Studies on critical Reynolds number indices for wind-tunnel experiments on flow within urban areas

Reynolds-number dependence of flow fields within a modelled urban area was studied in a wind tunnel. We measured flow around a single model building and around model city blocks at various wind speeds, and studied Reynolds number indices more appropriate than the building Reynolds number. Our results led to the following conclusions. Firstly, the flow around the models in the wind tunnel was roughly divided into three parts according to the intensities of viscous stress and Reynolds stress as follows: (1) the flow in the vicinity of the ground or the surfaces of the model, where viscous stress became dominant under certain conditions; (2) the flow detached from the surfaces of the model, where Reynolds stress was always dominant; and (3) the flow around the separation bubble at the leading edge of the building model, where the influences of both viscous stress near the wall and the Reynolds stress in the separated boundary layer were mixed.Secondly, the critical Reynolds number of the flow in the modelled urban area could be defined by using both the roughness Reynolds number Re_z0 (= z₀u_*/) and the dimensionless height z₊ (= zu_*/). Reynolds-number independence could be expected for whole flow fields in the modelled urban areas as long as the critical values of Re_z0 and z₊ were satisfied.     

High temperature infrared spectra of hydrous microcrystalline quartz

A series of in-situ high temperature infrared (IR) measurements of water in an agate sample and in a milky quartz has been conducted in order to understand the nature of water in silica at high temperatures (50–700?°C) and the dehydration behavior. IR absorption bands of water molecules trapped in the milky quartz showed a systematic decrease in intensities and a shift from 3425?cm^?1 at 50?°C toward 3590?cm^?1 at 700?°C without any loss of water. This indicates a change in IR absorption coefficients corresponding to different polymeric states of water at different temperatures. The broad 3430?cm^?1 band in the agate sample also showed a systematic decrease in IR intensity and a band shift toward higher frequency with increasing temperature (～700?°C). This indicates that the agate sample also contains fluid inclusion-like water. For this agate sample, a dehydration of loosely hydrogen-bonded molecular water occurred at lower temperatures (<200?°C). At higher temperatures (>400?°C), sharp bands around 3660 and 3725?cm^?1 (3740?cm^?1 at 50?°C) due to surface silanols, appeared. This indicates dehydration of H₂O molecules that are hydrogen bonded to surface silanols. SiOH species in the agate are divided into three groups, namely SiOH group located at structural defects, surface silanols hydrogen bonded to each other and free surface silanols. Former two dehydrate below 700?°C and the dehydration rate of the SiOH at structural defects is faster than the other. IR spectra show that SiOH species decrease continuously even after the dehydration of most of H₂O molecules. All these results provide realistic bases for the change in physicochemical states of different OH species in silica at high temperatures.     

Anomalous Rayleigh-Wave Propagation Along Oceanic Trench

A clear later phase of amplitude larger than the direct surface wave packet was observed at stations in Hokkaido, Japan, for several events of the December 1991 off-Urup earthquake swarm in the Kuril Islands region. From its particle motion, this phase is likely to be a fundamental Rayleigh wave packet that arrived with an azimuth largely deviated from each great-circle direction. As its origin, Nakanishi (1992) proposed that the sea-trench topography in this area as deep as 10 km may produce a narrow zone of low velocity for Rayleigh waves of periods around 15 sec. Following this idea, we compute ray paths and estimate how Rayleigh waves would propagate if we assume that lateral velocity variations are caused only by seafloor topography. We confirm that thick sea water in the trench indeed produces the phase velocity of Rayleigh waves to be smaller than in a surrounding area by the degree over 100%. Such a low-velocity zone appears only in a period range from 12 to 20 sec. Although this strong low-velocity zone disturbs the direction of Rayleigh wave propagation from its great circle, the overall ray paths are not so affected as far as an epicentre is outside this low-velocity zone, that is, off the trench axis. In contrast, the majority of rays are severely distorted for an event within the low-velocity zone or, in other words, in the neighborhood of the trench axis. For such an event, a part of wave energy appears to be trapped in this zone and eventually propagates outwards due to the curvature or bend of trench geometry, resulting in very late arriving waves of large amplitude with an incident direction clearly different from great circles. This phenomenon is observed only at a very limited period range around 16 sec. These theoretical results are consistent with the above mentioned observation of Nakanishi (1992).     

