Application of the Spatial Auto-Correlation Method for Shear-Wave Velocity Studies Using Ambient Noise     

M. W. Asten  K. Hayashi 《Surveys in Geophysics》2018,39(4):633-659

Ambient seismic noise or microtremor observations used in spatial auto-correlation (SPAC) array methods consist of a wide frequency range of surface waves from the frequency of about 0.1 Hz to several tens of Hz. The wavelengths (and hence depth sensitivity of such surface waves) allow determination of the site S-wave velocity model from a depth of 1 or 2 m down to a maximum of several kilometres; it is a passive seismic method using only ambient noise as the energy source. Application usually uses a 2D seismic array with a small number of seismometers (generally between 2 and 15) to estimate the phase velocity dispersion curve and hence the S-wave velocity depth profile for the site. A large number of methods have been proposed and used to estimate the dispersion curve; SPAC is the one of the oldest and the most commonly used methods due to its versatility and minimal instrumentation requirements. We show that direct fitting of observed and model SPAC spectra generally gives a superior bandwidth of useable data than does the more common approach of inversion after the intermediate step of constructing an observed dispersion curve. Current case histories demonstrate the method with a range of array types including two-station arrays, L-shaped multi-station arrays, triangular and circular arrays. Array sizes from a few metres to several-km in diameter have been successfully deployed in sites ranging from downtown urban settings to rural and remote desert sites. A fundamental requirement of the method is the ability to average wave propagation over a range of azimuths; this can be achieved with either or both of the wave sources being widely distributed in azimuth, and the use of a 2D array sampling the wave field over a range of azimuths. Several variants of the method extend its applicability to under-sampled data from sparse arrays, the complexity of multiple-mode propagation of energy, and the problem of precise estimation where array geometry departs from an ideal regular array. We find that sparse nested triangular arrays are generally sufficient, and the use of high-density circular arrays is unlikely to be cost-effective in routine applications. We recommend that passive seismic arrays should be the method of first choice when characterizing average S-wave velocity to a depth of 30 m (V_s30) and deeper, with active seismic methods such as multichannel analysis of surface waves (MASW) being a complementary method for use if and when conditions so require. The use of computer inversion methodology allows estimation of not only the S-wave velocity profile but also parameter uncertainties in terms of layer thickness and velocity. The coupling of SPAC methods with horizontal/vertical particle motion spectral ratio analysis generally allows use of lower frequency data, with consequent resolution of deeper layers than is possible with SPAC alone. Considering its non-invasive methodology, logistical flexibility, simplicity, applicability, and stability, the SPAC method and its various modified extensions will play an increasingly important role in site effect evaluation. The paper summarizes the fundamental theory of the SPAC method, reviews recent developments, and offers recommendations for future blind studies.  相似文献   

Geological,mineralogical, and oxygen isotope studies of the Chandmani Uul iron oxide–copper–gold deposit in Dornogobi Province,Southeastern Mongolia     

Luvsannyam Oyunjargal  Ken‐ichiro Hayashi  Teruyuki Maruoka 《Resource Geology》2020,70(3):233-253

The Chandmani Uul deposit is located in Dornogovi province, Southeastern Mongolia. Iron oxide ores are hosted in the andesitic rocks of the Shar Zeeg Formation of Neoproterozoic to Lower‐Cambrian age. Middle‐ to Upper‐Cambrian bodies of granitic rocks have intruded into the host rocks in the western and southern regions of the deposit. The wall rocks around the iron oxide ore bodies were hydrothermally altered to form potassic, epidote, and sericite–chlorite alteration zones, and calcite and quartz veinlets are ubiquitous in the late stage. Since granitic rocks also underwent potassic alteration, the activity of the granitic rocks must have a genetic relation to the ore deposit. The ore mineral assemblage is dominated by iron oxides such as mushketovite, euhedral magnetite with concentric and/or oscillatory zoning textures, and cauliflower magnetite. Lesser amounts of chalcopyrite and pyrite accompany the iron oxides. Among all these products, mushketovite is dominant and is distributed throughout the deposit. Meanwhile, euhedral magnetite appears in limited amounts at relatively shallow levels in the deposit. By contrast, cauliflower magnetite appears locally in the deeper parts of the deposit, and is associated with green‐colored garnet and calcite. Sulfide minerals are ubiquitously associated with these iron oxides. The oxygen isotope (δ¹⁸O) values of all types of magnetite, quartz, and epidote were found to be ?5.9 to ?2.8‰, 10.5 to 14.9‰, and 3.6 to 6.6‰, respectively. The δ¹⁸O values of quartz–magnetite pairs suggest an equilibrium isotopic temperature near 300°C. The calculated values of δ¹⁸O for the water responsible for magnetite ranged from 2 to 10‰. All the data obtained in this study suggest that the iron oxide deposit at the Chandmani Uul is a typical iron oxide–copper–gold deposit, and that this deposit was formed at an intermediate depth with potassic and sericite–chlorite alteration zones under the oxidized conditions of a hematite‐stable environment. The δ¹⁸O range estimated implies that the ore‐forming fluid was supplied by a crystallizing granodioritic magma exsolving fluids at depth with a significant contribution of meteoric water.  相似文献   

