Results of a sea-floor electromagnetic survey over a sedimented hydrothermal area on the Juan de Fuca Ridge     

D. C. Nobes  L. K. Law  R. N. Edwards 《Geophysical Journal International》1992,110(2):333-346

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选取岭参数的一个新方法   总被引：2，自引：1，他引：1  

归庆明 《测绘工程》1997,6(1):14-19

当法方程的系数阵呈病态时,平差参数的最小二乘估计不再是一个良好好估计。为改进最小二乘估计,许多学者提出众多的有偏估计方法,其中影响最大的是岭估计和主要估计。  相似文献   

Bathymetry of the Reykjanes Ridge     

Keeton  J. A.  Searle  R. C.  Peirce  C.  Parsons  B.  White  R. S.  Sinha  M. C.  Murton  B. J.  Parson  L. M. 《Marine Geophysical Researches》1997,19(1):55-64

We present a series of 1:200,000 scale maps of the bathymetry of the Reykjanes Ridge. The data are divided into four maps, extending 630 km along the ridge axis and between 30 and 100 km off-axis. This compilation of bathymetry data is extremely detailed, gridded at approximately 100 m resolution, and with almost no gaps. The Reykjanes Ridge is one of the best examples of a hotspot-dominated ridge, whose characteristics are influenced by its proximity to the Iceland plume. Many fundamental questions may be addressed at the Reykjanes Ridge, which is why the BRIDGE programme identified it as one of its four regional projects. These maps represent a BRIDGE contribution to the general scientific community.  相似文献   

Structural analysis of the segmentation of the Central Indian Ridge between 20°30′S and 25°30′S (Rodriguez Triple Junction)     

Anne Briais 《Marine Geophysical Researches》1995,17(5):431-467

The morphological characteristics of the segmentation of the Central Indian Ridge (CIR) from the Indian Ocean Triple Junction (25°30S) to the Egeria Transform Fault system (20°30S) are analyzed. The compilation of Sea Beam data from R/VSonne cruises SO43 and SO52, and R/VCharcot cruises Rodriguez 1 and 2 provides an almost continuous bathymetric coverage of a 450-km-long section of the ridge axis. The bathymetric data are combined with a GLORIA side-scan sonar swath to visualize the fabric of the ridge and complement the coverage in some areas. This section of the CIR has a full spreading rate of about 50 mm yr^–1, increasing slightly from north to south. The morphology of the CIR is generally similar to that of a slow-spreading center, despite an intermediate spreading rate at these latitudes. The axis is marked by an axial valley 5–35 km wide and 500–1800 m deep, sometimes exhibiting a 100–600 m-high neovolcanic ridge. It is offset by only one 40km offset transform fault (at 22°40S), and by nine second-order discontinuities, with offsets varying from 4 to 21 km, separating segments 28 to 85 km long. The bathymetry analysis and an empirical orthogonal function analysis performed on across-axis profiles reveal morphologic variations in the axis and the second-order discontinuities. The ridge axis deepens and the relief across the axial valley increases from north to south. The discontinuities observed south of 22°S all have morphologies similar to those of the slow-spreading Mid-Atlantic Ridge. North of 22°S, two discontinuities have map geometries that have not been observed previously on slow-spreading ridges. The axial valleys overlap, and their tips curve toward the adjacent segment. The overlap distance is 2 to 4 times greater than the offset. Based on these characteristics, these discontinuities resemble overlapping spreading centers (OSCs) described on the fast-spreading EPR. The evolution of one such discontinuity appears to decapitate a nearby segment, as observed for the evolution of some OSCs on the EPR. These morphological variations of the CIR axis may be explained by an increase in the crustal thickness in the north of the study area relative to the Triple Junction area. Variations in crustal thickness could be related to a broad bathymetric anomaly centered at 19°S, 65°E, which probably reflects the effect of the nearby Réunion hotspot, or an anomaly in the composition of the mantle beneath the ridge near 19°S. Other explanations for the morphological variations include the termination of the CIR at the Rodriguez Triple Junction or the kinematic evolution of the triple junction and its resultant lengthening of the CIR. These latter effects are more likely to account for the axial morphology near the Triple Junction than for the long-wavelength morphological variation.  相似文献   

Second-order ridge axis discontinuities in the south Atlantic: Morphology,structure, and evolution   总被引：1，自引：0，他引：1  

