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1.
The Kuroshio inflow northeast of Taiwan Island plays an important role in the heat and nutrient balances over the East China Sea(ECS). Based on merged satellite altimeter data and the PCM-1 mooring observation at the East Taiwan Channel(ETC), the study employs a correlation iteration scheme to find the optimal transport index for the Kuroshio inflow. The sea level difference with the highest correlation to the ETC transport is across the ECS shelf break rather than along the PCM-1 line. The counter-intuitive result is caused by large signal noise and poor track coverage of altimeters near the Taiwan coast. The optimal altimetric index is highly correlated with the two-year in-situ measurements as well as the ten-year output of the global assimilation model. It serves as a better estimator of Kuroshio inflow than those using tidal gauge data, and helps pinpoint a 5 cm mismatch of mean sea level in the Keelung tidal record. The mean transport of Kuroshio inflow based on the twenty-year altimetric index is 20.55 Sv with a standard deviation of 3.05 Sv. Wavelet spectrum of the index reveals that semi-annual period dominates the Kuroshio variation northeast of Taiwan Island.  相似文献   

2.
From May to June 2014, the geochemical characteristics of dissolved barium(Ba) in sea water and its influx from the Kuroshio into the East China Sea(ECS) were studied by investigation of the Kuroshio mainstream east of Taiwan Island and the adjacent ECS. This allowed for the scope and extent of the Kuroshio incursion to be quantitatively described for the first time by using Ba as a tracer. The concentration of Ba in the Kuroshio mainstream increased gradually downward from the surface in the range 4.91–19.2 μg L.1. In the surface layer of the ECS, the Ba concentration was highest in coastal water and gradually decreased seaward, while it was higher in coastal and offshore water but lowest in middle shelf for bottom layer. The influx of Ba from Kuroshio into the ECS during May to October was calculated to be 2.19×108 kg by a water exchange model, in which the subsurface layer had the largest portion. The distribution of Ba indicated that Kuroshio upwelled in the sea area northeast of Taiwan Island. The north-flowing water in the Taiwan Strait restrained the incursion of Kuroshio surface water onto the ECS shelf, while Kuroshio subsurface water gradually affected the bottom of the ECS from outside. The results of end member calculation, using Ba as a parameter, showed that the Kuroshio surface water had little impact on the ECS, while the Kuroshio subsurface water formed an intrusion current by climbing northwest along the bottom of the middle shelf from the sea area northeast of Taiwan Island into the Qiantang Estuary, of which the volume of Kuroshio water was nearly 65%. Kuroshio water was the predominant part of the water on the outer shelf bottom and its proportion in areas deeper than the 100 m isobath could reach more than 95%. In the DH9 section(north of Taiwan Island), Kuroshio subsurface water intruded westward along the bottom from the shelf edge and then rose upward(in lower proportion). Kuroshio water accounted for 95% of the ocean volume could reach as far as 122°E. Ba was able to provide detailed tracing of the Kuroshio incursion into the ECS owing to its geochemical characteristics and became an effective tracer for revealing quantitative interactions between the Kuroshio and the ECS.  相似文献   

3.
Introduction As far as the frequency and magnitude are concerned, the earthquakes in the sea area to the east of Shanghai are far more strong than in land area with the largest one in the sea area near the Yangtze River mouth being MS=436, while in land, only MS=434 occurred on Sept. 1, 1624. As a moderately strong earthquake active area, the sea area near the Yangtze River mouth, may cause a potential risk to Shanghai. In 1971 and 1996, earthquakes with MS=5~6 occurred in this area. Geo…  相似文献   

4.
The regional stress field and seismic dynamics along the border zone between Fujian, Guangdong and Jiangxi Provinces are studied based on the seismo-geological data, GPS measurement, and seismicity. The results show that: (1) the principal compressional stress of the stress field is oriented in NW-SE direction and the principal extensional stress is in NE-SW direction; (2) the WNW-ward compression and collision of the Philippine Sea Plate to the eastern coast of Taiwan Island are the most direct and most important dynamic source for preparation and occurrence of strong earthquakes in the Taiwan area and along the border zone between Fujian, Guangdong and Jiangxi Provinces.  相似文献   

