Near-field Tsunami Research Articles

NEAR-FIELD TSUNAMI FORECASTING BASED ON A TSUNAMI RUN-UP RESPONSE FUNCTION

Since near-field-generated tsunamis can arrive within a few minutes to coastal communities and cause immense damage to life and property, tsunami forecasting systems should provide not only accurate but also rapid tsunami run-up estimates. For this reason, most of the tsunami forecasting systems rely on pre-computed databases, which can forecast tsunamis rapidly by selecting the most closely matched scenario from the databases. However, earthquakes not included in the database can occur, and the resulting error in the tsunami forecast may be large for these earthquakes. In this study, we present a new method that can forecast near-field tsunami run-up estimates for any combination of earthquake fault parameters on a real topography in near real-time, hereafter called the Tsunami Run-up Response Function (TRRF).Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/tw1D29dDxmY

A novel agent-based model for tsunami evacuation simulation and risk assessment

Tsunami evacuation is an effective way to save lives from the near-field tsunami. Realistic evacuation simulation can provide valuable information for accurate evacuation risk assessment and effective evacuation planning. Agent-based modeling is ideal for tsunami evacuation simulation due to its capability of capturing the emergent phenomena and modeling the individual-level interactions among agents and the agents’ interactions with the environment. However, existing models usually neglect or simplify some important factors and/or mechanisms in tsunami evacuation. For example, uncertainties in seismic damages to the transportation network are not probabilistically considered (e.g., by simply removing the damaged links (roads/bridges) from the network). Typically a relatively small population (i.e., evacuees) is considered (due to computational challenges) while neglecting population mobility. These simplifications may lead to inaccurate estimation of evacuation risk. Usually, only single traffic mode (e.g., on foot or by car) is considered, while pedestrian speed adjustment and multi-modal evacuation (e.g., on foot and by car) are not considered concurrently. Also, pedestrian–vehicle interaction is usually neglected in the multi-modal evacuation. To address the above limitations, this study proposes a novel and more realistic agent-based tsunami evacuation model for tsunami evacuation simulation and risk assessment. Uncertainties in seismic damages to all links in the transportation network as well as uncertainties in other evacuation parameters are explicitly modeled and considered. A novel and more realistic multi-modal evacuation model is proposed that explicitly considers the pedestrian–vehicle interaction, walking speed variability, and speed adjustment for both the pedestrian and car according to traffic density. In addition, several different population sizes are used to model population mobility and its impact on tsunami evacuation risk. The proposed model is applied within a simulation-based framework to assess the tsunami evacuation risk assessment for Seaside, Oregon.

Improvement of near-field tsunami forecasting method using ocean-bottom pressure sensor network (S-net)

Since the installation of a dense cabled observation network around the Japan Trench (S-net) by the Japanese government that includes 150 sensors, several tsunami forecasting methods that use the data collected from the ocean floor sensors were developed. One of such methods is the tsunami forecasting method which assimilates the data without any information of earthquakes. The tsunami forecasting method based on the assimilation of the ocean-bottom pressure data near the source area was developed by Tanioka in 2018. However, the method is too simple to be used for an actual station distribution of S-net. To overcome its limitation, we developed an interpolation method to generate the appropriate data at the equally spaced positions for the assimilation from the data observed at sensors in S-net. The method was numerically tested for two large underthrust fault models, a giant earthquake (Mw8.8) and the Nemuro-oki earthquake (Mw8.0) models. Those fault models off Hokkaido in Japan are expected to be ruptured in the future. The weighted interpolation method, in which weights of data are inversely proportional to the square of the distance, showed good results for the tsunami forecast method with the data assimilation. Furthermore, results indicated that the method is applicable to the actual observed data at the S-net stations. The only limitation of the weighted interpolation method is that the computed tsunami wavelengths tend to be longer than the actual tsunamis wavelength.

