Maritime tsunami evacuation guidelines for the Pacific Northwest coast of Oregon

Recent tsunamis affecting the West Coast of the USA have resulted in significant damage to ports and harbors, as well as to recreational and commercial vessels attempting to escape the tsunami. With the completion of tsunami inundation simulations for a distant tsunami originating from the Aleutian Islands and a locally generated tsunami on the Cascadia subduction zone (CSZ), the State of Oregon is now able to provide guidance on the magnitudes and directions of the simulated currents for the Oregon coast and shelf region. Our analyses indicate that first wave arrivals for an Aleutian Island event would take place on the north coast,?~?3 h 40 min after the start of the earthquake,?~?20 min later on the southern Oregon coast. The simulations demonstrated significant along-coast variability in both the tsunamis water levels and currents, caused by localized bathymetric effects (e.g., submarine banks and reefs). A locally generated CSZ event would reach the open coast within 7–13 min; maximum inundation occurs at?~?30–40 min. As the tsunami current velocities increase, the potential for damage in ports and harbors correspondingly increases, while also affecting a vessels ability to maintain control out on the ocean. Scientific consensus suggests that tsunami currents?<?1.54 m/s are unlikely to impact maritime safety in ports and harbors. No such guidance is available for boats operating on the ocean, though studies undertaken in Japan suggest that velocities in the region of 1–2 m/s may be damaging to boats. In addition to the effects of currents, there is the added potential for wave amplification of locally generated wind waves interacting with opposing tsunami currents in the offshore. Our analyses explore potential wave amplification effects for a range of generic sea states, ultimately producing a nomogram of wave amplification for a range of wave and opposing current conditions. These data will be useful for US Coast Guard and Port authorities as they evaluate maritime tsunami evacuation options for the Oregon coast. Finally, we identify three regions of hazard (high, moderate, and low) across the Oregon shelf, which can be used to help guide final designation of tsunami maritime evacuation zones for the coast.     

Recurrence intervals of major paleotsunamis as calibrated by historic tsunami deposits in three localities: Port Alberni, Cannon Beach, and Crescent City, along the Cascadia margin, Canada and USA

We review geologic records of both historic and prehistoric tsunami inundations at three widely separated localities that experienced significant damage from the 1964 Alaskan tsunami along the Cascadia margin. The three localities are Port Alberni, Cannon Beach, and Crescent City, representing, respectively, the north, central, and south portions of the study area (1,000 km in length). The geologic records include anomalous sand sheets from marine surges that are hosted in supratidal peaty mud deposits. Paleotsunami sand sheets that exceed the thickness, continuity and/or extent of the 1964 historic tsunami are counted as major paleotsunami inundations. Major paleotsunamis (6–7 in number) at each locality during the last 3,000 years demonstrate mean recurrence intervals of 450–540 years, and within-cluster intervals (three events each) of 270–460 years. It has been 313 years since the last major paleotsunami from a great Cascadia earthquake in AD 1700. We compare the dated sequences of major paleotsunami inundations to the nearest regional records of coastal coseismic subsidence in Willapa Bay in the central margin, Waatch/Neah Bay in the northern margin, and Coquille in the southern margin. Similar numbers of events from both types of records suggest that the major paleotsunamis are locally derived (near-field) from ruptures of the Cascadia margin megathrust fault zone, rather than from transoceanic tsunamis (far-field) originating at other subduction zones around the Pacific Rim. Given the catastrophic hazard of the near-field Cascadia margin tsunamis, we propose a basic rule for reminding the general public of the need for self-initiated evacuation following a great earthquake at the Cascadia margin.     