5.
Zhang  Xiaodong  Xie  Rui  Fan  Daidu  Yang  Zuosheng  Wang  Hongmin  Wu  Chuang  Yao  Yuhan 《中国科学:地球科学(英文版)》2021,64(10):1687-1697
The evolution of the Changjiang Delta is obviously affected by current rapidly rising sea level and drastically declining river discharge, and it is also vital for the sustainable development of Shanghai and the Changjiang River Economic Belt, which represent China's economic development leader and major national strategic area, respectively. In this paper, the growth pattern of Jiuduansha Island, the largest uninhabited alluvial island in the Changjiang Estuary, is studied in terms of the change in elevation, position and area over the past 50 years through using satellite-derived instantaneous shoreline positions and high/low tide exposure areas based on 497 satellite images from 1974 to 2020; and the influencing factors and future development patterns are further discussed by comparison with other alluvial islands or sandbars in the estuary. The results show that Jiuduansha Island has maintained a rapid or even accelerated area growth rate, although the sediment discharge of the Changjiang River has sharply decreased in recent decades. This sustained growth is mainly attributed to the existence of the estuarine turbidity maximum zone, coarsening fluvial sediment, onshore sediment replenishment by tide, cone-like geomorphology of Jiuduansha Island, and siltation promotion effect of vegetation. The growth rate of the low tide exposure area of Jiuduansha Island increased from 1.9 km~2 a~(-1) in 1974–1990 to 3.0 km~2 a~(-1) in 1990–2020, and the growth rate of the high tide exposure area reached as high as 3.7 km~2 a~(-1) in 1994–2020. The implementation of the Deep-Water Channel Project has significantly affected the evolution of Jiuduansha Island, including shifting the heads of Shangsha and Zhongxiasha from severe retreat to rapid accretion, and promoting tidal flat progradation seaward of the Jiangyanansha and Zhongxiasha, but restricting the growth of the low tide exposure area of Jiuduansha Island.  相似文献   

6.
Based on the available and supplementary survey data,it analyzes the effect of seismicity in Taiwan and the Taiwan Straits on the southeastern coastal area of the Chinese mainland and discusses its roles in seismic hazard prevention and textual research of historical earthquakes. The results show that the frequency of strong earthquake in Taiwan area is high,with a time interval ranging from several to dozens of years,but the maximum influence intensity of seismicity from there to the coastal areas of the Chinese mainland is only VI degree; while the maximum influence intensity of the seismicity along the littoral fault zone located on the west of the straits reaches VIII ～ IX degree because of the shorter distance to the Chinese mainland,though the frequency of strong earthquakes is lower than that of the Taiwan area. Strategies for protecting against seismic hazards in the southeastern coastal area of China are proposed. Besides focusing on the effect of strong earthquakes of the littoral fault zone,attention also has to be paid to the low-cycle fatigue failure of engineering structures induced by the earthquakes in Taiwan and the stir effect on society induced by earthquake phobia. It is concluded that it would be more accurate and proper to take the May 19,1517 earthquake recorded in the Chinese mainland area as the influence of a strong earthquake in the Taiwan area.  相似文献   

7.
Deformation patterns, shortening amounts and rates in the late Quaternary across the Kalpin thrust system have received little attention in the past. This paper attempts to discuss them, mainly in the eastern part of the thrust system by doing field investigation along the faults and folds, measuring geomorphic deformation, excavating trenches in several important sites where young alluvial fans were obviously displaced and dating young deposits of alluvial terraces. There are two types of deformation in the surface and near surface for the Kalpin thrust system in the late Quaternary. They are movement of thrust faults on lower angles and bending of young folds. Both kinds of deformation are shown by shortening and uplifting of young geomorphic surfaces. The surface ages of 3 stages are calculated by dating 20 examples using the TL method in the study area and comparing the results of our predecessors on the deposition and incision times of alluvial terraces in the Tianshan mountain which are 100ka B.P., 33～18ka B.P. and 6.6～8.2ka B.P. respectively for the large-scale deformed alluvial surfaces: T_3, T_2 and T_1 in the Kalpin region. Then, 19 sets of shortening amounts and rates are obtained in 13 sites along 4 rows of anticlines in front of the Kalpin thrust system and Piqiang fold. The shortening amounts and rates show that there are two sections where deformation is stronger than others. The two sections consist of two arcs that are towards the south. The shortening rates near the top of arcs are 1.32mm/a in the west and 1.39mm/a in the east across the thrust system, respectively. In addition, deformation is stronger in the front rows than the rear ones for bifurcate folds.  相似文献   

