Comparing shear-wave velocity profiles inverted from multichannel surface wave with borehole measurements

Recent field tests illustrate the accuracy and consistency of calculating near-surface shear (S)-wave velocities using multichannel analysis of surface waves (MASW). S-wave velocity profiles (S-wave velocity vs. depth) derived from MASW compared favorably to direct borehole measurements at sites in Kansas, British Columbia, and Wyoming. Effects of changing the total number of recording channels, sampling interval, source offset, and receiver spacing on the inverted S-wave velocity were studied at a test site in Lawrence, Kansas. On the average, the difference between MASW calculated V_s and borehole measured V_s in eight wells along the Fraser River in Vancouver, Canada was less than 15%. One of the eight wells was a blind test well with the calculated overall difference between MASW and borehole measurements less than 9%. No systematic differences were observed in derived V_s values from any of the eight test sites. Surface wave analysis performed on surface data from Wyoming provided S-wave velocities in near-surface materials. Velocity profiles from MASW were confirmed by measurements based on suspension log analysis.     

Orientation of framboidal pyrite in shale

Ordered framboids from Devonian Chattanooga Shale (U.S.A.) and Rammelsberg Banderz (Germany) show a common orientation in any one sample. This observation was made using a stereographic method of reconstruction in which the lineations within the framboids were measured on each of three planes cut mutually at right angles from the rock samples. The explanation for this preferred orientation is not yet known, but it may originate from crystal-growth during compaction of the shales.

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Zusammenfassung Pyrit-Himbeeren aus dem devonischen Chattanooga Shale (U.S.A.) und vom Rammelsberg Banderz zeigen bevorzugte Orientierungen ihrer inneren Struktur (Figure I) gegenüber der Sedimentschichtung. Diese Beobachtungen sind in stereographischen Projektionen aufgezeichnet. Der Vorgang der Orientierung mag auf die Kristallisation der Pyrit-Netzwerke während der Diagenese zurückzuführen sein.

     

Cyclic nature of lamination in the Tithonian Solnhofen Plattenkalk of southern Germany and its palaeoclimatic implications

In the Tithonian Solnhofen Plattenkalk (Malm + 2) of southern Germany, layers of purely micritic limestone are rhythmically interbedded with ones of marly micritic limestone. It appears that this alternation was formed under control of the Tithonian orbital variations. The Fourier spectral analysis shows that, on a decimetric to metric scale, the long-term cyclicities in the number of laminae per centimetre are in agreement with those found in the bed-thickness series, varying from 0.7 to 1.3 m cycles. The number of laminae of the Solnhofen Formation ranges from about 5,800 to about 12,800 laminae per main cycle. This indicates that, under an assumption that the main cycle of the Solnhofen Formation corresponds to the Tithonian precessional one, a single lamina represents a multi-year time interval. Particularly, in the short-term cyclic domain, the laminated sequence contains clearly millimetric cycles consisting of about two to three cyclic components. It implies that laminae formation may result from the composite effect of two or three distinct climatic processes.     

Deposition of coarse-grained sediments in the Korea Strait during late Pleistocene low sea level

The wide area of the Korea Strait shelf is covered by a thin veneer of gravelly sands, sands, or muddy sands. Most gravels are sub- to well-rounded and their content reaches up to 25%. These sediments were derived from the Korean Peninsula through the paleochannel of the Nakdong River, which extended onto the mid-shelf during late Pleistocene low sea level. The gravel distribution pattern suggests reworking and transport of the sediments by strong currents during times of low sea level.     

Computer Simulation of Coastal Acoustic Tomography by a Two-Dimensional Vortex Model

Computer simulation of coastal acoustic tomography with four, five, seven and nine stations was applied to two-dimensional vortex fields of horizontal domain 5 km × 5 km. Travel time data obtained in reciprocal directions between all pairs of acoustic stations were analyzed to reconstruct the vortex fields by the stochastic inverse method, reduced to the damped least squares method. The weighting factor appearing in the inverse analysis was determined by applying the L-curve method, in which a point making both the size of estimated error ‖y - Ex‖ and solution ‖x‖ as small as possible in a balance is specified as an optimum. The performance of this method was examined using two-dimensional vortex models which have different wavenumber spectra and adding the random error of different levels to the travel time difference data y. This study suggests that in the selection of the optimal weighting factor the horizontal section of the simulated tidal vortex fields can be well reconstructed by the coastal acoustic tomography system composed of five to seven acoustic stations located in the periphery of the vortex fields. This revised version was published online in August 2006 with corrections to the Cover Date.