Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L1 are determined simultaneously with deep seismic sounding data in Changbai...Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L1 are determined simultaneously with deep seismic sounding data in Changbaishan Tianchi volcanic region, and then its Poisson's ratio is obtained. Calculated results show that this technique overcomes some defects of traditional forward calculation method, and it is also very effective to determine Poisson's ratio distribution of deep seismic sounding profile, especially useful for study on volcanic magma and crustal fault zone. Study result indicates that there is an abnormally high Poisson's ratio body that is about 30 km wide and 12 km high in the low velocity region under Tianchi crater. Its value of Poisson's ratio is 8% higher than that of surrounding medium and it should be the magma chamber formed from melted rock with high temperature. There is a high Poisson's ratio zone ranging from magma chamber to the top of crust, which may be the uprise passage of hot substance. The lower part with high Poisson's ratio, which stretches downward to Moho, is possibly the extrusion way of hot substance from the uppermost mantle. The conclusions above are consistent with the study results of both tomographic determination of 3D crustal structure and magnetotelluric survey in this region.展开更多
The Sinai Peninsula has been recognized as a subplate of the African Plate located at the triple junction of the Gulf of Suez rift,the Dead Sea Transform fault,and the Red Sea rift.The upper and lower crustal structur...The Sinai Peninsula has been recognized as a subplate of the African Plate located at the triple junction of the Gulf of Suez rift,the Dead Sea Transform fault,and the Red Sea rift.The upper and lower crustal structures of this tectonically active,rapidly developing region are yet poorly understood because of many limitations.For this reason,a set of P- and S-wave travel times recorded at 14 seismic stations belonging to the Egyptian National Seismographic Network(ENSN) from 111 local and regional events are analyzed to investigate the crustal structures and the locations of the seismogenic zones beneath central and southern Sinai.Because the velocity model used for routine earthquake location by ENSN is one-dimensional,the travel-time residuals will show lateral heterogeneity of the velocity structures and unmodeled vertical structures.Seismic activity is strong along the eastern and southern borders of the study area but low to moderate along the northern boundary and the Gulf of Suez to the west.The crustal V_P/V_S ratio is 1.74 from shallow(depth≤10 km) earthquakes and 1.76 from deeper(depth 〉 10 km) crustal events.The majority of the regional and local travel-time residuals are positive relative to the Preliminary Reference Earth Model(PREM),implying that the seismic stations are located above widely distributed,tectonically-induced low-velocity zones.These low-velocity zones are mostly related to the local crustal faults affecting the sedimentary section and the basement complex as well as the rifting processes prevailing in the northern Red Sea region and the ascending of hot mantle materials along crustal fractures.The delineation of these low-velocity zones and the locations of big crustal earthquakes enable the identification of areas prone to intense seismotectonic activities,which should be excluded from major future development projects and large constructions in central and southern Sinai.展开更多
The paper collects the records by the Fujian Digital Seismic Network of 40 shallow earthquakes in Taiwan with M_S≥5.0 from 1999 to 2013,analyzes the seismic phase(Pn,Sn phase)characteristics and travel-time rules,det...The paper collects the records by the Fujian Digital Seismic Network of 40 shallow earthquakes in Taiwan with M_S≥5.0 from 1999 to 2013,analyzes the seismic phase(Pn,Sn phase)characteristics and travel-time rules,determines travel-time models and develops a seismic phase travel-time equation based on the two-step fitting algorithm.With the deduction of processing time and network delay time,this method can provide an accurate estimation of early warning time of Taiwan earthquakes for the Fujian region,and has been officially employed in the earthquake early warning system of Fujian Province.展开更多
基金Key Project from China Earthquake Administration and the Project (95-11-02-01) from Ministry of Science and Technology (2001DIA10003).
文摘Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L1 are determined simultaneously with deep seismic sounding data in Changbaishan Tianchi volcanic region, and then its Poisson's ratio is obtained. Calculated results show that this technique overcomes some defects of traditional forward calculation method, and it is also very effective to determine Poisson's ratio distribution of deep seismic sounding profile, especially useful for study on volcanic magma and crustal fault zone. Study result indicates that there is an abnormally high Poisson's ratio body that is about 30 km wide and 12 km high in the low velocity region under Tianchi crater. Its value of Poisson's ratio is 8% higher than that of surrounding medium and it should be the magma chamber formed from melted rock with high temperature. There is a high Poisson's ratio zone ranging from magma chamber to the top of crust, which may be the uprise passage of hot substance. The lower part with high Poisson's ratio, which stretches downward to Moho, is possibly the extrusion way of hot substance from the uppermost mantle. The conclusions above are consistent with the study results of both tomographic determination of 3D crustal structure and magnetotelluric survey in this region.
文摘The Sinai Peninsula has been recognized as a subplate of the African Plate located at the triple junction of the Gulf of Suez rift,the Dead Sea Transform fault,and the Red Sea rift.The upper and lower crustal structures of this tectonically active,rapidly developing region are yet poorly understood because of many limitations.For this reason,a set of P- and S-wave travel times recorded at 14 seismic stations belonging to the Egyptian National Seismographic Network(ENSN) from 111 local and regional events are analyzed to investigate the crustal structures and the locations of the seismogenic zones beneath central and southern Sinai.Because the velocity model used for routine earthquake location by ENSN is one-dimensional,the travel-time residuals will show lateral heterogeneity of the velocity structures and unmodeled vertical structures.Seismic activity is strong along the eastern and southern borders of the study area but low to moderate along the northern boundary and the Gulf of Suez to the west.The crustal V_P/V_S ratio is 1.74 from shallow(depth≤10 km) earthquakes and 1.76 from deeper(depth 〉 10 km) crustal events.The majority of the regional and local travel-time residuals are positive relative to the Preliminary Reference Earth Model(PREM),implying that the seismic stations are located above widely distributed,tectonically-induced low-velocity zones.These low-velocity zones are mostly related to the local crustal faults affecting the sedimentary section and the basement complex as well as the rifting processes prevailing in the northern Red Sea region and the ascending of hot mantle materials along crustal fractures.The delineation of these low-velocity zones and the locations of big crustal earthquakes enable the identification of areas prone to intense seismotectonic activities,which should be excluded from major future development projects and large constructions in central and southern Sinai.
基金funded by the Spark Program of Earthquake Sciences (XH13012)China Earthquake Administration,and a Key Scientific and Technological Program of Earthquake Administration of Fujian Province (201202)
文摘The paper collects the records by the Fujian Digital Seismic Network of 40 shallow earthquakes in Taiwan with M_S≥5.0 from 1999 to 2013,analyzes the seismic phase(Pn,Sn phase)characteristics and travel-time rules,determines travel-time models and develops a seismic phase travel-time equation based on the two-step fitting algorithm.With the deduction of processing time and network delay time,this method can provide an accurate estimation of early warning time of Taiwan earthquakes for the Fujian region,and has been officially employed in the earthquake early warning system of Fujian Province.