Page 230 - Global Tectonics

216 CHAPTER 8

(c) Map
Releasing step-over
(a)
Pull-apart basin

Extensional (d) Cross sections
strike-slip duplex
at releasing bend
Restraining step-over

Negative
Push-up flower
structure

Releasing bend
(b)
Subsidence

Contractional
strike – slip duplex Positive
at restraining bend flower
Restraining bend structure
Uplift
Strike – slip fan

Figure 8.5 Map views of (a) step-overs and (b) bends and associated structures (after McClay & Bonora, 2001, Bull.
Am. Assoc. Petroleum Geols. AAPG © 2001, reprinted by permission of the AAPG whose permission is required for

further use). (c) Map and (d) cross-sections of strike-slip duplexes, fans and flower structures developed at bends (after
Woodcock & Rickards, 2003, with permission from Elsevier).

a series of contractional step-overs. East of contractional step-overs near San Francisco
the bay, Mt. Diablo (Fig. 8.7a) marks the core Bay by combining GPS velocities with
of an anticlinorium that has formed between interferometric synthetic aperture radar
the Greenville and Concord faults (Unruh & (InSAR) data (Section 2.10.5) collected over
Sawyer, 1997). The transfer of about 18 km an 8 year period. After filtering out seasonally

of dextral strike-slip motion across this step- varying ground motions, the InSAR residuals
over during the late Cenozoic has resulted in (Fig. 8.7b) showed that the highest uplift rates
a series of oblique anticlines, thrust faults, occur over the southern foothills of Mount
and surface uplifts that form a typical Diablo. Other zones of rapid uplift occur
stepped, overlapping en echelon pattern. Mt. in the Mission Hills step-over between the
Diablo is the largest push-up in the region. Hayward and Calaveras faults, and between
Studies of deformed fl uvial terraces suggest faults in the Santa Cruz Mountains. In the
−1
an uplift rate of 3 mm a over the last 10,000 former area, seismicity is consistent with the
years, which is comparable to the rates of transfer of slip on the Calaveras Fault onto
slip on the adjacent faults (Sawyer, 1999). the northern Hayward Fault through the
Bürgmann et al. (2006) resolved the rates of Mission Hills (Waldhauser & Ellsworth,
vertical crustal motion associated with several 2002). The origin of other vertical