Tsunami hazard assessment of Canada

We present a preliminary probabilistic tsunami hazard assessment of Canadian coastlines from local and far-field, earthquake, and large submarine landslide sources. Analyses involve published historical, palaeotsunami and palaeoseismic data, modelling, and empirical relations between fault area, earthquake magnitude, and tsunami run-up. The cumulative estimated tsunami hazard for potentially damaging run-up (≥1.5 m) of the outer Pacific coastline is ~40–80 % in 50 years, respectively one and two orders of magnitude greater than the outer Atlantic (~1–15 %) and the Arctic (<1 %). For larger run-up with significant damage potential (≥3 m), Pacific hazard is ~10–30 % in 50 years, again much larger than both the Atlantic (~1–5 %) and Arctic (<1 %). For outer Pacific coastlines, the ≥1.5 m run-up hazard is dominated by far-field subduction zones, but the probability of run-up ≥3 m is highest for local megathrust sources, particularly the Cascadia subduction zone; thrust sources further north are also significant, as illustrated by the 2012 Haida Gwaii event. For Juan de Fuca and Georgia Straits, the Cascadia megathrust dominates the hazard at both levels. Tsunami hazard on the Atlantic coastline is dominated by poorly constrained far-field subduction sources; a lesser hazard is posed by near-field continental slope failures similar to the 1929 Grand Banks event. Tsunami hazard on the Arctic coastline is poorly constrained, but is likely dominated by continental slope failures; a hypothetical earthquake source beneath the Mackenzie delta requires further study. We highlight areas susceptible to locally damaging landslide-generated tsunamis, but do not quantify the hazard.     

An assessment of educational tsunami evacuation map designs in Washington and Oregon

Educational tsunami evacuation map brochures in Washington and Oregon have been developed locally, resulting in significant differences between the types of tsunami hazard information they include. This paper identifies six tsunami hazard information types present in 38 brochures in Washington and Oregon: (1) tsunami hazard zone, (2) road network, (3) assembly areas, (4) evacuation guidance, (5) infrastructure, and (6) terrain. It compares and contrasts these information types in the maps and text of six of the brochures, including a proposed design standard in Oregon. Design differences of all 38 brochure maps are then organized using principles of cartographic abstraction, which describe mapmaker decisions about selection, generalization, and symbolization of information. We further use this framework to situate the information content of a new interactive Google Maps tool in Oregon. Our assessment identifies limitations of current tsunami hazard information that may be relevant to improving tsunami education. In theory, more advanced evacuation map tools can play an important role in reducing the limitations of tsunami hazard information relevant to the public. The new Google Maps tool addresses few of these limitations. Recognizing how map-making decisions define the underlying information content of evacuation maps can facilitate much needed future evaluations and developments in evacuation map design.     

Method to determine the locations of tsunami vertical evacuation shelters

The 2004 Indian Ocean tsunami and the 2011 Great Tohoku Japan earthquake and tsunami focused a great deal of the world??s attention on the effect of tsunamis on buildings and infrastructure. When a tsunami impacts structures in a coastal community, the structures are often not strong enough to withstand the forces and may collapse. Therefore, to maximize the survival probability, people evacuate to higher ground or move outside the inundation zone. However, this is not always possible because of short warning times for near-field tsunamis. Thus, sheltering-in-place or ??sheltering-near-place?? using vertical evacuation should be considered as an alternative approach to lateral evacuation from a tsunami inundation zone. This paper presents the method and results of a study to develop and demonstrate a methodology that applied genetic optimization to determine optimal tsunami shelter locations with the goal of reducing evacuation time, thereby maximizing the probability of survival for the population in a coastal community. The City of Cannon Beach, Oregon, USA, was used as an illustrative example. Several cases were investigated ranging from a single shelter to multiple shelters with locations of high elevation already in place near the city. The method can provide decision-support for the determination of locations for tsunami vertical evacuation shelters. The optimum location of the shelter(s), which was found to vary depending on the number of shelters considered, can reduce the evacuation time significantly, thereby reducing the number of fatalities and increasing the safety of a community.     

Reconstructing hydrodynamic flow parameters of the 1700 tsunami at Cannon Beach, Oregon, USA

