CMT or merged subcatalogs?


There is a trade-off between (sub)catalog length and magnitude threshold.  We present two choices:


subcatalogs of the Harvard Centroid Moment Tensor Catalog

1977.01.01-2002.09.30 (available at the time of our study)

nuclear events were excluded by Harvard

events in any of the 13 orogens of Bird [2003] excluded by us

threshold magnitude varies with tectonic setting from approximately 5.33 to approximately 5.66

15,015 events with depth £ 70 km

The large size of this catalog yields moderately-large subcatalogs, which provide accurate seismicity levels and spectral slopes.  However, there is some question whether these catalogs are long enough to determine corner magnitudes.


subcatalogs of a merged catalog:

            Pacheco & Sykes [1992] catalog 1900.01.01-1975.12.31 +

            Ekström & Nettles [1997] catalog 1976.01.01-1976.12.31 +

            Harvard Centroid Moment Tensor catalog 1977.01.01-2002.09.30 =

                        total duration 1900.01.01-2002.09.30

                        events in orogens included

                        threshold magnitude assumed to be approximately 6.99 (limited by early 20th-century data)

                        161 events with depth £ 70 km

The very small size of this catalog yields tiny subcatalogs, which should not be used to determine seismicity levels or spectral slopes.  In our study, we used these ONLY to give alternate estimates of corner magnitudes.


(For full bibliographic citations please see the accompanying paper in BSSA.)