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Volume 38, Issue 4
Displaying 1-12 of 12 articles from this issue
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Hitomi OHASHI, Hiroshi KAGAMI, Yutaka OHTA1985 Volume 38 Issue 4 Pages 485-496
Published: December 25, 1985
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSAt the 1983 May 26 Central Japan Sea earthquake (M=7.7), dwelling and agricultural facilities were severely damaged by sandy soil liquefaction in rural town Wakami, Akita prefecture. This paper presents how each household was affected by and responded to the earthquake disaster for a considerable period of time. Waiting for 6 months after the earthquake, a questionnaire survey was performed for all the 2198 households and interviews were made supplementally for the seriously affected 161 households. The questionnaire asks characteristics of family and housing, damage to dwelling, damage to farming, fishing, shops and so on, effects on daily life after the quake, economic impact, and surrounding conditions related to seismic intensity.
The results obtained are as follows.
1) Distribution of dwelling damage along 20km within the town, distinctly different between the northern and southern parts, is similar to those of seismic intensity and gas pipe damage. Micro topography of dune and coastal plain amplifies the damage.
2) Severe damage to rice field in the northern part of the town resulted in decrease of harvest. Damages to farm land and dwelling are economically equivalent and together amount to 60% of annual income there.
3) Methods to repair a dwelling depend mostly upon degree of damage, partially upon building age and insurance payment. Reconstruction costs ¥15 million in average and tends to make houses larger than before. However needy families find it difficult to get proper fund for restoration and suffer from insufficient repairing.
4) Economic loss is covered far more by public or private loans than by insurance payment. Among ¥2.9 billion of total direct damage to households in the town, only 18% can be paid by insurance. Economical hardship is likely to last for decades.
5) It takes from one week to one month to resettle surroundings, to recover gas supply and to return to daily lives. Repair of houses starts later and finishes 4 months after the quake in average. Repair works of dwellings scatter largely from just after the quake to late fall. Some were still waiting for the next spring. Reconstruction takes about 121 days in average and many families stay in temporary housing.View full abstractDownload PDF (1458K) -
Results of Seismic Reflection SurveyTakanobu YOKOKURA, Shiro WATANABE, Naomi KANO, Kazuo YAMAGUCHI, Shinic ...1985 Volume 38 Issue 4 Pages 497-511
Published: December 25, 1985
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSSeismic reflection survey was conducted at the Higashi-Ibaraki Terrace, the eastern foot of the Tsukuba Mountain Block, in order to clarify the shallow geological structures and the shape of the pre-Neogene basement. As a result, the followings are found. In the eastern part of the surveyed area, there are two major horizontal formation boundaries at about 50m and about 150m in depth. The former corresponds to the boundary between the middle-upper Pleistocene series (the Shimosa group) and the Pliocene-lower Pleistocene series (the Kazusa group), and the latter to that between the Kazusa group and the Miocene series. The Miocene series are unconformably overlain by the Kazusa group. The Shimosa and the Kazusa groups are nearly horizontal, but the Miocene series shows about 15-20° dip to the east. In the western part, there are also two major horizontal formation boundaries at the nearly same depths as in the eastern part. The former corresponds to the boundary between the Shimosa group and the unidentified formation, and the latter to that between this unidentified formation and the pre-Neogene basement, stretching from the Tsukuba Mountain Block. This basement is relatively flat in the western part, but it begins to dip eastward at the angle of about 15-20°, and is overlain by the Miocene series. The unidentified formation may be the heteropic facies of the Kazusa group in the eastern part, although no firm evidence is now available. The relation between the Miocene series and the pre. Neogene basement in the surveyed area is the same as that in the Toriashi, Torinoko and Yamizo Mountain Blocks, where both the Miocene series and the pre-Neogene basement outcrop at higher levels.View full abstractDownload PDF (2152K) -
Koji MATSUNAMI1985 Volume 38 Issue 4 Pages 513-527
Published: December 25, 1985
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSElastic wave scattering by random heterogeneities is studied by ultrasonic model experiments; these are carried out using two-dimensional models of media with randomly distributed velocity and density heterogeneities. The P-wave trains composed of several crests and troughs are observed along profiles transversal to the direction of wave propagation. The apparent amplitude attenuation due to the scattering and the amplitude fluctuations along the profiles are examined for the range of ka from 2 to 13.5, where ka is 2π times the ratio of heterogeneity size a to wave length λ. The main experimental results are as follows.
