The Mendocino fracture zone is a

fracture zone A fracture zone is a linear feature on the ocean floor—often hundreds, even thousands of kilometers long—resulting from the action of offset mid-ocean ridge axis segments. They are a consequence of plate tectonics. Lithospheric plates on eit ...

and

transform boundary A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subductio ...

over 4000 km (2500 miles) long, starting off the coast of

Cape Mendocino Cape Mendocino ( Spanish: ''Cabo Mendocino'', meaning "Cape of Mendoza"), which is located approximately north of San Francisco, is located on the Lost Coast entirely within Humboldt County, California, United States. At 124° 24' 34" W longit ...

in far northern

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

. It runs westward from a triple junction with the

San Andreas Fault The San Andreas Fault is a continental Fault (geology)#Strike-slip faults, right-lateral strike-slip transform fault that extends roughly through the U.S. state of California. It forms part of the tectonics, tectonic boundary between the Paci ...

and the

Cascadia subduction zone The Cascadia subduction zone is a convergent plate boundary, about off the Pacific coast of North America, that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is capable of producing 9.0+ m ...

for about 300 km to the southern end of the Gorda Ridge. It continues on west of its junction with the Gorda Ridge, as an inactive remnant section which extends for about 4,000 km to approximately 35°N 175°W. Technically, a fracture zone is not a transform fault, but in the case of the Mendocino, the term has been loosely applied to the

active fault An active fault is a fault that is likely to become the source of another earthquake sometime in the future. Geologists commonly consider faults to be active if there has been movement observed or evidence of seismic activity during the last 10,0 ...

segment east of the Gorda Ridge as well as to the true fracture zone segment west of it. Many

seismologist Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...

s refer to the active segment as the Mendocino Fault or Mendocino fault zone. The fault section demarcates the boundary between the northwestward-moving Pacific plate and the eastward-moving

Gorda plate The Gorda plate, located beneath the Pacific Ocean off the coast of northern California, is one of the northern remnants of the Farallon plate. It is sometimes referred to (by, for example, publications from the USGS Earthquake Hazards Program) ...

. The Gorda plate is subducting beneath the North American plate just offshore of Cape Mendocino. Where the Mendocino Fault intersects the undersea trench of the subduction zone, it also meets the San Andreas Fault. This seismically active intersection is called a

triple junction A triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction each of the three boundaries will be one of three types – a ridge (R), trench (T) or transform fault (F) – and triple junctions can be ...

, and specifically the Mendocino triple junction. In

tsunami A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...

studies, energy focusing around the fracture zone has been noted, leading to increased wave heights in the area around

Crescent City, California Crescent City ( Tolowa: ''Taa-’at-dvn''; Yurok: ''Kohpey''; Wiyot: ''Daluwagh'') is the only incorporated city in Del Norte County, California, of which it is also the county seat. The city is on the North Coast of California and had a tota ...

. The fracture zone is referred to as the Mendocino escarpment in these studies, descriptively rather than named from its geological origin.

History

Robert W. Pease observed in 1965 that the alignment of a transverse tectonic zone extending from

Mount Lassen Lassen Peak ( ), commonly referred to as Mount Lassen, is a lava dome volcano in Lassen Volcanic National Park in Northern California. Located in the Shasta Cascade region above the northern Sacramento Valley, it is the southernmost active vo ...

to the

Walker Lane The Walker Lane is a geologic trough roughly aligned with the California/Nevada border southward to where Death Valley intersects the Garlock Fault, a major left lateral, or sinistral, strike-slip fault. The north-northwest end of the Walker ...

at the north end of Honey Lake Fault, suggests it was once the continental terminus of the Mendocino Fault. It forms the boundary of the

Modoc Plateau __NOTOC__ The Modoc Plateau lies in the northeast corner of California as well as parts of Oregon and Nevada. Nearly of the Modoc National Forest are on the plateau between the Medicine Lake Highlands in the west and the Warner Mountains in the ...

and

Columbia Plateau The Columbia Plateau is an important geology, geologic and geography, geographic region that lies across parts of the U.S. states of Washington (state), Washington, Oregon, and Idaho. It is a wide flood basalt plateau between the Cascade Range a ...

provinces with the

Great Basin The Great Basin () is the largest area of contiguous endorheic watersheds, those with no outlets to the ocean, in North America. It spans nearly all of Nevada, much of Utah, and portions of California, Idaho, Oregon, Wyoming, and Baja Californi ...

. Where it meets Honey Lake Fault, it bends to trend northeast across the northwest corner of Nevada, where it accompanies the geological

trough Trough may refer to: In science * Trough (geology), a long depression less steep than a trench * Trough (meteorology), an elongated region of low atmospheric pressure * Trough (physics), the lowest point on a wave * Trough level (medicine), the l ...

that forms

Black Rock Desert The Black Rock Desert is a semi-arid region (in the Great Basin shrub steppe ecoregion) of lava beds and Dry lake, playa, or alkali flats, situated in the Black Rock Desert–High Rock Canyon Emigrant Trails National Conservation Area, a silt ...

References

External links

*
Mendocino Triple Junction Offshore Northern CaliforniaGeology of the Cape Mendocino, Eureka, Garberville, and Southwestern part of the Hayfork 30 x 60 Minute Quadrangles and Adjacent Offshore Area, Northern California, USGS, 2000
{{coord, 40, 25, N, 125, 00, W, type:landmark_region:US-CA_dim:300000, display=title Fracture zones Seismic faults of California Landforms of Humboldt County, California

History

See also

References

External links