Backbone Range Research Articles

Distribution and characteristics of landslides induced by the Iwate–Miyagi Nairiku Earthquake in 2008 in Tohoku District, Northeast Japan

The Iwate–Miyagi Nairiku Earthquake in 2008, whose seismic intensity was M. 7.2 in Japan Meteorological Agency (JMA) scale, induced innumerable landslides on the southern flank of Mt. Kurikoma volcano allocated along the Ou Backbone Range in Northeast Japan. Most landslides are detected in a hanging wall side of the seismic fault. Those landslides are classified into five types: deep-seated slide, debris slide, shallow debris slide, secondary shallow debris slide, and debris flow. Most common landslide types induced by the earthquake are shallow debris slides and subsequent debris flows. They are intensively distributed along steep gorges incising a volcanic skirt of Mt. Kurikoma, consisting of welded ignimbrite of the Pleistocene age. Debris flows are also distributed even along gentle river floors in the southern lower flank of the volcano. The area of densely distributed debris slides, shallow debris slides, and debris flows is concordant with that of severe seismic tremor. Thus, genetic processes of landslides induced by the Iwate–Miyagi Nairiku Earthquake in 2008 are attributed to multiple causative factors such as geology, topography, and seismic force.

Detrital zircon evidence for the antiquity of Taiwan

In-situ U-Pb geochronology and Hf isotopic studies of zircons from the Pre-Tertiary basement complex and Eocene rocks of the Central Range of Taiwan were carried out to elucidate the history of detrital zircons older than 2.3 Ga. Zircons from the eastern Backbone Range and Eastern Central Range show Paleoproterozoic to late Neoarchean ages (2.3−≥2.5 Ga), whereas those from the Hsuehshan Range yield Neoarchean to Mesoarchean ages (2.6–3.2Ga). The ɛHf(T) for the Paleoproterozoic to late Neoarchean zircons varies from −7.4 to +5.1, implying both juvenile crustal growth and reworking of old crusts. This dual origin could extend back to Mesoarchean-Paleoarchean (3.0–3.4 Ga) based on Hf isotopic model ages. Consistent but narrower ɛHf(T) values and Hf crustal model ages for zircons from Taiwan compared to Cathaysia suggest a possible common origin for these zircons, although Taiwan has a generally younger crustal evolution history than SE China.

Distribution of strain rates in the Taiwan orogenic wedge

To constrain the way Eurasian crust is accreted to the Taiwan orogenic wedge we investigate the present-day 3D seismogenic deformation field using the summation of 1129 seismic moment tensors of events ( M w > 4) covering a period of 11 years (1995 to 2005). Based on the analysis of the principal strain-rate field, including dilatation and maximum shear rates, we distinguish four domains. Domain I comprises the Coastal Plain and the Western Foothills. It is mainly contractional in both the horizontal plane and in cross-section. Domain II comprises the eastern Western Foothills, the Hsuehshan Range and the Backbone Range. It is characterized by the highest contraction rates of 10 − 6 yr − 1 in association with area expansion in cross-section and area contraction in the horizontal plane. Domain III corresponds to the Central Range. It is characterized by area contraction in cross-section and area expansion in the horizontal plane. The maximum contractional axis is typically low and plunges ~ 30°E. Extension is larger, horizontal and strikes parallel to the axis of the mountain range. Domain IV corresponding to the Coastal Range and offshore Luzon Arc shows deformation patterns similar to domain II. This seismogenic strain-rate field, which is found in good agreement with the main features of the geodetic field, supports shortening within a thick wedge whose basal décollement is relatively flat and located in the middle-to-lower crust > 20 km. The east plunges of maximum strain-rate axes below the Central Range argue for the development of top-to-the-east transport of rocks resulting from the extrusion of the whole crust along west-dipping crustal-scale shear zones. The study of seismogenic strain rates argues that the initiation of subduction reversal has already started in the Taiwan collision domain.

