Teleseismic receiver functions and travel-time residuals along the north Hi-Climb broadband seismic array in the central-southern Qinghai-Tibet Plateau show that the lithosphere structures in the central and western Q...Teleseismic receiver functions and travel-time residuals along the north Hi-Climb broadband seismic array in the central-southern Qinghai-Tibet Plateau show that the lithosphere structures in the central and western Qinghai-Tibet Plateau are different. In the central Qinghai-Tibet Plateau, the Indian Plate is northward subducted beneath the Qiangtang block and arrives at the greatest depth beneath the central-southern Qiangtang block. The delaminated Indian lithospheric slab remains beneath the central Lhasa block to a depth possibly greater than that of the upper interface of the mantle transform zone. In the western Qinghai-Tibet Plateau, the Indian lithospheric plate is gently northward subducted and may have arrived to the south of Tarim plate. Due to the resistance from the gently northward subduction of the Indian mantle lithosphere in the western Qinghai-Tibet Plateau, the upwelling mantle material be-neath the Qiangtang block moves mostly toward the east to bring about the lateral eastward flow of the deep mantle hot material in the central Qinghai-Tibet Plateau.展开更多
Based upon the deep seismic sounding profile conducted in the Tengchong volcanic-geothermal area, a two-dimensional crustal P velocity structure is obtained by use of the finite-difference inversion and the forward tr...Based upon the deep seismic sounding profile conducted in the Tengchong volcanic-geothermal area, a two-dimensional crustal P velocity structure is obtained by use of the finite-difference inversion and the forward travel-time fitting method. The crustal model shows that there is a low velocity zone in upper crust in the Tengchong area, which may be related to the volcanic-geothermal activities, and two intracrustal faults (the LonglingRuili fault and Tengchong fault) exist on the profile, where the Tengchong fault may extend to the Moho discontinuity. Meanwhile, based on teleseismic data recorded by a temporary seismic network, we obtained the S-wave velocity structures beneath the RehaiRetian region in the Tengchong area, which show the low S-wave velocity anomaly in upper crust. The authors discuss the causes of Tengchong volcanic eruption based on the deep crustal structure. The crustal structure in the Tengchong volcanic-geothermal area is characterized by low P-wave and S-wave velocity, low resistivity, high heat-flow value and low Q value. The P-wave velocity in the upper mantle is also low. For this information, it can be induced that the magma in the crust is derived from the upper mantle, and the low velocity anomaly in upper crust in the Tengchong area may be related to the differentiation of magma. The Tengchong volcanoes are close to an active plate boundary and belong to plate boundary volcanoes.展开更多
A new seismic ray-tracing method is put forward based on parabolic travel-time interpolation(PTI) method, which is more accurate than the linear travel-time interpolation (LTI) method. Both PTI method and LTI method a...A new seismic ray-tracing method is put forward based on parabolic travel-time interpolation(PTI) method, which is more accurate than the linear travel-time interpolation (LTI) method. Both PTI method and LTI method are used to compute seismic travel-time and ray-path in a 2-D grid cell model. Firstly, some basic concepts are introduced. The calculations of travel-time and ray-path are carried out only at cell boundaries. So, the ray-path is always straight in the same cells with uniform velocity. Two steps are applied in PTI and LTI method, step 1 computes travel-time and step 2 traces ray-path. Then, the derivation of LTI formulas is described. Because of the presence of refraction wave in shot cell, the formula aiming at shot cell is also derived. Finally, PTI method is presented. The calculation of PTI method is more complex than that of LTI method, but the error is limited. The results of numerical model show that PTI method can trace ray-path more accurately and efficiently than LTI method does.展开更多
Travel-time prediction has gained significance over the years especially in urban areas due to increasing traffic congestion. In this paper, the basic building blocks of the travel-time prediction models are discussed...Travel-time prediction has gained significance over the years especially in urban areas due to increasing traffic congestion. In this paper, the basic building blocks of the travel-time prediction models are discussed, with a small review of the previous work. A model for the travel-time prediction on freeways based on wavelet packet decomposition and support vector regression (WDSVR) is proposed, which used the multi-resolution and equivalent frequency distribution ability of the wavelet transform to train the support vector machines. The results are compared against the classical support vector regression (SVR) method. Our results indicated that the wavelet reconstructed coefficient when used as an input to the support vector machine for regression performed better (with selected wavelets only), when compared with the support vector regression model (without wavelet decomposition) with a prediction horizon of 45 minutes and more. The data used in this paper was taken from the California Department of Transportation (Caltrans) of District 12 with a detector density of 2.73, experiencing daily peak hours except most weekends. The data was stored for a period of 214 days accumulated over 5-minute intervals over a distance of 9.13 miles. The results indicated MAPE ranging from 12.35% to 14.75% against the classical SVR method with MAPE ranging from 12.57% to 15.84% with a prediction horizon of 45 minutes to 1 hour. The basic criteria for selection of wavelet basis for preprocessing the inputs of support vector machines are also explored to filter the set of wavelet families for the WDSVR model. Finally, a configuration of travel-time prediction on freeways is presented with interchangeable prediction methods.展开更多
