Thermodynamic properties of MgSiO3 ilmenite from vibrational spectra

Unpolarized infrared (IR) reflectance spectra for MgSiO₃ ilmenite taken from a single-crystal and from a densly packed polycrystalline sample possessed all eight peaks mandated by symmetry between 337 and 850 cm^?1. Polarizations were inferred from intensity differences between the two samples. IR peak positions differ by up to 250 cm^?1 from recent calculations, but on average are within 11%. Heat capacity C _p calculated from these data by using a Kieffer-type model are within the experimental uncertainty of calorimetric measurements from 170 to 700 K. Outside this range, calculated C _p is probably accurate within a few percent, based on recent results for garnets. Calculated entropy is only slightly less accurate, giving S ⁰ (298.15 K) as 54.1 ±0.5 J/ mol-K, which is 10% lower than recent estimates based on phase equilibria. The slope of the phase boundary between ilmenite and perovskite is used to predict S ⁰ (298.15 K) of perovskite as 58.7 ±1.4 J/mol-K, which is 10% lower than previous values.     

Large-Scale Mapping Observations of the C i (3P1-3P0) and CO (J = 3-2) Lines toward the Orion A Molecular Cloud

Large-scale mapping observations of the 3P1-3P0 fine-structure transition of atomic carbon (C i, 492 GHz) and the J=3-2 transition of CO (346 GHz) toward the Orion A molecular cloud have been carried out with the Mount Fuji submillimeter-wave telescope. The observations cover 9 deg2 and include the Orion Nebula M42 and the L1641 dark cloud complex. The C i emission extends over almost the entire region of the Orion A cloud and is surprisingly similar to that of 13CO (J=1-0). The CO (J=3-2) emission shows a more featureless and extended distribution than C i. The C i/CO (J=3-2) integrated intensity ratio shows a spatial gradient running from the north (0.10) to the south (1.2) of the Orion A cloud, which we interpret as a consequence of the temperature gradient. On the other hand, the C i/13CO (J=1-0) intensity ratio shows no systematic gradient. We have found a good correlation between the C i and 13CO (J=1-0) intensities over the Orion A cloud. This result is discussed on the basis of photodissociation region models.     

The 1998 Hida Mountain, Central Honshu, Japan, earthquake swarm: Double-difference event relocation, frequency–magnitude distribution and Coulomb stress changes

By using the double-difference relocation technique, we have determined the fine structure of seismicity during the 1998 Hida Mountain earthquake swarm. The distribution of seismic activity defines two main directions (N–S and E–W) that probably correspond to the regional stress pattern. The detailed structure of seismicity reveals intense spatio-temporal clustering and earthquake lineations. Each cluster of events contains a mainshock and subsequent aftershock activity that decays according to the Omori law. The seismicity and the b-value temporal and spatial patterns reflect the evolution of the static stress changes during the earthquake swarm. About 80% of the swarm's best-relocated events occur in regions of increased ΔCFF. The smaller value of b found in the northern part of the swarm region and a larger b-value observed to the south, for the same period of time, could be well explained by the static stress changes caused by the larger events of the sequence. We argue that the state of stress in the crust is the main factor that controls the variation of b-value.     

Decreases in turbidity during neap tides initiate late winter blooms of Eucampia zodiacus in a macrotidal embayment

Eucampia zodiacus Ehrenberg is harmful, as it causes reduction in the quality of the aquacultured Porphyra thalli owing to nutrient depletions during dense blooms in the late winter in the macrotidal Ariake Sea, Japan. To understand the mechanism of bloom development, changes in the abundance of E. zodiacus during a bloom were investigated along vessel transects from February to April 2012. In addition, marine environmental variables were continuously monitored by the Ariake Sea Monitoring Tower, which revealed that turbidity periodically decreased during neap tides. During the 16 February neap tide, a high Secchi depth (4.3 m) was recorded at offshore stations and the Z _1% depth, at which the light intensity attenuates to 1 % of that at the sea surface, exceeded the water depth. On 16 February, the abundance of E. zodiacus was 52–732 cells mL^?1, peaking at 7.0 m depth offshore. Subsequently, abundance increased at all stations. During the 22 February spring tide, abundance became vertically uniform. On 19 March, abundance at the tower reached 3758 cells mL^?1 at the surface. We conclude that an improvement in light conditions in the deeper layer triggered the bloom, although the size and the duration of the bloom were determined by nutrient availability. Thus, decreases in turbidity during neap tides and subsequent strong vertical mixing during spring tides may be instrumental in the population dynamics of the large diatom E. zodiacus in macrotidal environments.     

