The rupture process of the May 12, 2008 Ms8.0 Wenchuan earthquake was very complex. To study the rupture zones generated by this earthquake, four dense temporary seismic arrays across the two surface breaking traces o...The rupture process of the May 12, 2008 Ms8.0 Wenchuan earthquake was very complex. To study the rupture zones generated by this earthquake, four dense temporary seismic arrays across the two surface breaking traces of the main-shock were deployed in July and recorded a great amount of aftershocks. This paper focuses on the data interpretation of two arrays across the central main fault, the northern array line 1 and southern array line 3. The fault zone trapped waves recorded by the two arrays were used to study the structure of the central main fault and the difference between the northern and southern portions. The results show that the widths of the rupture zone are about 170-200 m and 200-230 m for northern and southern portions respectively. And the corresponding dip angles are 80° and 70°. The seismic velocity inside the fracture zone is about one half of the host rock. By comparison, the northern portion of the rupture zone is slightly narrower and steeper than the southern portion. Besides these differences, one more interesting and important difference is the positions of the rupture zone with respect to surface breaking traces. At the northern portion, the rupture zone is centered at the surface breaking trace, while at the southern portion it is not but is shifted to the northwest. This difference reflects the difference of rupture behaviors between two portions of the central main fault. The width of the rupture zone is smaller than that of MS.1 Kunlun earthquake though these two earthquakes have almost the same magnitudes. Multiple ruptures may be one factor to cause the narrower rupture zone.展开更多
The wave characteristics affecting coastal sediment transport include wave height, wave period and breaking wave direction. Wave height is a critical factor in determining the amount of sediment transport in the coast...The wave characteristics affecting coastal sediment transport include wave height, wave period and breaking wave direction. Wave height is a critical factor in determining the amount of sediment transport in the coastal area. The force of sediment transport is much more intense under breaking waves than under non-breaking waves. Breaking waves exhibit various patterns, principal- ly depending on the incident wave steepness and the beach slope. Based on the equations of con- servation of mass, momentum and energy, a theoretical model for wave deformation in and outside the surf zone was obtained, which is used to calculate the wave shoaling, wave set-up and set- down and wave height distributions in and outside the surf zone. The analysis and comparison were made about the breaking point location and the wave height decay caused by the wave breaking and the bottom friction. Flume experiments relating to the spilling wave height distribution across the surf zone were conducted to verify the theoretical model. Advanced wave maker, data sampling de- vices and data processing system were utilized in the flume experiments with a slope covered by sands of different diameters to facilitate the observation and research on the wave transformation and breaking. The agreement between the theoretical and experimental results is good.展开更多
This article is to review results from scientific drilling and fault-zone trapped waves （FZTWs） at the south Longman-Shan fault （LSF） zone that ruptured in the 2008 May 12 M8 Wenchuan earthquake in Sichuan,China.I...This article is to review results from scientific drilling and fault-zone trapped waves （FZTWs） at the south Longman-Shan fault （LSF） zone that ruptured in the 2008 May 12 M8 Wenchuan earthquake in Sichuan,China.Immediately after the mainshock,two Wenchuan Fault Scientific Drilling （WFSD） boreholes were drilled at WFSD-1 and WFSD-2 sites approximately 400 m and 1 km west of the surface rupture along the Yinxiu-Beichuan fault （YBF）,the middle fault strand of the south LSF zone.Two boreholes met the principal slip of Wenchuan earthquake along the YBF at depths of 589-m and 1230-m,respectively.The slip is accompanied with a 100-200-m-wide zone consisting of fault gouge,breccia,cataclasite and fractures.Close to WFSD-1 site,the nearly-vertical slip of ～4.3-m with a 190-m wide zone of highly fractured rocks restricted to the hanging wall of the YBF was found at the ground surface after the Wenchuan earthquake.A dense linear seismic array was deployed across the surface rupture at this venue to record FZTWs generated by aftershocks.Observations and 3-D finite-difference simulations of FZTWs recorded at this cross-fault array and network stations close to the YBF show a distinct low-velocity zone composed by severely damaged rocks along the south LSF at seismogenic depths.The zone is several hundred meters wide along the principal slip,within which seismic velocities are reduced by ～30-55％ from wall-rock velocities and with the maximum velocity reduction in the ～200-m-wide rupture core zone at shallow depth.The FZTW-inferred geometry and physical properties of the south LSF rupture zone at shallow depth are in general consistent with the results from petrological and structural analyses of cores and well log at WFSD boreholes.We interpret this remarkable low-velocity zone as being a break-down zone during dynamic rupture in the 2008 M8 earthquake.We examined the FZTWS generated by similar earthquakes before and after the 2008 mainshock and observed that seismic velocities within fault core zone was reduced by ～10％ due to severe damage of fault rocks during the M8 mainshock.Scientific drilling and locations of aftershocks generating prominent FZTWs also indicate rupture bifurcation along the YBF and the Anxian-Guangxian fault （AGF）,two strands of the south LSF at shallow depth.A combination of seismic,petrologic and geologic study at the south LSF leads to further understand the relationship between the fault-zone structure and rupture dynamics,and the amplification of ground shaking strength along the low-velocity fault zone due to its waveguide effect.展开更多