Distribution of crustal fluids in Northeast Japan as inferred from resistivity surveys

We carried out magnetotelluric (MT) surveys in central northeastern Japan. Two-dimensional resistivity profiles along three survey lines show similar features each other. By comparing the resistivity distribution to the distribution of seismic velocities, we inferred the distribution and flow of crustal fluids. Three fluid flow paths were detected based on the distribution of regions of low resistivity. The first path ascends from the top of the upper mantle, passes through the lower crust, and reaches the surface, forming a fluid chamber within the lower or middle crust. This path is related to the volcanic activity in the backbone range. The second path rises from the first fluid chamber and has produced small fluid reservoirs on both sides of the backbone range. These small reservoirs are considered to be related to the seismicity of the region. The third path is located to the east of the volcanic front and represents another fluid flow path from the uppermost mantle to the lower crust that may have formed a small fluid reservoir to the east of the volcanic front.

Chronological data for the Middle Miocene to Pliocene sequence around the southwestern Sendai Plain, with special reference to the uplift history of the Ou Backbone Range

Middle Miocene to Pliocene chronostratigraphic data were obtained from three sections on the southwestern margin of the Sendai Plain, northeast Japan. In this tectonically active area, we newly infer the numerical age of the coastal sedimentary sequence on the basis of 27 fission track ages in combination with planktonic foraminiferal and diatom analyses. The Hatatate Formation cropping out along the Natori-gawa Section approximately ranges from 13 Ma to 11.5 Ma in age. The Tsunaki Formation ranges from 10 Ma to 8.3 Ma, and the basal part of the Nashino Formation is assigned to 6.4 Ma. Four major unconformities were recognized in the Middle Miocene to Pliocene sequence in the study area from a compilation of chronological data: ca. 9 Ma, 6.4Ma, latest Miocene, and 3.5Ma, respectively. The oldest unconformity was newly identified in this study. Formative timings of these unconformities correlate well with the uplift history of the Ou Backbone range reconstructed by Nakajima et al. (2006). These data provide a restriction to reconstruct the uplift history of the Northeast Honshu Arc.

Simultaneous high P‐T measurements of ultrasonic compressional and shear wave velocities in Ichino‐megata mafic xenoliths: Their bearings on seismic velocity perturbations in lower crust of northeast Japan arc

Simultaneous measurements of ultrasonic compressional (Vp) and shear wave velocities (Vs) were conducted under pressures and temperatures representative of the lower crust on five mafic xenoliths derived from the northeast Japan arc crust. For comparison with the observed seismic heterogeneity of the lower crust of the northeast Japan arc, the velocity deviations (dVp and dVs) of the xenoliths were calculated using the average reference Vp (6.61 ± 0.1 km/s) and Vs (3.76 ± 0.1 km/s). The dVp and dVs values of the xenoliths at 700°C and 0.8 GPa are 0.8% and −1.2% for hornblende gabbro, 4.8% and 4.0% for hornblende‐pyroxene gabbro, 0.9% and −1.5% for amphibolite, 2.5% and 1.7% for pyroxene amphibolite, and 0.9% and −5.6% for hornblendite, respectively. We compared the velocity perturbations in the lower crust determined by seismic tomography with dVp and dVs of the xenoliths using “Vp−Vs−Vp/Vs deviation diagrams.” On the basis of our measurements, we suggest that (1) the seismically high‐Vp and Vs regions beneath the Tobishima Basin consist of hornblende‐pyroxene gabbro, (2) hornblende gabbro is a predominant rock type beneath the Dewa Hills and Ou Backbone Range, (3) the low‐velocity anomalies beneath the active volcano areas may be caused by the existence of partial melts of hornblende gabbro, and (4) the low‐Vp and high‐Vs regions beneath the Kitakami Mountains consist of quartz‐plagioclase‐bearing rocks. Our data demonstrate that the seismic heterogeneity in the lower crust of the northeast Japan arc reflects variations in rock composition and temperature that are related to the regional geological history.

Faulting processes controlled by the nonuniform thermal structure of the crust and uppermost mantle beneath the northeastern Japanese island arc

