The quake was preceded by the 6.1 magnitude Joshua Tree earthquake on April 23 , 1992 , which was south of the future Landers epicenter . The 6.5 magnitude Big Bear earthquake , which hit about three hours after the Landers mainshock , was originally considered an aftershock . However , the United States Geological Survey determined that this was a separate , but related , earthquake . These two earthquakes are considered a regional earthquake sequence , rather than a main shock and aftershock . The 5.7 magnitude Little Skull Mountain ( LSM ) earthquake the following day , June 29 , 1992 , at 10:14 UTC near Yucca Mountain , Nevada , is also considered part of the regional sequence and may have been triggered by surface wave energy produced by the Landers earthquake . Foreshock activity , in the form of a significant increase in micro-earthquakes , was observed at Little Skull Mountain following the Landers earthquake , and the activity continued until the main LSM earthquake
Big Bear earthquake
1992 Big Bear earthquake
1992 Landers earthquake