Trapped waves in the Qingchuan fault zone were observed at Muyu near the northeastern end of the fractured zone of the Wenchuan Ms8. 0 earthquake. The results indicate a fault-zone width of about 200 m and a great dif...Trapped waves in the Qingchuan fault zone were observed at Muyu near the northeastern end of the fractured zone of the Wenchuan Ms8. 0 earthquake. The results indicate a fault-zone width of about 200 m and a great difference in physical property of the crust on different sides of the fault. The inferred location of crustal changes is consistent with land-form boundary on the surface展开更多
Trapped waves in different sections of Longmenshan fault belt were observed, and the results show the difference between the northern and southern portions of this fault belt. Guanzhuang and Leigu surveying lines are ...Trapped waves in different sections of Longmenshan fault belt were observed, and the results show the difference between the northern and southern portions of this fault belt. Guanzhuang and Leigu surveying lines are located at the northern portion of the fault belt, and the result indicates that the width of the rupture zone underground in this area is about 160 - 180 m. The center position of rupture zone underground corresponds to the surface breaking trace, and is equally distributed at the edges of the two fault walls. However, Hongkou surveying line is located at the southern portion of the fault belt, and the result indicates that the width of the rupture zone underground in this area is about 180 -200 m. The rupture zone underground is mainly distributed below fault scarp. The Wenchuan MsS. 0 earthquake and Lushan Ms7.0 earthquake both occurred at the Longmenshan fault belt. The results will provide information for the structure background of the two violent earthquakes.展开更多
The purpose of this paper is to extend the validity of Li's parabolic model (1994) by incorporating a combined energy factor in the mild-slope equation and by improving the traditional radiation boundary condition...The purpose of this paper is to extend the validity of Li's parabolic model (1994) by incorporating a combined energy factor in the mild-slope equation and by improving the traditional radiation boundary conditions. With wave breaking and energy dissipation expressed in a direct form in the equation, the proposed model could provide an efficient numerical scheme and accurate predictions of wave transformation across the surf zone. The radiation boundary conditions are iterated in the model without use of approximations. The numerical predictions for wave height distributions across the surf zone are compared with experimental data over typical beach profiles. In addition, tests of waves scattering around a circular pile show that the proposed model could also provide reasonable improvement on the radiation boundary conditions for large incident angles of waves.展开更多
Large property contrasts between materials in a fault zone and the surrounding rock are often produced by repeating earthquakes. Fault zones are usually characterized by fluid concentration, clay-rich fault gouge, inc...Large property contrasts between materials in a fault zone and the surrounding rock are often produced by repeating earthquakes. Fault zones are usually characterized by fluid concentration, clay-rich fault gouge, increased porosity, and dilatant cracks. Thus, fault zones are thought to have reduced seismic velocities than the surrounding rocks. In this article, we first investigated the synthetic waveforms at a linear array across a vertical fault zone by using 3D finite difference simulation. Synthetic waveforms show that when sources are close to, inside, or below the fault zone, both arrival times and waveforms of P-and S-waves vary systematically across the fault zone due to reflections and transmissions from boundaries of the low-velocity fault zone. The arrival-time patterns and waveform characteristics can be used to determine the fault zone structure. Then, we applied this method to the aftershock waveform data of the 1992 Landers M7.4 and the 2008 Wenchuan （汶川） M8.0 earthquakes. Landers waveform data reveal a low-velocity zone with a width of approximately 270-370 m, and P-and S-wave velocity reductions relative to the host rock of approximately 35%-60%; Wenchuan waveform data suggest a low-velocity zone with a width of approximately 220-300 m, and P-and S-wave velocities drop relative to the host rock of approximately 55%.展开更多
Rapid population growth and major trends of world economy growth have led to significant energy needs in our country. Benin, Gulf of Guinea country, although with a significant coastal network powered by potential ene...Rapid population growth and major trends of world economy growth have led to significant energy needs in our country. Benin, Gulf of Guinea country, although with a significant coastal network powered by potential energy from breaking waves, has experienced a deficit and a critical energy instability, marked by recurrent power cuts and disruption of the national economy. To ensure the integration of this source of renewable energy in the Benin energy mix and sustainably reduce the energy deficit in progress, this work has aimed to study the dissipation of wave energy at the bathymetric breaking in the breakers zone of Cotonou coast. Sea conditions and the statistics parameters of the breaking waves under perturbation effect of the seabed were evaluated to predict the beginning of the breaking. The modeling is based on the Navier-Stokes equation in which the viscosity and the interactions between the molecules of the oceanic fluid are neglected. The nonlinear wave dispersion relation is also used. The results obtained for this purpose showed that water particles have an almost parabolic motion during their fall;their velocity is higher than those of the early breaking. In this area, the waves dissipate about 80% of their energy: it generates turbulence which leads to a strong setting in motion of sediments.展开更多