Scattering attenuation Q-1, determined from the ratio of scattering coefficient to wave number, increases remarkably with the increase of ka from 2.5 to 4, and has a peak at ka≅4, and decreases with increasing ka. The scattered energy contributing to the fluctuations of wave field is the order of about 10-1 of the total scattered energy for 2.5<ka<6, but almost all the scattered energy contributes to the fluctuations of wave field for ka>10. The intensity of the fluctuations becomes stronger for P later crests and troughs for 3<ka<6, but the fluctuations are nearly of the same intensity for all P parts for ka<3 and ka>10. The correlation distances of the fluctuations for P initial crests and troughs are seven to eight times the heterogeneity size at ka=2-2.5, and decreases with increasing ka, and are nearly equal to the heterogeneity size for ka>10. The correlation distances of the fluctuations for P later crests rnd troughs are nearly equal to those of the fluctuations for P initial crests and troughs for ka<3 and ka>10, but are considerably shorter than those of the fluctuations for P initial crests and troughs for 3<ka<6.
These results indicate that the scattering effect is different among the following three cases: ka<3; 3<ka<6; ka>10. The scattering effects for ka<3 and 3<ka<6 reflect a very complicated scattering process, respectively; but is well explained by forward scattering due to the randomly distributed heterogeneities for ka>10.View full abstractDownload PDF (1760K) -
Shigeki HORIUCHI, Akira YAMAMOTO, Toru MATSUZAWA, Toshio KONO, Akira H ...1985 Volume 38 Issue 4 Pages 529-539
Published: December 25, 1985
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA real-time system of automatic detection and location of seismic events has been developed by using a personal computer. Since speed of computation by a personal computer is low, a simple digital band-pass filter has been developed for the real-time system. The band-pass filter needs only several times of addition and subtraction to get an output. Event dection is based on a ratio of short to long term average of outputs of the filter whose cutoff frequencies are set to decrease amplitude of long period noise owing to microtremor and amplitude of short period noise owing to culture. Arrival times of the P and S waves are determined by applying Akaike Information Criterion (AIC) to outputs of the band-pass filter with narrow band whose central frequency is set to be a value of predominant frequency of the seismic signal.
A temporary seismic observation with 8 stations for the aftershocks of the 1984 Western Nagano Prefecture Earthquake has been made by the use of radio and telephone telemetries. The real-time system of the automatic location of the seismic events was tested to demonstrate that hypocenter distribution obtained by the real-time system is nearly consistent with that determined from arrival time data which were read manually. It is shown that hypocenters of 60% among triggered events can be determined by this real-time system.View full abstractDownload PDF (1300K) -
Kensuke YAMAZAKI, Takashi TAMURA, Ichiro KAWASAKI1985 Volume 38 Issue 4 Pages 541-558
Published: December 25, 1985
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSSeismogenic stress field off the western coast of the Tohoku District, north-east Japan, is clarified by means of focal mechanism of small-to-moderate size earthquakes using polarity data of P-wave first motion. Foreshocks and aftershocks of some moderate size events show irregular patterns of direction of the maximum compressive stresses and of faulting style. Exclusive of such foreshocks and aftershocks, the directions of the maximum compressive stresses are concordant with those derived from two major events in the area, the 1964 Niigata earthquake and 1983 Akita-oki (Central Japan Sea) earthquake. East-west direction of the maximum compressive stress is dominant off the western coast of the Tohoku district. The direction gradually changes to northwest-southeast toward the northern edge of the Itoigawa-Shizuoka Tectonic Line.
The isolated event of M 5.1 of May 16, 1975, which occurred in the southern edge of the middle part of the Japan Sea Basin appears to be peculiar in points that oean bottom topography in the source region shows no traces of seismotectonic deformation and that the maximum compressive stress of the event points to NNW-SSE, which is different from those of the seismogenic stress field off the western coast of the Tohoku district.View full abstractDownload PDF (1704K) -
Hideo WATANABE1985 Volume 38 Issue 4 Pages 559-569
Published: December 25, 1985
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe shape of tsunami source deforms ususlly elliptic and the earthquake origin situates on the edge of the tsunami elliptic source. Then, it seems that the tsunami occurrence elongates apparently from one edge of tsunami source to another.
The subject of this report is to study the relationship between such apparently elongated tsunami source and tectonics near occurrence area. Some obtained results are followings.
1) The apparently elongated direction of tsunami source has a close relation with the sea depth of tsunami occurrence area, plate formation and earthquake mechanism.
2) Tsunami sources is parallel to iso-depth lines, however, vertical to them in the Tokachi-oki and the Hyuganada, corresponding to changed point of the Pacific and the Philippine plates.
3) The elongated direction of tsunami source is parallel to the slip direction of earthquake fault in the Tokachi-oki, the Boso-oki and the Hyuganada, and vertical to other areas. This depends with the slip angle of earthquake fault.
4) Tsunami amplitude and earthquake intensity seem to be large at the direction of earthquake fault.
