Japan Island Arc Research Articles

A network-based comparative study of extreme tropical and frontal storm rainfall over Japan

Frequent and intense rainfall events demand innovative techniques to better predict the extreme rainfall dynamics. This task requires essentially the assessment of the basic types of atmospheric processes that trigger extreme rainfall, and then to examine the differences between those processes, which may help to identify key patterns to improve predictive algorithms. We employ tools from network theory to compare the spatial features of extreme rainfall over the Japanese archipelago and surrounding areas caused by two atmospheric processes: the Baiu front, which occurs mainly in June and July (JJ), and the tropical storms from August to November (ASON). We infer from complex networks of satellite-derived rainfall data, which are based on the nonlinear correlation measure of event synchronization. We compare the spatial scales involved in both systems and identify different regions which receive rainfall due to the large spatial scale of the Baiu and tropical storm systems. We observed that the spatial scales involved in the Baiu driven rainfall extremes, including the synoptic processes behind the frontal development, are larger than tropical storms, which even have long tracks during extratropical transitions. We further delineate regions of coherent rainfall during the two seasons based on network communities, identifying the horizontal (east–west) rainfall bands during JJ over the Japanese archipelago, while during ASON these bands align with the island arc of Japan.

Seismic status in Bangladesh

Seismic status in Bangladesh

Persistent inelastic deformation in central Japan revealed by GPS observation before and after the Tohoku-oki earthquake

We analyze strain rate distribution in central-northeastern Japan based on continuous GPS data before and after the occurrence of the Great Tohoku earthquake (Mw 9.0) on March 11th, 2011, focusing on the far-field response in the Niigata Kobe Tectonic Zone (NKTZ), an E-W contraction region along the Japan seacoast of central Japan. Wavelength decomposition of the strain rate on the E-W direction, calculated from GPS data, indicates that the long-wavelength pattern changed from preseismic E-W contraction to postseismic E-W extension, representing elastic response to plate interaction at the Japan Trench. However, the short wavelength patterns reveal a persistent localized contraction zone around northern NKTZ before and after the Tohoku-oki earthquake. The persistent localized deformation pattern can be reproduced by an aseismic slip on a fault cutting the lower crust and a part of the upper crust. These results demonstrate that an inelastic process plays an essential role in the deformation of the Japan island arc.

Heterogeneous stress state of island arc crust in northeastern Japan affected by hot mantle fingers

AbstractBy considering a thermal structure based on dense geothermal observations, we model the stress state of the crust beneath the northeastern Japan island arc under a compressional tectonic regime using a finite element method with viscoelasticity and elastoplasticity. We consider a three‐layer structure (upper crust, lower crust, and uppermost mantle) to define flow properties. Numerical results show that the brittle‐viscous transition becomes shallower beneath the Ou Backbone Range compared with areas near the margins of the Pacific Ocean and the Japan Sea. Moreover, several elongate regions with a shallow brittle‐viscous transition are oriented transverse to the arc, and these regions correspond to hot fingers (i.e., high‐temperature regions in the mantle wedge). The stress level is low in these regions due to viscous deformation. Areas of seismicity roughly correspond to zones of stress accumulation where many intraplate earthquakes occur. Our model produces regions with high uplift rates that largely coincide with regions of high elevation (e.g., the Ou Backbone Range). The stress state, fault development, and uplift around the Ou Backbone Range can all be explained by our model. The results also suggest the existence of low‐viscosity regions corresponding to hot fingers in the island arc crust. These low‐viscosity regions have possibly affected viscous relaxation processes following the 2011 Tohoku‐oki earthquake.

Evolution of crustal deformation in Japan Island arc in Quaternary – physical evaluation of fault activity –

Evolution of crustal deformation in Japan Island arc in Quaternary – physical evaluation of fault activity –

Magma plumbing system of the Aso-3 large pyroclastic eruption cycle at Aso volcano, Southwest Japan: Petrological constraint on the formation of a compositionally stratified magma chamber

