Nobi Earthquake Research Articles

A new model for the fault beneath the sedimentary basin in the 1891 Nobi earthquake

AbstractWe have investigated the geometry and detailed location of the Gifu-Ichinomiya (GI) fault, a buried fault considered to have ruptured during the 1891 Nobi earthquake. Based on an inversion of coseismic vertical displacements obtained by leveling surveys, we obtain an inclined fault plane showing a reverse fault-type mechanism, rather than the vertical fault plane assumed in previous models. The fault dips 60? to the east and its slip during the earthquake is estimated to have been 1.48 m along the fault dip. The fault is located 5 km east of the location assumed in the previous models. Recent earthquakes have been scattered along the new fault location, not the previously estimated one. Focal mechanisms of the earthquakes that have occurred around the fault are dominated by a reverse fault component, which is consistent with the focal mechanism of the GI fault obtained by the inversion of coseismic displacements. The seismic intensity distribution calculated using the new fault geometry and location explains well the distribution of observed damage caused by the 1891 Nobi earthquake.

Seismic Microzoning for Urban Planning

Since the Nobi Earthquake of 1891, seismology, engineering seismology, earthquake engineering, structural engineering and sciences which are related to the phenomena of earthquakes were developed in Japan. Especially pure sciences and engineering made great advances individually. However, actual earthquake damage has not yet ceased to exist, and this damage leads the loss of a great number of human lives. Undeveloped areas and not so important buildings have always suffered these disasters. From worldwise point of view, there is a more serious problem, sometimes more than 10,000 people are killed by an earthquake. The importance of these sciences and engineering is centered in such problems, but at their present stage of development they can not solve these serious problems. Primarily because there are many problems regarding the economical conditions. Seismic microzoning has its purpose in the solution of the serious problems mentioned above. The results of seismic microzoning should cover whole areas and structures, for saving money in construction and to minimize the danger posed to human life. Also seismic microzoning works are related to the disaster prevention programs of various areas. Investigations into seismic microzoning are mainly related to the field of engineering seismology and its applications are in earthquake engineering, but fundamental investigations and applications can not be separated, they are closely related. Thus difficult points still exist, because only a few investigators have interests in the applications of seismic microzoning work. In this paper the author tries to explain the theoretical background and the technique of application of seismic microzoning which developed mainly in Japan. But these theoretical and technical results are not yet completed, and the facts interpreted from the strong motion seismograms and other results of field observations will correct these conclusions.

Dynamic Rupture Propagation during the 1891 Nobi, Central Japan, Earthquake: A Possible Extension to the Branched Faults

The dynamic rupture process of the 1891 Nobi, Japan, earthquake was closely reinvestigated by using a boundary integral equation method based on currently available observations. We discussed mainly a possibility of the rupture propagation on branched faults, including a buried fault called the Gifu-Ichinomiya line. Several numerical simulations were made incorporating the information on the fault geometry based on the active fault traces on the ground surface and the maximum principal strain direction observed by the triangular surveys for the past 100 years. The results suggest that the rupture should propagate along the buried fault during the Nobi earthquake if a weak geological discontinuity exists along the Gifu- Ichinomiya line and is connected to the Neodani fault, which is one of the major surface faults appearing during the Nobi earthquake.

四国の中央構造線断層帯の最新活動に伴う横ずれ変位量分布

Recent paleoseismological studies revealed that the entire length of the right-lateral Median Tectonic Line active fault zone in Shikoku ruptured after the 16th century A.D. Based on aerial photograph interpretation and field observations, we identified geomorphic and artificial features offset along the fault zone that record the amount of right-lateral slip associated with the most recent and previous earthquakes. The amount of offset during the most recent earthquake varies considerably among the active faults that comprise the fault zone: about 7m along the Chichio and Ikeda faults in eastern Shikoku and 2-3m along the Shigenobu and Iyo faults in western Shikoku. In general, surface slip associated with the latest event is greater than 5m between the Zunden and Okamura faults, and decreases gradually to the east and west. There is a correlation between horizontal slip rates of the individual faults and surface slip during the most recent event. This is consistent with the paleoseismic observation that the recurrence intervals of the individual faults do not vary considerably along the fault zone and are in a range of 1000-2000 years. Based on the surface offsets and segmentation model by Goto and Nakata (2000b), we are able to calculate moment magnitudes for scenario earthquakes from the fault zone. Separate ruptures of the western Shikoku, Okamura, and eastern and east-central Shikoku segments would produce earthquakes with magnitudes of Mw7.3-7.4, Mw7.2-7.4, and Mw7.7-7.8, respectively. These ruptures would be as large as or greater than the largest recorded historical earthquake, the 1891 Mw7.4 Nobi earthquake.

