Lisbon Earthquake Research Articles

Seismic vulnerability assessment and fragility analysis of pre-code masonry buildings in Portugal

Despite the fact that in recent years Portugal has not seen the occurrence of high-magnitude earthquakes, it remains threatened by these events due to its geographic location. Since the 1960s, reinforced concrete has been the most used material for new constructions; however, the historic urban centers are dominated by old unreinforced masonry (URM) buildings, which techniques and construction materials have evolved since the Great Lisbon earthquake that occurred in 1755 (Mw = 8.5). Given the presence of these buildings in areas of significant seismicity, extensive research is needed to assess the seismic risk and define mitigation policies. This kind of studies is often supported by empirical methods and based on expert judgment due to the high variability of the building stock and lack of information. The main purpose of this work is: (i) to provide analytical fragility curves, supported by nonlinear static analysis, for the entire population of old masonry buildings, built before the introduction of the first design code for building safety against earthquakes (RSSCS) in 1958; (ii) define vulnerability curves to be used by the technical community for seismic assessment of pre code URM buildings. The characterization of the building stock geometry and material properties is based on information previously collected, which was essential to define representative archetypes and typologies.

Cascade earthquake and tsunami hazard assessment: A deterministic perspective for engineering purposes

Preventive management strategies are evolving towards multi-hazard risk estimates. Commonly, the multi-hazard characterization is pursued following a probabilistic approach. However, scenario-based evaluations can provide complementary key insights of relevance to design critical facilities.In this paper, an alternative deterministic analysis was explored to characterize the cascade seismic and tsunami actions of a 1755-alike Great Lisbon Earthquake and Tsunami event oriented to the container terminal of Sines deep-water seaport, Portugal, which is in expansion to increase the current 2.3 million TEU capacity to 7.1 million TEU.The analysis accounts source, propagation and site effects uncertainties influencing the multi-hazard estimates for different structural configurations representing the different stages of the extension plans for the infrastructure.The target-hazard assessment assumes ground motion acceleration and tsunami hydrostatic and hydrodynamic quantities as explanatory variables, respectively obtained from ground motion prediction equations and non-linear Shallow-Water equations. The intensity measures inherent to each of the inextricable candidate sources, Scandidate, were characterized over 864 seismic and 144 tsunami simulations and then compared to key-thresholds to identify the scenarios with damaging potential, Seligible. The quantities of each Seligible were assessed varying the earthquake and tsunami intensity measures as leading measures to define a set of combined worst-case scenarios for the infrastructure, Sworst. The cascading loading patterns for structural design purposes are then derived following the European and North American code provisions for earthquake and tsunami actions, respectively.The prediction of the cascading loading pattern at the terminal container of the Sines port quantifies PGA around 0.37 g for a seismic displacement-controlled behavior and peaks of hydrostatic and hydrodynamic components values around 1000 kNm−1 for tsunami force-controlled behavior during both the inflow and outflow cycles. A brief correlation between indicative action values and structural resistance of the current constructive solution raises awareness for the high probability of structural collapse of the pile-supported wharf due to an extreme 1755-alike Great Lisbon Earthquake and Tsunami threat, which would disrupt the port's operations and compromise its role as lifeline structure in case of emergency.

Digital Survey and Structural Investigation on the Triumphal Arch of Caracalla in the Archaeological Site of Volubilis in Morocco: Retracing the Timeline of Collapses Occurred during the 18th Century Earthquake

ABSTRACT The Lisbon earthquake occurred in 1755, which affected Morocco seriously, provoked the collapse of the Triumphal arch of Caracalla in Volubilis. The currently visible monument is the result of the rebuilding carried out in 1930 by French restores. In this paper, the timeline of collapses caused by the subsequent seismic quakes is retraced aimed at estimating the lower bound of the intensity of the 18th century earthquake, based on structural investigations carried out on rigid-block and continuous FE models. The historical investigations and the digital survey carried out by the authors in 2017 served as the base of knowledge to drive the analyses. Results of the analyses of the two models are very comparable and provide that a low acceleration of 0.168 g was sufficient to provoke the collapse of the arch and explain the reason why the expected earthquake acceleration in the zone of the archaeological site of Volubilis provided by the current Moroccan seismic code is exactly 0.16 g. Therefore, with the purpose of assessing also the current seismic vulnerability of the arch, this result leads to state that the capacity is equal to the seismic demand, and, therefore, too low to ensure the safety in the case of un unexpected event.

