Longitudinal primary waves which are called P waves in the present paper have their own velocities α, v_pl and v_rod respectively in a three, a two and an one dimentional media. The rule of conversion from v_pl to v_rod is equal to that from a to v_pl. Here, the transient from v_rod to a has been investigated experimentally as well as theoretically.
Several brass rods having various radii were used for the super sonic measurements. Onset of the longitudinal fundamental mode, namely the first mode, has the velocity equal to v_rod. Various higher modes ride on the fundamental one. Byond the fifth order, the maximum group velocities U_n, _max of the higher modes exceed v_rod and some of the rider waves become the forerunners against the fundamental mode. The higher the order of the mode, byond the fifth in case of the brass rod whose Poisson's ratio is 0.35, the larger the maximum group velocity which approaches α. The higher the order of the mode which we can observe, the more the forerunner which will appear. The curve connecting U_n, _max against wevelengths may be taken as the dispersion curve of P waves in a rod, where the order n is larger than five for Poisson's ratio of 0.35.

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Reliability of the tsunami source model inferred from the dislocation theory of faulting was approximately verified previously, comparing the result of a numerical experiment with tsunami records at the coast. On the basis of above results, water surface profiles on a 200m depth contour have been computed numerically by use of the tsunami source model obtained from the fault parameters of the Tokachi-oki earthquakes of 1968 and 1952. Computed water elevation-time histories indicate the significant character for the directivity of the wave radiation from the source, that is the sense of rise or fall in the leading wave and the wave period. The wave heights (H₀), of source, vary depending on locations on a 200m depth contour. Tsunami inundation heights (R) at a coast and H₀ are plotted along the Pacific coast of the Tohoku and Hokkaido districts. Then, average inundation heights (R_avg), which are used instead of R rather scattered, are fairly well parallel to H₀ and R_avg/H₀=2-3. It is recognised by a simple calculation that the values of R_avg/H₀ are reasonable as the amplification factor of water oscillations on a continental shelf. Therefore, the tsunami source model based on the dislocation theory of faulting seems to give results fairly consistent with the major character of tsunami, at least, in the Pacific coast of Tohoku district. Thus the kind of a numerical experiment may be a usefull method for a prediction of tsunami inundation at the coast of interest.

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The seismic crustal movement on the south Kanto district and the Philippine Sea coast of southwest Japan is characterised by the chronic (in the interseismic period) and acute (at the earthquake) tiltings with reverse sense. The accumulation of these tiltings in geological time scale explains the topographic features on the coast such as tilted terraces. The value “d”, which is defined as the ratio of the subsidence in the interseismic period to the coseismic upheaval, was expressed by two independent linear functions of recurrence interval T of series of great earthquakes. The coefficients of these functions are determined by the data of precise levellings and the heights of coastal terraces in the late Quaternary period. Then, the d and T can be determined on the cross point of the two lines which represent the above two functions. This scheme (called d-T diagram) was applied to the Seismotectonic areas of the southern Kanto and the outer arc of the southwest Japan. The results of T obtained are almost in concordance with the intervals of great earthquakes inferred from the historical documents and the rates of convergence of the Philippine Sea plate under the southwest Japan. It was also shown that the d-T diagram can be used as a tool of earthquake prediction taking an example of the Tokai region.

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Focal mechanisms of very shallow earthquakes on the west and the southwest of Lake Biwa have been determined by smoothing the first-motion radiation pattern and by individual solutions. Published focal mechanism solutions are also used to examine the tectonic stress which generates earthquakes in the north Kinki district. Along the west coast and the east coast of Lake Biwa seismic active regions of very shallow earthquakes occur and in Lake Biwa seismic activity is very low. Most of mechanism solutions in these active regions are reverse faultings with the maximum pressure axes in the direction of nearly east-west or southeast-northwest. In other regions of north Kinki district and west Chubu district dominant type of faulting is strike-slip with the same pressure direction. These types of faulting from earthquake focal mechanism solutions agree well with those of tectonic active faults developed in this area. The reverse faulting as well as the high seismicity on the both coasts of Lake Biwa is consistent with the subsedence of Lake Biwa which has been continued throuth the Quaternary.

