共查询到20条相似文献，搜索用时 31 毫秒
1.
Chan Hong Park Jeong Woo Kim Nobuhiro Isezaki Daniel R. Roman Ralph R. B. von Frese 《Marine Geophysical Researches》2006,27(4):253-266
To facilitate geological analyses of the Ulleung Basin in the East Sea (Japan Sea) between Korea and Japan, shipborne and satellite altimetry-derived gravity data are combined to derive a regionally coherent anomaly field. The 2-min gridded satellite altimetry-based gravity predicted by Sandwell and Smith [Sandwell DT, Smith WHF (1997) J Geophys Res 102(B5):10,039–10,054] are used for making cross-over adjustments that reduce the errors between track segments and at the cross-over points of shipborne gravity profiles. Relative to the regionally more homogeneous satellite gravity anomalies, the longer wavelength components of the shipborne anomalies are significantly improved with minimal distortion of their shorter wavelength components. The resulting free-air gravity anomaly map yields a more coherent integration of short and long wavelength anomalies compared to that obtained from either the shipborne or satellite data sets separately. The derived free-air anomalies range over about 140 mGals or more in amplitude and regionally correspond with bathymetric undulations in the Ulleung Basin. The gravity lows and highs along the basin’s margin indicate the transition from continental to oceanic crust. However, in the northeastern and central Ulleung Basin, the negative regional correlation between the central gravity high and bathymetric low suggests the presence of shallow denser mantle beneath thinned oceanic crust. A series of gravity highs mark seamounts or volcanic terranes from the Korean Plateau to Oki Island. Gravity modeling suggests underplating by mafic igneous rocks of the northwestern margin of the Ulleung Basin and the transition between continental and oceanic crust. The crust of the central Ulleung Basin is about a 14–15 km thick with a 4–5 km thick sediment cover. It may also include a relatively weakly developed buried fossil spreading ridge with approximately 2 km of relief. 相似文献
2.
《Marine Geodesy》2012,35(1):63-85
AbstractWe introduce an iterative inversion method to address the problems in high-order seafloor topography inversion using gravity data (gravity anomaly and vertical gravity gradient anomaly), such as the difficulty in computing the equation and the uniqueness of the calculation results. A part of the South China Sea is selected as the experimental area. Considering the coherence and admittance function of gravity topography and vertical gravity gradient topography, the inversion band of the gravity anomaly and vertical gravity gradient anomaly in the study area is 30?km–120?km. Seafloor topography models of different orders are constructed using an iterative method, and the performance of each seafloor topography model is analyzed against ETOPO1 and other seafloor topography models. The experimental results show that as the inversion order increases, the clarity and richness of seafloor topographic expression continuously improve. However, the accuracy of seafloor topography inversion does not improve significantly when the inversion order exceeds a certain value, which is related to the contribution of high-order seafloor topography to gravity information. The results show that the accuracy of BGT4 (inversion model constructed by the gravity anomaly) is slightly poorer than that of BVGGT4 (inversion model constructed by the vertical gravity gradient anomaly) in areas with complex topography, such as multi-seamounts and trenches, and the results are generally better in areas with flat seafloor topography. 相似文献
3.
In this paper, regional analog gravity anomaly map obtained from the General Directorate of Mineral Research and Exploration (MTA) was digitized and used for the calculation of the crustal thickness (Moho depth) variations in the Eastern Mediterranean and the southern part of the Aegean Region. In the gravity anomaly map, there are mainly E–W trending apparent gravity anomalies represented by the contours up to 150 mGal. They are generally parallel to the shorelines of Africa, Turkey and Crete. Crustal thickness variations were calculated from the gravity anomalies, using an empirical equation in this study. Obtained thicknesses (Moho depths) were mapped and correlated with the previous investigations and seismological findings. According to the estimations, crustal thicknesses are about 25–30 km along the coastal regions and more than 30 km on the onshore part of Turkey increasing up to 42 km through the eastern Anatolia. However, there are thin crustal zones around 17 km in the offshore Egypt, to the NW part of Cyprus and about 19 km to the north of Crete. They may be related with the main tectonic trends in this region except the circular thinning to the south of Kas (southwestern part of Turkey). In order to determine the locations and boundaries of prominent tectonic elements, Analytic Signal (AS) and maxspots maps of the gravity anomalies were also prepared in this study. All produced maps are generally consistent to each other and the boundaries of main tectonic units were apparently illustrated in the maxspots map from the horizontal gradient of Bouguer anomalies. 相似文献
4.
