Probabilistic Tsunami Hazard Research Articles

From regional to local SPTHA: efficient computation of probabilistic tsunami inundation maps addressing near-field sources

Abstract. Site-specific seismic probabilistic tsunami hazard analysis (SPTHA) is a computationally demanding task, as it requires, in principle, a huge number of high-resolution numerical simulations for producing probabilistic inundation maps. We implemented an efficient and robust methodology using a filtering procedure to reduce the number of numerical simulations needed while still allowing for a full treatment of aleatory and epistemic uncertainty. Moreover, to avoid biases in tsunami hazard assessment, we developed a strategy to identify and separately treat tsunamis generated by near-field earthquakes. Indeed, the coseismic deformation produced by local earthquakes necessarily affects tsunami intensity, depending on the scenario size, mechanism and position, as coastal uplift or subsidence tends to diminish or increase the tsunami hazard, respectively. Therefore, we proposed two parallel filtering schemes in the far- and the near-field, based on the similarity of offshore tsunamis and hazard curves and on the similarity of the coseismic fields, respectively. This becomes mandatory as offshore tsunami amplitudes can not represent a proxy for the coastal inundation in the case of near-field sources. We applied the method to an illustrative use case at the Milazzo oil refinery (Sicily, Italy). We demonstrate that a blind filtering procedure can not properly account for local sources and would lead to a nonrepresentative selection of important scenarios. For the specific source–target configuration, this results in an overestimation of the tsunami hazard, which turns out to be correlated to dominant coastal uplift. Different settings could produce either the opposite or a mixed behavior along the coastline. However, we show that the effects of the coseismic deformation due to local sources can not be neglected and a suitable correction has to be employed when assessing local-scale SPTHA, irrespective of the specific signs of coastal displacement.

A New Approximate Method for Quantifying Tsunami Maximum Inundation Height Probability

Regional and global tsunami hazard analysis requires simplified and efficient methods for estimating the tsunami inundation height and its related uncertainty. One such approach is the amplification factor (AF) method. Amplification factors describe the relation between offshore wave height and the maximum inundation height, as predicted by linearized plane wave models employed for incident waves with different wave characteristics. In this study, a new amplification factor method is developed that takes into account the offshore bathymetry proximal to the coastal site. The present AFs cover the North-Eastern Atlantic and Mediterranean (NEAM) region. The model is the first general approximate model that quantifies inundation height uncertainty. Uncertainty quantification is carried out by analyzing the inundation height variability in more than 500 high-resolution inundation simulations at six different coastal sites. The inundation simulations are undertaken with different earthquake sources in order to produce different wave period and polarity. We show that the probability density of the maximum inundation height can be modeled with a log-normal distribution, whose median is quite well predicted by the AF. It is further demonstrated that the associated maximum inundation height uncertainties are significant and must be accounted for in tsunami hazard analysis. The application to the recently developed TSUMAPS-NEAM probabilistic tsunami hazard analysis (PTHA) is presented as a use case.

Probabilistic Tsunami Hazard Assessment in South China Sea With Consideration of Uncertain Earthquake Characteristics

AbstractIn this paper, we have conducted a probabilistic tsunami hazard assessment (PTHA) for Hong Kong (China) and Kao Hsiung (Taiwan), considering earthquakes generated in the Manila subduction zone. The new PTHA methodology with the consideration of uncertainties of slip distribution and location of future earthquakes extends the stochastic approach of Sepúlveda et al. (2017). Using sensitivity analyses, we further investigate the uncertainties of probability properties defining the slip distribution, the location, and the occurrence of earthquakes. We demonstrate that Kao Hsiung and Hong Kong would be significantly impacted by tsunamis generated by MW > 8.5 earthquakes in the Manila subduction zone. For instance, a specific MW 9.0 earthquake scenario is capable of producing tsunami amplitudes exceeding 4.0 and 3.5 m in Kao Hsiung and Hong Kong, respectively, with a probability of 50%. Despite the significant tsunami impact, great earthquakes have long mean return periods. As a result, the PTHA shows that Kao Hsiung and Hong Kong are exposed to a relatively small tsunami hazard. For instance, maximum tsunami amplitudes in the assessed locations of Kao Hsiung and Hong Kong exceed 0.32 and 0.18 m, respectively, with a mean return period of 100 years. The inundation hazard in populated areas is small as well, with mean return periods exceeding 1,000 years. Sensitivity analyses demonstrate that the PTHA can be affected by the uncertainties of the probability properties defining the slip distribution, the location, and the occurrence of earthquakes. However, PTHA results are most sensitive to the choice of the earthquake occurrence model.

