A transform fault is formed when two plates move parallel to their common boundary in opposite directions or in the same direction but at different rates for an external framework. These margins are sometimes called conservative margins because lithosphere is neither created or destroyed. The movement of the plates is a strike-slip motion. Transform faults may link two spreading centers such as faults that run between two offset portions of the mid ocean Ridges. The Siqueiros transform fault is an example. The Queen Charlotte fault connects a ridge and a subduction zone trench. The Hunter fracture zone is an example of a transform fault that connects two trenches (Kennett 1982).
The Siqueiros transform fault joins two offset sections of the East Pacific Rise. This fault lies southwest of Acapulco at 8 degrees 20 minutes N latitude and 8 degrees 30 minutes N longitude. The length of the Siqueiros is about 138Km long and 20Km wide. (Fornari 1988) According to Sea Marc II sonar mapping the fault system is composed of five strike-slip faults and four intra transform spreading centers. The rate of slip along this fault is 63KmMa-1 (Klitgord and Mammerick, 1982).
Both intersection points of the Siqueiros Transform fault with the East Pacific Rise show a sharp curving of the ridge into the transform. This feature is seen in most transforms that exhibits a fast slip rate (Fornari 1988). The two western spreading centers seem to be older, more active. The two eastern centers are younger and less stable. They are still in their immature pull apart stages where no organized spreading has yet occurred (Fornari 1988).
REFERENCES
Diane Persing, 2/21/97
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