Historical Seismograms - Evidence from the AD 2000 Izu Islands ...

Data Bases on Historical Seismicity 133Figure 2. Catalog of strong earthquakes in USSR from ancient times to 1977(A4 > 6.75).2. Quality ControlThe usage of seismological data for prediction and other research requires continuousupdating and verification. NGDC (Rinehart, et al., in press) and IPE(Gvishiani and Zheligovsky, in press) have developed independent procedures forthis activity. The logical scheme for verifying and updating the NOAA data baseis shown in Figure 3.At IPE, the research applications begin with seismicity files that are compiledfrom data of different sources (Shebalin, in press). The data base contains morethan 70 catalogs , including the historical seismicity stored in sequential files, including:(1) worldwide catalogs - NOAA, ISS-ISC, Abe, Gutenberg and Richter, etc.;(2) New Catalog of Strong Earthquakes in the Territory of the USSR from AncientTimes to 1984; (3) republic and regional catalogs of the USSR; and (4) regional catalogs- USA, Japan, Italy, France, Spain, Canada, Turkey, New Zealand and others.The reliability of the earthquake information increases with the time delay betweenoccurrence of the event and publication of its parameters. (Immediate earthquakereports and bulletins are not as reliable as later catalogs.) Thus, it is necessary tocreate from the existing sources a file that contains for every time period the mostreliable earthquake data.Figure 4 shows how this problem is solved at IPE. Priorities of reliability areassigned to different sources according to the amount of primary information andthe time period between occurrence and publication. The lower the priority number,the greater the reliability of source. This system of updating assures that IPE’s database includes, for every time period, only the earthquake parameters from the sourceof highest priority. In this file, the delay of the data entry for certain regional datacatalogs is no longer than ten days after receipt of published listings.Thus, the data in the current IPE catalog have been verified, as illustrated inFigure 5, using an analytical approach to the geophysical data. Applying thisapproach to most of the IPE computer catalogs has led to the discovery of errorsin up to 10% of the records in some data files.