Mendocino triple junction

This triple junction is the location of a change in the broad tectonic plate motions which dominate the west coast of North America, linking convergence of the northern Cascadia subduction zone and translation of the southern San Andreas Fault system.

[3] This instigates different tectonic processes, which include surficial uplift, crustal deformation, intense seismic activity, high heat flow, and even the extrusion of volcanic rocks.

This activity is centered on the current triple junction position, but evidence for its migration is found in the geology all along the California coast, starting as far south as Los Angeles.

Once this hot mantle material is south of the triple junction, it cools, stiffens, and accretes to the adjacent lithosphere, eventually welding to it and moving along with it, analogous to the motion of a conveyor belt.

[5] The region is dominated by Mesozoic-to-Cretaceous aged rocks which make up an uplifted subduction zone accretionary wedge called the Franciscan Complex.

[4] The presence of hot asthenospheric mantle at shallow levels beneath the western margin of North America is likely to generate melt and cause magmatism.

An example of volcanic bodies that formed by magma upwelling and solidification are the Nine Sisters, located between Morro Bay and San Luis Obispo in California.

Similar to the general seismicity patterns in the region, the majority of the aftershocks for this event had vertical strike-slip motions and were located within the Gorda plate, or on the MTF at depths between 23 and 35 km.