Lisbon Earthquake Research Articles

The Lisbon Earthquake of 1755: Representations and Reactions

The Lisbon Earthquake of 1755: Representations and Reactions

The Lisbon Earthquake of 1755: Representations and Reactions by Theodore E. D. Braun, John B. Radner

The Lisbon Earthquake of 1755: Representations and Reactions by Theodore E. D. Braun, John B. Radner

Comment on "Lisbon 1755: A Case of Triggered Onshore Rupture?" by Susana P. Vilanova, Catarina F. Nunes, and Joao F. B. D. Fonseca

The work published recently by Vilanova et al. (2003) in the Bulletin of the Seismological Society of America proposes that the accounts of destruction and other effects reported in the Lisbon area as a result of the 1 November 1755 earthquake are best explained by a local rupture on the Lower Tagus Valley fault (ltvf), triggered by the static stress change produced by the main offshore source located in the Gorringe area. Because of the potential impact of this hypothesis on the seismic hazard of the Lisbon area, we discuss and complement the evidence presented by Vilanova and co-workers, concluding that the “local rupture model” should remain, for the moment, as an unsubstantiated speculation. Vilanova et al. (2003) (referred to herein as “the authors” or “the paper”) compare the intensities reported for the 1755 earthquake in Lisbon and Algarve to conclude that Lisbon intensities are abnormally high for the same distance, in particular, when compared with what was observed for the 28 February 1969 earthquake. They interpreted this as the result of local rupture. In Figure 1 we re-plot the macroseismic intensity as a function of the distance to the Gorringe Bank source presumed by the authors. We can see that “Lower Tagus Valley intensities” do not show any abnormal behavior. Similar plots could be made for all source areas proposed by other authors (Baptista, 1998; Baptista et al. , 1998a, 1998b; Zitellini et al. , 1999, 2001; Terrinha et al. , 2003) with minor changes to the conclusion we reached previously. The conclusions reached by the authors were based on their figure 8A, from which intensity values for the Algarve and Portuguese west coast corresponding to distances greater than 350 km are missing. Figure 1. Modified Mercalli (MM) intensities for the 1755 earthquake, plotted as a …

Reply to "Comment on 'Lisbon 1755: A Case of Triggered Onshore Rupture?' by Susana P. Vilanova, Catarina F. Nunes, and Joao F. B. D. Fonseca," by L. Matias, A. Ribeiro, M. A. Baptista, N. Zitellini, J. Cabral, P. Terrinha, P. Teves-Costa, and J. M. Miranda

In Vilanova et al. (2003), referred to in the sequence as “the article,” we suggested that several observations pertaining to the historical accounts of the 1755 Lisbon earthquake are better explained assuming the occurrence of a triggered onshore rupture near Lisbon, a few minutes after the main earthquake. Such observations include the distribution of intensities and the high values in and around Lisbon, the occurrence of an early tsunami-like wave inside the Tagus lagoon prior to the arrival of the external tsunami, a report of ground deformation near Lisbon, cartographic evidence of changes in the course of the Tagus river, and the distribution of destructive aftershocks. The proposed location of the triggered rupture is the well-established seismogenic Lower Tagus Valley (ltv) fault (Cabral, 1995). There is reasonable consensus that the Lisbon earthquake was composed of three shocks in quick succession (Reid, 1914). The main innovation introduced in the article is the thesis that the location of one of the subevents was close to Lisbon, at a significant distance from the first shock. The distance between the classical Gorringe Bank epicenter (Machado, 1966) and the ltv fault is about 350 km, but this value can be significantly reduced by taking into account the finite length of the offshore rupture or by adopting a source closer to the coast as proposed in recent literature (Zitellini et al. , 1999). In view of the progress in the understanding of fault interaction through dynamic or static stress changes, we believe that our hypothesis is plausible, besides it is effective as a way of explaining the observations. L. Matias and colleagues, next referred to as “the comment,” claim that our conclusion is speculative and unsubstantiated, arguing that each anomalous observation reported in the article can be explained in a way that is different from …

