Joshua Tree National Park Geology Hector Mine Earthquake Summary Updates at http://www-socal.wr.usgs.gov/report.html

Click on image to enlarge to full size. Map from U.S. Geological Survey Pasadena Office of Earthquake Information 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 assocated with the 1992 Joshua Trea-Landers earthquake sequence. Small stars show locations of Hector Mine aftershocks with a magnitude 4 or larger (as of noon on 10/19/99). (Updated 8:47 a.m., 10/19/99) Hector Mine Earthquake and related links Hector Mine earthquake summary Shaded Relief Map: Hector Mine earthquake (10/19/99) - 130 MB image Hector Mine EQ ground-shaking intensity maps Hector Mine EQ damage reports and more Map of seismograph network in the Joshua Tree region U.S. Geological Survey Earthquake Information Almost real-time map of California’s recent earthquakes Ground motion map of Hector Mine main shock Ground motion maps Hector Mine aftershocks Seismo-links Exhaustive link list! All About Earthquakes - Earthquake intensity - Earthquake magnitude - Faults - Earthquake epicenter and focus - See Sunset Crater’s seismograph

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| USGS Geology in the Parks home | NPS Park Geology Tour home | This site is a cooperative endeavor of the US Geological Survey Western Region Earth Surface Processes Team and the National Park Service. Please share your comments and suggestions with us! parkgeology@den.nps.gov http://www.nature.nps.gov/grd/usgsnps/jotr/jotreq1.html This page was last updated on 10/19/99