segment You now have the maximum depth of fault rupture, the total lengths of ea

Question

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You now have the maximum depth of fault rupture, the total lengths of each segment, and the slip per earthquake….

a) Using the seismic moment equation directly calculate the moment magnitude for a full rupture of each segment of the Wasatch Fault.

Moment = (shear modulus [i.e., rigidity] of crust) X (area that ruptured) X (mean displacement in the earthquake)

Mo = µ *A*D

The Shear modulus can be approximated through the relationship to s-wave velocities, because the velocity of an S wave (Vs) = [shear modulus (µ) / density ()]1/2

Therefore µ = Vs2 x

An S wave travels in continental crust at ~ 3.5 km/s and crustal densities are ~ 2.7 g/cm3

So if you can calculate a shear modulus µ (units should be in g/cm*s2) for the crust you can then calculate the moment for individual earthquakes on each segment of the Wasatch.

Please do this and then use the following logarithmic relationship to change your moment (energy) calculation to a moment magnitude (Mw) for earthquakes on each segment of the fault.

Mw = 2/3 Log (Mo) – 10.7

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Length km Slip Rate MaX dIsplacement m average displacement last EQ reccurance interval depth mileskm Brigham city 36.5 0.94 ±0.03 1.7 1.2 1,558 ± 49 10 Weber 56.5 1.71 ± 0.69 2.5 1.7 1,468 ± 528 16.09344 Salt Lake City 40 1.48 ± 0.53 2 1.4 1,345 ± 112 Provo 59 2.17 ± 1.20 3 2.1 1,827 ± 1,067 Nephi 41.5 1.74 ± 0.93 1.7 1.7 1,932 ± 1,109 Levan 26 1000 ±150 1.7 1.7 1000 ±150

Explanation / Answer

segment You now have the maximum depth of fault rupture, the total lengths of ea

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