8.
Using the focal mechanism solutions and slip distribution model data of the Taiwan Straits MS7.3 earthquake on September 16, 1994, we calculate the static Coulomb stress changes stemming from the earthquake. Based on the distribution of aftershocks and stress field, as well as the location of historical earthquakes, we analyze the Coulomb stress change triggered by the Taiwan Straits MS7.3 earthquake. The result shows that the static Coulomb stress change obtained by forward modeling based on the slip distribution model is quite consistent with the location of aftershocks in the areas far away from the epicenter. Ninety percent of aftershocks occurred in the stress increased areas. The Coulomb stress change is not entirely consistent with the distribution of aftershocks near the epicenter. It is found that Coulomb stress change can better reflect the aftershock distribution far away from the epicenter, while such corresponding relationship becomes quite complex near the epicenter. Through the calculation of the Coulomb stress change, we find that the stress increases in the southwest part of the Min-Yue (Fujian-Guangdong) coastal fault zone, which enhances the seismic activity. Therefore, it is deemed that the sea area between Nanpeng Island and Dongshan Island, where the Min-Yue coastal fault zone intersects with the NW-trending Shanghang-Dongshan fault, has a high seismic risk.  相似文献   

9.
The interaction zone between southern Tianshan and northern Tarim is located at the northeast side of Pamir. It is a region with high seismicity. We constructed a seismotectonic model for the west part of this zone from geological profiles, deep crust seismic detection and earthquake focal mechanisms data. Based on the synthesized geological features, deep crust structure, and earthquake focal mechanisms, we think that the main regional tectonic feature is that the Tianshan tecto-lithostratigraphic unit overthrusts on the Tarim block. The Tianshan tectonic system includes the Maidan fault and thrust sheets in front of the fault; The Tarim tectonic system includes the underground northern Tarim margin fault, conjugate faults in basement and overthrust fault in shallow. The northern Tarim margin fault is a high angle fault deep in the Tarim crust, adjusting different trending deformation between Tianshan and Tarim. It is a major active fault that can generate large earthquakes. The other faults, such as the Tianshan overthrust system and the Tarim basement faults in this area may generate moderately strong earthquakes with different styles.  相似文献   

10.
The continental slope of the Taiwan Shoal, which has cultivated numerous submarine canyons, is located in a passive continental margin environment. However, the trend of the Taiwan Canyon, with its 45° intersection angle, is obviously different from that of the erosion valley downward along the continental slope. A distinct break is present in the lower segment of the Taiwan Canyon, which then extends from west to east parallel to the continental slope until finally joining the Manila Trench. By utilizing multiple-beam water depth data, high-resolution seismic data, and sediment cores, this study describes the topographic characteristics of the Taiwan Canyon and provides a preliminary discussion on the origin of the Taiwan Canyon and its effect on deepwater sediment. The terrain, landform, and sediment of the Taiwan Canyon exhibit segmentation characteristics. The upper segment is characterized primarily by erosion, downward cutting with a V shape, and wide development of sliding, slumping, and other gravity flow types. The middle segment is characterized mostly by U-shaped erosion-sedimentation transition and development of an inner levee. The lower segment is characterized primarily by sedimentation and development of a sediment wave. The bottom current has a significant reworking effect on the interior sediments of the canyon and forms reworked sands. The formation and evolution of the Taiwan Canyon is closely related to sediment supply, gravity sliding(slumping), faulting activities, and submarine impaling. Given the sufficient terrigenous clastic supply, the sediments along the continental shelf edge continuously proceed seaward; gliding and slumping in the front edge provide driving forces for the formation of the canyon. Faulting activities result in stratum crushing, and the gravity flow takes priority in eroding the relatively fragile stratum. Thus, the direction of the extension of the canyon crosses the surrounding erosion valley obliquely. Seamounts are formed through submarine impaling. Owing to seamount blocking, the lower segment of the canyon is turned toward the east–west direction. Large amounts of sediments overflow at the turning, forming sediment waves.  相似文献   

