1) Gutenberg and Richter studied frequencies and magnitudes of earthquakes and obtained the following relation establishing a relationship between magnitude and energy released annually by earthquake waves (NE),
logNE=18.7+0.9M. (1)
This relation shows that “NE” becomes greater as M becmes bigger. And they concluded that smaller shocks almost never were sufficiently frequent to approximate the energy, released in larger shocks. This conclusion is, of course, not wrong, so far as the Richter's Magnitude-scale is concerned. But if E is adopted instead of M, the above formula is transformed into the following one,
logNE=cont.-0.5logE. (2)
This shows that the energy released annually by larger shocks is smaller than that by minor shocks. This seeming contradiction between (1) and (2) is due to how the magnitude is measured, by M or by E.
2) Kawasumi's results on energies and frequencies of earthquakes derived from the data of earthquakes in and near Japan fairly agree with those by Gutenberg and Richter.
3) The Ishimoto-lida's formula, n(a)da=ka-mda, can be changed into a formula, logN=cost.-bM, under some suitable assumptions. If m is 1.9, the value of b is 0.9.
4) The energy of the smallest micro-earthquakes observed by the present authors is of the order of 10¹⁰ erg. which is about 1/100 of that of the minimum earthquake observed by Richter and Nordquist. The Ishimoto-Iida's formula holds good even for such small earthquakes.

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The general discussion is made on the stationary response of an electromagnetic seismometer, when the output of pickup is shunted by a condenser. This device can be used as a displacement seismometer up to the long period of ground motion of u=3-4, if a highcut filter is adopted for the frequency range of u<1. The magnification of the order of 10K is easily obtained even when the sensitivity of amplifier is of the order of 10μV/mm. The phase response is as well as the mechanical displacement seismometer. This kind of seismometer, therefore, is very suitable for the measuement of micro-tremor using a small size pickup.

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The previous paper [SUZUKI and HASEGAWA (1970)] discussed the stationary response of electromagnetic seismometer when its pick-up is shunted with a condenser to have a flat displacement response for longer period than the natural period of the pendulum. A general study on the transient response of the same system is made in this paper. Main effects of shunt condenser on the impulse response are: (i) The response is more likely to be oscillatory than the case without condenser. (ii) The period of oscillatory impulse response becomes longer. (iii) Statical magnification decreases. (iv) The time of the first peak of oscillatory impulse response is not zero but has a finite positive value. (v) The ratio of amplitudes of the negative overshoot and the first peak becomes large. Some of these effects imply a deterioration of transient response. The quantitative computation, however, shows that it is not so serious for many seismometer commonly used.

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The resisting force by air damper is not exactly proportional to the velocity of the motion of seismometer, as already pointed out by Dr. T. Hagiwara. Hence the frequency response of the seismometer with air damper is different from that by the ordinary theory of seismometers. The author studied mathematically the motion of the seismometer in such a case, for both free and forced oscillations, and calculated the true frequency response curves. The numerical results of calculations for the seismometer of Ishimoto type (natural frequency; 50c/s, weight of mass; 15kg, sectional area of the damper; 50cm²) are shown in Figs. The difference between the true response curves in the present case and those by the ordinary theory are not always neglisible, especially when the damping coefficient is large.

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A simple formula is obtained for the accuracy of hypocenter estimated from S-P times at four stations. Assuming that the error exists only at the fourth station, the number of parameters is reduced so as to obtain a simple expression. The accuracy is expressed only by the non-dimensional ratios of locations of hypocenter and the fourth station to the radius of the circumscribed circle of other three stations, irrespective of the individual locations of these three stations. The formula are given by Eqs. (19), (22) and (26).

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A spectral analysis has been developed to obtain an approximate spectrum of short-period waves with nearly random phases. The analysis method has been applied to more than 900 short-period seismograms of recent great earthquakes in the world. Short-period seismic moment M₁, which represents an estimate of earthquake source spectrum at a period of about 1 to 2 seconds, has been evaluated for 79 earthquakes covering the range of seismic moment M₀ from 7.5×10²⁹ to 7.5×10²⁴ dyne·cm. It has been shown that seismic moment M₀ is approximately in proportion to the square of short-period seismic moment M₁ in the above dynamic range. A relation between short-period seismic moment and bodywave magnitude m_b* redetermined from maximum trace amplitudes of P-wave trains has been obtained;
logM₁=1.24m_b*+17.9.
The former relation would give constraint to understand the rupture mechanism of irregular faults and the latter would give a quantitative measure to evaluate the overall excitation of short-period seismic waves due to large earthquakes.