Coastal communities in the western United States face risks of inundation by distant tsunamis that propagate across the Pacific Ocean as well as local tsunamis produced by great (M_w?>?8) earthquakes on the Cascadia subduction zone. In 1964, the M_w 9.2 Alaska earthquake launched a Pacific-wide tsunami that flooded Cannon Beach, a small community (population 1640) in northwestern Oregon, causing over $230,000 in damages. However, since the giant 2004 Indian Ocean tsunami, the 2010 Chile tsunami and the recent 2011 Tohoku-Oki tsunami, renewed concern over potential impacts of a Cascadia tsunami on the western US has motivated closer examination of the local hazard. This study applies a simple sediment transport model to reconstruct the flow speed of the most recent Cascadia tsunami that flooded the region in 1700 using the thickness and grain size of sand layers deposited by the waves. Sedimentary properties of sand from the 1700 tsunami deposit provide model inputs. The sediment transport model calculates tsunami flow speed from the shear velocity required to suspend the quantity and grain size distribution of the observed sand layers. The model assumes a steady, spatially uniform tsunami flow and that sand settles out of suspension forming a deposit when the flow velocity decreases to zero. Using flow depths constrained by numerical tsunami simulations for Cannon Beach, the sediment transport model calculated flow speeds of 6.5?C7.6?m/s for sites within 0.6?km of the beach and higher flow speeds (~8.8?m/s) for sites 0.8?C1.2?km inland. Flow speed calculated for sites within 0.6?km of the beach compare well with maximum velocities estimated for the largest tsunami simulation. The higher flow speeds calculated for the two sites furthest landward contrast with much lower maximum velocities (<3.8?m/s) predicted by numerical simulations. Grain size distributions of sand layers from the most distal sites are inconsistent with deposition from sediment falling out of suspension. We infer that rapid deceleration in tsunami flow and convergences in sediment transport formed unusually thick deposits. Consequently, higher flow speeds calculated by the sediment model probably overestimate the actual wave speed at sites furthest inland.     

A data-driven approach to assess large fire size generation in Greece

The 2011 Tohoku earthquake and tsunami motivated an analysis of the potential for great tsunamis in Hawai‘i that significantly exceed the historical record. The largest potential tsunamis that may impact the state from distant, Mw 9 earthquakes—as forecast by two independent tsunami models—originate in the Eastern Aleutian Islands. This analysis is the basis for creating an extreme tsunami evacuation zone, updating prior zones based only on historical tsunami inundation. We first validate the methodology by corroborating that the largest historical tsunami in 1946 is consistent with the seismologically determined earthquake source and observed historical tsunami amplitudes in Hawai‘i. Using prior source characteristics of Mw 9 earthquakes (fault area, slip, and distribution), we analyze parametrically the range of Aleutian–Alaska earthquake sources that produce the most extreme tsunami events in Hawai‘i. Key findings include: (1) An Mw 8.6 ± 0.1 1946 Aleutian earthquake source fits Hawai‘i tsunami run-up/inundation observations, (2) for the 40 scenarios considered here, maximal tsunami inundations everywhere in the Hawaiian Islands cannot be generated by a single large earthquake, (3) depending on location, the largest inundations may occur for either earthquakes with the largest slip at the trench, or those with broad faulting over an extended area, (4) these extremes are shown to correlate with the frequency content (wavelength) of the tsunami, (5) highly variable slip along the fault strike has only a minor influence on inundation at these tele-tsunami distances, and (6) for a given maximum average fault slip, increasing the fault area does not generally produce greater run-up, as the additional wave energy enhances longer wavelengths, with a modest effect on inundation.     

Identification and possible recurrence of an oversized tsunami on the Pacific coast of northern Japan

Geological evidence of severe tsunami inundation has been discovered in northern Japan. In the dune fields of Shimokita, in northernmost Tohoku, we have found two distinctive sand layers that are tsunami deposits. The run-up height of >20 m and inland inundation of at least 1.4 km are notably larger than any known historical case in Japan. The tsunami-genic earthquake that resulted in these deposits is thought to have taken place in the Kuril Forearc-Trench system nearly 700 years ago. The recurrence interval of major tsunamis originating in the Kuril subduction zone is about 400 years. Given that the most recent unusually large earthquake took place in AD 1611 (corresponding to the Keicho earthquake tsunami), the findings presented here increase the potential and hazard for an outsized tsunami striking the Pacific coast of northern Japan.     

Tsunami risk reduction for densely populated Southeast Asian cities: analysis of vehicular and pedestrian evacuation for the city of Padang, Indonesia, and assessment of interventions