Disasters and History: The Vulnerability and Resilience of Past Societies by Bas van Bavel et al.

On May 17, 2021, cyclone Tauktae made landfall in the state of Gujarat on the west coast of India. Classified as an extremely severe cyclonic storm by the Indian Meteorological Department, Tauktae resulted in at least 169 deaths and the displacement of more than 200,000 people. Its destructive force was boosted by India’s struggle with the second global wave of covid-19 at the time. Tauktae made landfall on the day when India recorded its second highest single-day death toll at the time. India had to deal with two disasters simultaneously, one meteorological-hydrological and one biological.Disasters and History helps us to understand such disasters by treating historical disasters as a laboratory “to test theories with relevance beyond particular time-space contexts” (43). The authors show what seemingly diverse events such as earthquakes, droughts, or epidemics have in common. Although varying considerably in both their causes and consequences, these disasters are all triggered by biophysical shocks and hazards. Whether a particular shock, or set of shocks, turns into a disaster depends on the social, economic, political, and cultural setting in which it occurs. Various pre-conditions make a society more or less vulnerable to these hazards. Moreover, the manner in which people react to these shocks, or fail to do so, determines the results. Hence, the two central concepts that this book features, as the subtitle clearly suggests, are vulnerability and resilience.The authors have gained extensive experience in researching historical disasters, both independently and collaboratively. Their combined effort allows them to cover the period from the fourteenth to the twenty-first century. The case studies that illustrate the core arguments of the book may be limited in number, but they aptly represent different types of disaster—The Black Death of 1348, the medieval and early modern North Sea floods, the Lisbon earthquake of 1755, the 1930s American Dust Bowl, the twentieth-century famines of Sub-Saharan Africa, and the tsunami in Japan that led to the Fukushima disaster.This book is, above all, an excellent guide to research about historical disasters; each entry in the table of contents could apply to the design of a distinct research project. Chapter 3, about materials and methods, is particularly helpful in this respect. When attempting to assess the severity of an initial ecological shock in the period before instrumental recording, scholars often faced difficulties in finding reliable evidence. Whenever direct recordings of hazards by historical contemporaries, such as those in English manorial accounts, are not available, the authors suggest a turn to “indirect recordings of processes and phenomena that were influenced by environmental conditions,” such as harvest accounts or registers of taxes and rents (44). Similarly, a lack of direct evidence about the severity of a disaster, such as mortality statistics, can find some compensation in a range of proxy data like parish registers or burial records.For scholars who approach disasters from an interdisciplinary perspective, the sub-chapter about combining historical data with sources from the natural sciences is highly instructive (53–57). The rapidly developing discipline of paleoclimatology—an obvious boon to scholars of historical disasters—has opened new windows onto climate history and extreme weather events in the past. The authors present both the possibilities and the limitations of paleoclimatic reconstructions. Although these data add an additional layer to the written records mentioned above, they still need to be viewed critically since they vary in their geographical coverage and temporal resolution. The relevance of Disasters and History to every conceivable disaster, whether past, present, or future, makes it an invaluable resource for interdisciplinary scholars of climate and environment.

