What type of fault was northridge earthquake

The forces that cause these movements are the same ones responsible for continental drift. The motion of the Northern Pacific plate as it grinds past the North American plate causes strike-slip fault movements. The plate is moving at an average of about 0. Much more rapid jumps occur during earthquakes; in , movements as great as 21 ft 6. The San Andreas Fault is infamous for another reason. Such development in this and other parts of the world puts many at risk of the devastation of major fault movements.

Sudden fault movements fill the headlines for weeks, but, over the course of geologic time , they are relatively rare so the chances to study them and their effects are limited.

Request Interview. Skip to main content. Log In Register. The earthquake occurred beneath Northridge, a suburb in the San Fernando Valley, 30 km northwest of Los Angeles see map on next page. Systems of concealed faults under the Los Angeles area are more complex than previously thought. The significant fracturing of welds in steel frame buildings was unexpected because of the ductility of steel.

Understanding the cause and correcting the problem will be essential to continue building in earthquake prone regions. Damage in Santa Monica The hospital in Santa Monica shows classic "X"-pattern cracks as evidence of the damage it sustained during the Northridge earthquake.

CSUN Parking Structure Damage This car-capacity parking structure, a recent addition to the Cal State University - Northridge campus, suffered partial collapse in the intense shaking of the Northridge earthquake.

A close-up of of this entrance to the parking structure shows the closely spaced fractures in the reinforced concrete columns which allowed "bending" of the outer wall. San Fernando Valley Apartment Damage The apartment house on the left has collapsed onto the former garage level. Based on observations of strong ground motions and deformations of the land surface, scientists have portrayed the buried fault plane illustrated here.

The fault plane is located between 5 and 19 kilometers beneath the surface. The modeled slip surface is about square kilometers, although the slip did not occur over that entire surface.

The inferred amounts of slip on the plane are shown by different colors, and the color patterns suggest the progression of movement of the upper block of earth with respect to that below the plane. Maximum slip on the plane, seen in the northwest quadrant, was about 3 meters.

Apparently, movement that began at the hypocenter in the southeast quadrant generally proceeded upward and to the northwest arrow. Note that the plane is shown displaced well below the surface.

Portraying the Way the Fault Plane Ruptured. An earthquake is a rupture process that expands from an initial point on a fault plane called the hypocenter. The rupture does not occur instantaneously nor does it proceed uniformly along a fault plane. The Northridge earthquake ruptured the fault plane for about 8 seconds and had an average slip across the plane of about 1 meter.

The rupture proceeded across the plane northwesterly from the hypocenter at about 3 kilometers per second. However, some parts of the plane exhibited little or no slip and some parts slipped more than 3 meters. The concentrated areas of larger amounts of slip at , , and seconds are called asperities, which are the sources of pulses of energy that arrive at the surface at different times.

Modern seismological techniques allow scientists to model the details of this process to understand its complexity and the broad variety of effects it can cause. Lessons Learned. The direction in which an earthquake ruptures across its fault plane can greatly affect the intensity of strong ground motion. Depending on its particular fault geometry, another earthquake the same size as the Northridge event could produce even stronger shaking in populated areas of Los Angeles than the shaking experienced in the San Fernando Valley during In general, the earthquake caused uplift throughout the San Fernando Valley and adjacent mountain areas.

The Santa Susana Mountains were pushed up by at least 40 centimeters, based on direct measurements at Oat Mountain, and possibly by as much as 52 centimeters, based on modeling slip on the fault plane.