For more information about earthquakes and these data in particular, please see our FAQ page.
If you still have questions, you can contact us at:

Southern California Seismic Network
U.S. Geological Survey - Caltech Seismological Laboratory
Pasadena, California

Voice: 626/583-7823 or 626/395-6919
EQ Info: 626/395-6977
Fax: 626/583-7827
Email: usgswww@ehzsouth.caltech.edu