PROBABILISTIC TSUNAMI HAZARD ASSESSMENT AND DAMAGE ESTIMATION OF THE BUILT ENVIRONMENT: APPLICATION TO THE CASCADIA SUBDUCTION ZONE AND SEASIDE, OREGON

Risk-based damage estimation to the built environment from future tsunamis is fundamental for developing mitigation and evacuation plans. One of the challenging problems in the evaluation of damage from future tsunamis is that the uncertainty from the nature of tsunami itself (e.g. Magnitude, Epicenter, Fault slip distributions) and the lack of accumulated sufficient observed data for probabilistic studies due to the relatively small frequency of tsunami historical events. Even though tsunami modeling has matured over the past several decades and provides reliable estimation of tsunami hazards such as flow depth, velocity, arrival time, etc., questions remain on how to predict future tsunami hazards and how to estimate tsunami damage, especially for the engineers who want to design shelter-in-plate options or coastal planners who want to estimate the possible damage from future tsunami events on the built environment at community and regional scales. As a case study, we evaluate the probabilistic damage states of an urban coastal city, Seaside, Oregon from future tsunamis generated on the Cascadia Subduction Zone (CSZ). The methodology and the results are separated into two parts: (1) Probabilistic tsunami hazard assessment (Park et al., 2017) and (2) Probabilistic building damage assessment from the tsunamis hazards with a community scale.

PROBABILISTIC TSUNAMI HAZARD ASSESSMENT (PTHA) AND PTHA-BASED TSUNAMI SCENARIO AT A PACIFIC COAST OF TOHOKU

When planning tsunami disaster mitigation and designing important infrastructure from the viewpoint of tsunami resistance in coastal areas, the scale and frequency of tsunamis that will arrive at coastal areas in future are important information. On the other hand, there are large uncertainties in predicting future tsunamis, and thus it is difficult to predict a future tsunami correctly. The technology of probabilistic tsunami hazard assessment (PTHA) has been proposed to evaluate the relationship between the height and frequency of tsunamis that will arrive at coastal areas in future. To consider the uncertainties of the prediction in the PTHA, the logic-tree approach is often adopted. In this approach, both epistemic and aleatory uncertainties are considered systematically. The epistemic uncertainties are caused by lack of knowledge and the aleatory uncertainties are variabilities due to natural randomness. In the logic-tree approach, the epistemic uncertainties are expressed by tree branches and the aleatory uncertainties are expressed by the probabilistic density functions of predicted tsunami heights. By carrying out PTHA, we can obtain a hazard curve, which expresses the relationship between the tsunami height and annual frequency of exceedance. Recently, methodologies by which PTHA-based-tsunami-scenarios are determined have been proposed. By using tsunami scenarios, detailed inundation processes and patterns can be evaluated. In this study, we apply the technologies of PTHA to the pacific coast of Tohoku, Japan. Then, we determine PTHA-based tsunami scenarios, that overflow a seawall constructed at the target coast and can be used for the evaluation of inundation processes.

