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Volume 34, Issue 3
Displaying 1-12 of 12 articles from this issue
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Tsuneo YAMAUCHI, Mamoru YAMADA, Takashi OKUDA1981 Volume 34 Issue 3 Pages 301-310
Published: October 25, 1981
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSPrecursory abnormal strain responses associated with rainfall are discussed in the present paper. The data analized are the strains observed at the Mikawa Crustal Movement Observatory (Toyohashi City, central Japan) for the period from January 1973 to April 1980. Each extensometer at the observatory is equipped with two or three sensors for the detection of irregularity in strain. Usually the observation gallery deforms uniformly after a rainfall, because the ground strain responses observed by the sensors attached on the same quartz pipe show nearly the same variation. We can calculate accurately these strain responses by a tank model from the precipitation at the observatory, but sometimes remarkable disagreements between the ground strains caused by rainfalls and the calculated values expected from the model are clearly seen before and after the occurrence of nearby earthquakes. Irregular deformations at the observation site are also observed. These abnormal strain responses to rainfall are observed for 18 earthquakes during the period from January 1973 to December 1979. Distribution of earthquakes which were accompanied by these precursory abnormal strain responses are restricted in the block whose boundary is characterized by the distribution of microearthquakes.View full abstractDownload PDF (937K) -
Hideo YUKUTAKE, Mitsuhiko SHIMADA1981 Volume 34 Issue 3 Pages 311-321
Published: October 25, 1981
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSFor the purpose of investigating the fracture process of earthquake which will be affected by various kind of anisotropy in the earth's crust, we carried out triaxial test up to 500MPa (5 kbar) of confining pressure for the suitable anisotropic rocks for the present study, that is, gneiss and graywacke sandstone.
For gneiss with the anisotropy oriented at 45° to the principal stress axis, the strength was widely distributed and the small rapid stress drop occured frequently below 240MPa of confining pressure. Above 240MPa, on the other hand, the strengh was fitted well with a single curve, which was lower than that for gneiss with the anisotropy oriented at 90° to the pricipal stress axis, and the large stress drop occured.
These results means that at low confining pressures (less than 240MPa) the effect of anisotropy on the fracture is small and local, but at higher confining pressure (more than 240MPa), this effect spreads all over the sample.
It is interesting for earthquake prediction to study the complex strain variation and the phenomena of multiple stress drop, because they result from the fault formed in the inhomogeous distribution of strengh obtained for the moderate anisotropic rocks. It seems important for speculating micro-earthquake distribution for depth that the behaviour of stress drop and strength for gneiss are stongly affected by confining pressure.View full abstractDownload PDF (862K) -
Yoshinori KATOH, Kensuke YAMAZAKI, Ryohei IKEGAMI1981 Volume 34 Issue 3 Pages 323-339
Published: October 25, 1981
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSTemporal variation of seismic activity parameterized by the rate of earthquake occurrence, b-values, seismic energy release and randomness of interoccurrence time of shocks is investigated for three regions in the Pacific coast of north-eastern Japan over the period 1926-1978.
The statistical significance of difference in b-values between before and after large earthquakes, is occasionally recognized. Change in b-values is also related to energy release in that b-values are small when the cumulative energy release steeply increases.
It is well known that, if earthquake occurrence is represented by a stationary and random process in time, the length of time interval (=τ) between consecutive events is exponentially distributed. The stationarity and randomness of earthquake occurrence are examined by using a x2-test for the goodness of fit of the distribution of interoccurrence times of events to an exponential distribution. It is found that the goodness of fit is strongly related to the rate of earthquake occurrence, being the large x2 to the high rate of occurrence. Thus the τ-distribution of earthquake group which contains many aftershocks, does not conform itself to the exponential distribution. However, the group of earthquakes that exclude aftershocks of large earthquakes behaves itself like the Poisson process in time for all the period analyzed. Then earthquake occurrence in time can be modeled after the branching Poisson process by Vere-Jones and Davies. Seismic activity is composed of the primary and the secondary events. Activity of the primary events, which occur at random in time, is considered to be proper or stationary seismicity for a region. An actual seismic activity for the region is composed of the proper seismic activity and the secondary events which occur like the non-Poisson process. Accordingly, it can be considered that the temporal variation of seismic activity for a region is mainly due to the successive occurrence of the secondary events.
