Earthquakes in Human History: The Far-Reaching Effects of Seismic Disruptions
304
Earthquakes in Human History: The Far-Reaching Effects of Seismic Disruptions
304eBook
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Overview
On November 1, 1755--All Saints' Day--a massive earthquake struck Europe's Iberian Peninsula and destroyed the city of Lisbon. Churches collapsed upon thousands of worshippers celebrating the holy day. Earthquakes in Human History tells the story of that calamity and other epic earthquakes. The authors, Jelle Zeilinga de Boer and Donald Theodore Sanders, recapture the power of their previous book, Volcanoes in Human History. They vividly explain the geological processes responsible for earthquakes, and they describe how these events have had long-lasting aftereffects on human societies and cultures. Their accounts are enlivened with quotations from contemporary literature and from later reports.
In the chaos following the Lisbon quake, government and church leaders vied for control. The Marquês de Pombal rose to power and became a virtual dictator. As a result, the Roman Catholic Jesuit Order lost much of its influence in Portugal. Voltaire wrote his satirical work Candide to refute the philosophy of "optimism," the belief that God had created a perfect world. And the 1755 earthquake sparked the search for a scientific understanding of natural disasters.
Ranging from an examination of temblors mentioned in the Bible, to a richly detailed account of the 1906 catastrophe in San Francisco, to Japan's Great Kanto Earthquake of 1923, to the Peruvian earthquake in 1970 (the Western Hemisphere's greatest natural disaster), this book is an unequaled testament to a natural phenomenon that can be not only terrifying but also threatening to humankind's fragile existence, always at risk because of destructive powers beyond our control.
Product Details
| ISBN-13: | 9780691234205 |
|---|---|
| Publisher: | Princeton University Press |
| Publication date: | 08/10/2021 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 304 |
| File size: | 14 MB |
| Note: | This product may take a few minutes to download. |
About the Author
Read an Excerpt
Earthquakes in Human History
The Far-Reaching Effects of Seismic DisruptionsBy Jelle Zeilinga de Boer Donald Theodore Sanders
Princeton University Press
Princeton University PressAll right reserved.
ISBN: 0-691-12786-7
Chapter One
EARTHQUAKES: ORIGINS AND CONSEQUENCESA bad earthquake at once destroys our oldest associations: the earth, the very emblem of solidity, has moved beneath our feet like a thin crust over a fluid. -Charles Darwin, The Voyage of the Beagle
EARTHQUAKES ARE AMONG the most terrifying of natural phenomena. Striking without warning, and seemingly coming out of nowhere, they challenge our inherent assumptions about the stability of the very planet we live upon. Any shaking of the earth, whether lasting for minutes or only for seconds, seems eternal to those who experience it. A mild quake may inspire no more than passing interest, but a powerful quake can wreak awesome devastation. Figure 1-1 is an artist's interpretation of a quake that shook Naples, Italy, in 1805. A century later (in 1904) an American geologist, Clarence E. Dutton, published a seminal book about seismology (the study of earthquakes) in which he graphically described a strong temblor:
When the great earthquake comes, it comes quickly ... The first sensation is a confused murmuring sound of a strange and even weird character. Almost simultaneously loose objects begin to tremble andchatter. Sometimes, almost in an instant, sometimes more gradually, but always quickly, the sound becomes a roar, the chattering becomes a crashing ... The shaking increases in violence ... Through its din are heard loud, deep, solemn booms that seem like the voice of the Eternal One, speaking out of the depths of the universe.
Dutton's figurative reference to an "Eternal One" alludes to an age-old belief that earthquakes are visited upon sinful mortals by divine wrath, either as punishment for sins committed or as a warning to those who might yield to temptation. In ancient Greece it was the god Poseidon "the earthshaker" (also the god of the sea) whose wrath was to be feared. The Bible contains many verses in both Old and New Testaments that equate earthquakes with God's anger. In contrast, many ancient myths attributed earthquakes to the stirring of giant creatures that supported the earth. In Japan it was a catfish, in China a frog. In the Philippine Islands it was thought to be a snake, and Native Americans believed the earth rested upon the back of a turtle.
The Greek philosopher Aristotle (384-322 BCE) developed a somewhat more rational, if still fanciful, explanation for earthquakes. He believed that strong winds blew through caves and clefts inside the earth, creating "effects similar to those of the wind in our bodies whose force when it is pent up inside us can cause tremors and throbbings."
Among the early attempts at a scientific explanation of earthquakes was a book titled Conjectures concerning the Cause, and Observations upon the Phaenomena of Earthquakes, written in 1760 by John Michell (1724?-1793), a professor of geology at Cambridge University. From a study of the great Lisbon earthquake of 1755, Michell concluded that quakes were caused by shifting masses of rock many kilometers below the earth's surface.
