explain the difference and likeness that the GPS system using satellites to loca
ID: 284386 • Letter: E
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explain the difference and likeness that the GPS system using satellites to locate a GPS antenna and seismologists using seismometers to locate the epicenter of an earthquake. explain the difference and likeness that the GPS system using satellites to locate a GPS antenna and seismologists using seismometers to locate the epicenter of an earthquake. explain the difference and likeness that the GPS system using satellites to locate a GPS antenna and seismologists using seismometers to locate the epicenter of an earthquake.Explanation / Answer
LOCATE THE EPICENTER OF AN EARTHQUAKE.
In order to determine the location of an earthquake, epicenter travel times of P- and S-waves to at least three
seismic stations are necessary. The data from one station give only the distance of the epicenter from
that station. It could lie anywhere on a circle centered at the station. The data from an additional station define a
second circle which intersects the first circle at two points each of which could be the true epicenter. Data from a
third station remove the ambiguity: the common point of intersection of the three circles is the epicenter.
Generally, the circles do not intersect at a point but from a small spherical triangle. The optimum location of
the epicenter is at the center of the triangle. If data are available for more than three seismic stations, the epicentral location is improved; the triangle is replaced by a small polygon. This situation arises in part from observational errors, and because the theoretical travel times are imperfectly known. The interior of the Earth is neither homogeneous nor isotropic, as must be assumed. The exact location of earthquake epicenters requires detailed knowledge of the seismic velocities along the entire path, but especially under the source area and the receiving station. The main reason for the intersection triangle or polygon is, however, that the seismic rays travel to the seismograph from the focus, and not from the epicenter. The focal depth of the earthquake, d, which may be up to several hundred kilometers,must be taken into account. It can be estimated from simple geometry.
LOCATE A GPS ANTENNA
The GPS concept is based on time and the known position of specialized satellites. The satellites carry very stable atomic clocks that are synchronized with one another and to ground clocks. Any drift from true time maintained on the ground is corrected daily. Likewise, the satellite locations are known with great precision. GPS receivers have clocks as well; however, they are usually not synchronized with true time and are less stable. GPS satellites continuously transmit their current time and position. A GPS receiver monitors multiple satellites and solves equations to determine the precise position of the receiver and its deviation from true time. At a minimum, four satellites must be in view of the receiver for it to compute four unknown quantities (three position coordinates and clock deviation from satellite time).
Therefore the similarity between then is at least three seismogram necessary for epicenter locate and three satellites necessary for locating GPS antenna if we consider that the GPS antenna location is invariable with respect to time , otherwise for satellites is essential for solving three equation .
And their difference is that for epicenter location we use an elastic medium and two types of elastic wave P –wave and S –wave
But for GPS antenna location , no medium is essential , and here we use Electromagnetic Wave
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