Rapid prediction of alongshore run-up distribution from near-field tsunamis

Rapid prediction of the spatial distribution of the run-up from near-field tsunamis is critically important for tsunami hazard characterization. Even though significant advances have been made over the last decade, physics-based numerical models are still computationally intensive. Here, we present a response surface methodology (RSM)-based model called the tsunami run-up response function (TRRF). Derived from a discrete set of tsunami simulations, TRRF can produce a rapid prediction of a near-field tsunami run-up distribution that takes into account the influence of variable local topographic and bathymetric characteristics in a given region. This new method reduces the number of simulations required to build an RSM model by separately modeling the leading order contribution and the residual part of the tsunami run-up distribution. Using the northern region of Puerto Rico as a case study, we investigated the performance (accuracy, computational time) of the TRRF. The results reveal that the TRRF achieves reliable prediction while reducing the prediction time by six orders of magnitude (computational time: $$< 1$$ s per earthquake).

Tsunami Alert Efficiency in the Eastern Mediterranean Sea: The 2 May 2020 Earthquake (Mw6.6) and Near-Field Tsunami South of Crete (Greece)

The Mediterranean tsunami warning system is based on national monitoring centers (Tsunami Service Providers, TSPs) and operates under the IOC/UNESCO umbrella. For the first time we evaluate in depth the system’s performance for improving its operational effectiveness in conditions of extremely narrow time frames due to the near-field tsunami sources. At time 10 (± 2) min from the origin time, to, of the 2 May 2020 (Mw6.6) earthquake in Crete, the Greek, Italian and Turkish TSPs sent alerts to civil protection subscribers. A small tsunami (amplitude ~16 cm a.m.s.l.) of magnitude Mt6.8, arriving at south Crete in ~17 min from to, was documented from tide-gauge records and macroscopic observations. The analysis of the upstream alert messages showed that the tsunami alert efficiency is not adequate, since (1) earthquake parameters of low accuracy were used for the initial message, (2) alerts were issued after some forecasted wave arrival times had expired, (3) alert messages are characterized by various discrepancies and uncertainties. Our calculations showed that the upstream component improves if the alert time is shortened by a few minutes and the initial earthquake parameters are more accurate. Very late procedures were noted in the Greek civil protection downstream component, thus rendering response actions useless. In Israel, a bit more time was available to the authorities for decision making. A drastic improvement of the downstream component is needed to achieve timely alerting for local authorities and communities.

Comparative Analysis of Triggers for Evacuation during Recent Tsunami Events

AbstractIn the case of a near-field tsunami event, coastal residents must quickly become aware of the potential danger of a tsunami taking place and start taking actions to evacuate. The present pa...

Modeling pedestrian evacuation for near-field tsunamis fusing ALCD and agent-based approaches: A case study of Rincón, PR

Phenomena like tsunamis cannot be predicted, and simulation models are continuously being used in an attempt to understand how individuals will react in an emergency evacuation event. More specifically, pedestrian evacuation simulation can be used to better understand how pedestrians will escape an at-risk area. This work presents a pedestrian evacuation model (PEM) for the municipality of Rincón, Puerto Rico. This PEM provides insight on the vulnerability of Rincón to tsunamis using an iterative, optimization-based algorithm that fuses anisotropic least cost distance (ALCD) and agent-based (AB) approaches. This work advances the ALCD literature by providing a computationally-feasible PEM implementation capable of: (1) strategically initializing the location of pedestrians based on infrastructure and land use considerations, (2) managing individual as well as group-based evacuation, (3) assigning evacuation speeds and responses using probability and machine learning approaches, and (4) penalizing evacuation times using fatigue and reaction delays. The results of this PEM will provide emergency managers with a more realistic depiction of the time to reach safety using a systematic framework. Results, based on the worst-case scenario, indicate that 32.44% of the population in the tsunami evacuation zone (TEZ) would reach safety under 5 min, 41.96% between 5 and 15 min, and 25.60% would require more than 15 min. Unless effective public policy and mitigation strategies take place, the aftermath of a tsunami that inundates the Rincón coastline in less than 5 min could amount to up to 3312 casualties or 68% of the population in the TEZ.