Effects of nearby large earthquakes on the occurrence time of the Tokai earthquake—An estimation based on a 3-D simulation of plate subduction—

An eastern half of the focal region of the 1854 Ansei-Tokai earthquake was not ruptured at the 1944 Tonankai earthquake and the area around Suruga Bay remained as a seismic gap (Ishibashi, 1981). As to the cause that the fault motion in 1944 did not extend to the eastern part, Mogi (1981) and Pollitz and Sacks (1995) considered effects of the 1891 Nobi earthquake of M8.0. In this paper, we evaluate quantitatively effects of nearby large earthquakes, the 1891 Nobi, the 1923 Kanto and the 1944 Tonankai earthquakes, on the occurrence time of the Tokai earthquake that has been anticipated to occur soon to fill the seismic gap, using a three-dimensional simulation model with a rate- and state-dependent friction law (Ruina, 1983). It is suggested that the occurrence of the Tokai earthquake was delayed by the 1891 Nobi earthquake, while it was advanced by the 1923 Kanto and the 1944 Tonankai earthquakes. We show that the sense and degree of the effect of nearby large earthquakes on the occurrence time of the anticipated Tokai earthquake depend on whether and how much the stress perturbation produced by the nearby earthquakes strengthens or weakens the stress accumulated in the coupling region, especially in the highly shear-stressed ring zone (Kuroki et al., 2002). However it is difficult to say definitely how much the Tokai earthquake was delayed or advanced, because the magnitude of the effect is very sensitive to the location of the fault planes.

Source rupture processes of the 1944 Tonankai earthquake and the 1945 Mikawa earthquake derived from low-gain seismograms

In the 1940’s, several destructive earthquakes occurred in western Japan. Seismograms in this period were usually recorded on smoked paper and the quality was poor compared to modern digital data. But the recent development of image processing technology enabled us to reconstruct feasible waveform data, whereby we investigated source rupture processes of two devastating earthquakes: the Tonankai earthquake (M7.9) of December 7, 1944, and the Mikawa earthquake (M6.8) of January 13, 1945. The results for the Tonankai earthquake show that the source roughly consists of a single asperity with a length scale of 100 km, having no segment structure with a smaller length-scale. Such a feature seems to be reflected to the sea bottom topography above the source region. The main source parameters are as follows: the seismic moment = 1.0 × 1021 Nm (Mw=7.9); the fault area = 140 km × 80 km; (strike, dip, rake) = (225°, 15°, 79°); the maximum and averaged dislocations = 4.4 m and 3.0 m, respectively. The analysis of the seismograms for the Mikawa earthquake shows that the source is a reverse fault with a slight left-lateral component. The pressure axis is directed to ENE-WSW, which is a little rotated from the EW compression axis prevailing in western Japan. This fault can be regarded as the southern extension of the Nobi earthquake fault system. The main source parameters are as follows: the seismic moment = 1.0 × 1019 Nm (Mw=6.6); the fault area = 20 km × 15 km; (strike, dip, rake) = (135°, 30°, 65°); the maximum and averaged dislocations are 2.1 m and 1.1m, respectively. The slip distribution mainly consists of two asperities: the one near the hypocenter and the other 10–15 km northwest from it. The heavily damaged area is well correlated with the northwestern asperity.

Distribution of Ground Motion Intensity Evaluated Using Wooden House Damage During the 1891 Nobi Earthquake (M8) in Central Japan

Distribution of Ground Motion Intensity Evaluated Using Wooden House Damage During the 1891 Nobi Earthquake (M8) in Central Japan

岐阜-一宮断層の再評価

A concealed fault named “the Gifu-Ichinomiya Line” along the eastern margin of the Nobi Plain was stratigraphically reexamined. This fault has been regarded as an active fault concealed by Cenozoic strata of the Nobi Plain, which runs in the NNW-SSE direction, and connects Gifu with Ichinomiya and Inazawa. However, the exact location of the fault has not been well defined. We focused our attention on the vertical position of a pumice bed of 80, 000 to 90, 000 years old that appears in bore-hole records around the site, because the pumice bed is a key to stratigraphic correlation. The correlation of 97 bore-hole records showed a throw of the pumice bed amounting to 5.6m in average. The strike of this throw parallels to the JR-Tokaido Line and runs about 1, 100m to the east of the line. The vertical displacements were also recognized for two gravel beds (G1 and G2) above and under the pumice bed. The throw for the deeper strata tends to be larger. We regard this throw as an active fault that moved at the Nobi earthquake of 8.0 magnitude in 1891 and other earthquakes repeated during the Quaternary.Recently, Aichi Prefecture carried out stratigraphic examinations of shallow well records and geophysical prospecting and reported that neither fault nor flexure is realized around the presumed site of the fault in question. On the basis of the results, Governmental Earthquake Research Committee concluded the fault to be nonexistent. However, the survey by Aichi Prefecture exploited exclusively the area to the west of the fault disclosed from our stratigraphic work and scarcely covered the site of the fault mentioned above. Therefore, the survey by Aichi Prefecture is meaningless in the examination of the Gifu-Ichinomiya fault, and their conclusion is erroneous.