SKS and SKKS waveforms from 16 events occurring between 2003 and 2005 in the Tonga Trench that were recorded by the BOLIVAR array are analyzed to determine the structure of the D＂ layer beneath the Galapagos Islands....SKS and SKKS waveforms from 16 events occurring between 2003 and 2005 in the Tonga Trench that were recorded by the BOLIVAR array are analyzed to determine the structure of the D＂ layer beneath the Galapagos Islands. 248 differential travel-time residuals of SKKS-SKS are measured and reveal a region of positive residuals of differential travel times in the northeast portion of the sampled region. Analyzing correlation statistics between the measured SKKS-SKS residuals and the observed absolute travel time delay of the individual SKS and SKKS phases for two events with high data quality, we determine that the residual differential travel time is due to excess low velocity along the SKKS raypaths. First order modeling of three potential low velocity structures, ultra-low velocity zones （ULVZ）, plume conduit, D＂ structure, indicates that the observed SKKS-SKS residuals can be best explained by a low velocity anomaly within the D＂ layer. To determine the presence of lower mantle anisotropy, amplitude ratios of the radial and transverse component of SKS and SKKS waveform are calculated and compared. Regions with significant presence of seismic anisotropy are interpreted as the edge of the flow field associated with a hypothetical mantle upwelling.展开更多
Here,simultaneous in-situ calibration of pressures and temperatures was performed in a hinge-type second-stage cubic large volume press(LVP)up to 15 GPa and 1400 K by an acoustic travel-time approach.Based on the rece...Here,simultaneous in-situ calibration of pressures and temperatures was performed in a hinge-type second-stage cubic large volume press(LVP)up to 15 GPa and 1400 K by an acoustic travel-time approach.Based on the recently reported P-tSand P-T-tP-tSequations for Al2O3buffer rod,the cell pressures and temperatures in the chamber of LVP were insitu determined,in comparison with those by conventional off-line(or fixed-points)pressure calibration method and direct thermocouple measurement,respectively.It is found that the cell pressures of the LVP chamber are significantly reduced after annealing at simultaneous high pressures and high temperatures,owing to the stress relaxation as accumulate in the LVP chamber.This acoustic travel-time method is verified to be a good way for precise determination of thermal(cell)pressures at high temperature conditions,and is of great importance and necessity to conduct in-situ physical property measurements under extreme high P-T conditions,especially when the precious synchrotron x-ray/neutron diffraction beams are not available.展开更多
Local and global optimization methods are widely used in geophysical inversion but each has its own advantages and disadvantages. The combination of the two methods will make it possible to overcome their weaknesses. ...Local and global optimization methods are widely used in geophysical inversion but each has its own advantages and disadvantages. The combination of the two methods will make it possible to overcome their weaknesses. Based on the simulated annealing genetic algorithm （SAGA） and the simplex algorithm, an efficient and robust 2-D nonlinear method for seismic travel-time inversion is presented in this paper. First we do a global search over a large range by SAGA and then do a rapid local search using the simplex method. A multi-scale tomography method is adopted in order to reduce non-uniqueness. The velocity field is divided into different spatial scales and velocities at the grid nodes are taken as unknown parameters. The model is parameterized by a bi-cubic spline function. The finite-difference method is used to solve the forward problem while the hybrid method combining multi-scale SAGA and simplex algorithms is applied to the inverse problem. The algorithm has been applied to a numerical test and a travel-time perturbation test using an anomalous low-velocity body. For a practical example, it is used in the study of upper crustal velocity structure of the A＇nyemaqen suture zone at the north-east edge of the Qinghai-Tibet Plateau. The model test and practical application both prove that the method is effective and robust.展开更多
This paper studied some properties of PdSwr phase related to 670 km discontinuities in detail, and theoretically processed a preliminary analysis to this phase. We discussed the relationships between the incident angl...This paper studied some properties of PdSwr phase related to 670 km discontinuities in detail, and theoretically processed a preliminary analysis to this phase. We discussed the relationships between the incident angle ih of PdSwr phase with its path, epicentral distance, travel-time and relative amplitude due to low velocity zone (LVZ) of upper mantle, and preliminarily pointed out the main characters of PdSwr phase recorded in seismogram. The PdSwr phase is concentrated in range of 13.5~96.5. When epicentral distance is greater than 33, the start point of PdSwr phase is relatively well distinguishable and could thus be determined more easily. When the epicentral distance is between 13.5 to 33, the triplication of PdSwr's travel-time curve could be slightly distinguished due to the low velocity zone and 220 km seismic velocity discontirluity of upper mantle. The relevant observed PdSwr phase should be in a more complex pattern and it should be more difficult to determine its start point展开更多