11.
Qomolangma Feng——Mt. Everest (QF in shorter) is located in the east part of the China-Nepal boundary. QF is the highest mountain in China, also in the world. It lies in the collision zone along the boundary of Eurasian and Indian plates. It is one of focuses in geo- sciences study[1―7]. The northern slope area of the QF (QF area in shorter) is in Tibet, China, and the altitude of snow line in the QF area is around 6000 m. Spring in the QF area is March, April and May every year, a…  相似文献   

12.
Yangshan near-shore sea area is the multi-island and multi-channel area with strong flow velocity and high suspended sediment concentration. Based on the characteristics of tidal currents, waves, and sediment in the Yangshan area, a two-dimensional numerical model of tidal currents, sediment transport, and sea bed deformation is developed. In the model, the effects of tidal currents and wind waves on sediment transport are considered. According to characteristics of the study area, unstructured grids are applied to fit the boundaries of the near-shore sea area. The results show that the calculated values are in good agreement with the measured data. The field of tidal currents, suspended sediment concentrations, and the deformation of the seabed can be successfully simulated.  相似文献   

13.
A total of 48 earthquakes with M_s ≥5.0 occurred in China in 1994 (29 on the Chinese mainland and offshore, 19 in Taiwan). Among them 9 earthquakes were of M_s ≥6.0 (4 on the mainland and offshore, 5 in Taiwan). The M_s 7.3 earthquake that occurred in Taiwan Straits on September 16 was the greatest one offshore, which was generally included in the mainland area according to the previous statistics. The most powerful earthquakes in Taiwan were the 2 with M_s =7.0 that occurred on May  相似文献   

14.
A new species of the terrestrial protorosaur Macrocnemus is briefly described and named Macrocne-mus fuyuanensis sp. nov. The specimen was found from the marine Triassic of Yunnan Province, southwestern China. It differs from the type species M. bassanii in having the following characters: (1) 17 or 18 dorsal vertebrae; (2) relatively long humerus; and (3) femur longer than tibia. M. fuyuanensis is the only record of the genus outside Monte San Giorgio area and the first definite terrestrial reptile found from the marine Triassic of China. The age of the fossil-bearing Zhuganpo Member of the Falang Formation is believed to be the Ladinian based on associated vertebrate fauna. The existence of Mac-rocnemus in the limestone suggests the presence of a terrestrial ecosystem which probably originated from the Anisian and well developed in the Ladinian in this region. The island system along the north-coast of Tethyan during the Triassic was probably an important route for the exchanges of reptiles, especially the terrestrial reptiles between the west and east.  相似文献   

15.
As an important component of the cryosphere, sea ice is very sensitive to climate change. The study of sea ice physics needs accurate sea ice thickness. This paper presents an electromagnetic induction （EM） technique which can be used to measure the sea ice thickness distribution efficiently and its successful application in the Antarctic Neila Fjord. Based on the electrical properties of sea ice and seawater and the application of electromagnetic field theory, this technique can accurately detect the distance between the EM instrument and the ice/water interface to measure the sea ice thickness. Analyzing the apparent conductivity data obtained by the electromagnetic induction technique and drill-hole measurements at same location allows the construction of a transform equation for the apparent conductivity and sea ice thickness. The verification of the calculated sea ice thickness using this equation indicates that the electromagnetic induction technique is able to determine reliable sea ice thickness with an average relative error of only 5.5%. The ice thickness profiles show the sea ice distribution in Neila Fjord is basically level with a thickness of 0.8 - 1.4 m.  相似文献   

