A Reassessment of the Magnitude of the 1755 Lisbon Earthquake

2020 ◽  
Vol 110 (1) ◽  
pp. 1-17 ◽  
Author(s):  
Joao F. B. D. Fonseca
Keyword(s):  
Accretionary Prism ◽  
Macroseismic Data ◽  
Training Set ◽  
Intensity Pattern ◽  
Ground Motion Model ◽  
Lisbon Earthquake ◽  
Spatially Distributed ◽  
Data Points ◽  
Gorringe Bank ◽  
Epicentral Location

ABSTRACT The 1755 Lisbon earthquake is still poorly understood due to its offshore location and complex macroseismic intensity pattern. Gutenberg and Richter (1949) tentatively assigned a magnitude between 8¾ and 9 judging from an estimated perceptibility radius of 2500 km. More recent attempts to estimate the magnitude from isoseismal areas led to results in the 8.5–8.7 range. These values have been adopted in several studies of the seismic hazard of southwest Iberia. In this article, I use the available macroseismic data—a total of 1206 data points from Portugal, Spain, and Morocco—to reassess the magnitude of the 1755 Lisbon earthquake. Because a training set of instrumental earthquakes was not available, I apply the technique of Bakun and Wentworth (1997) in conjunction with the ground-motion model of Atkinson and Wald (2007), which was selected through comparison with the 1969 M 7.8 Gorringe bank earthquake data. I obtain a moment magnitude of 7.7±0.5, significantly lower than previous results. The epicentral location obtained with this analysis is offshore southwest Iberia—as expected given the tsunami effects—but poorly constrained. Based on the pattern of intensity data outliers, I suggest that the source was complex and spatially distributed, with part of the rupture taking place onshore or inshore. I propose an explanation for the large tsunamigenic power of the earthquake, which invokes the basal rupture of the Gulf of Cadiz accretionary prism. Finally, I discuss the implications for hazard assessment of the type of complex rupture proposed.

The 1755 Lisbon earthquake and the beginning of closure of the Atlantic

2006 ◽  
Vol 14 (2) ◽  
pp. 193-205 ◽  
Author(s):  
A. RIBEIRO ◽  
L. MENDES-VICTOR ◽  
J. CABRAL ◽  
L. MATIAS ◽  
P. TERRINHA
Keyword(s):  
Source Area ◽  
Accretionary Prism ◽  
Sumatra Earthquake ◽  
Alert System ◽  
Tsunami Modelling ◽  
2004 Sumatra Earthquake ◽  
Lisbon Earthquake ◽  
History Of ◽  
History Of Europe ◽  
Gorringe Bank

The 1755 Lisbon earthquake and tsunami had one of the highest magnitudes in the history of Europe. The source mechanism requires generation at a subduction zone. Intensity distribution and tsunami modelling excludes the Gorringe Bank as a source area and suggests generation by the incipient convergence of the Atlantic with the Southwest Iberia and Morocco margin rather than at the less active Gulf of Cadiz Accretionary Prism. The comparison with the 2004 Sumatra earthquake and tsunami supports this interpretation. A tsunami warning alert system is urgent for the Atlantic.

scholarly journals A method for parameterising roughness and topographic sub-grid scale effects in hydraulic modelling from LiDAR data

2010 ◽  
Vol 14 (8) ◽  
pp. 1567-1579 ◽  
Author(s):  
A. Casas ◽  
S. N. Lane ◽  
D. Yu ◽  
G. Benito
Keyword(s):  
Scale Effects ◽  
Mixing Layer ◽  
Roughness Parameter ◽  
Roughness Height ◽  
Lidar Data ◽  
Hydraulic Modelling ◽  
Topographic Complexity ◽  
Spatially Distributed ◽  
Data Points ◽  
Fine Resolution