We performed a finite element analysis, taking into account nonlinear viscoelasticity and plasticity, to construct a two‐dimensional model of the deformation and faulting processes that occur in the deeper parts of the seismogenic zone beneath northeastern Japan. Our finite element code was developed on the basis of the GeoFEM parallel finite element code using plug‐ins to adopt several nonlinear functions. An extensive onshore‐offshore wide‐angle seismic expedition conducted across northeastern Japan in 1997 revealed a detailed image of the deep crust and uppermost mantle structures. In modeling the deformation and faulting beneath the Ou Backbone Range and Dewa Hill, northeastern Japan, we consider a realistic crust and uppermost mantle structure revealed by the 1997 seismic expedition and the existence of the two hot regions revealed by geothermal observations in a compressional tectonic setting. The numerical results reveal that shortening deformation due to nonlinear viscous flow occurs in the hot region in the lower crust and the uppermost mantle, resulting in shear faulting in the upper crust. Our model reproduces three reverse fault zones that are consistent with those observed. We investigate the stress accumulation process over a period approximately corresponding to the earthquake recurrence interval by prohibiting plastic faulting and found that the stress is loaded along the fault zone at magnitudes much lower than the absolute stress level. The results indicate that the loading processes of large inland earthquakes in northeastern Japan are determined by the nonuniform thermal structure in the deeper crust and uppermost mantle.

Catalyst Stability Determines the Catalytic Activity of Non‐Heme Iron Catalysts in the Oxidation of Alkanes

AbstractA series of iron(II) bis(triflate) complexes [Fe(L)(OTf)2] containing linear tetradentate bis(pyridylmethyl)diamine ligands with a range of ligand backbones has been prepared. The backbone of the ligand series has been varied from a two‐carbon linkage [ethylene (1), 4,5‐dichlorophenylene (2) and cyclohexyl (3)] to a three‐carbon [propyl (4)) and a four‐carbon linkage (butyl (5)]. The coordination geometries of these complexes have been investigated in the solid state by X‐ray crystallography and in solution by 1H and 19F NMR spectroscopy. Due to the labile nature of high‐spin iron(II) complexes in solution, dynamic equilibria of complexes with different coordination geometries (cis‐α, cis‐β and trans) are observed with ligands 2–5. In these cases, the geometry observed in the solid state does not necessarily represent the only or even the major geometry present in solution. The ligand field strength in the various complexes has been investigated by variable temperature magnetic moment measurements and UV‐vis spectroscopy. The strongest ligand field is observed with the most rigid ligands 1 and 2, which generate complexes [Fe(L)(OTf)2] with a cis‐α coordination geometry and the corresponding complexes [Fe(L)(CH3CN)2]2+ display spin crossover behaviour. The catalytic properties of the complexes for the oxidation of cyclohexane, using hydrogen peroxide as the oxidant, have been investigated. An increased flexibility in the ligand results in a weaker ligand field, which increases the lability of the complexes. The activity and selectivity of the catalysts appear to be related to the strength of the ligand field and the stability of the catalyst in the oxidising environment.

Screening of a modular sugar-based phosphite ligand library in the Cu-catalyzed asymmetric 1,4-addition reactions

A sugar-based monophosphite ligand library L1– L5 was screened in the Cu-catalyzed asymmetric 1,4-addition to cyclic and aliphatic linear enones. These ligands are derived from d-glucose, d-galactose and d-fructose, which lead to a wide range of sugar backbones, and contain several substituents/configurations in the biaryl moiety, with different steric and electronic properties. Systematic variation of the ligand parameters indicates that the catalytic performance (activities and enantioselectivities) is highly affected by the configuration of C-4 of the carbohydrate backbone, the size of the ring of the sugar backbone and the cooperative effect between configurations of C-3 and of the binaphthyl phosphite moiety. Good activities and enantioselectivities up to 57% and 51% were achieved for cyclic and aliphatic linear enones, respectively.

Finite element analysis of crustal deformation in the Ou Backbone Range, northeastern Japan, with non-linear visco-elasticity and plasticity: effects of non-uniform thermal structure

AbstractA finite element analysis with non-linear visco-elasticity and plasticity was carried out with the aim of constructing a model of the slip and deformation processes in the deeper parts of the seismogenic zones of inland earthquakes. Our finite element code is based on the GeoFEM parallel finite element code and was developed using plug-ins to adopt several non-linear functions. We consider the effects of geothermal structures in the crust in a compressional tectonic setting to model the deformation and faulting that occur around the Ou Backbone Range in northeastern Japan. We set an area of high geothermal gradient in the center of the model. The numerical results show that shortening deformation due to non-linear viscous flow occurs in the high-temperature area in the lower part of the crust, which results in shear faulting in the upper part of the crust. In the case where the crust comprises two layers—the upper crust (quartz diorite) and the lower crust (wet diabase)—a weak viscous zone appears in the lower part of the upper crust and a strong viscous or plastic zone appears at the upper part of the lower crust. Our numerical results are able to explain the deformation and faulting that occur around the Ou Backbone Range in northeastern Japan.

