I chose to research earthquakes and the prediction of earthquakes because I was curious as to how they work. In this paper, Iwill discus the history of earthquakes, the kinds and locations of earthquakes, earthquake effects, intensity scales, prediction,and my own predictions. An earthquake can be defined as vibrations produced in the earth’s crust. Tectonic plates have friction between them whichbuilds up as it tries to push away and suddenly ruptures and then rebounds. The vibrations can range from barely noticeable toa disastrous, and destructive act of nature. Six kinds of shock waves are generated in the process.
Two are classified as bodywaves, that is, they travel through the inside of the earth and the other four are surface waves. The waves are further classifiedby the kinds of motions they incur to rock particles. Primary or compressional waves, known as P waves, send particlesmoving back and forth in the same direction as the waves are traveling, as secondary or transverse shear waves, known as Swaves, create vibrations perpendicular to their direction of travel. P waves always travel at faster speeds than S waves, sowhenever an earthquake occurs, P waves are the first to arrive and to be recorded at geophysical research stations worldwide. During ancient times very little was know about.
Some of the ancient Greek philosophers connected earthquakes tounderground winds, where others blamed them on fires in the depths of the earth. Around AD 130 the Chinese scholar ChangHeng, believing that waves must ripple through the earth from the source of an earthquake, created a bronze object to recordthe directions of such waves. Eight balls were carefully balanced in the mouths of eight dragons placed around the outside ofthe object. When a passing earthquake occurred the wave would cause one or more of the balls to drop. Earthquake waves were observed in this and other ways for centuries, but more scientific theories as to the causes of quakeswere not proposed until modern times. One such concept was recreated and advanced in 1859 by an Irish engineer, RobertMallet.
Perhaps recalling on his knowledge of the strength and behavior of construction materials, Robert Mallet proposed thatearthquakes occurred “either by sudden flexure and constraint of the elastic materials forming a portion of the earth’s crust orby their giving way and becoming fractured. ” Later, in the 1870s, an English geologist, John Milne created a device similar toone of today’s earthquake-recording device, a seismograph, which in Greek seismos means earthquake. A simple pendulumand needle suspended above a smoked-glass plate, it was the first instrument to allow visual difference of primary andsecondary earthquake waves. The modern seismograph was invented in the early 20th century by a Russian seismologist,Prince Boris Golitzyn. His device used a magnetic pendulum suspended between the poles of an electromagnet, created themodern era of earthquake research. There are three general classes of earthquakes that are now recognized: tectonic, volcanic, and artificially produced.
Thetectonic kind is by far the most devastating, and these earthquakes create many difficulties for scientists trying to develop waysto predict them. The main cause of tectonic earthquakes is stress set up by movements of the dozen major and minor platesthat make up the earth’s crust. Most tectonic quakes occur at the boundaries of these plates, in zones where one plate slidespast another, such as at the San Andreas Fault in California, North America’s most quake-prone area, or where one plateslides beneath the other plate, subduction. Subduction-zone earthquakes count for nearly half of the world’s destructive seismicevents and 75 percent of the earth’s seismic energy.
They are concentrated along the “Ring of Fire”, a narrow band about38,600 km long, that meet with the border of the Pacific Ocean. The points at which rupture occurs in these earthquakes tendto be far below the earth’s surface, at depths of up to 645 km. Alaska’s disastrous Good Friday earthquake of 1964 is anexample of one such event. Tectonic earthquakes beyond the “Ring of Fire” occur in a variety of geological settings.
Mid-oceanridges, which are the seafloor-spreading centers of tectonic plates, are the sites of many events of moderate intensity that takeplace at relatively shallow depths. These quakes are seldom felt by anyone and account for only 5 percent of the earth’s seismicenergy, but they are recorded daily on the instruments of the worldwide network of seismological stations. Another setting fortectonic earthquakes is an area stretching across the Mediterranean and Caspian seas, and the Himalaya, ending in the Bay ofBengal. In this zone, which releases about 15 percent of the earth’s seismic energy, continental landmasses riding on theEurasian, African, and Australian plates are being forced together to produce high, and new mountain chains.
The resultingearthquakes, which occur at shallow to intermediate depths, have often devastated areas of Portugal, Algeria, Morocco, Italy,Greece, the Former Yugoslav Republic of Macedonia, Turkey, and other countries partly or completely on the BalkanPeninsula, Iran, and India. One other category of tectonic earthquakes includes the not often happening but large and destructive earthquakes that occurin areas far from other forms of tectonic activity. Main examples of these “midplate earthquakes” are the three large tremorsthat shook the region around New Madrid, Missouri, in 1811 and 1812. Which was powerful enough to be felt 1000 milesaway, these tremors created movements that rerouted the Mississippi River. Another example is the quake that struckCharleston, South Carolina, in 1886.
Geologists believe that the New Madrid quakes are “a symptom of forces tearing apartthe earth’s crust, forces such as those that created Africa’s Rift Valley. ” Of the two classes of nontectonic earthquakes, those ofvolcanic origin are rarely very large or destructive. They are of interest mainly because they usually create threatening volcaniceruptions, as they did in the weeks before the eruption of Mount St. Helens in Washington, in May 1980.
Such earthquakesoriginate as magma which works its way upward, filling the spaces below a volcano. As the top and bottom of the volcanoswell and are tilted, explosion of the held back magma may create many small earthquakes. On the island of Hawaii,seismographs may register as many as 1000 small earthquakes a day before an eruption occurs. Humans can createearthquakes through a variety of ways, such as the filling of new reservoirs, the underground detonation of explosives, or thepumping of fluids deep into the earth through wells. For example, in 1962 the city of Denver, Colorado, began to experienceearthquakes for the first time in its history. The discovery was made that the tremors where created at the same time as thepumping of waste fluids into deep wells occurred.