In general, it seems that tsunami occurrence and tectonics at the changed points, are more complicated than other ones.View full abstractDownload PDF (1047K) -
Natadera FaultKazuo MINO, Norio HIRANO, Taroh SADAHIRO, Susumu NISHIMURA, Tohru MOGI1985 Volume 38 Issue 4 Pages 571-576
Published: December 25, 1985
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSWe have found a new active fault on aligned hot springs along the shore of the Japan Sea in the southern part of the Hokuriku district, Central Japan. The fault trace is determined by clear outcrops and fault topography and it is confirmed by γ-ray survey. The length of this fault is about 20-30km and its strike is N60°E. We denominate this fault the Natadera fault.
The Natadera fault is characterized by the linear arrangement of the hot springs. The aligned springs have often indicated a falut, especially a strikeslip type of fault. Such springs were observed at the Sanda-Yamasaki tectonic line and the Sabae fault.
The Natadera fault appears to be young in geological meanings, because the fault cuts up to the surface of the Quaternary sedimentary layers. It means that this fault is active.
This fault plays a role of a boundary of a large blocks which is made by four fault zones where large earthquakes have occurred in this recent time. Therfore, this fault must be closely related to tectonic movement in Central Japan.View full abstractDownload PDF (928K) -
Yagi·Yabu, Mitoke Fault ZoneTohru MOGI, Kazuo MINO, Susumu NISHIMURA1985 Volume 38 Issue 4 Pages 577-585
Published: December 25, 1985
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThere are many active faults in the Northwestern Kinki district, Southwest Japan. Among, them, the Yamasaki fault, the Arima-Takatsuki tectonic line, the Mitoke and the Yabu-Yagi faults are large scale ones, and their strikes are WNW-ESE direction, generally. In the previous paper, we showed that the Yamasaki fault was able to extend to the Jumantsuji fault, which is one of the branch of the Arima-Takatsuki tectonic line. This large fault which consists of a series of three faults, Yamasaki, Yashiro, Jumantsuji, is the boundary of two blocks. They show different pattern in each other in the topography, distribution of active faults and the occurrence of microeathquakes.
The similar boundary of two blocks could be seen in the Mitoke and Yabu-Yagi fault region. In this study, geological and geophysical surveys were carried out in the region between the west end of the Mitoke fault and the east end of the Yabu fault. From the geological survey, some remarkable outcrops and topographical evidences which show the existence of the fault were found in this region. The hidden fault was traced by γ-ray and ELF-MT surveys. γ-ray intencity was measured at 6 sites. Resistivity surveys by ELF-MT method were conducted in the 3 sites.
Results of these surveys showed that the Mitoke fault extends to the Yabu-Yagi fault. This newly composed fault is over 100km in length and has wide crushed zone of more than 1km, and is also the boundary of two blocks. The tectonic block that is bounded by these two large faults described in the previous and the present study was revealed. This block was characterized by wide highland region over 400m height and many NE-SW trend short active fault and many occurrencies of microearthquakes.View full abstractDownload PDF (1196K) -
Susumu NISHIMURA1985 Volume 38 Issue 4 Pages 587-596
Published: December 25, 1985
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSPrecursory phenomena before the large earthquakes have been investigated in many countries. In China and some other countries, they made a success of predictions of the large earthquakes by catching precursory phenomena. Variation of radon content of the underground gas and water is also one of these phenomena.
The gas monitor for continuous measurement of radon concentration was designed. Radon concentration, temperature, conductivity and rate of volume of self-spouting of hot spring has been observed at Odoi, Izu Peninsula, Central Japan.
These data effected by the air-temperature but not so effected with the production rate of spring. According to the results of these investigation during these five years, the increasing radon contents are observed at three times of the earthquake swarms in the east part of sea off Ito.View full abstractDownload PDF (665K) -
Shigeo KINOSHITA1985 Volume 38 Issue 4 Pages 597-608
Published: December 25, 1985
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSIn order to investigate the earthquake response of thick sedimintary layer on the pre-Tertiary basement in the Tokyo metropolitan area, the National Research Center for Disaster Prevention has established a small-scale strong-motion observation array at the Fuchu area in the west of Tokyo. In this paper, we report an earthquake response of sedimentary layer for the shallow earthquakes whose epicenters are located in the west of the array. The response characteristics of sedimentary layer for SH waves may be summarized as follows:
(1) A SH pulse train produced by total reflections at the upper boundary of dipping basement, is observed during the earthquakes whose shallow origins are located in the west of the array. The pulse train is modulated by the sedimentary layer and becomes a predominant pseudo-Love wave which appears just after the direct SH pulse in the Fuchu area.
(2) Such pseudo-Love wave is explained even by using a simple dipping layer model and the plane wave approximation. The train of total reflected pulses is calculated by using the Hilbert transform repeatedly.View full abstractDownload PDF (1079K) -
Hideo TSUNAKAWA, Toshi ASADA, Mono INO1985 Volume 38 Issue 4 Pages 609-610
Published: December 25, 1985
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (228K) -
Junji KOYAMA, Masahiro KOSUGA1985 Volume 38 Issue 4 Pages 610-613
Published: December 25, 1985
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (436K)
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