History of Seismology  Early science  seismology before computers 1880-1960  Seismology...

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Transcript of History of Seismology  Early science  seismology before computers 1880-1960  Seismology...

  • Slide 1
  • History of Seismology Early science seismology before computers 1880-1960 Seismology since computers 1960-present
  • Slide 2
  • Earthquake mythology ancient beliefs 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. From: www.fema.gov
  • Slide 3
  • Native tales and the Cascadia megathrust earthquakes Stories from the Hoh and Quillette tribes of the Olympic Peninsula of north west Washington describe an epic battle between the supernatural beings Thunderbird and Whale. 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
  • Slide 4
  • Beginning of the scientific method The Buddha (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.
  • Slide 5
  • Greek contributubtion - Nature Thales (6th Century BC) The crucial contribution of Thales to scientific thought was the discovery of nature. By this, we mean the idea that the natural phenomena we see around us are explicable in terms of matter interacting by natural laws, and are not the results of arbitrary acts by gods. Thales' theory of earthquakes, The (presumed flat) earth is actually floating on a vast ocean, and disturbances in that ocean occasionally cause the earth to shake or even crack, just as they would a large boat.
  • Slide 6
  • Greek contributubtion - geometry One of the most important contributions of the Greeks was their development of Geometry, culminating in Euclid's Elements, a giant textbook containing all the known geometric theorems at that time (about 300 BC), presented in an elegant logical fashion. E.g. The Pythagorean Theorem (the most famous theorem) The square on the hypotenuse of a right angle triangle = the sum of the squares on the other 2 sides Led to the discovery of irrational numbers such as SQRT(2.0)
  • Slide 7
  • Greek contribution - Archimedes Archimedes (287-212 BC) One of the greatest Greek mathematicians and Physicists Discovered Archimedes Principle ---laws of Buoyancy density etc Discovered law of lever, centre of gravity Almost invented logarithms and calculus
  • Slide 8
  • Greek contribution - Ptolemy Ptolemy (87-150AD) Astronomer, mathematician and geographer. He believed the planets and sun orbit the Earth in the order Mercury, Venus, Sun, Mars, Jupiter, Saturn. This system became known as the Ptolemaic system. The Ptolemaic view of the universe was the considered by western scientists and religious leaders to be the true picture of the universe for 1400 years
  • Slide 9
  • The first seismic instrument The Chinese Seismoscope Invented 132 AD The instrument is reported to have detected a four-hundred-mile distant earthquake which was not felt at the location of the seismoscope.
  • Slide 10
  • Arabic contribution Al-Hazen, as Europeans referred to Ibn Al-Haytham (d. 1040) was universally acknowledged to have gone beyond the Greeks in optics. European mathematics continued to build on Arab advances. Hindu-Arabic Science The modern system of numerals, which was replacing the old, cumbersome system of "Roman numerals" in the fifteenth and sixteenth centuries, was brought to Europe from India by Arabic traders. By streamlining calculations, "Hindu-Arabic numerals immeasurably expanded the ease of doing mathematics.
  • Slide 11
  • The European Scientific Revolution The Scientific Revolution (1543- ) 1543 - the year that Capernicus published his famous work on The Revolution of the Heavenly Bodies Put sun at centre of universe with planets circling the sun. Tycho Brahe (1546-1601) --- Invented telescope Frances Bacon (1561-1626) --- Pioneered the scientific method using inductive reasoning. Kepler (1571-1630) ---- showed orbits of planets are ellipses William Gilbert (1540-1603) --- argued that the Earth was a magnet
  • Slide 12
  • Sir Isaac Newton (1642-1727) Newton is ranked as the most influential figure in the history of Western science (Simmons,1996) Best known for his 3 laws of motion. (i) The law of inertia A body in motion moves with constant velocity unless acted upon by some force. A body at rest remains at rest unless acted upon by some force. (ii) An object's acceleration is directly proportional to the object's mass (F=ma) (iii) To every action there is an equal and opposite reaction Law of Gravity: The gravitational force between 2 bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them Invented Calculus
  • Slide 13
  • Robert Hooke (1635 - 1703) Natural philosopher, inventor Robert Hooke is one of the most neglected natural philosophers of all time. The inventor of: the iris diaphragm in cameras, the universal joint used in motor vehicles, the balance wheel in a watch the originator of the word 'cell' in biology Best known for Hooke's Law stress is proportional to strain
  • Slide 14
  • Christian Huygens (1629-1695) Improved telescope and resolved numerous astronomical questions Invented pendulum clock and balance clocks to improve the measurement of time worked on wave theory of light discovered polarized light deduced laws of reflection and refraction Huygen's Principal: Every point on a wave front can be regarded as a new source of waves
  • Slide 15
  • The first scientifically studied earthquake The Lisbon Earthquake (Nov 1, 1755) Probably magnitude 9 with a 3 large tsunamis, thousands killed epicentre 200 km off SW corner of Portugal destroyed the city of Lisbon, Portugal tsunami's struck England and were detected across the Atlantic Ocean in North America Its widespread physical effects aroused a wave of scientific interest and research into earthquakes. (From geology.about.com/library/ bl/bllisbon1755eq.htm)
  • Slide 16
  • The Lisbon Earthquake J. Mitchel (1761) and J. Drijhout (1765) Noted the separation of the earthquake source from the effects that it produced proposed that the distant motion was caused by a wave propagating from a specific location. Mitchel suggested that the vibrations close to the source were related to wave propagating through the elasticity of the rocks Suggested the cause of the earthquake itself was caused by water vaporized by sudden contact with underground fires.
  • Slide 17
  • Earthquake Studies before 1880 first systematic catalogue of shocks - Van Hoff and A Perry First intensity scale - P. Eagen (1828) followed by M De Rossi, F. Forel and G. Mercalli intensity scales first isoseismal map - J. Noggerath (1847) C. Lyell - showed earthquakes could cause vertical motions over large areas Studied the 1819 Rann and Cutch earthquake in India 1822 and 1835 Chulian earthquakes 1855 Wairrarapa earthquake in New Zealand R. Mallet (1810-1881 ) Irish geologist and engineer Constructed one of the most complete earthquake catalogues to date Made an attempt to measure seismic velocities using explosive sources believed earthquakes were caused by the sudden expansion of steam as water met hot rock
  • Slide 18
  • Earthquake Locations - Mallet, 1868.
  • Slide 19
  • Earthquake Studies before 1880 Early seismic instruments 1856: L. Palmiero built a seismoscope that also recorded time 1873: Verbeck first pendulum observations 1875: Cecchi, Italy built first seismometer 1880: Wegner constructed a common-pendulum seismometer which did not write records. Wegner detected 27 earthquakes. None of above instruments worked very well J. Milne, J. Ewing and T. Gray developed first successful working seismographs in 1880-1885 period
  • Slide 20
  • Ewing: used a horizontal pendulum seismometer to detect earthquakes Circular smoked paper record obtained by Ewing's seismograph of a local earthquake in Japan on March 8, 1881. Earthquake studies after 1880
  • Slide 21
  • Milne and Gray (1881) conducted experiments on the propagation of elastic waves artificial sources such as dynamite blasts. obtained an apparent velocity of 500 feet /sec. The farthest station was 400 feet from the source.
  • Slide 22
  • First recording of a distant earthquake April 18, 1889 In Potsdam, Germany, E. von-Rebeur-Pashwitz