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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