The rate of occurrence of the primary or proper events for the respective regions are estimated. When the rate of occurrence of actual events for a region drop near the primary rate, it may indicate that the seismicity in the region gets into a stage of seismic gap which is the period of quiescence.View full abstractDownload PDF (1498K) -
Nobuo HURUKAWA1981 Volume 34 Issue 3 Pages 341-350
Published: October 25, 1981
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA small array with a span of about 2km was temporarily set up in the eastern part of the Kii peninsula. A remarkable later phase has been recorded 1.2sec after a PMP phase (a reflected wave at the Mohorovicic discontinuity) in the case of an earthquake occurring at a depth of 3.5km in the western Kii peninsula. This is a P-type phase, of which apparent velocity is about 6.7km/sec, and has been interpreted as an sPMP phase, which is transmitted from a source as an S-wave, then is converted to a P-wave at a free surface and reflected at the Moho discontinuity. A travel time difference between PMP and sPMP phases is so sensitive to a focal depth that this sPMP phase is useful to determine a focal depth.
The P45P phase, which was interpreted by M. Mizoue as a wave reflected at the upper boundary of the Philippine Sea plate subducting beneath the Asian plate in the Kii peninsula, has been also reinvestigated and found to be an sPMP phase.View full abstractDownload PDF (881K) -
Minoru TAKEO, Katsuyuki ABE1981 Volume 34 Issue 3 Pages 351-364
Published: October 25, 1981
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSTo obtain near-field ground motions, both strong-motion seismographs and long-period seismographs were operated in the epicentral region of Mount Usu, Hokkaido, Japan. The earthquake swarm had occurred there since 1977, and hundreds of earthquakes of magnitudes from 2.1 to 4.4 were recorded on the digital recorder during the period from August, 1979 to July, 1980. The epicentral distances are all 3km and less. Using these seismograms we develop a new and efficient procedure for calculating velocities and displacements from digital strong-motion accelerograms. In the filtering operation we use a Chebyshev causal digital-filter with the automatic design algorithm described by M. Saito. This operation is applied in time domain by using a . standard recursive method, and preserves properties of the actual ground motion. A distortion in the calculated displacements is found very little in comparison with the actual ones. The application of the present method to strong-motion accelerograms will make the time-domain analysis easy and reliable.View full abstractDownload PDF (1327K) -
By Using Refraction and Reflection WavesToshihiko HASHIDA, Masataka ANDO, Ken SUDO1981 Volume 34 Issue 3 Pages 365-376
Published: October 25, 1981
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSRepeated measurements of P wave travel time changes were made within the Uji campus of Kyoto University, over a distance of 400-440m. A stack of 15 air-gun shots in a water=filled hole was carried out every 4-5 hours spanning one week. By the use of a wave form correlation method, we found 0.7% variation of travel time for refraction waves and 0.4% variation of travel time for reflection waves reflected at about 400m depth with an accuracy of 0.4-0.5msec. These variations of travel time seem to be more effectively induced by atmospheric pressure than by earth tide strain. These inferred high stress sensitivities of P wave velocities (10-1bar-1 order) may be attributed to the presence of thin cracks near the earth's surface. These travel time variations may be also attributed to rainfall-induced property changes in rocks. The differences between stress sensitivities in refraction and reflection wave velocities show that the stress sensitivity decreases with depth and that the average aspect ratio of cracks increases with depth.View full abstractDownload PDF (1210K) -
Yoshiteru KONO, Motoaki SUNAMI, Michiko FUJII1981 Volume 34 Issue 3 Pages 377-383
Published: October 25, 1981
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSGood correlation between local Bouguer anomaly in the Fukui plain and earthquake hazard caused by the Fukui earthquake (28, June 1948, 1948, M=7.3) was recognized: Lower local Bouguer anomaly corresponds to higher percentage of totally collapsed houses. This correlation comes essentially from an existence of soft sediment under the alluvial plain, because the thick soft sediment not only results low local Bouguer anomaly, but also amplifies ground motion during earthquake. This may useful to evaluate a zoning of forthcomming earthquake hazard within alluvial plains.View full abstractDownload PDF (919K) -
Hiroshi OGAWARA, Yoshiteru KONO1981 Volume 34 Issue 3 Pages 385-400
Published: October 25, 1981
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThinning process of the oceanic lithosphere was discussed with a consideration of an evolution of the Hawaiian-Emperor chain. The oceanic lithosphere increases or decreases its thickness under the heat balance between input heat flow from the asthenosphere, output thermal conduction within the lithosphere and release or sink of latent heat at the lithosphere-asthenosphere boundary. The heat flow from the asthenosphere controls this process. In ordinary condition, the lithosphere thickens with time, on the other hand, excess heat flow from deeper part of the mantle thins the lithosphere. A condition of the excess heat flow may realize under the Hawaii Island as a “Hot-spot”. Thinning and thickening processes of the Pacific plate along the Hawaiian-Emperor chain are examined mathematically. Observed data for ocean bottom topography, surface heat flow and gravity anomaly are successfully explained by this model.View full abstractDownload PDF (1169K) -
Yoshinobu TSUJI1981 Volume 34 Issue 3 Pages 401-411
Published: October 25, 1981
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSIn the early morning of Dec. 31, 1703 (Genroku 16), an enormous earthquake with magnitude of 8.2 occurred in the south sea region of the Kanto District. It is well known that after the occurrence of the earthquake a huge tsunmi was generated, and that the coasts of the Boso Peninsula, the north coasts of Sagami Bay, and the east coasts of the Izu Peninsula were seriously damaged.