The Shanxi rift zone is one of the largest and active Cenozoic grabens in the world, studying the velocity structure of the crust and upper mantle in this region may help us to understand the mechanisms of rift proces...The Shanxi rift zone is one of the largest and active Cenozoic grabens in the world, studying the velocity structure of the crust and upper mantle in this region may help us to understand the mechanisms of rift processes and the seismogenic environment of active seismicity in continental rifts. In this work, using the broadband seismic data of Shanxi, Hebei, Henan, Shaanxi provinces, and the Inner Mongolia Autonomous Region from February 2009 to November 2011, we have picked out 350 high-quality phase velocity dispersion curves of fundamental mode Rayleigh waves at periods from 8 to 75 s, and Rayleigh wave phase velocity maps have been constructed from 8 to 75 s period with horizontal resolution ranging from 40 to 50 km by two-station surface-wave tomography. Then, using a genetic algorithm, a 3D shear-wave speed model of the crust and uppermost mantle have been derived from these maps with a spatial resolution of 0.4° × 0.4°. Four characteristics can be outlined from the results： （1） Except in the Datong volcanic zone, in the depth range of 11-30 km, the location of a transition zone between the highand low-velocity regions is in agreement with the seismicity pattern in the study region, and the earthquakes are mostly concentrated near this transition zone; （2） In the depth range of 31-40 km, shear-wave velocities are higher to the south of the Taiyuan Basin and lower to the north, which is similar to the distribution pattern of Moho depth variations in the Shanxi region; （3） The shear-wave velocity pattern of higher velocities to the south of 38×N and lower velocities to the north is found to be consistent with that from the upper crustal levels to depth of 70 km. At the deeper depths, the spatial scale of the low-velocity anomalies zone in the north is gradually shrinking with depth increasing, the low-velocity anomalies are gradually disappearing beneath the Datong volcanic zone at the depth of 151-200 km. We proposed that the root of the Datong volcano may reach to a depth around 150 km; （4） Along the N-S vertical profile at 112.8°E, the 38°N latitude is the boundary between high and low velocities, arguing the tectonic difference between the Shanxi rift zone and its flanks, in the rift zone the seismic velocity is dominated by low-velocity anomalies while in the flanks it is high.展开更多
Fault zone trapped waves （FZTWs） mainly travel along the fractured fault zone （FZ） which is of low velocity and high attenuation. FZTWs often carry significant information about a fault＇s internal structure, so i...Fault zone trapped waves （FZTWs） mainly travel along the fractured fault zone （FZ） which is of low velocity and high attenuation. FZTWs often carry significant information about a fault＇s internal structure, so it is important to understand their wave field characteristics for FZ structure inversion. Most previous simulations are based on vertical faults, while in this paper we implement the FZTW simulations on vertical or inclined faults and compare their wave fields in both time and frequency domains. The results show that the existence of fault zone and inclined angle of fault can significantly influence the features of waves near faults. In amplitude, a fault zone can generate a larger amplitude of waves. The velocity contrast between two wails of fault may lead to amplification of amplitudes in the low velocity fault wall. In frequency, a fault zone tends to influence the waves in the low frequency range. In a pattern of particle polarization of FZTWs, it tends to be single direction for vertical faults but fork to multiple directions for inclined faults, which might provide a new way to study the fault zone with FZTWs. These conclusions may be valuable for FZ structure inversion, and will enhance the knowledge on near-fault strong ground motions.展开更多
Large earthquakes frequently occur along complex fault systems.Understanding seismic rupture and long-term fault evolution requires constraining the geometric and material properties of fault zone structures.We provid...Large earthquakes frequently occur along complex fault systems.Understanding seismic rupture and long-term fault evolution requires constraining the geometric and material properties of fault zone structures.We provide a comprehensive overview of recent advancements in seismological methods used to study fault zone structures,including seismic tomography,fault zone seismic wave analysis,and seismicity analysis.Observational conditions limit our current ability to fully characterize fault zones,for example,insufficient imaging resolution to discern small-scale anomalies,incomplete capture of crucial fault zone seismic waves,and limited precision in event location accuracy.Dense seismic arrays can overcome these limitations and enable more detailed investigations of fault zone structures.Moreover,we present new insights into the structure of the Anninghe-Xiaojiang fault zone in the southeastern margin of the Qinghai-Xizang Plateau based on data collected from a dense seismic array.We found that utilizing a dense seismic array can identify small-scale features within fault zones,aiding in the interpretation of fault zone geometry and material properties.展开更多
