Geology Reference
In-Depth Information
corresponding radiation pattern to set up a quan-
titative characterization of the kinematic and dy-
namic parameters associated with an earthquake.
couples, we obtain a rank-two tensor that is
termed the
moment tensor
.Clearly,iftheforce
couples must be used to build double couples
that are representative of real seismic sources,
we need to ensure that the total torque be
zero. This requirement then translates into a
specific condition of symmetry for the moment
tensor components:
M
ij
D
M
ji
. Therefore,
the moment tensor represents three different
double couples and three force pairs with zero
moment, corresponding to the diagonal elements.
The
10.3 Moment Tensor
Let us consider the set of all force couples
in a Cartesian coordinate system, such that
the opposing forces are directed as the
x
i
axis and separated in the
x
j
direction. The
nine possibilities are illustrated in Fig.
10.13
.
If
latter
system
of
forces
can
be
used
in
assign
a
magnitude
M
ij
to
each
of
these
the
modelling
of
explosive
sources
but
not
Fig. 10.13
The nine force couples composing the seismic moment tensor