Recently several old documents of the Genroku tsunami were also discovered on the coasts of the Tokai district, the Kii peninsula, and the Shikoku Island. In two towns, Nishina and Toi, on the west coast of the Izu Peninsula, inundation height was estimated 3 meters, and the residential areas of these towns were slightly submerged. At Miho village in Shimizu city on the west coast of Suruga Bay, residential areas were intermittently submerged for more than ten days, and the people took refuge in higher places. On the mouth district of the Lake Hamana, seaside banks were eroded, and the mouth of the lake became broader. Thirty-three large junks out of 36 anchored at the open sea of Arai town near the lake, were wrecked. In Ono town on the Chita Peninsula inside the Bay of Ise, a garden of Naiku shrine was washed and eroded, where inundation height was about 2 meters. Tsunami was also noticed at the port of Nagoya. Miwasaki and Taiji towns and Haida village on the south east coast of the Kii peninsula were seriously damaged in spite of the long distance from the tsunami origin. In these places 46 houses were washed away in total and the observed tsunami climbed up to 3 or 5 meters. Tidal irregulaity was also noticed in several ports of Kochi Prefecture on the Shikoku Island.View full abstractDownload PDF (1170K) -
Ikuo KATAYAMA, Tadashi ANNAKA1981 Volume 34 Issue 3 Pages 413-431
Published: October 25, 1981
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSSeismicity in the Iyonada and Bungo channel area is discussed with emphasis on the feature of focal distribution in recent earthquakes, including the microearthquakes detected by the Ikata microearthquake observation network during the period from Nov. 1975 to Jan. 1980.
The principal conclusions obtained for this region are:
(1) Seismicity in the uppermost mantle is very high, while that in the crust is remarkably low.
(2) Earthquakes in the uppermost mantle have their foci concentrated within a thin layer of almost 10km thickness. This active layer descends in low angle towards northwest direction at the depths of 30 to 50km, and then becomes steep in its slope to westerly direction as the depth exceeds 50km. These observations suggest that these earthquakes occurred in the near surface of descending Philippine Sea Plate.
(3) There seems to exist a northern boundary in the seimic area of the uppermost mantle.
(4) Infrequent microearthquakes (magnitude less than 2.0) detected in the upper crust seem to have an apparent linear distribution parallel to the trend of Sada-Misaki Peninsula.
(5) The magnitude-frequency relationship for the uppermost mantle earthquakes was in good agreement with those in both the recent earthquakes determined by Japan Meteorological Agency since 1961 and that reported major disastrous earthquakes in this region since the late 16th century. This fact suggests that those disastrous earthquakes in historic times could be better designated to seismic activity in the uppermost mantle descending beneath the crust, than to the activity in “Median Tectonic Line”.View full abstractDownload PDF (2003K) -
Rock Samples at Aburatsubo and OmaezakiYoshihiko FUJIMORI1981 Volume 34 Issue 3 Pages 433-435
Published: October 25, 1981
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (308K) -
Tetsuji HIRATA, Takafumi UCHIYAMA1981 Volume 34 Issue 3 Pages 435-437
Published: October 25, 1981
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (357K)
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