基金the National Basic Research Program of China (Grant No.2004CB418401)
文摘Teleseismic receiver functions and travel-time residuals along the north Hi-Climb broadband seismic array in the central-southern Qinghai-Tibet Plateau show that the lithosphere structures in the central and western Qinghai-Tibet Plateau are different. In the central Qinghai-Tibet Plateau, the Indian Plate is northward subducted beneath the Qiangtang block and arrives at the greatest depth beneath the central-southern Qiangtang block. The delaminated Indian lithospheric slab remains beneath the central Lhasa block to a depth possibly greater than that of the upper interface of the mantle transform zone. In the western Qinghai-Tibet Plateau, the Indian lithospheric plate is gently northward subducted and may have arrived to the south of Tarim plate. Due to the resistance from the gently northward subduction of the Indian mantle lithosphere in the western Qinghai-Tibet Plateau, the upwelling mantle material be-neath the Qiangtang block moves mostly toward the east to bring about the lateral eastward flow of the deep mantle hot material in the central Qinghai-Tibet Plateau.
基金The Climb Program (95-S-05-01) of National Scientific and Technological Ministry of China, the Key Project (95-11-02) from China Seismological Bureau, the State Natural Sciences Foundation of China (49974020) and the Joint Earthquake S
文摘Based upon the deep seismic sounding profile conducted in the Tengchong volcanic-geothermal area, a two-dimensional crustal P velocity structure is obtained by use of the finite-difference inversion and the forward travel-time fitting method. The crustal model shows that there is a low velocity zone in upper crust in the Tengchong area, which may be related to the volcanic-geothermal activities, and two intracrustal faults (the LonglingRuili fault and Tengchong fault) exist on the profile, where the Tengchong fault may extend to the Moho discontinuity. Meanwhile, based on teleseismic data recorded by a temporary seismic network, we obtained the S-wave velocity structures beneath the RehaiRetian region in the Tengchong area, which show the low S-wave velocity anomaly in upper crust. The authors discuss the causes of Tengchong volcanic eruption based on the deep crustal structure. The crustal structure in the Tengchong volcanic-geothermal area is characterized by low P-wave and S-wave velocity, low resistivity, high heat-flow value and low Q value. The P-wave velocity in the upper mantle is also low. For this information, it can be induced that the magma in the crust is derived from the upper mantle, and the low velocity anomaly in upper crust in the Tengchong area may be related to the differentiation of magma. The Tengchong volcanoes are close to an active plate boundary and belong to plate boundary volcanoes.
文摘A new seismic ray-tracing method is put forward based on parabolic travel-time interpolation(PTI) method, which is more accurate than the linear travel-time interpolation (LTI) method. Both PTI method and LTI method are used to compute seismic travel-time and ray-path in a 2-D grid cell model. Firstly, some basic concepts are introduced. The calculations of travel-time and ray-path are carried out only at cell boundaries. So, the ray-path is always straight in the same cells with uniform velocity. Two steps are applied in PTI and LTI method, step 1 computes travel-time and step 2 traces ray-path. Then, the derivation of LTI formulas is described. Because of the presence of refraction wave in shot cell, the formula aiming at shot cell is also derived. Finally, PTI method is presented. The calculation of PTI method is more complex than that of LTI method, but the error is limited. The results of numerical model show that PTI method can trace ray-path more accurately and efficiently than LTI method does.
文摘Travel-time prediction has gained significance over the years especially in urban areas due to increasing traffic congestion. In this paper, the basic building blocks of the travel-time prediction models are discussed, with a small review of the previous work. A model for the travel-time prediction on freeways based on wavelet packet decomposition and support vector regression (WDSVR) is proposed, which used the multi-resolution and equivalent frequency distribution ability of the wavelet transform to train the support vector machines. The results are compared against the classical support vector regression (SVR) method. Our results indicated that the wavelet reconstructed coefficient when used as an input to the support vector machine for regression performed better (with selected wavelets only), when compared with the support vector regression model (without wavelet decomposition) with a prediction horizon of 45 minutes and more. The data used in this paper was taken from the California Department of Transportation (Caltrans) of District 12 with a detector density of 2.73, experiencing daily peak hours except most weekends. The data was stored for a period of 214 days accumulated over 5-minute intervals over a distance of 9.13 miles. The results indicated MAPE ranging from 12.35% to 14.75% against the classical SVR method with MAPE ranging from 12.57% to 15.84% with a prediction horizon of 45 minutes to 1 hour. The basic criteria for selection of wavelet basis for preprocessing the inputs of support vector machines are also explored to filter the set of wavelet families for the WDSVR model. Finally, a configuration of travel-time prediction on freeways is presented with interchangeable prediction methods.