Earthquakes in human history: the far-reaching effects of seismic disruptions

Preface ix Acknowledgments xiii Table of Conversions xv CHAPTER 1: Earthquakes: Origins and Consequences 1 Sidebar: induced earthquakes Sidebar: mark twain's earthquake almanac CHAPTER 2: In the Holy Land: Earthquakes and the Hand of God 22 CHAPTER 3: The Decline of Ancient Sparta: A Tale of Hoplites, Helots, and a Quaking 45 Sidebar: euripides, homer, and aristotle CHAPTER 4: Earthquakes in England: Echoes in Religion and Literature 65 CHAPTER 5: The Great Lisbon Earthquake and the Axiom Whatever Is, Is Right 88 Sidebar: the wonderful one-hoss-shay CHAPTER 6: New Madrid, Missouri, in 1811: The Once and Future Disaster 108 Sidebar: a disastrous reprise? CHAPTER 7: Earthquake, Fire, and Politics in San Francisco 139 Sidebar: causes of quakes in the bay area CHAPTER 8: Japan's Great Kanto Earthquake: Hell Let Loose on Earth 170 Sidebar: the kamakura earthquake of 1257 and the rise of the lotus sect CHAPTER 9: Peru in 1970: Chaos in the Andes 194 Sidebar: in chile--tsunamis, devastation, and darwin CHAPTER 10: The 1972 Managua Earthquake: Catalyst for Revolution 221 Afterword 243 Glossary 245 Notes and References 253 Index 269

The Source of the Lisbon Earthquake

In his Perspective “What caused the Great Lisbon earthquake?” (27 Aug. 2004, p. [1247][1]) M.-A. Gutscher proposes an eastward-dipping subduction zone under the Straits of Gibraltar as a likely candidate responsible for the magnitude ( M ) 8.5 1755 Lisbon earthquake and associated tsunami ([1][2

Shallow-marine sediment cores record climate variability and earthquake activity off Lisbon (Portugal) for the last 2000 years

Sea Surface Temperature (SST), river discharge and biological productivity have been reconstructed from a multi-proxy study of a high-temporal-resolution sedimentary sequence recovered from the Tagus deposition center off Lisbon (Portugal) for the last 2000 years. SST shows 2 °C variability on a century scale that allows the identification of the Medieval Warm Period (MWP) and the Little Ice Age (LIA). High Iron (Fe) and fine-sediment deposition accompanied by high n -alkane concentrations and presence of freshwater diatoms during the LIA (1300–1900 AD) (Science 292 (2001) 662) suggest augmented river discharge, whereas higher total-alkenone concentrations point to increased river-induced productivity. During the MWP (550–1300 AD) (Science 292 (2001) 662) larger mean-grain size and low values of magnetic susceptibility, and concentrations of Fe, n -alkanes, and n -alcohols are interpreted to reflect decreased runoff. At the same time, increased benthic and planktonic foraminifera abundances and presence of upwelling related diatoms point to increased oceanic productivity. On the basis of the excellent match found between the negative phases of the North Atlantic Oscillation (NAO) index and the intensified Tagus River discharge observed for the last century, it is hypothesized that the increased influx of terrigenous material during the LIA reflects a negative NAO-like state or the occurrence of frequent extreme NAO minima. During the milder few centuries of the MWP, stronger coastal upwelling conditions are attributed to a persistent, positive NAO-like state or the frequent occurrence of extreme NAO maxima. The peak in magnetic susceptibility, centered at 90 cm composite core depth (ccd), is interpreted as the result of the well-known 1755 AD Lisbon earthquake. The Lisbon earthquake and accompanying tsunami are estimated to have caused the loss of 39 cm of sediment (355 years of record—most of the LIA) and the instantaneous deposition of a 19-cm sediment bed.

Geoscience. What caused the great Lisbon earthquake?