Quantitative risk assessment in El-Jadida (Northern Atlantic Coast of Morocco) for a tsunami scenario equivalent to that of the 1755 Lisbon earthquake

The Atlantic coasts of Morocco are exposed to tsunami risk. Although this risk level is low because of the rarity of tsunamis in the region, a future event would be catastrophic for the Moroccan society and economy because of the numerous issues at stake. In this paper, bathymetric/topographic data and parameters of three known tsunamigenic faults (Marquês do Pombal Fault, Gorringe Bank Fault and Horseshoe Fault) were used to simulate a potential tsunami event in the city of El-Jadida (Morocco) using MIRONE software. The simulation results of the worst-case scenario were then exploited to perform a quantitative risk assessment, using demographic and economic input data. Results show that choosing the Horseshoe Fault as source of the simulated event produces the largest tsunamis; with maximum wave heights ranging from 10 to 27 m. These results are found to be consistent with historical records and computer model simulations from previous studies. Quantitative risk assessment results indicate that the city of El-Jadida is exposed to a high risk of loss of lifes and loss of property with values of the order of 34 lives/year and 14 M$/year, respectively. For this reason, we underline the dire need for the implementation of tsunami risk prevention and mitigation strategies that should prioritize the protection of high-risk areas of the city and its population from a possible future catastrophic event.

Tsunami coastal hazard along the US East Coast from coseismic sources in the Açores convergence zone and the Caribbean arc areas

Tsunami coastal hazard is modeled along the US East Coast (USEC), at a coarse regional (450 m) resolution, from coseismic sources located in the Açores Convergence Zone (ACZ) and the Puerto Rico Trench (PRT)/Caribbean Arc areas. While earlier work only considered probable maximum tsunamis, here we parameterize and simulate 18 coseismic sources, with magnitude M8-9 and return periods \(\sim\)70–2000 year, using seismo-tectonic and historical data. The largest sources in the ACZ are repeats of the 1755 M8.6-9 Lisbon earthquake and tsunami; other sources are hypothetical. In the ACZ, due to the limited data on faults, each source is parameterized with a single fault plane, while in the PRT, coseismic sources are parameterized based on fault segmentation established during a 2019 USGS workshop of experts, using 10–26 SIFT subfault planes (Gica et al. in NOAA Tech. Memo., OAR PMEL-139, 2008). Tsunamis are simulated for each source using the fully nonlinear and dispersive model FUNWAVE-TVD, in two levels of nested grids. At the considered scales, dispersion is shown to affect tsunami propagation. Coastal hazard is quantified by four metrics computed at many save points (\(\sim\)20–30 thousand) defined along the 5-m isobath (due to the coarse resolution), i.e., maximum (1) surface elevation, (2) current, (3) momentum force; and (4) travel time, representing flooding, navigation, structural, and evacuation hazards. Overall, the first three metrics are larger, the larger the source magnitude, and their alongshore variation shows similar patterns of higher/lower values, due to the shelf bathymetric control (refraction). The fourth metric mostly differs between sources from each area, but less so among sources from the same area; its inverse quantifies evacuation hazard. A 1–5 score is given to results for each metric, based on five intensity classes representing low, medium low, medium, high, and highest tsunami hazard. A novel tsunami intensity index is computed as a weighted average of these scores, allowing both a comparison among sources and a quantification of tsunami hazard as a function of their estimated return periods. In the most impacted areas of the USEC, the highest tsunami hazard in the 250–500-year return period range is commensurate with that posed by 100-year category 3–5 tropical cyclones, taking into account the larger current velocities and forces caused by tsunami waves. Results of this work could serve as a basis for a future regional Probabilistic Tsunami Hazard Analysis for the USEC, considering additional source types such as underwater landslides, volcanic flank collapse, and meteotsunamis, that were studied elsewhere.

La ermita de San Sebastián de Moguer

This paper analyzes the origins and historical, architectural and heritage evolution of the hermitage of San Sebasti?n (Moguer). We are facing one of the oldest specimens of Andalusia, built due to the links of the town with the American commerce and for the cult of the image of San Sebasti?n that is widespread in the provinces of Huelva and Seville during the following centuries. The study allows us to understand the political, economic and social changes of Moguer, originated by the different events that took place in this municipality: American bonding, Lisbon earthquake, French invasion, Civil War, etc. In the same way, the evolution of the thaumaturgical origins of the building to the reforms, adaptations, conservation and maintenance of the factory from the 17th century onwards with the attachment of the society to popular religiosity: the image of Jesus Nazarene.

