History of Seismology Early science

seismology before computers 1880-1960

Seismology since computers 1960-present

Earthquake mythology – ancient beliefsIndia: 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

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”

Beginning of the scientific method The BuddhaThe 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.”

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.

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)

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

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

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.

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.

The European Scientific RevolutionThe 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

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

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”

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”

The first scientifically studied earthquakeThe 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)

The Lisbon EarthquakeJ. 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.

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

Earthquake Locations - Mallet, 1868.

Earthquake Studies – before 1880Early 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

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

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.

First recording of a distant earthquakeApril 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

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.

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.

Jeffreys-BullenJeffreys-BullenEarth ModelEarth Model

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.

Data is stored on photographic paper

and sent to others using microfilm

Seismic Vault in 1950s

The computer and seismologyThe 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

Maximum precision – 3 significant figures Price $395 US in 1972

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 - N*N= 36,000,000 - NlogN= 22,669 The FFT is 1,588 times faster in this example

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

WRA, GBA, YKA Seismic Arrays Constructed in 1960s

Upper mantle (400 and 650 km) discontinuities detected in the 1960s from analysis of array data

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.

Plate tectonic theory

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.

New developments – Passive experiments

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

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.”