Aso volcano has the largest caldera (18×25km in diameter) in the southwestern Japan Island Arc, and it formed as the result of four large (VEI=6–7) pyroclastic-eruption cycles. We study the penultimate large eruption cycle, the Aso-3 cycle, which occurred 123ka with an ejecta volume of more than 150km3. The processes in the pre-eruptive magma chamber and the magma genesis of the Aso-3 cycle were inferred from geological data, phenocryst chemistry, and whole-rock chemical and Sr-, Nd-, and Pb isotopic analyses of juvenile clasts. The geological and petrological data indicate that the pre-eruptive magma chamber was stratified compositionally into three layers: from top to bottom, silicic, intermediate, and mafic magma layers. The three magma layers had a uniform isotope composition, suggesting that all the magmas were generated from a single source. The silicic and intermediate magmas were not generated from the mafic magma by fractional crystallization. The silicic magma has higher Ni content (compatible element) than the mafic magma. This suggests that these magmas were produced by partial melting of the same mafic crust but with differing amounts of partial melting: the silicic magma was produced by a low degree of partial melting of the source rock without fractional crystallization, and the mafic magma was produced by a large degree of partial melting followed by fractional crystallization. The intermediate magma compositions plot on the tie line between the silicic magma and the melt of the mafic magma in variation diagrams, and the intermediate magma has phenocrysts whose compositions are identical with those in the silicic magma. This observation indicates that, before the Aso-3 eruption cycle, a two-layer stratified magma chamber of the silicic and mafic magmas was formed as a result of melting of the mafic crust, which was followed by formation of the intermediate layer as a result of interfacial mixing between the silicic magma and the melt of mafic magma. During the eruption the three-layer stratified magma chamber was tapped from the top to the bottom.

Aftereffects of Subduction-Zone Earthquakes: Potential Tsunami Hazards along the Japan Sea Coast.

The 2011 Tohoku-Oki Earthquake is a typical subduction-zone earthquake and is the 4th largest earthquake after the beginning of instrumental observation of earthquakes in the 19th century. In fact, the 2011 Tohoku-Oki Earthquake displaced the northeast Japan island arc horizontally and vertically. The displacement largely changed the tectonic situation of the arc from compressive to tensile. The 9th century in Japan was a period of natural hazards caused by frequent large-scale earthquakes. The aseismic tsunamis that inflicted damage on the Japan Sea coast in the 11th century were related to the occurrence of massive earthquakes that represented the final stage of a period of high seismic activity. Anti-compressive tectonics triggered by the subduction-zone earthquakes induced gravitational instability, which resulted in the generation of tsunamis caused by slope failing at the arc-back-arc boundary. The crustal displacement after the 2011 earthquake infers an increased risk of unexpected local tsunami flooding in the Japan Sea coastal areas.

Seismic constraints of the formation process on the back‐arc basin in the southeastern Japan Sea

AbstractTo clarify the formation process of the back‐arc basin in the Japan Sea, which is located next to the northwestern Pacific, a seismic survey using ocean bottom seismographs and an air gun array was undertaken in areas from the northern Yamato Basin to the coast of the northeastern Japan Island Arc off Awa‐shima Island. The crust beneath the northern Yamato Basin off Awa‐shima Island is approximately 16 km thick. The upper and lower crusts are, respectively, about 5 km thick with a steep velocity gradient and about 10 km thick with a gentle velocity gradient. In the basin, there are very few units with P wave velocity of 5.4–6.0 km/s, corresponding to the continental upper crust. The crustal structure of the northern Yamato Basin has characteristics of thicker oceanic crust. The high‐velocity lowermost crust in the northern Yamato Basin with 7.2–7.4 km/s might show melt formed by a slightly high mantle temperature during the opening of the basin. However, the crust beneath the areas from the Sado Ridge to the coast, which is approximately 25–26 km thick, is slightly thinner than that of the continental crust and island arc crust. The crustal structure beneath this area is inferred to be a rifted continental and/or a rifted island arc crust.

Japan's Earthquake Early Warning System on 11 March 2011: Performance, Shortcomings, and Changes

A well-developed public earthquake early warning (EEW) system has been operating in Japan since October 2007. At the time of the 2011 Tohoku-oki earthquake and tsunami (also known as 3.11), several million people near the epicenter received the EEW about 15 to 20 seconds before the most severe shaking occurred, and many more people in surrounding districts had greater lead time before less severe shaking started. Some 90% of these people were able to take advance actions to save their own lives and those of family members or to take other actions according to prior planning. Some actions were taken based on intuitive responses to the alerts. This high rate of effectiveness is assured to be the result of education regarding the EEW system, both in schools and in society at large. In spite of some shortcomings, the proven effectiveness of EEW has led Japan to strengthen the already extensive seismic- and tsunami-monitoring networks offshore, east of the Japan island arc at 150 sites, and to provide a special terminal for advanced uses of EEW in schools with more than 53,000 students. Efforts are also underway to improve analysis and dissemination schemes.

