ANISOTROPIC TRAVELTIME TOMOGRAPHY

Velocity estimation technique using seismic data is often based on time/distance equations which are independent of direction, and even though we now know that many rocks are quite anisotropic, useful results have been obtained over the years from these isotropic estimates. Nevertheless, if velocities are significantly direction-dependent, then the isotropic assumption may lead to serious structural interpretation errors. Additionally, information on angle-dependence may lead to a better understanding of the lithology of the rocks under measurement. VSP and cross-well data may each lack the necessary aperture to estimate more than two velocity parameters for each wave type, and if the data straddle a symmetry axis, then these may be usefully chosen to be the direct velocities (from time-and-distance measurements along the axis) and NMO velocities (from differential time-offset measurements). These sets of two parameters define ellipses, and provide intermediate models for the variation of velocity with angle which can later be assembled and translated into estimates of the elastic moduli of the rocks under scrutiny. If the aperture of the measurements is large enough e.g. we have access to both VSP and cross-well data, we divide the procedure into two independent steps, first fitting best ellipses around one symmetry axis and then fitting another set around the orthogonal axis. These sets of four elliptical parameters are then combined into a new, double elliptical approximation. This approximation keeps the useful properties of elliptical anisotropy, in particular the simple relation between group and phase velocities which simplifies the route from the traveltimes measurements to the elastic constants of the medium. The inversion proposed in this paper is a simple extension of well-known isotropic schemes and it is conceptually identical for all wave types. Examples are shown to illustrate the application of the technique to cross-well synthetic and field P-wave data. The examples demonstrate three important points: (a) When velocity anisotropy is estimated by iterative techniques such as conjugate gradients, early termination of the iterations may produce artificial anisotropy. (b) Different components of the velocity are subject to different type of artifacts because of differences in ray coverage, (c) Even though most rocks do not have elliptical dispersion relations, our elliptical schemes represent a useful intermediate step in the full characterization of the elastic properties.     

Hillslope erosion measurement—a simple approach to a complex process

The measurement of hillslope erosion can be a difficult, costly and time‐consuming activity. Many techniques are available, ranging from using environmental tracers, to LiDAR. Erosion measurements using erosion pins are assessed and compared with regional scale erosion data, hillslope data obtained using ¹³⁷Cs and erosion modelling results. The pins produced erosion rates which are within the range determined using ¹³⁷Cs and model data but above that of regional denudation rates. Our findings demonstrate that inexpensive erosion pins can provide reliable data on hillslope erosion. © 2015 Commonwealth of Australia. Hydrological Processes © 2015 John Wiley & Sons Ltd.     

ASPI experiment: measurements of fields and waves on board the INTERBALL-1 spacecraft

The plasma-wave experiment ASPI (analysis of spectra of plasma waves and instabilities) on board the INTERBALL spacecraft is a combined wave diagnostics experiment. It performs measurements of the DC and AC magnetic field vector by flux-gate and searchcoil sensors, the DC and AC electric field vector by Langmuir double probes and the plasma current by Langmuir split probe. Preliminary data analysis shows the low noise levels of the sensors and the compatibility of new data with the results of previous missions. During several months of in-orbit operation a rich collection of data was acquired, examples of which at the magnetopause and plasma sheet are presented in second part of the paper.     

Estimating recharge rates with analytic element models and parameter estimation

Quantifying the spatial and temporal distribution of recharge is usually a prerequisite for effective ground water flow modeling. In this study, an analytic element (AE) code (GFLOW) was used with a nonlinear parameter estimation code (UCODE) to quantify the spatial and temporal distribution of recharge using measured base flows as calibration targets. The ease and flexibility of AE model construction and evaluation make this approach well suited for recharge estimation. An AE flow model of an undeveloped watershed in northern Wisconsin was optimized to match median annual base flows at four stream gages for 1996 to 2000 to demonstrate the approach. Initial optimizations that assumed a constant distributed recharge rate provided good matches (within 5%) to most of the annual base flow estimates, but discrepancies of >12% at certain gages suggested that a single value of recharge for the entire watershed is inappropriate. Subsequent optimizations that allowed for spatially distributed recharge zones based on the distribution of vegetation types improved the fit and confirmed that vegetation can influence spatial recharge variability in this watershed. Temporally, the annual recharge values varied >2.5-fold between 1996 and 2000 during which there was an observed 1.7-fold difference in annual precipitation, underscoring the influence of nonclimatic factors on interannual recharge variability for regional flow modeling. The final recharge values compared favorably with more labor-intensive field measurements of recharge and results from studies, supporting the utility of using linked AE-parameter estimation codes for recharge estimation.     

Attenuation relations for strong seismic ground motion in the Himalayan region

Strong motion data from various regions of India have been used to study attenuation characteristics of horizontal peak acceleration and velocity. The strong ground motion data base considered in the present work consists of various earthquakes recorded in the northern part of India since 1986 with magnitudes 5.7 to 7.2. Using these data, relations for horizontal peak acceleration and velocity, which are $$\begin{gathered} log_{10} a = 1.14 + 0.31M + 0.65log_{10} R \hfill \\ log_{10} v = 0.571 + 0.41M + 0.768log_{10} R \hfill \\ \end{gathered} $$ have been proposed wherea is the peak horizontal acceleration in cm/sec²,v is the peak horizontal velocity in mm/sec,M is body wave magnitude, andR is the hypocentral distance in km. The proposed relations are in reasonable agreement with the small amount of strong ground motion data available for the northern part of India. The present results will be useful in estimating strong ground motion parameters and in the earthquake resistant design in the Himalayan region.     

