Beginning with the 1983 Coalinga earthquake , a blind thrust event in the central coast ranges of California , a change in perspective was brought about regarding these types of ( concealed ) faults . The October 1987 shock occurred on a previously unrecognized blind thrust fault that is now known as the Puente Hills thrust system . The fault was delineated by the mainshock and aftershock focal mechanisms , fault plane reflection studies , and high resolution seismic profiles , which also revealed that the fault runs from downtown Los Angeles to near Puente Hills . The system is considered one of the highest-risk faults in the United States due to its moderate dip and its location under a large metropolitan area
1983 Coalinga earthquake
1983 Coalinga earthquake
1987 Whittier Narrows earthquake