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

Historical Materials of Chinere Earthquakes 167The first and the fifth volumes were published in 1983. The second and the fourthvolumes were publislied in 1985 and 1986. The ~nanuscript of the third volume hasbeen sent to the publishing house recently.At the same time, the provinces, metropolis and autonomous regions with highseismic activity compiled materials of historical earthquakes of their respective regionsin more detail. Besides, monographs of individual great earthquakes werepublished. The sum total much exceeds ten million words.4. Use of Historical Materials in ChinaIn order to use the abundant material of historical earthquakes in modern seismologicalstudy, the macroseisniic data should be converted into seismic parameters.Chiefly on the basis of field observations and historical materials, with referenceto instrumental data, foreign seismic reports and other scales of seismic intensity,a new seismic intensity scale with characteristic Chinese criterions was compiled(Hsieh, 1957) for use in intensity assessment. The scale consists of 12 degrees, eachcorresponds approximately to the same degree in other 12-degree scales, such as theMM or the MSK scale. The destruction of buildings and structures is taken to bet,he main criteria of intensity evaluation. We tried our best to select typical Chinesebuildings and structures as criteria, and took that type of masonry building, whichis familiar in European countries and is built in large amount in new China as abridge linking Chinese and western buildings.Our colleagues published a Catalogue of Chinese Earthquakes in 1960 (Lee et a/.,1960). It contains about 10,000 earthquakes occurred between 1189 B.C. and 1955A.D. Among them, 1,180 have magnitudes greater or equal to 4.7. As the dataare not complete, these earthquakes are not evenly distributed in either time orspace. There are only 131 earthquakes between 1189 B.C. and 1500 A.D., mostlydistributed along the Yellow River Valley and in the south-western part of ourcountry; 405 events between 1501 and 1900 A.D., generally east of 100" E meridian;and 618 quakes from 1901 to 1055, mostly west of 100" E meridian.For earthquakes with instrumentally determined parameters, macroseismic datawere used simply for reference. When there were no instrumental data, they triedto draw isoseisrnals and took the center of the meizoseismic region as the epicenter.For earthquakes with insufficient data, the site of the county which suffered mostwas taken as the location of the epicenter.The magnitudes of historical earthquakes were deduced from their epicentralintensities. From the 35 earthquakes distributed all over the country with bothinstrumentally determined magnitudes and macroseismic materials, an empiricalequation between the magnitude, M, and the 'epicentral intensity, I," was obtained(A4 = 0.581, + 1.5), in which focal depth was not considered.In 1971, a revised and enlarged edition of the Catalogue of Chinese Earthquakes(Central Seismological Group, 1971) was published. It contains 2,257 earthquakeswith magnitudes greater or equal to 4.7 occurred between 1177 B.C. and 1969 A.D.Besides its prolongation in time span, supplement ation of materials and correctionof errors and mistakes, the instrumentally determined earthquake foci were redeteriiiiiiedwith electronic computer whenever possible.Several concise catalogues with earthquake parameters only (see e.g. State SeismologicalBureau, 1977, and Lee et al., 1978) and a Collection of Isoseismals