OFR 97–464: Page [7]
The resulting catalog used for computing the hazard is plotted in Figures 9a, 9b and 9c. We recognized that, in an effort to represent as many sources as possible in CEUS, we had used rather liberal counting time windows east of -105o. To adjust for any resulting incompleteness, we computed average "complete" rates for more recent times (since 1976 for magnitude >= 3, 1924 for magnitude >= 4, 1860 for magnitude >= 5) and "counted" rates (using 1924, 1860, and 1700) in three zones east of -105o, and multiplied the rate in each grid cell by the appropriate "complete" rate / "counted" rate ratio. This scheme is shown in Figure 10. For the New Madrid and Eastern Tennessee seismic zones (NMZ and ETZ in Figure 10) we determined zone-average rates by counting earthquakes with magnitude >= 3 since 1976, and then forced these values into each cell in the zone.
DisclaimerThe catalog files can be downloaded from our WWW site at http://gldage.cr.usgs.gov/eq. We understand why others might be interested in obtaining these files, but are concerned they might be misused. We have merged catalogs from several different sources, and used fairly subjective criteria to rank our preferences. We have used simple, automated schemes to compute magnitudes and remove aftershocks. The potential user should read and understand the above documentation, and then ask whether these catalogs suit his or her purpose.
AcknowledgementsS. Brockman of the USGS brought the indispensable winding-number algorithm (Godkin and Pulli, 1984) to our attention. D. Perkins of the USGS reviewed this report. We benefitted from conversations on catalog issues with D. Perkins, G. Reagor, T. OHara, I. Wong, W. Arabasz, J. Pechmann, and M. Petersen. S. Harmsen of the USGS provided a list of NTS events. All the figures in this report were created with the GMT data-display and mapping software (Wessel and Smith, 1991)....>>NEXT
Last Update: Thursday, February 16, 2006 9:58
