Download here - Stockton University

Historical Views of Earthquakes
&
The History of Seismology
Introduction
• Geologic evidence indicates the occurrence of earthquakes
throughout Earth history
• Historical records
– 3000 years in China
– 1500 years in Japan
• Terrifying phenomenon that was not understood
– Attributed to supernatural causes
– Church dogma attributed earthquakes to God’s punishment of the
wicked
Goals
•
•
•
•
•
Trace the process of learning about earthquakes
Look at curious sequences of events and connections
Relate to the scientific method
Look at some erroneous ideas which persisted for a long time
Introduce some of the cast of characters
Early Observations
• Richter says the earliest recorded earthquake was in Helice,
Greece in 373 B.C.E.
– Motessus de Ballore described the submergence of Helice
• A major city on the south side of the Gulf of Corinth
• May have disappeared due to faulting or landsliding
• First reliably recorded earthquake was in 856 C.E. Near Corinth,
Greece & killed 45,000 people
Early Observations
• The Earth sometimes shakes violently
• Earthquakes are more frequent in some localities than in others
• Earthquakes are sometimes accompanied by:
– Heavy rumblings
– Fissures in the ground
– Changes in the level of the land
– Tsunami
• Earthquakes are often associated with burning mountains or
volcanoes
Early Theories
• Thales—580 B.C.E.
– Greet writer from the island of Miletus
– Earth is like a great vessel floating on the ocean
– Earthquakes are the result of movements of the analog to the water
• Anaximenes (d. 526 B.C.E)
– Vibrations due to rock in the interior of the Earth falling in and striking
other rock masses
– Implies a hollow space within the interior of the Earth
Early Theories
• Anaxagoras (500-428 B.C.E.)
– Caverns within the earth contained thick vapors
– When vapors collided, fire was produced (much as lightning is
produced when clouds collide)
– Fire rises, and if obstructed explosively breaks through causing the
shaking
– Later modifications included the notion that the fire burned through the
supporting pillars causing the caverns to collapse
– Still calls upon a hollow earth
Early Theories
• Archelaus (5th century B.C.E.)
– Air found its way into the interior of the Earth through passages
leading to underground caverns
– If additional air was forced in, it was compressed and caused violent
storms that produced Earth movement and Earth sounds
Early Theories
• Calisthenes
– Follower of Archelaus
– Wrote that air entered Earth through hidden openings under the sea
– If air was trapped by water, the air moved around and undermined the
Earth
– This is why land near the sea was more likely to be subject to
earthquakes than other areas
Early Theories
• Seneca (4 B.C.E. To 65 C.E.)
– Wrote Quaestiones Naturales
– Follower of Archelaus
– Interior and exterior of Earth were identical except air trapped inside
was clammy, the waters torpid, and the animals slow-paced and almost
shapeless
• Many writers compared Earth to a human body
– Underground rivers of water & fire were compared to circulatory
system
– When the body became sick, earthquakes resulted
Early Theories
• Chang Heng in China (132 C.E.)
– Invented seismoscope
• Seismoscope—indicates an earthquake occurred; no record
• Seismograph—records permanent record called seismogram
• Seismometer—calibrated seismograph which permits determination of actual
ground motion
– Probably better known for his literary gifts
– Chang’s seismoscope
• Directional
• Ring of dragons with balls in their mouths
• Balls dropped into waiting mouth of carved toads
Early Theories
• The Venerable Bede (700 C.E.) in Jarrow, England
– Theorized sea best lies in ocean wrapped around the world
– Holds tail in his mouth
– When he is scorched by the sun, he struggles to seize the sun, and his
squirming causes earthquakes
– Beast is called Leviathan
– Changed to a giant fish which grasped its tail in the Middle Ages
Early Theories
• Agricola (1494-1555)
– Vapors in the Earth caused a reaction of central fire and moisture
– Under great compression they ripped the crust
• Cardan (1501-1576)
– Firey vapors charged with sulfur, nitre, and bitumen exploded causing
earthquakes
• Meanwhile, the Chinese earthquake of 1556 killed 830,000
people
Early Theories
• Galesius (1570)
–
–
–
–
Regions that are very hot or very cold had no earthquakes
Heat rarified vapors; cold prevented creation of exhalations
Areas away from the sea rarely had earthquakes
Islands far from land had few earthquakes because water cooled the
vapors
• 1693—John Flamsteed’s Letter Concerning the Natural Causes
of Earthquakes
The 1700’s
• Electricity as a cause of earthquakes
– Electric fluid was more powerful than mineral exhalations
– Heat within the Earth created created this exhalation, one part of which
was condensed to form metallic ores and the other part penetrated the
entire Earth
• 1750—Philsophic Transactions of the Royal Society of London
– “Those who are apt to be offended at any attempts to give a natural
account of earthquakes...” (an apology)
1700’s
• 1752—British Royal Society published a statement that
earthquakes occurred only where people needed chastening
• 1755—Lisbon, Portugal earthquake
–
–
–
–
9:30 a.m. On All Saints Day (November 1)
Many people in churches which collapsed
60,000 people died in fire and sea waves
Did these church-goers need chastening?????
