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

Historical Sezs mogra ms and the Mac rofilming Project 413Many earthquakes which were located far inside the Pacific Basin by the InternationalSeismological Summary (ISS) were examined by Gutenberg and Richter(1941) [hereafter GRa 1, but their locations could not be definitely placed. However,GRa commented that some events were not fully rejected and worth examining (seeRemarks in Table 5b). Moreover, considering that the International SeismologicalCenter (ISC) located many events far inside the Pacific Basin as shown in Table 5cand Figure 4, it seems necessary to investigate the locations of all those given inTable 5, for which their seismograms would be important. It is hoped that the filmingproject will not exclude such rare earthquakes even though their magnitudesare smaller than the thresholds.2.4. Selection of Destructive EarthquakesIt is well known that many small-magnitude earthquakes have caused catastrophicdamage. The Agadir, Morocco earthquake (February 29, 1960; MRO = 5.9; deathtoll about 15,000) was one of the most remarkable examples and it should not beforgotten in the filming project.In selecting earthquakes for the filming, damage of earthquakes is also consideredbeside magnitude, and SEB includes many destructive earthquakes havingmagnitude less than 7. (Regrettably, the Agadir earthquake was not included.)Although we have several standard magnitude catalogs, as mentioned in theprevious sections, we do not have a standard earthquake damage catalog for theworld. RN is probably one of the most comprehensive catalogs with many damagingearthquakes included. Bdth (1979) prepared a catalog using the number of deathsas a common measure to compare the damage from different earthquakes. As shownin Table 6, deaths in RN and B%th (1979) are quite different for some earthquakes.RN gives no death toll for some events listed by B%th (1979), and vice versa.Death tolls for some earthquakes not listed by RN and B%th (1979) are supplementedfrom a few local catalogs in Table 6. Geographical inhomogeneity is alsoobserved in damaging earthquakes. Death tolls are not accurate, and differ fromregion to region. Because Table 6 uses a selection threshold of 100 deaths, it doesnot list the Accra, Ghana earthquake of June 22, 1939, M = 6.5, deaths 66 (RN).No global catalog except Ganse and Nelson (1981) [hereafter SE27] lists Cartago,Costa Rica earthquake of May 4, 1910, deaths 272. SE27is an important contribution,but it needs many corrections and additions. It is not advisable to use asis. I have sent some corrections and additions privately to WDC-A. Cooperation ofmany colleagues is needed to improve this catalog.3. Selection of Stations3.1. Necessity of Auziliary StationsIn selecting a representative station of a region, it must be noted that one stationmay have been operated well in a certain period, and another station in anotherperiod. Of course, there are stations that have been operated almost without interruptionduring last several decades. However, they are rather exceptional. Manyold stations had been interrupted in operations by the two World Wars and/orother unavoidable reasons. Studying the history of old stations is a prerequisite for