PROBABILISTIC TSUNAMI HAZARD ASSESSMENTS WITH CONSIDERATION OF UNCERTAIN EARTHQUAKE CHARACTERISTICS

This study proposes a methodology to conduct probabilistic tsunami hazard assessments (PTHA) with consideration of uncertain earthquake characteristics. The methodology adopts a stochastic framework to model the earthquake slip and location as a random field and a random vector, respectively. The stochastic framework consists of three stages: (1) the definition of consistent probability properties for uncertain earthquake characteristics, (2) the generation of samples and (3) the uncertainty propagation. To complete each stage we follow the method recently proposed in Sepúlveda et al. (2017). We illustrate our PTHA methodology by assessing the tsunami hazard in Kao Hsiung and Hong Kong, with consideration of earthquakes in the Manila Trench.

Time-dependent probabilistic tsunami hazard analysis using stochastic rupture sources

This study conducts a time-dependent probabilistic tsunami hazard analysis using stochastic rupture sources, which enables the consideration of numerous heterogeneous earthquake slip distributions. Earthquake occurrence modeling is based on temporal renewal and magnitude recurrence models. To account for various combinations of alternative models for temporal occurrence process, earthquake magnitude distribution, and spatial earthquake slip distribution, a logic-tree approach is implemented, facilitating more comprehensive characterization of epistemic uncertainties for the stochastic rupture source approach. To demonstrate the effects of different model components on tsunami hazard curves, a case study for coastal plain areas of Miyagi Prefecture in Japan is set up. The sensitivity analysis clearly indicates that the selection of renewal and magnitude models has paramount influence on the tsunami hazard results. The results also depend on the situations of interest in terms of current time and time-horizon with respect to the recurrence process of the earthquake rupture. In light of significant uncertainties of tsunami hazard and risk due to future mega-thrust subduction events, consideration of epistemic uncertainties is of critical importance.

The probabilistic tsunami hazard assessment along Karnataka Coast from Makran Subduction Zone, west coast of India.

Coastal tsunami amplitudes were calculated to identify areas susceptible to tsunami hazard at selected locations of the coast of Karnataka, west of India, due to earthquakes in the Makran Subduction Zone. This is the first time that the probabilistic tsunami hazard assessment along this study area has been attempted. A series of earthquake source scenarios with magnitudes of Mw 8.0, Mw 8.5, and a mega thrust of Mw 9.1 were modeled by using the Community Model Interface for Tsunami interface with the MOST model of Titov and Synolakis (J. Waterway, Port, Coastal and Ocean Engineering, 121(6), 308-316, 1995). As per the previous occurrences, the two least magnitudes are probable, while Mw 9.1 is a worst-case scenario as described by Heidarzadeh et al. (Ocean Engineering, 36(5), 368-376, 2009) and the same is reported by Burbidge et al. (Geoscience Australia Professional Opinion No. 2009/11) as high magnitude. These are not at all historical earthquakes or specifically from historical catalogues. The results of modeling show that all the seven coastal locations are inundated barely in our worst-case scenario with maximum water levels in the range of 100-200cm. The first tsunami wave strikes the coast within 4-5h of earthquake occurrence.

Tsunami hazard from submarine landslides: scenario-based assessment in the Ulleung Basin, East Sea (Japan Sea)

In this study we use a scenario-based approach to highlight potential tsunami hazard from actual Late Pleistocene submarine landslides in the Ulleung Basin: two submarine landslides on the western slope of the Ulleung Basin, north and south of the Hupo Bank (2.53 and 1.12 km3 respectively) and a landslide (15.1 km3) on the continental slope south of the Ulleung Basin. The simulations attempt to highlight the consequences, should one of these events occur at Present. Results of the simulations indicate potential local hazard zones with very local waves 3 m in the stretch of coastline from Ulsan in the south to Uljin in the north. The timing available for early warning from landslide tsunamis originating in this area is 15–30 minutes along the affected section of the shoreline. We also suggest a Probabilistic Tsunami Hazard Assessment (PTHA) for comprehensive assessments of the Korean coast of the East Sea. PTHA accounts for uncertainties in location, release mechanisms, evolution, and return periods of submarine landslides as well as epistemic uncertainty. However, to constrain these uncertainties detailed information on source areas, recurrence period and dynamics of submarine landslides is necessary and calls for additional data collection and further studies.