Paleoposition of Southwest Japan at 16 Ma: Implication from paleomagnetism of the Miocene Ichishi Group

New paleomagnetic data from shallow-marine sediments of the Ichishi Group suggest a clockwise tectonic rotation of Southwest Japan in the Middle Miocene. Samples have been collected from mud or tuff layers at 17 sites. Stability of remanent magnetization has been examined by using alternating field and thermal demagnetization. The polarity sequence, composed of four normal and seven reversed polarity sites, is correlated to Polarity Epoch 16 (15.2–17.6 Ma), based on micropaleontological assignment of the upper Ichishi Group to Blow's Zone N8. The mean paleomagnetic direction of the 11 sites shows an anomalous declination toward the northeast. This result suggests that Southwest Japan was subjected to a clockwise rotation through 45° since 16 Ma. The clockwise rotation can be explained by the drift of Southwest Japan associated with the spreading of the Japan Sea during the Middle Miocene.     

Phase boundary between ilmenite and perovskite structures in MnGeO3 determined by in situ X-ray diffraction measurements

In situ X-ray observations of the phase transition from ilmenite to perovskite structure in MnGeO₃ were carried out in a Kawai-type high-pressure apparatus interfaced with synchrotron radiation. The phase boundary between the ilmenite and perovskite structures in the temperature range of 700–1,400°C was determined to be P (GPa) = 16.5(±0.6) − 0.0034(±0.0006)T (°C) based on Anderson’s gold pressure scale. The Clapeyron slope, dP/dT, determined in this study is consistent with that for the transition boundary between the ilmenite and the perovskite structure in MgSiO₃.     

Distinctive erosional and depositional structures formed at a canyon mouth: A lower Pleistocene deep‐water succession in the Kazusa forearc basin on the Boso Peninsula,Japan

The canyon mouth is an important component of submarine‐fan systems and is thought to play a significant role in the transformation of turbidity currents. However, the depositional and erosional structures that characterize canyon mouths have received less attention than other components of submarine‐fan systems. This study investigates the facies organization and geometry of turbidites that are interpreted to have developed at a canyon mouth in the early Pleistocene Kazusa forearc basin on the Boso Peninsula, Japan. The canyon‐mouth deposits have the following distinctive features: (i) The turbidite succession is thinner than both the canyon‐fill and submarine‐fan successions and is represented by amalgamation of sandstones and pebbly sandstones as a result of bypassing of turbidity currents. (ii) Sandstone beds and bedsets show an overall lenticular geometry and are commonly overlain by mud drapes, which are massive and contain fewer bioturbation structures than do the hemipelagic muddy deposits. (iii) The mud drapes have a microstructure characterized by aggregates of clay particles, which show features similar to those of fluid‐mud deposits, and are interpreted to represent deposition from fluid mud developed from turbidity current clouds. (iv) Large‐scale erosional surfaces are infilled with thick‐bedded to very thick‐bedded turbidites, which show lithofacies quite similar to those of the surrounding deposits, and are considered to be equivalent to scours. (v) Concave‐up erosional surfaces, some of which face in the upslope direction, are overlain by backset bedding, which is associated with many mud clasts. (vi) Tractional structures, some of which are equivalent to coarse‐grained sediment waves, were also developed, and were overlain locally by mud drapes, in association with mud drape‐filled scours, cut and fill structures and backset bedding. The combination of these outcrop‐scale erosional and depositional structures, together with the microstructure of the mud drapes, can be used to identify canyon‐mouth deposits in ancient deep‐water successions.     