Construction of Subsurface Geological Structures Using a Drilling Database: A Case Study for an Intra-Arc Basin, the Osaka Plain, Southwest Japan

Subsurface geological cross sections of 0 - 200 m depth were constructed using a dense drilling database of the Osaka Plain in the intra-arc Osaka Basin of the Japan island arc, an active plate margin. The cross sections revealed the subsurface geological structures and the geometry of folding and faulting in the basin. The comparison between the constructed subsurface cross sections and the seismic sections of the basement and basin fills at a depth of 1500 - 2000 m showed that the basement and shallow subsurface structures are similar; however, the shallow cross sections were of higher resolution than the deep seismic profiles.

Deformation caused by the 2011 eastern Japan great earthquake monitored using the GPS single-epoch precise point positioning technique

Crustal deformation can provide constraints for studying earthquake rupture and shock wave transmission for the Mw9.0 eastern Japan great earthquake. Using the single-epoch precise point positioning (PPP) method and the appropriate positioning flow, we process GPS data from six IGS (International GNSS Service) sites (e.g., MIZU, TSK2, USUD, MTKA, AIRA and KSMV) located in Japan and obtain the positioning results with centimeter scale precision. The displacement time series of the six sites are analyzed using the least squares spectral analysis method to estimate deformations caused by the Mw9.0 mainshock and the Mw7.9 aftershock, and the cumulative displacements after 1 day. Mainshock displacements at station MIZU, the nearest site to the mainshock in the North (N), East (E), and Up (U) directions, are −1.202 m, 2.180 m and −0.104 m, respectively, and the cumulative deformations after 1 day are −1.117 m, 2.071 m and −0.072 m, respectively. The displacements at station KSMV, the nearest site to the Mw7.9 aftershock in the N, E and U directions, are −0.032 m, 0.742 m and −0.345 m, respectively. The other sites obviously experienced eastern movements and subsidence. The deformation vectors indicate that the horizontal displacements caused by the earthquake point to the epicenter and rupture. Elastic bounds evidently took place at all sites. The results indicate that the crustal movements and earthquake were part of a megathrust caused by the Pacific Plate sinking under the North American Plate to the northeast of Japan island arc.

He–Ar and Nd–Sr isotopic compositions of late Pleistocene felsic plutonic back arc basin rocks from Ulleungdo volcanic island, South Korea: Implications for the genesis of young plutonic rocks in a back arc basin

We report analyses of noble gases and Nd–Sr isotopes in mineral separates and whole rocks of late Pleistocene (< 0.2 Ma) monzonites from Ulleungdo, South Korea, a volcanic island within the back arc basin of the Japan island arc. A Rb–Sr mineral isochron age for the monzonites is 0.12 ± 0.01 Ma. K–Ar biotite ages from the same samples gave relatively concordant ages of 0.19 ± 0.01and 0.22 ± 0.01 Ma. 40Ar/ 39Ar yields a similar age of 0.29 ± 0.09 Ma. Geochemical characteristics of the felsic plutonic rocks, which are silica oversaturated alkali felsic rocks (av., 12.5 wt% in K 2O + Na 2O), are similar to those of 30 alkali volcanics from Ulleungdo in terms of concentrations of major, trace and REE elements. The initial Nd–Sr isotopic ratios of the monzonites ( 87Sr/ 86Sr = 0.70454–0.71264, 143Nd/ 144Nd = 0.512528–0.512577) are comparable with those of the alkali volcanics ( 87Sr/ 86Sr = 0.70466–0.70892, 143Nd/ 144Nd = 0.512521–0.512615) erupted in Stage 3 of Ulleungdo volcanism (0.24–0.47 Ma). The high initial 87Sr/ 86Sr values of the monzonites imply that seawater and crustally contaminated pre-existing trachytes may have been melted or assimilated during differentiation of the alkali basaltic magma. A mantle helium component ( 3He/ 4He ratio of up to 6.5 RA) associated with excess argon was found in the monzonites. Feldspar and biotite have preferentially lost helium during slow cooling at depth and/or during their transportation to the surface in a hot host magma. The source magma noble gas isotopic features are well preserved in fluid inclusions in hornblende, and indicate that the magma may be directly derived from subcontinental lithospheric mantle metasomatized by an ancient subduction process, or may have formed as a mixture of MORB-like mantle and crustal components. The radiometric ages, geochemical and Nd–Sr isotopic signatures of the Ulleungdo monzonites as well as the presence of mantle-derived helium and argon, suggests that these felsic plutonic rocks evolved from alkali basaltic magma that formed by partial melting of subcontinental lithospheric mantle beneath the back arc basin located along the active continental margin of the southeastern part of the Eurasian plate.

