Dr. Aranguiz-Muñoz, Rafael

The destructive potential of a massive tsunami is not only related to society’s response capacity and evacuation plans, but also to the urban morphology and land cover. The Boca Sur neigh- borhood is one of the areas in central Chile that is most exposed to tsunamis, and it is framed in the context of increasing urban growth. Faced with the worst tsunami scenario (earthquake Mw = 9.0), residents’ evacuation potential is analyzed by using a least-cost-distance model, and two scenarios of land cover change are considered (2002 and 2018). Presently, the sector’s urban areas have grown by 83%, therefore its population has also grown. The evacuation times consider an average walking speed (1.22 m/s) for both years (2002 and 2018). This analysis establishes that over 40% of the study area is more than 60 min away from the safe zones established by authorities. This differs greatly from the 22-min average tsunami arrival time. Moreover, 19% of the area could not be evacuated in less than 30 min. Therefore, it can be concluded that the increased urbanization in the coastal area has not improved travel times, as urban planning did not consider the optimization of evacuation times to the designated safe zones. In this study, we propose new safe zones that would help reducing evacuation times to 30 min. In addition to the area’s high tsunami risk, the evacuated population’s strong travel time limitations are added, prioritizing the incorporation of social and urban resilience elements that help to effectively reduce the risk of disaster, by using land-use planning and community work.

Se evalúa el riesgo de inundación por tsunami en la localidad de Boca Sur, comuna de San Pedro de La Paz (37ºS), Región del Biobío. Se consideró un escenario extremo de tsunami generado por un sismo de magnitud Mw= 9.0. La inundación por tsunami se obtuvo mediante modelación numérica usando el código NEOWAVE con 4 mallas anidadas de diferente resolución espacial y topo-batimetría de detalle. El análisis de vulnerabilidad consideró las dimensiones física, socioeconómica y organizacional, con datos obtenidos a través del Instituto Nacional de Estadística a nivel de manzana censal y encuestas a la población. Se determinó que el primer tren de ondas llega a la costa luego de 22 minutos de ocurrido el terremoto, alcanzando la cota de 5 msnm y alturas de fl ujo de hasta 2 m. Los factores de vulnerabilidad que explican el riesgo se asociaron a una alta precariedad de la vivienda, bajo nivel de bienestar social, alta densidad poblacional y bajo nivel de organización comunitaria de la población en caso de evacuación frente a tsunamis.

A GIS analysis on the urbanization spread (1725 to present) in the Greater Concepcion Region demonstrates that increasing the tsunami disaster resilience of coastal communities is a pressing issue in Chile, due to the continuous presence of human settlements in tsunami-prone areas. This research assesses the contribution of “hard-infrastructure” for increasing disaster resilience within five coastal towns (Dichato, Coliumo, Tumbes, Penco and Talcahuano). Structures were considered beneficial to resilience-building if they had multi-functional properties which aided in the social and/or economic recovery of the affected community. The assessment was carried out through in-depth interviews with local inhabitants until the point of data-saturation. Results reveal that all surveyed coastal towns had hard-infrastructure that was built after 2010, in the form of promenades and elevated housing. The former structures contributed positively to building economic resilience in Dichato, Talchuano and Penco, through the promotion of tourism and small-scale fishing activities. However, the physical design of the elevated houses was found to only facilitate recovery of community economic functions in Tumbes, while causing strain on the social fabric and possibly hindering tsunami evacuation in all other study sites. The mixed contribution of hard-infrastructure to coastal resilience highlights the need for the de-centralization of planning and reconstruction processes for a successful contextualization of the issue.