Geological interpretation of ply structure of the Bulli Seam,Sydney Basin,N.S.W.

The ply structure of the Bulli seam in the Southern Coalfield of the Sydney Basin persists over the main part of the coalfield. Lateral variations were investigated using both petrographic profiles and swelling index profile sections. The results indicated that the thickness pattern of the whole Bulli seam was affected by three independent factors: (1) post‐depositional loss of the top portion of the seam; (2) pre‐depositional topography; and (3) differential subsidence during deposition. The lack of definite correlation between seam thickness and present geological structure suggests that no local tectonic movement took place during deposition of the seam. Tectonic movement cannot, therefore, be the main cause of variation in seam thickness. Subsidence during deposition of the Bulli seam in the northeastern margin of the coalfield appears to have been too rapid, and near the western margin too slow, to form a thick coal seam. However, in the main part of the coalfield, the rate of subsidence was suitable for peat accumulation and a thick seam was deposited under stable conditions, as indicated by the persistent ply structure.     

Geochemistry of lower Jurassic shales of the Shemshak Formation, Kerman Province, Central Iran: Provenance, source weathering and tectonic setting

Lower Jurassic shales of the Shemshak Formation of Kerman Province, Central Iran, were analyzed for major and selected trace elements to infer their provenance, intensity of palaeoweathering of the source rocks and tectonic setting. Plots of shales on Al₂O₃ wt.% versus TiO₂ wt.% diagram and Cr (ppm) versus Ni (ppm) diagram indicate that acidic (granitic) rocks constitute the source rocks in the provenance. Average CIA, PIA and CIW values (84%, 92%, 93%, respectively) imply intense weathering of the source material. Plots of shales on bivariate discriminant function diagram reveal an active continental margin setting for the provenance. The inferred tectonic setting for the Lower Jurassic shales of the Shemshak Formation of Kerman Province is in agreement with the tectonic evolutionary history of the Central Iran during the Jurassic period.     

Considerations on the seismotectonics of the Northern Apennines

The Northern Apennines have been subdivided into homogeneous zones, on the basis of recent structural evolution and crustal structure, in which the earthquake distribution can find a coherent framework. These zones, whose physiography is in strict connection with their structure, are: the Internal Peri-Tyrrhenian Belt; the External or Main Belt; the Buried Belt; and the Pede-Alpine Homocline. Earthquake activity has a tendency to cluster along well-defined bands, particularly in the easternmost border of the Peri-Tyrrhenian Belt, as well as along the zone between the External Belt and the Buried Belt, i.e. along the Padanian margin of the Northern Apennines.A minimum of seismic activity seems to be correlated with some zones of the External Belt, as well as with the Late Tertiary and Quaternary magmatic province of Tyrrhenian Southern Tuscany.The fault-plane solutions are coherent with the structural picture.A tentative seismotectonic model of the Northern Apennines is discussed.     

The Structure and Formation Conditions of the Bedenekir Formation Deposits (Thithonian Stage) of Mountainous Crimea

The composition and origin of the Bedenekir Formation deposits of Mountainous Crimea are detailed on the basis of our work results and analysis of both published and unpublished data.     

Ultrahigh-pressure metamorphism in the forbidden zone: the Xugou garnet peridotite, Sulu terrane, eastern China

The Xugou garnet peridotite body of the southern Sulu ultrahigh‐pressure (UHP) terrane is enclosed in felsic gneiss, bounded by faults, and consists of harzburgite and lenses of garnet clinopyroxenite and eclogite. The peridotite is composed of variable amounts of olivine (Fo₉₁), enstatite (En_92?93), garnet (Alm_20?23Prp_53?58Knr_6?9Grs_12?18), diopside and rare chromite. The ultramafic protolith has a depleted residual mantle composition, indicated by a high‐Mg number, very low CaO, Al₂O₃ and total REE contents compared to primary mantle and other Sulu peridotites. Most garnet (Prp_44?58) clinopyroxenites are foliated. Except for rare kyanite‐bearing eclogitic bands, most eclogites contain a simple assemblage of garnet (Alm_29?34Prp_32?50Grs_15?39) + omphacite (Jd_24?36) + minor rutile. Clinopyroxenite and eclogite exhibit LREE‐depleted and LREE‐enriched patterns, respectively, but both have flat HREE patterns. Normalized La, Sm and Yb contents indicate that both eclogite and garnet clinopyroxenite formed by high‐pressure crystal accumulation (+ variable trapped melt) from melts resulting from two‐stage partial melting of a mantle source. Recrystallized textures and P–T estimates of 780–870 °C, 5–7 GPa and a metamorphic age of 231 ± 11 Ma indicate that both mafic and ultramafic protoliths experienced Triassic UHP metamorphism in the P–T forbidden zone with an extremely low thermal gradient (< 5 °C km^?1), and multistage retrograde recrystallization during exhumation. Develop of prehnite veins in clinopyroxenite, eclogite, felsic blocks and country rock gneiss, and replacements of eclogitic minerals by prehnite, albite, white mica, and K‐feldspar indicate low‐temperature metasomatism.