For distinguishing the periodicity of strong earthquakes on the time scale of decades, we generalized the Rydelek-Sacks test (R) delek. Sacks. 1989) to explore whether a time series is modulated by a periodic process ...For distinguishing the periodicity of strong earthquakes on the time scale of decades, we generalized the Rydelek-Sacks test (R) delek. Sacks. 1989) to explore whether a time series is modulated by a periodic process or not. Thetest is conducted by comparing the total phasor of seismicity with that produced by a random Brownian motion.The phdse angle is defined by the origin time of earthquakes relative to a reference time scale. Using this methodwe tested two hypotheses in geodynamics and earthquake prediction study. One is the hypothesis of Romanowicz( 1993 ) who proposed that the great earthquakes alternate in a predictable fashion between strike-slip and thrustingmechanisms oil a 20~30 years cycle. The other hypothesis is that the strong earthquakes in and around China havean active period of about ten years. The test obtains a negative conclusion for the former hypothesis and a positiveconclusion for the latter at the 93% confidence level.展开更多
In this paper a group of long period seismic waves in Shanghai area induced by Taiwan large earthquake is presented by using the method of semi empirical Green function, the period is up to 20 s. Such seismic waves c...In this paper a group of long period seismic waves in Shanghai area induced by Taiwan large earthquake is presented by using the method of semi empirical Green function, the period is up to 20 s. Such seismic waves can be used as a reference curve to test the strength of long period structures and their aseismic design. The long period part of seismic influence curve presented in 'Architecture Aseismic Design Code'(GBJ11 89) is less than 3 s, and uncertainties exist in the effects of earthquake safety evaluation. This research will be able to eliminate these shortages.展开更多
In this paper we simulate the repeated occurrence of strong earthquakes along a strike-slip fault by using a finite element model. The fault valve mechanism is included in the model in order to take into account the e...In this paper we simulate the repeated occurrence of strong earthquakes along a strike-slip fault by using a finite element model. The fault valve mechanism is included in the model in order to take into account the effeCt of POre fluid pressure variation. Five parameters are used to characterize the rheology of the fault, POre pressure variation, and fracture criteria. By Systematically varying these parameters and calculating a large number of models we carried out a preliminary investigation on the alternatively quiet and active periods of seismicity and their relation to model Parameters and loading conditions. Under the action of a constant-rate boundary movement, in the case of intermediate stress and pore pressure, the models display a regular quiescence-activity phenomenon with a cycle length of 1/3-1 of the recurrence pened. When the model is under high stress or high pore pressure, this phenomenon becomes irregular or inexplicit. When the model is subject to periedic boundary forces and the amplitude of force variation is not too small, it results in an alternatively quiet and active seismicity Pattern with the same Period Of the force variation.展开更多
The sufficient estimation of the natural period of vibration constitutes an essential step in earthquake design and assessment and its role in the development of seismic damage is investigated in the current research....The sufficient estimation of the natural period of vibration constitutes an essential step in earthquake design and assessment and its role in the development of seismic damage is investigated in the current research. The fundamental period is estimated for typical reinforced concrete building types, representative of the building stock of Southern Europe, according to existing relationships. The building typologies also represent groups of 180,945 existing damaged buildings of an observational database created after the Athens (7-9-1999) near field earthquake. The estimated fundamental periods are correlated to several degrees of the recorded damage. Important conclusions are drawn on the parameters (height, structural type, etc.) that influence the seismic response and the development of damage based on the wide database. After conducting a correlation analysis, noticeable is the difference between the seismic demand of the elastic spectrum of the first (1959), the contemporary (2003) Greek Seismic Code and the values of peak ground accelerations of several Athens earthquake records. Moreover, PGAs in most records are often between the lower and the upper bound of the estimated fundamental periods for RC buildings with regular infills (n-normal) and with ground levels without infill panels (p-pilotis) regardless the height. A disparity is noticed when the estimated fundamental period is based on EC8 provisions for the considered as “high” buildings in S. Europe regarding the referring earthquake. The majority of buildings that developed several degree, type and extent of damage are considered of “low” height with estimated fundamental periods close to the PGA values of Athens earthquake ground motions. However, the developed damage was the result of the combination of parameters based on geological, tectonic and morphological characteristics of the affected area. In addition, a damage scale for the measurable recording, beyond the qualitative characterization of seismic damage in Greek post-earthquake surveys, is presented wherein the performance levels are defined according to the physical description of the seismic damage and, as well, in terms of structural and economic damage index.展开更多
