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CONTINENTAL TRANSFORMS AND STRIKE-SLIP FAULTS 223

In profile, the various splays of a strike-slip fault which in this area is nearly vertical. The

zone may converge downward at depth to contractional component of deformation that
produce a characteristic geometry in profi le arises from the oblique plate convergence is
known as a fl ower structure (Fig. 8.5d) accommodated by structures located both
(Harding, 1985; Christie-Blick & Biddle, west and east of the Alpine Fault. On the
1985). Negative fl ower structures are those western side, a 25-km-wide thrust wedge is
where the upward-branching faults display composed of a series of active thrust, reverse,
mostly normal offsets beneath a synform or and oblique-slip faults that steepen downward
surface depression (e.g. Fig. 8.9b). Positive toward the Alpine Fault. This fault segment
fl ower structures are those where the illustrates how shortening occurs
upward-branching faults display mostly simultaneously with dextral strike-slip motion
reverse offsets beneath an antiform or surface in different places along the plate boundary.
culmination. A positive fl ower structure A similar strike-slip partitioned system occurs in
is illustrated by the geometry of faults in the “Big Bend” region of southern California
southern Dagg Basin (Fig. 8.10). where thrust faults accommodate contraction
simultaneously with dextral strike-slip
5 Strike-slip partitioning in transpression and motion. Within the San Gabriel Mountains
transtension. There are several ways in which (Fig. 8.8a), the San Andreas Fault lies at
displacements may be distributed between the about 35° to the direction of relative motion

boundaries of obliquely converging or diverging between the Pacific and North American
blocks and plates. One common way is by plates. This oblique angle results in
simultaneous motion on separate strike-slip and a component of contraction that is
contractional or extensional structures. In this accommodated by reverse faulting and
scenario, strike-slip faults accommodate the folding within the mountains north of the
component of oblique convergence/divergence Los Angeles Basin. The oblique angle
that parallels the plate boundary and the also results in strike-slip motion, which is
contractional or extensional structures accommodated by a series of steep west–
accommodate the component oriented northwest-trending faults includes the San
orthogonal to the plate boundary. Such systems, Andreas Fault itself (Fuis et al., 2003).
where strike-slip and dip-slip motion occur in An example of a very weakly or nonpartitioned
different places and on separate structures, are style of transpressional deformation occurs
strike-slip partitioned. Alternatively, both strike-slip along the central segment of the Alpine Fault
and margin-perpendicular components of the on the South Island of New Zealand. Here,
deformation may occur either on the same the Alpine Fault strikes to the northeast (55°)
structure, such as occurs presently on the central and dips moderately to the southeast (Fig.
oblique-slip section of the Alpine Fault in New 8.2b, Section 8.3.3). Norris & Cooper (2001)
Zealand (Section 8.3.3), or both components showed that, unlike the Fiordland segment,
may be distributed more or less uniformly across slip on the central segment of the fault is
a zone. The relative contributions of strike-slip oblique and approximately parallels the
and margin-perpendicular deformation allow interplate vector (Section 8.3.3). At the

further classification into strike-slip-dominated eastern and western limits of deformation on
and thrust- (or normal-) dominated systems. the South Island, reverse faults approximately
The southern segment of the Alpine Fault parallel the Alpine fault but are inferred to
illustrates a strike-slip partitioned style of have relatively low rates and minor
transpression. Near the Fiordland margin components of strike-slip motion (Norris &
(Fig. 8.9a), the fault lies at a low angle (11– Cooper, 2001; Sutherland et al., 2006). These
25°) to the azimuth of Pacifi c–Australian characteristics indicate that the central
plate motion (Barnes et al., 2005). This low segment of the Alpine Fault system is at best
angle results in almost pure strike-slip motion weakly partitioned and appears to be
along the active trace of the Alpine Fault, nonpartitioned in some areas.