A major tsunamigenic earthquake is expected in the near future along the coast of West Sumatra Province of Indonesia. In the city of Padang, the arrival time of the tsunami is expected to be ~30 min. Currently, there are approximately 400,000 people in the city living within the potential inundation zone. This study aimed to complement the existing research in appraising possible risk reduction interventions, specifically looking at enabling the timely evacuation of the area. This research, developed in consultation with national and local authorities, emergency planners and NGOs, analysed interventions for tsunami risk reduction in Padang through the development of a pedestrian and vehicular evacuation model and the appraisal of possible solutions to enhance the evacuation rates. Some of the conclusions from this research can be applied to other areas in Southeast Asia where the traffic patterns are similar to those in Padang and where the distance to safety is greater than 4–5 km. For the case of Padang, the results show that pedestrian evacuation is strongly preferable to vehicular evacuation due to the limited road capacity and the high population density. In the present situation, however, 70–80 % of the population in Padang could not evacuate within 30 min, even by foot. Common interventions such as widening roads and building bridges prove to be relatively ineffective in this case due to the large distance that has to be covered in a short time. These interventions would only have a decisive impact if a longer evacuation time was available (more than 60 min). In the case of Padang, the evacuation rate in the first 30 min is strongly dependent on the presence/absence of evacuation shelters, whose effectiveness is limited by the capacity of the structures. Building a few high-capacity and high-resilience structures such as evacuation hills is a more effective and robust evacuation strategy than constructing many small high-raised buildings. Even with evacuation structures, wider roads and bridges, about 20 % of the population would still be unable to reach safety by the time the tsunami arrives. This means about 70,000 people of Padang’s current population, which is rapidly increasing. The building of evacuation shelters may be a viable option for saving lives in the short term, but it is not a sustainable option in the medium to long term. It is therefore also necessary to set up and enforce regulations for land use planning that take into account the tsunami risk and prevent further urban development for the areas that may be affected by a tsunami.     

Hazard assessment of underwater landslide-generated tsunamis: a case study in the Padang region, Indonesia

Submarine landslides can generate local tsunamis with high run-ups, posing a hazard to human lives and coastal facilities. Both ancient (giant Storegga slide off Norwegian coast, 8200 B. P.) and recent (Papua New Guinea, 1998) events show high potential danger of tsunamigenic landslides and the importance of mitigation efforts. This contribution presents newly discovered landslides 70 km off Padang (Western Sumatra, Indonesia) based on recent bathymetry measurements. This highly populated city with over 750,000 inhabitants exhibits high tsunami vulnerability due to its very low elevation. We model tsunamis that might have been induced by the detected landslide events. Estimations of run-up heights extrapolated from offshore tsunami amplitudes for Padang and other locations in the northern Mentawai fore-arc basin yield maximum values of about 3 m. We also provide a systematic parametric study of landslide-induced tsunamis, which allows us to distinguish potentially dangerous scenarios for Padang. Inside the fore-arc basin, scenarios involving volumes of 0.5–25 km³ could endanger Padang. Apart from slide volume, the hazard distribution mainly depends on three landslide parameters: distance to Padang, water depth in the generation region, and slide direction.     

Tsunami hazard evaluation for Kuwait and Arabian Gulf due to Makran Subduction Zone and Subaerial landslides

Given the recent historical disastrous tsunamis and the knowledge that the Arabian Gulf (AG) is tectonically active, this study aimed to evaluate tsunami hazards in Kuwait from both submarine earthquakes and subaerial landslides. Despite the low or unknown tsunami risks that impose potential threats to the coastal area’s infrastructures and population of Kuwait, such an investigation is important to sustain the economy and safety of life. This study focused on tsunamis generated by submarine earthquakes with earthquake magnitudes (M _w ) of 8.3–9.0 along the Makran Subduction Zone (MSZ) and subaerial landslides with volumes of 0.75–2.0 km³ from six sources along the Iranian coast inside the AG and one source at the Gulf entrance in Oman. The level of tsunami hazards associated with these tsunamigenic sources was evaluated using numerical modeling. Tsunami model was applied to conduct a numerical tsunami simulation and predict tsunami propagation. For landslide sources, a two-layer model was proposed to solve nonlinear longwave equations within two interfacing layers with appropriate kinematic and dynamic boundary conditions. Threat level maps along the coasts of the AG and Kuwait were developed to illustrate the impacts of potential tsunamis triggered by submarine earthquakes of different scales and subaerial landslides at different sources. GEBCO 30 arc-second grid data and others were used as bathymetry and topography data for numerical modeling. Earthquakes of M _w 8.3 and M _w 8.6 along the MSZ had low and considerable impacts, respectively, at the Gulf entrance, but negligible impacts on Kuwait. An earthquake of M _w 9.0 had a remarkable impact for the entire Gulf region and generated a maximum tsunami amplitude of up to 0.5 m along the Kuwaiti coastline 12 h after the earthquake. In the case of landslides inside the AG, the majority impact occurred locally near the sources. The landslide source opposite to Kuwait Bay generated the maximum tsunami amplitudes reaching 0.3 m inside Kuwait Bay and 1.8 m along the southern coasts of Kuwait.

