The rupture front spread out across the fault plane, so that the eventual size of the rupture covered an area of approximately 15 by 20 kilometers. The rupture then terminated at a depth of about 5-6 kilometers. Using data from 38 of the more than 200 accelerographs throughout southern California, and data from other instruments and land surveys, scientists were able to make an accurate portrayal of the dynamic properties of the movement along the fault. This information is used primarily by engineers to help establish seismic safety codes for future earthquakes. It is also used by seismologists to understand the details of the fault-rupture process and the complicated wave propagation effects that control the intensity of earthquake shaking.
Earthquakes are broad, areal events that move through time and space.
The main shock and aftershock areas of three recent earthquakes in the Los Angeles region show the approximate dimensions of fault slip beneath the land. The fault movements were characterized by at least three distinct subevents, or pulses of motion, a few seconds apart. Another large subevent was centered about 12 kilometers updip to the north from the hypocenter. The Northridge earthquake exhibited an amplification effect, known as directivity, where the amplitude of the seismic waves was larger in the forward direction of the rupture. Consequently, ground motions in the most populated and built-up areas of the valley to the south were modest relative to those in the Santa Susana Mountains and the Santa Clara River valley.