Ligand Topology Variations and the Importance of Ligand Field Strength in Non-Heme Iron Catalyzed Oxidations of Alkanes

A series of iron(II)-bis(triflate) complexes [Fe(L)(OTf)2] containing linear tetradentate bis(quinolyl)-diamine and bis(quinolylmethyl)-diamine ligands with a range of ligand backbones has been prepared. The coordination geometries of these complexes have been investigated in the solid state by X-ray crystallography and in solution by 1H and 19F NMR spectroscopy. Because of the labile nature of high-spin iron(II) complexes in solution, dynamic equilibria of complexes with different coordination geometries (cis-alpha, cis-beta, and trans) are observed with certain ligand systems. In these cases, the geometry observed in the solid-state does not necessarily represent the only or even the major geometry present in solution. The ligand field strength in the various complexes has been investigated by variable-temperature (VT) magnetic moment measurements and by UV-vis spectroscopy. The strongest ligand field is observed with the most rigid ligand that generates [Fe(L)(OTf)2] complexes with a cis-alpha coordination geometry, and the corresponding [Fe(L)(CH3CN)2]2+ complex displays spin crossover behavior. The catalytic properties of the complexes for the oxidation of cyclohexane have been investigated using hydrogen peroxide as the oxidant. An increased flexibility in the ligand results in a weaker ligand field, which increases the lability of the complexes. The activity and selectivity of the catalysts appear to be related to the strength of the ligand field and the stability of the catalyst.

Uplift of the Ou Backbone Range in Northeast Japan at around 10 Ma and its implication for the tectonic evolution of the eastern margin of Asia

The Late Cenozoic uplift history of a sedimentary basin located in the axial part of the Ou Backbone Range, Northeast Japan, was studied using detailed mapping, fission-track dating and basin analysis. The subsidence analysis of the basin clarified the more complex stepwise uplift of the Ou Backbone Range. Three stages of uplift have been recognized and are interpreted to be the result of compressional stress, possibly accompanied by basin inversion. The three stages are identified as (1) a phase of surface uplift and regional unconformity (12–9 Ma), (2) a stage of differential uplift and compression (6.5–3 Ma) and (3) an intense compression stage (∼ 3 Ma). In the first stage, the eastern sector of the Backbone Range uplifted and a notable unconformity was formed at ∼ 10 Ma. The western sector remained submerged, suggesting that the eastern sector uplifted earlier than the western sector. Although the first uplift stage has been regarded as a tectonically quiet period in Northeast Japan, this tectonic event at ∼ 10 Ma is supposed to have a regional origin because coeval tectonic events took place across all Northeast Japan, as well as on the eastern margin of Asia. This study thus provides new insights into the Neogene tectonic evolution in the eastern margin of Asia.

Deep structure of the northeastern Japan arc and its implications for crustal deformation and shallow seismic activity

Seismic tomography studies in the northeastern Japan arc have revealed the existence of an inclined sheet-like seismic low-velocity and high-attenuation zone in the mantle wedge at depths shallower than about 150 km. This sheet-like low-velocity, high-attenuation zone is oriented sub-parallel to the subducted slab, and is considered to correspond to the upwelling flow portion of the subduction-induced convection. The low-velocity, high-attenuation zone reaches the Moho immediately beneath the volcanic front (or the Ou Backbone Range) running through the middle of the arc nearly parallel to the trench axis, which suggests that the volcanic front is formed by this hot upwelling flow. Aqueous fluids supplied by the subducted slab are probably transported upward through this upwelling flow to reach shallow levels beneath the Backbone Range where they are expelled from solidified magma and migrate further upward. The existence of aqueous fluids may weaken the surrounding crustal rocks, resulting in local contractive deformation and uplift along the Backbone Range under the compressional stress field of the volcanic arc. A strain-rate distribution map generated from GPS data reveals a notable concentration of east–west contraction along the Backbone Range, consistent with this interpretation. Shallow inland earthquakes are also concentrated in the upper crust of this locally large contraction deformation zone. Based on these observations, a simple model is proposed to explain the deformation pattern of the crust and the characteristic shallow seismic activity beneath the northeastern Japan arc.