The observation of the fault-zone trapped waves was conducted using a seismic line with dense receivers across surface rupture zone of the M=8.1 Kunlun Mountain earthquake. The fault zone trapped waves were separated ...The observation of the fault-zone trapped waves was conducted using a seismic line with dense receivers across surface rupture zone of the M=8.1 Kunlun Mountain earthquake. The fault zone trapped waves were separated from seismograms by numerical filtering and spectral analyzing. The results show that: a) Both explosion and earthquake sources can excite fault-zone trapped waves, as long as they locate in or near the fault zone; b) Most energy of the fault-zone trapped waves concentrates in the fault zone and the amplitudes strongly decay with the distance from observation point to the fault zone; c) Dominant frequencies of the fault-zone trapped waves are related to the width of the fault zone and the velocity of the media in it. The wider the fault zone or the lower the velocity is, the lower the dominant frequencies are; d) For fault zone trapped waves, there exist dispersions; e) Based on the fault zone trapped waves observed in Kunlun Mountain Pass region, the width of the rupture plane is deduced to be about 300 m and is greater than that on the surface.展开更多
Pingtong Town is located on the fractured zone of the Wenchuan 8.0 earthquake, and is seriously damaged by the earthquake. Our observation line is centered at an earthquake exploration trench across the fractured zone...Pingtong Town is located on the fractured zone of the Wenchuan 8.0 earthquake, and is seriously damaged by the earthquake. Our observation line is centered at an earthquake exploration trench across the fractured zone in the NW-SE direction, and is about 400 m long. The results reveal trapped waves in the rup- tured fault zone of the earthquake, and indicate a great difference in physical property between the media inside and outside the fault zone. The predominant frequency of the fault-zone trapped waves is about 3 -4 Hz. The wave amplitudes are larger near the exploration trench. The width of the fault zone in the crust at this location is estimated to be 200 m. In some records, the waveforms and the arrival times of S waves are quite different between the two sides of the trench. The place of change coincides with the boundary of uplift at the surface.展开更多
When waves propagate from deep water to shallow water, wave heights and steepness increase and then waves roll back and break. This phenomenon is called surf. Currently, the present statistical calculation model of su...When waves propagate from deep water to shallow water, wave heights and steepness increase and then waves roll back and break. This phenomenon is called surf. Currently, the present statistical calculation model of surf was derived mainly from the wave energy conservation equation and the linear wave dispersion relation, but it cannot reflect accurately the process which is a rapid increasing in wave height near the broken point. So, the concept of a surf breaking critical zone is presented. And the nearshore is divided as deep water zone, shallow water zone, surf breaking critical zone and after breaking zone. Besides, the calculation formula for the height of the surf breaking critical zone has founded based on flume experiments, thereby a new statistical calculation model on the surf has been established. Using the new model, the calculation error of wave height maximum is reduced from 17.62% to 6.43%.展开更多
In the paper, we report about the possibilities to apply the photon sieve principle to binary diffractive lens in millimeter wave band. The FDTD simulation showing the idea of the photon sieve application to millimete...In the paper, we report about the possibilities to apply the photon sieve principle to binary diffractive lens in millimeter wave band. The FDTD simulation showing the idea of the photon sieve application to millimeter wave optics does not allow increasing the resolution power. The reason is the small number of holes in the FZP aperture. But such simulation results may be used as computational experiments of simple scale in millimeter wave allowing obtaining insight into physical systems which are characterized by nanometric objects, because the D/f and D/λ are almost the same.展开更多
A coupled ocean-ice-wave model is used to study ice-edge jet and eddy genesis during surface gravity wave dissipation in a frazil-pancake ice zone. With observational data from the Beaufort Sea, possible wave dissipat...A coupled ocean-ice-wave model is used to study ice-edge jet and eddy genesis during surface gravity wave dissipation in a frazil-pancake ice zone. With observational data from the Beaufort Sea, possible wave dissipation processes are evaluated using sensitivity experiments. As wave energy dissipated, energy was transferred into ice floe through radiation stress. Later, energy was in turn transferred into current through ocean-ice interfacial stress. Since most of the wave energy is dissipated at the ice edge, ice-edge jets, which contained strong horizontal shear, appeared both in the ice zone and the ocean. Meanwhile, the wave propagation direction determines the velocity partition in the along-ice-edge and cross-ice-edge directions, which in turn determines the strength of the along-ice-edge jet and cross-ice-edge velocity. The momentum applied in the along-ice-edge(cross-ice-edge)direction increased(decreased) with larger incident angle, which is favorable condition for producing stronger mesoscale eddies, vice versa. The dissipation rate increases(decreases) with larger(smaller) wavenumber, which enhances(reduces) the jet strength and the strength of the mesoscale eddy. The strong along-ice-edge jet may extend to a deep layer(> 200 m). If the water depth is too shallow(e.g., 80 m), the jet may be largely dampened by bottom drag, and no visible mesoscale eddies are found. The results suggest that the bathymetry and incident wavenumber(magnitude and propagation direction) are important for wave-driven current and mesoscale eddy genesis.展开更多
基金sponsored by National Natural Science Foundation of China (No.40674043, 90814001)China Earthquake Admini-stration (Wenchuan Earthquake Scientific Survey 03-05)The contribution No. of this paper is RCEG 0905 of Geophysical Prospecting Center,China Earthquake Administration
