From the near-field records of aftershock of Datong earthquakes in October 1989 and March 1991,an extra phase between P and S arrivals is found. High-precision epicenter location shows that some of these records are o...From the near-field records of aftershock of Datong earthquakes in October 1989 and March 1991,an extra phase between P and S arrivals is found. High-precision epicenter location shows that some of these records are obtained with the incidental angle less than the critical angle. This excludes the possibility that the extra wave phase is a refractive wave from ground surface. Particle motion analysis shows that the characteristic of the extra wave is similar to that of wave, so it is possible that the extra phase is an S to P convert wave from the bottom of sediment basin. Suppose a low velocity layer covers a high velocity basement. Successful simulation by the synthetic seismogram confirms that the extra phase is an S-P convert wave from the interface of the basin bottom. Modifying the depth of interface at each ray path to match the waveform, we obtain an interface distribution in space. In this way, a brief bottom image could be shown, and the Datong basin has a 'V' shaped bottom.展开更多
Based on numerous high-resolution seismic profiles,sediment waves and their distribution,morphological characteristics,internal structure,and potential origins were revealed in the eastern waters of Taiwan.The sedimen...Based on numerous high-resolution seismic profiles,sediment waves and their distribution,morphological characteristics,internal structure,and potential origins were revealed in the eastern waters of Taiwan.The sediment waves are located at the junction between the Taitung Canyon and other canyons in the slope.The wave length and the wave height of a single waveform ranged from 0.8 to 7.2 km and from 18 to 75 m,respectively(NE-SW direction).Sediment waves,located inside the bend of the Taitung Canyon,were characterized by an upward migration and showed mass transport deposits(MTDs)at the bottom,while the inner curve of the bend was subdivided into lower and upper wavy transition units.The sediment waves on the outer curve of the bend were characterized by vertical accumulation,and there was no mass flow deposit at the bottom.According to the geometry of the sediment waves,the calculated flow thicknesses across the entire wave field ranged from 196 to 356 m,and the current velocity ranged from 15 to 21 cm/s.The morphological characteristics,the internal structure,and the distribution of sediment waves,as well as the numerical calculations,evidenced that these sediment waves had formed by turbidity currents.The development of the sediment wave field in eastern Taiwan was found to be similar to that in southwestern Taiwan.It was the sedimentary response of the tectonic movement between 3 and^1 Ma which created the sedimentary systems where gravity flow processes predominated.Turbidity current sediments settled in the place of less topographical constraints or overflowed in the bend section of the Taitung Canyon,which resulted in the formation of sediment wave fields.展开更多
Standing waves in the cylinder hasins with inhomogeneous bottom are considered in this paper. We assume that the inviscid, incompressible fluid is in irrotational undulatory motion. For convenience sake, cylindrical c...Standing waves in the cylinder hasins with inhomogeneous bottom are considered in this paper. We assume that the inviscid, incompressible fluid is in irrotational undulatory motion. For convenience sake, cylindrical coordinates are chosen. The velocitv potentials, the wave profiles and the modified frequencies are determined (to the third order) as power series in terms of the amplitude divided by the wavelength. Axisymmetrical analytical solutions are worked out. When w=0 , the second order frequency are gained.As an example, we assume that cylinder bottom is an axisymmetricat paraboloid. We find out that the uneven bottom has influences on standing waves. In the end. we go into detail on geometric factors.展开更多
High-resolution seismic models of sediment basins are critical inputs for earthquake ground motion prediction and petroleum resource exploration.In this study we employed a newly developed technique that utilizes the ...High-resolution seismic models of sediment basins are critical inputs for earthquake ground motion prediction and petroleum resource exploration.In this study we employed a newly developed technique that utilizes the frequency-dependent nonlinear P-wave particle motion to estimate sedimentary structure beneath the Bohai Bay basin.A recent study suggests that the delay of the P wave on the horizontal component relative the vertical component and its variations over frequency are caused by interference of the direct P wave with waves generated at the sediment base.The frequency-dependent delay time can be used to constrain sediment thickness and seismic velocity beneath recording stations.We measured the particle motions of teleseismic P waves recorded by 249 broadband stations of the North China Array,which covers the western Bohai Bay basin and its surrounding areas.We found that the P waves of 90 stations inside the Bohai Bay basin and other local basins within the Taihang and Yanshan mountain ranges exhibit significant frequency-dependent nonlinear particle motions,and used the particle motion data to invert the sediment thickness(Z0)and surface S-wave velocity(β0).The estimated sediment thickness inside the Bohai Bay Basin varies from 1.02 km to 3.72 km,with an average of 3.20 km,which roughly agrees with previous active source studies.展开更多