Relation between Gravity Field Feature and Tectonics and Earthquakes in Taiwan and Its Adjacent Seas
Short wave gravity anomaly is correlated to sea floor topography in the gravity field of Taiwan and its adjacent seas. Gravity values of 200 × 10-5ms-2 at Yushang and -160 × 10-5ms-2 at Liuqiu sea trench are respectively the maximum and minimum gravity values in this area.Bouguer gravity anomaly reflects not only Moho interface undulation, but also fault distribution.The inflexion of gradient belt of Bouguer gravity anomaly is a spot liable to earthquakes. Middlelong wave geoid is the best data to invert crustal thickness. We calculate crustal thickness by using geoid data, and the maximum value is 38km; the minimum value is 12km in Taiwan and its adjacent seas. 相似文献
5.
本文基于中国南极考察第30航次、第32航次所获得的实测重力资料,结合NGDC资料,开展12个航次重力场数据的平差融合工作,全部386个交点平差后标准差减小为±1.53×10−5 m/s2,与卫星重力差值平均值为1.49×10−5 m/s2,均方差为±3.81×10−5 m/s2,并在此基础上采用频率域界面反演法计算莫霍面深度。研究发现,与沉积盆地对应重力异常低值相悖,在罗斯海北部盆地、维多利亚地盆地、中央海槽、东部盆地4个主要盆地腹地却表现为重力异常高值,跨度达100 km以上。莫霍面深度分布整体呈南深北浅之势,范围为10~28 km。伴随着罗斯海西部盆地的多次拉张及岩浆活动,该区域的地壳厚度和莫霍面深度高值和低值相间分布,并表现出越来越大的差异性。综合剖面结果表明,罗斯海重力异常值的长波长变化与莫霍面的起伏呈正相关关系,但是反演的莫霍面深度与区域重力场特征并非完全对应,所以岩浆底侵和地壳侵入仍不足以导致罗斯海盆地的重力异常或盆地几何形状。 相似文献
6.
7.
利用中国-尼日利亚国际合作航次获得的船载重力数据,分析了尼日利亚南部大陆边缘的自由空间重力异常和布格重力异常特征,并通过两条从陆架—陆坡—陆隆一直延伸到深海盆地的重力剖面拟合出地壳密度结构。研究结果表明,地壳厚度总体上从陆架、陆坡至深海平原呈现阶梯状减薄的趋势,东侧的减薄幅度大于西侧,东侧从24 km减小到10 km,西侧从21 km减小到14 km。 相似文献
8.
Manoj Mukhopadhyay 《Marine Geophysical Researches》1988,9(3):197-210
The Andaman arc is associated with a major Free-air anomaly pair of mean amplitude 180 mgal. Two-dimensional gravity interpretation suggests significant mass anomalies below the arc that presumably have resulted due to subduction of the Indian plate below the Burma plate. It is inferred that the Andaman trench is of asymmetric V-shape containing about 7 km sediments. An outer bathymetric rise seaward of the trench possibly corresponds to a lithospheric flexure by 500 m. The Cretaceous-Tertiary sediments constituting the Andaman sedimentary arc attain their maximum thickness of about 13 km under the Nicobar. Deep at the subduction zone. At this location a mafic mass is emplaced within the sedimentary section. The underlying oceanic crust apparently experiences phase transition at about 27 km depth in a Benioff zone environment. The Andaman volcanic arc underlies a low density zone that is at least 60 km wide. Along the east margin of the Andaman Sea, cuustal transition presumably occurs below the Mergui Terrace at the Malayan coast. 相似文献
9.