A crack-like rupture model for the 19 September 1985 Michoacan,Mexico, earthquake

Evidence supporting a smooth crack-like rupture process of the Michoacan earthquake of 1985 is obtained from a major earthquake for the first time. Digital strong motion data from three stations (Caleta de Campos, La Villita, and La Union), recording near-field radiation from the fault, show unusually simple ramped displacements and permanent offsets previously only seen in theoretical models. The recording of low frequency (0 to 1 Hz) near-field waves together with the apparently smooth rupture favors a crack-like model to a step or Haskell-type dislocation model under the constraint of the slip distribution obtained by previous studies. A crack-like rupture, characterized by an approximated dynamic slip function and systematic decrease in slip duration away from the point of rupture nucleation, produces the best fit to the simple ramped displacements observed. Spatially varying rupture duration controls several important aspects of the synthetic seismograms, including the variation in displacement rise times between components of motion observed at Caleta de Campos. Ground motion observed at Caleta de Campos can be explained remarkably well with a smoothly propagating crack model. However, data from La Villita and La Union suggest a more complex rupture process than the simple crack-like model for the south-eastern portion of the fault.     

Relationship between growth of albite porphyroblasts and deformation in a sambagawa schist, Central Shikoku, Japan

Albite porphyroblasts in a basic schist of the Sambagawa metamorphic belt (Besshi—Bashi, Central Shikoku) show zonal variation of inclusions defined by inclusion-free mantles and inclusion-rich cores, though matrix minerals are partly incorporated in the outer zones of the mantles. From comparison of the crystallographic and dimensional fabrics of inclusion and matrix epidote, it has been concluded that the orientation of the principal axes of strain was different for the deformation of matrix fabrics and inclusion fabrics (fabrics produced before formation of cores). Inclusion amphibole in the cores belongs to the actinolite—common hornblende group, with Si content more than 7.0, whereas amphibole in the matrix and outer zones of mantles belongs to the common hornblende group, with Si content less than 7.1. This shows that the metamorphic temperature was higher during the phase of formation of the outer zones of the mantles than during that of the cores. The average direction of maximum growth of the mantles, which has been estimated from differences between the average shapes of porphyroblasts and those of cores, is parallel to the linear orientation of amphibole and epidote in the matrix. The average direction of minimum growth of the mantles coincides with the normal to the schistosity of the matrix. The mantles appear to be of the same generation as the matrix fabrics.     

Thermal expansion of fayalite,Fe2SiO4

Thermal expansion of single-crystal fayalite has been measured by a dilatometric method at temperatures between 25 °C and 850 °C. The results show the presence of anomalous expansion in the b axis, which is correlated to the anomalous variation of elastic moduli with temperature. Grüneisen's parameter is 1.10 and the thermal Debye temperature is 565 K, which is close to the acoustic Debye temperature of 511 K.     

Dynamic response of the KII building to the San Fernando earthquake

The KII Building was subjected to the San Fernando earthquake on 9 February 1971 without suffering any damage. During the earthquake, strong motion accelerations were recorded at the base, middle and top of the building. The simulation analysis of the building was carried out taking into account the interaction between the building and the soil. The internal viscous damping theory considering the different damping coefficients for the building and the soil was adopted. Comparison of the calculated and observed acceleration time histories as well as the floor response spectra showed satisfactory agreement. On the basis of the response spectrum values, the fact that no damage was observed in this building is justified theoretically.     

Ground cracks in Ethiopian Rift Valley: facts and uncertainties

No accurate relationship has been obtained in this study between ground cracks in Ethiopian Rift Valley and the most common causes of earth fissures such as aquifer-system compaction and increased horizontal seepage stresses. This is due to the fact that the level of groundwater withdrawal responsible for these processes is still negligible in Ethiopia. If aquifer-system compaction and increased horizontal seepage stresses have a certain role, then it should be through the long-term effect of groundwater flow from basins to neighboring lakes. The ground cracks appeared also not to have a direct link with active faulting or distant earthquakes. Structurally, the Ethiopian Rift Valley is dominated by NE–SW-trending tensional faults, but no evidence is obtained in this study to associate the process of surface cracking with major tectonics. However, an aseismic elastic strain, which originates at depth and propagates upward through sediments without the formation of bedrock faults, could result in conditions conducive to the development of cracks. Then, fissures might ultimately be created after heavy rainfalls by near-surface processes such as piping and hydrocompaction along water-line sources.