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NCSEA Press Release: Parkfield California Earthquake 09-28-04

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                            203 N. Wabash Ave., Suite 2010, Chicago, Illinois 60601;


The Parkfield California Earthquake of September 28, 2004


Ronald O. Hamburger, SE


At 10:15 am Pacific Daylight Time, an M6.0 earthquake occurred on the San Andreas fault near Parkfield California.  Fortunately, Parkfield, located approximately half way between Los Angeles and San Francisco is sparsely populated and little damage occurred.  There were no reported fatalities or significant injuries.  However, the earthquake is of great potential scientific importance. 


Parkfield sits on an extremely active segment of the San Andreas fault.  Moderate-size earthquakes of about magnitude 6 have occurred at regular intervals on this segment of the fault at roughly 20-year intervals.  Known events include earthquakes in 1857, 1881, 1901, 1922, 1934, and 1966.  In the mid-1980s, the United States Geologic Survey, recognizing this pattern and expecting that an M6 earthquake was likely to occur in the late 1980s or perhaps early 1990s, initiated the Parkfield Experiment” which included installation of the densest array of seismic monitoring equipment anywhere in the world.  Earth scientists working on this experiment hoped both to detect indicators of large magnitude events, that could be used in prediction and also to collect valuable data on the propagation and characteristics of ground motion in the near field. 


As the 1990s passed, the great hopes for this experiment waned and some of the instrumentation was decommissioned or moved elsewhere.  However, Parkfield remains the most heavily instrumented region in the Untied States and a wealth of valuable ground motion data was obtained from this earthquake and will likely be analyzed for years and eventually suggest changes to the building codes to improve the seismic resistance of our built environment.  More information can be obtained at and at


The National Council of Structural Engineers Associations was formed to constantly improve the level of standard of practice of the structural engineering profession throughout the United States, and to provide an identifiable resource for those needing communication with the profession.  The National Council represents State Organizations of Licensed, Practicing Structural Engineers.


For additional information, contact the NCSEA President Ron Hamburger (415) 495-3700 or the NCSEA  Executive Director Jeanne Vogelzang  (312) 372-5708