VELOCITY ANALYSIS IN THE p—x-PLANE FROM A SLANT STACK WAVEFIELD*

Classical methods of interpretation of reflection seismic data are such that interpretation and processing usually occur in the “collected” frame of reference. However, in recent times other data planes have gained increasing acceptance in seismology as a viable alternative. Through linear transformations applied to a record section, both the t—p- and p—x-planes can be produced. The r—p-domain may be obtained from the t—x-plane by a transformation known as slant stacking. Normal practice has been to do most of the data processing in the t—x-plane and then transforming to the r—p-plane. However, many of the procedures used in the t—x-domain can be modified for use in the t—p-plane to increase the coherence. Velocity inversion may be carried out either in the r—p-domain or further transformed to the p—x-plane where the modified Herglotz-Wiechert inversion may be applied. To perform the inversion, the t—p-wavefield is converted to a p—x-representation by the use of a new linear transformation technique, the cross-stack. By a simple sampling process along a particular p—x-trajectory, the Herglotz-Wiechert method can be used to reconstruct an acceptable velocity model of the subsurface. A comparison of derived velocity structures is made between that produced by the Herglotz-Wiechert technique and that of the Dix method.     

加拿大Sudbury地区地壳结构特征──AGT（1992）地震折射波资料初步解释

根据1992年加拿大岩石圈组织的Abitibi－GrenvilleTransect（AGT）实验计划中的高精度地震折射波资料的处理与解释,讨论了Sudbury地区的地壳结构特征对2条纵剖面及2条扇形剖面的地震折射波数据做了正反演计算．此外,应用层析成像技术对地震资料进行了处理根据数值计算结果,明确了该区Moho界面的变化形态并发现了Sudbury结构下部透镜状高速异常体的存在．     

Mudslides Developed on Waitemata Group Rocks, Tawharanui Peninsula, North Auckland

On Tawharanui Peninsula mudslides occur in soils developed on Waitemata Group flysch similar to that underlying much of the Auckland metropolitan area. Mudslides are shallow soil failures with a bowlshaped source area, an elongated track, and an accumulation zone. Movement may continue for decades to centuries. Modelling suggests that failure of saturated soils occurs along a basal surface defined by the regolith / bedrock contact; rates of movement and time of initiation have not been established. Reactivation or increased mobility of mudslides due to climatic change represents an increased hazard for infrastructure in Auckland City.     

Preface to the Special Issue: Climate Change and Variability of Tropical Cyclone Activity

Tropical cyclones(TCs) are one of the most destructive natural phenomena on Earth in terms of human-life and economic losses. It is currently a matter of prodigious public and scientific interest how TC activity has changed and will change in a warming climate. This special issue focuses on a challenging subject raised in the Intergovernmental Panel on Climate Change(IPCC) report and numerous research papers.     

桩基系统在地基液化和土体流动过程中的三维响应

松散的饱和砂土在液化之前可作为固体看待,但当过量的孔隙水压达到初始侧应力时它成为液体,之后又恢复其强度。这个过程不能各自单独处理,而应视为一个从固态到液态,或从液态到固态的连续变化过程。因此,整个伴随着地基液化———土体流动现象全过程应作为一个在固态和液态之间相变的系列过程。本文导出了一个简单的基本方程式,可以表达松散饱和砂土在液化和地基侧向滑移现象期间的固-液相转换。该基本方程式可用作桩基系统的动力分析,其适用性通过与弹塑性基本方程的比较得到验证。     

Association between Tropical Convection and Boreal Wintertime Extratropical Circulation in 1982／83 and 1988／89

