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The strongest and most widely felt earthquake in Oklahoma occurred on April 9, 1952. The intensity VII (Modified Mercalli Scale) tremor was felt over 362,000 sqaure kilometres. A second intensity VII earthquake, felt over a very small area, occurred in October 1956. In addition, 15 other shocks, intensity V or VI, have originated within Oklahoma.
Most of New Mexico's historical seismcity has been concentrated in the Rio Grande Valley between Socorro and Albuquerque. About half of the earthquakes of intensity V or greater (Modified Mercalli intensity) that occurred in teh State between 1868 and 1973 were centered in this region.
Since 1852, more than 30 shocks of intensity VI or greater (Modified Mercalli scale) have occurred in western Nevada. At least three of these were classified as intensity X. In addition, seven earthquakes (intensity VI or greater) were centered in the eastern part of the State. Almost 2,000 other shocks have been cataloged in the nearly 125-year period of historical records. Thus, Nevada ranks among the most seismically active States.
Nebraska is in a region of moderate seismicity occasionally punctuated by rather strong earthquakes. Most of the State is seismic risk zone 1, with a small part in the southeast corner in risk zone 2. the first significant earthquake felt in Nebraska occurred in 1867, the year that statehood was achieved. the tremor occurred on April 24, 1867, and was apparently centered near Lawrence, Kansas. It affected an area estimated at 780,000 km 2 including much of Nebraska. Since 1867, at least seven earthquakes of intensity V or greater have originated within Nebraska's boundaries. Several strong earthquakes centered in neighboring States have also been felt over limited portions of Nebraska. None of these caused damage.
Montana is one of the most seismically active States in the Union. Since 1925, the State has experienced five shocks that reached intensity VIII or greater (Modified Mercalli Scale). During the same interval hundreds of less severe tremors were felt within the State. Montana's earthquake activity is concentrated mostly in the mountainous western third of the State which lies within a seismic zone that also includes southeastern Idaho, western Wyoming, and central Utah.
Most of Missouri's earthquake activity has been concentrated in the southeast corner of the State, which lies within the New Madrid seismic zone. As recently as Merch 29, 1972, the region was jolted by a magnitude 3.7 shock that was felt over a 168,000 square kilometre area including parts of Arkansas, Illinois, Mississippi, and Tennessee.
Since its admission into the Union in 1817, Mississippi has had only four earthquakes of intensity V or greater within its borders. Although the number of earthquakes known to have been centered within Mississippi's boundaries is small, the State has been affected by numerous shocks located in neighboring States. In 1811 and 1812, a series of great earthquakes near the New Madrid Missouri area was felt in Mississippi as far south as the gulf coast. The New Madrid series caused the banks of the Mississippi River to cave in as far as Vicksburg, mroe than 300 miles from the epicentral region. As a result of this great earthquake series, the northwest corner of Mississippi is in seismic risk zone 3, the highest risk zone. Expect for the new Madrid series, effects in Mississippi from earthquakes located outside of the State have been less than intensity V.
French traders and missionaries were active in the region that is now Minnesota as early as the 1650's; however, settlement proceeded slowly and the area was not organized as a territory until 1849. Minnesota was admitted to the Union as the 32nd State on May 11, 1858. the earthquake history of the State is incomplete, owing to the scarity of residents prior to the middle of the 19th century.
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The Fifth European Conference on Earthquake Engineering was held on September 22 through 25 in Istanbul, Turkey. The opening speech by the Honorable H. E. Nurettin Ok, Minister of Reconstruction and Resettlement of Turkey, introduced the several hundred delegates to the realities of earthquake hazards in Turkey:
Changes in sea level have long been used as a measure of local uplift and subsidence associated with large earthquakes. For instance, in 1835, the British naturalist Charles Darwin observed that sea level dropped by 2.7 meters during the large earthquake in Concepcion, CHile. From this piece of evidence and the terraces along the beach that he saw, Darwin concluded that the Andes had grown to their present height through earthquakes. Much more recently, George Plafker and James C. Savage of the U.S Geological Survey have shown, from barnacle lines, that the great 1960 Chile and the 1964 Alaska earthquakes caused several meters of vertical displacement of the shoreline.
Whether in a castle in Italy, a police station in Iceland, o an abandoned gold mine in Australia, the sensitive instruments in the Worldwide Seismograph Network send a steady flow of standard earthquake records to the geophysical scientific community. They provide the raw data that make possible very precise earthquake studies, precise because the instruments are identical and their product standard. A truly international program, this network of 115 stations in 61 countires and territories has laid the foundation for reserach in seismology for many years to come.
Following on from the concepts of plate tectonics, the earth sciences are now embarking on a challenging course- the time prediction of geologic phenomena. Earthquake prediction is an outstanding example of this. However, earthquake prediction is not the only scientific goal. The destructive power of a large earthquake requires that we also take mitigating actions; these include earthquake engineering research to design construction that will resist earthquake shaking. Nevertheless, earthquake prediction has a vital role to play not only in the saving of lives, but in the reduction of economic loss and social disruption from large earthquakes. There are two distinct motivations for earthquake prediction. The mechanistic approach aims to understand the processes leading to a large earthquake. The empirical approach is governed by the immediate need to protect lives and property. With our current lack of knowledge about the earthquake process, future progress cannot be made without gathering a large body of measurements. These are required not only for the empirical prediction of earthquakes, but also for the testing and development of hypotheses that further our understanding of the processes at work. The earthquake prediction program is basically a program of scientific inquiry, but one which is motivated by social, political, economic, and scientific reasons. It is a pursuit that cannot rely on empirical observations alone nor can it carried out solely on a blackboard or in a laboratory. Experiments must be carried out in the real Earth.
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The October 7 earthquake near Blue Mountain Lake in the central Adirondack Mountains registered a preliminary Richter magnitude of 5.2. It was widely felt throughout the Northeastern United States and Canada and occurred in an area that has been periodically shaken by earthquakes throughout recorded history. Since 1737, at least 346 felt earthquakes have occurred in New York; an earthquake of similar magnitude last shook the Blue Mountain Lake area on June 9, 1975.
One of the specific objectives of the Earthquake Hazard Reduction Act of 1977 is to educate the public, including State and local officials, about earthquakes. Although the Federal Government is significantly increasing its research efforts in earthquake studies, the ultimate benefits of this program will depend on whether the individual citizen living in an earthquake zone can accurately understand what is meant by an earthquake hazard. With this in mind, I organized a small workshop for approximately 30 people on February 2 and 3, 1978, in Menlo Park, Calif. the purpose of the meeting was to discuss methods of involving volunteers in a meaningful way in earthquake research and in educating the public about earthquake hazards. The emphasis was on earthquake prediction research, but the discussions covered the whole earthquake hazard reduction program. Representatives attended from the earthquake research community, from groups doing socioeconomic research on earthquake matters, and from a wide variety of organizations who might sponsor volunteers.
Earthquake predictions is a rapidly advancing field of research and development. And now is the time to begin planning how we should use the results of this research.
The Tangshan earthquake of 1976 was one of the largest earthquakes in recent years. It occurred on July 28 at 3:42 a.m, Beijing (Peking) local time, and had magnitude 7.8, focal depth of 15 kilometers, and an epicentral intensity of XI on the New Chinese Seismic Intensity Scale; it caused serious damage and loss of life in this densely populated industrial city. Now, with the help of people from all over China, the city of Tangshan is being rebuild.