I NEED HELP WITH THESE QUESTIONS FROM ARTICLE ,PLEASE HELP EARTHQUAKE Few natura
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I NEED HELP WITH THESE QUESTIONS FROM ARTICLE ,PLEASE HELP
EARTHQUAKE Few natural phenomena attract as much public attention earthquakes. Seldom does a month go by that we do not hear of a destructive earthquake somewhere in the world. Events like the October 17, 1939 event near San Frncisco Loma Prieta earthquake] and the January 17, 1994 event near Los Angeles [Northridge earthquake] are grimremind- ers that parts of the United States are atrisk from these terrible atural hazards. Even in the so-called stable interior of the United States, a strong public interest exists in earthquake does some concern about the potential of destructive earth- quakes in the Midwest SHAKES CITY Over Northern Minnesota, Accord Earth Tremor FeltA Down at Bemidji-Chimney Knocled Down at Brain erd-No Damage Here, Although Shock Was Felt in Nearly Every Building-Roar Like That ofAutomobil Truck Engine Accompanies Quake. An carthquske which shook neelyimna knocked down in the of northern Minnesota w.x felt|torh part of the city. Excqt Little Falls between 3 and 3 bltht reported from Berni here What Causes an Earthquake? Earthquakes are produced by movement of rock in the n every bailding in Little Falls be leamad At Lincoln, poople in was atrong cnough to rttle oas om the lake se* the quake arth's interior. In volcanic regions, movement of molten rock and associated steam can result in earthquakes. Most earth quakes, however, occur when solid rock masses move past one another along fracture planes called faults. In large earth quakes, such as the San Francisco earthquake of 1906 displacements of tens of feet occur along many tens of miles of the faultplane. By comparison, the 1989 Loma Prieta earth axEware and windows in manyThe staking of the bildngs w The quake w accomp-like tht producod byheavy truck The shock wws cvidently of wideand it was thoeghfirst tha a pomb to reporta. wa aid thi ar The oi wa like the prodaced that some housca had boen byapowerfultomobile engine Piez,ong the neawer towns, feli bout 25 miles of fault plane. The fault movement creates eries of waves through the earth, and we perceive these waves t the surface as the shaking of an earthquake. At Fort Ripley and Brainerd iwa Monday's quake laxied about 20 e center ot the main ru Figure1. Article froun the Little Falls Daily Transcript, September 4 everal miles below the land surface and, like the Loma Prieta and Northridge earthquakes (focal depths = 1 8 km-about 11 miles), may produce little or no surface evidence of the sense of movement. The surface location directly above the focus is called an epicenter, and earthquakes are commonly referred to by the geographic location of the epicenter. The direction and distance of fault movement, as well as focal depth and strength, are usually determined by analysis of earthquake- wave records from a network of sensitite insuuments called eismographs, which are located around the world. 917. Reports of the dammage were exaggerated, but the excitement was earthquakes are comon wbere one plate is driven under the otherin a"subduction zone" as is occuring in the active earth quake regions of the circum-Pacific, including Japan, Alaska, and South America. Destructive earthquakes also occur where plates shear past one another borizontally on what are some times called "transform faults", the San Andreas fault system is a notorious example. Although much of the differential movement between plates may be taken up along a single fault Most earthquakes are related to plate tectonic processes or what used to be understood as "continental drift. In the plate tectonic model, the earth's outermost shell consists of sa number of rigid plates that are roughly 60 miles thick and in clude both the earth's crust and the uppermost mantle. These rigid plates are in a state of continual, but very slow (about an inch a year or about as fast as a fingemail grows) movemn"Some Minnesotans recently had the almost unbehesable experience that forms the plate boundary significant movement can occur along hundreds or even thousands of faults that flank the plate boundaries. For example, the recent Northridge earthquake near Los Angeles occurred along a previously nknown off- hoot of the San Andreas fault er the less solid mantle material, with new plate materia of feeling a subduction-related earthquake which occured on June 9 being created and pushed outward by volcanic processes at 1994 deep beloa Bolvia South America. The usually large size mid-ocean ridges, called "spreading centers." Some earth- (agniude 2) and focal depth (630 km; 390 miles) conmbuted to quakes are generated by faulting and magma movement at its being weasly felt over a wide region of North America. In the spreading centers. Larger and more destructive earthquakes history of seismo.ogy, this appears to be the greatest distance that anExplanation / Answer
Answer -
1) Earthquakes are caused by tectonic movements in the Earth's crust. The main cause is that when tectonic plates , one rides over the other, causing orogeny collide (mountain building), earthquakes.
2) Difference between the focus and epicenter of an earthquake? Thefocus is the point within the earth where seismic waves originate; it is centered on the part of the fault that has the greatest movement. The epicenter is on the earth's surface directly above the focus.
3) Earthquakes are measured using seismographs, which monitor the seismic waves that travel through the Earth after an earthquake strikes. Scientists used the Richter Scale for many years but now largely follow the "moment magnitude scale," The Richter magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. Measure the strength of an earthquake is to use the Mercalli scale. Like The San Andreas Fault is 800 miles long and only about 10-12 miles deep, so thatearthquakes larger than magnitude 8.3 are extremely unlikely. The largestearthquake ever recorded by seismic instruments anywhere on the earth was amagnitude 9.5 earthquake in Chile on May 22, 1960.
4) A temporary increase or decrease in seismicity is part of the normal fluctuation of earthquake rates. Neither an increase or decrease worldwide is a positive indication that a large earthquake is imminent.The ComCat earthquake catalog contains an increasing number of earthquakes in recent years not because there are more earthquakes, but because there are more seismic instruments and they are able to record more earthquakes.The National Earthquake Information Center now locates about 20,000 earthquakes each year, or approximately 55 per day.
5) Scientists have tried lots of different ways of predicting earthquakes, but none have been successful. They have a pretty good idea of where an earthquake is most likely to hit, but they still can't tell exactly when it will happen.However, there are still some ways of monitoring the chances of an earthquake:
A) Laser beams can be used to detect plate movement.
B) A seismometer is used to pick up the vibrations in the Earth's crust. An increase in vibrations may indicate a possible earthquake.
C) Radon gas escapes from cracks in the Earth's crust.
6) Earthquakes occur all the time all over the world, both along plate edges and along faults. Most earthquakes occur along the edge of the oceanic and continental plates. The earth's crust (the outer layer of the planet) is made up of several pieces, called plates.everal major and numerous minor earthquakes have occurred in themidwestern and eastern United States, as well aseastern Canada.midwestern and eastern United States are more prone to earthquakes than others. The most earthquake-prone areas include Charleston, South Carolina, eastern Massachusetts, the St. Lawrence River area, and the central Mississippi River Valley.The central Mississippi River Valley and the Charleston, South Carolina, are more prone to damage during earthquakes than the northern part of the country. These areas have sandy soils that shake more than solid rock, resulting in damage from subsidence during an earthquake. The high water tables along the Mississippi and near the coast also increase the risk of soil liquefaction during strong earthquakes.
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