A new regional ground-motion prediction equation based on regional data has been proposed. It was used in combination with published ground-motion prediction equations derived using European and Mediterranean data. The application of this methodology leads to the definition of seismic hazard maps for 475- and 1,975-year return periods for spectral accelerations at periods of 0 (corresponding to peak ground acceleration), 0.1, 0.3, 0.6, 1 and 2 s. Median and percentiles 15% and 85% acceleration contour lines are represented. Finally, the seismic catalogue is used to produce a map of the maximum acceleration expected for comparison with the probabilistic hazard maps. The hazard maps are produced using a grid of 0.1°. The results obtained may be useful for civil protection and risk prevention purposes in France, Spain and Andorra.

Probabilistic landslide risk analysis considering direct costs in the area north of Lisbon (Portugal)

The purpose of the present study is the analysis of landslide risk for roads and buildings in a small test site (20 km 2) in the area north of Lisbon (Portugal). For this purpose, an evaluation is performed integrating into a GIS information obtained from multiple sources: (i) landslide hazard; (ii) elements at risk; and (iii) vulnerability. Landslide hazard is assessed on a probabilistic basis for three different types of slope movement (shallow translational slides, translational slides and rotational slides), based on some assumptions such as: (i) the likelihood of future landslide occurrence can be measured through statistical relationships between past landslide distribution and specified spatial data sets considered as landslide predisposing factors; and (ii) the rainfall combination (amount–duration) responsible for past slope instability within the test site will produce the same effects (i.e. same type of landslides and similar total affected area), each time they occur in the future. When the return period of rainfall triggering events is known, different scenarios can be modelled, each one ascribed to a specific return period. Therefore, landslide hazard is quantitatively assessed on a raster basis, and is expressed as the probability for each pixel (25 m 2) to be affected by a future landslide, considering a rainfall triggering scenario with a specific return period. Elements at risk within the test site include 2561 buildings and roads amounting to 169 km. Values attributed to elements at risk were defined considering reconstruction costs, following the guidelines of the Portuguese Insurance Institute. Vulnerability is considered as the degree of loss to a given element resulting from the occurrence of a landslide of a given magnitude. Vulnerability depends not only on structural properties of exposed elements, but also on the type of process, and its magnitude; i.e., vulnerability cannot be defined in absolute terms, but only with respect to a specific process (e.g. vulnerability to shallow translational slides). Therefore, vulnerability was classified for the three landslide groups considered on hazard assessment, taking into account: (i) landslide magnitude (mean depth, volume, velocity); (ii) damage levels produced by past landslide events in the study area; and (iii) literature. Finally, a landslide risk analysis considering direct costs was made in an automatic way crossing the following three layers: (i) Probabilistic hazard map for a landslide type Z, considering a particular rainfall triggering scenario whose return period is known; (ii) Vulnerability map (values from 0 to 1) of the exposed elements to landslide type Z; and (iii) Value map of the exposed elements, considering reconstruction costs.

Time probabilistic evaluation of seismically induced landslide hazard in Irpinia (Southern Italy)

A recently proposed method, which incorporates the Newmark model to evaluate the earthquake-induced landslide hazard at regional scale, was applied to Irpinia, one of the most seismically active regions of Italy. The method adopts a probabilistic approach to calculate values of critical acceleration a c representing the minimum strength required for a slope not to fail at a fixed probability level in a given time interval. Regional probabilistic hazard maps were generated for the two failure types most common in Irpinia (slump–earthflows and rock falls). The results suggest that quite moderate critical acceleration (0.05–0.08 g) could suffice to keep the slope failure probability low. However, the available data indicate that potential slide surfaces with a c below these values could be common in Irpinia, where, perhaps in relation to particular geo-environmental conditions, a relative large number of marginally stable slopes might survive other destabilising actions and fail even on occasion of not particularly strong earthquake shaking.

