Resistivity inversion of cross-hole and borehole-to-surface EM data using axially symmetric models1

We describe a least-squares inversion approach to estimating the subsurface resistivity structure from cross-hole or borehole-to-surface electromagnetic data. It is assumed that the resistivity distribution is symmetric about the axis of a borehole and that vertical magnetic dipoles are located on the borehole axis. The receivers are placed either in another borehole or on the earth's surface. The inversion scheme uses the finite-element and smoothness-constrained least-squares methods. The computational effort required to obtain partial derivatives is reduced considerably by using the reciprocity principle. Numerical simulations show that the reconstructions are generally in good agreement with the true structures when the assumption of an axisymmetric earth structure holds. An example involving the breakdown of this assumption, which can be obtained by interchanging the source and receiver boreholes, suggests that the inversion result may also be useful for locating a general 3D anomaly although artifacts are present.     

Assessment of uncertainties related to seismic hazard using fuzzy analysis

Seismic hazard analysis in the last few decades has become a very important issue. Recently, new technologies and available data have been improved that have helped many scientists to understand where and why earthquakes happen, the physics of earthquakes, etc. Scientists have begun to understand the role of uncertainty in seismic hazard analysis. However, how to handle existing uncertainty is still a significant problem. The same lack of information causes difficulties in quantifying uncertainty accurately. Usually, attenuation curves are obtained in a statistical manner: regression analysis. Statistical and probabilistic analyses show overlapping results for the site coefficients. This overlapping takes place not only at the border between two neighboring classes but also among more than three classes. Although the analysis starts from classifying sites using geological terms, these site coefficients are not classified at all. In the present study, this problem is solved using fuzzy set theory. Using membership functions, the ambiguities at the border between neighboring classes can be avoided. Fuzzy set theory is performed for southern California in the conventional way. In this study, standard deviations that show variations between each site class obtained by fuzzy set theory and the classical manner are compared. Results of this analysis show that when we have insufficient data for hazard assessment, site classification based on fuzzy set theory shows values of standard deviations less than those obtained using the classical way, which is direct proof of less uncertainty.     

Consistency of the spatial autocorrelation method with seismic interferometry and its consequence

We have cross‐checked the conventional theory of the spatial autocorrelation method and the consequence of seismic interferometry: the retrieval of the elastodynamic Green's function. Their mutual consistency is almost complete. The basic formulas of the conventional spatial autocorrelation theory can be derived by an alternative approach based on the retrieval of the elastodynamic Green's function. The only discrepancy is found with the average of the complex coherence function over azimuth in a wavefield dependent on azimuth. It is hypothesized, in discussion, that this discrepancy is due to the way of representing the wavefield in the background theory of seismic interferometry that can produce only wavefields moderately dependent on azimuth and that the mentioned consequence of seismic interferometry can also only make sense in a wavefield moderately dependent on azimuth. Our field experiment with a wavefield dependent on azimuth showed that the consequence of seismic interferometry in the logical framework of the conventional spatial autocorrelation theory is appropriate under such degrees of approximation as the measure proposed in this study, i.e., the deviation of the total dispersion curves is between about 10 and 16 per cent at the maximum from those averaged over azimuth. The acceptance of the retrieval of Green's function gives a proper physical meaning to the complex coherence function: the real part of the elastodynamic Green's function normalized by its zero‐offset version. This makes it possible to take a deterministic approach rather than the statistical one on which the conventional spatial autocorrelation method is based and gives fruitful new aspects and perspectives. For example, the formula for the multi‐mode case is given and the possibility of exploration of two or three dimensional velocity structures is suggested.     

Estimation of sensible heat flux by a hybrid method of temperature profile and light-beam deflection

A new method of sensible heat flux estimation by a hybrid use of temperature profile and light-beam deflection is proposed and tested over an asphalt pavement on fine days.A helium-neon gas laser with wavelength 0.6328 m was used as a light-beam source. Temperature gradient near the surface was measured by the deflection of a light-beam propagated nearly horizontally at a distance of 25 m. Measurement of the air temperature profile in the upper part of the surface layer was made by means of a copper-constantan thermocouple thermometer. The sensible heat flux was estimated from the temperature profile using profile-flux relationships.The surface temperature of the asphalt pavement rose to as high as 63 °C in the daytime and never decreased below the air temperature even in the morning in summer. The maximum value of heat flux obtained from this observation attained 365 W m^-2, which was about 48% of incoming solar radiation.     