Probabilistic Tsunami Hazard Assessment (PTHA) for resilience assessment of a coastal community

Probabilistic Tsunami Hazard Analysis (PTHA) can be used to evaluate and quantify tsunami hazards for planning of integrated community-level preparedness, including mitigation of casualties and dollar losses, and to study resilient solutions for coastal communities. PTHA can provide several outputs such as the intensity measures (IMs) of the hazard quantified as a function of the recurrence interval of a tsunami event. In this paper, PTHA is developed using a logic tree approach based on numerical modeling for tsunami generated along the Cascadia Subduction Zone. The PTHA is applied to a community on the US Pacific Northwest Coast located in Newport, Oregon. Results of the PTHA are provided for five IMs: inundation depth, flow speed, specific momentum flux, arrival time, and duration of inundation. The first three IMs are predictors of tsunami impact on the natural and built environment, and the last two are useful for tsunami evacuation and immediate response planning. Results for the five IMs are presented as annual exceedance probability for sites within the community along several transects with varying bathymetric and topographic features. Community-level characteristics of spatial distribution of each IM for three recurrence intervals (500, 1000, 2500 year) are provided. Results highlight the different pattern of IMs between land and river transects, and significant magnitude variation of IMs due to complex bathymetry and topographic conditions at the various recurrence intervals. IMs show relatively higher magnitudes near the coastline, at the low elevation regions, and at the harbor channel. In addition, results indicate a positive correlation between inundation depth and other IMs near the coastline, but a weaker correlation at inland locations. Values of the Froude number ranged 0.1–1.0 over the inland inundation area. In general, the results in this study highlight the spatial differences in IMs and suggest the need to include multiple IMs for resilience planning for a coastal community subjected to tsunami hazards.

Incorporating Tidal Uncertainty into the Methodology of Probabilistic Tsunami Hazard Analysis

Wu, E.C.; Chen, Y.L.; Wu, H.L.; Hu, K.C.; Hsiao, S.C., and Wu, Y.C., 2018. Incorporating Tidal Uncertainty into the Methodology of Probabilistic Tsunami Hazard Analysis. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 691–695. Coconut Creek (Florida), ISSN 0749-0208.The Circum-Pacific Belt has become active in recent years, and the earthquake in the border area of land and sea probably causes tsunami disaster. The hazard includes overflow flooded, building damage, casualties, and radiation crisis of nuclear power plant. To quantify the risk, probabilistic tsunami hazard analysis (PTHA) serves as a robust methodology. The uncertainty stemming from the deviation of modeling, named aleatory uncertainty, is considered with including the tidal effect on the tsunami. To deal with the aleatory uncertainty, we incorporate tidal uncertainty into PTHA. Different static tidal stages are set in Cornell Multi-grid Coupled Tsunami model (COMCOT) to evaluate tsunami hazards. Three kinds of method are presented. One could apply theoretical probability distribution to different maximum wave height by the Gaussian Method. On the other hand, the Δt method and the Pattern Method combine tsunami events with a typical year of tidal record. The difference between these methods are discussed, and the Pattern Method is regarded as the most rigorous way. Finally, the method of incorporating tidal uncertainty into PTHA has been established and been utilized to Maanshan nuclear power plant in Taiwan.

Transport Reversal for Model Reduction of Hyperbolic Partial Differential Equations

In order to perform probabilistic tsunami hazard assessment (PTHA) based on subduction zone earthquakes, it is necessary to start with a catalog of possible future events along with the annual probability of occurance, or a probability distribution of such events that can be easily sampled. For nearfield events, the distribution of slip on the fault can have a significant effect on the resulting tsunami. We present an approach to defining a probability distribution based on subdividing the fault geometry into many subfaults and prescribing a desired covariance matrix relating slip on one subfault to slip on any other subfault. The eigenvalues and eigenvectors of this matrix are then used to define a Karhunen-Lo\`eve expansion for random slip patterns. This is similar to a spectral representation of random slip based on Fourier series but conforms to a general fault geometry. We show that only a few terms in this series are needed to represent the features of the slip distribution that are most important in tsunami generation, first with a simple one-dimensional example where slip varies only in the down-dip direction and then on a portion of the Cascadia Subduction Zone.