The Horseshoe Abyssal plain Thrust could be the source of the 1755 Lisbon earthquake and tsunami

The southwest Iberia margin is widely believed to have hosted the 1755 Great Lisbon earthquake and ensuing tsunami, one of the most destructive natural events in European history. Here we combine geophysical data and numerical tsunami modelling to investigate the source and mechanism responsible for this event. We find that an intra-plate, lithospheric¬-scale thrust fault located at the Horseshoe Abyssal Plain coincides with the location and focal mechanisms of the largest regional earthquakes and is likely to have suitable dimensions and fault-rock properties to account for the magnitude of the 1755 event. We present tsunami simulations with this fault as the source, and find that they reproduce reported tsunami energy propagation patterns, arrival-times and run up heights more successfully than other modelled sources. We propose that a reverse dip-slip mechanism on the northwest verging Horseshoe Abyssal plain Thrust, combined with the two-state mechanical behaviour of serpentinite, is the most likely candidate for the source of the 1755 Great Lisbon earthquake and for other recent large regional earthquakes.

Suggestions on Improving the Seismic Performance of Portuguese Old ‘Pombalino’ Buildings

There was a destructive earthquake in Lisbon, 1755. After that earthquake people built ‘Pombalino’ masonry building in Lisbon downtown. As time goes by, these buildings need to be reinforced and refitted because of the degeneration of the elements, the requirements for seismic performance and the new functions these buildings should be adapted to. This paper aims to provide some suggestions on how to reinforce the ‘Pombalino’ building and improve the seismic performance. These three suggestions are discussed and concluded by the theoretical analysis of three kinds of reinforcement measures, which include strengthening the connections with FRP elements, pasting carbon fiber sheets to improve the shear strength of masonry, setting laminated rubber pad isolation system to improve the seismic performance and the advantages and feasibility of these suggestions. Considering the advantages of the FRP materials, which are discussed in the following paper, the FRP connecting elements, as well as carbon fiber sheets can be a good choice to replace the aging connecting elements. To improve the seismic performance of this building, laminated rubber pad isolation system can be installed to absorb the energy caused by earthquake and reinforce the degenerated piles footing.

Can Modeling the Geologic Record Contribute to Constraining the Tectonic Source of the 1755 CE Great Lisbon Earthquake?

AbstractThe precise location of the seismic source of 1755 CE Great Lisbon earthquake is still uncertain. The aim of this work is to use an onland sedimentary record in southern Portugal to test and validate seismic sources for the earthquake. To achieve this, tsunami deposit thicknesses from over 150 cores collected at Salgados in southern Portugal were compared to the results of a tsunami sediment transport model (Delft3D‐FLOW) that simulates tsunami propagation, inundation, erosion, and deposition. Five different hypothetical seismic sources were modeled with varying bed roughness coefficients to assess how well they reproduced observed patterns of tsunami deposit thicknesses and dune. Modeled and observed historical tsunami arrival times were also used to test different earthquake sources. Based on these comparisons, three modeled earthquake sources were able to reproduce the observed data, suggesting they should be regarded as somewhat more likely sources for the 1755 earthquake in contrast to four other modeled sources. The fault closest to shore (Marquês de Pombal) yielded the best correlations between model and observations.

