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USGS Low Frequency Geophysical Data available

October 19, 2001

The Northern California Earthquake Data Center (NCEDC) and the U.S. Geological Survey (USGS) are pleased to announce the availablity of extensive "low frequency" geophysical and fault monitoring data.

With National Earthquake Hazards Program (NEHRP) funding, the USGS has supported various fault monitoring efforts. In addition to monitoring at seismic frequency bands, the USGS also has supported strain, creep, water level and other instrumental systems operating at "low frequency". Principal investigators include both USGS and academic scientists. The typical observation interval for these data sets is 10 minutes (0.00167 hz).

Raw data from most of these instruments are now available at the NCEDC, and are archived with the FDSN assigned network code "UL". The "SeismiQuery" web interface, initially developed by IRIS, can be used at the NCEDC to query the inventory and responses for this data. The raw low frequency data can be accessed with seismic querying tools such as NETDC and BREQ_FAST, and NCEDC web forms, and are are retrieved in SEED format, a standard format adopted for seismic data. The NCEDC raw data archive for this network consists of data from 1974 to the present, contains over 800 channels of data, and includes over 354 active data channels that are updated on a daily basis.

In a companion effort, the USGS is providing access to preliminary cleaned versions of these data that have been automatically scaled and modified to remove offsets and telemetry glitches. No checking of these data or the parameters used to generate them is currently being done. Careful review of the data should be done before any scientific conclusions can be drawn. The data do however provide a starting point for general viewing of fault behavior. The cleaned time series are available as plots (most recent week, most recent month, most recent year, and complete time series) and as downloadable files in either a tabular format or as an eXtensible Markup Language (XML) file.

The raw data can be found at:

The cleaned data can be found at:

The NCEDC is a joint project of the University of California, Berkeley and the USGS. For more information on this data set, please contact