Regional compilation and analysis of aeromagnetic anomalies for the Transantarctic Mountains–Ross Sea sector of the Antarctic     

M. Chiappini  F. Ferraccioli  E. Bozzo  D. Damaske 《Tectonophysics》2002,347(1-3)

Magnetic observations over the area of the Transantarctic Mountains (TAM) and the Ross Sea have been compiled into a digital database that furnishes a new regional scale view of the magnetic anomaly crustal field in this key sector of the Antarctic continent. This compilation is a component of the ongoing IAGA/SCAR Antarctic Digital Magnetic Anomaly Project (ADMAP). The aeromagnetic surveys total 115 000 line km, and are distributed across the Victoria Land sector of the TAM, the Ross Sea, and Marie Byrd Land. The magnetic campaigns were performed within the framework of the national and international Italian–German–US Antarctic research programs and conducted with differing specifications during nine field seasons from 1971 until 1997. Generally flight line spacing was less than 5 km while survey altitude varied from about 610 to 4000 m above sea level for barometric surveys and was equal to 305 m above topography for the single draped survey. Reprocessing included digitizing the old contour data, improved levelling by means of microlevelling in the frequency domain, and re-reduction to a common reference field based on the DGRF90 model. A multi-frequency grid procedure was then applied to obtain a coherent and merged total intensity magnetic anomaly map. The shaded relief map covers an area of approximately 380 000 km². This new compilation provides a regional image of the location and spatial extent of the Cenozoic alkaline magmatism related to the TAM–Ross Sea rift, Jurassic tholeiites, and crustal segments of the Early Palaeozoic magmatic arc. A linear, approximately 100-km wide and 600-km long Jurassic rift-like structure is newly identified. Magnetic fabric in the Ross Sea rift often matches seismically imaged Cenozoic fault arrays. Major buried onshore pre-rift fault zones, likely inherited from the Ross Orogen, are also delineated. These faults may have been reactivated as strike-slip belts that segmented the TAM into various crustal blocks.  相似文献   

Sequential inversion of local earthquake traveltimes and gravity anomaly—the example of the western Alps   总被引：1，自引：0，他引：1  

Philippe Vernant  Frédéric Masson  Roger Bayer  Anne Paul 《Geophysical Journal International》2002,150(1):79-90

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全球海温距平对月预报影响的数值试验   总被引：6，自引：0，他引：6       下载免费PDF全文

骆美霞  纪立人  张道民  李金龙  游荣高  A. Longhetto 《大气科学》1997,21(5):552-556

对1992年7月19日个例，进行了有、无海温距平的对比数值试验，研究了海温距平对月预报的影响。个例试验结果表明，海温距平对月预报的影响是重要的。海温距平不仅对全球降水量的影响明显，而且对温度场预报的影响也很明显。大气（温度、降水和高度场）对异常海温强迫开始响应的时间大约是10天。  相似文献   

复杂场地上结构地震反应的研究   总被引：1，自引：0，他引：1  

杨柏坡  杨笑梅 《地震工程与工程振动》1997,17(2):10-15

介绍了局部复杂场地上结构震害异常的实例。使用显式有限元法分析了陡坎和山坡止方结构地震反应的特点，计算结果表明，复杂场地上地面运动的差动对结构地震应力的影响是不容忽视的。  相似文献   

1976年唐山7.8级地震前各类地震前兆异常信息熵的场,源兆特征     

张昭栋  张华 《华北地震科学》1997,15(3):53-60

利用“专家系统”的思想对每一地震前兆异常事件进行了综合评估，以每一异常的最可能发震时间计算发震概率，利用各类地震前兆异常群体信息熵研究了系统熵值与地震场，源兆的关系，分析了１９７６年唐山７．８级地震前各类地震前兆异常的时空分布特征，然后以唐山为中心在空间上划分三个区，近区，中间区和远区，分别计算了三个区各类地震前兆异常信息熵的时间演化值，分析了震前这种信息熵的场，源兆特征，震中近区的信息熵值要比中  相似文献   

Curie-temperature depth estimation using a self-similar magnetization model   总被引：4，自引：0，他引：4  

Stefan Maus  Dan Gordon  Derek Fairhead 《Geophysical Journal International》1997,129(1):163-168