When pumping was discontinued, the earthquakes continued for a little whileand then stopped. Earthquakes produce many effects that concern the populations of seismically active regions. They can create many deaths bydestroying structures such as buildings, bridges, and dams, and they can also start devastating landslides. For example, anearthquake near Hebgen, Montana, in 1959 caused a landslide that killed several people and temporarily blocked the MadisonRiver, which created a lake and threatened the town of Ennis with a major flood. Another destructive effect of earthquakes isthe creation of tidal waves. Because these waves are not related to the tides, they are called seismic sea waves or, theirJapanese name tsunamis.
These huge waves of water have hit populated coastlines with such violent actions that entire townshave been destroyed. In 1896 in Sanriku, Japan, with a population of 20,000, suffered from such and event. Where buildingshave been constructed on filled ground, the liquefaction of soils is another seismic hazard. When subjected to the shock wavesof an earthquake, soil used in landfills may lose all its bearing strength and create a substance like quicksand.
Buildings restingon these materials have literally sank into the ground. Seismologists have created two scales of measurement to enable them to describe an earthquakes power. One is the Richterscale, named after the American seismologist Charles Francis Richter, which measures the energy released at the focus of anearthquake. It is a scale that runs from 1 to 9. A magnitude 7 earthquake is 10 times more powerful than a magnitude 6earthquake, 100 times more powerful than a magnitude 5 earthquake, 1000 times more powerful than a magnitude 4earthquake, and so on. An estimated 800 earthquakes of magnitudes 5 to 6 occur annually worldwide, in comparison withabout 50,000 quakes of magnitudes 3 to 4, and only about one earthquake of magnitudes 8 to 9.
Theoretically, the Richterscale is an open-ended one, meaning that the earth can create an earthquake more powerful than 9, but until 1979 anearthquake of magnitude 8. 5 was thought to be the most powerful possible. Since then, improvements in seismic measuringtechniques have enabled seismologists to redefine the scale, and 9. 5 is now considered to be the practical limit.
On the basis ofthe new scale, the magnitude of the 1906 San Francisco earthquake has been revised from 8. 3 to 7. 9, while the Alaskanearthquake of 1964 has been upgraded from 8. 4 to 9. 2. The other scale, introduced at the turn of the 20th century by anItalian seismologist, Giuseppe Mercalli, measures the intensity of shaking with gradations from I to XII.
Because seismicsurface effects decrease with further distances from the focus of the earthquake, the Mercalli rating assigned to the earthquakedepends on the site of the measurement. Intensity I on this scale is defined as an event felt by very few people, where intensityXII is assigned to a catastrophic event that causes total destruction. Events of intensities II to III are roughly equivalent toquakes of magnitude 3 to 4 on the Richter scale, and XI to XII on the Mercalli scale can be correlated with magnitudes 8 to 9on the Richter scale. Attempts at predicting when and where earthquakes will occur have had some success in recent years.
At this time China,Japan, Russia, and the U. S. are the countries most actively supporting this research. In 1975 the Chinese predicted themagnitude 7. 3 earthquake at Haicheng, evacuating 90,000 people only two days before the earthquake destroyed or damaged90 percent of the city’s buildings. One of the clues that led to this prediction was a chain of low-magnitude tremors, calledforeshocks, that had started about five years earlier in the area.
Other potential clues being investigated are tilting or bulging ofthe land surface and changes in the earth’s magnetic field, in the water levels of wells, and even in animal behavior. A newmethod under study in the U. S. involves measuring the buildup of stress in the crust of the earth. On this idea of suchmeasurements the U.
S. Geological Survey, in April 1985, predicted that an earthquake of magnitude 5. 5 to 6 would occur onthe San Andreas fault, near Parkfield, California, sometime before 1993. Many unofficial predictions of earthquakes have alsobeen made. In 1990 a zoologist, Dr.
Iben Browning, warned that a major earthquake would occur along the New Madrid faultbefore the end of the year. Like most predictions of this type, it was proved wrong. While I was trying to predict earthquakes, my first prediction wasnt too far off of my target, I predicted one about 100 milessouth of the California-Mexico border. There were a couple of earthquakes that occurred in California, near L.
A, they were ofcourse very minor and couldnt be felt, they were only detectable by seismographs. The next day I predicted that there wasgoing to be an earthquake in the same spot that it occurred the day before. I was correct, in fact there were three. The nextday I picked a spot about 50 miles north of the earthquake that occurred the day before, this time I was wrong, there weretwo that occurred near the San Francisco bay area and none within a 50 mile radius of my approximation. The next coupledays I predicted earthquakes that were within a 100 mile radius than were they actually occurred. From my experiments Iconcluded that predicting earthquakes was easy, you just have to pick a spot on the fault.
The only thing that troubled me andprobably most scientists, is magnitude, there is no possible way of predicting an earthquakes magnitude. Which is what we arereally trying to predict. Earthquakes happen all the time, but what we are really trying to figure out how to predict is when amajor earthquake is going to occur. I learned that earthquakes are almost unpredictable, and devastating acts of nature. I also learned how earthquakes occur andalmost all of the “earthquake dictionary”. There is still alot more to be known about earthquakes that we still do not knowabout today.
Prediction of large earthquakes is still under development, where prediction of small, unnoticeable earthquakescan be easy to predict because they happen mainly around fault lines.Science
