Reconstruction of the 1755 Earthquake

McGill University 2011F-X Capelle – Eric Munro – Adrien Iredale

Table of Content

• 1) Reconstruction based on geophysical data• Tectonic setting• Generated tsunami wave

• 2) Local destruction and aftershocks• Post 1755 earthquakes• 1st interests in seismology

• 3) Impact on European culture and society• Colonial ambitions restricted • Cultural repercussions

Part 1 – Reconstruction of 1755 earthquake based on geophysical data

Magnitude• Felt area radii Mw 8.7 ± 0.4• Compare to 1969 earthquake tsunami wave height

• Energy release 40 times greater than the 1969 earthquake (Mw 7.9) Implies a 1755 magnitude between 8.9 and 9.4

The Tectonic Setting

Summary of proposed sources

Figure 1: Principle tectonic structures identified around SW Iberian continental margin

Duration and Complexity – Ground Motion

Figure 2 – Reported Durations of the 1755 mainshock

Macroseismic Field

Figure 3 – Macroseismic MSK intensities of the 1755 mainshock

Farfield long period affects• Malaga: “tops of high buildings fell”• Milan and Amsterdam: “oscillating chandeliers from cathedral

roofs”• Across Holland and Germany: “many rivers and canals were

sent into pronounced oscillation”• Scotland: “water levels rose and fell 0.8m for a period of 10

minutes”… “so violent to threaten destruction to some houses built on lake shores”

Coseismic deformation

Figure 4 – Potential coseismic deformation from the 1755 earthquake

The Local Tsunami

Figure 5 – Tsunami arrival times after the 1755 mainshock

The Farfield Tsunami

Figure 6 – Farfield tsunami arrival time from 1755 mainshock

Part 2 – Local destruction and aftershocks

Aftershocks and Triggered Earthquakes

- Many aftershocks in the hours and days to follow.- Algiers, Algeria; city and harbour severely damaged.

- November 27th, 1755 Meknes, Morocco - MSK IX-X, Mw 8.5-9.4

- March 31st , 1761 - MSK IX, Mw 8.5 (inferred)

- 2.4m high Tsunami in Cork, Ireland- 1.9m high Tsunami in Cornwall, England- 1.2m high Tsunami in Barbados

3 min

2.5 min

3 min

5 min

Local DamageMw 8.7 +/- 0.4, MSK IX-X

- City of 240,000 , and deaths between 10,000 and 100,000.

- 85% of the buildings were destroyed.

- Art, literature, and explorations records destroyed.

- Restricted colonial ambitions.

The Fire

- Caused by thousands of candles and unattended cooking fires

- Spread fast across small streets

- Lack of rescue organization

- Destroyed lots of important buildings that were not affected by the earthquake

The Start of Seismology• The Prime Minister designed a

national survey concerning the earthquake.

• Cataloging of times, locations, and physical effects began.• Construction of the first

earthquake resistant buildings.

Part 3 – Impact on European culture and society

Loss of Colonial Presence

- Economic effort went to re-building coastal cities, not colonies.

- Loss of grounds in colonies, later defeats against Spain.

First Earthquake Theories

Kant: First non-religious earthquake theories, including movement of gases in caves.

The Earthquake in European Culture

Age of Enlightenment: Developing philosophy leading to the modern human rights, with the distinct separation of God from life.

Voltaire’s Candide: Denying a perfect world created by God

J.J. Rousseau: Support for his theory that man is naturally good, and that society corrupts him.

References

- R.A. Hindson, C. Andrade (1999), Sedimentation and hydrodynamicprocesses associated with the tsunami generated by the 1755 Lisbon earthquake, Quaternary International, Vol. 56, pp 27-38

• - A.C. Johnson (1996), Seismic moment assessment of earthquakes in stable continental regions—III. New Madrid 1811-1812, Charleston 1886 and Lisbon 1755, Geophysical Journal International, Vol. 126, pp. 314-344

• - J.T. Kozak, C.D. James (1998), Historical depictions of the 1755 Lisbon Earthquake, NISEE, University of Berkeley.

• - N. Zitinelli, F. Chierici, R.Sartori and L.Torelli (1999), The tectonic source of the 1755 Lisbon earthquake and tsunami, Annali de geofisica, Vol. 42, pp. 49-55