16.
Based on the drilling data,the geological characteristics of the coast in South China,and the interpretation of the long seismic profiles covering the Pearl River Mouth Basin and southeastern Hainan Basin,the basin basement in the northern South China Sea is divided into four structural layers,namely,Pre-Sinian crystalline basement,Sinian-lower Paleozoic,upper Paleozoic,and Mesozoic structural layers.This paper discusses the distribution range and law and reveals the tectonic attribute of each structural layer.The Pre-Sinian crystalline basement is distributed in the northern South China Sea,which is linked to the Pre-Sinian crystalline basement of the Cathaysian Block and together they constitute a larger-scale continental block—the Cathaysian-northern South China Sea continental block.The Sinian-lower Paleozoic structural layer is distributed in the northern South China Sea,which is the natural extension of the Caledonian fold belt in South China to the sea area.The sediments are derived from southern East China Sea-Taiwan,Zhongsha-Xisha islands and Yunkai ancient uplifts,and some small basement uplifts.The Caledonian fold belt in the northern South China Sea is linked with that in South China and they constitute the wider fold belt.The upper Paleozoic structural layer is unevenly distributed in the northern South China.In the basement of Beibu Gulf Basin and southwestern Taiwan Basin,the structural layer is composed of the stable epicontinental sea deposit.The distribution areas in the Pearl River Mouth Basin and the southeastern Hainan Basin belong to ancient uplifts in the late Paleozoic,lacking the upper Paleozoic structural layers.The stratigraphic distribution and sedimentary environment in Middle-Late Jurassic to Cretaceous are characteristic of differentiation in the east and the west.The marine,paralic deposit is well developed in the basin basement of southwestern Taiwan but the volcanic activity is not obvious.The marine and paralic facies deposit is distributed in the eastern Pearl River Mouth Basin basement and the volcanic activity is stronger.The continental facies volcano-sediment in the Early Cretaceous is distributed in the basement of the western Pearl River Mouth Basin and Southeastern Hainan Basin.The Upper Cretaceous red continental facies clastic rocks are distributed in the Beibu Gulf Basin and Yinggehai Basin.The NE direction granitic volcanic-intrusive complex,volcano-sedimentary basin,fold and fault in Mesozoic basement have the similar temporal and spatial distribution,geological feature,and tectonic attribute with the coastal land in South China,and they belong to the same magma-deposition-tectonic system,which demonstrates that the late Mesozoic structural layer was formed in the background of active continental margin.Based on the analysis of basement structure and the study on tectonic attribute,the paleogeographic map of the basin basement in different periods in the northern South China Sea is compiled.  相似文献   

17.
The Sulawesi Sea and Sulawesi Island are located in the western Pacific area where volcanic activity,plate subduction,and seismic activity are very active.The Sulawesi basin formed during the Middle Eocene-Late Eocene and nearly half of the Eocene oceanic crust has subducted below the North Sulawesi Trench.The Sulawesi Island was spliced and finalized in the Early Pliocene-Pleistocene during volcanic activity and is recently very active.This area is an optimal location to study volcanic geothermal conditions and subduction initiation mechanisms in the southern part of the western Pacific plate margin,which are important in geothermal and geodynamic research.In this study,we combined 133 heat flow data with gravity and magnetic data to calculate the Moho structure and Curie point depth of the Sulawesi Sea and periphery of the Sulawesi Island,and analyze the distribution characteristics of the geothermal gradient and thermal conductivity.The results show that the average depths of the Moho and Curie surfaces in this area are 18.4 and 14.3 km,respectively,which is consistent with the crustal velocity layer structure in the Sulawesi Basin previously determined by seismic refraction.The average geothermal gradient is 4.96°C(100 m)-1.The oceanic area shows a high geothermal gradient and low thermal conductivity,whereas the land area shows a low geothermal gradient and high thermal conductivity,both of which are consistent with statistical results of the geothermal gradient at the measured heat flow points.The highest geothermal gradient zone occurs in the transition zone from the Sulawesi Sea to Sulawesi Island,corresponding to the spreading ridge of the southward-moving Sulawesi Basin.Comprehensive gravity,magnetic,and geothermal studies have shown a high crustal geothermal gradient in the study area,which is conducive to the subduction initiation.The northern part of the Palu-koro fault on the western side of Sulawesi is likely the location where subduction initiation is occurring.During the process of moving northwest,the northern and eastern branches of Sulawesi Island have different speeds;the former is slow and the latter is fast.These branches also show different deep tectonic dynamic directions;the northern branch tilts north-up and the eastern branch tilts north-down.  相似文献   

