EPS 20: Earthquakes in your backyard Summer 2021, session D Homework #2 – Due 07/28/2021 Problem 1: Stress magnitudes (5 points) Determine what stress regime will result from the following principal stress combinations: 1.
a) S
hmin
= 7,000 psi, S
Hmax
= 11,200 psi, S
v
= 12,100 psi 2.
b) S
hmin
=7,400 psi, S
Hmax
=12,100psi, S
v
=10,800psi 3.
c) S
hmin
= 10,900 psi, S
Hmax
= 12,100 psi, S
v
=8,100 psi 4.
d) S
hmin
=10,200psi, S
Hmax
=12,100psi,S
v
=10,200psi 5.
e) S
hmin
= 9,500 psi, S
Hmax
= 11,100psi, S
v
= 11,100psi Problem 2: Fault Slip rate (5 points) Material in an old channel near a fault was carbon dated to 3000 years ago when the channel was last active. The total displacement on the channel is 600m. If the fault moved 0.2 m with every earthquake (the fault is fully locked, no creep) what is the earthquake average yearly rate on this fault? Problem 3: Magnitude calculations (5 points) 1.
a) Use the following information to calculate the surface (M
s
) and body (m
b
) earthquake magnitudes using the following parameters: P-wave: A = 1.45 x 10
-6 m T = 10 sec Δ = 29° Rayleigh wave: A = 3.0 x 10
-6 m Δ = 24° 2.
b) A fault plane of length 1 km and width 3 km slipped 4 m. If the rock rigidity is 3.1 x 10
10 N/m
2
. Calculate the moment magnitude M
w for the earthquake produced when the fault slipped. Problem 4: Seismic Hazards in the PNW (5 points) In no more than 200 words, discuss the importance of the Lawson Report to understanding why earthquakes occur.