文摘The rupture process of the May 12, 2008 Ms8.0 Wenchuan earthquake was very complex. To study the rupture zones generated by this earthquake, four dense temporary seismic arrays across the two surface breaking traces of the main-shock were deployed in July and recorded a great amount of aftershocks. This paper focuses on the data interpretation of two arrays across the central main fault, the northern array line 1 and southern array line 3. The fault zone trapped waves recorded by the two arrays were used to study the structure of the central main fault and the difference between the northern and southern portions. The results show that the widths of the rupture zone are about 170-200 m and 200-230 m for northern and southern portions respectively. And the corresponding dip angles are 80° and 70°. The seismic velocity inside the fracture zone is about one half of the host rock. By comparison, the northern portion of the rupture zone is slightly narrower and steeper than the southern portion. Besides these differences, one more interesting and important difference is the positions of the rupture zone with respect to surface breaking traces. At the northern portion, the rupture zone is centered at the surface breaking trace, while at the southern portion it is not but is shifted to the northwest. This difference reflects the difference of rupture behaviors between two portions of the central main fault. The width of the rupture zone is smaller than that of MS.1 Kunlun earthquake though these two earthquakes have almost the same magnitudes. Multiple ruptures may be one factor to cause the narrower rupture zone.
基金Supported by Doctoral Fund of Education Ministry of China ( No. 20010056033) , National Natural Science Foundation of China(No. 10202003, No. 50479015) ,and National Science Fund for Distinguished Young Scholars(No. 03QMH1408).
文摘The wave characteristics affecting coastal sediment transport include wave height, wave period and breaking wave direction. Wave height is a critical factor in determining the amount of sediment transport in the coastal area. The force of sediment transport is much more intense under breaking waves than under non-breaking waves. Breaking waves exhibit various patterns, principal- ly depending on the incident wave steepness and the beach slope. Based on the equations of con- servation of mass, momentum and energy, a theoretical model for wave deformation in and outside the surf zone was obtained, which is used to calculate the wave shoaling, wave set-up and set- down and wave height distributions in and outside the surf zone. The analysis and comparison were made about the breaking point location and the wave height decay caused by the wave breaking and the bottom friction. Flume experiments relating to the spilling wave height distribution across the surf zone were conducted to verify the theoretical model. Advanced wave maker, data sampling de- vices and data processing system were utilized in the flume experiments with a slope covered by sands of different diameters to facilitate the observation and research on the wave transformation and breaking. The agreement between the theoretical and experimental results is good.
基金supported by the "Wenchuan Earthquake Fault Scientific Drilling" of the National Science Foundation of China
文摘This article is to review results from scientific drilling and fault-zone trapped waves （FZTWs） at the south Longman-Shan fault （LSF） zone that ruptured in the 2008 May 12 M8 Wenchuan earthquake in Sichuan,China.Immediately after the mainshock,two Wenchuan Fault Scientific Drilling （WFSD） boreholes were drilled at WFSD-1 and WFSD-2 sites approximately 400 m and 1 km west of the surface rupture along the Yinxiu-Beichuan fault （YBF）,the middle fault strand of the south LSF zone.Two boreholes met the principal slip of Wenchuan earthquake along the YBF at depths of 589-m and 1230-m,respectively.The slip is accompanied with a 100-200-m-wide zone consisting of fault gouge,breccia,cataclasite and fractures.Close to WFSD-1 site,the nearly-vertical slip of ～4.3-m with a 190-m wide zone of highly fractured rocks restricted to the hanging wall of the YBF was found at the ground surface after the Wenchuan earthquake.A dense linear seismic array was deployed across the surface rupture at this venue to record FZTWs generated by aftershocks.Observations and 3-D finite-difference simulations of FZTWs recorded at this cross-fault array and network stations close to the YBF show a distinct low-velocity zone composed by severely damaged rocks along the south LSF at seismogenic depths.The zone is several hundred meters wide along the principal slip,within which seismic velocities are reduced by ～30-55％ from wall-rock velocities and with the maximum velocity reduction in the ～200-m-wide rupture core zone at shallow depth.The FZTW-inferred geometry and physical properties of the south LSF rupture zone at shallow depth are in general consistent with the results from petrological and structural analyses of cores and well log at WFSD boreholes.We interpret this remarkable low-velocity zone as being a break-down zone during dynamic rupture in the 2008 M8 earthquake.We examined the FZTWS generated by similar earthquakes before and after the 2008 mainshock and observed that seismic velocities within fault core zone was reduced by ～10％ due to severe damage of fault rocks during the M8 mainshock.Scientific drilling and locations of aftershocks generating prominent FZTWs also indicate rupture bifurcation along the YBF and the Anxian-Guangxian fault （AGF）,two strands of the south LSF at shallow depth.A combination of seismic,petrologic and geologic study at the south LSF leads to further understand the relationship between the fault-zone structure and rupture dynamics,and the amplification of ground shaking strength along the low-velocity fault zone due to its waveguide effect.