Sequences of wave-enhanced sediment-gravity flows(WESGFs) have been widely recognized in the marine shelf environment. In this study, we show observations of WESGF deposits in lacustrine settings using well core and t...Sequences of wave-enhanced sediment-gravity flows(WESGFs) have been widely recognized in the marine shelf environment. In this study, we show observations of WESGF deposits in lacustrine settings using well core and thin section data from the Paleogene in the Jiyang sub-basin, Bohai Bay basin, eastern China. The findings of this study include the following: 1) the sequence of WESGFs in the lacustrine basin is similar to that of marine; it consists of three units, MF1 unit: siltstone with basal erosion surface, MF2 unit: silt-streaked claystone, and MF3 unit: silty-mudstone; and 2) prodelta sand sheets are found in the lacustrine WESGF sequence and are classified as the MFd unit: clay-streaked siltstone. However, because the system size and variability in hydrodynamic conditions are different between the lacustrine and marine basins, lacustrine WESGFs do appear to have three distinguishable features: 1) the sediment grain size and sand content are slightly higher than those of the marine WESGFs; 2) lacustrine WESGFs may contain prodelta sediments or sedimentary sequences of other types of gravity flows, such as hyperpycnal flows; and 3) the scale of the sedimentary structures for lacustrine WESGFs is smaller. The WESGFs found in the continental lacustrine basin provide a new model for sediment dispersal processes in lake environments and may be helpful to explain and predict the distribution of sandy reservoirs for oil and gas exploration.展开更多
New version of SWAN model includes the wave diffraction effect which is the main improvement compared with the previous versions. Experimental data collected in the wave basin of the University of Delaware were used t...New version of SWAN model includes the wave diffraction effect which is the main improvement compared with the previous versions. Experimental data collected in the wave basin of the University of Delaware were used to test its performance. Wave heights were compared in the four cases (with different wave energies and directional spreading spectra). The results agreed well with the measurements, especially for the broad directional spectra cases. The effect of wave diffraction was analyzed by switching on/off the corresponding tenn. By introducing the diffraction term, the distributions of wave height and wave direction were smoothed, especially obvious for the narrow spectrum cases. Compared with the calculations without diffraction, the model with diffraction effect gave better results.展开更多
Developing serpent-type wave generators to generate solitary waves in a 3D-basin was investigated in this study. Based on the Lagrangian description with time-marching procedures and finite differences of the time der...Developing serpent-type wave generators to generate solitary waves in a 3D-basin was investigated in this study. Based on the Lagrangian description with time-marching procedures and finite differences of the time derivative, a 3D multiple directional wave basin with multidirectional piston wave generators was developed to simulate ocean waves by using BEM with quadrilateral elements, and to simulate wave-caused problems with fully nonlinear water surface conditions. The simulations of perpendicular solitary waves were conducted in the first instance to verify this scheme. Furthermore, the comparison of the waveform variations confirms that the estimation of 3D solitary waves is a feasible scheme.展开更多
Surf-zone hydrodynamics forced by oblique wave shoaling and breaking on beach slopes were investigated.The results showed that in wave-basin experiments with incident angles in the range of 15°-30°,wave brea...Surf-zone hydrodynamics forced by oblique wave shoaling and breaking on beach slopes were investigated.The results showed that in wave-basin experiments with incident angles in the range of 15°-30°,wave breaking was initiated at a breaker coefficient of around 0.67,which was significantly less than that predicted from empirical relations based on normally incident waves for a given beach slope and deep-water wave steepness.The measurements also showed that subsequent saturated breaking occurred at a breaker coefficient of around 0.47 that was inde-pendent of beach slope in the range of 1∶10 to 1∶100.This result is likely applicable to both oblique and normally incident waves.It is shown that the measured wave heights and longshore velocity profiles in wave-basin studies can be reasonably well predicted by theory with proper ad-justments to the process parameters.Best-match formulations were identified for quantifying bottom friction,eddy viscosity,and energy loss due to surface rollers.展开更多
基金State Key Basic Research Development and Programming Project (95-13-05-02) the Federal Institute for Geosciences and Natural Resources, Germany.