Polymetalic sulfide is the main product of sea-floor hydrothermal venting, and has become an important sea-floor mineral resources for its rich in many kinds of precious metal elements. Since 2007, a number of investigations have been carried out by the China Ocean Mineral Resources Research and Development Association(COMRA)cruises(CCCs) along the Southwest Indian Ridge(SWIR). In 2011, the COMRA signed an exploration contract of sea-floor polymetallic sulfides of 10 000 km2 on the SWIR with the International Seabed Authority. Based on the multibeam data and shipborne gravity data obtained in 2010 by the R/V Dayang Yihao during the leg 6 of CCCs21, together with the global satellite surveys, the characteristics of gravity anomalies are analyzed in the Duanqiao hydrothermal field(37°39′S, 50°24′E). The "subarea calibration" terrain-correcting method is employed to calculate the Bouguer gravity anomaly, and the ocean bottom seismometer(OBS) profile is used to constrain the two-dimensional gravity anomaly simulation. The absent Moho in a previous seismic model is also calculated.The results show that the crustal thickness varies between 3 and 10 km along the profile, and the maximum crustal thickness reaches up to 10 km in the Duanqiao hydrothermal field with an average of 7.5 km. It is by far the most thicker crust discovered along the SWIR. The calculated crust thickness at the Longqi hydrothermal field is approximately 3 km, 1 km less than that indicated by seismic models, possibly due to the outcome of an oceanic core complex(OCC). 相似文献
10.
In this paper we focused on understanding the isostatic compensation of the Ninetyeast Ridge in the overall context of the
Bay of Bengal oceanic lithosphere and the interaction of the ridge system with the north Andaman subduction zone from north
of 7–18°N. This region is characterized by the initial interaction of the Kerguelen hotspot with the Bay of Bengal oceanic
lithosphere. We used satellite altimeter-derived marine geoid, as it should comprehensively reflect the compensations caused
by large spatial wavelength dominated deeper anomaly sources in a hotspot affected lithospheric load like the Ninetyeast Ridge.
Our analyses of the geoid-to-topography ratio (GTR), residual geoid, gravity-to-topographic kernel and upward continuation
of anomalies show the existence of two different types of source compensation bodies beneath the northern (12–18°N) and southern
(7–12°N) Ninetyeast Ridge. In the northern region, the geoid to topography ratio varies from 0.63 ± 0.05 to 0.44 ± 0.03, while
in the southern region it ranges from 1.34 ± 0.09 to 1.31 ± 0.07 which resulted in a north to south increase in the apparent
compensation depth from ~9 to 28 km. The presence of a shallow Moho, low GTR, broader gravity to topography kernel and the
absence of a ridge anomaly from the mantle density dominated upward continued anomaly at z = 300 km indicates that at the northern segment the underplated low density crustal melt is the dominant isostatic compensating
body. However, at the southern ridge segment the high GTR, strong gravity-to-topography kernel and the subsistence of the
anomaly at long wavelengths, even at z = 300 km represents the existence of large volumes of hotspot related underplated dense material as the source of compensation.
The proximity of the dense source compensating body of the southern Ninetyeast Ridge to the Andaman subduction zone affected
the regional mantle driven density gradient flow, as observed from the z = 300 km continued gravity anomaly. The existence of a southern Ninetyeast Ridge in such a transpressional regime has caused
the formation of a forearc sliver at its eastern flank, which is a major crustal deformational structure developed as a result
of ridge-trench collision. 相似文献
11.
The crenulated geometry of the Southeast Indian ridge within the Australian-Antarctic discordance is formed by numerous spreading ridge segments that are offset, alternately to the north and south, by transform faults. Suggested causes for these offsets, which largely developed since ~ 20 Ma, include asymmetric seafloor spreading, ridge jumps, and propagating rifts that have transferred seafloor from one flank of the spreading ridge to the other. Each of these processes has operated at different times in different locations of the discordance; here we document an instance where a small (~ 20 km), young (< 0.2 Ma), southward ridge jump has contributed to the observed asymmetry. When aeromagnetic anomalies from the Project Investigator-1 survey are superposed on gravity anomalies computed from Geosat GM and ERM data, we find that in segment B4 of the discordance (between 125° and 126° E), the roughly east-west-trending gravity low, correlated with the axial valley, is 20–25 km south of the ridge axis position inferred from the center of magnetic anomaly 1. Elsewhere in the discordance, the inferred locations of the ridge axis from magnetics and gravity are in excellent agreement. Ship track data confirm these observations: portions of Moana Wave track crossing the ridge in B4 show that a topographic valley correlated with the gravity anomaly low lies south of the center of magnetic anomaly 1; while other ship track data that cross the spreading ridge in segments B3 and B5 demonstrate good agreement between the axial valley, the gravity anomaly low, and the central magnetic anomaly. Based on these observations, we speculate that the ridge axis in B4 has recently jumped to the south, from a ridge location closer to the center of the young normally magnetized crust, to that of the gravity anomaly low. The position of the gravity low essentially at the edge of normally magnetized crust requires a very recent (< 0.2 Ma) arrival of the ridge in this new location. Because this ridge jump is so young, it may be a promising location for future detailed studies of the dynamics, kinematics, and thermal effects of ridge jumps.The U.S. Government right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged. 相似文献
12.
