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The interfacial structure of heptane and toluene at oil-silica interfaces has previously been studied by sum frequency generation [Z. Yang et al., J. Phys. Chem. C.113, 20355 (2009)]10.1021/jp9043122. It was found that the toluene molecule is almost perpendicular to the silicasurface with a tilt angle of about 25°. Here, we have investigated the structural properties of toluene and heptane at oil-silica interfaces using molecular dynamics simulations for two different surfaces: the oxygen-bridging (hydrophobic) and hydroxyl-terminated (hydrophilic)surfaces of quartz (silica). Based on the density profile, it was found that both heptane and toluene oscillate on silicasurfaces, with heptane showing more oscillation peaks. Furthermore, the toluene molecules of the first layer were found to have an asymmetric distribution of orientations, with more CH[3] groups pointed away from the silicasurface than towards the silicasurface. These findings are generally consistent with previous experiments, and reveal enhanced molecular structures of liquids at oil-silica interfaces.

The recent discovery that molecular CO[2] transforms under compression into carbon four-coordinated, 3-dimensional network solid phases has generated considerable interests on possible new phases in the fourth-main-group elemental oxides. Based on density-functional theory calculations, we have investigated the thermodynamic stability, mechanical properties and electronic structure of proposed guest-free clathrates, quartz and cristobalite phases for CO[2], SiO[2], and GeO[2], and the dry ice phase for CO[2]. It was predicted that a GeO[2]clathrate, likely a semiconductor, could be synthesized presumably with some suitable guest molecules. The hypothetical CO[2] guest-free clathrate phase was found hardly to be formed due to the large energy difference with respect to the other polymorphs. This phase is unstable at all pressures, which is also implied by its different electronic structure in comparison with SiO[2] and GeO[2]. Finally, the SiO[2]clathrate presents a uniquely high bulk modulus, which is higher than that of quartz and three times of the experimental data, might not be a weak point of ab-initio calculations such as pseudopotentials, correlation functional etc., instead it can be readily understood by the constraint as imposed by the high symmetry. Either temperature or an "exhausted" relaxation (without any symmetry constraint) can remedy this problem.

To reveal the extent of freezing in subglacial sediments, we estimated S-wave velocity along a glacier using surface-wave analysis. Because the S-wave velocity varies significantly with the degree of freezing of the pore fluid in the sediments, this information is useful for identifying unfrozen zones within subglacial sediments, which again is important for glacier dynamics. We used active-source multichannel seismic data originally acquired for reflection analysis along a glacier at Spitsbergen in the Norwegian Arctic and proposed an effective approach of multichannel analysis of surface waves (MASW) in a glacier environment. Common-midpoint crosscorrelation gathers were used for the MASW to improve lateral resolution because the glacier bed has a rough topology. We used multimode analysis with a genetic algorithm inversion to estimate the S-wave velocity due to the potential existence of a low-velocity layer beneath the glacier ice and the observation of higher modes in the dispersion curves. In the inversion, we included information of ice thickness derived from high-resolution ground-penetrating radar data because a simulation study demonstrated that the ice thickness was necessary to estimate accurate S-wave velocity distribution of deep subglacial sediment. The estimated S-wave velocity distribution along the seismic line indicated that low velocities occurred below the glacier, especially beneath thick ice (~1300 m/s for ice thicknesses larger than 50 m). Because this velocity was much lower than the velocity in pure ice (~1800 m/s), the pore fluid was partially melted at the ice–sediment interface. At the shallower subglacial sediments (ice thickness less than 50 m), the S-wave velocity was similar to that of the pure ice, suggesting that shallow subglacial sediments are more frozen than sediments beneath thick ice.

We estimated the changes in seismic velocity in the southern Tohoku district of Japan during the six-month period centered on the 11 March 2011 Tohoku-oki earthquake, using scattered waves retrieved by autocorrelation of ambient seismic noise. The estimated velocity decrease after the earthquake, and after two large aftershocks in the study area, was as great as 1.5% in the area nearest to the mainshock. The velocity changes displayed gradual healing. The spatial distribution of the velocity change showed a correlation with both the changes in static strain, derived from GPS records, and the peak particle velocity experienced during the three earthquakes, derived from strong-motion records. Therefore, our results show that velocity changes possibly contain information from deep in the crust bearing on coseismic stress release, in addition to shallower effects due to strong ground motion.

We apply the cross-coherence method to the seismic interferometry of traffic noise, which originates from roads and railways, to retrieve both body waves and surface-waves. Our preferred algorithm in the presence of highly variable and strong additive random noise uses cross-coherence, which uses normalization by the spectral amplitude of each of the traces, rather than crosscorrelation or deconvolution. This normalization suppresses the influence of additive noise and overcomes problems resulting from amplitude variations among input traces. By using only the phase information and ignoring amplitude information, the method effectively removes the source signature from the extracted response and yields a stable structural reconstruction even in the presence of strong noise. This algorithm is particularly effective where the relative amplitude among the original traces is highly variable from trace to trace. We use the extracted, reflected shear waves from the traffic noise data to construct a stacked and migrated image, and we use the extracted surface-waves (Love waves) to estimate the shear velocity as a function of depth. This profile agrees well with the interval velocity obtained from the normal moveout of the reflected shear waves constructed by seismic interferometry. These results are useful in a wide range of situations applicable to both geophysics and civil engineering.

Faults related to the tsunamigenic 2011 Tohoku-Oki Earthquake (Mw 9.0) were investigated by using multi-channel seismic reflection data acquired in 1999 and submersible seafloor observations from 2008. The location of the fault system interpreted in the seismic reflection profile is distributed around the area with largest slip and tsunami induction of the 2011 event. Cold-seep communities along the trace of the branch reverse fault and a high scarp associated with the trace of a normal fault suggest current activity on these faults. We interpret the fault system in the seismic profile as a shallow extension of the seismogenic fault that may have contributed to the resulting huge tsunami.

Crosswell reflection method is a high-resolution seismic imaging method that uses recordings between boreholes. The need for downhole sources is a restrictive factor in its application, for example, to time-lapse surveys. An alternative is to use surface sources in combination with seismic interferometry. Seismic interferometry (SI) could retrieve the reflection response at one of the boreholes as if from a source inside the other borehole. We investigate the applicability of SI for the retrieval of the reflection response between two boreholes using numerically modeled field data. We compare two SI approaches - crosscorrelation (CC) and multidimensional deconvolution (MDD). SI by MDD is less sensitive to underillumination from the source distribution, but requires inversion of the recordings at one of the receiver arrays from all the available sources. We find that the inversion problem is ill-posed, and propose to stabilize it using singular-value decomposition. The results show that the reflections from deep boundaries are retrieved very well using both the CC and MDD methods. Furthermore, the MDD results exhibit more realistic amplitudes than those from the CC method for downgoing reflections from shallow boundaries. We find that the results retrieved from the application of both methods to field data agree well with crosswell seismic-reflection data using borehole sources and with the logged P-wave velocity.