Seismic pounding phenomena, particularly the collision of neighboring buildings under long-period ground motion, are becoming a significant issue in Japan. We focused on a specific apartment structure called the Nuevo...Seismic pounding phenomena, particularly the collision of neighboring buildings under long-period ground motion, are becoming a significant issue in Japan. We focused on a specific apartment structure called the Nuevo Leon buildings in the Tlatelolco district of Mexico City, which consisted of three similar buildings built consecutively with narrow expansion joints between the buildings. Two out of the three buildings collapsed completely in the 1985 Mexican earthquake. Using a finite element code based on the adaptively shifted integration (ASI)-Gauss technique, a seismic pounding analysis is performed on a simulated model of the Nuevo Leon buildings to understand the impact and collapse behavior of structures built near each other. The numerical code used in the analysis provides a higher computational efficiency than the conventional code for this type of problem and enables us to address dynamic behavior with strong nonlinearities, including phenomena such as member fracture and elemental contact. Contact release and recontact algorithms are developed and implemented in the code to understand the complex behaviors of structural members during seismic pounding and the collapse sequence. According to the numerical results, the collision of the buildings may be a result of the difference of natural periods between the neighboring buildings. This difference was detected in similar buildings from the damages caused by previous earthquakes. By setting the natural period of the north building to be 25% longer than the other periods, the ground motion, which hada relatively long period of 2 s, first caused the collision between the north and the center buildings. This collision eventually led to the collapse of the centerbuilding, followed by the destruction of the north building.展开更多
We report here the observation result of joint observation of long period tremor signals with broadband seismome-ter,tiltmeter and gravimeter at the HUST(Huazhong University of Science and Technology)station.The obser...We report here the observation result of joint observation of long period tremor signals with broadband seismome-ter,tiltmeter and gravimeter at the HUST(Huazhong University of Science and Technology)station.The observed data were compared and analyzed.Since 2005,the several tens of abnormal tremor signals which are weak,com-plex and duration of 2 to 3 days have been synchronously recorded by the different instruments.The tremor signals have the periodic domain in the range of 3 to 5 minutes,20 to 30 minutes and even more than 1 hour.The observa-tion shows such tremors are a physical existence.The analysis indicates that a part of the tremors caused by the typhoon from the western Pacific Ocean.These tremors have a close relationship with wind velocity of typhoon and distance between the typhoon center and the station.Except these,the cause of others is still unclear.展开更多
The sub-regions are divided for the seismicity of the Chinese mainland based on the hypothesis of the active crustal blocks and the division of the active boundaries. On this result, the seismicity of each active crus...The sub-regions are divided for the seismicity of the Chinese mainland based on the hypothesis of the active crustal blocks and the division of the active boundaries. On this result, the seismicity of each active crustal blocks are studied by calculating the accumulated and released strain of the earthquakes based on strain accumulating and releasing model, and the different seismicity stages of the sub-regions are discussed basically. Finally we have discussed the premise of the model application and the potential problems of the model results.展开更多
This paper introduces a new seismic isolation system called a periodic foundation (PF), where inclusions are periodically arranged. The PF is different from traditional base isolation in that it causes a fundamental...This paper introduces a new seismic isolation system called a periodic foundation (PF), where inclusions are periodically arranged. The PF is different from traditional base isolation in that it causes a fundamental frequency shift in the structure, thus reducing its response and generating a frequency gap. If the frequency contents of a seismic wave fall into the gap, it can not propagate in the foundation. Thus, it will exert no influence on the structure above. A systematic study of the band of frequency gap for a 2D PF is conducted. The influence of physical and geometrical parameters such as density and elastic modulus as well as filling fraction of the PF and its materials on the band of frequency gap are investigated, and a design with a frequency gap as low as 2.49-3.72 Hz is achieved. This band of frequency gap corresponds well to the design spectra in earthquake engineering. Numerical simulations of a six-story frame structure with different foundations demonstrate that a proposed PF can greatly reduce the seismic response of an isolated structure. This investigation shows that PFs have great potential in future applications of seismic isolation technology.展开更多
