Geology Reference
In-Depth Information
Fig. 11.9
Lateral strain as a function of the bending an-
gle at different distances
x
from the trench. The three plots
show that the lateral strain is shortening at any offset
x
for
small bending angles, whereas large extensional strain is
predicted when the bending angle exceeds the equilibrium
value. The curves have been built assuming a curvature
radius ยก
2,500 km. Note that the range of subduction
angles for which lateral shortening (or extension) occurs
is independent from the horizontal offset from the trench
(After Schettino and Tassi
2012
)
D
Fig. 11.10
Lateral strain rate as a function of the bending
angle for different trench curvatures. These plots show that
the lateral strain rate has a small component of shortening
for small bending angles, whereas large extensional strain
rates (up to 4%Myr
1
) are predicted when the bending
angle exceeds the equilibrium value. The curves have been
built assuming a convergence velocity
v
D 50 mm/year
(After Schettino and Tassi
2012
)
Intraslab seismicity has been widely used
to study geometry, pattern of deformation, and
state of stress of slabs. After the classic papers
of Isacks et al. (
1968
) and Isacks and Molnar
(
1971
) mentioned above, Bevis and Isacks (
1984
)
performed an analysis of the geometry of Wadati-
Benioff zones through a determination of trend
surfaces fitting earthquake hypocenters. The
existence of a large number of events that could
not be associated with downdip deformation was
also observed by Apperson and Frohlich (
1987
),
while Bevis (
1988
) estimated an average downdip
strain rate of
10
15
s
1
(
0.032 %/Myr) using
Brune's formula (
11.2
). Nothard et al. (
1996
),
in a study of the deformation of the Tonga slab
based on Kostrov's formula (
11.4
), suggested
that the downdip and lateral strain rates were
of the order of
10
16
10
15
s
1
, one-two
