Name: Course: Section: Date: (a) What is m, for an earthquake with exactly the s
ID: 117426 • Letter: N
Question
Name: Course: Section: Date: (a) What is m, for an earthquake with exactly the same P-wave amplitude as the example in the figure below but with an at is mb for an earthquake with exactly the same P-wave amplitude as the example in the figure below but with an S-P delay of 30 seconds?10 seconds? (b) What is the relationship between wave amplitude, magnitude, and distance from the epicenter? (c) What is m, for an earthquake with exactly the same S-P delay time as the example in the figure below bur with a P-wave amplitude of 2 mm? 100 mm? d) What is the magnitude of the earthquake based on the follcwing data from three stations close to the epicenter determined in Exercise 16.47 Station A: P-S lag = 20 s, wave amplitude amplitude 12 mm; Station C: P-S lag 50s, P-wave amplitude 7 min 100 mm; Station 3: F-Stag 40 s, P-wave lote: The seismograms in Exercise 16.4 are artificial. If they were from a real earthquake, the values for m, calculated from ch should be nearly identical Determining the body wave magnitude of an earthquake. Maximum wave amplitude Distance S-P delay Magnitude 50 100 400 6 40 50 300 20 30 10 5.0 2.0 200 20 4 10010 608 3 6 40 0.5 0.2 0.1 4 20Explanation / Answer
A)
Body wave magnitude Mb
For earthquakes measured at distances greater than 600 km magnitude can be estimated from the formula.
mb = log10(A/T) + 0.01*50 + 5.9
= log(2.5/30) + 0.01*50 + 5.9
= log(0.08 ) + 6.4
=-1.096+6.4
=5.30 mb
Where A is the maximum amplitude (in micrometres)of the P-waves measured at period T (generally about one second) the event D
mb = log10(A/T) + 0.01*D + 5.9
= log(2.5/10) + 0.01*50 + 5.9
=log(0.25) + 6.4
= -0.60 +6.4
=5.79 mb.
b)
Amplitude and the distance from the epicentre is worn to compute the magnitude in Richter scale. The process differs for the strength of quake to quake and position to position. The modern enhanced method is using instant magnitude method.
Just for rough idea you can compute like this for S wave. The quantity of vibration will be 0.1 mm when deliberate from the distance of 100 Kilometers. This shaking will boost by ten fold for each Richter scale. The distance will decrease the amplitude according the opposite square of the distance from epicenter.
But more intricate calculations are adopted. Nothing gives accurate result. We get only fairly unswerving results.
c)
for 2 Amplitude
mb = log10(A/T) + 0.01*D + 5.9
= log (2/8)+ 0.01*75 + 5.9
=-0.60+6.35.
= 5.74 mb
for 100 Amplitude
mb = log10(A/T) + 0.01*D + 5.9
=log ( 100/50) + 0.01*450 + 5.9
= 0.301+10.4
= 10.70 mb
d)
mb = log10(A/T) + 0.01*D + 5.9
=log( 100/40) + 0.01*400 + 5.9
=0.397 +9.9
=10.29
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