Abstract. High resolution airborne laser data provide new ways to explore the role of topographic complexity in hydraulic modelling parameterisation, taking into account the scale-dependency between roughness and topography. In this paper, a complex topography from LiDAR is processed using a spatially and temporally distributed method at a fine resolution. The surface topographic parameterisation considers the sub-grid LiDAR data points above and below a reference DEM, hereafter named as topographic content. A method for roughness parameterisation is developed based on the topographic content included in the topographic DEM. Five subscale parameterisation schemes are generated (topographic contents at 0, ±5, ±10, ±25 and ±50 cm) and roughness values are calculated using an equation based on the mixing layer theory (Katul et al., 2002), resulting in a co-varied relationship between roughness height and topographic content. Variations in simulated flow across spatial subscales show that the sub grid-scale behaviour of the 2-D model is not well-reflected in the topographic content of the DEM and that subscale parameterisation must be modelled through a spatially distributed roughness parameterisation. Variations in flow predictions are related to variations in the roughness parameter. Flow depth-derived results do not change systematically with variation in roughness height or topographic content but they respond to their interaction. Finally, subscale parameterisation modifies primarily the spatial structure (level of organisation) of simulated 2-D flow linearly with the additional complexity of subscale parameterisation.

scholarly journals A Reappraisal of the Lurøy, Norway, Earthquake of 31 August 1819

2020 ◽  
Vol 91 (5) ◽  
pp. 2462-2472 ◽  
Author(s):  
Päivi B. Mäntyniemi ◽  
Mathilde B. Sørensen ◽  
Tatiana N. Tatevossian ◽  
Ruben E. Tatevossian ◽  
Björn Lund
Keyword(s):  
Historical Seismicity ◽  
Macroseismic Intensity ◽  
Macroseismic Data ◽  
Sources Of Information ◽  
Royal Swedish Academy ◽  
Intensity Assessment ◽  
Adequate Information ◽  
Data Points ◽  
Academy Of Sciences ◽  
Written Sources

Abstract Archives and libraries were visited to find previously unknown documents testifying to the Lurøy, Norway, earthquake of 31 August 1819 in northernmost continental Europe. The focus here is on Sweden, Finland, and Russia, which are important for determining the area of perceptibility east of Norway. The new written sources include 12 notes or entries in original archived documents, six contemporary newspaper reports, and two recollections written down years later. The original documentation uncovered is contributory to establishing the authenticity of the observations in Finland and Sweden. The dates of the original documentation allow tracing of the dissemination of eyewitness accounts in writing from the inner area of perceptibility southward to the larger documentation and population centers. New sources of information include weather reports of the Royal Swedish Academy of Sciences, minutes of its meetings, and correspondence sent to the Senate in Finland. The minutes of meetings of the Academy indicate that ample data were collected in the Swedish province of Västerbotten. We found no original Russian documentation but uncovered national newspapers that are more reliable than the previously used Parisian newspaper. To increase transparency, we provide the first list of macroseismic data points (MDPs) including the respective documentation that testify to the Lurøy earthquake. A macroseismic intensity was assigned to a locality, using the European Macroseismic Scale of 1998, when adequate information was available. Accounting for the uncertainty of intensity assessment, the magnitude was estimated as moment magnitude M=5.9±0.2, reconfirming the ranking as the largest onshore or nearshore earthquake in the historical seismicity record of Fennoscandia. In addition to the reappraisal of the 31 August 1819 earthquake, a macroseismic map is provided for the earthquake of 17 February 1819, which was felt in northern Finland and Sweden. Some of its MDPs were previously associated with the Lurøy earthquake.

scholarly journals Areal parameter estimates from multiple datasets

2019 ◽  
Vol 475 (2231) ◽  
pp. 20190352 ◽  
Author(s):  
B. L. N. Kennett
Keyword(s):  
Significant Contribution ◽  
A Priori ◽  
Relative Weight ◽  
Parameter Estimates ◽  
Multiple Datasets ◽  
Wide Range ◽  
Spatially Distributed ◽  
Data Points ◽  
Spatial Terms ◽  
Weighted Combination

A wide range of methods exist for interpolation between spatially distributed points drawn from a single population. Yet often multiple datasets are available with differing distribution, character and reliability. A simple scheme is introduced to allow the fusion of multiple datasets. Each dataset is assigned an a priori spatial influence zone around each point and a relative weight based on its physical character. The composite result at a specific location is a weighted combination of the spatial terms for all the available data points that make a significant contribution. The combination of multiple datasets is illustrated with the construction of a unified Moho surface in part of southern Australia from results exploiting a variety of different styles of analysis.

