Transcript History of Seismology  Early science  Seismology before computers   1880-1960 Seismology since computers  1960-present Earthquake mythology – ancient beliefs Early understanding of earthquakes was based on folklore, written.

History of Seismology

Early science

Seismology before computers


1880-1960
Seismology since computers

1960-present
Earthquake mythology – ancient beliefs
Early understanding of earthquakes was
based on folklore, written stories, and were
somewhat superstitious.
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
Earthquake mythology – ancient beliefs
Mexico: El Diablo, an Indian devil
god, made a giant rip in the ground so
that he and his cohorts did not have to
take the long way around, whenever
they wanted to stir up mischief on the
earth.
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
From:
www.fema.gov
Earthquake mythology – ancient beliefs
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
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”
Cascadia megathrust
earthquakes
Cascadia Megathrust 1705
Estimated at
Mg 8.7 – 9.2
January 26, 1705
Rupture length: 1000 km
The earthquake caused
tsunami that struck the
coast of Japan, and may
also be linked to the
Bonneville Slide.
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.
Early Detectors of Ground Movement
Zhang Heng was a celebrated astronomer of
ancient China. An inventor of the
seismograph and armillary sphere, he made
great contributions to the development of
astronomy in ancient China.
132 AD, Eastern Han Dynasty
Physics, Wave energy:
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





(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:


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.
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
Physical Properties:
Robert Hooke (1635 - 1703)

Natural philosopher, inventor

Robert Hooke is one of the most neglected
natural philosophers of all time. The inventor of:





the
the
the
the
iris diaphragm in cameras,
universal joint used in motor vehicles,
balance wheel in a watch
originator of the word 'cell' in biology
Best known for Hooke's Law

“stress is proportional to strain”
Wave theory:
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
1800's
Couchy
Poisson
Stokes
Lord Rayleigh
A.E. H. Love
}
Found the major waves that
pass through solid material.
- Body waves (P,S)
- Surface waves (Rayleigh, Love)
Developed theory on elastic wave propagation “ahead” of any
observations (no seismometers!).
Earthquake Studies – before 1880

Robert Mallet (1810-1881 ) Irish geologist and engineer

Visited Naples, Italy to study damage from a large earthquake
Earthquake Studies – before 1880

Robert Mallet (1810-1881 ) Irish geologist and engineer







Theorized that earthquakes radiate energy from a focal point
Assumed that earthquakes were explosions and predicted P
wave energy only.
Caused by sudden expansion of steam as water contacted hot
rock
Determined EQ location by projecting energy back to original
source
Made an attempt to measure seismic velocities using
explosive sources
Suggested creation of observatories to monitor earthquakes
Made one of the first comprehensive earthquake catalogues
Earthquake Locations - Mallet, 1868.
(Plate tectonics still not accepted at this date)
Earthquake Instrumentation
– before 1880
Early seismic instruments
The first seismometers were undamped pendulums
No recording of time.




1856: L. Palmiero built a seismoscope that also recorded
time
1873: Verbeck first pendulum observations
1875: Filippo Cecchi, Italy built first seismometer with time
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 (British working in Japan)
developed first successful working seismometers with time
recording in 1880-1885 period
– Horizontal pendulum, rotating disk of smoked glass

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 a teleseismic event from the 1989 earthquake in Japan
All instruments upto this date were undamped oscillators.
(only measured ground motion accurately at start of EQ)
Lick Observatory
1897 - 1906
–
Lick Observatory built in San Jose, California
–
(Now operated by the UC university system)
Recorded the 1906 earthquake in San Francisco
- 280 miles displacement
- Shaking ~1 minute
Seismology - Instrumentation
1898 Emil. Weichert
- Used viscous damping
- Measured earthquake energy for entire EQ duration
1903 B.B. Galtizen
- Developed electromagnetic seismometers.
- Here a moving pendulum was used to generate electric current in a coil
- Deployed a chain of stations across Russia.
(now all seismometers are electromagnetic and are easier to deploy)
Seismology Observations:
Earth Structure (1900-)
Increase and improvements in
instrumentation recording multiple
earthquakes at greater distances led
to measurements of deep Earth
structure.

Richard Oldham (1900) – observed
P, S, and surface waves on a
seismogram.

Oldham (1906) noticed that direct P
and S wave arrivals were absent at
distances beyond 100o and
confirmed the existence of the
Earth's core.
Seismology Observations:
Earth Structure (1900-)
Andrija Mohorovicic (1909) Discovered the Moho from
meticulous analysis of seismic
data at relatively short distance
from the Kulpa Valley earthquake
(in Croatia).
Seismology Observations:
Earth Structure (1900-)
Travel Time Tables:
Zoppritz (1907), produced firsts comprehensive
travel time tables.
Beno Gutenbert (1914), Travel times for core
penetration and reflection
Picture of travel times...
Seismology Observations:
Earth Structure (1900-)


I. Lehman (1936) showed that the core has a solid inner core.
Introduced the “I” phase.
Earth structure
H. Jeffereys (1891-1989) and K. Bullen (19061976)
 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
Earth's Interior
Structure
mantle
Compositional Layers
– Crust (~7-70m thick)
• Very thin outer rocky
shell of Earth
– Mantle (~2900 km thick)
• Solid interior that
flows slowly over time
– Core (~3400 km radius)
The Earth's total radius is 6480 km
• Outer core – liquid iron
• Inner core - solid iron
Preliminary Reference Earth Model (PREM),
(Dziewonski & Anderson, 1981)
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
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.
USArray:
Passive experiments
EarthScope
http://www.usarray.org/




400 portable 3
component broadband
instruments on a
regular grid
400 portable 3
component short-period
and broadband
seismographs and 2000
single channel highfrequency recorders
Permanent array of
broadband 3 component
stations across the
country as part of the
USGS Advanced
National Seismic
System
Movie