Geology Reference
In-Depth Information
Fig. 10.16
Lower-half
(
left
) and lateral (
center
)
views of some basic focal
spheres and corresponding
fault geometry and
kinematics (
right
). Only
one of the two possible
focal mechanisms is
displayed. The
compressional quadrants
are shown in
black
Z
T
s
.x;y/
T
s
.x;y/
dS (10.53)
1
S
caused by fault slip. Observed value of the seis-
mic moment range between
4
10
22
Nm (the
largest earthquake included in the Harvard CMT
catalog) and
10
5
Nm for microearthquakes. If
T
s
(
x
,
y
)and
T
0
s
(
x
,
y
) are the shear stresses exerted
on the fault plane before and after an earthquake,
then the stress drop can be defined as the average
change of stress along the fault plane:
•T
s
D
S
The stress drop represents the fraction of stress
that is employed to generate slip along the fault.
In a similar way, we can define the average shear
stress during the coseismic phase.
