History of Seismology. Early science seismology before computers 1880-1960 Seismology since computers 1960-present. Earthquake mythology – ancient beliefs.
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India: The earth is held up by 4 elephants that stand on the back of a turtle. The turtle is balanced on top of a cobra. When the animals move, the earth trembles and shakes
Siberia: The Earth rests on a sled driven by the god named Tuli. The dogs have fleas, When they stop to scratch, the Earth shakes
Japan: A great catfish, or namazu, lies curled up under the sea, with the islands of Japan resting on its back. A demigod, or daimyojin, holds a heavy stone over his head to keep him from moving. Once in a while, though, the daimyojin is distracted, the namzu moves and the earth trembles
New Zealand; Mother Earth has a child in its womb, the young god Ru. When he stretches and kicks as babies do, he causes earthquakes.
“The great Thunderbird finally carried the weighty animal to its nest in the lofty mountains and there was a final and terrible contest fought. There was shaking, jumping up and down and trembling of the earth beneath, and the rolling up of the great waters.”
A reference to the Cascadia Megathrust earthquake of 1705?
From: “The Pacific Northwest Seismograph Network: www.ess.washington.edu”
(563-483 century BC)
“Believe nothing merely because you have been told it, or because it is tradition, or because you yourself have imagined it.
Do not believe what your teacher tells you merely out of respect for him.
But whatever, after due examination and analysis, you find to be conducive to the good, the benefit, the welfare of all beings, believe and cling to that doctrine, and take it as your guide.”
The Scientific Revolution (1543- )
proportional to the product of their masses and
inversely proportional to the square of the distance
The Lisbon Earthquake (Nov 1, 1755)
J. Mitchel (1761) and J. Drijhout (1765)
Early seismic instruments
None of above instruments worked very well
Circular smoked paper record obtained by Ewing's seismograph of a local earthquake in Japan on March 8, 1881.
April 18, 1889
H. Jeffereys (1891-1989) and K. Bullen (1906-1976)
Jeffreys-Bullen propagation of elastic waves
Data is stored on photographic paper
and sent to others using microfilm
The practical computer (1960 onwards)
Memory-- diskettes, CD , DVD, flash sticks, 300 gigabyte drives
Maximum precision – 3 significant figures
Price $395 US in 1972
- NlogN= 22,669
WRA, GBA, YKA Seismic Arrays Constructed in 1960s propagation of elastic waves
Upper mantle (400 and 650 km) discontinuities detected in the 1960s from analysis of array data
1984: propagation of elastic waves The US National Science Foundation and US Geological Survey provide funding for a new, digital seismic network, the GSN. to replace the aging WWSSN.
1996: The International Data Center is established in Vienna and seismic monitoring is done through the International Monitoring System (IMS). The IMS makes use of many stations of the GSN.