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Dynamic and static characteristics of stick-slip motion are studied experimentary for Horoman peridotite. Pressure system is similar to that of HOSKIN et al. Normal stress is constant (80bar) throughout all experiments. Stress rate is varied from 20bar/sec to 0.001bar/sec. Strain is measured at the side surface which is parallel to two pressure axes. Shocks accompanied by slips are detected by a piezoelectric transducer which is attached on a slip plane of central rock block. Overall dynamic range and frequency range of recording system is about 90dB and DC-10MHz respectively.
Samples which have rough, middle rough and fine polished surface are prepared. Asperity height of fine polished surface is less than 10μm. The contact area is 9×9cm².
Characteristic features obtained in present study are as follows;
A) In the case of fine polished surfaces.
a) There are several modes of slip;
1) Rapid speed partial area slip which emits small fore shock or preshock.
2) Slow speed partial area slip which may be detected using strain gauges.
3) Slow speed slip which extends over the contact area. This mode of slip may be divided into two submodes. One is followed by a rapid slip which extends over contact area. Therefor, this slow slip may be called a preslip. The other is not followed by a rapid slip.
4) Rapid slip extended over contact surface which is called the main slip and emits a large shock which is called the main shock.
b) There is a shock sequence for each main slip. This sequence of shocks contains several preshocks and a main shock. Preshocks can be observed 1-100msec prior to the main shock, and their amplitudes increase as exp((t-t₀)ⁿ) where, at the main shock time, t=t₀.
c) Stress drop increases as successive main slips time interval ΔT increases. This relation may be expressed as A{1-exp(-C/(σ_c-σ)·ΔT)} where σ_c is the critical shear stress, σ is shear stress, A and C are some constants which may be varied with surface roughness or rock types.
d) Shear stress is more effective than normal stress to increase stress drop.
B) In the case of rough surfaces.
a) There is only one mode of slip which corresponds to A)-a)-4).
b) No preshocks can be observed.
c) Stress drop increases as in the case of A), but constant C is smaller than the case of A).
d) The effectiveness of shear stress to increase stress drop is same to the case of A).
The feature of the fore-shock sequence of the earthquake Off Nemuro 1969 good fits to that of the preshock sequence A)-b). This shows that dynamic features of stic slip motion in the case of fine polished surface are more suitable than the case of rough surface to simulate earthquakes.
There is a possibility to predict occurences of earthquakes in some case using the features of the preshock sequence and the preslip.

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An earthquake swarm started its activity in the northern somma of the Aso caldera on January 20, 1975. In the course of the earthquake swarm activity, on January 23, an earthquake of magnitude 6.0 representing the largest one among the whole earthquake swarm took place. After this earthquake, the activity of the earthquake swarm declined gradually until the end of January. By using available data obtained from all the seismological stations in the Kyushu district, 120 foci of these earthquake swarm were determined with fairly a high accuracy.
Analysing the time variation of the frequency of earthquakes, the migration of their foci, the variation of b-values, and so on, it was found that these features seen in the earthquake swarm were having quite a similar character in the fracturing of the stressed rocks.
1) The b-values showed fairly a large differrence in the two periods, i. e. before and after the largest earthquake. Before the earthquake, b=0.73 while after the earthquake b=1.01.
2) The series of the earthquake swarm activity can be divided into 6 stages, from the consideration of the migration of the earthquake foci or their characters. The temporal change in the spatial distribution of these foci was noteworthy. In the early stage of the activity a void space (seismicity gap) was observed in the central part of the area in which many foci were distributed. In the next stage, small earthquakes began to take place inside of the above mentioned void space, then at last the largest earthquake occurred at the edge of the void space.
3) A volume of the void space may be taken to be 1.8×10¹⁷cm³ from the locations of foci during the stage II and the ultimate stress energy that can be stored up in the void space until a break-down takes place can be estimated to be 5.6₅×10²⁰ erg. According to the relation between the energy of an earthquake and its magnitude i. e. log E=11.8+1.5M, the magnitude of the largest possible earthquake M=5.9₇ is obtained. This value agrees with the magnitude which has been determined from the maximum amplitude on the seismograph of the above mentioned largest earthquake (M=6.0) among the whole swarm.
4) Considering the migration of the earthquake foci, it may be concluded that this earthquake swarm activity have not been related to a volcanic activity of the Volcano Aso.

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In order to investigate the seismicity of microearthquakes in relation to the occurrence of large shocks, an array of observation stations spread widely over the northern part of the Kinki District, was being operated since 1963.
The array was substituted for a new telemetered system in 1975, to get the simultaneous and real time recordings. A data processing system with a digital computor was, at the same time, equipped and is playing an important role in analysing and filing an abundant supply of data. This total system is, therefore, of practical use for saving labor and refining data.
In this report, the constitution and function of the system are described in some details, together with some examples of more refined analyses.

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