The geophysically unusual Laxmi Ridge (eastern basin, Arabian Sea) is associated with a prominent elongated negative gravity anomaly. A seismically and geodynamically constrained detailed 2D gravity modeling suggests an 11-km-thick normal oceanic crust and an asthenospheric upwarp to a depth of 35 km. We attribute the apparent thickening of the crust to a possible emplacement of an anomalous subcrustal low-density layer between 11 and 19 km depth. We hypothesize that a K-T boundary bolide impact near the Bombay offshore led to several geological events, including eruption of Deccan flood basalts. The spreading Carlsberg Ridge in the Indian Ocean and rifting associated with Deccan volcanism generated the compressive regime, which perhaps originated the Laxmi Ridge. 相似文献
13.
Pan Jiayi Wang Junqin Wang Yanfeng Zhang Xinmei Yuan Yeli Zheng Quan''an 《海洋学报(英文版)》1999,18(4):523-533
INTRODUCTIONThegeoidistheiargeopotentials~econfidingmostlywiththemeanseasurfaceandisdenotedastheheightrelativetotheidealelliPSes~eoftheearth.Thegeoidundulationsinglobalaceareupto100m.TheunevenstructureOftheearthgivesrisetotheunevenfeatureofthecitysot... 相似文献
14.
Active oceanic spreading in the northern North Fiji Basin: Results of the NOFI cruise of R/V L'Atalante (newstarmer project) 总被引：1，自引：0，他引：1
Yves Lagabrielle Etienne Ruellan Manabu Tanahashi Jacques Bourgois Georges Buffet Giovanni de Alteriis Jérôme Dyment Jean Goslin Eulàlia Gràcia-Mont Yo Iwabushi Philip Jarvis Masato Joshima Anne-Marie Karpoff Takeshi Matsumoto Hélène Ondréas Bernard Pelletier Olivier Sardou 《Marine Geophysical Researches》1996,18(2-4):225-247
The South Pandora and the Tripartite Ridges are active spreading centers located in the northern part of the North Fiji Basin. These spreading centers were surveyed over a distance of 750 km during the NOFI cruise of R/V L'Atalante (August–September 1994) which was conducted in the frame of the french-japanese Newstarmer cooperation project. SIMRAD EM12-dual full coverage swath bathymetric and imagery data as well as airgun 6-channel seismic, magnetics and gravity profiles were recorded along and offaxis from 170°40 E to 178° E. Dredging and piston coring were also performed along and off-axis. The axial domain of the South Pandora Ridge is divided into 5 first-order segments characterized by contrasted morphologies. The average width of the active domain is 20 km and corresponds either to bathymetric highs or to deep elongated grabens. The bathymetric highs are volcanic constructions, locally faulted and rifted, which can obstruct totally the axial valley. The grabens show the typical morphology of slow spreading axes, with two steep walls flanking a deep axial valley. Elongated lateral ridges may be present on both sides of the grabens. Numerous volcanoes, up to several kilometers in diameter, occur on both flanks of the South Pandora Ridge. The Tripartite Ridge consists of three main segments showing a sigmoid shape. Major changes in the direction of the active zones are observed at the segment discontinuities. These discontinuities show various geometrical patterns which suggest complex transform relay zones. Preliminary analysis of seismic reflection profiles suggest that the Tripartite Ridge is a very young feature which propagates into an older oceanic domain characterized by a significant sedimentary cover. By contrast, a very thin to absent sedimentary cover is observed about 100 km on both flanks of the South Pandora Ridge active axis. The magnetic anomaly profiles give evidence of long and continuous lineations, parallel to the South Pandora Ridge spreading axis. According to our preliminary interpretation, the spreading rate would have been very low (8 km/m.y. half rate) during the last 7 Ma. The South Pandora and Tripartite Ridges exhibit characteristics typical of active oceanic ridges: (1) a segmented pattern, with segments ranging from 80 to 100 km in length; (2) an axial tectonic and volcanic zone, 10 to 20 km wide; (3) well-organized magnetic lineations, parallel to the active axis; (4) clear signature on the free-air gravity anomaly map. However, no typical transform fault is observed; instead, complex relay zones are separating first-order segments. 相似文献
15.