Broad band and very broad band (BB and VBB) records of Chinese Digital Seismograph Network (CDSN) from 65 earthquakes are used to calculate the horizontal relative displacement, relative velocity and absolute accelera...Broad band and very broad band (BB and VBB) records of Chinese Digital Seismograph Network (CDSN) from 65 earthquakes are used to calculate the horizontal relative displacement, relative velocity and absolute acceleration response spectra with critical damping ratio ζ =0.005, 0.01, 0.02, 0.05 and 0.10, respectively. The results show that it is insufficient to obtain the credible characteristics of long-period ground motion response spectra only with the common ground acceleration records in engineering, while the broad band records of CDSN, as an important supplementary to ground acceleration records, can be used to study the characteristics of long-period ground motion response spectra.展开更多
The available models for eff ective periods of site and structure are reviewed in context of frequency tuning in the inelastic seismic response of soil-structure system. The eff ect of seismic intensity and ductility ...The available models for eff ective periods of site and structure are reviewed in context of frequency tuning in the inelastic seismic response of soil-structure system. The eff ect of seismic intensity and ductility demand, on the eff ective periods, is investigated, and inelastic site amplifi cation is shown to be strongly correlated to the normalized eff ective period. Two non-dimensional parameters, analogous to the conventional site amplifi cation factors in codes, are defi ned to quantify the inelastic site amplifi cation. It is shown that the inelastic site amplifi cation factor (i.e. ratio of constant ductility spectral ordinates at soil site to those at rock outcrop) is able to represent the site eff ects more clearly, as compared to the inelastic site amplifi cation ratio (i.e. ratio of inelastic spectral ordinates at soil site to the corresponding elastic spectral ordinates at rock outcrop). Further, the peak in the amplifi cation factor corresponding to the eff ective site period diminishes rapidly with increasing ductility demand.展开更多
Based on the study of activity of earthquakes with M**********】7.0 in China's Mainland,we have found a dynamic pattern,i.e.,the cyclic characteristics in time and migration from one seismic zone to another in spa...Based on the study of activity of earthquakes with M**********】7.0 in China's Mainland,we have found a dynamic pattern,i.e.,the cyclic characteristics in time and migration from one seismic zone to another in space.In order to understand the physical mechanism of this pattern,we use a nonlinear dynamic model to simulate the seismic activity in fault zones under a unified tectonic stress field.The basic elements in our model consist of a Maxwell body and a rigid sliding block.Basic elements in a column represent a fault,and coupling elements connecting different columns simulate the interaction among faults and fault segments.The results provide insights to the cyclic activity of strong earthquakes and to the feature of mutual influence between strong earthquakes in groups in the climax of seismic activity.展开更多
This paper analyzes the seismicity in Bohai Sea,introducing a shape factor K to characterize the seismic risk distribution in sub-regions of the sea. Based on the seismic design ground motions for 46 platforms located...This paper analyzes the seismicity in Bohai Sea,introducing a shape factor K to characterize the seismic risk distribution in sub-regions of the sea. Based on the seismic design ground motions for 46 platforms located in the Bohai Sea,a statistical analysis was performed for different peak ground acceleration (PGA) ratios at two different probability levels. In accordance with the two-stage design method,a scheme of two seismic design levels is proposed,and two seismic design objectives are established respectively for the strength level earthquake and the ductility level earthquake. By analogy with and comparison to the Chinese seismic design code for buildings,it is proposed that the probability level for the strength level earthquake and ductility level earthquake have a return period of 200 and 1000 - 2500 years,respectively. The validity of these proposed values is discussed. Finally,the PGAs corresponding to these two probability levels are calculated for different sub-regions of the Bohai Sea.展开更多
