The Great Lisbon earthquake of 1755

By: Max Goetz & Matt Simons

Presentation outlineEarthquake introductionDamage & hazardsTheology vs scientific reasoningRebuilding the city with PombalMethods and research Conclusion

1755 Lisbon earthquake: Quick Facts

Where: Kindom of PortugalWhen: November 1st 1755 – All Saints’ DayEstimated Moment of Magnitude: 8.5-9.0Epicenter: 200 km WSW of Cape St. Vincent

(l’Ocean Atlantique)Duration of shaking: 10 minutes 3 distinct joltsFelt in North Africa, Spain, France, Switzerland,

ItalyThe largest documented felt area of any shallow

earthquake

Isoseismal map

Recipe for disaster: a seismically active zoneMany earthquakes in the region

before 17551531 earthquake destroyed lots of

Lisbon, (many of the churches destroyed)

Eight in 14th century, five in 16th century, and three in 17th century (all were far less severe).

Seismic RegionThe Azores-Gibraltar Transform Fault

(boundary between the African and the Eurasian continental plates) = complex and active tectonic behavior.

Also, a shallow fault plane under the Gulf of Cadiz (associated with active subduction) is another possible source for the earthquake.

Damage and hazardsDirect Earthquake hazards

TsunamisFires

Direct Earthquake hazardsfissures 5 meters wide to opened in the city

centre.Buildings being destroyed, debris falling.Many tall buildings made of masonry at riskNot a good time to be at church (remember

it’s a religious holiday) Lisbon built on soft soil = soil liquefaction

TsunamiAfter the earthquake, people looked for safety on the

sea by boarding ships on the river. 40 minutes after the quake, a large wave came down

the mouth of the Tagus. "so fast that several people riding on horseback ... were

forced to gallop as fast as possible to the upper grounds for fear of being carried away."

3 waves struck the shore, each dragging people and debris out to sea. Boats capsized and sank.

Waves as high as 15m (usually 5 meters)Coastal regions had more tsunami damage than quakeReached as far (with less intensity) as Ireland

FiresFires started by cooking fires and candles. Many inhabitants fled from their homes and

left fires burning. Narrow streets full of fallen debris prevented

access to the fire sitesAlternative reason for fires: Looters setting

fire to abandoned housesLasted for five days!

85% of buildings destroyed or heavily damaged12/72 churches survived, all hospitals

destroyedDeath toll: 10,000-100,000 people

Lets talk religion This disaster occurred on a religious holiday

and most of the churches in Lisbon were destroyed.

PUNISHMENT FROM GOD12/72 churches survived the earthquake and

the events that followed

What good came out of this mess?Birth of modern seismology and earthquake

engineeringNewly designed Lisbon (clean slate)Effect on Europe, breakthrough in seismology

and seismic engineering

Pombal, the man, the legend.-Sebastião José de Carvalho e Melo, the Marquis of

Pombal (what a mouthful!)-Prime Minister at the time-”One of the founders of seismology”-Famous quote: “bury the dead and fed the living”-Huge contributions in reconstruction and relief-designer of the first earthquake resistant buildings

Post Quake Innovation -no buildings built on hills, only on flat

ground-houses built low and wide = low center of

gravity-streets built 3x as wide as houses were tall

He’s also an architect! Pombal also introduced ideas to help

counteract the damaging effect of earthquakes on buildings.

He placed a flexible wooden structure in the walls of buildings, so that they would shake but not fall.

He built scale models of these buildings and marched troops around them to simulate tremors.

Archaic Data CollectionPombal sent out scientific questionnaires to

all the parishes in PortugalQuestions included:--time they felt the earthquake hit,--whether they felt it come from a particular

direction--how many people died. This data has helped modern scientists to

recreate the earthquake and better understand it.

Finding the sourceCompared historical tsunami travel times to

modeled travel times and to travel times from a quake in 1969 (7.9 magnitude)

Compared sizes of different seismic structure to identify plausible sources

(The Gibraltar Arc seismogenic zone (part 2): Constraints on a shallow east dipping fault plane source for the 1755 Lisbon earthquake provided by tsunami modeling and seismic intensity)

by M.–A Gutscher et al.

Possible sourcesThree sources have been proposed for the 1755

earthquake:Gorringe Bank Marquis de PombalHorseshoe fault.

Using Tsunami wave travel times3 different travel times were compared: -Historical -Modeled -Times from the 1969 earthquakeTsunami wave travel times results showed that the Marquis

de Pombal was the most likely source of the quake.

However…The Marquis de Pombal structure is not large enough.The only structure in the area capable of producing a

quake of necessary magnitude is the Gorringe Bank…. But the modeled travel times do not match up with historical reports!

It was likely a combination of multiple sites that produced the devastating earthquake of 1755

In line with historical reports of 2-3 shaking events

How does the 1755 earthquake stack up compared to other major ones?

Empirical relation between fault rupture length and earthquake moment magnitude

ConclusionThe Great Lisbon Earthquake of 1755 was a

double edged sword:Devastating earthquake that took many lives,

unthinkable destruction and chaos The silver lining: it caused of the beginning of

research in seismology and earthquake engineering.

You gotta break some eggs to make a P’omblette

(applause)(please)