4.) The next actual Parkfield earthquake occurred in 2004 (surprise, does this a
ID: 286765 • Letter: 4
Question
4.) The next actual Parkfield earthquake occurred in 2004 (surprise, does this agree with your answer to question 3?) yields another data value for the time interval between the historically recorded earthquakes at Parkfield. The time intervals between these successive earthquakes, after 2004 (and until the next one), are now 24, 20, 21 12, 32 and 38 years. Determine the mean value for the time interval between these reported earthquakes.
a.) 25.6
b.) 27.3
c.) 18.9
d.) 24.5
Answer __________
5.) Consider two seismograph stations A and B. An earthquake occurs and is registered by these two seismographs. The time interval between the arrival times of the P waves and the S waves is recorded at both stations, nominally tA and tB . tA = 3.0 minutes and tB = 1.0 minutes . Therefore, the distances
xA and xB from the epicenter of the earthquake to the seismographs A and B, respectively can be summarized as follows:
a.) xA < xB
b.) xA = xB
c.) xA > xB
d.) no summary is possible.
Explanation / Answer
We know that both primary and secondary waves(P and S waves respectively) are body wave (they don't travel on the surface but go inside the surface and hence are known as body waves). Normally in any medium the velocity of S wave is approximately 60% of the velocity of P-waves. Now, as per the question we know the difference in the travel time of P and S wave for two stations as follows:
tA = 3.0 minutes = (primary wave velocity)A - (secondary waves velocity)A
tB = 1.0 minutes = (primary wave velocity)B - (secondary waves velocity)B
On the basis of above equations we can say that it takes more time for body waves to travel from the epicenter of the earthquake "A" to the seismographs A then to epicenter of the earthquake "B" to the seismographs B.
We know speed = Distance/Time
And speed of waves are constant and hence more time means more distance thereofore distance of "A" is greater than distance of "B" or xA > xB.
Hence option "C" is correct.
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