. The geography of New Zealand. Historical, physical, political, and commercial . *3 Scale 59 mm s I h OUP Fig. 3: Christchurch record of the great Guatemala earthquake of 19thApril, 190-2. (Greenwichmean civil time.) a record of the oscillations of the boom. If thesudden disturbing cause be the vibrations of anearthquake, the photogram becomes a seismogram,or earthquake record. On one of the two black bands at the edges ofthe paper (which also record the oscillations of thependulum) are hour-marks produced by the minutehand of a watch, which is lengthened so as to passonce in each hour ov
. The geography of New Zealand. Historical, physical, political, and commercial . *3 Scale 59 mm s I h OUP Fig. 3: Christchurch record of the great Guatemala earthquake of 19thApril, 190-2. (Greenwichmean civil time.) a record of the oscillations of the boom. If thesudden disturbing cause be the vibrations of anearthquake, the photogram becomes a seismogram,or earthquake record. On one of the two black bands at the edges ofthe paper (which also record the oscillations of thependulum) are hour-marks produced by the minutehand of a watch, which is lengthened so as to passonce in each hour over the end of the fixed slit, thuseclipsing the light. Figures 3, 4, 5, 6, are the copiesof four seismograms taken on the New Zealandinstruments. The small letters a, h,. .. .Ji, above Fig. 3 mark thebeginning of the eight phases into which Professor 236 GEOGRAPHY OP NEW ZEALAND C O -C. Omori divides the most important ofthese are: a, the beginning I of the preliminary tremors; ^ e, the chief of the large I waves; h, the last markedJ phase of the series; the^- S position of the correspond-s-g mg waves on Fig. 4 isi marked bv the letters a, e,^^ li. In Figs 5 and 6 the$ •§ downstroke on the margin~ a shows the beginning of the;5| preliminary tremors (a);^ H the black line right across£ I the seismogram gives the II position of c, d, and e; last phase (Ji) is shown inz t^ Fig. 5 by another down-I ^J stroke, but cannot be dis-^1 tinguished in fig. 6.* Jg The Guatemala earth-i ^ quake occurred at atS the origin, so that theX preliminary tremors tookT minutes to travel toS Christchurch. a distance of7164 miles; their velocityof propagation (or transit * The fact that the interval between the arrival of the preliminarytremors and of the normal waves is very small when the origin is near,and increases with the distance from the origin is expla
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Keywords: ., bookauthorgregoryj, bookcentury1900, bookdecade1900, bookyear1905