And Yet It Quakes! (Nietzsche and Voltaire)

One of a handful of texts written by Sarah Kofman in the interim between the publication of her Explosion (1992, 1993), a 700-page analysis of Ecce Homo, and her sudden death in 1994, ‘And Yet It Quakes!’ is an unflinching contribution to her perennial analysis of Nietzsche's legacy. The essay opens with a presentation of the responses of Voltaire and Nietzsche to natural catastrophe: an earthquake in Lisbon in the case of the former, an earthquake in Ischia for the latter. Drawing on a metaphoric architecture of quaking or shakenness to draw together a variety of themes and problematics, the essay elaborates a rich comparative study of these two thinkers on the basis of their hasty passing-on from the ‘“humanitarian” considerations’ which such catastrophes might evoke. After analysing the influence of Voltaire on Nietzsche and the rich synergies between the two, with particular reference to irony and laughter, to aristocratism, and to the function of a polemical hostility to Rousseau within their various projects, Kofman's essay closes with a complex — and somewhat ambivalent — affirmation of the radicality of the Nietzschean project. (This text, first published in Furor shortly before Kofman's death, is collected in the posthumous Imposture de la beauté et autres textes (Galilée, 1995) and in Tributs à Voltaire (Furor, 2017). The ayant-droit is favourable to publication.)

A Twin of the Great Lisbon Earthquake (Based on Materials from the Newspaper Sankt-Peterburgskie vedomosti for the 18th Century)

The article generalizes materials on the earthquake of March 31, 1761, which is almost unknown in our scientific discourse, although very significant in its seismological impacts; it can therefore be considered as a twin of the Great Lisbon disaster of November 1, 1755. The 1761 earthquake struck a large part of Europe and, although it did not involve such disastrous consequences as the 1755 Lisbon quake, it significantly changed the seismic regime observed after after the latter. Both earthquakes were followed by tsunamis on the western margins of Europe and the eastern coasts of North America; they also triggered seismic activations of vast, spatially different regions in Western Europe and North Africa. It is possible to associate a number of strongest seismic events in the West Atlantic region with the 1761 earthquake. In the recent research literature on the topic, predominantly by Portuguese authors, the sources of both earthquakes are located in the eastern part of the Azores–Gibraltar Transform Fault. It is of particular interest that the initial data for this article were taken from the newspaper Sankt-Petersburgskie vedomosti for the 18th century and were supplemented with information from historical catalogs and recent foreign papers.

The Portuguese National Seismic Network—Products and Services

AbstractPortugal, located in the southwest region of the Eurasian plate, has been affected by several destructive earthquakes throughout its history, the most well-known being the 1755 Great Lisbon earthquake. The seismicity of the territory, both in the mainland and in the Azores and Madeira islands, has prompted the continuous development of seismic monitoring, from the first known macroseismic inquiry, following the 1755 Great Lisbon earthquake, to the current state-of-the-art seismic network. Once scattered in separate efforts, at present, most seismic stations in Portugal relay its data to a common data center, at Instituto Português do Mar e da Atmosfera, where data are automatically processed for the downstream generation of both manually revised and automatically generated products and services. In this article, we summarize the evolution of the permanent seismic network, its current status, the products and services that are publicly available, a recent effort of rapid deployment of a dense network following a mainshock, and state-of-the-art ocean-bottom seismometer developments.

Onshore flow characteristics of the 1755 CE Lisbon tsunami: Linking forward and inverse numerical modeling

The 1755 CE Lisbon earthquake triggered the largest historical tsunami ever impacting the Atlantic coasts of Europe. Despite recent efforts to better understand this event, there are still unanswered questions about the location of its epicenter and whether physical and historical evidences are in agreement.Inverse modeling using tsunami sediments can be applied to quantify onshore flow characteristics. Forward numerical modeling is also a powerful tool capable of simulating tsunami hydrodynamics and the induced sediment transport. This work presents novel results from a combination of inverse and forward modeling to assess tsunami characteristics onshore. The study site is located on the Portuguese southern coast, at the Salgados lowland where inverse modeling was performed using TsuSedMod (Jaffe and Gelfenbaum, 2007) based on data retrieved from sediment samples. Forward modeling, including tsunami generation and propagation, was performed using the FLOW module of Delft3D suite model. Onshore topography was corrected for the 1755 CE scenario based on extensive tsunami sedimentary deposit thickness data. The tsunami source was chosen based on recent results from the authors that pointed to a good correlation between modeled and field tsunami data for the Marques de Pombal Fault (MPF), Horseshoe Fault (HSF) and a hypothetical scenario represented by a simple combination between Gorringe Bank and Horseshoe Fault (Scenario 1 - SC1).Results from inverse model show tsunami onshore average speed varying from 7.3 up to 9.3 m/s and shear velocities from 0.52 up to 0.66 m/s. Forward modeling results show a wide variation according to the seismic source and tsunami onshore velocities can range from around 7 m/s when considering MPF to even an absence of inundation (SC1). The good agreement between both modeling approaches estimating tsunami velocity confirms the potential of numerical modeling coupled with geological records to improve the understanding of historical events.