In 2015 and 2017 unusual ocean and atmospheric conditions produced many years’ worth of rainfall in short periods over Northern Chile’s Atacama Desert, resulting in catastrophic flooding in the town of Chañaral. However, the town is not only at risk of fluvial flooding, it is also at risk of tsunamis. Through a community mapping exercise, the authors attempted to establish the level of community awareness about tsunamis, and contrasted it with that of other types of water-related hazards facing the town (namely that of flooding due to high intensity rain). This was then compared with the results of field surveys and tsunami hazard simulations, indicating than overall the community appears to have better awareness than authorities about the threat posed by these types of events. The authors thus concluded that in cases when the community has a high level of hazard awareness (which in the case of Chile was the result of traditional knowledge being transmitted from previous generations) it would be advantageous to include them in discussions on how to improve disaster resilience.

The Sendai Framework for Disaster Risk Reduction emphasizes the need to rebuild better after a disaster to ensure that the at-risk communities can withstand a similar or stronger shock in the future. In the present work, the authors analyzed the reconstruction paths through a comparative analysis of the perspective of a community in Japan and another in Chile, and their respective local governments. While both countries are at risk to tsunamis, they follow different reconstruction philosophies. Data was gathered through key informant interviews of community members and local government officials, by adapting and modifying the Building Resilience to Adapt to Climate Extremes and Disasters (BRACED) 3As framework to a tsunami scenario. The 3As represent anticipatory, adaptive, and absorptive capacities as well as transformative capacities and respondents were asked to rate this according to their perspectives. It was found that while both communities perceive that much is to be done in recovery, Kirikiri has a more holistic and similar perspective of the recovery with their government officials as compared to Dichato. This shows that community reconstruction and recovery from a disaster requires a holistic participation and understanding.

On September 28, 2018, a large earthquake and its accompanying tsunami waves caused severe damage to the coastal area of Palu Bay, in the central western part of Sulawesi Island, Indonesia. To clarify the distribution of tsunami inundation and run-up heights, and damage to coastal communities due to the tsunami, the authors conducted a field survey 1 month after the event. In the inner part of Palu Bay tsunami inundation and run-up heights of more than 4 m were measured at many locations, and severe damage by the tsunami to coastal low-lying settlements was observed. In the areas to the north of the bay and around its entrance the tsunami inundation and run-up heights were lower than in the inner part of the bay. The tsunami inundation distance depended on the topographical features of coastal areas. The southern shore of the bay experienced a longer inundation distance than other shores, though generally severe damage to houses was limited to within around 200 m from the shoreline. The main lessons that can be learnt from the present event are also discussed.

This study assesses physical infrastructure vulnerability for infrastructure network components exposed during the 2015 Illapel tsunami in Coquimbo, Chile. We analyse road and utility pole vulnerability to damage, based on interpolated and simulated tsunami hazard intensity (flow depth, flow velocity, hydrodynamic force and momentum flux) and network component characteristics. A Random Forest Model and Spearman’s Rank correlation test are applied to analyse variable importance and monotonic relationships, with respect to damage, between tsunami hazards and network component attributes. These models and tests reveal that flow depth correlates higher with damage, relative to flow velocity, hydrodynamic force and momentum flux. Scour (for roads and utility poles) and debris strikes (for utility poles) are strongly correlated with damage. A cumulative link model methodology is used to fit fragility curves. These fragility curves reveal that, in response to flow depth, Coquimbo roads have higher vulnerability than those analysed in previous tsunami event studies, while utility poles demonstrate lower vulnerability than with previous studies. Although we identify tsunami flow depth as the most important hydrodynamic hazard intensity metric, for causing road and utility pole damage, multiple characteristics correlate with damage and should also be considered when classifying infrastructure damage levels.