In 1793 Benjamin Franklin, among the leading scientists of his day, suggested a mechanism for Michell's shifting masses:
I ... imagined that the internal part [of the earth] might be a fluid more dense, and of greater specific gravity than any of the solids we are acquainted with; which therefore might swim in or upon that fluid. Thus the surface of the globe would be a shell, capable of being broken and disordered by any violent movements of the fluid on which it rested.
Scientists had to wait more than a century before they could definitely establish a relationship between shifting masses of rock (Franklin's broken "shell") and earthquakes. Then in 1891 a powerful temblor shook the island of Honshu, in Japan. Known as the Mino-Owari earthquake, it left a zone of destruction marked by a fracture, or fault, that extended across the island from the Sea of Japan to the Pacific Ocean. In some places, vertical movement had created fault scarps several meters high (see figure 1-2). From that convincing evidence a Japanese scientist, Bunjiro Koto, concluded that the quake had been triggered by the fracturing of the earth's crust, thus for the first time demonstrating a causal relationship between earthquakes and faulting.
Early in the twentieth century, by studying earthquake waves and the time it takes for them to pass through the earth, scientists deduced that our planet has a dense, at least partly molten core at its center, and that the core is surrounded by a thick layer of less dense material, which they named the mantle. Above the mantle lies the thin, rocky crust (or "shell") upon which we live. The crust can be several tens of kilometers thick where it comprises the continents, but it is only a few kilometers thick beneath the oceans. In some respects we might say that the earth resembles an apple. If an apple is sliced in two, the cross section reveals a small "core" (where the seeds are), a thick "mantle" (the edible flesh), and a "crust" (the skin). The relative proportions of those parts of an apple are not unlike the proportions of the main parts of the earth.
In the 1960s geologists began to understand that the outer part of the earth is made up of individual rigid plates, some very large, others small, as shown in figure 1-3 (and not entirely different from Benjamin Franklin's speculation in 1793). The plates move very slowly over a ductile, or plastic, layer within the mantle. The movement of these tectonic (structural) plates, typically a few centimeters a year, is responsible for most earthquakes, as well as for volcanic activity. This is the theory of plate tectonics, which revolutionized the science of geology by providing a single, unifying concept that helps explain most geological processes and features. The block diagrams in figure 1-4 illustrate the kinds of faults that develop in the earth's crust when plates collide, when they separate, and when they move past one another laterally.
The rigid tectonic plates are made up of rocky crustal material and a thin layer of the uppermost part of the mantle. Together they form what geologists call the lithosphere (from the Greek lithos, meaning "stone"). The ductile layer of mantle material over which the plates move is called the asthenosphere (from asthenos, meaning "weak").
Tectonic plates are in motion presumably because of convection currents within the mantle. The currents are thought to be driven by heat from the earth's core, much as convection currents are created in a pot of water heated on a stove. Hot water, being less dense than cold water, rises to the surface, where it cools and becomes more dense. Therefore it returns to the bottom of the pot. A similar process is believed to be at work, albeit far more slowly, within the earth. Along their boundaries, tectonic plates may be separating from one another, colliding with other plates, or grinding past one another laterally.
Plates spread apart along oceanic ridges, where molten rock, or magma, from the asthenosphere rises through the resulting fractures to create new crust on the bottom of the ocean. Oceanic crust is more dense, thus heavier, than continental crust.
Where oceanic and continental plates collide, the heavier oceanic plate ordinarily is thrust beneath the continental plate, an earthshaking process known as subduction. The Pacific plate, for example, is being subducted beneath the Aleutian Islands and the islands of Japan, and this movement is responsible for volcanism and frequent earthquakes in those areas. Where the collision is between two continental plates-as, for example, where the northward-moving Indian subcontinent is colliding with Eurasia-the result usually is the uplifting of mountain ranges such as the Himalayas of Tibet, Nepal, and northern India, again accompanied by frequent earthquakes.
The infamous San Andreas fault in California lies within a highly active tectonic zone that forms the boundary between the Pacific and North American plates. Both plates are moving laterally in a generally westerly direction, but the Pacific plate is moving slightly faster. Stresses therefore build up along the San Andreas and neighboring faults within the boundary zone until, from time to time, friction is overcome in one area or another and the sudden release of accumulated stress creates an earthquake.
The boundaries of tectonic plates are by far the most common sites of earthquakes, but plate interiors are not invulnerable. The same forces that created the plates can tear them apart, as today the Arabian platelet is being separated from the African plate along the axis of the Red Sea. Branching southward from the mouth of the Red Sea is the East African rift system, a zone of crustal weakness that includes the famous African rift valleys. That region is the site of volcanic activity and frequent earthquakes. Similarly (but without volcanoes), the lower Mississippi Valley is underlain by an ancient rift. Presumably reactivated by the movement of the North American plate, old faults related to the rift gave way in 1811 and 1812, and the region was shaken by some of the most powerful earthquakes in American history.