N. R. Grindlay  P. J. Fox  K. C. MacDonald 《Marine Geophysical Researches》1991,13(1):21-49

Continuous along-axis Sea Beam coverage of the slow-intermediate spreading (34–38 mm yr⁻¹ full rate) southern Mid-Atlantic Ridge (25°–27°30′S and 31°–38° S) shows that the ridge axis is segmented by both rigid and non-rigid discontinuities. Following the model of Macdonald et al. (1988b), a hierarchy of four orders is proposed for ridge axis discontinuities based on a continuum of relative age and distance offset across the discontinuites. This paper discusses the characteristics associated with five second-order discontinuities found in the areas surveyed. First-order discontinuities represent rigid offsets, transform faults, whereas non-rigid discontinuities fall into the second, third and fourth orders. Like transform fault boundaries, second-order discontinuities have distinctive morphologic signatures both on and off-axis-discordant zones — and therefore are better defined than third- or fourth-order discontinuities. Second-order discontinuities are offsets that range in distance from less than 10 km to approximately 30 km and vary in age offset from 0.5 to approximately 2.0 m.y. The variable morphotectonic geometries associated with these discontinuities indicate that horizontal shear strains are accommodated by both extensional and strike-slip tectonism and that the geometries are unstable in time. Three characteristic geometries are recognized: (1)en echelon jog in the plate boundary where ridge axis tips overlap slightly, (2)en echelon jog in the plate boundary where ridge axes are separated by an extensional basin whose long axis is oriented parallel to the strike of the adjoining ridge axes, and (3) oblique offset characterized by a large extensional basin that is oriented approximately 45° to the strike of the ridge axes. In the case of the third type, evidence for short strands of strike-slip tectonism that link an obliquely oriented extensional basin flanking ridge tips is often apparent. Analysis of the detailed bathymetric and magnetic data collected over the second-order discontinuities and their off axis terrain out to 5–7 m.y. documents that second-order discontinuities can follow several evolutionary paths: they can evolve from transform fault boundaries through prolonged asymmetric spreading, they may migrate along strike leaving a V-shaped wake, and they may remain in approximately the same position but oscillate slightly back and forth. In addition, a small change in the pole of relative motion occurring 4–5 Ma is thought to have resulted in the initiation of at least one second-order discontinuity in the survey area. A geologic model is proposed which involves the interplay of lithospheric thickness, asymmetric spreading, temporal and spatial variability of along-axis magmatic input and changes in the poles of relative motion to explain the origin, morphology and evolution of second-order ridge axis discontinuities.  相似文献   

Structure and Stability of Non-Transform Discontinuities on the Mid-Atlantic Ridge between 24° N and 30° N     

Sara Spencer  Deborah K. Smith  Johnson R. Cann  Jian Lin  Edward McAllister 《Marine Geophysical Researches》1997,19(4):339-362

Observations of the median valley within the 24–30° N area ofthe Mid-Atlantic Ridge (MAR), using the IOSDL high resolutionside-scan sonar instrument TOBI, image four separate areas of themedian valley, containing part or all of nine spreading segments, and fivenon-transform discontinuities between spreading segments (NTDs).These high resolution side scan images were interpreted in parallel withmultibeam bathymetry (Purdy et al., 1990), giving a greater degree ofstructural precision than is possible with the multibeam data alone. Threedistinct types of NTD were identified, corresponding in part to typespreviously identified from the multibeam bathymetric survey of the area.Type 1 NTDs are termed septal offsets, and are marked by a topographic ridgeseparating the two spreading segments. The offset between the spreadingsegments ranges from 9 to 14 km. These can be further subdivided into Type1A in which the septa run parallel to the overall trend of the MAR and Type1B in which the septa lie at a high angle to the bulk ridge trend. Type 1ANTDs are characterised by overlap of the neovolcanic zones of the segmentson each side, and strong offaxis traces, while Type 1B NTDs show no overlapof neovolcanic zones, and weak offaxis traces. Type 2 NTDs arebrittle/ductile extensional shear zones, marked by oblique extensionalfractures, and associated with rotation of tectonic and volcanic structuresaway from the overall trend of the MAR. Type 3 NTDs are associated withoffsets of less than 5 km, and show no sign of any accommodating structure.In this type of NTD, the offset zone is covered with undeformed volcanics.The type of NTD developed at any locality along the ridge axis appears todepend on the amount of segment offset and segment overlap, the overalltrend of the mid-ocean ridge, the width of the zone of discontinuity, themedian valley offset and the longevity of the offset. These factorsinfluence the mechanical properties of the lithosphere across thediscontinuity, and ultimately the tectonic style of the NTD that can besupported. Thus brittle/ductile extensional shear zones are long-livedstructures favoured by large segment offsets, and small or negative segmentoverlaps. Septa can be short or long lived, and are associated with largesegment offsets. Segment overlaps vary from negative (an along axis gap) tozero, for Type 1B septal offsets, or positive to zero for Type 1A septaloffsets. Non-tectonised NTDs are generally short lived structures,characterised by small segment offsets and zero or positive overlaps.  相似文献   

The Bremen ocean bottom tiltmeter (OBT) – a technical article on a new instrument to monitor deep sea floor deformation and seismicity level     

Marcus Fabian  Heinrich Villinger 《Marine Geophysical Researches》2007,28(1):13-26

