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CONTINENTAL TRANSFORMS AND STRIKE-SLIP FAULTS 217

260° 264° 268° 272° 276°
(a) North American plate 18°
19 Motagua
Caribbean

14° 8 plate 14°
El Salvador
14
Middle America Trench
Cocos plate
73 N 10°
Inset
268° 272°

Río Lempa Faults with dominant vertical
MAP LEGEND
(b) Faults with dominant horizontal
component of displacement

Lago 1 component of displacement
Sites of structural measurements
Ilopango
1 Main volcanic edifices
2 Caldera borders
N 3
W E San Vicente 5
Volcano 4
S
0 5 10 km
Lago Ilopango Río Lempa Area of maximum Berlin
pull-apart Volcano
San
subsidence Río Lempa Miguel
San Vicente
segment San Miguel
Berlin segment Volcano
Figure 8.6 (a) Shaded relief map and (b) interpretation of the Río Lempa pull-apart basin between the San Vicente
and Berlin fault segments of the El Salvador Fault Zone (images provided by G. Corti and modified from Corti et al.,

2005, with permission from the Geological Society of America). Digital elevation model is derived from SRTM
data (http://srtm.usgs.gov/) and Landsat ETM 7 satellite images processed by the University of Maryland, Global
−1
Land Cover facility. Inset shows the plate tectonic setting of Central America and plate velocities (mm a ) after
DeMets, 2001.

movements is more uncertain and may refl ect linear trend following a small circle on the
some nontectonic displacements, such as Earth’s surface. In these areas, the curvature
active landslides, subsidence and rebound over of the fault plane creates zones of localized
aquifers, and the settling of unconsolidated shortening and extension according to whether
sediments along the bay margins. the two sides of the bend converge or diverge
Nevertheless, the data reveal a pattern of (Harding, 1974; Christie-Blick & Biddle, 1985)
highly localized vertical motion associated (Fig. 8.5b). These zones are similar to those
with regions of active strike-slip faulting. that form in step-overs. Pull-apart basins,
zones of subsidence and deposition, and
3 Releasing and restraining bends. In zones where normal faults characterize releasing bends.
strike-slip faults are continuous, the strike of Restraining bends display thrust faults, folds,
the faults may locally depart from a simple and push-ups.