Distribution,Seismic Characteristics and Controlling Factors of Carbonate Platforms on the Northwestern Margin of the South China Sea

Newly-acquired seismic data reveal widespread carbonate deposits covering a large part of the northwestern South China Sea margin.Three carbonate platforms are identified to have developed on the topographic highs inherited from tectonic deformation and volcanic accretion.Across the carbonate platforms,the Miocene strata are characterized by high-amplitude seismic reflections and distinct platform architecture that overlaps older strata.The Guangle and Xisha carbonate platforms grew on faulted blocks due to South China Sea continental rifting,while the Zhongjian carbonate platform developed on a structural high induced by early Miocene volcanism.During the late Miocene,partial drowning resulted in the inhibition of platform growth,eventual platform drowning and termination of most carbonate deposition.The drowning of the Guangle and Zhongjian carbonate platforms is shown by the supply of siliciclastic sediments during the late Miocene and seems to be closely linked to late Neogene volcanic activity,whilst the drowning of the Xisha carbonate platform is primarily related to relative eustatic changes.Our results imply that tectonic activity,volcanism and eustasy are the dominant controls on the evolution of carbonate platforms on the northwestern margin of the South China Sea.

Closure to“Discussion on‘Optimum placement and characteristics of velocity-dependent dampers under seismic excitation' by SA Mousavi and AK Ghorbani-Tanha”by Izuru Takewaki

The authors would like to thank the discusser for his considerations and comments. The discusser believes that some of the derived formulations need to be referred to his previously published works and also some related studies have not been cited.

Impact of seismic excitation characteristics on the efficiency of tuned liquid column dampers

Various types of passive control systems have been used to suppress the seismic response of structures in recent years. Among these systems, Tuned Liquid Column Dampers （TLCDs） dissipate the input earthquake energy by combining the effects of the movement of the liquid mass in the container, the restoring force on the liquid due to the gravity loads and the damping due to the liquid movement through orifices. In this study, the effects of seismic excitation characteristics such as frequency content and soil condition on the seismic performance of TLCDs are investigated using nonlinear time-history analyses. In this regard, among the past earthquake ground motion records of Iran, 16 records with different parameters were selected. In the structural model developed, the attached TLCD is simulated as a Tuned Mass Damper （TMD） having the same vibration period and damping ratio as the original TLCD. The numerical results show that the seismic excitation characteristics have a substantial role on the displacement reduction capability of TLCDs and they should be considered accordingly in the design of TLCDs.

The Seismic Response Characteristics of Polyhalite with Shaded Potash Mine in Central Sichuan

Potash deposition is the result of final phase of brine sedimentary evolution,it’s a limited distribution and easily soluble mineral,it is difficult to find the features on the ground,therefore the prospecting is extremely tough.

Discussion on “Optimum placement and characteristics of velocity-dependent dampers under seismic excitation” by Seyed Amin Mousavi and Amir K. Ghorbani-Tanha

The authors presented an interesting aspect in viscous or visco-elastic damper optimization under earthquake excitation. They also reviewed the research development in the field of passive damper optimization.

Quantitative estimation of bubble volume fraction of submarine seep plumes by modeling seismic oceanography data

Submarine seep plumes are a natural phenomenon in which different types of gases migrate through deep or shallow subsurface sediments and leak into seawater in pressure gradient.When detected using acoustic data,the leaked gases frequently exhibit a flame-like structure.We numerically modelled the relationship between the seismic response characteristic and bubble volume fraction to establish the bubble volume fraction in the submarine seep plume.Results show that our models are able to invert and predict the bubble volume fraction from field seismic oceanography data,by which synthetic seismic sections in different dominant frequencies could be numerically simulated,seismic attribute sections(e.g.,instantaneous amplitude,instantaneous frequency,and instantaneous phase)extracted,and the correlation between the seismic attributes and bubble volume fraction be quantitatively determined with functional equations.The instantaneous amplitude is positively correlated with bubble volume fraction,while the instantaneous frequency and bubble volume fraction are negatively correlated.In addition,information entropy is introduced as a proxy to quantify the relationship between the instantaneous phase and bubble volume fraction.As the bubble volume fraction increases,the information entropy of the instantaneous phase increases rapidly at the beginning,followed by a slight upward trend,and finally stabilizes.Therefore,under optimal noise conditions,the bubble volume fraction of submarine seep plumes can be inverted and predicted based on seismic response characteristics in terms of seismic attributes.