Triggering and inhibition of great Japanese earthquakes: the effect of Nobi 1891 on Tonankai 1944, Nankaido 1946 and Tokai

There are two unusual features of the most recent great earthquakes off southwest Honshu. The Tonankai and Nankaido earthquakes were relatively early compared to the historical record of past occurrence, and the Tokai section of the Tonankai fault did not fail in 1944 whereas it probably had for the previous ∼1000 years. We show that both phenomena can be explained by postseismic strain diffusion from the great Nobi, Japan, earthquake (M 8.0) in 1891. It is believed to have produced stress changes that influenced the time of occurrence of the great Tonankai (M 7.9) and Nankaido (M 8.0) earthquakes in the mid-1940’s. The pattern of long-term viscoelastic deformation following the Nobi earthquake suggests that the failure threshold was reduced in the southwest section of the Nankai Trough, which may have acted to trigger the Tonankai and Nankaido events. In contrast, the threshold was increased in the eastern Tokai section of the thrust zone and therefore failure of this section may have been inhibited. We model fault failure and show that the stress levels from Nobi are adequate to account for the advance of Tonankai and the inhibition of Tokai.

トレンチ調査に基づく1891年濃尾地震断層系・温見断層の活動履歴

トレンチ調査に基づく1891年濃尾地震断層系・温見断層の活動履歴

死亡危険度に関する1891年濃尾地震, 1948年福井地震, 1995年兵庫県南部地震の比較

死亡危険度に関する1891年濃尾地震, 1948年福井地震, 1995年兵庫県南部地震の比較

法務省旧本館の木構造技術に関する研究

The old building was designed by Ende & Bockmann. The construction began in 1888 and was completed in 1895. It had a floor frame and a roof frame in a style known at that time as 'German construction'. The beams of the single flooring were ca. 7 meters in length and were placed every ca.90 centimeters. They were reinforced by intertruss bracings and filled with cinder for soundproofing, as was often done in Berlin. The roof frame was similar to roof frames in Germany, but in Germany there were no examples where posts of the roof were reinforced by braces on either side using many diagonal posts. The reason may be because attic space was unnecessary in Japan and the roof frame was designed to strengthen the frame after the Nobi Earthquake of 1891.

Distribution of shortening landward and oceanward of the eastern Nankai trough due to the Izu-Ogasawara ridge collision

The convergence of the Philippine Sea and Eurasia plates is accommodated primarily by plate subduction along the Nankai trough west of about 137.3°E, but additionally by widely distributed onshore and offshore deformation to the east. This zone, with a total dimension of 200 km (parallel to the Nankai trough) by 350 km, has developed as one highly coupled region since the collision of the Izu peninsula with mainland Japan about 1–2 m.y. ago. The onshore faulting in central Japan is consistent with a WNW-ESE direction of maximum horizontal stress, while the oceanward deformation is driven by diffuse NW-SE shortening of the Izu-Ogasawara volcanic ridge which produces a kinematic discontinuity with respect to the Philippine Sea oceanic crust to its west. The strain release associated with the 1891 Nobi earthquake, and the onshore deformation as a whole, suggests that the Philippine Sea-Eurasia convergence is partially accommodated by onshore shortening between the Tsuruga Bay-Ise Bay Tectonic Line and the Izu peninsula.

Consequences of stress changes following the 1891 Nobi earthquake, Japan

Abstract Great earthquakes along the Philippine Sea interplate boundary, central Honshu, usually rupture a large portion of the Nankai Trough and Suruga Trough. However, the 1944 Tonankai and 1946 Nankaido earthquakes, the most recent great Philippine Sea events, did not rupture the Suruga Trough. Mogi proposed that strain release from the 1891 Nobi earthquake is responsible for the apparently premature northeast termination of the 1944 rupture zone. Using a recently derived fault model of the 1891 earthquake, combined with a suitable rheological model of central Honshu, we quantify both the inland and offshore consequences of the Nobi earthquake. North of the Median Tectonic Line, the co-seismic plus postseismic stress changes of the Nobi earthquake promoted the failure of faults which subsequently ruptured in the decades following 1891. In contrast, along the Philippine Sea interplate boundary, the co-seismic plus postseismic strain release of the Nobi earthquake during the decades following 1891 has delayed the anticipated Tokai earthquake by at least 20 yr.