A new set of seismic zoning maps were published in August 1, 2001. It includes two maps, one is the seismic zon-ing map of peak acceleration, and the other is the zoning map of the characteristic period of the respons...A new set of seismic zoning maps were published in August 1, 2001. It includes two maps, one is the seismic zon-ing map of peak acceleration, and the other is the zoning map of the characteristic period of the response spectrum. The exceeding probability of the map is 10% within 50 years. The scale of the map is 1:4 000 000. These maps serve as the national standard. The background of this project, technical approach and key scientific measures, the basic feature and the application of the maps are introduced in this paper.展开更多
On the basis of the past research and utilization on the windows and belts of seismic regime, the seismic regime network which has been supposed and proved in the past is set up by using the monthly frequency data of ...On the basis of the past research and utilization on the windows and belts of seismic regime, the seismic regime network which has been supposed and proved in the past is set up by using the monthly frequency data of small earthquakes from 1970 to 1991 over the whole country. Through checking its function in practice, it is found that the spatial distribution of precursor information is not an isolate window or belt, but a broad precursor information field before the Ms≥7. 0 earthquakes in China and its nearby regions. According to the windows and belts in the field, synchronism and generality of initial time and place of prediction, the comprehensive prediction of activity time periods of groups of strong earthquakes and the detail method of correspondence of groups are proposed. After restrict mathematical test, 10 prediction methods for references are set forth, in which two best methods are selected as references for the whole case prediction in one to three years. Some related problems are discussed at the end of this paper.展开更多
Formed on top of the Gulf of Cadiz, the Al Idrissi mud volcano is the shallowest and largest mud volcano in the El Arraiche mud volcano field of the northwestern Moroccan margin. The development and morphology of mud ...Formed on top of the Gulf of Cadiz, the Al Idrissi mud volcano is the shallowest and largest mud volcano in the El Arraiche mud volcano field of the northwestern Moroccan margin. The development and morphology of mud volcanoes from the El Arraiche mud volcanoes group have been studied at a large scale. However, the time interval related to their formation period still needs to be better understood. In this regard, we interpreted and analyzed the seismic facies from the 2D reflection data of the GEOMARGEN-1 campaign, which took place in 2011. The aim was to identify the seismic sequences and draw the Al Idrissi mud volcano system to determine the formation period of the Al Idriss mud volcano. And as a result, the Al Idrissi mud volcano system is made of both buried and superficial bicone and was identified along with the Upper Tortonian to Messinian-Upper Pliocene facies. As the initial mud volcano extrusive edifice, the buried bicone was formed in the Late-Messinian to Early-Pliocene period. However, the superficial bicone, as the final extrusive edifice, was included in the Late Pliocene. In this case, the timing interval between the buried and superficial bicone is equivalent to the Late-Messinian to Upper-Pliocene period. Therefore, the latter corresponds to the Al Idrissi mud volcano formation period.展开更多
Estimation of seismic hazard for the fast developing coastal area of Pakistan is carried out using deterministic and probabilistic approaches. On the basis of seismotectonics and geology, eleven faults are recognized ...Estimation of seismic hazard for the fast developing coastal area of Pakistan is carried out using deterministic and probabilistic approaches. On the basis of seismotectonics and geology, eleven faults are recognized in five seismic provinces as potential hazard sources. Maximum magnitude potential for each of these sources is calculated. Peak ground acceleration (PGA) values at the seven coastal cities due to the maximum credible earthquake on the relevant source are also obtained. Cities of Gwadar and Ormara with acceleration values of 0.21g and 0.25g respectively fall in the high seismic risk area. Cities of Turbat and Karachi lie in low seismic risk area with acceleration values of less than 0.1g. The Probabilistic PGA maps with contour interval of 0.05g for 50 and 100 years return period with 90% probability of non-exceedance are also compiled.展开更多
文摘For distinguishing the periodicity of strong earthquakes on the time scale of decades, we generalized the Rydelek-Sacks test (R) delek. Sacks. 1989) to explore whether a time series is modulated by a periodic process or not. Thetest is conducted by comparing the total phasor of seismicity with that produced by a random Brownian motion.The phdse angle is defined by the origin time of earthquakes relative to a reference time scale. Using this methodwe tested two hypotheses in geodynamics and earthquake prediction study. One is the hypothesis of Romanowicz( 1993 ) who proposed that the great earthquakes alternate in a predictable fashion between strike-slip and thrustingmechanisms oil a 20~30 years cycle. The other hypothesis is that the strong earthquakes in and around China havean active period of about ten years. The test obtains a negative conclusion for the former hypothesis and a positiveconclusion for the latter at the 93% confidence level.