文摘From the near-field records of aftershock of Datong earthquakes in October 1989 and March 1991,an extra phase between P and S arrivals is found. High-precision epicenter location shows that some of these records are obtained with the incidental angle less than the critical angle. This excludes the possibility that the extra wave phase is a refractive wave from ground surface. Particle motion analysis shows that the characteristic of the extra wave is similar to that of wave, so it is possible that the extra phase is an S to P convert wave from the bottom of sediment basin. Suppose a low velocity layer covers a high velocity basement. Successful simulation by the synthetic seismogram confirms that the extra phase is an S-P convert wave from the interface of the basin bottom. Modifying the depth of interface at each ray path to match the waveform, we obtain an interface distribution in space. In this way, a brief bottom image could be shown, and the Datong basin has a 'V' shaped bottom.
基金supported by the National Natural Science Foundation of China(No.41576048)the Open Fund of Key Laboratory of Marine Mineral Resourcesthe Ministry of Land and Resources(KLMMR-2015-A-11)
文摘Based on numerous high-resolution seismic profiles,sediment waves and their distribution,morphological characteristics,internal structure,and potential origins were revealed in the eastern waters of Taiwan.The sediment waves are located at the junction between the Taitung Canyon and other canyons in the slope.The wave length and the wave height of a single waveform ranged from 0.8 to 7.2 km and from 18 to 75 m,respectively(NE-SW direction).Sediment waves,located inside the bend of the Taitung Canyon,were characterized by an upward migration and showed mass transport deposits(MTDs)at the bottom,while the inner curve of the bend was subdivided into lower and upper wavy transition units.The sediment waves on the outer curve of the bend were characterized by vertical accumulation,and there was no mass flow deposit at the bottom.According to the geometry of the sediment waves,the calculated flow thicknesses across the entire wave field ranged from 196 to 356 m,and the current velocity ranged from 15 to 21 cm/s.The morphological characteristics,the internal structure,and the distribution of sediment waves,as well as the numerical calculations,evidenced that these sediment waves had formed by turbidity currents.The development of the sediment wave field in eastern Taiwan was found to be similar to that in southwestern Taiwan.It was the sedimentary response of the tectonic movement between 3 and^1 Ma which created the sedimentary systems where gravity flow processes predominated.Turbidity current sediments settled in the place of less topographical constraints or overflowed in the bend section of the Taitung Canyon,which resulted in the formation of sediment wave fields.
文摘Standing waves in the cylinder hasins with inhomogeneous bottom are considered in this paper. We assume that the inviscid, incompressible fluid is in irrotational undulatory motion. For convenience sake, cylindrical coordinates are chosen. The velocitv potentials, the wave profiles and the modified frequencies are determined (to the third order) as power series in terms of the amplitude divided by the wavelength. Axisymmetrical analytical solutions are worked out. When w=0 , the second order frequency are gained.As an example, we assume that cylinder bottom is an axisymmetricat paraboloid. We find out that the uneven bottom has influences on standing waves. In the end. we go into detail on geometric factors.
文摘High-resolution seismic models of sediment basins are critical inputs for earthquake ground motion prediction and petroleum resource exploration.In this study we employed a newly developed technique that utilizes the frequency-dependent nonlinear P-wave particle motion to estimate sedimentary structure beneath the Bohai Bay basin.A recent study suggests that the delay of the P wave on the horizontal component relative the vertical component and its variations over frequency are caused by interference of the direct P wave with waves generated at the sediment base.The frequency-dependent delay time can be used to constrain sediment thickness and seismic velocity beneath recording stations.We measured the particle motions of teleseismic P waves recorded by 249 broadband stations of the North China Array,which covers the western Bohai Bay basin and its surrounding areas.We found that the P waves of 90 stations inside the Bohai Bay basin and other local basins within the Taihang and Yanshan mountain ranges exhibit significant frequency-dependent nonlinear particle motions,and used the particle motion data to invert the sediment thickness(Z0)and surface S-wave velocity(β0).The estimated sediment thickness inside the Bohai Bay Basin varies from 1.02 km to 3.72 km,with an average of 3.20 km,which roughly agrees with previous active source studies.