A sequence of destructive earthquakes and the coupling of fault systems in central Japan

In the western part of central Japan, large successive inland earthquakes have occurred causing serious damage. The 1891 M=8.0 Nobi earthquake was followed by the 1909 M=6.8 Anegawa, the 1945 M=6.8 Mikawa, and the 1948 M=7.1 Fukui earthquakes. The two major fault systems, termed the Tsurugawan-Isewan tectonic line (TITL) and the Fukui-Neodani block boundary line (FNBB) have been identified as lines linking NW-SE-oriented active faults in the study area. An examination of the vertical displacement of ground surfaces indicates that tilting of the central part of the FNBB caused by the Nobi earthquake begins around the Sekigahara fault, on the central part of the TITL. Ruptures and vertical displacements can also be found along the Ogaki-Kisozaki fault close to the TITL. Therefore, it was concluded that the influence of the Nobi earthquake extended to a part of the TITL. Eighteen years after the Nobi earthquake, the Anegawa earthquake occurred along the Sekigahara fault. These features and the earthquake sequence can be explained by a block rotation model with strike-slip faulting. The Nobi earthquake created en echelon ruptures over an 80-km-long line with a left-lateral slip of up to 8 m along the Neodani fault. According to the model, this left-lateral slip must be accompanied by a clockwise rotation of the block between the FNBB and TITL. The block rotation should, in turn, induce a left-lateral slip on the TITL. Since the TITL exhibits a sharp bend along the Sekigahara fault, a transtensional region should appear along the fault owing to the left-lateral slip of the TITL. The expected transtensional region is consistent with areas damaged by the Anegawa earthquake, suggesting that the earthquake occurred in the transtensional regime. About 40 years after the Anegawa earthquake, the Mikawa and Fukui earthquakes were generated on the southern and northern ends of the FNBB, respectively. This implies that the fault movement of the Nobi and Anegawa earthquakes created a concentration of stress at both ends of the FNBB, resulting in the Mikawa and Fukui earthquakes. Approximately two years prior to the Nobi earthquake, seismic activity was initiated over a wide zone along the FNBB. Also, notable earthquakes aligned along the TITL were observed ten years prior to the Anegawa earthquake. The onset of seismicity along a fault system can be used in predicting destructive inland earthquakes which eventually occur along the fault.

Fault Model of the 1891 Nobi Earthquake from Historic Triangulation and Leveling.

The faulting associated with the 1891 Nobi earthquake, central Honshu, is re-examined on the basis of horizontal displacement vectors determined between the periods 1882/1899-1950/1961. These vectors are modelled in terms of two components: (1) strain accumulation and release along the Nankai Trough and Suruga Trough, and (2) postseismic relaxation following the 1891 earthquake. We assume a rheological model of the central Honshu crust and upper mantle consisting of a 33-km thick elastic lithosphere overlying a 130 km thick viscoelastic sublithosphere. The modelling demonstrates that the observed displacement vectors are dominated by post-seismic displacements following the Nobi earthquake. The Nukumi-Neodani faults are inferred to have accommodated 7-8 m of left lateral strike-slip displacement, in good agreement with those estimates based on the observed surface rupture. In addition, we identify two northeast-southwest trending blind thrust faults, together comprising a 70-km-long region of compressional deformation, each of which accommodated several meters of reverse slip during the Nobi earthquake. These thrust faults consist of a 20-km-long western segment and a 50-km-long eastern segment. The western thrust begins near the southern termination of the strike-slip faulting component, has shallow (31°) dip, is buried by 15 km and has a prominent coseismic signal in the leveling data. Examination of the topography east of Nagoya suggests that the eastern thrust is buried 5-10 km below the surface and represents the subterranean continuation of the exposed thrust fault on the eastern flank of the Kiso Range to the northeast. The model of strain accumulation and release includes the various effects of the 1854 Ansei and 1944 Tonankai earthquakes, as well as the effect of steady state Philippine Sea interplate convergence. A model consisting of only tectonic strain accumulation and release along the Philippine Sea interplate boundary provides a poor fit to the data. The modelling suggests that the 1944 rupture did not extend beyond the Atsumi Peninsula. The ob-served displacement vectors and an independent set of Suruga Bay uplift data contain a moderate signal due to 1854 postseismic displacements. Considering that this signal has tradeoffs with the slip accumulation rate in Suruga Bay, this enables us to constrain the central Honshu sublithospheric viscosity to lie near 2×1019 Pa·s.

