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

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

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76S. K. SinghESKUPPWIECHERT ELPZ A-80" A - 88"Mq=750 4 -35" 4 - 26'P-P (cm)1979 11.3Ma= 7.619822 1.6M,= 7.01982' 1.4Ma= 6.91968 10.3M,= 7.4Js.-..- M,= 1978 7.8 22.81970 4.2Ma= 7.3STUGALlTZlN Zp-P 10.5cm'i'M,= 7.01.2t t tP PP PPP3 IT.,"Figure 6. LPZ WWSSN seismograms <strong>from</strong> ESK for large earthquakes along <strong>the</strong> middleAmerican trench. Note that except for <strong>the</strong> 1973 and <strong>the</strong> 1970 earthquakes, all P-wavesare simple. E-W Wiechert seismograms <strong>from</strong> UPP are also shown for some of <strong>the</strong>seearthquakes. The 1973 earthquake which is complex at ESK also appears complex at UPP(low-amplitude high-frequency P-waves). Four o<strong>the</strong>r earthquakes at UPP appear simplejust as <strong>the</strong>y do at ESK. Like ESK and UPP seismograms <strong>the</strong> Galitzin-Wilip seismogramfor <strong>the</strong> 1965 earthquake is simple. We conclude that <strong>the</strong> simplicity or complexity of <strong>the</strong>P-waves can be studied in a qualitative and a quantitive manner <strong>from</strong> <strong>the</strong> Wiechert and<strong>the</strong> Galitzin seismograms, respectively. (From Singh et al., 198413).

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