An assessment of low-temperature, ductile lithospheric deformation using existing broadband seismic data from around South Island, New Zealand

板块构造涉及刚性岩石圈板块在软流圈上移动，软流圈可以在地质时间尺度上流动。然而，有新的证据表明，“刚性”岩石圈可能会变形。这个项目将研究新西兰南岛的阿尔卑斯断层是否存在延展性行为——当物质流动而不是断裂时。结果将对全球构造过程产生影响。更广泛的影响包括对早期职业科学家的支持以及与该项目相关的软件的传播。本研究的主要目的是评估剪切应力是否导致岩石圈的低温韧性变形。地震各向异性是粘性应变的代表，将用于测试新西兰南岛阿尔卑斯断层周围岩石圈地幔是否在低温下发生韧性变形。虽然先前的研究表明，与横越阿尔卑斯断层的相对运动相关的应变被容纳在一个宽达200公里的区域内，但先前通过横波分裂和地震Pn进行的各向异性测量并没有提供足够的空间分辨率来确定变形是发生在远离板块边界的岩石圈还是软流圈。现有的海底地震数据集将用于计算接收函数，应用最近开发的去除沉积物和水柱混响的技术，谐波分解将用于测量南岛两侧岩石圈地幔的方位各向异性。这将解决阿尔卑斯断层周围地震各向异性的横向和垂直变化，并确定岩石圈-软流圈系统中韧性变形发生的位置。本项目由海洋科学部海洋地质与地球物理项目和地球科学部地球物理项目资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Plate tectonics involves rigid lithospheric plates moving over an asthenosphere which can flow on geologic time scales. However, there is new evidence that the ‘rigid’ lithosphere might be able to deform. This project will study if ductile behavior – when material flows instead of breaking – is present at the Alpine Fault in South Island, New Zealand. Results will have implications for global tectonic processes. Broader impacts include support for an early career scientist and dissemination of software related to the project.The main goal of the proposed research is to assess whether shear stress leads to low-temperature ductile deformation in the lithosphere. Seismic anisotropy, a proxy for viscous strain, will be used to test whether ductile deformation is occurring at low temperatures in the lithospheric mantle around the Alpine Fault in South Island, New Zealand. While previous studies have shown that strain associated with relative motion across the Alpine Fault is accommodated in a zone up to 200 km wide, prior anisotropy measurements from shear wave splitting and earthquake Pn have not provided sufficient spatial resolution to determine whether deformation is occurring in the lithosphere or the asthenosphere away from the plate boundary. An existing ocean bottom seismic dataset will be used to calculate receiver functions, applying recently developed techniques for removing sediment and water column reverberations, and harmonic decomposition will be used to measure azimuthal anisotropy in the lithospheric mantle on both sides of South Island. This will resolve lateral and vertical variations in seismic anisotropy around the Alpine Fault and determine where ductile deformation is occurring in the lithosphere-asthenosphere system.This project is supported by the Marine Geology and Geophysics program in the Division of Ocean Sciences and the Geophysics program in the Division of Earth Sciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.