Environmental Engineering Reference
In-Depth Information
where
strike-slip:
a
5.16 m,
b
1.12 m,
s
0.28
reverse:
a
5.00 m,
b
1.22 m,
s
0.28
normal:
a
4.86m,
b
1.32 m,
s
0.34
all:
a
5.08 m,
b
1.16 m,
s
0.28
with SRL being the surface rupture length in km.
Various investigators have proposed relationships to predict ground-motion relationships
with fault length. In two recent events (Izmit, Turkey, and Chi-Chi, Taiwan, both in 1999 with
M
w
7.6) investigators found that peak accelerations were significantly below predictions
when several of the relationships were used. An explanation may be in terms of fault char-
acteristics. Faults with a large total slip may be smooth and devoid of asperities, thus radi-
ating less high-frequency energy than a fault with less total slip and a rough interface.
Rupture Width and Area
For a specific fault, the
M
w
of a potential earthquake can be estimated by relating it to the
potential rupture width
of the fault in the western United States (NRC, 1997) using the Wells
and Coppersmith (1994) relationship
M
w
a
b
log (RW)
(11.19)
where
strike-slip:
a
3.80 m,
b
2.59 m,
s
0.45
reverse:
a
4.37 m,
b
1.95 m,
s
0.32
normal:
a
4.04 m,
b
2.11 m,
s
0.31
all:
a
4.06 m,
b
2.25 m,
s
0.41
with RW being surface rupture width in km.
For a specific fault, the
M
w
of a potential earthquake can be estimated by relating it to
the
potential rupture area
of the fault in the western United States (NRC, 1997) using the
Wells and Coppersmith (1994) relationship
M
w
a
b
log (RA)
(11.20)
where
strike-slip:
a
3.42 m,
b
0.90 m,
s
0.22
reverse:
a
3.99 m,
b
0.98 m,
s
0.26
normal:
a
2.87 m,
b
0.82 m,
s
0.22
all:
a
3.49 m,
b
0.91 m,
s
0.24
with RA being surface rupture area in km
2
.
Duration vs. Length
Shaking duration in large earthquakes depends heavily on the length of faulting. The
longer the length of fault rupture, the greater is the duration of the time in which the seis-
mic waves reach a given site. A fault can however, rupture progressively over a long dura-
tion such as in Alaska (1964), or it can rupture in a sequence of breaks resulting in a
duration such as in San Francisco in 1906 (see
Section 11.2.3)
.
Attenuation from the Fault
Close Proximity to Rupture
Peak intensities or magnitudes are not necessarily located at the surface expression of the
fault; the depth of focus and fault inclination will affect surface response. Housner (1970a)