In 1755, the great Lisbon earthquake (estimated magnitude 8.7) killed 60,000 people in southern Iberia and northwest Morocco and generated a 5- to 10-m-high tsunami wave. In his Perspective, Gutscher discusses the current research on the tectonic source of the earthquake. Recent evidence suggests that an eastward-dipping subduction zone beneath Gibraltar may have caused the earthquake. Though no interplate earthquakes have been recorded here, evidence from mud volcanoes, seismic images of deformed sediments, and heat flow data suggest that subduction is active and that the seismogenic fault zone may be locked. Numerous cruises planned in 2004 and 2005 may help to provide a definitive answer.

Seismic hazard impact of the Lower Tagus Valley Fault Zone (SW Iberia)

The seismic hazard of SW Iberia is composed of two contributions: offshore, large to very large events on the plate boundary between Africa and Eurasia such as the Lisbon earthquake of 1755 or the Gorringe Bank earthquake of 1969; and onshore, moderate to strong intraplate earthquakes on inherited crustal fractures. One of these zones of crustal weakness is the Lower Tagus Valley (LTV) fault zone, which displays the highest level of seismic hazard in Western Iberia. In this paper we review the active tectonics and seismicity of the LTV, integrating previous geophysical data with recent results of paleoseismological investigations, and discuss its impact on the seismic hazard of SW Iberia. We conclude that the seismic zonation for hazard assessment currently in force in the building code is biased towards the scenario of distant offshore rupture, and does not take adequately into account the LTV seismic source.

Cliff-top megaclast deposits of Ireland, a record of extreme waves in the North Atlantic—storms or tsunamis?

Past occurrences of major tsunami in the global record have often been inferred from the presence of megaclast accumulations at significant heights above sea level, which sometimes exhibit a pronounced seaward-directed imbricate fabric. The Aran Islands, off the west coast of Ireland, exist in a marine environment which is totally unprotected from the most extreme sea states encountered in the North Atlantic. Spectacular megaclast accumulations are found along the tops of vertical cliffs on these islands. The elevation of these deposits varies from 0 m to 50 m above mean sea level and they include clasts weighing 250 tonnes at sea level, over 117 tonnes at 12 m and 2.9 tonnes at 50 m above sea level. Imbrication measurements on these megaclasts indicate a well defined and consistent mean direction from the southwest for the emplacing waves, one that is consistent with the prevalent storm wind direction for the area. The megaclast accumulations are subject to episodic and on-going erosion by cliff retreat but the existing accumulations are estimated to record events since at least 1839. Recent emplacement and reworking is evidenced by trapped plastic detritus within the deposits and eyewitness accounts of large storms during which clasts have been emplaced. Similar deposits are found on the exposed coasts of the Shetland and Orkney islands off Scotland. There is at present no evidence of any tsunami in recorded history affecting the western Irish and Scottish coasts other than those generated by the Lisbon earthquake of 1755, where the wave effects were slight. Thus, the presence of megaclast accumulations at significant heights above sea level, on exposed coasts, and exhibiting imbrication should not be used as a definitive criterion for the past occurrence of tsunami. These deposits attest to extreme wave conditions occasionally encountered in the North Atlantic and act as a record of such events extending back at least 160 years. Such data on extreme wave conditions are essential for the prediction of the effects of deepwater waves on structures such as offshore drilling platforms.

Reading the Lisbon Earthquake: Adorno, Lyotard, and the Contemporary Sublime

The Lisbon earthquake of 1755 famously shook the metaphysical optimism of Europe's leading philosophers. Immanuel Kant would eventually manage its threat in "The Analytic of the Sublime" of his 1790 Critique of Judgment. In the twentieth century, human-inflicted catastrophes have supplanted the natural disaster as the source of sublime feeling. Auschwitz, however, is the name of an "event" that permits no compensatory retreat to an ostensible human dignity and is not recuperable within a transcendental tale of progress and greater good. The essay traces the qualitative transformation of the sublime across the texts of Kant, Walter Benjamin, Theodor W. Adorno, and Jean-Fran�ois Lyotard.