Repeated large-scale eruptions from a single compositionally stratified magma chamber: An example from Aso volcano, Southwest Japan

Aso volcano has the largest caldera (18 × 25 km) in the southwestern Japan Island Arc, which was formed as a result of four gigantic pyroclastic-eruption cycles. The latest eruption cycle (Aso-4 cycle, 90 ka) produced the most voluminous deposits (> 600 km 3) among the four eruption cycles. We investigated pre-eruptive magma chamber configurations and processes in compositionally stratified Aso-4 pyroclastic eruptions based on whole-rock chemical, phenocryst mineralogical, and Sr isotope analyses of juvenile clasts. Previous stratigraphical studies have suggested that the Aso-4 cycle is divided into two subcycles, in both of which eruption of voluminous silicic is followed by eruption of mafic magma. Geochemical and mineralogical results indicate that the pre-eruptive magma chamber was composed of three layers: silicic, hybrid, and mafic magma layers from the top to the bottom. The silicic magma layer was relatively homogenous, whereas the mafic magma layer was compositionally zoned where magma became more silicic with height. The hybrid magma was generated by mixing the silicic magma and the silicic end of the zoned mafic magma layer (i.e. the uppermost part of the mafic magma layer). The first subcycle began with evacuation of the upper silicic magma and successively proceeded to tap the lower hybrid and mafic magmas. The eruption of the first subcycle stopped before the whole magma chamber evacuated. During this subcycle, the hybrid magma and the upper part of the mafic magmas layer were selectively withdrawn and mixed with the overlying silicic magma. The second subcycle eruption started with the new hybrid magma, and followed by eruption of the mafic magma.

Last stage of the Japan Sea back‐arc opening deduced from the seismic velocity structure using wide‐angle data

The Japan Sea is one of the most well studied back‐arc basins in the northwestern Pacific. The seismic crustal model, however, has been inadequate to elucidate the detailed opening model of the Japan Sea. In 2002, to clarify the late stage of the formation style of the Japan Sea opening, a seismic experiment using 35 ocean bottom seismographs (OBSs), an air gun array, and a multichannel hydrophone streamer was undertaken in the areas from the southwestern Yamato Basin, the Oki Ridge, and the southwestern Oki Trough to the coast of the southwestern Japan Island Arc. The crusts beneath the southwestern Yamato Basin and the Oki Ridge are estimated as having approximately 13 km and 19.5 km, respectively. The upper and lower crusts of the southwestern Yamato Basin are approximately 3.2 km and 8 km thick, respectively. Those of the Oki Ridge are approximately 8.2 km and 10.5 km thick, respectively. The upper crust of the Oki Ridge thickens more steeply than that of the southwestern Yamato Basin; however, the lower crust thickens more gently. The crustal structure of the southwestern Yamato Basin shows the extended continental crust accompanied with the opening of the Japan Sea. A remarkable structural characteristic, the upper crust being thinner than the lower crust, caused by listric or complicated normal faults developed in the upper crust of the southwestern Yamato Basin. This deformed upper crust is a common structural characteristic in the southern Japan Sea, which includes the Yamato Basin. The southern Yamato Basin, including the southwestern Yamato Basin, has the thinnest upper and lower crusts in the Japan Sea. For that reason, it is suggested that the southern Yamato Basin had the strongest deformation by a back‐arc opening and that the period of the opening in the southern Yamato Basin had been longest in the southern Japan Sea. The formation process of the southern Yamato Basin is inferred to have two stages: rifting and extension of continental crust separating the northeastern and southwestern Japan Island Arcs from the Asian continent and, further, the extension affected by the rotation of the southwestern Japan Island Arc.