Isotopic Composition of Carbonaceous Material in Metamorphic Rocks from the Mountain Belt of Taiwan

Carbonaceous (organic) material was extracted from pelitic rocks and marbles collected along three highways transecting the mountain belt of Taiwan. δ13C values of carbonaceous matter show a general increasing trend with elevated metamorphic grade. The first prominent, systematic change in δ13C values occurs in samples of the middle greenschist facies, with δ13C values higher than -24%‰. Carbon isotope fractionation between coexisting calcite and carbonaceous material suggests that this marked change might have taken place at around 300-350°C. From systematic temperature variations, two thermal maxima, 430°C and 460-490°C, were delineated in the central part of the Hsuehshan Range and the Backbone Range, respectively, and are attributed to Cenozoic mountain building. High temperatures (>500°C) were detected in some marble samples adjacent to Mesozoic granite intrusions, indicating that pre-existing thermal records are preserved in these marbles. The carbon isotope fractionation preserved in rocks across the mountain belt therefore may not have been synchronous.

Lower crustal fluid distribution in the northeastern Japan arc revealed by high-resolution 3D seismic tomography

The Ou Backbone Range strikes northwards through the central northeastern Japan arc and is bounded on both sides by the active reverse Uwandaira and Sen'ya faults. We have applied a traveltime inversion method (seismic tomography) with spatial velocity correlation to active and passive seismic data in order to investigate a three-dimensional (3-D) velocity structure. The data set contains 33,993 P- and 18,483 S-wave arrivals from 706 natural sources and 40 blasts, as well as 2803 P-wave traveltime data from 10 explosions detonated during the 1997 controlled source experiment. The traveltime inversion reveals a zone beneath the Ou Backbone Range in which P-wave velocities ( V P) are approximately 6–8% lower than the average velocity at equivalent depths. The low V P and a low V P to S-wave velocity ( V S) ratio ( V P/ V S) of about 1.65 suggest the presence of aqueous fluids in the middle crust.

GPS連続観測による長町-利府断層帯およびその周辺 (東北地方中部) の地殻変動

We constructed eight continuous GPS stations across the Nagamachi-Rifu fault zone, northeastern Japan to reveal the detailed spatial pattern of crustal deformation. High strain rate around the fault zone observed by the GEONET and the occurrence of the MJMA 5.2 Sendai earthquake on September 15, 1998, at the deep edge of the seismogenic part of the fault motivated us to confirm the aseismic sliding of the fault in or below the seismogenic depth from the contemporary deformation. We analyzed the GPS data of new stations as well as existing stations, totaling up to 50 stations in central Tohoku, using GIPSY 2.6.1 software and estimated GPS site velocity and strain rate by a least square method. One component of the principal strain rate shows distinctive compression in the E-W or ESE-WNW direction in the whole region. In the forearc region, the other component of the principal strain rate are almost zero in the south of 38°15′, while NNE-SSW extension in the north of 38°15′. Strain rate distribution is spatially heterogeneous in the region. We found a high strain rate zone west of the Nagamachi-Rifu fault zone and that between Honshu and Awashima in the eastern margin of the Sea of Japan. Low strain rate zones exist in the west of the high strain region of the Nagamachi-Rifu fault zone and in the western half of Yamagata Prefecture. Strain rate distribution pattern on the hanging wall side of the Nagamachi-Rifu fault can be modeled by aseismic sliding of 10mm/yr on a horizontal detachment fault connecting to the Nagamachi-Rifu fault at a depth of about 15km beneath the Ou backbone range. However, it is difficult to constrain a fault model for the strain rate distribution from the present dataset uniquely.

Precisely relocated hypocentres, focal mechanisms and active orogeny in Central Taiwan

Abstract The 1999 Chi-Chi earthquake series occurred in Central Taiwan, where ongoing mountain building is most active. The pre- and post-Chi-Chi seismicity helps to clarify the internal orogenic activity. The 27 000 earthquakes from the 1993–2002 catalogues have been relocated with greater precision. By associating the seismicity with focal mechanisms, many structures inside the orogen have been mapped. Among them are a steeply dipping thrust fault in the deep crust; a 50-km-long left-lateral strike-slip fault in the south; and an Eastern Central Range NNE-striking normal fault. While the deep crustal thrust appears to contribute to the root-building, the southern strike-slip slip fault accommodates the mainshock fault motion, and the Eastern Central Range normal faulting probably occurs mainly after a major western Taiwan thrust type earthquake. Much of the Backbone Range and the Eastern Central Range were seismically quiescent before and after the Chi-Chi earthquake. The contrast in the seismicity of the Central Range and the surrounding regions implies different material behaviour in these different regimes of the orogen.

