1. The Great Lisbon earthquake of 1755
By: Max Goetz & Matt Simons

2. Presentation outline Earthquake introduction Damage & hazards
Theology vs scientific reasoning
Rebuilding the city with Pombal
Methods and research
Conclusion

3. 1755 Lisbon earthquake: Quick Facts
Where: Kindom of Portugal
When: November 1st 1755 – All Saints’ Day
Estimated Moment of Magnitude:
Epicenter: 200 km WSW of Cape St. Vincent (l’Ocean Atlantique)
Duration of shaking: 10 minutes
3 distinct jolts
Felt in North Africa, Spain, France, Switzerland, Italy
The largest documented felt area of any shallow earthquake

4. Isoseismal map

5. Recipe for disaster: a seismically active zone
Many earthquakes in the region before 1755
1531 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).

6. Seismic Region
The 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.

7. Damage and hazards
Direct Earthquake hazards
Tsunamis
Fires

8. Direct Earthquake hazards
fissures 5 meters wide to opened in the city centre.
Buildings being destroyed, debris falling.
Many tall buildings made of masonry at risk
Not a good time to be at church (remember it’s a religious holiday)
Lisbon built on soft soil = soil liquefaction

9. Tsunami
After 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 quake
Reached as far (with less intensity) as Ireland

10. Fires Fires 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 sites
Alternative reason for fires: Looters setting fire to abandoned houses
Lasted for five days!

11. 85% of buildings destroyed or heavily damaged
12/72 churches survived, all hospitals destroyed
Death toll: 10, ,000 people

12. Lets talk religion
This disaster occurred on a religious holiday and most of the churches in Lisbon were destroyed.
PUNISHMENT FROM GOD
12/72 churches survived the earthquake and the events that followed

13. What good came out of this mess?
Birth of modern seismology and earthquake engineering
Newly designed Lisbon (clean slate)
Effect on Europe, breakthrough in seismology and seismic engineering

14. 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

15. 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

16. 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.

17. Archaic Data Collection
Pombal sent out scientific questionnaires to all the parishes in Portugal
Questions 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.

18. Finding the source
Compared 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.

19. Possible sources
Three sources have been proposed for the 1755 earthquake:
Gorringe Bank
Marquis de Pombal
Horseshoe fault.

21. Using Tsunami wave travel times
3 different travel times were compared:
-Historical
-Modeled
-Times from the 1969 earthquake
Tsunami wave travel times results showed that the Marquis de Pombal was the most likely source of the quake.

22. 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

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

24. Empirical relation between fault rupture length and earthquake moment magnitude

25. You gotta break some eggs to make a P’omblette
Conclusion
The 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

26. (applause)
(please)