Ridgeridge transform faults

Sykes (1967) determined focal mechanism solutions for earthquakes occurring in the vicinity of the fracture zones that offset the Mid-Atlantic Ridge to the left at equatorial latitudes (Fig. 4.17). Events along the ridge axis are consistent with normal faulting along north-south planes. Events along the fracture zones are much more common and the energy release is about a hundred times greater than along the ridge crest. Between the offset ridge segments events are of strike-slip type with one nodal plane consistent with dextral transform motion. Events along the fracture zone beyond the ridge extremities are rare. These results provided striking confirmation of the transform fault concept and further, independent, confirmation of the hypothesis of sea floor spreading.

Before the recognition of transform faulting, the parallel fracture zones which appear to displace the crest of the Mid-Atlantic Ridge in equatorial latitudes between Africa and South America were believed to represent sinistral transcurrent faults that displaced an originally straight crest (Fig. 4.15b). However their

Atlantic Transform Faults

Figure 4.17 Epicenters of earthquakes that occurred on the Mid-Atlantic ridge in the equatorial Atlantic between 1955 and 1965. The arrows beside four of the earthquakes indicate the sense of shear and the strike of the fault plane inferred from focal mechanism solutions (modified from Sykes, 1967, by permission of the American Geophysical Union. Copyright © 1967 American Geophysical Union).

Figure 4.17 Epicenters of earthquakes that occurred on the Mid-Atlantic ridge in the equatorial Atlantic between 1955 and 1965. The arrows beside four of the earthquakes indicate the sense of shear and the strike of the fault plane inferred from focal mechanism solutions (modified from Sykes, 1967, by permission of the American Geophysical Union. Copyright © 1967 American Geophysical Union).

North Termination Mid Atlantic Ridge

Figure 4.18 Northern termination of the Mid-Atlantic Ridge (redrawn from Wilson, 1965, with permission from Nature 207,334-47. Copyright © 1965 Macmillan Publishers Ltd).

Figure 4.18 Northern termination of the Mid-Atlantic Ridge (redrawn from Wilson, 1965, with permission from Nature 207,334-47. Copyright © 1965 Macmillan Publishers Ltd).

re-interpretation, as ridge-ridge transform faults (Fig. 4.15a), implies that the offsets on them do not change with time. Thus the geometry, or locus, of the step-like ridge crest-transform fault sequence in the equatorial Atlantic has remained essentially unchanged throughout the opening of the South Atlantic. As a result the locus parallels the continental shelf edges of South America and Africa and reflects the geometry of the original rifting of the Gondwana supercontinent in this area.

Wilson (1965) also suggested examples of transform faults in the extreme North Atlantic area (Fig. 4.18). In early Paleogene times the Mid-Atlantic Ridge bifurcated to the south of Greenland. The western branch, which is now inactive, passed through Baffin Bay and terminated against the Wegener Fault, an extinct, sinistral ridge-ridge transform fault. The active eastern branch passes through Iceland, and terminates southwest of Spitsbergen at the De Geer Fault. This dextral ridge-ridge transform fault connects to the Gakkel Ridge in the Arctic Basin. Wilson predicted that this is a very slow spreading ridge that is transformed into the Verkhoyansk Mountains of Siberia by rotation about a fulcrum near the New Siberian Islands (Fig. 4.18 inset).

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How To Have A Perfect Boating Experience

How To Have A Perfect Boating Experience

Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.

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