基金support by the National Nature Science Foundation of China (General Program) Grant No. 41572134National Program on Key Basic Research Project of China (973 Program) Grant No. 2014CB239102
文摘Sequences of wave-enhanced sediment-gravity flows(WESGFs) have been widely recognized in the marine shelf environment. In this study, we show observations of WESGF deposits in lacustrine settings using well core and thin section data from the Paleogene in the Jiyang sub-basin, Bohai Bay basin, eastern China. The findings of this study include the following: 1) the sequence of WESGFs in the lacustrine basin is similar to that of marine; it consists of three units, MF1 unit: siltstone with basal erosion surface, MF2 unit: silt-streaked claystone, and MF3 unit: silty-mudstone; and 2) prodelta sand sheets are found in the lacustrine WESGF sequence and are classified as the MFd unit: clay-streaked siltstone. However, because the system size and variability in hydrodynamic conditions are different between the lacustrine and marine basins, lacustrine WESGFs do appear to have three distinguishable features: 1) the sediment grain size and sand content are slightly higher than those of the marine WESGFs; 2) lacustrine WESGFs may contain prodelta sediments or sedimentary sequences of other types of gravity flows, such as hyperpycnal flows; and 3) the scale of the sedimentary structures for lacustrine WESGFs is smaller. The WESGFs found in the continental lacustrine basin provide a new model for sediment dispersal processes in lake environments and may be helpful to explain and predict the distribution of sandy reservoirs for oil and gas exploration.
基金This study was supported by the National Key Basic Research Project of China (Grant No2002CB412403)the Research Project in Science and Technology Commission of Shanghai Municipality,China (Grant No04DZ12049)
文摘New version of SWAN model includes the wave diffraction effect which is the main improvement compared with the previous versions. Experimental data collected in the wave basin of the University of Delaware were used to test its performance. Wave heights were compared in the four cases (with different wave energies and directional spreading spectra). The results agreed well with the measurements, especially for the broad directional spectra cases. The effect of wave diffraction was analyzed by switching on/off the corresponding tenn. By introducing the diffraction term, the distributions of wave height and wave direction were smoothed, especially obvious for the narrow spectrum cases. Compared with the calculations without diffraction, the model with diffraction effect gave better results.
基金supported by the Science Council under the Project Nos.NSC-95-2221-E-019-075-MY3(CRC)andNSC-97-2221-E-236-011-(RSS)
文摘Developing serpent-type wave generators to generate solitary waves in a 3D-basin was investigated in this study. Based on the Lagrangian description with time-marching procedures and finite differences of the time derivative, a 3D multiple directional wave basin with multidirectional piston wave generators was developed to simulate ocean waves by using BEM with quadrilateral elements, and to simulate wave-caused problems with fully nonlinear water surface conditions. The simulations of perpendicular solitary waves were conducted in the first instance to verify this scheme. Furthermore, the comparison of the waveform variations confirms that the estimation of 3D solitary waves is a feasible scheme.
文摘Surf-zone hydrodynamics forced by oblique wave shoaling and breaking on beach slopes were investigated.The results showed that in wave-basin experiments with incident angles in the range of 15°-30°,wave breaking was initiated at a breaker coefficient of around 0.67,which was significantly less than that predicted from empirical relations based on normally incident waves for a given beach slope and deep-water wave steepness.The measurements also showed that subsequent saturated breaking occurred at a breaker coefficient of around 0.47 that was inde-pendent of beach slope in the range of 1∶10 to 1∶100.This result is likely applicable to both oblique and normally incident waves.It is shown that the measured wave heights and longshore velocity profiles in wave-basin studies can be reasonably well predicted by theory with proper ad-justments to the process parameters.Best-match formulations were identified for quantifying bottom friction,eddy viscosity,and energy loss due to surface rollers.