Tsunami evacuation analysis in the urban built environment: a multi-scale perspective through two modeling approaches in Viña del Mar, Chile

ABSTRACT In the case of near-field tsunami emergencies, evacuation is considered the most important and effective method to save human lives. While significant efforts have been carried out to examine tsunami evacuation within the urban built environment, challenges remain on delivering a more detailed examination of the latter’s suitability for this task, and on addressing different scales of analysis. Along these lines, this paper draws upon a multi-scale framework for examining resilience of the urban form, to carry out a multi-scale tsunami evacuation analysis of the Great Valparaíso Metropolitan Area (GVMA) and the city of Viña del Mar, Chile, supported by both LCD and agent-based modeling approaches. The results show a significant macro-scale tsunami exposure of some areas in the territory, particularly in the Población Vergara and downtown neighborhoods. In line with this, the meso-scale evacuation analysis shows moderate escape rates (as low as 61.4%) in these areas. Moreover, the comparison between the models’ outcomes show that micro-scale vulnerabilities can potentially increase evacuation travel times by roughly 11%. These results, however, are noticeably dependent on the modeling choice.

A study of people-centered early warning system in the face of near-field tsunami risk for Indonesian coastal cities

PurposeThis study aims to identify the gaps in current policy and propose a viable framework for policy improvement regarding people-centered tsunami early warning chain in Padang City. The objectives are: to describe the gaps and flaws in the current policy regarding local tsunami early warning chain, to identify potential actors to be involved in the tsunami early warning chain and to assess the roles and capacity of actors, and their potential for involvement in early warning.Design/methodology/approachThis study is an exploratory study using social network analysis (SNA) on regulations and other legal documents, and primary data sources from a focus group discussion and semi-structured interviews.FindingsThe study found that the existed regulation lacks extension nodes to relay warnings to the populations at risk, often referred to as “the last mile.” Moreover, receiving warning information from both formal and informal sources is important to mobilize people evacuation more effectively during an emergency. The study found that mosque communities and disaster preparedness leaders are the potential actors who should be involved in the local early warning chain.Practical implicationsThe research findings were presented as a recommendation to Padang City Government and have been legalized as the new tsunami early warning chain procedure in the Padang City Mayor Regulation 19/2018.Originality/valueThis research investigated local tsunami early warning dissemination in Padang City using SNA. The study demonstrates a close collaboration between researchers, practitioners and the community.

Tsunami hazard assessment in the Makran subduction zone

The lack of offshore seismic data caused uncertainties associated to understating the behavior of future tsunamigenic earthquakes in the Makran Subduction Zone (MSZ). Future tsunamigenic events in the MSZ may trigger significant near-field tsunamis. Run-up heights in the near-field are controlled by the heterogeneity of slip over the rupture area. Considering a non-planar geometry for the Makran subduction zone, a range of random k^{-2} slip models were generated to hypothesize rupturing on the fault zone. We model tsunamis numerically and assess probabilistic tsunami hazard in the near-field for all synthetic scenarios. The main affected areas by tsunami waves are the area between Jask and Ormara along the shorelines of Iran and Pakistan and the area between Muscat and Sur along the Oman coastline. The maximum peak-run-up along the shores of Iran and Pakistan is about 16 m and about 12 m for the Oman shoreline. The slip distributions control the run-up along the Makran coastlines. The dependency of run-up to the heterogeneity of slip is higher in the most impacted areas. Those areas are more vulnerable to tsunami hazard than other areas.

Near-real time tsunami inundation forecast for Central America : case study of the 1992 Nicaragua tsunami earthquake

ABSTRACT A near-field tsunami inundation forecast method (NearTIF) for the Pacific coast of Central America is developed and tested on the basis of the 1992 Nicaragua tsunami earthquake case. The appropriate source model of the 1992 Nicaragua earthquake, estimated using the W-phase inversion with a depth dependent rigidity curve from a previous study, is used as a reference model to test the proposed NearTIF method. The tsunami inundation along the Pacific coast of Nicaragua is computed from the reference model of the 1992 Nicaragua earthquake. The tsunami inundation obtained using the NearTIF method matches the tsunami inundations computed from the reference model. The tsunami heights and the tsunami inundation of the 1992 Nicaragua tsunami surveyed by a previous study are roughly matched by the tsunami inundations obtained using the NearTIF method in this study. Although the computational time for the tsunami inundation from the reference source model is about 95 min, the computational time plus the database search time for the NearTIF method is approximately 2–4 min. The method presented in this study can be used as a near-real time tsunami inundation forecast method for the Pacific coast of Central America.