Gravity and multichannel seismic reflection constraints on the lithospheric structure of the Canary Swell 总被引：1，自引：0，他引：1
Deep penetrating multichannel seismic reflection and gravity data have been used to study the lithospheric structure of the Canary Swell. The seismic reflection data show the transition from undisturbed Jurassic oceanic crust, away from the Canary Islands, to an area of ocean crust strongly modified by the Canary volcanism (ACV). Outside the ACV the seismic records image a well layered sedimentary cover, underlined by a bright reflection from the top of the igneous basement and also relatively continuous reflections from the base of the crust. In the ACV the definition of the boundary between sedimentary cover and igneous basement and the crust-mantle boundary remains very loose. Two-dimensional gravity modelling in the area outside the influence of the Canary volcanism, where the reflection data constrain the structure of the ocean crust, suggests a thinning of the lithosphere. The base of the lithosphere rises from 100 km, about 400 km west of the ACV, to 80 km at the outer limit of the ACV. In addition, depth conversion of the seismic reflection data and unloading of the sediments indicate the presence of a regional depth anomaly of an extension similar to the lithospheric thinning inferred from gravity modelling. The depth anomaly associated with the swell, after correction for sediment weight, is about 500 m. We interpret the lithospheric thinning as an indication of reheating of old Mesozoic lithosphere beneath the Canary Basin and along with the depth anomaly as indicating a thermal rejuvenation of the lithosphere. We suggest that the most likely origin for the Canary Islands is a hot spot. 相似文献
16.
Deflections of the vertical (DOVs) over oceans cannot be directly measured, which restricts their applications. A local covariance function of anomalous potential is put forward in this paper in conjunction with the least-squares collocation (LSC) method to compute the oceanic DOVs utilization of oceanic gravity data along a profile. The covariance functions of gravity field quantities have been derived directly as functions of x, y and z without the need to introduce coordinate transformations corresponding to along- or cross-profile components. In the proposed methodology, gravity data along a profile were used to calculate the residual gravity anomaly using the remove-compute-restore technique. The residual gravity anomaly was used to calculate the parameters of the proposed covariance function of the local anomalous gravity field, which was used in the LSC to compute the residual DOVs along the profile. The residual DOVs added model DOVs to recover the DOVs along the profile. The results of a simulation experiment prove that the proposed methodology is feasible and effective. 相似文献
17.
Two long seismic refraction lines along the crest of the Iceland-Faeroe Ridge reveal a layered crust resembling the crust beneath Iceland but differing from normal continental or oceanic crust. The Moho was recognised at the south-eastern end of the lines at an apparent depth of 16–18 km. A refraction line in deeper water west of the ridge and south of Iceland indicates a thin oceanic type crust underlain by a 7.1 km/s layer which may be anomalous upper mantle.An extensive gravity survey of the ridge shows that it is in approximate isostatic equilibrium; the steep gravity gradient between the Norwegian Sea and the ridge indicates that the ridge is supported by a crust thickened to about 20 km rather than by anomalous low density rocks in the underlying upper mantle, in agreement with the seismic results. An increase in Bouguer anomaly of about 140 mgal between the centre of Iceland and the ridge is attributed to lateral variation in upper mantle density from an anomalous low value beneath Iceland to a more normal value beneath the ridge. Local gravity anomalies of medium amplitude which are characteristic of the ridge are caused by sediment troughs and by lateral variations in the upper crust beneath the sediments. A steep drop in Bouguer anomaly of about 80 mgal between the ridge and the Faeroe block is attributed partly to lateral change in crustal density and partly to slight thickening of the crust towards the Faeroe Islands; this crustal boundary may represent an anomalous type of continental margin formed when Greenland started to separate from the Faeroe Islands about 60 million years ago.We conclude that the Iceland-Faeroe Ridge formed during ocean floor spreading by an anomalous hot spot type of differentiation from the upper mantle such as is still active beneath Iceland. This suggests that the ridge may have stood some 2 km higher than at present when it was being formed in the early Tertiary, and that it has subsequently subsided as the spreading centre moved away and the underlying mantle became more normal; this interpretation is supported by recognition of a V-shaped sediment filled trough across the south-eastern end of the ridge, which may be a swamped sub-aerial valley. 相似文献
18.