18.
For the first time on the Chinese mainland, long-range wide-angle seismic reflection/refraction profiling technology has been applied to seismic wave phases from different depths and with different attributes within the various blocks of the North China Craton to characterize the structure of the crust and upper mantle lithosphere. By comparative analysis of the seismic wave phase characteristics in each block across a 1500-km-long east-west profile, we have identified conventional Pg, Pci, PmP and Pn phases in the crust, made a clear contrast between PL1 and PL2 waves belonging to two groups of lithospheric-scale phases, and produced a model of crust-mantle velocity structures and tectonic characteristics after one- and two-dimensional calculations and processing. The results show that the thickness of the crust and lithosphere gradually deepens from east to west along the profile. However, at the reflection/refraction interface, seismic waves in each group show obvious localized changes in each block. Also, the depth to the crystalline basement changes greatly, from as much as 7.8 km in the North China fault basin to only about 2 km beneath the Jiaodong Peninsula and Taihang-Lüliang area. The Moho morphology as a whole ranges from shallow in the east to deep in the west, with the deepest point in the Ordos Block at 47 km; in contrast, the North China Plain Block is uplifting. The L1 interface of the lithosphere is observed only to the west of Taihang Mountains, at a relatively slowly changing depth of about 80 km. The L2 interface varies from 75 to 160 km and shows a sharp deepening to the west of Taihang Mountains, forming a mutation belt.  相似文献   

19.
Xu Jie 《中国地震研究》2006,20(1):101-107
The Indonesian region is one of the most seismically active zones on the earth. On December 26, 2004, an Ms 8.7 earthquake （as measured by the China Seismograph Network, or Mw = 9.3 as measured by USGS） struck the west coast of northern Sumatra, Indonesia. By its magnitude it is classified as the world＇s fourth largest earthquake since 1900 and the largest one since the 1964 Alaska earthquake. The spatial distribution of the relocation of larger aftershocks （ M 〉 4.5） following the main shock suggests a length and width of the rupture of about 1200km and 200km, respectively. The shock triggered massive tsunamis that affected several countries throughout South and Southeast Asia. It is a shallow interplate event of thrust type in the trench. Its epicenter is located at the northwestern end of the Indonesia-Melanesia plate boundary tectonic zone. In 2004, eight shocks of M≥ 7.0 occurred in this area, showing a migration from east to west. It implies that these shocks represent a correlated and consistent dynamic process along this subduction zone. These interplate events are associated with convergence of several plates and their fast motion in this region, which result in strong and complex structures and deformation. The India-Australia plate is underthrusting toward the Sunda continental block or Burma plate at a low angle, producing a great locked area on the shallow portion of the subduction zone where enormous strain is accumulated. Interseismic uplift recorded by coral growth and horizontal velocities measured by GPS show the geometry of the locked portion of the Sumatra subduction zone. The vertical and horizontal data reasonably match with a model in which the plate interface is fully locked over a significant width. This locked fault zone extends to a horizontal distance of 132km from the trench, which corresponds to a depth of 50km. The sudden ruptures and large-scale slip of this locked area as a release of stress occurred, are the direct cause of the M8.7 earthquake near Indonesia in 2004.  相似文献   

20.
Penetrating fronts are frequently observed off the Zhejiang-Fujian coast,but their life cycles are poorly understood because of the lack of time series data.In this study,Geostationary Ocean Color Imager data are used to describe the complete evolutionary process of a penetrating front,and the impacts of wind and circulation on evolution are explored.Based on the horizontal coverage and the front of the penetrating water,the evolutionary process is divided into three stages of development,maturation and decay.During the development stage,the area of the penetrating water increases rapidly with eastward extension,and the penetrating front is well connected to the Zhejiang-Fujian coastal front in the southwestern area.During the maturation stage,the penetrating water continues to extend eastward at a low speed and finally arrives at the Kuroshio area on the continental slope.Moreover,the southwestern part of the penetrating front is gradually separated from the coastal front.During the decay stage,the coverage of the penetrating water decreases rapidly,and the penetrating front disappears first in the south.In this stage,the penetrating front is rarely moves east but completely separated from the coastal front south of 30°N.Dynamic analysis suggests that the typhoon-induced southward extension of the Changjiang Diluted Water off the Zhejiang-Fujian coast is an important precondition for the generation of the penetrating front.The eastward extension of the penetrating front during the development stage is mainly driven by a southwesterly wind,while in the maturation stage,it is affected by both the wind and the offshore branch of the Taiwan Warm Current.The detachment of penetrating water from coastal water is caused by the inshore branch of the Taiwan Warm Current.Numerical tracer experiments confirm the wind and Taiwan Warm Current impacts on the eastward extension and detachment of penetrating water.In addition,the Kuroshio frontal eddy may play an important role in the dissipation of the penetrating front during the decay stage.  相似文献   

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