* * *
Earthquakes are caused by the sudden release of energy when slippage occurs where stresses created by tectonic movement have strained the earth's crust to the breaking point. The place on a fault where an earthquake originates is called the focus, or hypocenter. The place on the earth's surface directly above the focus is the epicenter (see figure 1-5). The waves of seismic energy released by the rupture-called body waves-are propagated through the crust either as push-pull (P) waves or as shear (S) waves. P waves move by successively compressing and dilating crustal material in the direction of propagation, while S waves shake particles of material in directions perpendicular to that direction. In typical midcrustal rocks, S waves travel at about 3 kilometers per second, whereas P waves move at about 5 kilometers per second. The faster P waves arrive at seismographs ahead of S waves, so P waves are also referred to as primary waves, and S waves as secondary waves.
When seismic waves reach the earth's surface they move along the surface in either of two forms, known as Rayleigh waves and Love waves. Rayleigh waves, named after the British physicist Baron Rayleigh (John William Strutt), cause particles in their path to move about in an elliptical fashion. Love waves, named for a British mathematician, A. H. Love, are surface shear waves. Particles in their path move in a horizontal plane at right angles to the direction of wave propagation. Both kinds of surface waves oscillate with lower frequencies, hence with larger amplitudes, than body waves and are largely responsible for earthquake damage.
Before the seismograph was invented in the late nineteenth century, the intensity of ground shaking during earthquakes was estimated by how and where the quakes were felt and by the amount of damage they caused. In 1902 an Italian seismologist, Giuseppe Mercalli, developed a scale with ten degrees of intensity, later modified to twelve as shown in table 1-1. Because the Mercalli scale is qualitative, its accuracy depends on subjective observation or, for past quakes, the accuracy of historical accounts.
In 1935 Charles Richter, a seismologist at the California Institute of Technology, developed a quantitative scale for measuring the magnitude, rather than the qualitative intensity, of earthquakes. Magnitudes originally were calculated from the deflection measured by a particular kind of seismograph corrected for the distance of the instrument from the epicenter of the quake. In time it became apparent that such calculations did not work well for the strongest earthquakes, and seismologists have developed other, more sophisticated magnitude scales, which are used today.
Table 1-2 indicates the relative amounts of seismic energy that are released by earthquakes of various Richter magnitudes. In the table, one "energy unit" represents an arbitrary value equal to the amount of energy that would be released by a magnitude 4 earthquake that lasted from one to five seconds. A magnitude of 4 generally is considered the threshold for causing significant damage. The amount of energy released by earthquakes increases greatly from one magnitude value to the next, as graphically illustrated in figure 1-6.
Some earthquakes are preceded by foreshocks if slippage along the responsible faults begins gradually. And many quakes are followed by aftershocks caused by continued, intermittent slippage along the responsible faults. Aftershocks have been known to continue for years.
Movement along some faults is more or less continuous, so that seismic energy is released gradually and there is no abrupt rupturing to cause any but minor earthquakes. Such faults are said to "creep." Typically, however, because of friction, faults remain "locked" for a time, in effect storing energy just as a compressed spring does-until enough stress has accumulated to overcome the friction, and the slippage occurs. In figure 1-7, erosion has exposed the surface of a fault that was polished smooth by the grinding of one block against the other.
On rare occasions, notably in California and Japan, emissions of bright white light have been reported along faults that have broken through to the earth's surface. Most likely the light is generated when electrons from the freshly ruptured rock collide with atoms in the air above the fault.
Because the earth's crust absorbs and scatters seismic waves, the intensity of ground shaking usually decreases rapidly with increasing distance from a quake's epicenter. The severity of an earthquake is also affected by local geological conditions. Seismic waves in hard bedrock, for example, vibrate with higher frequencies and lower amplitudes than do waves in unconsolidated sediments. Conversely, seismic waves in unconsolidated material, such as marshes and filled land, tend to be amplified because ordinarily they vibrate with lower frequencies and higher amplitudes. For that reason buildings constructed on bedrock tend to survive earthquakes that would destroy structures built on less firm material such as reclaimed swamplands.
Major earthquakes usually are followed, in cities, by fires that result from broken gas mains, sparking electrical wires, and overturned stoves used for cooking or heating. Quake-related conflagrations often cause much more damage, and many more deaths, than the quakes themselves. Lisbon in 1755, San Francisco in 1906, and Tokyo and Yokohama in 1923 all suffered powerful earthquakes, but it was fire, not the quakes, that completed the destruction of the cities.