1700’s
• 1760—John Mitchell at Cambridge University published a
memoir on earthquakes
– Vibratory motion of the Earth was the result of elastic waves in the
Earth’s crust
– These waves are transmitted outward from their point of origin for
large distances and then disappear
– Estimated velocity was greater than that of sound
1700’s
• Important observations
– Different directions from which earthquake arrived as observed at
different places
– Interval between earthquake and succeeding waves
– Time of arrival of waves at different places
– Engineers began to recognize effects of earthquakes on buildings
• Buildings on soft ground suffered damage
• Buildings on bedrock were less damaged
Early 1800’s
• 1840–von Hoff published an earthquake catalogue of the world
• 1846—Robert Mallet presented a paper on the dynamics of
earthquakes to the Irish Academy
– Father of instrumental seismology
– Suggested setting up a series of observatories over the Earth’s surface
Mid 1800’s
• Palmieri in Italy invented a seismograph capable of detecting
earthquakes farther away than 1000 km
• Noggerath and Schmidt in Germany introduced the use of
isoseismal lines to estimate the epicenter of an earthquake
• 1884—deRossi (Italy) and Forel (Switzerland) developed the
Rossi-Forel intensity scale
• 1892—John Milne, in Japan, developed a seismograph
1800’s
• The theoretical front
– Studies of wave motion were in vogue and this happened to apply to
seismology
– 1828—Cauchy and Poisson determined the equations of motion of a
perfectly elastic substance
– Poisson showed 2 types of waves (P & S) transmitted at different
speeds through the Earth
– Stokes showed P waves were compressional and S waves were
rotational
– Rayleigh described waves at the boundary of a homogeneous elastic
substance
Late 1800’s & Early 1900’s
• 1897—Richard Dixon Oldham recognized P, S, and surface
waves on a seismograph
• 1904—Lamb attacked the problem of the generation of surface
waves
• 1906—Oldham presented evidence suggesting the existence of
the Earth’s core
• 1909—Andrija Mohorovicic, at Zagreb, Yugoslavia
Seismographic Observatory found the first convincing evidence
for a boundary separating crustal rocks from the shell below
Early 1900’s
• 1911—Love showed two types of surface waves
– Later they were named Rayleigh and Love waves
• 1914—Gutenburg began the accurate determination of epicenters
– Used Zoppritz-Turner travel time tables
– These were replaced by Jeffreys-Bullen tables in 1940
Early 1900’s
• Inge Lehmann
– Postulated the existence of the inner core
– Attended the first coeducational school in Denmark
• Run by Hanna Adler, an Aunt of Neils Bohr
• Boys and girls were treated identically; there was no assumption that they had
different abilities
• Lehmann said this caused her difficulties later in life when she learned such an
attitude was not universal
– Graduated from the University of Copenhagan in 1925
– In 1928 she was appointed Chief of the Seismological Department of
the Royal Danish Geodetic Instituted, which she held until retirement
in 1953
More Modern Times
• By 1940 the essentials of Bullen’s Model A were known
• Nuclear explosions provided a vast amount of new information
– Cold War efforts to monitor Soviet nuclear program
– Provided “earthquakes” of known size, location, and time
– Provided precise control for seismograms