We interpret seismic activity in the active spreading centers of the Salton Trough to indicate 1) a magmatic intrusion in the lower crust beneath the active Brawly, Cerro Prieto, Imperial, Elsinore, and San Jacinto fa...We interpret seismic activity in the active spreading centers of the Salton Trough to indicate 1) a magmatic intrusion in the lower crust beneath the active Brawly, Cerro Prieto, Imperial, Elsinore, and San Jacinto fault systems;and 2) fluids in the upper crust that have been released from that magmatic body. The absence of a magmatic body and fluids at the location of fossil spreading centers along the Sand Hill and Algodones faults ndicated by little or no seismic activity in those areas. We show several lines of evidence to point out that both melt and fluids related to the seismic activity. In particular, receiver function analysis, Vp/Vs ratios, and tomographic data reveal low velocity zones coincide with the location of the active spreading centers. High Vp/Vs ratios and low velocity zones in the lower crust and upper mantle attributed to melt inclusion, while low Vp/Vs ratios in the upper crust are attributed water inclusions. Frequency-mag- nitude distributions characterized by high b-values in southern California;high b-values have also been associated with crustal fluids. A crustal scale model developed from the receiver functions, gravity, and magnetic data supports the existence of a magmatic intrusion within about 20 km of the surface southwest of the Salton Sea, that intrusion extends for 70 km in a SW-NE direction.展开更多
The Salton Trough of southwestern California is inferred to be an incipient ocean basin, and is a polyphase basin with significant extension in addition to dextral shear. To further explore the origin and evolution of...The Salton Trough of southwestern California is inferred to be an incipient ocean basin, and is a polyphase basin with significant extension in addition to dextral shear. To further explore the origin and evolution of this basin, we have incorporated receiver function, gravity, and aeromagnetic data to construct new subsurface crustal scale models. Receiver function analysis suggests the Moho is 20 km deep to the southwest of the Salton Sea and deepens to 32 km in the region east of the Salton Trough and dome in shape. Crustal modeling shows that the density of the lower crust is 2950 kg/m3, which is an indication for gabbroic com- position, while the density of the upper crust varies from 2500 kg/m3 to 2600 kg/m3 and the depth of sedi- mentary and meta-sedimentary rocks appears to be 8 - 10 km. Most magnetic anomalies show shallow relief and are low amplitude with some exceptions in the marginal areas, suggesting the absence of shallow buried mafic intrusions and deep basement. Our models show a magmatic body to the southwest of the Salton Sea at depth of about 18 km and extend in SW-NE direction for about 90 km, We expect this magmatic body (mix- ture of lower crust and upper mantle material) is responsible for crustal thinning, stretching and rifting, ac- cording to the crustal models this body doesn’t exist in the north region of Salton Trough, thus, no further propagate of the rift is expected in the north.展开更多
Historic Native American and modern civilizations have been forcing the unstable use of the Colorado River and adjacent land resources for centuries. Much can be learned from past Native American cultures that created...Historic Native American and modern civilizations have been forcing the unstable use of the Colorado River and adjacent land resources for centuries. Much can be learned from past Native American cultures that created irrigation systems to offset low rainfall. These lessons learned can be applied to our modern civilization. We can learn a lot from their previous behavior and experiences and could apply the lessons learned to our current disappearing Colorado River situation. Little of the Colorado River water flow reaches the international border with Mexico near Yuma, Arizona. Intensive consumption, mostly in the United States, has dried up the lower 160 km of the river. Since the 1960s, the Colorado River has rarely flowed into the Gulf of California and when it does it becomes is a major international news event. The Colorado River Delta is drought prone and its headwater tributaries are a vital source of water for 40 million people. The Colorado River has whitewater rapids, canyons, and many United States National Parks. The tributary and river flow is managed by an extensive system of dams, aqueducts, and reservoirs. Most years the entire Colorado River flow is used for United States agricultural irrigation and domestic water supply purposes. The agricultural and urban needs in the United States are continuing to grow and it appears the days of Colorado River flowing into Mexico and the Gulf of California are numbered and declining every decade. The Colorado River is disappearing and restoration efforts appear to be too little too late. If the Colorado River valley is ever going to recover management lessons and failures learned from the Native Americans, including the Hohokam, must be applied. A balanced approach to water management is needed and must include aggressive conservation and efficiency measures.展开更多