Fault model of the 2012 doublet earthquake, near the up-dip end of the 2011 Tohoku-Oki earthquake, based on a near-field tsunami: implications for intraplate stress state

On December 7, 2012, an earthquake occurred within the Pacific Plate near the Japan Trench, which was composed of deep reverse- and shallow normal-faulting subevents (Mw 7.2 and 7.1, respectively) with a time interval of ~10 s. It had been known that the stress state within the plate was characterized by shallow tensile and deep horizontal compressional stresses due to the bending of the plate (bending stress). This study estimates the fault model of the doublet earthquake utilizing tsunami, teleseismic, and aftershock data and discusses the stress state within the incoming plate and spatiotemporal changes seen in it after the 2011 Tohoku-Oki earthquake. We obtained the vertical extents of the fault planes of deep and shallow subevents as ~45–70 km and ~5 (the seafloor)–35 km, respectively. The down-dip edge of the shallow normal-faulting seismic zone (~30–35 km) deepened significantly compared to what it was in 2007 (~25 km). However, a quantitative comparison of the brittle strength and bending stress suggested that the change in stress after the Tohoku-Oki earthquake was too small to deepen the down-dip end of the seismicity by ~10 km. To explain the seismicity that occurred at a depth of ~30–35 km, the frictional coefficient in the normal-faulting depth range required would have had to be ~0.07 ≤ μ ≤ ~0.2, which is significantly smaller than the typical friction coefficient. This suggests the infiltration of pore fluid along the bending faults, down to ~30–35 km. It is considered that the plate had already yielded to a depth of ~35 km before 2011 and that the seismicity of the area was reactivated by the increase in stress from the Tohoku-Oki earthquake.

Understanding the Multimodal Evacuation Behavior for a Near-Field Tsunami

This paper presents an agent-based tsunami evacuation modeling (ABTEM) framework in Netlogo to analyze the impact of various multimodal evacuation behaviors on life safety for a near-field tsunami. The objective of this work is to investigate how: milling time, choice of modes (i.e., walking and automobile), and critical variables involved in an evacuation scenario (e.g., walking, driving speed), affect life safety. Using the city of Seaside, Oregon, which is one of the most vulnerable cities on the Oregon coast, as a study site, different evacuation scenarios are included in the model to assess the impact of parameters involved on the mortality rate in a tsunami evacuation event. The results show that: choice of evacuation mode strongly and non-linearly influences the expected number of casualties; use of vehicles leads to the creation of congestion and bottlenecks, and thus, higher mortality rate; the mortality rate is strongly correlated with milling time; and the mortality rate is sensitive to the variations in average walking speed of the population. The results will help emergency managers, community leaders, and city and state agencies in their decision-making process for creating effective and efficient evacuation plans to increase life safety and community resilience.

Performance-Based Tsunami Engineering for Risk Assessment of Structures Subjected to Multi-Hazards: Tsunami following Earthquake

ABSTRACT Tsunamis are low-probability high-consequence events, usually caused by an earthquake in the ocean and can result in high casualty rates and billions of dollars in damage. Tsunamis can be divided into two main categories: near-field and far-field tsunamis, based on the location of their origin with respect to the site of interest. To perform risk assessment of communities subjected to tsunamis, the current approach would be to use empirical data from historical events, making the data site specific. Recently, researchers have developed approaches to estimate the risk of structures subjected to far-field earthquake generated tsunamis using a simulated tsunami force on a structure numerically. However, for near-field tsunamis, ground motions caused by the earthquake will reach the structure earlier than the tsunami, damaging the structure, which can substantially impair its structural performance in the following tsunami. The multi-hazard case of tsunami following earthquake is discussed herein and a physics-based approach to estimate the risk of structures subjected to them is presented. An illustrative example is presented to elaborate the methodology for a steel building. Successive nonlinear analyses are used to develop fragility functions based on joint earthquake-tsunami intensity measures (spectral acceleration-flow depth-flow velocity). These functions are used in combination with hazard analysis of a specific location to obtain loss estimates. Three different approaches were used for this process and the results showed that the use of the joint three intensity-measure fragilities is essential for the accuracy when estimating damage or structural loss and neglecting their interaction results in substantial errors.