Analysis Method and Application of Multiple Antiquities Sources in the Shahejie Formation of the Paleogene in the Southern Bohai Sea

B Oilfield is the most representative mid to deep oil field in the Bohai Sea, with the main oil bearing intervals being the upper and middle Shahejie-3 sections of the Paleogene Shahejie Formation. Through the development of ancient landforms, characterization of material source channels, analysis of missing heavy mineral sources, and seismic reflection characteristics of multiple material source missing, the material sources of the middle and upper Shahejie-3 sections are analyzed. During the sedimentation period of the II oil formation in the middle section of the Shasan Formation, the study area was mainly dominated by the Kendong Uplift source rocks;During the sedimentation period of the I oil formation in the middle section of the Shasan Formation, there were three material sources in the study area, namely the Kendong Uplift, the Laibei Low Uplift, and the Weibei Uplift. The Kendong Uplift was the main material source, followed by the Laibei Low Uplift;During the sedimentation period of the Upper Shasan Formation, the study area still had three sources of material supply simultaneously. At this time, the Laibei Low Uplift was the main source area, while the Kendong Uplift and Weibei Uplift had a relatively small supply capacity for the study area. In the analysis of archaeological sources, the distribution characteristics of the sedimentary system in the third section of the Shahejie Formation have been clarified, providing a research basis for the later development and adjustment of the oilfield.

Seismic Recognition and Origin of Miocene Meishan Formation Contourite Deposits in the Southern Qiongdongnan Basin,Northern South China Sea

Research into the contourite deposits in the Upper Meishan Formation of the southern Qiongdongnan Basin in South China Sea is weak;their characteristics,distribution and original geological conditions are not clear.Using geologic al and geophysical methods including seismic and drilling data,based on seismic reflection characteristics,geometrical configuration description,and wave impedance inversion,two types of contourite deposits are recognized.Contourite deposits have blurred boundaries between each deposit and disordered internal seismic reflections;They are mound-shaped only in transverse section,and banded in the longitudinal direction.TypeⅠcontourite deposits are conical,with mediumhigh amplitude,low-continuity,low-frequency mound-shaped seismic facies,and subparallel-chaotic reflections internally.These deposits are conical with sharp tops,the canal between mounds is V-shaped and deep.The western wing is gentle and the eastern wing is steep,with the slope toe mostly between 10°and 20°,and width height ratio about 1-2.TypeⅡcontourite deposits are flat,exhibiting medium-amplitude,medium-continuity,low-frequency mound-shaped seismic facies,with subparallel weak reflections internally.Their mounds are flat with gently arced tops,with shallow canals between.The slope toe is between 5°and 10°,with a width height ratio of about 2-5.The wave impedance value of these contourite deposits is 4.6 kg/m^(3)×m/s to 6.8 kg/m^(3)×m/s,about 5.8 kg/m^(3)×m/s on average,which is presumed to represent marlycalcareous clastic sediments.The contourite deposits mainly develop beneath the slope break at the margin of the faultcontrolled platform in the Southern Uplift zone of the basin.In plane view,they are distributed approaching a west-to-east direction,and in section,lie in low-lying areas near the faults at fault-controlled terraces of the Southern Uplift zone,with a paleo-current direction nearly west-to-east.The paleotectonic setting of the gentle monoclinic platform was favorable for the development of such contourite deposits.The intensification of the Mid-Miocene deepest bottom current gave rise to the contourite-forming currents around the Southern Uplift zone in the northern South China Sea,which flow from Hainan Island to the Xisha Trough in a nearly west-to-east direction leading to the contourite deposits developing in the late MidMiocene transgressive environment,with multiple slow sea-level fall cycles.

Study on the Source Characteristics of Downhole Airgun with Different Excitation Environments

The measurement of underground medium variation using a repeated artificial source has gradually become an important goal to pursue. In recent years,we have developed and improved a technology system with large capacity airguns excited in land reservoirs by transplanting marine seismic exploration technology. The excitation effect has a close relationship to airgun capacity,water environment,and excitation conditions. In view that large capacity airgun must be excited without a water environment,we expand the system to use in downhole. Based on the BHS-2200 LL downhole airgun with a capacity of250in3,this paper carries out a comparative analysis on the characteristics of an airgun source excited in 0. 2m- and 5. 0m-diameter wells,and the results show that:( 1) The dominant frequency of the airgun signal excited in a 5. 0m well is mainly from 10 Hz to40Hz,lower than that in a 0. 2m well,and the larger body of water is good for bubble oscillation.( 2) In terms of exciting energy,the signal excited in a 5. 0m well has stronger energy than in a 0. 2m well,with a difference of 1 order in magnitude,and the signal can be detected up to 9km excited in a 5. 0m well with a single shot.( 3) The airgun signal has good repeatability in both excitation wells. The downhole airgun excitation technology system has potential application in dynamic monitoring near a fault zone with a small scale range, exploration of oil and mineral resources, and modern urban geophysical environment.