Boreal wintertime extratropical circulation is studied in relation to the tropical convection during the 1982/83 El Nino and 1988/89 La Nina. The anomaly structure of 1982/83 and 1988/89 over the extratropics reveals remarkably different features as the longitudinal tropical forcing region changes. The Rossby wave source (Positive) shows the largest maximum over East Asia in both years due to the persistent heating from the western Pacific warm pool area. However, the sink term shows contrasting features over the subtropics and extratropics between the two years. In the El Nino year, enhanced tropical convection over the eastern Pacific produces the Rossby wave sink at 10?N and shifted eastward over the North Pacific, while in the La Nina year, the sink area is shifted westward over the North Pacific. The contrasting features between the two events in mean-eddy interaction appears especially over the downstream area of the East Asian Jet. The extension (retraction) of the meanflow eastward (westward) to     

The Hunghae Formation, SE Korea: Miocene debris aprons in a back-arc intraslope basin

ABSTRACT During early to middle Miocene times a sudden opening of the Ulleung (Tsushima) back-arc basin in the East Sea (Sea of Japan) led to the development of intraslope basins along the rifted southwestern margin (southeast Korea). Abrupt subsidence resulted in the deposition of the 200 m thick Hunghae Formation (middle Miocene), a sand/mudstone sequence that can be divided into five facies. Facies I (sand and mudstone couplet) and II (coarse sand) are turbiditic in origin, as evidenced by massive, graded, crudely-layered and parallel-laminated sand beds. Facies III (homogeneous mudstone) is characterized by various lignite and plant fragments, clastic and biogenic grains that are randomly oriented, suggestive of hemipelagic deposition. Facies IV (chaotic deposit) is characterized by the disruption of beds, the presence of isolated siltstone blocks (or balls) and large clasts in the muddy matrix, indicative of retrogressive rockfall and slide/slump. Facies V (conglomerate) is of debris flow origin, as evidenced by clast- and matrix-supported features, floating large clasts and absence of traction structures. Individual facies are organized into two types of facies association: (1) homogeneous mudstone (facies III) associated randomly with the rest (facies I, II, IV and V), indicative of hemipelagic and episodic sediment-gravity flow processes, respectively; (2) conglomerate (facies V), coarse sand (facies II) and sand/mudstone couplet (facies I), representing the flow transformation from debris flow to high- and low-concentration turbidity currents. These facies associations are similar in many respects to modern and ancient debris (or slope) aprons found elsewhere. Numerous isolated slide/slump blocks, wedged conglomerates with armoured mudstone balls, discontinuous lignite-containing sand/mudstone beds, chaotic structure and growth faults suggest that the deposition occurred on a steep slope (intraslope basin) off coalescing fan-deltas, mainly by unchannellized sediment-gravity flows. Ancient deposits with irregular facies sequences can be viewed as debris-apron systems, which provide alternatives to submarine-fan models in many clastic basins with a line rather than point source.     

Spatial Scale and the Geography of Tobacco Smoking in New Zealand: A Multilevel Perspective

Smoking in New Zealand is more common in deprived areas and in areas with a significant Maori population. Despite its status as a major health problem there has been little work investigating this apparent geography of smoking Data from the 1996 Census is used to construct a multilevel ‘proportions‐as‐responses’ model of smoking prevalence. This enables an exploration of the geography of smoking at different spatial scales. Levels within the model distinguish contextual variation between local authorities, census area units and meshblocks. Particular account is taken of the influence of deprivation and ethnicity on smoking. Results confirm the importance of ethnicity and deprivation and indicate that cross‐level interaction between meshblock and census area unit measures is significant. They also challenge crude stereotypes about the apparent geography of smoking and suggest that, while levels of smoking may be high in parts of North Island, they are less high than might be expected given the socio‐demographic composition of the areas concerned. Conversely, smoking is more prevalent than expected in parts of South Island. The paper notes the health policy implications of these emergent geographies.     

High voltage electron microscopy of fine quartz particles from Norwegian marine clay

The high voltage electron microscope allows the internal structure of fine quartz sediment particles to be examined. With high accelerating voltages sufficient penetration is obtained for actual particles to be directly examined in the transmission mode. Dislocations have been observed and also various substructures—indicated by Moire patterns—some of which may be due to Dauphine twinning. Some areas of great distortion have been observed at particle edges, but a certain degree of crystallinity appears to be retained.