The Bremen ocean bottom tiltmeter is a new 6000 m-depth deep sea instrument for autonomous observation of sea floor tilt with signal periods longer than 7.5 s. The instrument also records vertical acceleration in the frequency range from DC to 1 Hz. The tiltmeter has an Applied Geomechanics Inc. 756 wide angle biaxial bubble tilt sensor with a resolution of 1.0μ rad (0.2 arc second). A Kistler Corp. MEMS accelerometer of type Servo K-Beam 8330A2.5 with about 10⁻⁵m/s² resolution is used for the acceleration measurements. An Oceanographic Embedded Systems AD24 24 bit Sigma-Delta converter, which is controlled by a low-power Persistor Inc. embedded computer system of type CF 2, samples the data. The duration of tiltmeter operation is more than one year, which is controlled by the battery life. In our design the tiltmeter does not need active leveling devices, i.e., servo motors or other moving components to adjust sensors or frame. We designed the instrument for deployments by means of a remote operated vehicle. Since May 2005 the Bremen ocean bottom tiltmeter has recorded sea floor deformation and seismicity level in the Logatchev hydrothermal vent field, Mid-Atlantic Ridge. The tiltmeter is a part of the monitoring system of project ‘Logatchev Long-Term Environmental Monitoring,’ called LOLEM, of the German research program with the name ‘Schwerpunktprogramm 1144: Vom Mantel zum Ozean.’  相似文献   

Two- and three-dimensional inversions of magnetic anomalies in the MARK area (Mid-Atlantic Ridge 23° N)     

Norbert J. Schulz  Robert S. Detrick  Stephen P. Miller 《Marine Geophysical Researches》1988,10(1-2):41-57

Magnetic data collected in conjunction with a Sea Beam bathymetric survey of the Mid-Atlantic Ridge south of the Kane Fracture Zone are used to constrain the spreading history of this area over the past 3 Ma. Two-dimensional forward modeling and inversion techniques are carried out, as well as a full three-dimensional inversion of the anomaly field along a 90-km-long section of the rift valley. Our results indicate that this portion of the Mid-Atlantic Ridge, known as the MARK area, consists of two distinct spreading cells separated by a small, zero-offset transform or discordant zone near 23°10′ N, The youngest crust in the median valley is characterized by a series of distinct magnetization highs which coalesce to form two NNE-trending bands of high magnetization, one on the northern ridge segment which coincides with a large constructional volcanic ridge, and one along the southern ridge segment that is associated with a string of small axial volcanos. These two magnetization highs overlap between 23° N and 23°10° N forming a non-transform offset that may be a slow spreading ridge analogue of the small ridge axis discontinuities found on the East Pacific Rise. The crustal magnetizations in this overlap zone are generally low, although an anomalous, ESE-trending magnetization high of unknown origin is also present in this area. The present-day segmentation of spreading in the MARK area was inherited from an earlier ridge-transform-ridge geometry through a series of small (∼ 10 km) eastward ridge jumps. These small ridge jumps were caused by a relocation of the neovolcanic zone within the median valley and have resulted in an overall pattern of asymmetric spreading with faster rates to the west (14 mm yr⁻¹) than to the east (11 mm yr⁻¹). Although the detailed magnetic survey described in this paper extends out to only 3 Ma old crust, a regional compilation of magnetic data from this area by Schoutenet al. (1985) indicates that the relative positions and dimensions of the spreading cells, and the pattern of asymmetric spreading seen in the MARK area during the past 3 Ma, have characterized this part of the Mid-Atlantic Ridge for at least the past 36 Ma.  相似文献   

印度洋无震海岭及海底高原的初步研究   总被引：1，自引：0，他引：1  

王述功  高仰 《海洋与湖沼》1994,25(2):124-131

根据１９８６年１０月－１９８７年５月第三次南极考察和首次环球科学考察所获的印度洋实测重力资料，对印度洋一些典型构造进行了分析研究。初步主人为：无震海岭，海底高原和大洋中脊都有着复杂的壳－幔结构，其上都伴有一个布格异常的低值带，但引种布格局异常低值原因却不尽相同。虽然上述３者都是大洋中的隆起地带，但前两者的地壳增厚，莫氏丰下拱，软流圈变深，影响布格异常的主要因素是其下存在着一个较大的负山根。相反，在  相似文献   

马尔库斯海脊富钴结壳的钙质超微化石生物地层学研究   总被引：1，自引：1，他引：1  

马维林  金翔龙  钟石兰  初凤友 《海洋学报》2007,29(5):174-180

分布于大洋盆地高地形区的富钴结壳是一种经历了上千万年生长历程的、含多种有价值金属的特殊“沉积物”.与一般沉积物一样,富钴结壳也保存了海洋环境变迁更替的信息.正确解读结壳的生长历史,不仅对认识这种有用金属矿产的成因和成矿机制有重要意义,而且对研究第三纪以来的大洋古环境乃至这一时段的全球环境变化也有不容忽视的价值.  相似文献