Waveform characteristics of deep low-frequency earthquakes: time-series evolution based on the theory of the KM2O-Langevin equation

SUMMARY Since the 1970s, deep low-frequency earthquakes (DLF) with depths ranging 20–40 km have been observed just beneath the Japan Island Arc. Almost all of these earthquakes are recognized up to now have had magnitudes less than 2.5, so that we have little information concerning DLF. Employing the theory of KM2O-Langevin equations, we develop a new method to represent the characteristics of the coda parts of DLF, and propose a new concept of ‘average dissipation spectrum’. The new averaging algorithm for the KM2O-Langevin matrix function was applied in the analysis of DLF (M: 1.0), which occurred in Akita prefecture on 2001 July 11, and we succeeded in separating the characteristics of the source vibration system and the source excitation process into the averaged dissipation term and the fluctuation term, respectively. The gaps between the arrival times of the fluctuation term's peaks at three stations near the epicentre are slightly different than the gaps between the S-wave arrival times. Assuming a homogenous crust structure with an S-wave velocity of 4.3 km s−1 and assuming the depth of the second source to be the same as that of the hypocentre, the second source lies about 1.5 km, N 56°E of the hypocentre. We estimate the common characteristics of this DLF successfully by using the ‘average dissipation spectrum’, which is made up of typical frequencies, θk, attenuation factors, Qk and amplitude factors, Ak. The common elements of (θk∼ 1.5, Qk∼−0.3) and (θk∼ 3.25, Qk∼−0.45) among all stations indicate the characteristics of the source dynamics of the Akita DLF. The major parts of the coda waves of DLF satisfy the stationary property, and the causality values for the linear and odd-degree non-linear transformations are relatively higher than those for the even-degree non-linear transformations. These characteristics are quite different from the characteristics of tectonic earthquakes. This quantitative property is common among all DLF.

P-wave velocity structure of the margin of the southeastern Tsushima Basin in the Japan Sea using ocean bottom seismometers and airguns

The Tsushima Basin is located in the southwestern Japan Sea, which is a back-arc basin in the northwestern Pacific. Although some geophysical surveys had been conducted to investigate the formation process of the Tsushima Basin, it remains unclear. In 2000, to clarify the formation process of the Tsushima Basin, the seismic velocity structure survey with ocean bottom seismometers and airguns was carried out at the southeastern Tsushima Basin and its margin, which are presumed to be the transition zone of the crustal structure of the southwestern Japan Island Arc. The crustal thickness under the southeastern Tsushima Basin is about 17 km including a 5 km thick sedimentary layer, and 20 km including a 1.5 km thick sedimentary layer under its margin. The whole crustal thickness and thickness of the upper part of the crust increase towards the southwestern Japan Island Arc. On the other hand, thickness of the lower part of the crust seems more uniform than that of the upper part. The crust in the southeastern Tsushima Basin has about 6 km/s layer with the large velocity gradient. Shallow structures of the continental bank show that the accumulation of the sediments started from lower Miocene in the southeastern Tsushima Basin. The crustal structure in southeastern Tsushima Basin is not the oceanic crust, which is formed ocean floor spreading or affected by mantle plume, but the rifted/extended island arc crust because magnitudes of the whole crustal and the upper part of the crustal thickening are larger than that of the lower part of the crustal thickening towards the southwestern Japan Island Arc. In the margin of the southeastern Tsushima Basin, high velocity material does not exist in the lowermost crust. For that reason, the margin is inferred to be a non-volcanic rifted margin. The asymmetric structure in the both margins of the southeastern and Korean Peninsula of the Tsushima Basin indicates that the formation process of the Tsushima Basin may be simple shear style rather than pure shear style.