Impact of earthquake source complexity and land elevation data resolution on tsunami hazard assessment and fatality estimation

This study investigates the impact of model complexity in source characterization and digital elevation model (DEM) resolution on the accuracy of tsunami hazard assessment and fatality estimation through a case study in Padang, Indonesia. Two types of earthquake source models, i.e. complex and uniform slip models, are adopted by considering three resolutions of DEMs, i.e. 150 m, 50 m, and 10 m. For each of the three grid resolutions, 300 complex source models are generated using new statistical prediction models of earthquake source parameters developed from extensive finite-fault models of past subduction earthquakes, whilst 100 uniform slip models are constructed with variable fault geometry without slip heterogeneity. The results highlight that significant changes to tsunami hazard and fatality estimates are observed with regard to earthquake source complexity and grid resolution. Coarse resolution (i.e. 150 m) leads to inaccurate tsunami hazard prediction and fatality estimation, whilst 50-m and 10-m resolutions produce similar results. However, velocity and momentum flux are sensitive to the grid resolution and hence, at least 10-m grid resolution needs to be implemented when considering flow-based parameters for tsunami hazard and risk assessments. In addition, the results indicate that the tsunami hazard parameters and fatality number are more sensitive to the complexity of earthquake source characterization than the grid resolution. Thus, the uniform models are not recommended for probabilistic tsunami hazard and risk assessments. Finally, the findings confirm that uncertainties of tsunami hazard level and fatality in terms of depth, velocity and momentum flux can be captured and visualized through the complex source modeling approach. From tsunami risk management perspectives, this indeed creates big data, which are useful for making effective and robust decisions.

Probabilistic Tsunami Hazard Analysis: Multiple Sources and Global Applications

AbstractApplying probabilistic methods to infrequent but devastating natural events is intrinsically challenging. For tsunami analyses, a suite of geophysical assessments should be in principle evaluated because of the different causes generating tsunamis (earthquakes, landslides, volcanic activity, meteorological events, and asteroid impacts) with varying mean recurrence rates. Probabilistic Tsunami Hazard Analyses (PTHAs) are conducted in different areas of the world at global, regional, and local scales with the aim of understanding tsunami hazard to inform tsunami risk reduction activities. PTHAs enhance knowledge of the potential tsunamigenic threat by estimating the probability of exceeding specific levels of tsunami intensity metrics (e.g., run‐up or maximum inundation heights) within a certain period of time (exposure time) at given locations (target sites); these estimates can be summarized in hazard maps or hazard curves. This discussion presents a broad overview of PTHA, including (i) sources and mechanisms of tsunami generation, emphasizing the variety and complexity of the tsunami sources and their generation mechanisms, (ii) developments in modeling the propagation and impact of tsunami waves, and (iii) statistical procedures for tsunami hazard estimates that include the associated epistemic and aleatoric uncertainties. Key elements in understanding the potential tsunami hazard are discussed, in light of the rapid development of PTHA methods during the last decade and the globally distributed applications, including the importance of considering multiple sources, their relative intensities, probabilities of occurrence, and uncertainties in an integrated and consistent probabilistic framework.

Probabilistic seismic and tsunami hazard analysis (PSTHA) conditioned on a mega-thrust rupture of the Cascadia Subduction Zone.