The Earth's crust is magnetized down to the Curie-temperature depth at about 10 to 50 km. This limited depth extent of the crustal magnetization is discernible in the power spectra of magnetic maps of South Africa and Central Asia. At short wavelengths, the power increases as rapidly towards longer wavelengths as expected for a self-similar magnetized crust with unlimited depth extent. Above wavelengths of about 100 km the power starts increasing less rapidly, indicating the absence of deep-seated sources. To quantify this effect we derive the theoretical power spectrum due to a slab carved out of a self-similar magnetization distribution. This model power spectrum matches the power spectra of South Africa and Central Asia for a self-similarity parameter of β = 4 and Curie temperature depths of 15 to 20 km.  相似文献   

On the construction of geomagnetic timescales from non-prejudicial treatment of magnetic anomaly data from multiple ridges     

Stephen P. Huestis  Gary D. Acton 《Geophysical Journal International》1997,129(1):176-182

When marine magnetic-anomaly data are used to construct geomagnetic polarity timescales, the usual assumption of a smooth spreading-rate function at one seafloor spreading ridge forces much more erratic rate functions at other ridges. To eliminate this problem, we propose a formalism for the timescale problem that penalizes non-smooth spreading behaviour equally for all ridges. Specifically, we establish a non-linear Lagrange multiplier optimization problem for finding the timescale that (1) agrees with known chron ages and with anomaly-interval distance data from multiple ridges and (2) allows the rate functions for each ridge to be as nearly constant as possible, according to a cumulative penalty function. The method is applied to a synthetic data set reconstructed from the timescale and rate functions for seven ridges, derived by Cande & Kent (1992) under the assumption of smooth spreading in the South Atlantic. We find that only modest changes in the timescale (less than 5 per cent for each reversal) are needed if no one ridge is singled out for the preferential assumption of smoothness. Future implementation of this non-prejudicial treatment of spreading-rate data from multiple ridges to large anomaly-distance data sets should lead to the next incremental improvement to the pre-Quaternary geomagnetic polarity timescale, as well as allow a more accurate assessment of global and local changes in seafloor spreading rates over time.  相似文献   

Contribution of serpentinized ultramafics to marine magnetic anomalies at slow and intermediate spreading centres: insights from the shape of the anomalies   总被引：1，自引：0，他引：1  

Jérôme Dyment    Jafar Arkani-Hamed  Abdolreza Ghods 《Geophysical Journal International》1997,129(3):691-701

Detailed characteristics of marine magnetic anomalies 33r and 20r suggest that the magnetization of the deeper magnetic layers, including the lower crust and possibly the uppermost mantle, is horizontally displaced with respect to that of the upper crust. We examine the possibility that serpentinization of ultramafics in the lower crust and possibly the uppermost mantle delays the acquisition of magnetization and introduces a shift between the upper- and lower-crustal magnetization patterns. Thermal evolution models and the resulting magnetization patterns of the oceanic lithosphere are calculated for a wide range of physical parameters such as the Nusselt number and the depth of hydrothermal circulation in the crust, and the temperature range of serpentinization. The models with moderate hydrothermal cooling of the whole crust and serpentinization temperatures ranging between 200 and 300 C successfully explain the anomalous skewness and the 'hook shape' of observed sea-level magnetic anomalies created at slow and intermediate spreading rates.  相似文献   

Implications of Late Pleistocene Glaciation of the Tibetan Plateau for Present-Day Uplift Rates and Gravity Anomalies     

Georg Kaufmann  Kurt Lambeck 《Quaternary Research》1997,48(3):267-279

Minimal and maximal models of Late Pleistocene Glaciation on the Tibetan Plateau are considered. The large ice sheet models indicate that disintegration of the ice sheet could have contributed up to 7 mm/yr of present vertical uplift and 2 mm/yr of horizontal extension. The former value can account for more than 50% of the observed uplift in central Tibet. The peak free-air gravity anomaly arising from the deglaciation would be around −5.4 mGal. In contrast, the smaller ice sheet models do not contribute significantly to the signals of present uplift and gravity anomalies. Modern geodetic measurements therefore have the potential to constrain the Late Pleistocene glaciation of the Tibetan Plateau. Assuming a large ice sheet over the Tibetan Plateau, the disintegration can contribute up to 6 m of eustatic sea-level rise.  相似文献   

Global seafloor topography from a least-squares inversion of altimetry-based high-resolution mean sea surface and shipboard soundings   总被引：1，自引：0，他引：1  

Stéphane Calmant  Muriel Berge-Nguyen  Anny Cazenave 《Geophysical Journal International》2002,151(3):795-808

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