User:Guptapriyu0

'Earthquakes represent the vibration of Earth because of'' movements on faults. The focus is the point on the fault surface where motion begins. The epicenter is the point on Earth's surface directly above the focus.The deadly Izmit earthquake struck northwest Turkey on August 17, 1999, at 3 a.m. Over 14,000 residents of the region were killed as poorly constructed apartment,complexes pancaked to the ground, each floor collapsing on the one below (Fig. 1). The death toll from this single event was greater than the average annual loss of life from all earthquakes worldwide. An earthquake occurs when Earth’s surface shakes because of the release of seismic energy following the rapid movement of large blocks of the crust along a fault. Faults are breaks in the crust that may be hundreds of kilometers long and extend downward 10 to 20 km (6-12 miles) into the crust. The 1,200 km (750 miles) long San Andreas Fault that separates the North American and Pacific Plates in California is the most active fault system in the contiguous U.S. The Izmit earthquake occurred on the North Anatolian Fault, a fault that is of similar length and sense of movement as the San Andreas Fault. Unraveling the movement history of large faults that produce devastating but infrequent earthquakes can help predict the potential threat from similar faults elsewhere.The point on the fault surface where movement begins, the earthquake source, is termed the focus. Seismic waves radiate outward from the focus. Earthquake foci occur at a range of depths. The majority of earthquakes occur at shallow depths that range from the surface down to 70 km (44 miles). Less frequent intermediate (70-300 km; 44-188 miles) and deep (300-700km; 188-438 miles) earthquakes are generally associated with subduction zones where plates descend into the mantle. Damage is greatest from shallow earthquakes because the seismic waves travel a shorter distance before reaching the surface. The earthquake effects, the type of damage associated with earthquakes, include changes in the natural environment such as landslides but most attention is focused on Collapsed structures destroyed by the shallow 1999 Izmit,Turkey, and 1994 Northridge, California , earthquakes. Building codes are in place in most earthquake-prone areas but they are of little use if enforcement is lax, as was the case in Turkey. Following the earthquake it was discovered that some contractors had cut corners in the construction of multistory apartment complexes. The poorly built structures were left as piles of rubble amongst other apartments that remained standing. In contrast, on February 28, 2001, the strong Nisqually earthquake occurred below western Washington 56 km (35 miles) south of Seattle. Buildings in Seattle and the surrounding communities sustained relatively little structural damage, no one was killed, and only a handful of people received anything more than minor injuries. Seattle has enforced a stringent building code over the last 30 years that requires new structures to be able to withstand large earthquakes. In addition, over the last decade, many older buildings and bridges were retrofitted to ensure that they could endure the big earthquake predicted for the region. Residents in western Washington were doubly fortunate, not only did they have well-built structures but the earthquake occurred much further below the surface than the Izmit quake, further reducing the resulting ground shaking. Seismic waves are captured by a recorder known as a seismograph. The relative arrival times of different types of seismic waves is used to determine the distance of the seismograph station from the origin of the earthquake. Three or more records can be used to pinpoint the earthquake's epicenter, the geographic location of the point on the earth’s surface directly above the focus. Earthquakes are named for the epicenter location, for example, the Nisqually earthquake occurred 53 km (33 miles) below the mouth of the Nisqually River in western Washington. Loss of life in the Turkish earthquake was greatest in the city of Izmit, located close to the earthquake's epicenter. Earthquake distribution is far from random. Earthquakes occur on faults that are preferentially located along plate boundaries. The largest earthquakes along convergent plate boundaries.'''