Surface Faulting: A New Paradigm for the Pacific Northwest

The past twenty years have witnessed three major paradigm shifts in our understanding of earthquake hazards in the Pacific Northwest. The first paradigm shift was the recognition in the 1980's that the Cascadia subduction zone is capable of great earthquakes. The locked part of the Cascadia subduction zone lacks instrumental seismicity, but geological evidence shows that it can produce an earthquake of MW 9, larger than any expected for California south of Cape Mendocino. In response to the geological evidence, building codes have been upgraded, tsunami inundation maps have been prepared for coastal areas from northern California to northern Washington, and earthquake hazard maps have been constructed for northwestern cities, including Victoria, British Columbia. Earthquake awareness has increased among the general public and within many private companies. Earthquake awareness has increased among the general public and within many private companies in the Pacific Northwest. The second paradigm shift, the alignment of seismic provisions in building codes to reflect greatly increased scientific understanding, has been subtle but of overarching societal importance. This alignment began in the early 1990's when Washington, under the leadership of the Structural Engineers Association of Washington, expanded the Uniform Building Code seismic zone III to include the Mount St. Helens seismic zone, and Oregon adopted a greatly revamped designation of seismic zone maps. This trend toward direct use of scientific results in the building code has accelerated in the last two years, with the State of Washington adopting the International Building Code (IBC). The IBC uses the U.S. Geological Survey (USGS) probabilistic hazard map as its basis, thus aligning current best science with engineering practice. Oregon may follow suit; currently 32 states have adopted the IBC. The IBC literally brings USGS hazard calculations onto the desktops of structural engineers. Despite the paradigm shifts related to Cascadia …

Statistical Assessment for the Hazard of Large Aftershocks Post to the Chi-Chi Mainshock

Real-time hazard assessment for large aftershocks from a major earthquake is usually needed for disaster relief and rescue efforts. In this paper, we employ the Reasenberg-Jones (RJ) model to describe the time-magnitude distribution of aftershocks after the Chi-Chi earthquake (M = 7.3, 1999/ 9/21). Both the maximum likelihood estimated RJ model and the Bayesian estimated RJ model are used to compute the probability of having at least one future M 5.0 aftershock. A probabilistic aftershock hazard map (PAHM) is also constructed for estimating the likely spatial distribution of M 5.0 aftershocks over the study region. This map gives then alarming for potential hazardous area of future M 5.0 aftershocks. Finally, we evaluate the association between the future M 5.0 aftershocks and the alarming obtained from the maximum likelihood estimated PAHM and Bayesian estimated PAHM, denoted by LPAHM and BPAHM, respectively. The results suggest that the LPAHM-based alarming is superior to the BPAHM-based one for locating future M 5.0 aftershocks after the Chi-Chi earthquake.

A Probabilistic Displacement-based Vulnerability Assessment Procedure for Earthquake Loss Estimation

Earthquake loss estimation studies require predictions to be made of the propor- tion of a building class falling within discrete damage bands from a specified earthquake demand. These predictions should be made using methods that incorporate both computa- tional efficiency and accuracy such that studies on regional or national levels can be effec- tively carried out, even when the triggering of multiple earthquake scenarios, as opposed to the use of probabilistic hazard maps and uniform hazard spectra, is employed to real- istically assess seismic demand and its consequences on the built environment. Earthquake actions should be represented by a parameter that shows good correlation to damage and that accounts for the relationship between the frequency content of the ground motion and the fundamental period of the building; hence recent proposals to use displacement response spectra. A rational method is proposed herein that defines the capacity of a building class by relating its deformation potential to its fundamental period of vibration at different limit states and comparing this with a displacement response spectrum. The uncertainty in the geometrical, material and limit state properties of a building class is considered and the first- order reliability method, FORM, is used to produce an approximate joint probability density function (JPDF) of displacement capacity and period. The JPDF of capacity may be used in conjunction with the lognormal cumulative distribution function of demand in the classi- cal reliability formula to calculate the probability of failing a given limit state. Vulnerability curves may be produced which, although not directly used in the methodology, serve to illus- trate the conceptual soundness of the method and make comparisons with other methods.

Probabilistic modeling of uncertainties in earthquake-induced landslide hazard assessment

Probabilistic analysis is gaining more attention in the field of landslide hazard assessment, due to the possibility of taking into account estimation uncertainties and spatial variability of geological, geotechnical, geomorphological and seismological parameters. In this paper, an implementation of a simple approach to derive probabilistic earthquake triggered landslide hazard maps is described. The method is based on the simplified Newmark slope stability model, applied on a pixel-by-pixel basis, which fully integrates into current GIS computational environments. Uncertainties and fluctuations in input parameters are considered by treating these quantities as statistical distributions. Various probability density functions can be simulated through Monte Carlo techniques on a pixel-by-pixel basis, and the simulated samples are retained through all the computing steps. This allows the resulting quantities to be cast into probabilistic hazard maps, without restrictions about the symmetry or the mathematical complexity of the underlying distributions. First results on a test landslide site in Southern Italy show good performances for realistic landslide hazard zonation. The simplicity of the adopted framework allows the current approach to be easily expanded and improved the current approach.

Book Review: National Earthquake Probabilistic Hazard Mapping Program: Lessons for Knowledge Transfer

Book Review: National Earthquake Probabilistic Hazard Mapping Program: Lessons for Knowledge Transfer