This paper presents a framework for a probabilistic hazard assessment for the multi-hazard seismic and tsunami phenomena (PSTHA). For this work, we consider a full-rupture event along the Cascadia Subduction Zone and apply the methodology to the study area of Seaside, Oregon, along the US Pacific Northwest coast. In this work, we show that the annual exceedance probabilities ( ) of the tsunami intensity measures ( ) are qualitatively dissimilar to the IMs of the seismic ground motion in the study area. Specifically, the spatial gradients for the tsunami IM are much stronger across the length scale of the city owing to the physical differences of energy dissipation of the two mechanisms. Example results of probabilistic seismic hazard analysis (PSHA) and probabilistic tsunami hazard analysis (PTHA) are shown for three observation points in the study area of Seaside. For the seismic hazard, the joint mean annual rate of exceedance shows similar trends for the three observation points, even though there is a large scatter between and . For the tsunami hazard, the joint of and shows a high correlation between the two in the study area. The joint at each of the three observation points follows a particular Froude number ( ) due to the local site-specific conditions locally rather than the distributions of fault slips. The joint probability distribution of and throughout the study region falls between (i.e., the flow is subcritical) regardless of return interval (500-, 1,000-, and 2,500-yr). However, the peak of the joint probability distribution with respect to and varies with the return interval, and the largest values of and were observed with the highest return intervals (2,500 yr) as would be expected. The results of the PSTHA can be the basis for a probabilistic multi-hazard damage assessment and help to understand the uncertainties of the multi-hazard assessments.

Probabilistic Tsunami Hazard Analysis of the Pacific Coast of Mexico: Case Study Based on the 1995 Colima Earthquake Tsunami

This study develops a novel computational framework to carry out probabilistic tsunami hazard assessment for the Pacific coast of Mexico. The new approach enables the consideration of stochastic tsunami source scenarios having variable fault geometry and heterogeneous slip that are constrained by an extensive database of rupture models for historical earthquakes around the world. The assessment focuses upon the 1995 Jalisco-Colima Earthquake Tsunami from a retrospective viewpoint. Numerous source scenarios of large subduction earthquakes are generated to assess the sensitivity and variability of tsunami inundation characteristics of the target region. Analyses of nine slip models along the Mexican Pacific coast are performed and statistical characteristics of slips (e.g. coherent structures of slip spectra) are estimated. The source variability allows exploring a wide range of tsunami scenarios for a moment magnitude (Mw) 8 subduction earthquake in the Mexican Pacific region to conduct thorough sensitivity analyses and to quantify the tsunami height variability. The numerical results indicate a strong sensitivity of maximum tsunami height to major slip locations in the source, and indicate major uncertainty at the first peak of tsunami waves.

Simulation-Based Probabilistic Tsunami Hazard Analysis: Empirical and Robust Hazard Predictions

Probabilistic tsunami hazard analysis (PTHA) is the prerequisite for rigorous risk assessment and thus for decision-making regarding risk mitigation strategies. This paper proposes a new simulation-based methodology for tsunami hazard assessment for a specific site of an engineering project along the coast, or, more broadly, for a wider tsunami-prone region. The methodology incorporates numerous uncertain parameters that are related to geophysical processes by adopting new scaling relationships for tsunamigenic seismic regions. Through the proposed methodology it is possible to obtain either a tsunami hazard curve for a single location, that is the representation of a tsunami intensity measure (such as inundation depth) versus its mean annual rate of occurrence, or tsunami hazard maps, representing the expected tsunami intensity measures within a geographical area, for a specific probability of occurrence in a given time window. In addition to the conventional tsunami hazard curve that is based on an empirical statistical representation of the simulation-based PTHA results, this study presents a robust tsunami hazard curve, which is based on a Bayesian fitting methodology. The robust approach allows a significant reduction of the number of simulations and, therefore, a reduction of the computational effort. Both methods produce a central estimate of the hazard as well as a confidence interval, facilitating the rigorous quantification of the hazard uncertainties.