Tsunami inundation maps are crucial for understanding the impact of tsunamis and planning mitigation measures. Our research focuses on creating a database of stochastic tsunami scenarios along the Chilean subduction zone and probabilistic inundation maps for 11 coastal cities. We divided the Chile-Perú subduction zone into four seismic segments based on historical seismicity. Stochastic rupture scenarios, ranging from 8.0 to 9.6 magnitudes, were generated using the Karhunen-Loeve expansion. The Stochastic Reduced Order Model (SROM) helped select representative tsunami scenarios for each segment and magnitude bin. We then used the NEOWAVE model to simulate these scenarios to an inundation level, creating probabilistic tsunami maps for various return periods. Our findings reveal that local geography significantly influences tsunami inundation, with some areas facing high inundation risks while others experience minimal impacts. As a result, a uniform planning and design criterion across the entire country is not advisable; site-specific studies are necessary. These probabilistic scenarios can provide tailored solutions for different Chilean coastal cities, enhancing their resilience. Additionally, this research marks the first comprehensive probabilistic tsunami hazard analysis for the Chilean coast, considering multiple seismic sources, marking a crucial step toward full tsunami risk assessment for coastal communities.

A cascading rainfall–landslide–tsunami event occurred on June 29th, 2022, in Todos los Santos Lake, located in southern Chile, affecting the tourist town of Petrohué. The event took place after several days of heavy rain during an extratropical cyclone. Important data were collected during a field survey, including hillslope 3D scans, lake–river bathymetry, orthomosaic photos, and an assessment of damage to public infrastructure. The analysis showed that the landslide had an estimated length, width, and depth of 175 m, 40 m, and 1.5 m, respectively, which resulted in a total volume of 10,500 m3. The underwater runout distance of the landslide was estimated at 40 m, with a final water depth of 12 m. The initial tsunami wave was observed to be ~1 m, and since the distance from the landslide to the town was ~500 m, an arrival time of ~1 min was observed. Despite the small tsunami amplitudes, the pedestrian bridge of the floating pontoon collapsed due to the flow current and vertical oscillations. The results of the numerical simulation of the tsunami supported the observed data. They showed that the impact of the tsunami was only in the near field and was influenced by the bathymetry, such that refraction and edge waves were observed. The landslide occurred in an area where previous debris flows took place in 2013 and 2015. The main finding of the present research is that the occurrences of this and previous landslides were controlled by the presence of the Liquiñe–Ofqui fault zone, which generates broad areas of structural damage, with mechanical and chemical weathering significantly reducing rock strength. These observations provide a warning regarding the susceptibility of similar regions to other trigger events such as earthquakes and rainfall. This recent landslide highlights the need for a more comprehensive hazard assessment, for which probabilistic analysis could be focused on large active strike-slip fault systems. It also highlights the importance of community awareness, particularly in areas where tourism and real estate speculation have significantly increased urban development.

A submarine eruption in Cumberland Bay, Robinson Crusoe Island, was reported by Thomas Sutcliffe, the former British Governor, shortly after the earthquake that struck the coast of Chile on 20 February 1835. This episode was described by Charles Darwin in his Voyage of the Beagle and extensive mention has been made since then, especially stimulated by a renowned painting by J.M. Rugendas. Because of the apparent causal relation, this event has also been widely cited as an example of remote tectonically triggered eruption. However, there are inconsistencies that pose doubts about the actual occurrence of an eruption. Here we present evidence against the hypothetical eruption based on both the absence of any geological evidence and a reinterpretation of the historical accounts. We first observe that no bathymetric anomaly is present immediately below the place of the depicted ‘eruptive column’. We also note the absence of any deposit or recent volcano morphology and then unravel some incompatibility between the expected volcanological parameters and the featured column. In addition, we analyse the historical records and conclude that they are compatible with a tsunami entering the bay. By means of numerical simulations we further demonstrate that the accounts well match with the expected behaviour of a distant earthquake-triggered tsunami. We infer that some tsunami-related processes (sound waves, rockfalls, lightning) may have been misunderstood at that time. The latter corresponds to the current knowledge of natural processes but also could have been deliberatively amplified in Sutcliffe’s report. Our multidisciplinary approach provides full consistent geographical evidence of a fact that did not happen. This finding is relevant from the hazard’s perspective, but also for the science of earthquakes and eruptions, or the knowledge of processes that control the late secondary volcanism at oceanic islands and seamounts.