An assessment of uncertainties in VS profiles obtained from microtremor observations in the phased 2018 COSMOS blind trials

Journal of Seismology - Site response is a critical consideration when assessing earthquake hazards. Site characterization is key to understanding site effects as influenced by seismic site...     

Tropical cyclone genesis frequency over the western North Pacific simulated in medium-resolution coupled general circulation models

This study examines the tropical cyclone (TC) genesis frequency over the western North Pacific simulated in atmosphere–ocean coupled general circulation models from the World Climate Research Programme’s Coupled Model Intercomparison Project phase 3. We first evaluate performances of eight models with atmospheric horizontal resolution of T63 or T106 by analyzing their daily-mean atmospheric outputs of twentieth-century climate simulations available from the Program for Climate Model Diagnosis and Intercomparison database. The genesis frequency is validated against the best-track data issued by the Japan Meteorological Agency. Five of the eight models reproduce realistic horizontal distribution of the TC genesis with a large fraction over the 10°–20°N, 120°–150°E area. These five high-performance models also realistically simulate the summer–winter contrast of the frequency. However, detailed seasonal march is slightly unrealistic; four of the models overestimate the frequency in the early season (May–June) while all of them underestimate the frequency in the mature season (July–September). Reasons for these biases in the seasonal march for the five high-performance models are discussed using the TC genesis potential (GP) index proposed by Emanuel and Nolan (in Am Meteor Soc, pp 240–241, 2004). The simulated GP has seasonal biases consistent with those of the TC genesis frequency. For all five models, the seasonal biases in GP are consistent with those in environmental lower-tropospheric vorticity, vertical wind shear, and relative humidity, which can be attributed to the simulated behavior of monsoon trough. The observed trough migrates northward from the equatorial region to reach the 10°–20°N latitudinal band during the mature season and contributes to the TC frequency maximum, whereas the simulated trough migrates northward too rapidly and reaches this latitude band in the early season, leading to the overestimation of the TC genesis frequency. In the mature season, the simulated trough reaches as far as 15°–25°N, accompanied by a strong vertical shear south of the trough, providing an unfavorable condition for TC genesis. It is concluded that an adequate simulation of the monsoon trough behavior is essential for a better reproduction of the TC frequency seasonal march.     

A Reynolds-averaged turbulence modelling approach to the maintenance of the Venus superrotation

Abstract

A maintenance mechanism of an approximately linear velocity profile of the Venus zonal flow or superrotation is explored, with the aid of a Reynolds-averaged turbulence modelling approach. The basic framework is similar to that of Gierasch (Meridional circulation and maintenance of the Venus atmospheric rotation. J. Atmos. Sci. 1975, 32, 1038–1044) in the sense that the mechanism is examined under a given meridional circulation. The profile mimicking the observations of the flow is initially assumed, and its maintenance mechanism in the presence of turbulence effects is investigated from a viewpoint of the suppression of energy cascade. In the present work, the turbulent viscosity is regarded as an indicator of the intensity of the cascade. A novelty of this formalism is the use of the isotropic turbulent viscosity based on a non-local time scale linked to a large-scale flow structure. The mechanism is first discussed qualitatively. On the basis of these discussions, the two-dimensional numerical simulation of the proposed model is performed, with an initially assumed superrotation, and the fast zonal flow is shown to be maintained, compared with the turbulent viscosity lacking the non-local time scale. The relationship of the present model with the current general circulation model simulation is discussed in light of a crucial role of the vertical viscosity.     

Carbon deflagration models for type-I supernovae and theoretical optical spectra

A carbon deflagration model in the accreting C+O white dwarf is presented as a plausible model for type-I supernovae (SN I). The evolution of the white dwarf is calculated from the beginning of accretion through complete disruption. The propagation of a carbon deflagration wave from center to the surface and associated nucleosynthesis are calculated. About 0.6M ⁵⁶Ni and substantial amounts of Ca, Ar, S, Si, Mg, and O are synthesized.The synthetic spectrum at maximum light for this carbon deflagration model is calculated and compared to the observed spectrum of SN 1981b in NGC 4536 at maximum light. If the radial stratification of composition in the outer layers of the model is removed by mixing, the theoretical spectrum is in good agreement with the observed spectrum.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.