基金supported by the National Natural Science Foundation ofChina(41074069,40974053,90814001)RRCEG201103
文摘Trapped waves in the Qingchuan fault zone were observed at Muyu near the northeastern end of the fractured zone of the Wenchuan Ms8. 0 earthquake. The results indicate a fault-zone width of about 200 m and a great difference in physical property of the crust on different sides of the fault. The inferred location of crustal changes is consistent with land-form boundary on the surface
基金supported by the National Natural Science Foundation of China(4107406940974053+1 种基金40774043)RCEG201301
文摘Trapped waves in different sections of Longmenshan fault belt were observed, and the results show the difference between the northern and southern portions of this fault belt. Guanzhuang and Leigu surveying lines are located at the northern portion of the fault belt, and the result indicates that the width of the rupture zone underground in this area is about 160 - 180 m. The center position of rupture zone underground corresponds to the surface breaking trace, and is equally distributed at the edges of the two fault walls. However, Hongkou surveying line is located at the southern portion of the fault belt, and the result indicates that the width of the rupture zone underground in this area is about 180 -200 m. The rupture zone underground is mainly distributed below fault scarp. The Wenchuan MsS. 0 earthquake and Lushan Ms7.0 earthquake both occurred at the Longmenshan fault belt. The results will provide information for the structure background of the two violent earthquakes.
基金This research is supported by the National Science Council of Taiwan under the grant of NSC 86-2611-E-006-019.
文摘The purpose of this paper is to extend the validity of Li's parabolic model (1994) by incorporating a combined energy factor in the mild-slope equation and by improving the traditional radiation boundary conditions. With wave breaking and energy dissipation expressed in a direct form in the equation, the proposed model could provide an efficient numerical scheme and accurate predictions of wave transformation across the surf zone. The radiation boundary conditions are iterated in the model without use of approximations. The numerical predictions for wave height distributions across the surf zone are compared with experimental data over typical beach profiles. In addition, tests of waves scattering around a circular pile show that the proposed model could also provide reasonable improvement on the radiation boundary conditions for large incident angles of waves.
基金supported by the Open Fund of the Key Labo-ratory of Geo-detection (China University of Geosciences, Bei-jing),Ministry of Education (No. GDL0708)
文摘Large property contrasts between materials in a fault zone and the surrounding rock are often produced by repeating earthquakes. Fault zones are usually characterized by fluid concentration, clay-rich fault gouge, increased porosity, and dilatant cracks. Thus, fault zones are thought to have reduced seismic velocities than the surrounding rocks. In this article, we first investigated the synthetic waveforms at a linear array across a vertical fault zone by using 3D finite difference simulation. Synthetic waveforms show that when sources are close to, inside, or below the fault zone, both arrival times and waveforms of P-and S-waves vary systematically across the fault zone due to reflections and transmissions from boundaries of the low-velocity fault zone. The arrival-time patterns and waveform characteristics can be used to determine the fault zone structure. Then, we applied this method to the aftershock waveform data of the 1992 Landers M7.4 and the 2008 Wenchuan （汶川） M8.0 earthquakes. Landers waveform data reveal a low-velocity zone with a width of approximately 270-370 m, and P-and S-wave velocity reductions relative to the host rock of approximately 35%-60%; Wenchuan waveform data suggest a low-velocity zone with a width of approximately 220-300 m, and P-and S-wave velocities drop relative to the host rock of approximately 55%.