文摘In this paper a group of long period seismic waves in Shanghai area induced by Taiwan large earthquake is presented by using the method of semi empirical Green function, the period is up to 20 s. Such seismic waves can be used as a reference curve to test the strength of long period structures and their aseismic design. The long period part of seismic influence curve presented in 'Architecture Aseismic Design Code'(GBJ11 89) is less than 3 s, and uncertainties exist in the effects of earthquake safety evaluation. This research will be able to eliminate these shortages.
文摘In this paper we simulate the repeated occurrence of strong earthquakes along a strike-slip fault by using a finite element model. The fault valve mechanism is included in the model in order to take into account the effeCt of POre fluid pressure variation. Five parameters are used to characterize the rheology of the fault, POre pressure variation, and fracture criteria. By Systematically varying these parameters and calculating a large number of models we carried out a preliminary investigation on the alternatively quiet and active periods of seismicity and their relation to model Parameters and loading conditions. Under the action of a constant-rate boundary movement, in the case of intermediate stress and pore pressure, the models display a regular quiescence-activity phenomenon with a cycle length of 1/3-1 of the recurrence pened. When the model is under high stress or high pore pressure, this phenomenon becomes irregular or inexplicit. When the model is subject to periedic boundary forces and the amplitude of force variation is not too small, it results in an alternatively quiet and active seismicity Pattern with the same Period Of the force variation.
文摘The sufficient estimation of the natural period of vibration constitutes an essential step in earthquake design and assessment and its role in the development of seismic damage is investigated in the current research. The fundamental period is estimated for typical reinforced concrete building types, representative of the building stock of Southern Europe, according to existing relationships. The building typologies also represent groups of 180,945 existing damaged buildings of an observational database created after the Athens (7-9-1999) near field earthquake. The estimated fundamental periods are correlated to several degrees of the recorded damage. Important conclusions are drawn on the parameters (height, structural type, etc.) that influence the seismic response and the development of damage based on the wide database. After conducting a correlation analysis, noticeable is the difference between the seismic demand of the elastic spectrum of the first (1959), the contemporary (2003) Greek Seismic Code and the values of peak ground accelerations of several Athens earthquake records. Moreover, PGAs in most records are often between the lower and the upper bound of the estimated fundamental periods for RC buildings with regular infills (n-normal) and with ground levels without infill panels (p-pilotis) regardless the height. A disparity is noticed when the estimated fundamental period is based on EC8 provisions for the considered as “high” buildings in S. Europe regarding the referring earthquake. The majority of buildings that developed several degree, type and extent of damage are considered of “low” height with estimated fundamental periods close to the PGA values of Athens earthquake ground motions. However, the developed damage was the result of the combination of parameters based on geological, tectonic and morphological characteristics of the affected area. In addition, a damage scale for the measurable recording, beyond the qualitative characterization of seismic damage in Greek post-earthquake surveys, is presented wherein the performance levels are defined according to the physical description of the seismic damage and, as well, in terms of structural and economic damage index.
文摘Seismic pounding phenomena, particularly the collision of neighboring buildings under long-period ground motion, are becoming a significant issue in Japan. We focused on a specific apartment structure called the Nuevo Leon buildings in the Tlatelolco district of Mexico City, which consisted of three similar buildings built consecutively with narrow expansion joints between the buildings. Two out of the three buildings collapsed completely in the 1985 Mexican earthquake. Using a finite element code based on the adaptively shifted integration (ASI)-Gauss technique, a seismic pounding analysis is performed on a simulated model of the Nuevo Leon buildings to understand the impact and collapse behavior of structures built near each other. The numerical code used in the analysis provides a higher computational efficiency than the conventional code for this type of problem and enables us to address dynamic behavior with strong nonlinearities, including phenomena such as member fracture and elemental contact. Contact release and recontact algorithms are developed and implemented in the code to understand the complex behaviors of structural members during seismic pounding and the collapse sequence. According to the numerical results, the collision of the buildings may be a result of the difference of natural periods between the neighboring buildings. This difference was detected in similar buildings from the damages caused by previous earthquakes. By setting the natural period of the north building to be 25% longer than the other periods, the ground motion, which hada relatively long period of 2 s, first caused the collision between the north and the center buildings. This collision eventually led to the collapse of the centerbuilding, followed by the destruction of the north building.
