Re: East Pacific Rise Earthquake Forecast
Posted by Don In Hollister on November 08, 2001 at 23:19:22:

Hi Lowell. You could be right. At the rate the geomagnetic storms have been occurring it wouldn’t surprise me one bit if we have another one.

You can correct me if I’m wrong about this. The quakes along the Atlantic Ridge are for the most part are caused by separation. Where as the quakes along the East Pacific Rise are for the most part caused by closely spaced outward-dipping faults that form antithetic to larger inward-dipping faults. Accordingly, inward-dipping faults are less abundant (35-45%) but accommodate more (50-55%) of the roughly ~4.0% strain.

Starting in the south Pacific, there is spreading taking place along the "East Pacific Rise" spreading center, with oceanic crust moving west to Asia and Australia, and east until it runs into South America (where it is subducted and leads to the formation of the volcanic Andes Mountains). This spreading and subduction continues north along the length of South and Central America and up the west coast of Mexico, where it runs up the Gulf of California. It is this spreading motion, which is separating Baja California from mainland Mexico, and has led to the formation of the Imperial Valley and Salton Sea in southernmost California.

From there it becomes a transform fault namely the San Andreas fault. There isn't a very clean break - a two-dimensional fault on a three dimensional sphere makes for some weird geometry, and there are many offsets along the ridge. These "transform faults" actually stagger the axis of spreading, and are very common along all known zones of divergence.

With this kind of staggering you don’t need a geomagnetic storm to trigger a quake. I will have to admit though that it would help. Take Care…Don in creepy town