     

Analysis of Factors Influencing Simulations of the 1993 Hokkaido Nansei-Oki and 1964 Alaska Tsunamis

The purpose of this paper is to examine factorsinfluencing numerical simulations of tsunamis, andtheir implications for hazard mitigation. We focus ona specific finite element hydrodynamic model, chosenfor its role in the systematic development ofinundation maps for regions threatened primarily byCascadia Subduction Zone (CSZ) tsunamis. However, inpart for generality and in part because of poorhistorical records for CSZ events, we discuss here theperformance of the model in the context of betterdocumented past events with epicenters locatedelsewhere: the July 12, 1993 Hokkaido Nansei-Oki andthe March 28, 1964 Alaska tsunamis. Our analysisincludes the influence of grid refinement,interactions between tides and tsunamis, artificialenergy loss, and numerical parameterization. We showthat while the ability exists to reproduce pastevents, limitations remain in the modeling processthat should be accounted for in translating modelingresults into information for tsunami mitigation andresponse.     

Tsunami inundation in Napier, New Zealand, due to local earthquake sources

Deterministic analysis of local tsunami generated by subduction zone earthquakes demonstrates the potential for extensive inundation and building damage in Napier, New Zealand. We present the first high-resolution assessments of tsunami inundation in Napier based on full simulation from tsunami generation to inundation and demonstrate the potential variability of onshore impacts due to local earthquakes. In the most extreme scenario, rupture of the whole Hikurangi subduction margin, maximum onshore flow depth exceeds 8.0 m within 200 m of the shore and exceeds 5.0 m in the city centre, with high potential for major damage to buildings. Inundation due to single-segment or splay fault rupture is relatively limited despite the magnitudes of M_W 7.8 and greater. There is approximately 30 min available for evacuation of the inundation zone following a local rupture, and inundation could reach a maximum extent of 4 km. The central city is inundated by up to three waves, and Napier Port could be inundated repeatedly for 12 h. These new data on potential flow depth, arrival time and flow kinematics provide valuable information for tsunami education, exposure analysis and evacuation planning.     

Subaqueous landslide-triggered tsunami hazard for Lake Zurich,Switzerland

Subaqueous landslides can induce potentially damaging tsunamis. Tsunamis are not restricted to the marine environment, but have also been documented on lakes in Switzerland and worldwide. For Lake Zurich (central Switzerland), previous work documented multiple, assumedly earthquake-triggered landslides. However, no information about past tsunamis is available for Lake Zurich. In a back-analysis, we model tsunami scenarios as a consequence of the earthquake-triggered landslides in the past. Furthermore, on the basis of a recent map of the earthquake-triggered subaqueous landslide hazard, we present results of a tsunami hazard assessment. The subaqueous landslide progression, wave propagation and inundation are calculated with a combination of open source codes. Although no historic evidence of past tsunamis has been documented for Lake Zurich, a tsunami hazard exists. However, only earthquakes with long return periods are assumed to cause considerable tsunamis. An earthquake with an exceedance probability of 0.5% in 50 years (corresponding to an earthquake with a return period of 9975 years) is assumed to cause tsunamigenic landslides on most lateral slopes of Lake Zurich. A hypothetical tsunami for such an event would create damage especially along the shores of the central basin of Lake Zurich with estimated peak flow depths of up to ~?4.6 m. Our results suggest that for an earthquake with an exceedance probability of 10% in 50 years (i.e., mean return period of 475 years), no considerable tsunami hazard is estimated. Even for a worst-case scenario, the cities of Zurich and Rapperswil, located at the northern and southern ends of the lake, respectively, are assumed to experience very little damage. The presented first-order results of estimated wave heights and inundated zones provide valuable information on tsunami-prone areas that can be used for further investigations and mitigation measures.     

