Strain Accommodation in the Walker Lane: Understanding the Evolution of a Diffuse Plate Boundary with Geochronology and Geodesy

这项研究汇集了来自佐治亚理工学院的一组科学家，以调查加利福尼亚州东部和内华达州西部沃克巷地区(太平洋-北美板块边界的一个不断演变的部分)短期和长期应变率之间的差异。为了实现这一目标，现有的大地测量基础设施，包括区域运动和连续的全球定位系统数据，在该区域增加了10个新的纪念碑。所有竞选活动地点将在2010至2012年间分三次年度活动进行衡量。对GPS数据的分析将产生当今应变场的详细图像。地质填图结合了航空摄影、野外测量和偏置冲积扇的宇宙成因核素年代学的评价，用来确定穿过正断层的运动日期，从而确定长期运动速率。长期的地质和短期的大地测量数据集的整合将产生沿这一重要的板块边界断裂系统的晚更新世到最近时间尺度的分布应变场的综合视图。最终，这将有助于更好地理解结构复杂的岩石圈如何沿着板块边界演化。在一些板块边界系统，包括圣安德烈亚斯和北安纳托利亚断层，构造变形速度在广泛的时间范围内似乎是恒定的。然而，在其他板块边界带的部分地区，由GPS测量确定的短期速率与从地质推断的长期滑动速率并不一致。例如，根据构造地貌断层研究确定的加州东部莫哈韦沙漠剪切带和中央Walker Lane的晚更新世变形速率，其屈服速率仅为由GPS数据确定的短期速率的一半至三分之一。Walker Lane的短期和长期速率之间的不匹配与目前的理解相反，并对岩石圈如何适应构造变形，以及最终这种变形与地震灾害的关系具有重要意义。通过确定沃克盆地每年到10万年的构造活动速度，将为断层系统在多个地震周期中的行为和演化提供新的见解，并解决关于地壳应变分布的几个基本问题：应变累积和释放的速度在时间和空间上是如何恒定的？多个地震周期的平均地质滑移率与GPS数据确定的短期形变率是否具有可比性？如果短期和长期形变率之间存在差异，这种差异发生在什么时间和空间尺度上？这些差异是与特定区域的结构复杂性有关，还是整个板块边界的特征？

This study brings together a team of scientists from Georgia Institute of Technology to investigate the discrepancies between short- and long-term strain rates in the Walker Lane region of eastern California and western Nevada; an evolving segment of the Pacific-North America plate boundary. To accomplish this objective, existing geodetic infrastructure, including regional campaign and continuous GPS data, is augmented with 10 new monuments in the region. All campaign sites will be measured in three annual campaigns between 2010 and 2012. Analysis of the GPS data will yield a detailed image of the present-day strain field. Geologic mapping incorporating evaluation of aerial photography, field surveying and cosmogenic nuclide geochronology of offset alluvial fans are used to determine the dates, and hence the long-term rates, of motion across normal faults. The integration of the long-term geologic and short-term geodetic datasets will yield a comprehensive view of the distributed strain field over late Pleistocene to Recent time scales along this important plate boundary fault system. Ultimately, this will lead to improved understanding of how the structurally complex lithosphere behaves along evolving plate boundaries.Along some plate boundary systems, including the San Andreas and North Anatolian faults, rates of tectonic deformation appear to be constant over a wide range of time scales. However, on parts of other plate boundary zones short-term rates determined from GPS measurements do not coincide with longer-term geologically inferred slip rates. For example, late Pleistocene rates of deformation across the eastern California shear zone in the Mojave Desert and in the central Walker Lane, determined from tectono-geomorphic fault studies, yield rates that are only one-half to one-third the short-term rate determined from GPS data. The mismatch between short- and long-term rates in the Walker Lane is contrary to current understanding, and has important implications for how tectonic deformation is accommodated in the lithosphere, and ultimately the relationship of this deformation to earthquake hazards. By determining rates of tectonic activity in the Walker Lave over annual to 100,000 year timescales will provide new insights into how fault systems behave and evolve over multiple earthquake cycles, and address several fundamental questions about crustal strain distribution: How constant are rates of strain accumulation and release in time and space? Are geologic slip rates averaged over multiple earthquake cycles comparable with short-term rates of deformation determined from GPS data? If discrepancies between short- and long-term rates of deformation exist, over what temporal and spatial scales does the discrepancy occur? Are these differences related to the structural complexity of a specific region or are they characteristic of entire plate boundaries?