Near-field beam pattern measurement of qualification model of ALMA band 8 (385–500 GHz) cartridge receiver

We have developed a near-field vector beam measurement system covering the range of frequencies from 385 to 500 GHz. The measurement set-up is capable of measurements with dynamic range exceeding 50 dB and amplitude and phase stability respectively of 0.1 dB/h and 1 degree/5 min at room temperature. Beam patterns of the ALMA band 8 corrugated horns and receiver optics block were measured at room temperature and lately compared with physical optics calculations obtained in the far-field. Both co-polar and cross-polar beam patterns of a qualification model of the ALMA band 8 cartridge cooled in a cartridge-test-cryostat have also been measured in the near-field as a detector of a submillimeter vector network analyzer. The measurements presented in this work refer to the lowest, middle and upper frequencies of band 8. The comparisons between software model and experimental measurements at these frequencies show good agreement down to ?30 dB for the main polarization component. The cross-polarization level of the beam propagating through the receiver optics block was also characterized. We found that a cross-polarization level better than ?28 dB can be achieved at all measured frequencies. The measured beam pattern of this receiver corresponds to efficiency of greater than 92% at the sub reflector (diameter of 750 mm) of the ALMA 12 m optics.     

Discontinuity of the Mozumi–Sukenobu fault low-velocity zone, central Japan, inferred from 3-D finite-difference simulation of fault zone waves excited by explosive sources

We delineate shallow structures of the Mozumi–Sukenobu fault, central Japan, using fault zone waves generated by near-surface explosions and detected by a seismometer array. Two explosive sources, S1 and S2, were placed at a distance of about 2 km from the array, and the other two, S3 and S4, were at a distance of about 4 km. Fault zone head waves and fault zone trapped waves following direct P wave arrivals were clearly identified in the seismograms recorded by a linear seismometer array deployed across the fault in a research tunnel at a depth of 300 m. Synthetic waveforms generated by a 3-D finite-difference (3-D FD) method were compared with observed fault zone waves up to 25 Hz. The best fitting model indicates a 200-m-wide low-velocity zone extending at least to shot site S1 located 2 km east of the seismic array with a 20% decrease in the P wave velocity relative to the wall rock. The width of the low-velocity zone is consistent with the fault zone defined by direct geological observation in the research tunnel. However, the low-velocity zone should disappear just to the east of the site S1 to explain the observed fault zone waves for shot S3 and S4 located 4 km east of the seismometer array. Yet the observation and the simulation show notable trapped wave excitation even though shots S3 and S4 are outside the fault zone. These results indicate that (1) the effective waveguide for seismic waves along the fault does not exist east of source site S1 although the surface traces of the fault are observed in this region, and (2) considerable trapped waves can be excited by sources well outside the fault zone. These results highlight the along-strike variability in fault zone structure.     

Simple monitoring method for precaution of landslides watching tilting and water contents on slopes surface

A low-cost and simple monitoring method for early warning of landslides is proposed. To detect abnormal deformation of a slope, this method employs a tilt sensor in place of an extensometer on the slope surface. In order to examine the relevance of measuring rotation angle on a slope surface by tilt sensor, model tests were conducted, and rotation on the slope surface was observed together with slide displacement along the surface. The rotation data responded 30 min before failure in a model test, which could be useful as a signal for early warning. However, the behavior of rotation before failure varies from case to case, and thus, criteria to issue warning should be defined more carefully. For a model slope made of uniform loose sand, measurement of slide displacement along the slope surface is sensitive to failure at the toe, while the measurement of rotation on the slope surface is useful to detect the development of progressive failure upward along the slope. Wireless sensor units with microelectromechanical systems (MEMS) tilt sensor and volumetric water content sensor were also examined on a real slope in Kobe City, and a long-term monitoring was attempted. A simple but possible way to define the criteria of judgment to issue warning can be proposed based on combination of data obtained by the tilt sensors and volumetric water content sensors.