Probabilistic Tsunami Hazard Assessment from Incomplete and Uncertain Historical Catalogues with Application to Tsunamigenic Regions in the Pacific Ocean

The paper presents a new method for empirical assessment of tsunami recurrence parameters, namely the mean tsunami activity rate $$\lambda_{\text{T}}$$ , the Soloviev–Imamura frequency–magnitude power law $$b_{\text{T}}$$ -value, and the coastline-characteristic, maximum possible tsunami intensity $$i_{ \text{max} }$$ . The three coastline-characteristic recurrence parameters are estimated locally by maximum likelihood techniques using only tsunami event catalogues. The method provides for incompleteness of the tsunami catalogue, uncertainty in the tsunami intensity determination, and uncertainty associated with the parameters in the applied tsunami occurrence models. Aleatory and epistemic uncertainty is introduced in the tsunami models by means of the use of mixture distributions. Both the mean tsunami activity rate $$\lambda_{\text{T}}$$ of the Poisson occurrence model, and the $$b_{\text{T}}$$ -value of the Soloviev–Imamura frequency–intensity power law are random variables. The proposed procedure was applied to estimate the probabilities of exceedance and return periods for tsunamis in the tsunamigenic regions of Japan, Kuril–Kamchatka, and South America.

New constraints on coseismic slip during southern Cascadia subduction zone earthquakes over the past 4600 years implied by tsunami deposits and marine turbidites

Forecasting earthquake and tsunami hazards along the southern Cascadia subduction zone is complicated by uncertainties in the amount of megathrust fault slip during past ruptures. Here, we estimate slip on hypothetical ruptures of the southern part of the megathrust through comparisons of late Holocene Cascadia earthquake histories derived from tsunami deposits on land and marine turbidites offshore. Bradley Lake in southern Oregon lies ~600 m landward of the shoreline and contains deposits from 12 tsunamis in the past 4600 years. Tsunami simulations that overtop the 6-m-high lake outlet, generated by ruptures with most slip south of Cape Blanco, require release of at least as much strain on the megathrust as would accumulate in 430–640 years (>15–22 m). Such high slip is inconsistent with global seismic data for a rupture ~300-km long and slip deficits over the past ~4700 years on the southern Cascadia subduction zone. Assuming slip deficits accumulated during the time intervals between marine turbidites, up to 8 of 12 tsunami inundations at the lake are predicted from a marine core site 170 km north of the lake (at Hydrate Ridge) compared to 4 of 12 when using a core site ~80 km south (at Rogue Apron). Longer time intervals between turbidites at Hydrate Ridge imply larger slip deficits compared to Rogue Apron. The different inundations predicted by the two records suggest that Hydrate Ridge records subduction ruptures that extend past both Rogue Apron and Bradley Lake. We also show how turbidite-based estimates of CSZ rupture length relate to tsunami source scenarios for probabilistic tsunami hazard assessments consistent with lake inundations over the last ~4600 years.

The New Zealand Probabilistic Tsunami Hazard Model: development and implementation of a methodology for estimating tsunami hazard nationwide

Abstract For New Zealand, a country straddling the Pacific ‘Ring of Fire’, effective mitigation of the risks posed by tsunamis is an urgent priority. Mitigation measures include evacuation mapping, land-use planning and engineering of tsunami resilient buildings and infrastructure; but for these to be effective, a quantitative estimate of the tsunami hazard is needed. For this purpose we present the New Zealand Probabilistic Tsunami Hazard Model (NZPTHM). The model uses a Monte Carlo method for sampling from the geophysical parameters that constrain the magnitude–frequency distributions of the earthquake sources that can cause tsunamis affecting New Zealand. The sampled parameters are used to construct synthetic catalogues of the source events and the subsequent tsunami heights. Processing of these synthetic catalogues produces hazard curves, describing maximum tsunami height as a function of return period, which include ‘error bars’ (confidence intervals) as determined by the Monte Carlo model. Most practical mitigation measures require inundation modelling, and for this purpose we propose using de-aggregation, a process by which a small set of scenarios can be extracted from the NZPTHM for the purpose of detailed inundation modelling.