Research on Crust Structure and Lithosphere Property Beneath the Okinawa Through Area

AbstractA mass of geological, geophysical and geochemical data and information from the Okinawa Trough area are collected for comprehensive research in the study area from East China through Okinawa Trough to the Ryukyu Island Arc region. According to the seismic tomography results (P and S wave) and the processing results of free‐air and Bouguer gravity and magnetic data in the study area, the comprehensive interpretation is carried out. The Moho depth distribution of the study area is obtained by the inversion calculation based on gravity data using the Harmonious Series method. The crust properties are analyzed. Meantime, some Cenozoic basalt data from Kuandian (Northeast China), Hannuoba (North China), Minxi (South China), Penghu Islands (Taiwan Strait), Okinawa Trough and Japan Island Arc regions are chosen to make the comparison research on element‐isotopes. The result indicateic that the lithospheric thickness in the Okinawa Trough area has obviously decreased, where a low ‐velocity layer of the upper‐mantle has reached the Moho interface and the metasometized asthenosphere has formed. The research result on element‐isotopes shows that the characteristic of the crust below the Okinawa Trough area is different from that beneath East China area and the Ryukyu Island Arc area. It is considered that the crust under the Okinawa Trough area belongs to the transition type, which has features quite similar to the those of the oceanic crust.

Transtensional deformation at the junction between the Okinawa trough back-arc basin and the SW Japan island arc

Abstract The Okinawa trough is a back-arc basin currently forming above the subducting Philippine Sea plate by crustal stretching of the Eurasia lithosphere. Existing geophysical investigations have revealed that the northern part of the Okinawa trough consists of a series of en echelon left-stepping grabens or half-grabens, some of which were formed in Miocene times and are presently inactive. In the Kyushu island, three major zones of extensional deformation are recognized. They are characterized by 20–40 km long sediment-filled basins lying on the hanging-wall side of N60°- to N80°-trending, north- or NW-dipping normal faults. These basins display an en echelon left-stepping arrangement. The ages of faulted rocks, the ages of graben-filling sediments and radiometric ages newly obtained on pseudotachylites associated with normal faulting indicate that extension started at 13 Ma at the southern end of Kyushu and migrated northwards in the middle part of Kyushu (Beppu Bay), where it is still active today. The continentward-dipping, listric geometry inferred in depth for the fault systems is consistent with that of faults imaged by existing seismic profiles obtained off-shore in the Okinawa trough and across the Beppu Bay. The spatial association between Miocene or younger normal faults and pre-Miocene regional low-angle thrust faults suggests the possibility of a reactivation of some of the thrust faults as low-angle detachment faults merging in depth into a mid-crustal partial attachment zone.

Temporal variation of seismic b‐values beneath northeastern Japan island arc

Analysis of a high quality seismic catalog reveals that the average of seismic b‐values in the crust beneath most part of northeastern Japan island arc decreased from 0.86 between 1984 and 1990, to 0.73 between 1991 and 1995. The two areas with the largest decrease are found to be in the same areas where the coupling between the North American and the Pacific plates is the highest, as suggested by a recent geodetic study. In the same time period, the annual seismic moment release increased by 10 times. In addition, there seems to be a corresponding increase in volcanic activities in the same area. One of the most likely interpretations for the observations is an increase in the subduction rate starting from 1991. The timing of this possible increase in subduction rate is consistent with an apparent increase in global seismic activity.

東北日本における火山噴火および内陸地震（Ｍ≧６．２）と三陸沖の巨大地震（Ｍ８クラス）との時間的関連性について

Great earthquakes, inland shallow earthquakes and volcanic eruptions occurred historically in and around the northern Honshu region, the northeastern part of the Japan island arc system. We studied statistically the time-space correlation among great offshore earthquakes with magnitudes (M) larger than 7.8 near the Japan trench, inland shallow earthquakes with M 6.2 and the volcanic eruptions, for the period from 1851 to 1996. We focus on the northern Honshu region in this study. During the period, there were four offshore great earthquakes near the Japan trench. Their magnitudes are M7.9 (1856), M8.2 (1896), M8.1 (1933), and M7.9 (1968). To estimate the temporal correlation among these events, we applied a statistical analysis that is one of the currently used methods in earthquake prediction research works. Our analysis suggests that alarm-like information could be issued for the inland volcanoes and the large inland earthquakes in the northern Honshu, at the occurrence time of the four great earthquakes near the Japan trench. We then found some simultaneous occurrence pattern between the large inland earthquakes and the volcanic eruptions, just prior to the four great earthquakes or just afterwards. As a result, the temporal correlation among the volcanic eruptions, the large inland shallow earthquakes and the four great earthquakes is not statistically negligible. This result suggests that the space-time relationship among the volcanic eruptions, the large inland shallow earthquakes and the great earthquakes near the trench is not only useful for researches on long-term earthquake prediction and volcanic eruption, but also important for understanding seismotectonics in the northern Honshu region.