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The Hayward Fault Zone is a geologic fault zone capable of generating significantly destructive earthquakes. This fault is about long, situated mainly along the western base of the hills on the east side of San Francisco Bay. It runs through densely populated areas, including the cities of Richmond, El Cerrito, Berkeley, Oakland, San Leandro, Hayward, Union City, Fremont, and San Jose, in order from north-to-south. The Hayward Fault is parallel to its more famous (and much longer) westerly neighbor, the San Andreas Fault, which lies offshore and through the San Francisco Peninsula. To the south of the Hayward lies the Calaveras Fault. In 2007 the Hayward Fault was discovered to merge with the Calaveras Fault east of San Jose at a depth of , with the potential of creating earthquakes much larger than previously expected. Some geologists have suggested that the Southern Calaveras should be renamed as the Southern Hayward. North of San Pablo Bay, and somewhat offset from the Hayward Fault is the Rodgers Creek Fault. This structure may be an extension of the Hayward Fault Zone. Another fault further north, the Maacama Fault, is also considered to be part of the "Hayward Fault subsystem".〔(Paleoseismic Investigation Of The Maacama Fault At The Haehl Creek Site, Willits, California )〕 While the San Andreas Fault is the principal transform boundary between the Pacific Plate and the North American Plate, the Hayward Fault takes up a share of the overall motion between the plates. ==Tectonic setting== The Pacific Plate is a major section of the Earth's crust, gradually expanding by the eruption of magma along the East Pacific Rise to the southeast. It is also being subducted far to the northwest into the Aleutian Trench. In California, the plate is sliding northwestward along a transform boundary, the San Andreas Fault, toward the subduction zone. At the same time, the North American Plate is moving southwestward, but relatively southeast along the fault. The westward component of the North American Plate's motion results in some compressive force along the San Andreas and its associated faults, thus helping lift the Pacific Coast Ranges and other parallel inland ranges to the west of the Central Valley, in this region most notably the Diablo Range. The Hayward Fault shares the same relative motions of the San Andreas. As with portions of other faults, a large extent of the Hayward Fault trace is formed from a narrow complex zone of deformation which can span hundreds of feet in width. The transform boundary defined by the San Andreas Fault is not perfectly straight, and the motion of the North American plate is not entirely parallel to the plate boundary. Thus, movement along the boundary here creates stresses in the crust on either side of the boundary, resulting in additional faulting on both sides of the San Andreas Fault. The Hayward Fault is one of the larger faults created this way, along with the Calaveras Fault to the east and the San Gregorio Fault, west of the San Andreas. The complete fault zone, including the Rodgers Creek fault, is divided by seismologists into three segments – Rodgers Creek, Northern Hayward, and Southern Hayward. It is expected that these segments may fail singly or in adjacent pairs, creating earthquakes of varying magnitude. The Association of Bay Area Governments (ABAG) in concert with other government agencies has sponsored the analysis of local conditions and the preparation of maps indicative of the destructive potential of these earthquakes. The various ABAG maps shown below represent some of the more likely possible combinations. While there are indications that a substantial earthquake on a nearby parallel fault can release stress and so also decrease the near-term probability of an earthquake, the opposite appears to be true concerning sequential segments. A release on a major segment can substantially increase the likelihood of an earthquake on an adjacent fault segment, increasing the likelihood of two major regional earthquakes within a period of a few months. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hayward Fault Zone」の詳細全文を読む スポンサード リンク
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