A magnitude 7.1 earthquake rocked the Joshua Tree National Park region at 2:46 a.m. local time Saturday, October 16, 1999. The event was located in the Mojave desert, about 47 miles east-southeast of Barstow and 32 miles north of Joshua Tree.
On average, an earthquake of magnitude 7.0 is expected to generate about four aftershocks of magnitude 5 or larger within the next week. 25 aftershocks of magnitude 4.0 or larger occurred within 36 hours of the main shock.
The earthquake occurred on the Lavic Lake fault, which slices in a north-northwest direction through the eastern Mojave shear zone. Scientists have identified a 40-kilometer long surface rupture within the Twenty Nine Palms Marine Base. So far, a maximum offset of 3.8 - 4.7 meters was measured.
The map below shows the location of Hector Mine earthquake as well as the epicenters of events associated with the 1992 Joshua Tree-Landers earthquake sequence. Small stars show locations of Hector Mine aftershocks with a magnitude 4 or larger (as of noon on 10/19/99).