Harvard Seismology Project: Seismic Noise

Analysis of repaired data originally recorded on the IDA MK 7 data logger.

In the spring of 2001, a problem was discovered with data recorded at IDA GSN stations equipped with the IDA MK7 data logger. A programming error in the Digital Signal Processing (DSP) Unit introduces long-period noise for channels that are derived through decimation of the raw data stream. This affects all recorded channels.

An algorithm was developed by the IDA group to repair the archived data. An effort is underway to repair all of the broad-band (BH), long-period (LP) and very long-period (VH) data in the IDA and IRIS DMC data archives.

This page presents an analysis that compares the long-period noise characteristics of the data before and after repair.

The table below provides links to figures that show the noise levels for several affected IDA stations before and after repair of the data. In general the VH component shows the greatest noise reduction, since it was affected by a cascade of errors. The greatest improvement is seen in the period band 25-200 seconds.