mouth of the Gulf of California where the East Pacific Rise currently meets the San Andreas Fault zone. The Guadeloupe and Fallaron microplates were previously being subducted under the North American Plate and the northern end of this boundary met the San Andreas Fault. Material for this subduction was provided by a ridge equivalent to the modern East Pacific Rise slightly displaced to the west of the trench. As the ridge itself was subducted an RTF triple junction momentarily existed but subduction of the ridge caused the subducted lithosphere to weaken and ‘tear’ from the point of the triple junction. The loss of slab pull caused by the detachment of this lithosphere ended the RTF junction giving the present day ridge – fault system. An RTF(a) is stable if ab goes through the point in velocity space C, or if ac and bc are colinear. Trench-Trench-Trench junctions A TTT(a) junction can be found in central Japan where the Eurasian plate overrides the Philippine and Pacific plates, with the Philippine plate also overriding the Pacific. Here the Japan Trench effectively branches to form the Ryukyu and Bonin arcs. The stability criteria for this type of junction are either ab and ac form a straight line or that the line bc is parallel to CA. Examples The junction of the Red Sea, the Gulf of Aden and the East African Rift centered in the Afar Triangle (the Afar Triple Junction) is the only Ridge-Ridge-Ridge (R-R-R) triple junction above sea level. The Rodrigues Triple Junction is a R-R-R triple junction in the southern Indian Ocean, where the African, the Indo-Australian and the Antarctic Plates meet. The Galapagos Triple Junction is an R-R-R triple junction where the Nazca, the Cocos, and the Pacific Plates meet. The East Pacific Rise extends north and south from this junction and the Galapagos Rise goes to the east. This example is made more complex by the Galapagos Microplate which is a small separate plate on the rise just to the southeast of the triple junction. Chiapas coast off Tapachula where Guatemala, North America and Pacific join and small earthquakes occur weekly. This is pushed eastward by the Cocos plate. On the west coast of North America is another unstable triple junction offshore of Cape Mendocino. To the south, the San Andreas Fault, a strike-slip fault and transform plate boundary, separates the Pacific Plate and the North American Plate.