History of Seismology

1
History of Seismology

• Early science
• seismology before computers
• 1880-1960
• Seismology since computers
• 1960-present

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

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

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.

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.

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)

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

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

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.

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.

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

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 (Fma)
• (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

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

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

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)
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.

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

18
Earthquake Locations - Mallet, 1868.
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

20
Earthquake studies after 1880

• 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.

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.

22
First recording of a distant earthquake

• April 18, 1889
• In Potsdam, Germany, E. von-Rebeur-Pashwitz had
  built a sensitive horizontal pendulum seismograph
  for measuring tidal tilts, his interest was
  primarily astronomical.
• The figure below is an engraving of the recording
  he made of the 1989 earthquake in Japan

23
Seismology milestones (1880-)

• Waves
• Lord Rayleigh (1842-1919) - Predicted Rayleigh
  waves (1885)
• Richard Oldham (1900) - identified P waves, S
  waves and Rayleigh waves from records of the
  1897 Assam earthquake
• A E. H. Love (1863-1940) - predicted existence
  of Love waves (1911)
• Earth structure
• Oldham (1906) - confirmed the existence of the
  Earth's core
• A. Mohorovicic (1909) - Discovered the Moho from
  analysis of data at relatively short distance
  from earthquake (the Kulpa Valley earthquake in
  Croatia)
• I. Lehman (1936) showed that the core has a solid
  inner core.

24
Earth structure

• H. Jeffereys (1891-1989) and K. Bullen
  (1906-1976)
• Used large volumes of data and improved analysis
  of epicentre locations and derived new standard
  earth model
• The Jeffreys-Bullen Seismological Tables (1940)
• Showed earth nearly spherical symmetrical with
  only a few discontinuities.
• Showed core-mantle boundary separated a solid
  mantle from a liquid core.

25
Jeffreys-Bullen Earth Model
26
Earthquake mechanism (1911-1950)

• 1911 Reid's strain rebound theory -
  earthquakes related to faults
• 1917 T. Shida first to show that the first
  motions could be divided into quadrants separated
  by nodal lines
• 1923 Nekano provided the first theoretical
  treatment of the fault source mechanism
• 1935 Richter developed the Richter magnitude
  scale
• Other pioneers in this area
• Byerly, S. Nakamura, S. Kunitomi, H.Honda, M.
  Ishimoto and Keilis Borok
• Arguments both for single couple and
  double-couple sources were presented.
• J. Hodgson attempted to use S waves to
  distinguish between the double-and single couple
  sources.

27
Seismic Vault in 1950s
Data is stored on photographic paper and sent to
others using microfilm
28
The computer and seismology

• The practical computer (1960 onwards)
• The tape recorder--- analogue, then digital---
  reel to reel, cassettes, Exabyte etc
• Punch cards and paper tape replaced with
  interactive terminal - 1980
• Personal computers 1985 -
• GPS and satellite communication -
• The internet 1995-
• Memory-- diskettes, CD , DVD, flash sticks, 300
  gigabyte drives
• The memory of 1 DVD approximately that of 4000
  diskettes
• The slide-rule was replaced with the pocket
  calculator in 1972

Price 395 US in 1972
29
New tools for seismologists

• Finite difference analysis
• Synthetic Seismograms
• Ray tracing
• Numerous Inversion techniques
• Digital filtering numerous filters --- band-pass,
  wave shaping, stacking , velocity etc
• Fast Fourier Transform (FFT) --- Cooley Tukey
  1967 ---
• reduce the number of computations from N N to
  NlogN
• Example-- get the spectrum of a seismic trace 60
  seconds long sampled at 100 samples/sec
• N 6000 - NN 36,000,000
• - NlogN 22,669
• The FFT is 1,588 times faster in this example

30
The Nuclear Test Ban Treaty

• 1963 The limited test-ban treaty signed
• Funding resulted in improved instrumentation
  around the world
• This was particularly for the World Wide
  Standardized Seismic Network (WWSSN)
• 120 standardized recording stations located
  world-wide
• Numerous seismic arrays were also set up around
  the world
• e.g. WRA Australia, YKA Canada, GBA India,
  ESK Scotland, NORSAR Norway
• ESSN seismic network of 100 stations in Soviet
  Union and eastern block
• Late 1970s --- Analogue to digital conversion
  begun

31
WRA, GBA, YKA Seismic Arrays Constructed in
1960s
Upper mantle (400 and 650 km) discontinuities
detected in the 1960s from analysis of array data
32
Further milestones in seismology

• 1966 Keiiti Aki defines seismic moment
• A physical measure of the magnitude of an
  earthquake.
• Mo Area slip rigidity
• 1969-72 Apollo astronauts place a seismometer
  on he Moon, and the first "moonquakes" are
  registered.
• 1977 Hiroo Kanamori establishes the moment
  magnitude scale
• A measure of earthquake magnitude based on
  seismic moment.

33
Plate tectonic theory
34
1984 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.
35
New developments Passive experiments
36
Passive experiments

• EarthScope
• 400 portable 3 component broadband instruments on
  a regular grid
• 400 portable 3 component short-period and
  broadband seismographs and 2000 single channel
  high-frequency recorders
• Permanent array of broadband 3 component stations
  across the country as part of the USGS Advanced
  National Seismic System

37

• Message From the SSA - April 14, 2006
• The complete archive of BSSA from 1911-2006 is
  now available online
• In conjunction with our 100th anniversary, SSA
  is pleased to announce that all issues of the
  Bulletin of the Seismological Society of America
  (BSSA) back from Volume 1 Number 1 (March 1911)
  are now available (and searchable) on the World
  Wide Web through Geoscience World.