Integrative method in lithofacies characteristics and 3D velocity volume of the Permian igneous rocks in H area, Tarim Basin

This paper introduces horizon control, seismic control, logging control and facies control methods through the application of the least squares fitting of logging curves, seismic inversion and facies-controlled techniques. Based on the microgeology and thin section analyses, the lithology, lithofacies and periods of the Permian igneous rocks are described in detail. The seismic inversion and facies-controlled techniques were used to find the distribution characteristics of the igneous rocks and the 3D velocity volume. The least squares fitting of the logging curves overcome the problem that the work area is short of density logging data. Through analysis of thin sections, the lithofacies can be classified into eruption airfall subfacies, eruption pyroclastic flow subfacies and eruption facies.

Development of the Miocene Guangle Carbonate Platform in the South China Sea:Architecture and Controlling Factors

This study investigates the evolution of the Miocene Guangle carbonate platform(or Triton Horst)of the northwestern South China Sea margin.The platform is located at a junction area surrounded by Yinggehai basin,Qiongdongnan basin and Zhongjiannan basin.Well and regional geophysical data allow the identification of the morphologic and stratigraphic patterns.The Guangle carbonate platform was initiated on a tectonic uplift during the Early Miocene.The early platform was limited at Mesozoic granitic basement,pre-Paleogene sediments localized tectonic uplift and was small extension at the beginning stage.While during the Middle Miocene,the carbonate buildup flourished,and grow a thrived and thick carbonate succession overlining the whole Guangle Uplift.The isolated platforms then united afterward and covered an extensive area of several tens of thousands of square kilometers.However,it terminated in the Late Miocene.What are the control factors on the initiation,growth and demise of the Guangle carbonate platform?The onset of widespread carbonate deposits largely reflected the Early Miocene transgression linked with early post-rift subsidence and the opening of the South China Sea.Stressed carbonate growth conditions on the Guangle carbonate platform probably resulted from increased inorganic nutrient input derived from the adjacent uplifted mainland,possibly enhanced by deteriorated climatic conditions promoting platform drowning.Therefore,tectonics and terrigenous input could be two main controlling factors on the development of the Guangle carbonate platforms and main evolution stages.

Large scale characteristic distance between strong earthquake

The global seismicity shows a characteristic distance of about 23°. The middle deep and deep earthquakes in the European and Asian blocks concentrate on several zones which separate about 23° away from earch other. The shallow strong earthquakes ( M S≥7) form belts of over 20°, the ends of these belts are near the concentration points of middle deep and deep earthuakes. The Circular Pacific island arcs, volcanoes, shallow earthquakes, middle deep and deep earthquakes also show the characteristic distance of about 23°.

A Study on the Early Warning Time of Strong Earthquakes in Taiwan

The paper collects the records by the Fujian Digital Seismic Network of 40 shallow earthquakes in Taiwan with M_S≥5.0 from 1999 to 2013,analyzes the seismic phase(Pn,Sn phase)characteristics and travel-time rules,determines travel-time models and develops a seismic phase travel-time equation based on the two-step fitting algorithm.With the deduction of processing time and network delay time,this method can provide an accurate estimation of early warning time of Taiwan earthquakes for the Fujian region,and has been officially employed in the earthquake early warning system of Fujian Province.

THE SEISMIC PROFILER FOR DEEP SEDIMENT LAYERS AND ITS CHARACTERISTICS

DDCl-1 type seismic profiler for deep sediment layers is a large scale marine survey equipment. Its penetrating strata depth may reach to 1 km. This equipment suits surveys for continental shelf,seafloor trench and geological structure under seafloor etc. It suits also geological environment surveys of seafloor resources.The working principle, block diagrams composition and echo signal processing characteristics are presented, and some typical strata profiles are shown.