La Croix and the Swastika: The Ambiguities of Catholic Responses to the Fall of France

Studies of identification with authoritarian Vichy regime's professed mission of national renewal have devoted little attention to how so-called Marshal's pious parishioners1 viewed 1940 fall of France.2 Emphasizing political factors above all else, historians have situated defeat as a catalyst that activated French Catholicism's nascent Right-wing tendencies,3 or less typically as beginning of an epreuve that galvanized faithful to resist Nazism (which they had always found abhorrent) through a steadfast presence in form of parish-level solidarity.4 These historiographical approaches forgo a close look at what Etienne Fouilloux has referred to as the history of religious mentalites,5 and in so doing they arguably narrow our appreciation of full import of 1940 collapse. Revisiting fall of France from perspective of religious discourse raises question of how Catholics viewed Nazi victory within framework of a Christian belief in an omnipotent and righteous deity. Theologians refer to questions of justice as theodicy, and historically theodicy has usually centered on reconciling claims of religious belief with agonies of natural evil (e.g., 1755 Lisbon earthquake) or moral evil (e.g., September 11, 2001, terrorist attacks).6 Throughout summer of 1940 discourse on spiritual meanings of defeat reveals itself most prominently in pages of La Croix, a daily newspaper described by W. D. Halls as the semiofficial organ of [French] Catholicism.7 A close reading of La Croix's editorials, articles, reprinted homilies, and pastoral letters illustrates how political helplessness provokes religious questioning. titles of some of these pieces question cataclysmic events in hope of invoking religious assurance:Punishment?... or Sacrifice?Has God Punished France?, and even The Passion of France.8 Quite often their tentative answers blame perceived decadence of prewar years, encapsulated in interlocking themes such as secular education (laicite) and population decline (denatalite). Yet a rejection of democracy does not materialize in La Croix, even as its writers emphasize Marshal Philippe Petain's potential to reconcile finally ideas of liberty and authority and bring about France's rebirth as a Christian nation, hopes already entertained by La Croix's writers while Third Republic still lived. Accordingly La Croix's response to unfolding disaster avoids a mere religious reiteration of what Charles Maurras (no believer he) called divine surprise9 of 1940. Rather, La Croix's pages reflect lamenting of a shattered France, and a newspaper literally following trajectory of defeat, its staff fleeing Paris first for Bordeaux, and then for Limoges in Unoccupied Zone,10 where it would harmonize with chorus of praise for Marshal, at least for a time. Defeat La Croix of 1940 had traveled some historical distance from its notoriously anti-Semitic and anti-Republican stance during fin-de-siecle Dreyfus Affair. Run by Assumptionist order, since December, 1927, paper had as its chief editor Father Leon Merklen, whose appointment had been decreed rather atypically (selon une procedure insolite) by Pope Pius XI himself as a means of underscoring papal condemnation of Action francaise. Merklen's liberal Catholic credentials put him on a sort of Action francaise enemies' list,15 and made for a difficult transition during his first years at helm of a journal previously sympathetic to Maurras. Nevertheless, -while at least one historian writes of ambivalent ralliement of La Croix14 paper had by World War II undergone a fundamental reorientation toward supporting-though not uncritically-French democracy. According to Rene Remond, based on a consistent attempt to follow papal lead after 1927, the influence of La Croix led its readers from Action francaise to Christian Democracy, a Third Republic renversement which would have significant consequences in Fourth. …

The Great Lisbon Earthquake

GEOPHYSICS On 1 November 1755, an estimated 8.5 magnitude earthquake occurred along the Africa-Eurasia plate boundary in the Atlantic Ocean southwest of Lisbon. This literally earthshaking event devastated one of the most beautiful cities in Europe, producing ground liquefaction, seiches, a tsunami

New study of the 1755 earthquake source based on multi-channel seismic survey data and tsunami modeling

Abstract. In the last years, large effort has been done to carry out multi-channel seismic reflection surveys (MCS) in SW Iberia to locate the active tectonic structures that could be related to the generation of the 1755 Lisbon earthquake and the tsunami. The outcome of these researches led to the identification of a large, compressive tectonic structure, named Marques de Pombal thrust that, alone can account for only half the seismic energy released by the 1755 event. However, these investigations have shown the presence of additional tectonic structures active along the continental margin of SW Iberia that are here evaluated to model the tsunami waves observed along the coasts of Iberia, Morocco and Central Atlantic. In this paper we present a new reappraisal of the 1755 source, proposing a possible composite source, including the Marques de Pombal thrust fault and the Guadalquivir Bank. The test of the source is achieved through numerical modelling of the tsunami all over the North Atlantic area. The results presented now incorporate data from the geophysical cruises and the historical observation along the European coasts and also from the Western Indies. The results of this study will, hopefully, improve the seismic risk assessment and evaluation in the Portuguese territory, Spain, Morocco and Central/North Atlantic.

