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

200180The Standardization of Seismological Data 437Preliminary analysis of traveltime residuals was made using the above standardizeddata (Figure 4). Information on hypocenters, origin times, and a standard traveltimecurve were taken from data compiled by the Japan Meteorological Agency(JMA). In this analysis only the post-1951 records were used, because JMA beganestimating the origin time to the nearest 0.1 sec after 1951. An analysis such asthis would be impossible unless the data were standardized and machine readable.AZIMUTH 0 - 90FlZIMUlH 90 ~I-CJfP. 0 40 KH N =50920 0 coo 600 BDQKfl DELTR0i*-4;-~ o5OfP 80 - 200 Kn Y = I120a I I I >O O O6DO BOOM 0tLTA400 600 BOOKN DtLTAAZIMUTH 180 - 270RLItiUlH 270 - 360OtP. 80 ~KM N =?5Figure 4. Residuals of P-wave travel time for the years 1951 to 1966. The hypocentersare divided into three layers by focal depth and into four areas by azimuth in every 90degrees from the north.