Tsunamis recorded in tide gauges at Costa Rica Pacific coast and their numerical modeling

Here we perform an inventory of tsunamis recorded by tide gauges in the Pacific coast of Costa Rica. This paper also reveals nine tsunami records that had not been published before, at Puntarenas tide gauge corresponding to the 1979 Colombia tsunami and at Quepos tide gauge corresponding to the 1985 Mexico twin tsunamis, the 2010, 2014 and 2015 Chile tsunamis, the 2006 Tonga tsunami, the 2011 Japan tsunami and the 2013 Solomon Islands tsunami. The original record of 1990 Cóbano tsunami at Quepos was digitized again at a higher resolution and re-processed. The arrival of 1979, 1985, 2006 and 2014 tsunamis to Costa Rica is not listed on tsunami catalogs. The maximum tsunami height obtained here after processing 1990, 2011 and 2013 records was higher than reported on catalogs. The opposite happened for the 2010 tsunami. Quepos gauge record for January 2007 was analyzed as it seemed to have registered the Kuril Islands tsunami, but the results were not conclusive due to the low sample rate and the small tsunami amplitude if any. All those eleven tsunamis were modeled and the results compared with the records. A good agreement was obtained for the Quepos gauge, although the modeled 2011 and 2013 tsunamis had a difference of 8 min on the arrival time. An acceptable agreement was obtained for the Puntarenas gauge for 1979 tsunami, considering at least the first 4 h of the marigram is lost.     

Magnetic fingerprint of tsunami-induced deposits in the Ixtapa–Zihuatanejo Area,Western Mexico

The Pacific coast of Mexico has repeatedly been exposed to destructive tsunamis. Recent studies have shown that rock magnetic methods can be a promising approach for identification of tsunami- or storm-induced deposits. We present new rock magnetic and anisotropy of magnetic susceptibility (AMS) results in order to distinguish tsunami deposits in the Ixtapa–Zihuatanejo area. The sampled, 80 cm-deep sequence is characterized by the presence of two anomalous sand beds within fine-grained coastal deposits. The lower bed is probably associated with the 14 March 1979 Petatlán earthquake (M _W = 7.6), whereas the second one formed during the 21 September 1985 Mexico earthquake (M _W = 8.1). Rock magnetic experiments discovered significant variations within the analysed sequence. Thermomagnetic curves reveal two types of behaviour: one in the upper part of the sequence, after the occurrence of the first tsunami, and the other in the lower part of the sequence, during that event and below. Analysis of hysteresis parameter ratios in a Day plot also allows us to distinguish two kinds of behaviour. The samples associated with the second tsunami plot in the pseudo-single-domain area. In contrast, specimens associated with the first tsunami and the time between both tsunamis display a very different trend, which can be ascribed to the production of a considerable amount of superparamagnetic grains, which might be due to pedogenic processes after the first tsunami. The studied profile is characterized by a sedimentary fabric with almost vertical minimum principal susceptibilities. The maximum susceptibility axis shows a declination angle D = 27°, suggesting a NNE flow direction which is the same for both tsunamis and normal currents. Standard AMS parameters display a significant enhancement within the transitional zone between both tsunamis. The study of rock magnetic parameters may represent a useful tool for the identification and understanding of tsunami deposits.     

Anisotropic path modeling to assess pedestrian-evacuation potential from Cascadia-related tsunamis in the US Pacific Northwest

Recent disasters highlight the threat that tsunamis pose to coastal communities. When developing tsunami-education efforts and vertical-evacuation strategies, emergency managers need to understand how much time it could take for a coastal population to reach higher ground before tsunami waves arrive. To improve efforts to model pedestrian evacuations from tsunamis, we examine the sensitivity of least-cost-distance models to variations in modeling approaches, data resolutions, and travel-rate assumptions. We base our observations on the assumption that an anisotropic approach that uses path-distance algorithms and accounts for variations in land cover and directionality in slope is the most realistic of an actual evacuation landscape. We focus our efforts on the Long Beach Peninsula in Washington (USA), where a substantial residential and tourist population is threatened by near-field tsunamis related to a potential Cascadia subduction zone earthquake. Results indicate thousands of people are located in areas where evacuations to higher ground will be difficult before arrival of the first tsunami wave. Deviations from anisotropic modeling assumptions substantially influence the amount of time likely needed to reach higher ground. Across the entire study, changes in resolution of elevation data has a greater impact on calculated travel times than changes in land-cover resolution. In particular areas, land-cover resolution had a substantial impact when travel-inhibiting waterways were not reflected in small-scale data. Changes in travel-speed parameters had a substantial impact also, suggesting the importance of public-health campaigns as a tsunami risk-reduction strategy.     