Large tsunamis reset growth of massive corals

Corals at Ishigaki Island, Japan, are characterized by their high species diversity. Not only are they struck by storm waves generated annually by typhoons, the corals, especially the massive ones, in the fringing reef were buffeted by huge tsunami waves with a run-up height of ca. 30 m in 1771 Meiwa tsunami and its predecessors at few hundred-year intervals. We present field survey and numerical results demonstrating that such near-field large tsunamis could have reset the growth of massive corals, a phenomenon which large typhoons have not caused. Our field survey revealed that the massive corals in the lagoon are not attached to the bedrock but are instead located on the sandy sea bottom. Therefore, those are movable of sufficiently large wave inundated in the lagoon. Our numerical results further showed that the maximum velocity of the tsunami at the reef edge, calculable as < 21.2 m/s at the study area, is still high in the shallow lagoon, perhaps generating sufficiently strong hydrodynamic force to devastate the massive corals in the shallow lagoon entirely, as well as some presumed damages on tabular and branching corals on the reef crest and reef slope. This numerical result is consistent with the observed fact that even a 9-m long Porites boulder (about 220 t) was cast ashore by the 1771 tsunami. The sizes of the presently living massive corals of Porites spp. are consistent with our hypothesis that they started to grow after the latest 1771 tsunami event. At the coral reefs of high tsunami-risk countries, severe destruction of corals by large tsunami waves should be considered for their growth history because, depending on the bathymetry, coral characteristics, and tsunami hydrodynamic features, tsunamis can radically alter coral habitats.

Examining the Impact of Risk Perception on the Accuracy of Anisotropic, Least-Cost Path Distance Approaches for Estimating the Evacuation Potential for Near-Field Tsunamis

Coastal hazards that can strike with little or no warning, such as tsunamis, are problematic in terms of population exposure and the threat of loss of life. With projected increases in coastal populations, exposure is likely to increase among these communities. For near-field tsunamis, the evacuation window can be as little as 15 to 20 min, and evacuation can be problematic for numerous reasons, such as population demographics, limited road networks, local topographic constraints, lack of proper education, and misaligned risk perception of the general populace. It is therefore critical for tsunami evacuation planning and education to be highly effective. To address this need, we employed a participatory mapping approach to explore potential evacuation enhancement by evaluating existing least-cost path pedestrian evacuation models, perception of landscape constraints, and additional risks to nearfield tsunamis in Aberdeen, Washington. Stakeholders were tasked with drawing their understood evacuation routes on maps which were analyzed for approximate time to reach safety and compared to least-cost path pedestrian evacuation models. A quantitative analysis of selected evacuation pathways revealed participants consistently overestimated evacuation time and did not follow modeled least-cost pathways. The results suggest traditional modeling (e.g., least-cost path and agent-based models) underestimate travel time to safety. Thus, there is a need for additional outreach, notably in communities where traditional evacuation models might create a false sense of security.

The Role of Built Environment's Physical Urban Form in Supporting Rapid Tsunami Evacuations: Using Computer-Based Models and Real-World Data as Examination Tools

Cities are increasingly becoming hot-spots for nature-originated disasters. While the role of the urban built environment in fostering disaster resilience has been recognized for some time, it has been difficult to translate this potential into practice. This is especially challenging in the case of rapid onset crises such as near-field tsunamis when appropriate urban forms have to support the populations’ ability to autonomously carry out safe and timely responses. In this respect, much of current research remains focused on large-scale elements of urban configuration (streets, squares, parks, etc.) through which people move during an emergency. In contrast, the critical micro-scale of evacuees’ experiences within the built environment is not commonly examined. This paper addresses this shortfall through a macro- and micro-scale analysis of a near-field tsunami scenario affecting the city of Vina del Mar, Chile, including a mixed-methods approach that combines computer-based models and fieldwork. The results show significant macro-scale tsunami vulnerability throughout major areas of the city, which nonetheless could be mitigated by existing nearby high ground and an urban form that allows short evacuation times. However, micro-scale outcomes show comparatively deficient spatial conditions that during an emergency might lead to dangerous outcomes including bottlenecks, falls and panic. Vertical evacuation, in turn, is confirmed as a suitable option for reducing vulnerability, but further examination of each shelter’s characteristics is required.