Lisbon 1755: A Case of Triggered Onshore Rupture?

It has been widely recognized, both in classical and in modern studies, that the Lisbon earthquake of 1755 was a multiple event, composed of three shocks separated by a few minutes (see, e.g., Reid, 1914). Attempts to constrain the location of the source have led to a diversity of proposals, reflecting apparent contradictions in the data. The tsunami and damage along the south and southwest Iberian coast and in Morocco favor an offshore source, whereas the presence of an additional zone of strong shaking in the Lower Tagus Valley (LTV), near Lisbon, favors a more northerly location. By combining the contemporary accounts with intensity data from other earthquakes, we favor a compound source with a large distance between the faults. We propose that, although the mainshock was offshore, the resulting stress changes induced the rupture of the LTV fault, at a distance on the order of 350 km (but subject to large uncertainty in the offshore location), a few minutes after the mainshock. We favor this model, rather than site effects causing high intensities in the Lisbon area, because the highest intensities show a negative correlation to soft soil. Several other phenomena described in the eyewitness accounts can also be explained by the local rupture now proposed, such as a tsunamilike wave in the Tagus River, ground deformation affecting the course of the Tagus River, and the spatial pattern of damaging aftershocks. Recognition of this “missing” episode of rupture on the LTV fault significantly changes the hazard estimate for the Lisbon area.

The 1755 “Meknes” earthquake (Morocco): field data and geodynamic implications

The source of the famous 1 November, 1755 “Lisbon” earthquake has been constrained to be an up to 200 km long structure in the offshore west of Cabo de S. Vincente. The magnitude of this earthquake was estimated in the range of 8.5–9.4. The stress regime argued for this shock would have been characterised by an around NNW–SSE-oriented compression. Less well studied is the successive “Meknes” earthquake, which occurred a few days later in Morocco (27 November), and was erroneously confused by the European contemporary reports with a strong aftershock, occurred on 18 November, of the main seismic sequence of the 1 November earthquake. The Meknes earthquake had destructive effects in the region of Meknes and Fes and along the E–W trending Rides Prérifaines, the main frontal thrust of the Rif. Historical data indicate a macroseismic field closed around the towns of Meknes and Fes. Our structural–geological fieldwork and remote sensing analysis in the epicentral area of the Meknes earthquake, along the local major recent faults, indicate that the E–W-oriented thrusts of the Rides Prérifaines are active. Through a re-examination of historical sources compared with field work and air photo interpretation, we could individuate the traces of coseismic surface faulting of the 1755 Meknes earthquake in two areas of the Rides Prérifaines, both part of the local thrust front: the Jebel Zerhoun area and the Jebel Zalagh area. Tectonic data on the Quaternary stress fields derived from our fieldwork and from literature, consistently with the revised focal mechanisms in the region, indicate active shortening oriented NNW–SSE to N–S in northern Morocco. The data collected seem therefore to indicate the thrusts of the Rides Prérifaines, located within the macroseismic area of the Meknes earthquake, as the most probable seismic source of that event. As such, the activation of the thrusts of the Rides Prérifaines would be consistent with this stress regime, which in turn would be similar to the stress field maintained as responsible for the 1 November, 1755 Lisbon earthquake. We also attempted an estimate of the change due to the Lisbon earthquake of the Coulomb Failure Function (CFF) on the Meknes structure, as identified in this paper, in order to evaluate if the Meknes earthquake could have been induced by the 1 November, 1755 Lisbon earthquake, or a local distinct earthquake. Our modelling suggests that the latter hypothesis is the more likely one.