Spatial relationship between recent compressional structures and older high-velocity crustal structures; examples from the Vøring Margin, NE Atlantic, and Northern Honshu, Japan

The geological evolution of the volcanic passive margin off mid-Norway, NE Atlantic, and the active volcanic arc in northern Honshu, related to the subduction of the Pacific plate beneath Japan, are similar in the sense that long periods of extensional deformation has shifted to recent compression with formation of domal structures. Seismic wide-angle data have been acquired across six contractional domes in the Vøring Basin, mid-Norwegian Margin, and over the Ou Backbone Range ‘pop-up’ structure, northern Honshu. The models derived from the seismic data reveal that the location of all investigated structures in the Vøring Basin is between, or in the vicinity of pre-Eocene high-velocity structures, which may act as rigid blocks during compression. It is proposed that the existence and trend of these structures, subject to mild NW–SE compression, is the most important factor controlling the formation, spatial distribution and trend of the domes. Structures in the high-velocity lower crust may be the single most important element in controling the domal formation; all modelled highs in the lower crustal early Tertiary intrusive layer seem to be related to the formation of domes in the NW–SE direction. The Ou Backbone Range pop-up structure is localised at a low rigidity zone mapped as low upper crustal seismic velocities. The structure coincides with the present day volcanic front, which may be interpreted as the main reason for the existence of low velocities and the main factor controling the localization of compressional deformation. The Ou Backbone Range is squeezed between a high velocity upper crustal block to the east and a high velocity lower crustal block to the west, and it is speculated that the corresponding lateral and vertical variations in crustal rigidity may have contributed to the actual localization of the present day volcanic front.

Snow load and seasonal variation of earthquake occurrence in Japan

Snow load along the western flank of the backbone range of the Japanese Islands causes seasonal crustal deformation. It perturbs the interseismic strain buildup, and may seasonally influence the seismicity in Japan. Intraplate earthquakes in northeastern Japan occur on reverse faults striking parallel with the snow-covered zone. In central and southwestern Japan, they occur on strike-slip faults striking either parallel with, or perpendicular to the snow cover. The snow load enhances compression at these faults, reducing the Coulomb failure stress by a few kPa. This is large enough to modulate the secular stress buildup of a few tens of kPa/yr. Past inland earthquakes with magnitudes ≥7.0 that occurred in regions covered with snow in winter, tend to occur more in spring and summer than in autumn and winter, while those in the snow-free regions do not show such variation. Although its statistical significance is not strong due to limited number of past earthquakes, it suggests that the spring thaw enhances seismicity beneath the snow cover.

Strain accumulation in and around Ou Backbone Range, northeastern Japan as observed by a dense GPS network

A dense GPS network was established in 1997 around Ou Backbone Range (OBR), northeastern Japan, by deploying 28 continuous GPS stations to complement the sparse portion of GEONET operated by the Geographical Survey Institute of Japan. The aim of the network is to investigate the present surface deformation and understand the relationship between earthquake occurrence and the deformation process of the island-arc crust. Our GPS data are analyzed using a precise point positioning strategy of GIPSY/OASIS-II. Results of GEONET in daily SINEX files have been supplied by the GSI. Producing grid data of horizontal velocities and taking spatial derivatives, we derived a map of strain rate distribution. The results show that the region between 38.8° and 39.8°N in the OBR experiences notable concentration of east-west contraction. The region coincides with the area of active seismicity, including the focal areas of large earthquakes occurring in 1896 (M7.2), 1900 (M7.0), 1962 (M6.5), 1970 (M6.2), and 1998 (M6.1). Observed strain is larger than can be explained by the total moment release of earthquakes that occurred in the same period as this study. Possible sources of strain concentration may be viscoelastic deformation due to large earthquakes and/or aseismic slip along the deeper extension of the active faults.