An agent-based vertical evacuation model for a near-field tsunami: Choice behavior, logical shelter locations, and life safety

In the event of near-field tsunamis, vertical evacuation can be an alternative protective action to horizontal evacuation. The objective of this paper is to present an agent-based modeling (ABM) framework to evaluate vertical evacuation behavior and shelter locations for a near-field tsunami hazard from a Magnitude 9.0 Cascadia Subduction Zone (CSZ) earthquake. The expected mortality rate depending on the location of the vertical evacuation shelter (VES) has been chosen as the primary criterion to assess the effectiveness of the vertical evacuation. In addition, maximum tsunami wave height and the vertical evacuation behavior changes with changes in the placement of the VES have been assessed from a constraint point of view. The results revealed that (1) the choice of VES locations will directly impact the proportion of the people who evacuate vertically; (2) The percentage of people who evacuate vertically exponentially drops as the shelter gets farther from the population centroid; (3) the location of shelter significantly impacts the total mortality rates; (4) improvements in evacuees’ mobility, such as faster walking speed or shorter milling time, will significantly reduce mortality rate and expand the area of choices for VES locations; and (5) when more people choose to evacuate vertically, the total mortality rate reduces notably. However, wrong placement of VES, and at the same time promoting vertical evacuation behavior can result in catastrophic mortality rates. In addition, a study on the impact of the distance of the VES to the ocean, to the population centroid, and to the horizontal shelters outside of the inundation zone, on the total mortality rate and the evacuation efficiency has been performed. This work reveals the non-linear correlation between the aforementioned characteristics of the VES on the expected mortality rate. The results of this research provide an evidence-driven vertical evacuation modeling framework to guide decision makers at city, state, and federal level to understand the dynamics of vertical evacuation behavior and choice of vertical evacuation shelter locations for a community.

Pohutukawa bio-shield on the coast of New Zealand as a tsunami mitigation strategy

New Zealand is vulnerable to both far-field and near-field tsunamis. The Pohutukawa tree (Metrosideros excelsa), a native tree to New Zealand, is commonly found in the New Zealand coastal environment. This tree has strong roots that grow deep into the ground, as well as have a wide spreading branching system. It is considered that these characteristics would enable the Pohutukawa tree to act effectively as a bio-shield against tsunamis in New Zealand. However, there is no research to show its capability in reducing the hydrodynamic force of a tsunami. Field investigation of the Pohutukawa tree in Maraetai Beach, and the use of a one-dimensional depth-integrated shallow water numerical model, was conducted to assess the capability of a Pohutukawa bio-shield against a tsunami wave. A Pohutukawa bio-shield of 35 m width against a tsunami wave of height of 3.5 m at shoreline with wave period of 20 min reduced the hydrodynamic force of a tsunami directly behind the bio-shield by approximately 21%. This study, therefore, elucidates the capability of a Pohutukawa bio-shield as a tsunami mitigation strategy.

Pedestrian evacuation modelling of a Canadian West Coast community from a near-field Tsunami event

Large near-field tsunamis pose a significant threat to the Canadian West Coast due to its proximity to the circum-Pacific belt where a significant tsunami-inducing earthquake event from the Cascadia subduction zone is expected. This study investigated the risks associated with such an event in terms of pedestrian evacuation needs and plans for the Town of Tofino, a small community located on the West Coast of Vancouver Island. The population-at-risk within the hazard zone and its ability to evacuate to safety is evaluated using anisotropic path-distance modelling. Mitigation measures, such as vertical evacuation buildings, are quantitatively evaluated. Site-specific inundation modelling was not performed as part of this study; tsunami hazard and safe zones were computed using a range of run-ups varying between 3 and 25 m. It was established that up to 80% of the population is within the maximum hazard zone considered. This evacuation modelling exercise indicates that a maximum of 13% of the population would have insufficient time to reach safety when using a mobility-impaired ambulatory speed. The use of three vertical evacuation buildings can reduce the risk of losing population in this category by 99%. Although some conservative assumptions were used (vertical datum at higher high water, reductions in safe zones by generalization process and mobility-impaired evacuation speeds), the evacuation potential is likely overestimated due to the coarseness of the topographic data used in the evacuation modelling and from an overestimated first wave arrival time. This is the first Canadian study which used anisotropic evacuation modelling to evaluate the vulnerability of a Canadian community to tsunami inundation.