Method of selecting spatially distributed information for constructing training set of artificial neural networks

2019 ◽  
Author(s):  
Ashat Sydikhov ◽  
Alexander Buevich ◽  
Alexander Sergeev ◽  
Andrey Shichkin ◽  
Irina Subbotina ◽  
...  
Keyword(s):  
Neural Networks ◽  
Artificial Neural Networks ◽  
Training Set ◽  
Distributed Information ◽  
Spatially Distributed ◽  
Artificial Neural

The 1755 Lisbon Tsunami: Tsunami Source Determination and its Validation

2009 ◽  
Vol 4 (1) ◽  
pp. 41-52 ◽  
Author(s):  
Angela Santos ◽  
◽  
Shunichi Koshimura ◽  
Fumihiko Imamura ◽  
Keyword(s):  
North Atlantic Ocean ◽  
Source Area ◽  
Tsunami Source ◽  
The North ◽  
Source Determination ◽  
Historical Tsunami ◽  
Wave Ray ◽  
Lisbon Earthquake ◽  
Gorringe Bank ◽  
Historical Accounts

The Lisbon Earthquake of November 1, 1755, one of the most catastrophic events that has ever occurred in Portugal, Spain, or Morocco, caused severe damage and many casualties. The tsunami generated by this earthquake is well documented in historical accounts, it was reported throughout the North Atlantic Ocean, as it reached not only Portugal, Spain, and Morocco, but also the Madeira and Azores Archipelagos, England, Ireland, and the Caribbean. In spite of the importance of this event, the source of the tsunami remains unknown. In this paper, the authors reevaluate some of the historical tsunami travel times obtained by previous authors. Based on these times, wave ray analysis is used to determine the location of the tsunami source area. These results, combined with turbidites obtained by previous authors at the Tagus and Horseshoe Abyssal Plains, lead to the conclusion that the source of the 1755 Lisbon Tsunami could be located in the area of the Gorringe Bank. Then, a hydrodynamic simulation is carried out with this area presupposed as the source. The numerical model results provide good agreement when compared with both historical and sedimental records. However, in the past, the Gorringe Bank has been dismissed as the source of this tsunami for several reasons. Therefore, these issues are discussed and discredited. As a consequence of all these facts, it can be concluded that the origin of the 1755 Lisbon Earthquake and Tsunami could be located in the area of the Gorringe Bank.

scholarly journals A critical history of British earthquakes

2009 ◽  
Vol 47 (2-3) ◽  
Author(s):  
R. M. W. Musson
Keyword(s):  
Large Scale ◽  
18Th Century ◽  
Primary Source ◽  
Historical Earthquakes ◽  
Critical History ◽  
Lisbon Earthquake ◽  
History Of ◽  
Data Points ◽  
High Standards ◽  
The 19Th Century

This paper reviews the history of the study of historical British earthquakes. The publication of compendia of British earthquakes goes back as early as the late 16th Century. A boost to the study of earthquakes in Britain was given in the mid 18th Century as a result of two events occurring in London in 1750 (analogous to the general increase in earthquakes in Europe five years later after the 1755 Lisbon earthquake). The 19th Century saw a number of significant studies, culminating in the work of Davison, whose book-length catalogue was published finally in 1924. After that appears a gap, until interest in the subject was renewed in the mid 1970s. The expansion of the U.K. nuclear programme in the 1980s led to a series of large-scale investigations of historical British earthquakes, all based almost completely on primary historical data and conducted to high standards. The catalogue published by BGS in 1994 is a synthesis of these studies, and presents a parametric catalogue in which historical earthquakes are assessed from intensity data points based on primary source material. Since 1994, revisions to parameters have been minor and new events discovered have been restricted to a few small events.