南极布兰斯菲尔德海峡及周边区域是南极大陆火山、地震等新构造活动最活跃的地区,与南设得兰海沟、南设得兰群岛一同构成南极大陆边缘现存唯一的"沟-弧-盆"构造体系。本文基于"雪龙"船第28、第30航次实测数据及两个航次的国际共享资料,利用均衡改正数据处理方法获得布兰斯菲尔德海峡的莫霍面深度及其分布规律,分析深部构造-断裂的区域分布及其重力异常特征等。布兰斯菲尔德海峡内的空间重力异常呈条带状分布,走向总体与地形相近,布格重力异常则由两侧向中间升高,大致在坡折处形成异常场值为100×10-5 m/s2的分界线,在中央次海盆和东部次海盆海山处形成两个异常高值圈闭,异常值最高为150×10-5 m/s2。莫霍面深度以弧后扩张中心为最低值,向南设得兰群岛和南极半岛两个方向递增,深度从12 km递增至陆坡位置的24 km。 相似文献
19.
Xin’gang Luo Wanyin Wang Ying Chen Zhizhao Bai Dingding Wang Tao He Yimi Zhang Ruiyun Ma 《海洋学报(英文版)》2023,42(3):227-242
As one of the main controlling factors of oil and gas accumulation, faults are closely related to the distribution of oil and gas reservoirs. Studying how faults control petroliferous basins is particularly important. In this work, we investigated the plane positions of major faults in the China seas and its adjacent areas using the normalized vertical derivative of the total horizontal derivative (NVDR-THDR) of the Bouguer gravity anomaly, the fusion results of gravity and magnetic anomalies, and the residual Bouguer gravity anomaly. The apparent depths of major faults in the China seas and its adjacent areas were inverted using the Tilt-Euler method based on the Bouguer gravity anomaly. The results show that the strikes of the faults in the China seas and its adjacent areas are mainly NE and NW, followed by EW, and near-SN. Among them, the lengths of most ultra-crustal faults are in the range of 1 000–3 000 km, and their apparent depths lie between 10 km and 40 km. The lengths of crustal faults lie between 300 km and 1 000 km, and their apparent depths are between 0 km and 20 km. According to the plane positions and apparent depths of the faults, we put forward the concept of fault influence factor for the first time. Based on this factor, the key areas for oil and gas exploration were found as follows: the east of South North China Basin in the intracontinental rift basins; the southeast region of East China Sea Shelf Basin, the Taixinan and Qiongdongnan basins in the continental margin rift basins; Zhongjiannan Basin in the strike-slip pull-apart basins; the Liyue, Beikang, and the Nanweixi basins in the rifted continental basins. This work provides valuable insights into oil and gas exploration, mineral resource exploration, and deep geological structure research in the China seas and its adjacent areas. 相似文献
20.
Regional gravity and magnetic studies over the continental margin of the central west coast of India
L. V. Subba Raju K. A. Kamesh Raju V. Subrahmanyam D. Gopala Rao 《Geo-Marine Letters》1990,10(1):31-36
Gravity studies over the continental margin of the central west coast of India show a sediment thickness of 2–3 km on the
shelf associated with deeper horst and graben structures, of 6 km in the shelf margin basin, and about 1 km in the deep sea.
The upward trend in free-air gravity anomaly toward the deep sea region is interpreted as crustal thinning. Model studies
indicate a 25-km-thick crust in the shelf region and a minimum of 18 km in the more offshore region. An abrupt magnetic signature
change suggests differential basement depths in the shelf region. Major faulting in the region is confirmed in water depths
of approximately 100–200 m. 相似文献