Special Earthquake Report No: 99-013

Regional Location:

Preliminary Magnitude:

Moment Magnitude:

Greenwich Mean Date:
Greenwich Mean Time:
Focal Depth (km):
Analysis Quality (A-D):


5.0 ML (SCSN)

n/a Mw ( -- )

1.9 km

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An earthquake registering a preliminary magnitude of ML 5.0 (SCSN) occurred at 07:54:03 UTC (12:54 a.m. PDT), May 14, in the high desert region of Southern California. The focal point was placed at 1.9 km deep and we do not have a fault plane solution for this event as of yet.
The quake was centered about 5 miles south of Yucca Valley and 19 miles northeast of Palm Springs in the Little San Bernardino Mountains, in the Joshua Tree National Monument (See Map). It occurred along the Eureka Peak fault one of the faults that ruptured during the Landers M7.3 earthquake in 1992, therefore, qualifying this earthquake as a Landers aftershock. The April 22, 1992, Joshua Tree M6.1 earthquake probably was centered along the same fault but about 7 miles to the southeast.
The earthquake was sharply felt in epicentral area, including Yucca Valley, Landers, Twentynine Palms, in the north and Palm Springs, Palm Desert and Desert Hot Springs and Indio to the south. It was felt as far west as East Los Angeles and northern San Diego County.
In Palm Springs, the quake jarred many people from sleep and jolted others while watching the Late Show on television. Residents reported the shaking as a broad rolling motion with some minor shudders. Nobody in Coachella Valley reported anything toppling but several people's nerves were thoroughly shaken.
Residents in Yucca Valley, however, felt a initial sharp jolt (P-wave) followed a moment later by moderate, but vigorous jiggling (S-wave). Windows and glassware tinkled and hanging plants swung. Several people said that just as quake began to intensify, it relaxed then passed. Many said they had just enough time to stand up, but just as they did the shaking stopped. There were only a few reports of items toppling, mostly were light items like picture frames on tables and shelves and cereal boxes. No one reported anything breaking.
The main jolt was followed by a brief but vigorous aftershock sequence which included 12 M3's and a pair in the M4 range, a M4.0 at 1:22 a.m., and a M4.2 at 3:53 a.m. Both quakes in the M4 range were locally felt and some in Yucca Valley and Desert Hot Springs reported feeling several of the M3 aftershocks. As to be expected, peak aftershock activity occurred during the first few hours of the main M5.0 quake and decreased rapidly thereafter. Whereas 83 aftershocks registering M2.0 or stronger were recorded on May 14, only six happened the following day, and just one M2+ aftershock was detected five days later.
The earthquake was the largest to strike Southern California since a pair of M5's struck the Coso Range north of Ridgecrest in early March of 1998 (M5.2 and M5.0). The Landers M7.3 earthquake was the last large quake to occur along this portion of the Eureka fault and since the aftershock activity has yet to wane, this recent jolt is consider an aftershock to the Landers quake. The sequence of quakes that followed this recent event can be considered as aftershocks of the recent quake but in the big picture are actually aftershocks to the Landers quake.
Here is a list of the M5's in Southern California since the Northridge M6.7 earthquake in January 1994, the last M6+ event in the region:
  • June 26, 1995, Northridge M5.0 aftershock
  • August 17, 1995, Ridgecrest M5.4 earthquake
  • September 20, 1995, Ridgecrest M5.8 earthquake
  • January 7, 1996, Ridgecrest M5.2 earthquake
  • November 27, 1996, Coso Range M5.3 earthquake
  • March 18, 1997, Calico (Barstow) M5.3 earthquake
  • April 26, 1997, Northridge M5.1 aftershock
  • March 6, 1998, Coso Range M5.2 earthquake
  • March 7, 1998, Coso Range M5.0 earthquake
  • May 14, 1999, Joshua Tree M5.0 earthquake

Appendix: This quake was later reassessed at M4.9. (990701)

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Subtract 8 hours from Greenwich Mean Time to obtain PST or 5 hours for EDT
Location Quality: A (good), B (fair), C (poor), D (bad)
Magnitude: Ml (local or Richter magnitude), Lg (mblg), Md (duration), Mb (body wave), Ms (surface wave), Mw (moment)

Standard Sources Include:
U.S. Geological Survey, National Earthquake Information Center, Golden, CO (NEIC)
Harvard Geophysical Observatory, Harvard University, Cambridge, MA (HRV)
U.S. Geological Survey, Northern California Seismic Network (NCSN)
University of California, Berkeley, Seismological Laboratory (UCBSL)
Southern California Seismic Network (USGS & Caltech), Pasadena, California (SCSN)
California Institute of Technology, Pasadena, California (Caltech)
various wire reports and/or personal communications

All data are preliminary and subject to change.
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