A geological record of multiple Pleistocene tsunami inundations in an oceanic island: The case of Maio,Cape Verde

In the Central Atlantic archipelagos – the Canaries, Cape Verde, Madeira and the Azores – tsunami hazard is often regarded as low, when compared with other extreme wave events such as hurricanes and storms. The geological record of many of these islands, however, suggests that tsunami hazard may be underestimated, notwithstanding being lower than in areas adjacent to subduction zones, such as the margins of the Pacific and Indian oceans. Moreover, tsunamis in oceanic islands are generally triggered by local large-scale volcanic flank collapses, for which little is known about their frequency, making it difficult to estimate the probability of a new occurrence. Part of the problem lies in the fact that tsunami deposits are usually difficult to date, and few islands in the world exhibit evidence for repeated tsunami inundation on a protracted timescale. This study reports on the presence of abundant tsunami deposits (conglomerates and sandstones) on Maio Island (Cape Verde) and discusses their stratigraphy, sedimentological characteristics, probable age and tsunamigenic source. Observations indicate that four distinct inundation events of variable magnitude took place during the Pleistocene. One of the tsunami deposits yielded a high-confidence U/Th age of 78·8 ± 0·9 ka, which overlaps within error with the 73 ± 7 ka age proposed for Fogo volcano's flank collapse, an event known to have had a significant tsunami impact on nearby Santiago Island. This shows that the Fogo tsunami also impacted Maio, resulting in runups in excess of 60 m above coeval sea-level at ca 120 km from the source. Two older deposits, possibly linked to recurrent flank collapses of the Tope de Coroa volcano in Santo Antão Island, yielded lower-confidence ages of 479 to 390 ka and 360 to 304 ka. A younger deposit (<78 ka) remains undated. In summary, the geological record of Maio exhibits well-preserved evidence of repeated tsunami inundation, reinforcing the notion that tsunami hazard is not so low at volcanic archipelagos featuring prominent and highly-active volcanoes such as in Cape Verde.     

Probabilistic tsunami hazard assessment along Oman coast from submarine earthquakes in the Makran subduction zone

The Sultanate of Oman is among the Indian Ocean countries that were subjected to at least two confirmed tsunamis during the twentieth and twenty-first centuries: the 1945 tsunami due to an earthquake in the Makran subduction zone in the Sea of Oman (near-regional field tsunami) and the Indian Ocean tsunami in 2004, caused by an earthquake from the Andaman Sumatra subduction zone (far - field tsunami). In this paper, we present a probabilistic tsunami hazard assessment for the entire coast of Oman from tectonic sources generated along the Makran subduction zone. The tsunami hazard is assessed taking into account the contribution of small- and large-event magnitudes. Results of the earthquake recurrence rate studies and the tsunami numerical modeling for different magnitudes were used through a logic-tree to estimate the tsunami hazard probabilities. We derive probability hazard exceedance maps for the Omani coast considering the exposure times of 100, 250, 500, and 1000 years. The hazard maps consist of computing the likelihood that tsunami waves exceed a specific amplitude. We find that the probability that a maximum wave amplitude exceeds 1 m somewhere along the coast of Oman reaches, respectively, 0.7 and 0.85 for 100 and 250 exposure times, and it is up to 1 for 500 and 1000 years of exposure times. These probability values decrease significantly toward the southern coast of Oman where the tsunami impact, from the earthquakes generated at Makran subduction zone, is low.     

The hydrodynamics of landslide tsunamis: current analytical models and future research directions

Landslide-generated tsunamis are lesser-known yet equally destructive than earthquake tsunamis. Indeed, the highest tsunami wave recorded in recent history was generated by a landslide in Lituya Bay (Alaska, July 9, 1958) and produced run-up in excess of 400 m. In this paper, we review the state of the art of landslide tsunami analytical modelling. Within the framework of a linearised shallow-water theory, we illustrate the dynamics of landslide tsunami generation and propagation along beaches and around islands. Finally, we highlight some intriguing new directions in the analytical modelling of landslide tsunamis to support early warning systems.