文摘We report here the observation result of joint observation of long period tremor signals with broadband seismome-ter,tiltmeter and gravimeter at the HUST(Huazhong University of Science and Technology)station.The observed data were compared and analyzed.Since 2005,the several tens of abnormal tremor signals which are weak,com-plex and duration of 2 to 3 days have been synchronously recorded by the different instruments.The tremor signals have the periodic domain in the range of 3 to 5 minutes,20 to 30 minutes and even more than 1 hour.The observa-tion shows such tremors are a physical existence.The analysis indicates that a part of the tremors caused by the typhoon from the western Pacific Ocean.These tremors have a close relationship with wind velocity of typhoon and distance between the typhoon center and the station.Except these,the cause of others is still unclear.
基金The Development and Planning Project of National Important Base Research on the Mechanism and Forecast for Continental Strong Earthquake (G19980407).
文摘The sub-regions are divided for the seismicity of the Chinese mainland based on the hypothesis of the active crustal blocks and the division of the active boundaries. On this result, the seismicity of each active crustal blocks are studied by calculating the accumulated and released strain of the earthquakes based on strain accumulating and releasing model, and the different seismicity stages of the sub-regions are discussed basically. Finally we have discussed the premise of the model application and the potential problems of the model results.
基金National Natural Science Foundation of China Under Grant No.90715006
文摘This paper introduces a new seismic isolation system called a periodic foundation (PF), where inclusions are periodically arranged. The PF is different from traditional base isolation in that it causes a fundamental frequency shift in the structure, thus reducing its response and generating a frequency gap. If the frequency contents of a seismic wave fall into the gap, it can not propagate in the foundation. Thus, it will exert no influence on the structure above. A systematic study of the band of frequency gap for a 2D PF is conducted. The influence of physical and geometrical parameters such as density and elastic modulus as well as filling fraction of the PF and its materials on the band of frequency gap are investigated, and a design with a frequency gap as low as 2.49-3.72 Hz is achieved. This band of frequency gap corresponds well to the design spectra in earthquake engineering. Numerical simulations of a six-story frame structure with different foundations demonstrate that a proposed PF can greatly reduce the seismic response of an isolated structure. This investigation shows that PFs have great potential in future applications of seismic isolation technology.
文摘Broad band and very broad band (BB and VBB) records of Chinese Digital Seismograph Network (CDSN) from 65 earthquakes are used to calculate the horizontal relative displacement, relative velocity and absolute acceleration response spectra with critical damping ratio ζ =0.005, 0.01, 0.02, 0.05 and 0.10, respectively. The results show that it is insufficient to obtain the credible characteristics of long-period ground motion response spectra only with the common ground acceleration records in engineering, while the broad band records of CDSN, as an important supplementary to ground acceleration records, can be used to study the characteristics of long-period ground motion response spectra.
文摘The available models for eff ective periods of site and structure are reviewed in context of frequency tuning in the inelastic seismic response of soil-structure system. The eff ect of seismic intensity and ductility demand, on the eff ective periods, is investigated, and inelastic site amplifi cation is shown to be strongly correlated to the normalized eff ective period. Two non-dimensional parameters, analogous to the conventional site amplifi cation factors in codes, are defi ned to quantify the inelastic site amplifi cation. It is shown that the inelastic site amplifi cation factor (i.e. ratio of constant ductility spectral ordinates at soil site to those at rock outcrop) is able to represent the site eff ects more clearly, as compared to the inelastic site amplifi cation ratio (i.e. ratio of inelastic spectral ordinates at soil site to the corresponding elastic spectral ordinates at rock outcrop). Further, the peak in the amplifi cation factor corresponding to the eff ective site period diminishes rapidly with increasing ductility demand.
文摘Based on the study of activity of earthquakes with M**********】7.0 in China's Mainland,we have found a dynamic pattern,i.e.,the cyclic characteristics in time and migration from one seismic zone to another in space.In order to understand the physical mechanism of this pattern,we use a nonlinear dynamic model to simulate the seismic activity in fault zones under a unified tectonic stress field.The basic elements in our model consist of a Maxwell body and a rigid sliding block.Basic elements in a column represent a fault,and coupling elements connecting different columns simulate the interaction among faults and fault segments.The results provide insights to the cyclic activity of strong earthquakes and to the feature of mutual influence between strong earthquakes in groups in the climax of seismic activity.