What is the Meaning of Immanuel Kant’s Notion of the Human Being as the Ultimate End of Nature?

The article explores Kant’s notion of the human being as the ultimate end of nature, presenting an ethical interpretation of this notion. The author of this article believes that the analysis of Kant’s assumptions will allow a deeper understanding of our own hermeneutical situation, in which ecological problems force us to rethink our relationship with nature and the meaning of human existence. Analyzing Kant’s early texts on Lisbon earthquake and his reflection on the sublime in the Critique of Judgement, the author asks how the experience of an uncontrolled natural element complements Kant’s ethical vision of nature’s teleology. Emphasizing the importance of insight into human vulnerability for the implementation of moral purpose in nature, the article outlines guidelines for interpretation that allow the relevance of Kant’s position in the context of contemporary environmental ethics.

A 1600 year-long sedimentary record of tsunamis and hurricanes in the Lesser Antilles (Scrub Island, Anguilla)

The Lesser Antilles are a densely populated region where local populations and industrial facilities are concentrated at the coastlines, and are therefore exposed to many rapid-onset hazards such as hurricanes and tsunamis. However, the historical catalog of these events is too short to allow risk assessment and return period estimations, and it needs to be completed with long-term records of washover deposits in coastal sedimentary environments such as lagoons. In this study, two sediment cores were taken in March 2018 in a small coastal lagoon on Scrub Island (northeastern Caribbean). Sedimentological, geochemical, microfaunal and chronological analyses enabled us to identify 25 sandy layers resulting from high-energy-marine floods. Two of these layers were interpreted as tsunami deposits based on sedimentological (rip-up clast of the underlying cohesive substrate and internal mud laminae), and geochemical evidence. The most recent deposit is associated with the transatlantic tsunami triggered by the 1755 CE Lisbon earthquake. The older one is the thickest sandy layer recorded in the lagoon, with an age range of 1364–1469 cal. CE, as determined using 14C dating. This event was recorded in sedimentary archives of both the northern and the southern part of the Caribbean, with its large spatial extent, supporting a distant tsunamigenic origin. The 23 remaining sandy layers were interpreted as storm deposits, based on sedimentological and chronological data, with the three most recent layers being correlated with historical hurricanes. This new 1600 year-long record displays similarities with that of the Bahamas, with the periods of intense hurricane activity being in antiphase with those of the north-eastern US coast. This regional comparison may provide evidence for a latitudinal forcing of hurricane tracks through time in relation to climate fluctuations.

재난의 정치학: 리스본 대지진과 근대국가에 대한 21세기적 성찰

이 논문은 코로나-19로 혼란에 봉착한 오늘날의 세계가 처한 상황을 이해하기 위하여 1755년의 리스본 대지진이 근대 초기에 어떻게 받아들여졌고, 또 어떤 영향을 미쳤는가를 집중적으로 살펴본다. 21세기의 코로나-19 사태가 더 이상 근대의 패러다임으로 해결하기 어려운 상황에서, 이러한 대지진의 경험은 재난과 정치의 연관성을 이해하는 하나의 실마리를 제공해줄 수 있기 때문이다. 따라서 이 논문은 리스본 대지진의 사례에 관한 고찰을 한 축으로, 그리고 그로부터 얻을 수 있는 함의와 교훈을 다른 축으로 하여 논의를 전개한다. 특히 각각의 위기 인식, 세계관에 미친 영향, 그리고 재난 관리를 위한 정치체의 변화가 어떻게 전개되었고 또 어떤 의미를 갖는가를 살펴본다.