Faulting and displacement of the seafloor during earthquakes can produce the destructive ocean waves called tsunamis, a Japanese word meaning "harbor waves." Tsunamis (often mislabeled "tidal waves," though they are unrelated to tides) are fast-moving waves that can traverse entire oceans in hours. Approaching land, a tsunami can build to a great height in shoaling water and crash ashore with devastating results, especially in bays and harbors where its energy may be focused by a narrowing configuration of the shoreline.
In mountainous regions, earthquakes can produce ruinous landslides and mudflows. Damage can range from blocked roads, washed-out bridges, and disrupted irrigation systems to the destruction of entire towns and cities.
Other possible aftereffects of catastrophic earthquakes include famine, disease, economic disruption, and even political repercussions, as discussed in the following chapters.
* * *
About 75 percent of the earth's seismic energy is released along the boundaries of the Pacific plate. Another 23 percent comes from a zone of seismic activity that extends eastward from the Mediterranean area to Indonesia. The rest of the world accounts for only about 2 percent. Thus it is not difficult to predict, in general, where earthquakes are likely to happen. But any attempt to predict specifically where or when a quake may strike is fraught with difficulty.
(Continues...)
Excerpted from Earthquakes in Human History by Jelle Zeilinga de Boer Donald Theodore Sanders Excerpted by permission.
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Table of Contents
Preface ix
Acknowledgments xv
Table of Conversions xvii
Earthquakes: Origins and Consequences 1
Sidebar: Induced Earthquakes
Sidebar: Mark Twain's Earthquake Almanac
In the Holy Land: Earthquakes and the Hand of God 22
The Decline of Ancient Sparta: A Tale of Hoplites, Helots, and a Quaking Earth 45
Sidebar: Euripides, Homer, and Aristotle
Earthquakes in England: Echoes in Religion and Literature 65
The Great Lisbon Earthquake and the Axiom "Whatever Is, Is Right" 88
Sidebar: The Wonderful "One-Hoss-Shay"
New Madrid, Missouri, in 1811: The Once and Future Disaster 108
Sidebar: A Disastrous Reprise?
Earthquake, Fire, and Politics in San Francisco 139
Sidebar: Causes of Quakes in the Bay Area
Japan's Great Kanto Earthquake: "Hell Let Loose on Earth" 170
Sidebar: The Kamakura Earthquake of 1257 and the Rise of the Lotus Sect
Peru in 1970: Chaos in the Andes 194
Sidebar: In Chile-Tsunamis, Devastation, and Darwin
The 1972 Managua Earthquake: Catalyst for Revolution 221
Afterword 243
Glossary 245
Notes and References 253
Index 269
What People are Saying About This
"Earthquakes in Human History moves through the centuries and across the continents to show how earthquakes have shaped different societies. With a cast of characters that includes God and his ever-feared wrath, Cleopatra, Voltaire, Mark Twain, and the Sandinistas, it is an engaging and at times thrilling tale. I am confident that it will accomplish the authors' goal of nudging scientists to recognize the social and cultural impact of the geosciences and encouraging historians and others to explore scientific explanations for natural disasters."—Charles Walker, University of California, Davis"Zeilinga de Boer and Sanders have provided us with evidence that natural phenomena, in this case earthquakes, can sometimes have long-term historical consequences in changing the fate of cultures. With examples ranging from biblical to modern times, they show how destructive earthquakes have interacted with wars, religious beliefs, and political movements in changing history. Each account is preceded by a generally accessible account of the geological processes that led to the fateful earthquake. A fascinating read and an antidote to the usual anthropocentric views of history such as that of Arnold Toynbee."—Christopher H. Scholz, Lamont-Doherty Earth Observatory, Columbia University
Recipe
"Earthquakes in Human History moves through the centuries and across the continents to show how earthquakes have shaped different societies. With a cast of characters that includes God and his ever-feared wrath, Cleopatra, Voltaire, Mark Twain, and the Sandinistas, it is an engaging and at times thrilling tale. I am confident that it will accomplish the authors' goal of nudging scientists to recognize the social and cultural impact of the geosciences and encouraging historians and others to explore scientific explanations for natural disasters."—Charles Walker, University of California, Davis
"Zeilinga de Boer and Sanders have provided us with evidence that natural phenomena, in this case earthquakes, can sometimes have long-term historical consequences in changing the fate of cultures. With examples ranging from biblical to modern times, they show how destructive earthquakes have interacted with wars, religious beliefs, and political movements in changing history. Each account is preceded by a generally accessible account of the geological processes that led to the fateful earthquake. A fascinating read and an antidote to the usual anthropocentric views of history such as that of Arnold Toynbee."—Christopher H. Scholz, Lamont-Doherty Earth Observatory, Columbia University