Passive seismic study of a magma-dominated rift: the Salton Trough

岩浆主导的裂谷的被动地震研究：索尔顿海槽

• 批准号: 0911743
• 负责人: Simon Klemperer
• 金额: $ 25.24万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-15 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0911743&HistoricalAwards=false
• 关键词: Passive; seismic; study; magma; dominated

Non-technical explanationA well-accepted paradigm explains the architecture of structurally dominated continental rifts (that is, regions of the continents that are stretching or have been stretched, by extension on earthquake-faults) in terms of crustal thickness and heat flow. No equivalent paradigm explains the evolution of magmatically dominated rifts (stretched provinces in which volcanoes and their underlying igneous intrusions force the amount of extension), largely because we lack the observational data-sets to test numerical models. Understanding the formation and evolution of such rift basins is societally important because they contain much of Earth?s hydrocarbon reserve. NSF?s Geophysics program through this project is teaming with NSF?s MARGINS and Earthscope-Science programs to provide a detailed set of such observations for a rift in which the key features in the crust and upper mantle are buried beneath a deep basin, the Salton Trough in southernmost California. The Salton Trough is located across the southern end of the San Andreas transform system that has high risk of producing a devastating earthquake, and all new information obtained in this project will become a part of the community Southern California velocity model that is the basis for assessing strong ground motion and earthquake hazard throughout that areaTechnical descriptionThe Salton Trough is a magma-dominated rift linking the Gulf of California to the San Andreas fault system. Because the rift is buried beneath a thick pile of Colorado River sediments, surprisingly little is currently known about the total volume of intrusion into the crust and the magma distribution within and beyond the rift margins. We are determining these distributions and volumes with velocity measurements in the lower lithosphere. Wavespeeds are largely controlled within the crust by composition, and within the uppermost mantle by temperature (and fluid content). Lithology of the lower crust is best determined by combining P-wave velocities that are most reliably obtained from controlled-source refraction profiles with S-wave velocities that are typically better constrained by the joint surface-wave/receiver-function inversions that we are carrying out. We are deploying 40 passive seismometers across the Salton Trough, at nominal 5-km spacing, collinear with the NSF(MARGINS-Earthscope)-USGS controlled-source seismic profile. The NSF-USGS refraction/reflection profile is providing structural constraints, including Moho travel-time, and a vastly improved P-wave velocity model. Previous surface-wave studies carried out using permanent broadband stations across southernmost California will provide the phase-velocities for joint inversions with new receiver functions calculated from the data acquired here. Additional structural constraints (based on the P-wave reflection and refraction profiling) can be imposed on the joint inversions to obtain one of the best-determined Vp-Vs-lithologic profiles across a magmatic rift. The combination of dense receiver functions and well-determined velocity profiles allow a new test of whether the plate-bounding (San Andreas) strike-slip faults offset the Moho or disappear into a ductile middle crust.The Salton Trough is the northernmost part of the Gulf of California extensional province that rifted the North American continent and transferred Baja California and the Peninsular Ranges to the Pacific plate. Despite similar total extension along the province, very different extensional structures have been produced, from seafloor spreading in the southern Gulf to 14-20 km thick continental or transitional crust in the northern Gulf and Salton Trough. The new profile across the Salton Trough provide a comparative section to those recently determined across the Gulf, to enhance our knowledge of early ocean rifting and its propagation into a continent, and to understand the causes of along-strike variation in magmatic activity.

一种广为接受的范式从地壳厚度和热流的角度解释了以结构为主的大陆裂谷（即大陆上因地震断层的延伸而正在伸展或已经伸展的地区）的结构。没有等价的范式可以解释岩浆主导的裂谷（火山及其底层火成岩侵入体迫使伸展量的伸展省份）的演化，这主要是因为我们缺乏观测数据集来测试数值模型。 了解这些裂谷盆地的形成和演化对社会很重要，因为它们包含了地球的大部分。的油气储量。 国家科学基金会通过这个项目的地球物理学计划是与NSF合作？美国地质调查局的MARGINS和地球科学计划提供了一套详细的这样的观测裂缝，其中地壳和上地幔的关键特征被埋在一个深盆地，索尔顿槽在最南端的加州。索尔顿海槽位于圣安德烈亚斯转换系统的南端，具有产生毁灭性地震的高风险，该项目中获得的所有新信息将成为社区南加州速度模型的一部分，该模型是评估整个地区强地面运动和地震危险的基础。连接加州湾和圣安德烈亚斯断层系统的主要裂谷。 由于裂谷埋在厚厚的科罗拉多河沉积物之下，令人惊讶的是，目前对侵入地壳的总体积和裂谷边缘内外的岩浆分布知之甚少。 我们正在确定这些分布和体积与速度测量在较低的岩石圈。波速在很大程度上受地壳成分的控制，而在最上层地幔内则受温度（和流体含量）的控制。下地壳的岩性最好是通过组合纵波速度来确定的，纵波速度是从受控源折射剖面中最可靠地获得的，而横波速度通常更好地受到我们正在进行的联合面波/接收器函数反演的约束。 我们在索尔顿海槽部署了40个无源地震仪，标称间距为5公里，与NSF（MARGINS-Earthscope）-USGS可控源地震剖面共线。 NSF-USGS折射/反射剖面提供了结构约束，包括莫霍面走时和一个大大改进的P波速度模型。以前的面波研究进行了使用永久宽带站横跨最南端的加州将提供联合反演的相速度与新的接收器功能计算从这里获得的数据。 附加的结构约束（基于P波反射和折射剖面）可以施加在联合反演，以获得一个最好的确定的Vp-Vs-岩性剖面横跨岩浆裂谷。 密集的接收器功能和良好的速度剖面的组合允许一个新的测试是否板块边界（圣安德烈亚斯）走滑断层偏移莫霍面或消失到一个韧性的中地壳。索尔顿槽是最北端的部分海湾的加州伸展省份，断裂的北美大陆和转移下加利福尼亚和半岛山脉的太平洋板块。尽管沿该省沿着的总延伸程度相似，但产生了非常不同的延伸结构，从南部海湾的海底扩张到北方海湾和索尔顿海槽的14-20公里厚的大陆或过渡地壳。 横跨索尔顿海槽的新剖面提供了一个与最近确定的横跨海湾的剖面相比较的剖面，以增强我们对早期海洋裂谷及其向大陆传播的认识，并了解岩浆活动沿走向变化的原因。