Geoscience Reference
In-Depth Information
(b)
(a)
6
24
( )
5
23
( )
( )
4
22
21
3
2
20
1
19
18
19
20
21
22
23
log M
0
18
17
7
9
6
8
M
s
Figure 4.12.
(a) The relationship between
A
(the surface area of the fault in km
2
)
and
M
0
(the seismic moment in N m). (b) The relationship between
M
0
and
M
S
(the
surface-wave magnitude). Straight lines are for circular cracks with a constant stress
drop
σ
(in MPa). Both (a) and (b) show some difference in stress drop for interplate
(•) and intraplate (o) earthquakes (After Kanamori and Anderson (1975).) (c) The
relationship between the seismic moment of an earthquake and the length of the
fault that it ruptures. There may be a difference between large- and small- thrust
earthquakes: above some earthquake size, once the whole down-dip extent of the
fault plane ruptures, the rupture can then continue only by extending along the
length of the fault. This shows in the change of slope at ∼10
20
Nm: the seismic
moment increases approximately as (fault length)
3
but for large earthquakes it
increases as (fault length)
2
. For strike-slip earthquakes, however, the seismic
moment increases as (fault length)
2
up to 10
21
Nm. (After Henry and Das (2001).)