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A simple method is developed to determine seismic moments of earthquakes by using tabulated data in usual seismological bulletins. The method is qualified through the criteria such as simplicity of calculations, coverage of wide magnitude range, and insensitivity of the instrumental response: At first, characteristic period T_c of each earthquake is defined as the average value of apparent periods of wavelets which give maximum amplitudes of ground displacement at epicentral distances between 200 and 700km. Secondly, amplitude information is taken into consideration, making a product of maximum amplitude, its period and epicentral distance. Seismic-moment factor M_e for a given earthquake is defined at the characteristic period T_c as the average value of those products evaluated from horizontal components at stations within epicentral distance range from 200 to 400km. The narrow range of epicentral distance in evaluating M_e is taken so as to reduce the uncertainty due to seismic-energy attenuation into a permissible range and to be able to obtain equal number of observations for small earthquakes to that for large ones. The relation between the seismic-moment factors and characteristic periods for 163 intraplate earthquakes in Japan from 1926 to 1977 clearly demonstrates that M_e is proportional to the cube of T_c. A scaling model of earthquakes that satisfies the empirical relations among surface-wave magnitude, JMA magnitude, and body-wave magnitude facilitates the estimate of static seismic-moments from calculated M_e's. The seismic moments of 16 earthquakes determined by conventional analyses from near- and/or far-field observations are consistent with static seismic-moments thus estimated. This shows the potential in practice of the present method especially in routine processing of seismic data.

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Mt. Kurikoma is an active volcano located nearly at the center of the northeastern part of Honshu, Japan. The activity of this volcano has been very low in the last decade, and we have few geophysical data about this volcano. The seismic observation was carried out at Mt. Kurikoma in August and September, 1971 in order to know the seismic activity of this volcano and surrounding area in the quiet period. The hypocenters of sixteen earthquakes observed with a tripartite network were determined under a reasonable assumption of crustal structure. Besides these events, thirty epicenters were estimated from P～S times at Mt. Kurikoma and at several observatories of Tohoku University. Some seismic activity beneath and near Mt. Kurikoma was found separately from the aftershocks of an earthquake, which occurred in the southeastern part of Akita Prefecture on October 16, 1970. The activity has a tendency of successive occurrence. The daily number of events is 0.7 on an average except for the period of group occurrence. The seismic activity, even including the aftershocks, is limited within the region under the central mountain range.

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A complete expression of dynamical characteristics for electromagnetic seismographs with no electric amplifier has been derived by Tazime. In this paper the same expression is deduced in another way, which is more familiar to seismologists. The method is conducive to easy understanding of physical meanings of the expression. Further, the expression is reduced to one of practical convenience. The new expression is written in terms of usual constants for galvanometer, i. e., period, coil resistance, critical damping resistance, and sensitivity.

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1) Statistics of electrotherapies in Japan (1961-1966): Questionnaires concerning on clinical application of low frequency electrotherapy were sent to 142 big clinics in all over the Japan. Answers were obtained from 70 clinics. The total number of the cases was 8973 who were treated for past five years.
It is clarified from the analysis of this questionnaires and answers that low frequency electrotherapy have been applyed in many clinics by following the basis of neuro-physiological principles and some improvements were noticed on 56.4% of 8858 cases.
2) Statistics of electrotherapy in our clinic during past five years:
The principle in the treatment of the nervous system in our clinic were as follows;
a) The diseases in the muscle and peripheral nerve fibers: They will be treated by the third effect of polarization.
b) The disease in neuro-muscular junction: It will be treated by the post-tetanic potentiation on neuro-muscular junction.
c) The disease in the spinal synapses:
It will be treated by two theoretical bases; firstly post-tetanic potentiation on spinal mono-synaptic reflex and secondly the third effect of spinal polarization on the reflex action.
3) Therapeutic application of low frequency current on progressive muscular dystrophy:
Recent advancement in electrotherapy on progressive muscular dystrophy in our clinic was reported in the view point of electromyography and biochemistry. The best result was gained by the administration of post-tetanic potentiation on the spinal mono-synaptic pathway.
4) Several problems in future:
The size and shape of electrode, wave-form, amplitude modulation, frequency modulation, telemetry, mechanical vibration, electrical narcosis, and heart and bladder stimulation with pace maker and so on were discussed.

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The epicenter of the Numadate Earthquake on March 28, 1914 (JMT) has been reported to be at 140°.9E, 39°.8N in the “Rika-Nenpyo”, which is a standard reference on big earthquakes in Japan. However, this location is inconsistent with the distribution of damage or with other evidences. The epicenter is relocated in this paper based on the newly collected reports about damage as well as the S-P times at several stations. Both the macroseismic and instrumental results give the epicenter at 140°.4E, 39°.2E.

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