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The semi-annual report reflects the technical status of internal/ surface wave interaction and microstructure projects conducted within the Advanced Ocean Engineering Laboratory at the Scripps Institution of Oceanography. These projects are: Thermal Microstructure - to examine in detail the structure and dynamics of temperature and salinity; and Atmospheric Boundary Layer - to provide an understanding of the interaction between atmospheric boundary effects and surface waves.

To improve seismic calibration for nuclear explosion monitoring, we use 3D sensitivity kernels of finite-frequency body and surface waves to develop models of the crustal and mantle structures beneath eastern Eurasia. We have collected and processed available broadband data from both permanent stations and temporary networks in eastern Eurasia. We obtained a regional P-wave velocity model for the mantle structures down to 1,500 km beneath the eastern Eurasia. We also carried out a detailed study of the P- and S-wave velocity structures in southeastern Tibet, which led to some interesting geological findings. Our P- and S-wave velocity models reveal a low-velocity anomaly in the crust and upper mantle to 300 km depth beneath a north-south-trending rift zone in southeastern Tibet. This low-velocity anomaly is situated above a tabular, high- dipping-angle, high-velocity anomaly that extends into the upper-mantle transition zone. These results are evidence for the delamination of the mantle lithosphere and its causal relationship to the formation of the north-south trending rift in southeastern Tibet.

To improve seismic calibration for nuclear explosion monitoring, we use 3D sensitivity kernels of finite-frequency body and surface waves to develop models of the crustal and mantle structures beneath eastern Eurasia. We have collected and processed available broadband data from both permanent stations and temporary networks in eastern Eurasia. We obtained a regional P-wave velocity model for the mantle structures down to 1,500 km beneath the eastern Eurasia. We also carried out a detailed study of the P- and S-wave velocity structures in southeastern Tibet, which led to some interesting geological findings. Our P- and S-wave velocity models reveal a low-velocity anomaly in the crust and upper mantle to 300 km depth beneath a north-south-trending rift zone in southeastern Tibet. This low-velocity anomaly is situated above a tabular, high- dipping-angle, high-velocity anomaly that extends into the upper-mantle transition zone. These results are evidence for the delamination of the mantle lithosphere and its causal relationship to the formation of the north-south trending rift in southeastern Tibet.

Body wave travel-times, surface wave dispersion, and gravity data have been used to refine the structural details of the crust and upper mantle within the northern Basin and Range. The crust varies in thickness from 35-40 km SE of Reno to 28 km in the western Battle Mountain heat flow high and 45-50 km in central Oregon. The mantle lid structure derived from fundamental mode surface wave data has been confirmed by higher mode surface wave data. Fundamental and higher mode dispersion data for southern Nevada and Arizona indicate the structure of the southern Basin and Range is similar to that of the Great Basin.

We have developed and tested a set of three computer programs which yield path correction estimates from surface wave observations. The sequence of steps involved in estimating travel path effects on phase and amplitude of a surface wave are: Retrieval of phase and group velocity dispersion curves from the seismogram by phase matched filtering; extraction of spectral amplitudes by narrow-band filtering; removal of multipath arrivals; Inversion of dispersion curves in terms of an average structure along the path; Calculation of synthetic seismograms from the average structure; and Estimation of source moment and attenuation function from synthetic/observed spectral ratios.

We report x-ray reflectivity (XR) and small angle off-specular diffuse scattering (DS) measurements from the surface of liquid Indium close to its melting point of $156^\circ$C. From the XR measurements we extract the surface structure factor convolved with fluctuations in the height of the liquid surface. We present a model to describe DS that takes into account the surface structure factor, thermally excited capillary waves and the experimental resolution. The experimentally determined DS follows this model with no adjustable parameters, allowing the surface structure factor to be deconvolved from the thermally excited height fluctuations. The resulting local electron density profile displays exponentially decaying surface induced layering similar to that previously reported for Ga and Hg. We compare the details of the local electron density profiles of liquid In, which is a nearly free electron metal, and liquid Ga, which is considerably more covalent and shows directional bonding in the melt. The oscillatory density profiles have comparable amplitudes in both metals, but surface layering decays over a length scale of $3.5\pm 0.6$ \AA for In and $5.5\pm 0.4$ \AA for Ga. Upon controlled exposure to oxygen, no oxide monolayer is formed on the liquid In surface, unlike the passivating film formed on liquid Gallium.

Earlier study of Great Basin structure using surface waves have been extended to include the Southern Basin and Range of Arizona, and the Volcanic Plateau of Northern Nevada and Southern Oregon. The crust of the Southern Basin and Range is slightly thinner than that of the Great Basin while the mantle structure is similar. The Volcanic Plateau has a thicker crust (based on refraction data) than the Great Basin while the mantle lid zone is either thin or absent. (Author)

The main focus of the research reported on here is the development of new nonlinear Fourier spectral analysis methods, based upon the inverse scattering than form (IST), for analyzing measured time series of laboratory and oceanic wave trains. A major emphasis has been the use of the technique for the analysis of substantial quantities of wave data in order to better understand the nonlinear effects which are important in oceanic surface and internal wave fields. A secondary objective of the research has been the analysis of time series of measured wave trains for the effects of chaos and to contrast these results with nonlinear stochastic models. New data analysis procedures for the study of chaotic and stochastic dynamics in ocean waves have also been developed.