文摘Rapid population growth and major trends of world economy growth have led to significant energy needs in our country. Benin, Gulf of Guinea country, although with a significant coastal network powered by potential energy from breaking waves, has experienced a deficit and a critical energy instability, marked by recurrent power cuts and disruption of the national economy. To ensure the integration of this source of renewable energy in the Benin energy mix and sustainably reduce the energy deficit in progress, this work has aimed to study the dissipation of wave energy at the bathymetric breaking in the breakers zone of Cotonou coast. Sea conditions and the statistics parameters of the breaking waves under perturbation effect of the seabed were evaluated to predict the beginning of the breaking. The modeling is based on the Navier-Stokes equation in which the viscosity and the interactions between the molecules of the oceanic fluid are neglected. The nonlinear wave dispersion relation is also used. The results obtained for this purpose showed that water particles have an almost parabolic motion during their fall;their velocity is higher than those of the early breaking. In this area, the waves dissipate about 80% of their energy: it generates turbulence which leads to a strong setting in motion of sediments.
基金supported by Open Grant from State key Laboratory of Geodesy and Earth’s Dynamics (Grant No. SKLGED2014-4-4-E)Office of Science and Technology in Shanxi province based on research Projects (2012011029)+1 种基金Scientific and Technological Research Projects in Shanxi province (20100311129-2, 20090311084)the China Earthquake Administration spark Project (XH15007)
文摘The Shanxi rift zone is one of the largest and active Cenozoic grabens in the world, studying the velocity structure of the crust and upper mantle in this region may help us to understand the mechanisms of rift processes and the seismogenic environment of active seismicity in continental rifts. In this work, using the broadband seismic data of Shanxi, Hebei, Henan, Shaanxi provinces, and the Inner Mongolia Autonomous Region from February 2009 to November 2011, we have picked out 350 high-quality phase velocity dispersion curves of fundamental mode Rayleigh waves at periods from 8 to 75 s, and Rayleigh wave phase velocity maps have been constructed from 8 to 75 s period with horizontal resolution ranging from 40 to 50 km by two-station surface-wave tomography. Then, using a genetic algorithm, a 3D shear-wave speed model of the crust and uppermost mantle have been derived from these maps with a spatial resolution of 0.4° × 0.4°. Four characteristics can be outlined from the results： （1） Except in the Datong volcanic zone, in the depth range of 11-30 km, the location of a transition zone between the highand low-velocity regions is in agreement with the seismicity pattern in the study region, and the earthquakes are mostly concentrated near this transition zone; （2） In the depth range of 31-40 km, shear-wave velocities are higher to the south of the Taiyuan Basin and lower to the north, which is similar to the distribution pattern of Moho depth variations in the Shanxi region; （3） The shear-wave velocity pattern of higher velocities to the south of 38×N and lower velocities to the north is found to be consistent with that from the upper crustal levels to depth of 70 km. At the deeper depths, the spatial scale of the low-velocity anomalies zone in the north is gradually shrinking with depth increasing, the low-velocity anomalies are gradually disappearing beneath the Datong volcanic zone at the depth of 151-200 km. We proposed that the root of the Datong volcano may reach to a depth around 150 km; （4） Along the N-S vertical profile at 112.8°E, the 38°N latitude is the boundary between high and low velocities, arguing the tectonic difference between the Shanxi rift zone and its flanks, in the rift zone the seismic velocity is dominated by low-velocity anomalies while in the flanks it is high.
基金sponsored by the Key Basic Scientific Research Program of Institute of Earth Science,CEA(0213241302)
文摘Fault zone trapped waves （FZTWs） mainly travel along the fractured fault zone （FZ） which is of low velocity and high attenuation. FZTWs often carry significant information about a fault＇s internal structure, so it is important to understand their wave field characteristics for FZ structure inversion. Most previous simulations are based on vertical faults, while in this paper we implement the FZTW simulations on vertical or inclined faults and compare their wave fields in both time and frequency domains. The results show that the existence of fault zone and inclined angle of fault can significantly influence the features of waves near faults. In amplitude, a fault zone can generate a larger amplitude of waves. The velocity contrast between two wails of fault may lead to amplification of amplitudes in the low velocity fault wall. In frequency, a fault zone tends to influence the waves in the low frequency range. In a pattern of particle polarization of FZTWs, it tends to be single direction for vertical faults but fork to multiple directions for inclined faults, which might provide a new way to study the fault zone with FZTWs. These conclusions may be valuable for FZ structure inversion, and will enhance the knowledge on near-fault strong ground motions.
基金supported by the National Key R&D Program of China(No.2022YFF0800601)the National Natural Science Foundation of China(No.U2039204)the Special Fund of the Institute of Geophysics,China Earthquake Administration(No.DQJB23B22).
文摘Large earthquakes frequently occur along complex fault systems.Understanding seismic rupture and long-term fault evolution requires constraining the geometric and material properties of fault zone structures.We provide a comprehensive overview of recent advancements in seismological methods used to study fault zone structures,including seismic tomography,fault zone seismic wave analysis,and seismicity analysis.Observational conditions limit our current ability to fully characterize fault zones,for example,insufficient imaging resolution to discern small-scale anomalies,incomplete capture of crucial fault zone seismic waves,and limited precision in event location accuracy.Dense seismic arrays can overcome these limitations and enable more detailed investigations of fault zone structures.Moreover,we present new insights into the structure of the Anninghe-Xiaojiang fault zone in the southeastern margin of the Qinghai-Xizang Plateau based on data collected from a dense seismic array.We found that utilizing a dense seismic array can identify small-scale features within fault zones,aiding in the interpretation of fault zone geometry and material properties.
