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Abstract: We analyzed gravity data obtained in Juneau and global positioning system (GPS) data obtained from three PBO sites in southeastern Alaska (SE-AK), which are part of a US research facility called ‘EarthScope’, and we compared the obtained tidal amplitudes and phases with those estimated from the predicted tides including both effects of the body tide and ocean tide. Global tide models predict the ocean tides in this region of complex coastline and bathymetry. To improve the accuracy of prediction, we developed a regional ocean tide model in SE-AK. Our comparison results suggest: (1) by taking into account the ocean tide effect, the amplitude differences between the observation and the predicted body tide is remarkably reduced for both the gravity and displacement (e.g. for the M2 constituent, 8.5–0.3μGal, and 2.4–0.1cm at the AB50 GPS site in Juneau in terms of the vector sum of three components of the north–south, east–west and up–down), even though the ocean tide loading is large in SE-AK. (2) We have confirmed the precise point positioning (PPP) method, which was used to extract the tidal signals from the original GPS time series, works well to recover the tidal signals. Although the GPS analysis results still contain noise due to the atmosphere and multipath, we may conclude that the GPS observation surely detects the tidal signals with the sub-centimeter accuracy or better for some of the tidal constituents. (3) In order to increase the accuracy of the tidal prediction in SE-AK, it is indispensable to improve the regional ocean tide model developed in this study, especially for the phase. [Copyright &y& Elsevier]

The array measurements of microtremors were carried out at nine sites to estimate the subsurface S-wave velocity (β) structures of the sedimentary deposits beneath the metropolitan area of Anchorage, Alaska. The data were recorded by ten three-component accelerometers arranged in a triangular manner for three different array sizes. The phase velocities (C(f)) were estimated at each site from the vertical component of the recorded microtremor data by using the frequency-wavenumber technique. The C(f) data from different arrays were combined after checking their consistency for a series of overlapped frequency bands from different arrays and were inverted using a stochastic least-squares inversion technique to estimate the 1D β-structure underneath each site. The inversion results show that the engineering basement (β >750 m/sec) lies at a relatively shallower depth (∼40 m) in the eastern part of the basin along the foothills of the Chugach Mountains (CM) and at deeper depths toward the southcentral (∼100 m) and western (∼150 m) parts of the basin in accord with the general dip of the basin. Below the engineering basement, a well-developed low-velocity zone (LVZ) with β-values in the range of 900-1040 m/sec is found to be present in the eastern as well as along the Knik Arm side in the western part of the basin at a depth of 200 m and 900 m, respectively. Moreover, the central part of the basin is associated with a weakly developed LVZ below the engineering basement depth. In the rest of the basin, the β-value increases gradually with depth. The spatial variations of β in the basin at different depths from 20 to 500 m are represented by using 2D interpolation of the β-structures obtained from the inversion of C(f) data. The depth to the crystalline basement of the basin, however, could not be ascertained and it seems to be much deeper than the maximum depth (2000 m) resolved by the data gathered in this study. To validate the results of inversion, the spectral ratio between the horizontal and vertical components (H/V) of the recorded microtremor data at each site has been compared with the computed H/V of Rayleigh waves based on the respective β-structure. The results showed good agreement in the frequency range of about 0.4-6.0 Hz. In this frequency range, the H/V peaks are due to the overall effect of the velocity contrasts between layers representing the subsurface β-structure. [ABSTRACT FROM AUTHOR]