Facts on the 1994 Northridge California Earthquake

California Earthquake InsuranceThe California Institute of Technology issued a summary of facts on the Northridge earthquake’s first anniversary.

  • The magnitude 6.7 Northridge earthquake started on Jan. 17, 1994 at 5 seconds before 4:31 a.m.
  • There were no immediate foreshocks. No systematic change in strain above the background noise occurred during the hours to milliseconds before the event.
  • The fault ruptured by the Northridge earthquake rises from a depth of about 19 kilometers (12 miles) at its southern edge to a depth of about 5 kilometers (3 miles) at its northern edge. The fault is blind – it does not break the surface – and was previously unknown.
  • The rupture started at the southern, deepest edge and spread up to the northwest, north, and northeast. The final dimension of the fault plan broken in the earthquake is about 16 by 19 kilometers (10 by 12 miles).
  • The actual rupture of the fault only lasted about 8 seconds, but because of amplification and reverberation of the seismic waves through the complex of faults, sediment, and mountains, most people felt shaking for 20 to 30 seconds.
  • Geodetic measurements (those made by satellite) show permanent changes in the topography of the San Fernando Valley of up to 40 to 50 centimeters (16 to 20 inches) of vertical gain, and up to 20 centimeters (8 inches) of horizontal displacement.
  • The earthquake caused very large ground motions with peak accelerations of 0.5 to 1.0 g in the Northridge area, decreasing to 0.1 g at distances of about 50 kilometers (31 miles). (A “g” of acceleration is equivalent to the acceleration of gravity. There were a few sites near the Northridge earthquake that recorded over 1 g of vertical acceleration. These ground movements would have been capable of throwing objects of any size into the air).
  • The pattern of damage and strong ground shaking was irregular, with severe damage in places like Sherman Oaks and Santa Monica.

Early following the 1994 earthquake, many home owners were searching for reasonable earthquake insurance; after a few years,  the interest died down. Nearing the 20th anniversary, there is once again an expanded interest in California earthquake insurance; this may be due to the fact that the prior large earthquake in the region occurred approximately 20 years prior where there were many damaged homes, injured people, and devastated infrastructure which caused building code changes.

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