Unveiling the formation of stars and planets with a large infrared-optical telescope     

Saeko S. Hayashi 《Astrophysics and Space Science》1995,224(1-2):479-480

Diffraction-limited imaging in the near-IR (with the aid of adaptive optics) to middle-IR wavelengths will be a major breakthrough with 8m IR-optical telescopes. Special interest is on the scale of planet formation, that is, within 100 AU of the embedded sources in the nearby Taurus or Ophiuchus clouds. In this report, we demonstrate the sensitivity of a telescope with a virtual instrument that covers a wide spectral range.  相似文献   

Shallow and deep fresh impact craters in Hesperia Planum,Mars     

Peter J. Mouginis-Mark  Joan N. Hayashi 《Earth, Moon, and Planets》1993,61(1):1-20

The depths of 109 impact craters 2–16 km in diameter, located on the ridged plains materials of Hesperia Planum, Mars, have been measured from their shadow lengths using digital Viking Orbiter images (orbit numbers 417S–419S) and the PICS computer software. On the basis of their pristine morphology (very fresh lobate ejecta blankets, well preserved rim crests, and lack of superposed impact craters), 57 of these craters have been selected for detailed analysis of their spatial distribution and geometry. We find that south of 30°S, craters <6.0 km in diameter are markedly shallower than similar-sized craters equatorward of this latitude. No comparable relationship is observed for morphologically fresh craters >6.0 km diameter. We also find that two populations exist for older craters <6.0 km diameter. When craters that lack ejecta blankets are grouped on the basis of depth/diameter ratio, the deeper craters also typically lie equatorward of 30° S. We interpret the spatial variation in crater depth/diameter ratios as most likely due to a poleward increase in volatiles within the top 400 m of the surface at the times these craters were formed.  相似文献   

Stress Concentration at the Bottom of a Borehole and its Effect on Borehole Breakout Formation     

T. Ito  K. Kurosawa  K. Hayashi 《Rock Mechanics and Rock Engineering》1998,31(3):153-168

Summary Stress concentration at the bottom of a borehole due to the corners with small radius of curvature in an axial section and its effect on the azimuth of breakout was studied. To this end, a 3-D finite element analysis was conducted and the stress around the borehole was examined for boreholes arbitrarily oriented to three principal axes of remote stress. Results show that, in the case of high strength rock, compressive failure resulting in spalling of a borehole may occur only at the bottom of the borehole. The spalling can occur continuously with drilling, and results in continuous spalling with depth, i.e., a breakout. This type of breakout tends to form on one side of the borehole and its orientation is approximately perpendicular to the orientation of standard breakouts, inferred from the stress concentration due to the cylindrical shape of the borehole.  相似文献   

Melt water driven stream and groundwater stage fluctuations on a glacier forefield (Dammagletscher,Switzerland)          下载免费PDF全文

Jan Magnusson  Florian Kobierska  Stephan Huxol  Masaki Hayashi  Tobias Jonas  James W. Kirchner 《水文研究》2014,28(3):823-836

In many mountain regions, large land areas with heterogeneous soils have become ice‐free with the ongoing glacier retreat. On these recently formed proglacial fields, the melt of the remaining glaciers typically drives pronounced diurnal stream level fluctuations that propagate into the riparian zone. This behaviour was measured on the Damma glacier forefield in central Switzerland with stage recorders in the stream and groundwater monitoring wells along four transects. In spite of the large groundwater stage variations, radon measurements in the near‐stream riparian zone indicate that there is little mixing between stream water and groundwater on daily time scales. At all four transects, including both losing and gaining reaches, the groundwater level fluctuations lagged the stream stage variations and were often damped with distance from the stream. Similar behaviours have been modelled using the diffusion equation in coastal regions influenced by tidal sea level variations. We thus tested the ability of such a model to predict groundwater level fluctuations in proglacial fields. The model reproduced several key features of the observed fluctuations at three of four locations, although discrepancies also arise due to non representative input data and model simplifications. Nevertheless, calibration of the model for the individual transects yielded realistic estimates of hydraulic diffusivities between the stream and groundwater monitoring wells. We conclude that studying diurnal groundwater fluctuations can provide important information about the subsurface hydrology of alpine watersheds dominated by glacier melt. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Simulating preferential flow and snowmelt partitioning in seasonally frozen hillslopes     

Aaron A. Mohammed  Edwin E. Cey  Masaki Hayashi  Michael V. Callaghan 《水文研究》2021,35(8):e14277

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Watershed-scale response of groundwater recharge to inter-annual and inter-decadal variability in precipitation (Alberta,Canada)     