文摘SKS and SKKS waveforms from 16 events occurring between 2003 and 2005 in the Tonga Trench that were recorded by the BOLIVAR array are analyzed to determine the structure of the D＂ layer beneath the Galapagos Islands. 248 differential travel-time residuals of SKKS-SKS are measured and reveal a region of positive residuals of differential travel times in the northeast portion of the sampled region. Analyzing correlation statistics between the measured SKKS-SKS residuals and the observed absolute travel time delay of the individual SKS and SKKS phases for two events with high data quality, we determine that the residual differential travel time is due to excess low velocity along the SKKS raypaths. First order modeling of three potential low velocity structures, ultra-low velocity zones （ULVZ）, plume conduit, D＂ structure, indicates that the observed SKKS-SKS residuals can be best explained by a low velocity anomaly within the D＂ layer. To determine the presence of lower mantle anisotropy, amplitude ratios of the radial and transverse component of SKS and SKKS waveform are calculated and compared. Regions with significant presence of seismic anisotropy are interpreted as the edge of the flow field associated with a hypothetical mantle upwelling.
基金supported by the National Natural Science Foundation of China(Grant Nos.12075215,11872198,and U2030110)the National Key Research and Development Program of China(Grant No.2016YFA0401503)。
文摘Here,simultaneous in-situ calibration of pressures and temperatures was performed in a hinge-type second-stage cubic large volume press(LVP)up to 15 GPa and 1400 K by an acoustic travel-time approach.Based on the recently reported P-tSand P-T-tP-tSequations for Al2O3buffer rod,the cell pressures and temperatures in the chamber of LVP were insitu determined,in comparison with those by conventional off-line(or fixed-points)pressure calibration method and direct thermocouple measurement,respectively.It is found that the cell pressures of the LVP chamber are significantly reduced after annealing at simultaneous high pressures and high temperatures,owing to the stress relaxation as accumulate in the LVP chamber.This acoustic travel-time method is verified to be a good way for precise determination of thermal(cell)pressures at high temperature conditions,and is of great importance and necessity to conduct in-situ physical property measurements under extreme high P-T conditions,especially when the precious synchrotron x-ray/neutron diffraction beams are not available.
基金supported by the National Natural Science Foundation of China (Grant Nos.40334040 and 40974033)the Promoting Foundation for Advanced Persons of Talent of NCWU
文摘Local and global optimization methods are widely used in geophysical inversion but each has its own advantages and disadvantages. The combination of the two methods will make it possible to overcome their weaknesses. Based on the simulated annealing genetic algorithm （SAGA） and the simplex algorithm, an efficient and robust 2-D nonlinear method for seismic travel-time inversion is presented in this paper. First we do a global search over a large range by SAGA and then do a rapid local search using the simplex method. A multi-scale tomography method is adopted in order to reduce non-uniqueness. The velocity field is divided into different spatial scales and velocities at the grid nodes are taken as unknown parameters. The model is parameterized by a bi-cubic spline function. The finite-difference method is used to solve the forward problem while the hybrid method combining multi-scale SAGA and simplex algorithms is applied to the inverse problem. The algorithm has been applied to a numerical test and a travel-time perturbation test using an anomalous low-velocity body. For a practical example, it is used in the study of upper crustal velocity structure of the A＇nyemaqen suture zone at the north-east edge of the Qinghai-Tibet Plateau. The model test and practical application both prove that the method is effective and robust.
文摘This paper studied some properties of PdSwr phase related to 670 km discontinuities in detail, and theoretically processed a preliminary analysis to this phase. We discussed the relationships between the incident angle ih of PdSwr phase with its path, epicentral distance, travel-time and relative amplitude due to low velocity zone (LVZ) of upper mantle, and preliminarily pointed out the main characters of PdSwr phase recorded in seismogram. The PdSwr phase is concentrated in range of 13.5~96.5. When epicentral distance is greater than 33, the start point of PdSwr phase is relatively well distinguishable and could thus be determined more easily. When the epicentral distance is between 13.5 to 33, the triplication of PdSwr's travel-time curve could be slightly distinguished due to the low velocity zone and 220 km seismic velocity discontirluity of upper mantle. The relevant observed PdSwr phase should be in a more complex pattern and it should be more difficult to determine its start point
