离散点数据自动绘制等深线方法探究

提出用反距离插值法将多波束离散数据点插值成规则格网DEM数据,再根据海图生产规范自动绘制不等间距相对光滑的DEM。将自动绘制的等深线与一般软件生成的等深线、海底地形图成果等深线进行比较分析得出：文中方法绘制的等深线相比以前有较大改善且更符合地形,可作为人工绘制的参考线。     

New seismogenic source and deep structures revealed by the 1999 Chia-yi earthquake sequence in southwestern Taiwan

In a tectonically active setting large earthquakes are always threats; however, they may also be useful in elucidating the subsurface geology. Instrumentally recorded seismicity is, therefore, widely utilized to extend our knowledge into the deeper crust, especially where basement is involved. It is because the earthquakes are triggered by underground stress changes that usually corresponding to the framework of geological structures. Hidden faults, therefore, can be recognized and their extension as well as orientation can be estimated. Both above are of relevance for assessment on seismic hazard of a region, since the active faults are supposed to be re-activated and cause large earthquakes. In this study, we analysed the 1999 October 22 earthquake sequence that occurred in southwestern Taiwan. Two major seismicity clusters were identified with spatial distribution between depths of 10 and 16 km. One cluster is nearly vertical and striking 032°, corresponding to the strike-slip Meishan fault (MSF) that generated the 1906 surface rupture. Another cluster strikes 190° and dips 64° to the west, which is interpreted as west-vergent reverse fault, in contrast to previous expectation of east vergence. Our analysis of the focal solutions of all the larger earthquakes in the 1999 sequence with the 3-D distribution of all the earthquakes over the period 1990–2004 allows us reinterpret the structural framework and suggest previously unreognized seismogenic sources in this area. We accordingly suggest: (1) multiple detachment faults are present in southwestern Taiwan coastal plain and (2) additional seismogenic sources consist of tear faults and backthrust faults in addition to sources associated with west-vergent fold-and-thrust belt.     

The reflection seismic survey of project TIPTEQ—the inventory of the Chilean subduction zone at 38.2° S

We describe results of an active-source seismology experiment across the Chilean subduction zone at 38.2°S. The seismic sections clearly show the subducted Nazca plate with varying reflectivity. Below the coast the plate interface occurs at 25 km depth as the sharp lower boundary of a 2–5 km thick, highly reflective region, which we interpret as the subduction channel, that is, a zone of subducted material with a velocity gradient with respect to the upper and lower plate. Further downdip along the seismogenic coupling zone the reflectivity decreases in the area of the presumed 1960 Valdivia hypocentre. The plate interface itself can be traced further down to depths of 50–60 km below the Central Valley. We observe strong reflectivity at the plate interface as well as in the continental mantle wedge. The sections also show a segmented forearc crust in the overriding South American plate. Major features in the accretionary wedge, such as the Lanalhue fault zone, can be identified. At the eastern end of the profile a bright west-dipping reflector lies perpendicular to the plate interface and may be linked to the volcanic arc.     

扬子地块西、北缘中元古代地层的划分与对比

广泛分布于扬子地块西缘和北缘的中元古代地层经历了强烈的变形和绿片岩相的变质改造。根据形成时代,该区的中元古代可以识别出两个阶段,中元古代早期(1.8~1.4Ga)和中元古代晚期(1.4~1.0Ga)。中元古代早期的地层包括大红山群、东川群、河口群和通安组(1~4段),中元古代晚期的地层主要由分布在扬子地块西南缘的昆阳群、会理群和分布于扬子地块北缘的神农架群和打鼓石群组成。新的锆石原位定年结果表明,通安组的凝灰岩形成于1744±14Ma左右,河口群角斑岩形成于1659±23Ma左右,侵入会理群天宝山组的辉长辉绿岩形成于1026±7Ma左右。根据岩石组合、形成环境以及年代学资料,中元古代早期的大红山群、东川群、河口群和通安组(1~4段)形成时代相近,地层组成基本相同,它们都含有与岩浆热液有关的铁氧化物铜金(IOCG)矿床或层状铜矿床(SSC),都在1.75~1.45Ga期间形成于大陆裂解环境。扬子地块北缘的火地垭群也可能属于中元古代早期地层。中元古代晚期地层在扬子地块西缘北缘均有分布,其中的昆阳群和会理群大体形成于1.2~1.0Ga,神农架群和打鼓石群形成于1.4~1.0Ga,它们的顶界可能延伸到新元古代早期。在中元古代晚期的地层中含有大量叠层石,表明它们形成于温暖潮湿的浅海环境。除上述的中元古代晚期地层之外,云南元谋地区的苴林群、川西的登相营群、通安组五段等也属于中元古代晚期的地层。     

一等水准点之记标准化与规范化研究

为保证一等水准点之记精度与质量,提高测绘人员野外工作效率,对目前的一等水准点之记进行了探讨与分析,指出了其详细位置图与点位,详细说明表达、标石断面图绘制和经纬度书写及交通路线描述中存在的缺点,并基于此提出了若干改进意见,这在一定程度上促进了一等水准点之记信息的标准化与规范化。     

绘图方式对直流电测深等值线断面图的影响

以一条测线的直流电测深资料为例,分别用人工和Surfer软件绘制出视电阻率等值线断面图进行比较,从而说明:正确地应用Surfer软件绘制等值线图非常重要,关键是网格化前对x、y值的表达方式以及选择那种插值方法,如何插值才能取得理想的效果,否则会直接影响资料解释,甚至会得出错误的结论。     

不等边基四边形的等距曲线设计

根据等距曲线的成形原理和几何特性,讨论了在有条件下的不等边基四边形等距曲线设计以及基四边形边长和形状的变化对等距曲线的影响,阐述了等距曲线的图形设计原则、轮廓曲线作图方法并加以证明,从而确定了不等边基四边形的设计作图范围和应用特性,扩展了机械传动机构型面联接中的等距曲线设计途径和方法。     

Area balancing as a test of models for the deep structure of mountain belts,with specific reference to the Alps

Basic concepts of structural restoration are applied to crustal cross-sections through mountain belts to explore large-scale tectonic models and deep structure. However, restored sections should account for variations in pre-orogenic crustal thicknesses. Crustal balancing approaches are reviewed and applied to two Alpine sections, coinciding with deep seismic experiments: NRP-20 East (Central Alps) and ECORS-CROP (Western Alps). Existing studies assume large (>300 km) orogenic contraction and only moderately thinned pre-orogenic crust. The resulting restored sections contain more crust than is imaged beneath the present-day Alps, the missing crust generally assumed to be subducted. Two kinematic modifications reduce the requirement for subduction: thinning and buoyancy-driven return flow of ultra-high-pressure metamorphic rocks during orogenesis; and pre-orogenic hyperextension. Using large stretching factors for the pre-orogenic crust negates crustal subduction on both Alpine transects. If the lower crust was approximately rigid, restorations of the Central Alps require strongly depth-heterogeneous stretching of upper and lower crust during Mesozoic rifting. Relaxing this requirement allows uniform lithospheric stretching, a corollary consistent with published subsidence estimates. Restorations make implicit statements on the form of pre-orogenic basins and the structure of continental margins incorporated into mountain belts that can in turn provide tests of tectonic models.