# Presentation: 296447

## History of Seismology

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

## 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

## 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 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

**Notes:**
Much of Archimedes fame comes from his relationship with Hiero, the king of Syracuse, and Gelon, Hiero's son. The great geometer had a close friendship with and may have been related to the monarch. In any case, he seemed to make a hobby out of solving the king's most complicated problems to the utter amazement of the sovereign. At one time, the king ordered a gold crown and gave the goldsmith the exact amount of metal to make it. When Hiero received it, the crown had the correct weight but the monarch suspected that some silver had been used instead of the gold. Since he could not prove it, he brought the problem to Archimedes. 

One day while considering the question, "the wise one"entered his bathtub and recognized that the amount of water that overflowed the tub was proportional the amount of his body that was submerged. 

This observation is now known as Archimedes' Principle and gave him the means to solve the problem. He was so excited that he ran naked through the streets of Syracuse shouting "Eureka! eureka!" (I have found it!). The fraudulent goldsmith was brought to justice.

## 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

**Notes:**
He synthesized and extended Hipparchus's system of epicycles and eccentric circles to explain his geocentric theory of the solar system. Ptolemy's system involved at least 80 epicycles to explain the motions of the Sun, the Moon, and the five planets known in his time. 

## 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.

**Notes:**
The instrument was said to resemble a wine jar of diameter six feet . On the outside of the vessel there were eight dragon-heads, facing the eight principal directions of the compass. Below each of the dragon-heads was a toad, with its mouth opened toward the dragon. The mouth of each dragon held a ball. At the occurrence of an earthquake, one of the eight dragon-mouths would release a ball into the open mouth of the toad situated below. The direction of the shaking  determined which of the dragons released its ball. The instrument is reported to have detected a four-hundred-mile distant earthquake which was not felt at the location of the seismoscope. (From neic.usgs.gov/neis/seismology)

## 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.

**Notes:**
Arab observations were used by European astronomical theoreticians into the eighteenth century. 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. Evidence of the influence of
Arab mathematics can be seen from the fact that the words "algebra" and "algorithm," along with other mathematical terms, were originally Arabic. 

## 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

## 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 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)

## 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.

## 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 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

## 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.

- 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. 

- 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 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

## 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-Bullen

- Earth 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.

## Seismic Vault in 1950s

- Data is stored on photographic paper
- and sent to others using microfilm

## 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
-  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

**Notes:**
PTT new idea this cent accepted in the 1960s after discovering mag stripes in the oceans

## 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

**Notes:**
 EARTHSCOPE

The USArray component of the EarthScope experiment is a continental-scale seismic observatory designed to provide a foundation for integrated studies of continental lithosphere and deep Earth structure over a wide range of scales. USArray will provide new insight and new data to address fundamental questions
in earthquake physics, volcanic processes, core-mantle interactions, active deformation and tectonics, continental structure and evolution, geodynamics, and crustal fluids (magmatic, hydrothermal, and meteoric). The USArray facility will consist of three major seismic components:

1. A transportable array of 400 portable, unmanned three-component broadband seismometers deployed on a uniform grid that will systematically cover the US;

2. A flexible component of 400 portable, three-component, short-period andbroadband seismographs and 2000 single-channel high frequency recorders for active and passive source studies that will augment the transportable array, permitting a range of specific targets to be addressed in a focused manner; and 
3. A permanent array of high-quality, three-component seismic stations, coordinated as part of the US Geological Survey's Advanced National Seismic System (ANSS), to provide a reference array spanning the contiguous United States and Alaska.

- 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.”