文摘We interpret seismic activity in the active spreading centers of the Salton Trough to indicate 1) a magmatic intrusion in the lower crust beneath the active Brawly, Cerro Prieto, Imperial, Elsinore, and San Jacinto fault systems;and 2) fluids in the upper crust that have been released from that magmatic body. The absence of a magmatic body and fluids at the location of fossil spreading centers along the Sand Hill and Algodones faults ndicated by little or no seismic activity in those areas. We show several lines of evidence to point out that both melt and fluids related to the seismic activity. In particular, receiver function analysis, Vp/Vs ratios, and tomographic data reveal low velocity zones coincide with the location of the active spreading centers. High Vp/Vs ratios and low velocity zones in the lower crust and upper mantle attributed to melt inclusion, while low Vp/Vs ratios in the upper crust are attributed water inclusions. Frequency-mag- nitude distributions characterized by high b-values in southern California;high b-values have also been associated with crustal fluids. A crustal scale model developed from the receiver functions, gravity, and magnetic data supports the existence of a magmatic intrusion within about 20 km of the surface southwest of the Salton Sea, that intrusion extends for 70 km in a SW-NE direction.
文摘The Salton Trough of southwestern California is inferred to be an incipient ocean basin, and is a polyphase basin with significant extension in addition to dextral shear. To further explore the origin and evolution of this basin, we have incorporated receiver function, gravity, and aeromagnetic data to construct new subsurface crustal scale models. Receiver function analysis suggests the Moho is 20 km deep to the southwest of the Salton Sea and deepens to 32 km in the region east of the Salton Trough and dome in shape. Crustal modeling shows that the density of the lower crust is 2950 kg/m3, which is an indication for gabbroic com- position, while the density of the upper crust varies from 2500 kg/m3 to 2600 kg/m3 and the depth of sedi- mentary and meta-sedimentary rocks appears to be 8 - 10 km. Most magnetic anomalies show shallow relief and are low amplitude with some exceptions in the marginal areas, suggesting the absence of shallow buried mafic intrusions and deep basement. Our models show a magmatic body to the southwest of the Salton Sea at depth of about 18 km and extend in SW-NE direction for about 90 km, We expect this magmatic body (mix- ture of lower crust and upper mantle material) is responsible for crustal thinning, stretching and rifting, ac- cording to the crustal models this body doesn’t exist in the north region of Salton Trough, thus, no further propagate of the rift is expected in the north.
文摘Historic Native American and modern civilizations have been forcing the unstable use of the Colorado River and adjacent land resources for centuries. Much can be learned from past Native American cultures that created irrigation systems to offset low rainfall. These lessons learned can be applied to our modern civilization. We can learn a lot from their previous behavior and experiences and could apply the lessons learned to our current disappearing Colorado River situation. Little of the Colorado River water flow reaches the international border with Mexico near Yuma, Arizona. Intensive consumption, mostly in the United States, has dried up the lower 160 km of the river. Since the 1960s, the Colorado River has rarely flowed into the Gulf of California and when it does it becomes is a major international news event. The Colorado River Delta is drought prone and its headwater tributaries are a vital source of water for 40 million people. The Colorado River has whitewater rapids, canyons, and many United States National Parks. The tributary and river flow is managed by an extensive system of dams, aqueducts, and reservoirs. Most years the entire Colorado River flow is used for United States agricultural irrigation and domestic water supply purposes. The agricultural and urban needs in the United States are continuing to grow and it appears the days of Colorado River flowing into Mexico and the Gulf of California are numbered and declining every decade. The Colorado River is disappearing and restoration efforts appear to be too little too late. If the Colorado River valley is ever going to recover management lessons and failures learned from the Native Americans, including the Hohokam, must be applied. A balanced approach to water management is needed and must include aggressive conservation and efficiency measures.
