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(4) Earthquakes and Tsunamis

Introduction to Geophysics and Planetary Physics

Historical Earthquakes

Effects of an earthquake: Xylograph in the „World Chronicle“ („Weltchronik“) by Hartmann Schedel, 1493. Historical reports on earthquake damages allow to determine the epicenter and the intensity of past earthquakes. With the latter the magnitude can be estimated. This is important for Earthquake risk assessment.

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The „Villach Earthquake“ in 1348 was the largest (known) to be felt in Austria in historical times. The Fresco from 1361 shows the destruction of the castle Arnoldstein (http://nisee.berkeley.edu/elibrary/browse/kozak). The quake caused a massive rockslide, creating the South Wall of Mount Dobratsch in its present form (Source and ©: Roland Schiegl).

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Historical Earthquakes

Earthquake Intensities in Austria

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The largest earthquakes in Austria (also many without major damage) occur in well-known earthquake regions; notably in Northern Tyrol (lower Inn valley, Lechtal Alps) und in the zone Mur valley, Mürz valley – Semmering – southern Vienna Basin (close to the “Thermal Line”). The map (Source: ZAMG) shows the geographic distribution of the most energetic earthquakes in Austria (red). Weak earthquakes can occur anywhere (yellow). ÖNORM B 4015 regulates the (safe) construction of buildings depending on earthquake risk.

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Earthquake Risk in Austria

Earthquake in San Francisco, 1906

On April 18, 1906 the San Andreas Fault ruptured over a length of 430 km (with horizontal displacement of ~3 m, right). Even more devastating than the quake itself (with a magnitude Mw = 7.8) were the fires caused by it, especially in San Fransisco (broken gas pipelines were particularly harmful, rigth: a recent ecample). Since the water pipes were broken too, ...

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Earthquake in Valdivia, Chile, 1960

The 1960 megathrust earthquake near Valdivia in Chile with a moment magnitude = 9.5 was the strongest ever recorded (so far). It was the first time that free oscillations of the planet Earth could be detected – going on for weeks. The quake caused a Tsunami, which even killed 138 people in Japan (Source: USGS).

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Earthquake in Kobe, 1995

The quake on January 15, 1995 in Kobe, Japan reached a magnitude of („just“) 6.9.

The urban freeway was supposed to be „earthquake-safe“, but its pillars collapsed immediately (due to in-adequate construction).

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Earthquake in Bam, 2003

The famous citadel of Bam, Iran, before and after the earthquake on December 26, 2003. The quake with a magnitude 6.6 had a death toll of 30 000.

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Indian Ocean, 26. 12. 2004

M = 9.1

Source: USGS

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The quake of December 26, 2004 on a seismogram from Cyprus. (!)

The rupture extended over a length of more than 1000 km.

The quake – an the strongest Tsunami in historical times – caused more than 227 000 fatalities.

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Indian Ocean, 26. 12. 2004

Indischer Ozean, 26. 12. 2004

Vertical ground movement as function of distance from the epicenter in the global seismometer network.Rayleigh Waves (Surfaces waves) dominate. R1 refers to waves that traveled along the “direct way”, R2 to those, which traveled in the opposite direction. R3 and R4 are Rayleigh waves that traveled twice around the world. The amplification at the antipodal point is due to converging waves (uppermost seismogram). The lowermost seismogram shows the strong aftershock with M = 7.1 (Source: Park et al., EOS, 2005).

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Japan, 11. 3. 2011

On March 11, 2011 an earthquake happened off the coast of Honshu, 130 km away from Sendai. With a moment-magnitude of Mw = 9.0 it was the fourth largest since global measurements are taken – an likely the strongest in Japanese history (Source: USGS and Spiegel)

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The largest Earthquakes since 1900

Rank Location Date Magnitude (Mw) 1 Valdivia, Chile 22.05.1960 9.5 2 Prince William Sound, Alaska27.03.1964 9.2 3 Sumatra–Andaman Islands 26.12.2004 9.1 4 Honshu, Japan 11.03.2011 9.0 5 Kamchatka, Russia 04.11.1952 9.0 6 Maule, Chile (Concepcion) 27.02.2010 8.8 7 Ecuador–Columbia 31.01.1906 8.8 8 Rat Islands, Aleutians, Alaska 04.02.1965 8.7 9 North-Sumatra, Indonesia 28.03.2005 8.610 Assam–Tibet 15.08.1950 8.611 Off North-Sumatra, Indonesia 11.04.2012 8.6 12 Adreanof Islands, Aleutians 09.03.1957 8.613 South-Sumatra, Indonesia 12.09.2007 8.514 Banda-Sea, Indonesia 01.02.1938 8.515 Kamchatka 03.02.1923 8.516 Chile–Argentina 11.11.1922 8.5A Moment magnitude of 9.0 is likely for the Earthquakes in Arica, Chile (13.08.1868) and at the Cascadia Subduction zone (26.01.1700). Mw = 8.7 was reached by the quakes in Lisbon (01.11.1755) und Valparaiso, Chile (08.07.1730) (Source: USGS, as of November 2011.)

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Earthquake and Avalanche, Peru, 1970

The deadliest avalanche of the 20th century was initiated by an earthquake that caused a massive landslide near the summit of Huascaran, the highest mountain in Peru (above, Picture: A.W. Brettschneider). The rocks hit the glacier underneath, leading to a catastrophic chain reaction. The city of Yungay with 20 000 inhabitants was completely covered with mud (right, USGS). The region was declared cemetery, and the city was rebuilt at a different location.

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