1989 Loma Prieta Earthquake

The 1989 Loma Prieta earthquake occurred on October 18, 1989 at 00:04 UTC in the Santa Cruz Mountains of Central California.

  • Date: October 18, 1989 at 00:04 UTC (October 17, 1989 at 05:04 PM local time)
  • Location: 37.040 -121.877
  • Depth: 16.79 km
  • Magnitude: 6.9 Mw, 7.1 Ms, 6.7 Ml
  • Faulting:This earthquake was the first major event to occur along the San Andreas fault zone since the 1906 earthquake. The Loma Prieta earthquake ruptured the southernmost 40 km of the 1906 break, in comparable amounts of right-lateral strike slip and reverse slip motion. The average strike-slip displacement was 1.2 meters while the average reverse-slip displacement was 1.6 meters. This type of motion is not typical of the San Andreas fault and suggests that the earthquake occurred on a sub-parallel fault and not on the San Andreas itself. Consequently, the potential for a damaging earthquake on the San Andreas in the Santa Cruz mountains may still exist.
  • Deaths: 63
  • Injuries: 3,757
  • Property Damage: $ 5,900,000,000. At the time, this was the most costly natural disaster in the United States.

Because of its proximity to the San Francisco Bay Area, the earthquake was felt extensively over the area:

  • 16 km ( 10 miles) ENE ( 61 degrees) of Santa Cruz, CA
  • 22 km ( 13 miles) WSW ( 244 degrees) of Morgan Hill, CA
  • 34 km ( 21 miles) S ( 177 degrees) of San Jose, CA
  • 47 km ( 29 miles) N ( 5 degrees) of Monterey, CA
  • 71 km ( 44 miles) S ( 188 degrees) of Livermore, CA
  • 91 km ( 57 miles) SSE ( 158 degrees) of Oakland, CA
  • 95 km ( 59 miles) SSE ( 150 degrees) of San Francisco, CA
  • 100 km ( 62 miles) SSE ( 159 degrees) of Berkeley, CA

This earthquake has been extremely well-studied and numerous resources are available. Here is a brief list.



    At the time of the Loma Prieta earthquake, the Berkeley Seismological Laboratory operated a small network of 16-bit digital seismometers. Because of the limited digital range of the 16-bit systems, all of these instruments "clipped". In addition, some of the seismometers displayed non-linear effects from the strong shaking. The data were useful for providing P-wave travel times in order to locate the earthquake, but it was not possible to use the amplitude information until the largest amplitude waves had passed. Here are two example seismograms from these recordings.

    The difficulties experienced in 1989 were motivation for the upgrade of the Berkeley Digital Seismic Network in 1991. Today the BDSN consists of 28 broadband stations with 24-bit digitizers. Each station consists of a broadband seismometer and a strong-motion instrument in order to ensure that the full range of ground motions are recorded on scale.

  • Recording from BKS
  • Recording from CMB

On-line Information

Earthquake Photographs


  • McNutt, S., and Sydnor, R. (ed.),The Loma Prieta (Santa Cruz Mountains), California, Earthquake of 17 October 1989, CDMG Special Publication 104, 1990.
  • National Research Council,Practical Lessons from the Loma Prieta Earthquake, National Academy Press, 1994.
  • Schultz, S., and R. Wallace, The San Andreas Fault, USGS General Interest Publication, 1989.
  • This "General Interest Publication" is a nice introduction to the San Andreas for a general audience.
  • Seismological Society of America (ed),The 1989 Loma Prieta, California, Earthquake and its effects, Bulletin of the Seismological Society of America, Vol. 81, 1991.
  • Spudich, P. (ed.), The Loma Prieta, California, Earthquake of October 17, 1989 - Main shock characteristics, USGS Professional Paper 1550, Denver, CO, 297 pp., paperback, 1996.
  • Wallace, R.R. (ed.), The San Andreas Fault System, California, USGS Professional Paper 1515, Denver, CO, 283 pp., paperback, 1990. A collection of review articles on the San Andreas Fault, covering the evolution, physiography, seismicity, and deformation along the fault. Excellent reference.