Masaki Hayashi  Christopher R. Farrow 《Hydrogeology Journal》2014,22(8):1825-1839

Groundwater recharge sets a constraint on aquifer water balance in the context of water management. Historical data on groundwater and other relevant hydrological processes can be used to understand the effects of climatic variability on recharge, but such data sets are rare. The climate of the Canadian prairies is characterized by large inter-annual and inter-decadal variability in precipitation, which provides opportunities to examine the response of groundwater recharge to changes in meteorological conditions. A decadal study was conducted in a small (250 km²) prairie watershed in Alberta, Canada. Relative magnitude of annual recharge, indicated by water-level rise, was significantly correlated with a combination of growing-season precipitation and snowmelt runoff, which drives depression-focussed infiltration of meltwater. Annual precipitation was greater than vapour flux at an experimental site in some years and smaller in other years. On average precipitation minus vapour flux was 10 mm y^?1, which was comparable to the magnitude of watershed-scale groundwater recharge estimated from creek baseflow. Average baseflow showed a distinct shift from a low value (4 mm y^?1) in 1982–1995 to a high value (15 mm y^?1) in 2003–2013, indicating the sensitivity of groundwater recharge to a decadal-scale variability of meteorological conditions.  相似文献   

High-resolution imaging polarimetry of HL Tau and magnetic field structure     

P. W. Lucas  Misato Fukagawa  Motohide Tamura  A. F. Beckford  Yoichi Itoh  Koji Murakawa  Hiroshi Suto  Saeko S. Hayashi  Yumiko Oasa  Takahiro Naoi  Yoshiyuki Doi  Noboru Ebizuka  Norio Kaifu 《Monthly notices of the Royal Astronomical Society》2004,352(4):1347-1364

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Aeolian dust experiment on climate impact: An overview of Japan–China joint project ADEC   总被引：1，自引：1，他引：0  

M. Mikami  G.Y. Shi  I. Uno  S. Yabuki  Y. Iwasaka  M. Yasui  T. Aoki  T.Y. Tanaka  Y. Kurosaki  K. Masuda  A. Uchiyama  A. Matsuki  T. Sakai  T. Takemi  M. Nakawo  N. Seino  M. Ishizuka  S. Satake  K. Fujita  Y. Hara  K. Kai  S. Kanayama  M. Hayashi  M. Du  Y. Kanai  Y. Yamada  X.Y. Zhang  Z. Shen  H. Zhou  O. Abe  T. Nagai  Y. Tsutsumi  M. Chiba  J. Suzuki 《Global and Planetary Change》2006,52(1-4):142

The Aeolian Dust Experiment on Climate Impact (ADEC) was initiated in April 2000 as a joint five-year Japan–China project. The goal was to understand the impact of aeolian dust on climate via radiative forcing (RF). Field experiments and numerical simulations were conducted from the source regions in northwestern China to the downwind region in Japan in order to understand wind erosion processes temporal and spatial distribution of dust during their long-range transportation chemical, physical, and optical properties of dust and the direct effect of radiative forcing due to dust. For this, three intensive observation periods (IOP) were conducted from April 2002 to April 2004.The in situ and network observation results are summarized as follows: (1) In situ observations of the wind erosion process revealed that the vertical profile of moving sand has a clear size dependency with height and saltation flux and that threshold wind velocity is dependent on soil moisture. Results also demonstrated that saltation flux is strongly dependent on the parent soil size distribution of the desert surface. (2) Both lidar observations and model simulations revealed a multiple dust layer in East Asia. A numerical simulation of a chemical transport model, CFORS, illustrated the elevated dust layer from the Taklimakan Desert and the lower dust layer from the Gobi Desert. The global-scale dust model, MASINGAR, also simulated the dust layer in the middle to upper free troposphere in East Asia, which originated from North Africa and the Middle East during a dust storm in March 2003. Raman lidar observations at Tsukuba, Japan, found the ice cloud associated with the dust layer at an altitude of 6 to 9 km. Analysis from lidar and the radio-sonde observation suggested that the Asian dust acted as ice nuclei at the ice-saturated region. These results suggest the importance of dust's climate impact via the indirect effect of radiative forcing due to the activation of dust into ice nuclei. (3) Studies on the aerosol concentration indicated that size distributions of aerosols in downwind regions have bimodal peaks. One peak was in the submicron range and the other in the supermicron range. The main soluble components of the supermicron peak were Na⁺, Ca²⁺, NO₃⁻, and Cl⁻. In the downwind region in Japan, the dust, sea salt, and a mixture of the two were found to be dominant in coarse particles in the mixed boundary layer. (4) Observation of the optical properties of dust by sky-radiometer, particle shoot absorption photometer (PSAP), and Nephelometer indicated that unpolluted dust at source region has a weaker absorption than originally believed.A sensitivity experiment of direct RF by dust indicated that single scattering albedo is the most important of the optical properties of dust and that the sensitivity of instantaneous RF in the shortwave region at the top of the atmosphere to the refractive index strongly depends on surface albedo. A global scale dust model, MASINGAR, was used for evaluation of direct RF due to dust. The results indicated the global mean RF at the top and the bottom of the atmosphere were − 0.46 and − 2.13 W m^− 2 with cloud and were almost half of the RF with cloud-free condition.  相似文献