基金the 2007 Special Research Project 8-55 of the Department of Finance and the State Science and Technology Support Project 2006BAC13B02
文摘This paper analyzes the seismicity in Bohai Sea,introducing a shape factor K to characterize the seismic risk distribution in sub-regions of the sea. Based on the seismic design ground motions for 46 platforms located in the Bohai Sea,a statistical analysis was performed for different peak ground acceleration (PGA) ratios at two different probability levels. In accordance with the two-stage design method,a scheme of two seismic design levels is proposed,and two seismic design objectives are established respectively for the strength level earthquake and the ductility level earthquake. By analogy with and comparison to the Chinese seismic design code for buildings,it is proposed that the probability level for the strength level earthquake and ductility level earthquake have a return period of 200 and 1000 - 2500 years,respectively. The validity of these proposed values is discussed. Finally,the PGAs corresponding to these two probability levels are calculated for different sub-regions of the Bohai Sea.
文摘A new set of seismic zoning maps were published in August 1, 2001. It includes two maps, one is the seismic zon-ing map of peak acceleration, and the other is the zoning map of the characteristic period of the response spectrum. The exceeding probability of the map is 10% within 50 years. The scale of the map is 1:4 000 000. These maps serve as the national standard. The background of this project, technical approach and key scientific measures, the basic feature and the application of the maps are introduced in this paper.
文摘On the basis of the past research and utilization on the windows and belts of seismic regime, the seismic regime network which has been supposed and proved in the past is set up by using the monthly frequency data of small earthquakes from 1970 to 1991 over the whole country. Through checking its function in practice, it is found that the spatial distribution of precursor information is not an isolate window or belt, but a broad precursor information field before the Ms≥7. 0 earthquakes in China and its nearby regions. According to the windows and belts in the field, synchronism and generality of initial time and place of prediction, the comprehensive prediction of activity time periods of groups of strong earthquakes and the detail method of correspondence of groups are proposed. After restrict mathematical test, 10 prediction methods for references are set forth, in which two best methods are selected as references for the whole case prediction in one to three years. Some related problems are discussed at the end of this paper.
文摘Formed on top of the Gulf of Cadiz, the Al Idrissi mud volcano is the shallowest and largest mud volcano in the El Arraiche mud volcano field of the northwestern Moroccan margin. The development and morphology of mud volcanoes from the El Arraiche mud volcanoes group have been studied at a large scale. However, the time interval related to their formation period still needs to be better understood. In this regard, we interpreted and analyzed the seismic facies from the 2D reflection data of the GEOMARGEN-1 campaign, which took place in 2011. The aim was to identify the seismic sequences and draw the Al Idrissi mud volcano system to determine the formation period of the Al Idriss mud volcano. And as a result, the Al Idrissi mud volcano system is made of both buried and superficial bicone and was identified along with the Upper Tortonian to Messinian-Upper Pliocene facies. As the initial mud volcano extrusive edifice, the buried bicone was formed in the Late-Messinian to Early-Pliocene period. However, the superficial bicone, as the final extrusive edifice, was included in the Late Pliocene. In this case, the timing interval between the buried and superficial bicone is equivalent to the Late-Messinian to Upper-Pliocene period. Therefore, the latter corresponds to the Al Idrissi mud volcano formation period.
文摘Estimation of seismic hazard for the fast developing coastal area of Pakistan is carried out using deterministic and probabilistic approaches. On the basis of seismotectonics and geology, eleven faults are recognized in five seismic provinces as potential hazard sources. Maximum magnitude potential for each of these sources is calculated. Peak ground acceleration (PGA) values at the seven coastal cities due to the maximum credible earthquake on the relevant source are also obtained. Cities of Gwadar and Ormara with acceleration values of 0.21g and 0.25g respectively fall in the high seismic risk area. Cities of Turbat and Karachi lie in low seismic risk area with acceleration values of less than 0.1g. The Probabilistic PGA maps with contour interval of 0.05g for 50 and 100 years return period with 90% probability of non-exceedance are also compiled.