濃尾活断層系から発生した古地震の考察 梅原断層のトレンチ調査

The Nobi Active Fault System, one of the most active fault systems in Japan, is composed of a series of active faults extending 80 km in the NW-SE direction with en echelon arrange-ment. These faults display predominantly left-lateral displacement. In 1891, major strands within the system were ruptured during the great (M=a8.0) seismic event (the Nobi earthquake) of 1891. The magnitude of this event was extraordinarily large for normal intraplate earth-quakes.In order to clarify the long-term behavior of the fault system, the activity of each segment or strand has been examined by geological and geomorphological methods. A section of the Late Pleistocene-Holocene sediments broken by one of the segmented faults (Umehara Fault) was studied to establish the timing of faulting mainly by trench excavation The results are summarized as follows:(1) An accumulated displacement ensures that the Neodani Fault lying at the middle of whole length of the Nobi Fault System is the most active and longest strand. The Neodani Fault has ruptured at least, once every few thousand years with higher frequency than other strands.(2) The entrenchment across the Umehara Fault provided recognition of the horizons on which paleo-seismic events had taken place on the fault zone. The six events were inferred within trench logs. The ages are 1891 A. D.(Event 1), 20, 000 y. B. P.(Event 2), 28, 000 y. B. P.(Event 3) and prior to 30. 000 y. B. P.(Event 4-6). The ages of Events 2, 3 and 6 are not conclusive.(3) The recurrence intervals of the Umehara Fault between the last three events are over 10, 000 years, which are ten times longer than that of the Neodani Fault.(4) Thus, other strands in this fault system are inferred to have been dormant even when the Neodani Fault ruptured. It is likely that very large earthquake seldom occurred in association with faulting not only along the Neodani Fault but also along the other less active strand such as the Umehara Fault.(5) The 1891 Nobi earthquake was an extraordinarily large one. However, the record of the great Nobi earthquake should be used in evaluating future seismic hazards. especially in areas where long active faults are densely distributed.

The Midori Fault Scarp from the Nobi Earthquake of 1891, Central Japan and its Excavated Trench

The Midori Fault Scarp from the Nobi Earthquake of 1891, Central Japan and its Excavated Trench

根尾谷断層水鳥断層崖のトレンチ壁面の地質

An exploratory trench was excavated across the Midori fault scarp associated with the Nobiearthquake (M 8.0) of 1891, which was the largest earthquake recorded on inland Japan. The trench has been preserved for exhibition by covering it with a building and grouting it to prevent leaking of ground water. This preservation and exhibition of an exploratory trench across a seismic fault is the first attempted in the world.The Midori Fault exposed on the trench walls has a strike of N 35°W and is almost vertical. The upthrown side of the fault consists of Mesozoic sedimentary rocks and alluvial gravel. The downthrown side consists, in ascending order, of wide fault gouge derived from Mesozoic rocks, alluvial gravel, paleo-soil, gravel due to collapse from the upthrown side and artificial fill. Clasts within alluvial gravel along the fault are rotated by the fault movement. The pre-1891 sediments have been displaced vertically by 5.5 to 6 meters and left-laterally by about 3 meters, indicating the Nobi earthquake of 1891 was the only seismic event on this fault over at least 1, 000 years that caused displacement.

断層の幾何学的バリヤと破壊プロセス

Geometric patterns of surface earthquake faults are closely related to rupture propagation processes especially in the case of strike-slip faults. In this paper, the author examined geometric features of four strike-slip earthquake faults in Japan, that is, the Kita-Izu earthquake fault system of 1930, Izu-Oshima Kinkai earthquake fault system of 1978, the Nobi earthquake fault system of 1891 and the Kita-Tango earthquake fault system of 1927. Bends or jogs along a fault can be called as geometric barriers, which are classified into two categories as extensional and compressional, from a view point of volumetric change (Fig. 1). Studies of earthquake surface faults of recent inland large earthquakes in Japan show that ruptures were initiated from compressional barriers and terminated at extensional barriers. A compressional barrier in the course of rupture propagation could be the position of next rupture nucleation. Compressional barriers can be commonly described as “fragmentation barriers” (King, 1987) because short faults of various orientation are very popular in and around compressional barriers. The location of severe damage area is also closely related to that of barrier.Study of geometric characteristics of active faults will become very important because they give us a key idea on rupture initiation and termination as in the case of surface earthquake faults. Recognition of barriers along an active fault system from geometrical investigation will provide us some locations of detailed observation for geodetical, geophysical and geochemical anomalies along precautious faults.