基金Joint Earthquake Science Foundation of China (201001).
文摘The observation of the fault-zone trapped waves was conducted using a seismic line with dense receivers across surface rupture zone of the M=8.1 Kunlun Mountain earthquake. The fault zone trapped waves were separated from seismograms by numerical filtering and spectral analyzing. The results show that: a) Both explosion and earthquake sources can excite fault-zone trapped waves, as long as they locate in or near the fault zone; b) Most energy of the fault-zone trapped waves concentrates in the fault zone and the amplitudes strongly decay with the distance from observation point to the fault zone; c) Dominant frequencies of the fault-zone trapped waves are related to the width of the fault zone and the velocity of the media in it. The wider the fault zone or the lower the velocity is, the lower the dominant frequencies are; d) For fault zone trapped waves, there exist dispersions; e) Based on the fault zone trapped waves observed in Kunlun Mountain Pass region, the width of the rupture plane is deduced to be about 300 m and is greater than that on the surface.
基金supported by the Natural Science Fundation of China(40774043,40674043,90814001)
文摘Pingtong Town is located on the fractured zone of the Wenchuan 8.0 earthquake, and is seriously damaged by the earthquake. Our observation line is centered at an earthquake exploration trench across the fractured zone in the NW-SE direction, and is about 400 m long. The results reveal trapped waves in the rup- tured fault zone of the earthquake, and indicate a great difference in physical property between the media inside and outside the fault zone. The predominant frequency of the fault-zone trapped waves is about 3 -4 Hz. The wave amplitudes are larger near the exploration trench. The width of the fault zone in the crust at this location is estimated to be 200 m. In some records, the waveforms and the arrival times of S waves are quite different between the two sides of the trench. The place of change coincides with the boundary of uplift at the surface.
基金The National Natural Science Foundation of China under contract Nos 41076048 and 40906044
文摘When waves propagate from deep water to shallow water, wave heights and steepness increase and then waves roll back and break. This phenomenon is called surf. Currently, the present statistical calculation model of surf was derived mainly from the wave energy conservation equation and the linear wave dispersion relation, but it cannot reflect accurately the process which is a rapid increasing in wave height near the broken point. So, the concept of a surf breaking critical zone is presented. And the nearshore is divided as deep water zone, shallow water zone, surf breaking critical zone and after breaking zone. Besides, the calculation formula for the height of the surf breaking critical zone has founded based on flume experiments, thereby a new statistical calculation model on the surf has been established. Using the new model, the calculation error of wave height maximum is reduced from 17.62% to 6.43%.
文摘In the paper, we report about the possibilities to apply the photon sieve principle to binary diffractive lens in millimeter wave band. The FDTD simulation showing the idea of the photon sieve application to millimeter wave optics does not allow increasing the resolution power. The reason is the small number of holes in the FZP aperture. But such simulation results may be used as computational experiments of simple scale in millimeter wave allowing obtaining insight into physical systems which are characterized by nanometric objects, because the D/f and D/λ are almost the same.
基金The National University of Defense Technology under contract No. ZK18-03-29.
文摘A coupled ocean-ice-wave model is used to study ice-edge jet and eddy genesis during surface gravity wave dissipation in a frazil-pancake ice zone. With observational data from the Beaufort Sea, possible wave dissipation processes are evaluated using sensitivity experiments. As wave energy dissipated, energy was transferred into ice floe through radiation stress. Later, energy was in turn transferred into current through ocean-ice interfacial stress. Since most of the wave energy is dissipated at the ice edge, ice-edge jets, which contained strong horizontal shear, appeared both in the ice zone and the ocean. Meanwhile, the wave propagation direction determines the velocity partition in the along-ice-edge and cross-ice-edge directions, which in turn determines the strength of the along-ice-edge jet and cross-ice-edge velocity. The momentum applied in the along-ice-edge(cross-ice-edge)direction increased(decreased) with larger incident angle, which is favorable condition for producing stronger mesoscale eddies, vice versa. The dissipation rate increases(decreases) with larger(smaller) wavenumber, which enhances(reduces) the jet strength and the strength of the mesoscale eddy. The strong along-ice-edge jet may extend to a deep layer(> 200 m). If the water depth is too shallow(e.g., 80 m), the jet may be largely dampened by bottom drag, and no visible mesoscale eddies are found. The results suggest that the bathymetry and incident wavenumber(magnitude and propagation direction) are important for wave-driven current and mesoscale eddy genesis.