scholarly journals A Data-Driven Approach to Identify Flight Test Data Suitable to Design Angle of Attack Synthetic Sensor for Flight Control Systems

Aerospace ◽  
2020 ◽  
Vol 7 (5) ◽  
pp. 63 ◽  
Author(s):  
Angelo Lerro ◽  
Alberto Brandl ◽  
Manuela Battipede ◽  
Piero Gili
Keyword(s):  
Control Systems ◽  
Test Data ◽  
Flight Control ◽  
Flight Test ◽  
Data Driven ◽  
Training Set ◽  
Consequent Reduction ◽  
Data Driven Approach ◽  
Data Points ◽  
Data Pruning

Digital avionic solutions enable advanced flight control systems to be available also on smaller aircraft. One of the safety-critical segments is the air data system. Innovative architectures allow the use of synthetic sensors that can introduce significant technological and safety advances. The application to aerodynamic angles seems the most promising towards certified applications. In this area, the best procedures concerning the design of synthetic sensors are still an open question within the field. An example is given by the MIDAS project funded in the frame of Clean Sky 2. This paper proposes two data-driven methods that allow to improve performance over the entire flight envelope with particular attention to steady state flight conditions. The training set obtained is considerably undersized with consequent reduction of computational costs. These methods are validated with a real case and they will be used as part of the MIDAS life cycle. The first method, called Data-Driven Identification and Generation of Quasi-Steady States (DIGS), is based on the (i) identification of the lift curve of the aircraft; (ii) augmentation of the training set with artificial flight data points. DIGS’s main aim is to reduce the issue of unbalanced training set. The second method, called Similar Flight Test Data Pruning (SFDP), deals with data reduction based on the isolation of quasi-unique points. Results give an evidence of the validity of the methods for the MIDAS project that can be easily adopted for generic synthetic sensor design for flight control system applications.

2 February 1816, an Overlooked North Atlantic M 8 Earthquake

2020 ◽  
Vol 91 (5) ◽  
pp. 2912-2921
Author(s):  
José R. Ribeiro ◽  
Ana P. S. Correia ◽  
Ana I. C. Ribeiro
Keyword(s):  
North Atlantic ◽  
Fracture Zone ◽  
Scientific Community ◽  
Geographical Area ◽  
Seismic Events ◽  
International Scientific Community ◽  
Macroseismic Observations ◽  
Lisbon Earthquake ◽  
Macroseismic Intensities ◽  
Epicentral Location

Abstract The 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.

Escalation of Prediction Accuracy With Virtual Data

2018 ◽  
pp. 433-461
Author(s):  
Sarat Chandra Nayak ◽  
Bijan Bihari Misra ◽  
Himansu Sekhar Behera
Keyword(s):  
Time Series ◽  
Prediction Accuracy ◽  
Financial Time Series ◽  
Training Set ◽  
Target Price ◽  
Macroeconomic Factors ◽  
Financial Time ◽  
Data Points ◽  
The Given ◽  
Virtual Data

Random fluctuations occur in the trend of financial time series due to many macroeconomic factors. Such fluctuations lead to sudden fall after a constant raise or a sudden rise after a constant fall, which are difficult to predict from previous data points. At the fluctuation point, previous data points that are not too close to the target price adversely influence the prediction trend. Far away points may be ignored and close enough virtual data points are explored and incorporated in order to diminish the adverse prediction trend at fluctuations. From the given data points in the training set, virtual data positions (VDP) can be explored and used to enhance the prediction accuracy. This chapter presents some deterministic and stochastic approaches to explore such VDPs. From the given data points in the training set, VDPs are explored and incorporated to the original financial time series to enhance the prediction accuracy of the model. To train and validate the models, ten real stock indices are used and the models developed with the VDPs yields much better prediction accuracy.

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