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Volume 6, Issue 3
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Ryutaro TAKAHASI1953 Volume 6 Issue 3 Pages 117-121
Published: December 25, 1953
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThis accelerometer has been designed and constructed by the “Strong Motion Accelerometer Committee, ” members of which are Nobuji NASV, Hiroshi KAWASUMI, Takahiro HAGIWARA, Kiyoshi MERO, Kiyoshi LANAI, Kenzaburo TAKEYAMA, Kazuhiko AKASHI and I. “SMAC” stands for the name of the committee. Expenses were granted from the Fund for the Experimental Researches of the Education Department.
The merits of the present accelerometer lie in that it has been very carefully constructed so as it can record faithfully the acceleration of earthquakes as large as 1000 gals, and also in that it has large recording speed and a special device to record automatically two more after-shocks which would follow the main one. Easiness of maitenance is another merit; the investigation by an expert once a year and care taken by a watchman once or twice a month are all that is necessary.
It starts automatically to record earthquakes greater than 1.0 gals, stops recording automatically after a 3-minute running, and repeats this start-and-stop motion for successive threee earthquakes. It has a mechanical starter besides an electric one. Record is made by scratching a roll of stylus paper by a saphire needle. We can obtain by this means a very sharp record, which enables us direct printing on to photographic paper, or photographic enlarging up to 10 times the original.
It has also a special equipment for inspecting the action of the instrument.
Essentials of the accelerometer are as follows:
(A) Accelerometer proper
1) Type: 3-component pendulum type accelerometer.
2) Proper period: 0.1 sec.
3) Sensitivity: 25 gals per mm on the record.
4) Magnification: X16, mechanical.
5) Recording method: Scratching stylus paper.
6) Working Range: 10 to 1000 gals.
7) Recording speed: 1cm/sec.
(B) Driving device
1) Type: Hand-wound spring clockwork.
2) Action: Starting thrice, 3-minute running for each start.
3) Starter: Falling ball starter. (Sensitivity: 100 gals)
4) Governer: Centrifugal, instantaneous start.
(C) Time-marker
1) Type: hand-wound clock with electric contact points and electric starter.
2) Time mark: every 1 sec.
(D) Electric starter
1) Type: Vertical accelerometer with period 0.3 sec.
2) Sensitivity: 10 gals.
3) Electric contact points: 6 platinum pts in parallel.
(E) Electric Source
1) Dry cells: 12 volts.View full abstractDownload PDF (1217K) -
The Reserch Group for Explosion Seismology1953 Volume 6 Issue 3 Pages 122-129
Published: December 25, 1953
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSAt 03h 35m oos, 7th of December 1952, 29.7 tons of dynamite were exploded at Kamaisi mine, located about 15km west of the city of Kamaisi, Iwate-ken. This explosion was a good opportunity for us to acertain the results obtained from the observations of the seismic waves caused by the great explosions which took place at Isibuti for 3 times.
13 and 6 observation points were spread as southern and western profiles for about 500km and 200km length respectively. The velocities of P-wave were calculated as 6.19km/sec, 7.37km/sec and 8.20km/sec from the travel-time curves obtained by the observations of southern profile. The 1st value seems to correspond to that of the 3rd layer in Isibuti's case. The 3rd is what has never been observed in Japan, while similar values have often been observed in other regions from the explosion seismic waves. The. 2nd value, 7.37km/sec is to be examined. in the next opportunity. The depth of the boundaries of the layers in which P wave travels with the velocities given above were calculated as 27.7km and 32.3km respectively.
The velocity of P-wave obtained from the travel-time curve of the western profile was 5.76km/sec, which is quite the same with that obtained from the western profile of the 2nd Isibuti explosion. This fact suggests that the thickness of the layer of these regions becomes thinner towards east.View full abstractDownload PDF (734K) -
Relations between gravity and distribution of density of subterranean mattersMotohiko KATO1953 Volume 6 Issue 3 Pages 130-146
Published: December 25, 1953
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe author assumes a model in which the density of subterranean matters is distributed as shown by the formula (8). This formula satisfies the two conditions, the one being the formula (1) which defines the variation of the mean density with respect to depth, and the other the formula (6) which does the distribution of density on a subterranean plane at any depth.
If the gravity and the density on the earth surface are given by (10) and (5), then the coefficients Cm in (8) take the forms (12).
In the case of prospecting, most probable values for the coefflcients of the rate of change of density with depth will be λ=0.5×10-5 C. G. S. and λm=λ or αm. Putting λm=αm, this model produces a subterranean structure which is consistent with that inferred by seismic method.
He also discusses the relations between the residual gravity (g′) and the regional gravity (g″).View full abstractDownload PDF (1441K) -
Mitsuo KEIMATSU1953 Volume 6 Issue 3 Pages 147-157
Published: December 25, 1953
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSPrevious to the year 1468 it seems difficult to find the data of the earthquakes concerning Hainan Island. The Table is thought not always to coincide with the real conditions of the historical earthquakes, by the lack of data, though sought as hard as possible. The marks O, Θ both indicate that the earthquake was felt there at that time, and besides the latter mark Θ means that the earthquakes seated on the same line are no other than the same one. The figures, VI-II in parentheses stand for the seismic intensities presumed, VI being the disastrous earthquake, V strong, strong, IV strong, III rather strong, II moderate. The seismic intensity of the earthquakes unaccompanied by these figures are uncertain, but they can be presumed not over II, namely the moderate earthquake.View full abstractDownload PDF (1056K)
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