재난의 정치학: 리스본 대지진과 근대국가에 대한 21세기적 성찰

이 논문은 코로나-19로 혼란에 봉착한 오늘날의 세계가 처한 상황을 이해하기 위하여 1755년의 리스본 대지진이 근대 초기에 어떻게 받아들여졌고, 또 어떤 영향을 미쳤는가를 집중적으로 살펴본다. 21세기의 코로나-19 사태가 더 이상 근대의 패러다임으로 해결하기 어려운 상황에서, 이러한 대지진의 경험은 재난과 정치의 연관성을 이해하는 하나의 실마리를 제공해줄 수 있기 때문이다. 따라서 이 논문은 리스본 대지진의 사례에 관한 고찰을 한 축으로, 그리고 그로부터 얻을 수 있는 함의와 교훈을 다른 축으로 하여 논의를 전개한다. 특히 각각의 위기 인식, 세계관에 미친 영향, 그리고 재난 관리를 위한 정치체의 변화가 어떻게 전개되었고 또 어떤 의미를 갖는가를 살펴본다.

SEISMIC VULNERABILITY ASSESSMENT OF THE TRIUMPHAL ARCH OF CARACALLA IN VOLUBILIS (MOROCCO): PAST EVENTS AND PROVISIONS FOR THE FUTURE

Abstract. The triumphal arch of Caracalla in the Roman archaeological site of Volubilis dates back to 216 AD. It was built in a strategic position at the intersection of the main roads leading to the Forum, the decumanus maximus to the east and the roads from Porte à trios baies to the west, that almost certainly was the main gate to the city. The current arrangement of the monument is the result of a restoration intervention carried out in the 1930s by French restorers. Some ancient photos witness that the monument was just a ruin in 1915, when Chatelain carried out the former archaeological excavations and, as a consequence, that it was totally rebuilt. In fact, the monument suffered wide damages provoked by the 1755 Lisbon earthquake, that affected also Morocco, which almost completely destroyed it. By means of the drawings made by the travelers Henry Boyde and John Windus, that retraced the monument thirty years before the earthquake, the original configuration of the monument can be observed and the timeline of events can be reconstructed. In this paper, the timeline of the seismic events that affected the triumphal arch is reconstructed and investigated by means of a structural analysis based on a rigid-block model. Finally, with the purpose of preventing future damage, the seismic vulnerability level of the construction is assessed with reference to its current configuration.

2 February 1816, an Overlooked North Atlantic M 8 Earthquake

AbstractThe 2 February 1816 North Atlantic earthquake is virtually unknown to the international scientific community, and the few existing studies—solely based on two or three macroseismic intensities—pointed to a magnitude near 7 and a location at the eastern end of the Gloria fault in the Azores-Gibraltar Fracture Zone (AGFZ). Through careful search, we discovered more than 40 independent macroseismic observations and were able to estimate a total of 26 values of intensity, covering a wide geographical area (Iberian Peninsula, Madeira, and Azores). To apply the Bakun and Wentworth (B&W) method to the macroseismic dataset, we also deduced intensity–distance attenuation equations for the three different Atlantic coasts. The B&W procedure enabled us to conclude that the 2 February 1816 earthquake had a moment magnitude of 8.6±0.3 at the 95% confidence level and an epicentral location of 37.8° N and 19.8° W, near the central part of the Gloria fault. These results place the event as the greatest known earthquake in the Gloria fault domain and as one of the greatest ever seismic events along the AGFZ, probably only surpassed by the 1755 Lisbon earthquake.