no-fault insurance, type of indemnity plan, usually applied to automobile coverage, in which those injured in an accident receive direct payment from the company with which they themselves are insured. Originated (1947) in Saskatchewan, Canada, no-fault insurance eliminates the need for accident victims to establish another's liability, or fault, through a civil lawsuit. Lawyers' groups oppose no-fault, saying that it limits the citizen's right to sue. Supporters say that it leads to quicker settlement of accident claims and lower premium rates than the traditional tort liability system because it reduces legal fees and court costs. The first comprehensive no-fault plan in the United States was adopted (1971) in Massachusetts. Currently 13 states have no-fault auto insurance laws that in some way restrict the right of parties to file legal suits. Provisions defining when a person can sue in no-fault states vary, but motorists can generally sue for severe injuries. Recently, however, rising insurance costs have led some states to reexamine the effectiveness of no-fault insurance laws.

fault, in geology, fracture in the earth's crust in which the rock on one side of the fracture has measurable movement in relation to the rock on the other side. Faults on other planets and satellites of the solar system also have been recognized. Evidence of faults are found either at the surface (fault surface) or underground (fault plane). Faults are most evident in outcrops of sedimentary formations where they conspicuously offset previously continuous strata. Movement along a fault plane may be vertical, horizontal, or oblique in direction, or it may consist in the rotation of one or both of the fault blocks, with most movements associated with mountain building and plate tectonics. The two classes of faults include the dip-slip (up and down movement), which is further divided into normal and thrust (reverse) faults; and strike-slip (movement parallel to the fault plane). The San Andreas fault of California is of this type. In dip-slip faults the term "hanging wall" is used for the side that lies vertically above the other, called the "footwall." A fault in which the hanging wall moves down and the footwall is stationary is called a normal fault. Normal faults are formed by tensional, or pull-apart, forces. A fault in which the hanging wall is the upthrown side is called a thrust fault because the hanging wall appears to have been pushed up over the footwall. Such faults are formed by compressional forces that push rock together and are by far the most common of the dip-slip faults. All types of faults have been recognized on the ocean floor: normal faults occur in the rift valleys associated with mid ocean ridges spreading at slow rates; strike-slip faults appear between the offset portions of mid-ocean ridges; and thrust faults occur at subducting plate boundaries. Active faults, though they may not move for decades, can move many feet in a matter of seconds, producing an earthquake. The largest earthquakes occur along thrust faults. Some faults creep from a half inch to as much as 4 in. (1 to 10 cm) per year. Fault movements are measured using laser and other devices. Faults create interpretation problems for geologists by altering the relations of strata (see stratification), such as making the same rock layer offset in two vertical cross sections of a formation or making layers disappear altogether. Faults are often seen on the surface as topographical features, including offset streams, linear lakes, and fault scarps.

San Andreas fault, great fracture (see fault) of the earth's crust in California. It is the principal fault of an intricate network of faults extending more than 600 mi (965 km) from NW California to the Gulf of California. The San Andreas fault, a strike-slip fault, also extends vertically at least 20 mi (30 km) into the earth. It is located on the boundary between two sections of the earth's lithosphere—the North American plate and the Pacific plate (see plate tectonics)—and separates SW California from the North American continent. The Pacific plate is moving northwest in relation to the North American plate, and it is believed that the total displacement along the fault since its formation more than 30 million years ago has been about 350 mi (560 km). Movement along the fault causes earthquakes; several thousand occur annually, although only a few are of moderate or higher magnitude. The destructive San Francisco earthquake of 1906 was caused by a movement in which land surfaces on either side of the fault were displaced horizontally up to 21 ft (6.4 m).

New Madrid Fault System: see under New Madrid, Mo.

In geology, a fracture in the rocks of the Earth's crust, where compressional or tensional forces cause the rocks on the opposite sides of the fracture to be displaced relative to each other. Faults range in length from a few inches to hundreds of miles, and displacement may also range from less than an inch to hundreds of miles along the fracture surface (the fault plane). Most, if not all, earthquakes are caused by rapid movement along faults. Faults are common throughout the world. A well-known example is the San Andreas Fault near the western coast of the U.S. The total movement along this fault during the last few million years appears to have been several miles.

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