NCEDC News/Blog

Changes to Northern California earthquake catalog search

Categories:   USGS Northern California Seismic Network (NCSN)  |  Magnitude  |  Earthquake Catalogue  |  Catalogs

November 21, 2002 

November 21, 2002

Today the NCEDC implemented modifications to eqselect and catlist, programs which search and reformat earthquake catalogs. These programs are used by the Web catalog search as well as by users with research accounts. The changes will affect the magnitudes reported from searches of the NCSN catalog for northern California.

Previously, if a specific magnitude type was not selected by the user, eqselect and catlist reported magnitude according to the hierarchy: Mw (UCB moment magnitude), Mlm (NCSN local magnitude computed from UCB amplitudes), Ml (UCB local magnitude), Md (NCSN coda duration magnitude), Mx (NCSN amplitude duration magnitude).

In the new version of these codes, the preferred magnitude (as selected by the NCSN) will be reported as the default magnitude. If no preferred magnitude is defined, then eqselect and catlist will use the magnitude hierarchy above for reporting.

The change will bring the reported NCSN magnitudes in line with the CNSS catalog, which has always reported the preferred magnitude. This change will result in different magnitudes being reported from the NCSN catalog (if you are using the default option).

The NCEDC is a joint project of the University of California, Berkeley and the USGS. Please send us email at or fill out our comments form if you have questions or comments about these changes.