30.地震計初動の理論的及び實験的研究並びに地震初動の定量的研究 : (其の2)地震計初動の實験的研究

A proposal was made by the Subcommittee on Seismology of the National Research Council of Japan to the forthcoming Congress of the International Union of Geodesy and Geophysics at Edinburgh in view of the unofficial circular letter of Prof. M. Ishimoto addressed to seismological stations throughout the world for the international co-operation with respect to quantitative studies of the initial motion of earthquakes. With the object of supporting the idea, Prof. Ishimoto advised us to study experimentally the initial motion of seismographs. At the same time one of the authors showed that simple method, first suggested by Dr. Tsuboi, of reducing the first ground impulsion by observing the magnitude of the initial deflection and time of first zero from the beginning of motion on seismograms, may be applied with tolerable accuracy regardless of the form of the ground motion. This conclusion was derived by comparing the results of theoretical calculations for some types of ground motion of regular mathematical form. But the result of our present shaking table experiments proved the applicability of the above simple method to cases of somewhat irregular motions imparted to the shaking table by the unaided hand irrespective of the type of external motion. It also proved the applicability of the usual equation of motion a+2εx+n2a=-V(σ-gi) (1) either in the statical or dynamical state including the beginning of motion. The seismographs used were an acceleration-seismograph designed by Prof. Ishimoto and the velocity- and displacement-seismographs designed by Mr. T. Hagiwara. All the seismographs are of the inverted pendulum type with air damper and mechanical recording, the construction details and the results of applications of which as well as comparative studies of them have already been reported by the respective designers on a number of occasions.本論文第1部に於て得たる所を確める爲に振動塞を用ひて地震計の初動實驗を行つた.此れに用ひた地震計は石本式加速度地震計,萩原式速度及び變位地震計である.靜力學的,動力學的方法により出来るだけ器械常數を測定し,各實驗毎に動力學的檢定を行つた.其の結果理論的に研究されて居る様な形に近い運動を手にて振動塞に與へた場合にも,又其の他の運動をさせた場合にも第1部に於て得た第1動に對する倍率曲線B1m(t0/T0)が相當な精度に於て利用出来る事を確め,更に項別積分の方法により各種地震計よりその連動を求め極めて満足なる結果が得られた.かくて地震計の運動方程式 a+2εa+n2a=-V(σ-gi) が靜力學的にも動力學的にも,ことに初動の場合にもあてはまろ事を知つた