Ancient Seismites

For most of us who were born and raised in cratonic interiors or at passive margins, earthquakes are the stuff of occasional newscasts about faraway mountain belts and subduction zones. We may forget what the great Lisbon earthquake of 1755 did to western Europe: shocking the likes of Voltaire, thereby precipitating an intellectual revolt against the Church and helping to launch the Age of Reason. Perhaps civilizations came and went in Asia Minor because their world was sporadically rent asunder by calamitous earthquakes. Surely it is no accident, then, that the greatest centers of learning have thrived historically in places of persistent tectonic stability.

A transient coastal wetland: from estuarine to supratidal conditions in less than 2000 years—Boca do Rio, Algarve, Portugal

AbstractPalaeoecological analysis of a 3 m sediment core from a coastal site in the western Algarve, near Lagos, Portugal, reveals the changing ecological characteristics of the wetland environment during the late Holocene. The dinoflagellate record and sedimentary characteristics show that approximately 2000 years ago the modern Boca do Rio wetlands were an estuary. By about 1200 14C years BP, transition to a lower energy environment was taking place. The pollen record at this time indicates the existence of typical salt marsh vegetation. There is a likely hiatus in the sedimentary record caused by the tsunami associated with the Lisbon earthquake of ad 1755. A barrier lake, impounded by tsunami deposits, existed for approximately 60 years before being breached, followed by a reoccurrence of saline conditions. A comparison of the mineral magnetic signature of the sediments with that of soil samples from the catchment suggests a relatively local provenance for some of the sediments, rather than the highly erodible Carboniferous rocks of the Algarve's Serra uplands. However, it is also suggested that there is a biogenic component to the magnetic mineralogy. Coastal wetlands are among the most vulnerable Mediterranean environments. The history and future of the Boca do Rio wetlands is examined in the context of alluviation history, rising sea levels, both past and future, and catchment land use. Changing patterns of cultivation, irrigation and land abandonment during the last 50 years are likely to have increased water demands within the catchment and therefore decreased river discharge to the wetlands. Consequently, the continued existence of the wetlands in their present form is in doubt, despite being part of a protected natural park. Copyright © 2003 John Wiley & Sons, Ltd.

Mapping active faults offshore Portugal (36°N–38°N): Implications for seismic hazard assessment along the southwest Iberian margin

Swath-bathymetry and acoustic-backscatter data from the southwest Iberian margin, which hosts the present-day boundary between the European and African plates, reveal the surficial expression of several fault structures <100 km offshore of Portugal. High-resolution and multichannel seismic reflection profiles collected perpendicular to these structures show folding and reverse faulting of the Quaternary units, suggesting present-day tectonic activity. Successive submarine-landslide deposits at the base of the scarps provide evidence of cyclic fault activity. The location and dimension of these newly identified structures agree with the modeled source suggested for the A.D. 1755 Lisbon earthquake and tsunami, possibly the most destructive event in western Europe during historical time. These fault escarpments and deformed seafloor sediments associated with a cluster of shallow seismicity suggest that these thrusts are active and may pose a significant earthquake and tsunami hazard to the coasts of Portugal, Spain, and Morocco.

Sedimentary record of a tsunami during Roman times, Bay of Cadiz, Spain

AbstractHistorical data show that the Gulf of Cadiz has been exposed to destructive tsunamis during at least the past 2000 yr. The last tsunami was generated by the AD 1755 Lisbon earthquake, which affected the Atlantic coasts of Spain, Portugal and Morocco. Today, these littoral areas are intensely populated and the expected damage could be much greater. Tsunami studies are of great importance in helping to determine the recurrence interval of these events.The presence of washover fan deposits on the inland margin of the Valdelagrana Spit bar (Cadiz, Spain) indicates the occurrence of a high energy marine event ca. 2300 cal. yr BP. Historical, geomorphological, sedimentological, palaeontological and geochronological data suggest that a tsunami could have affected the area during Roman times. Copyright © 2002 John Wiley &amp; Sons, Ltd.