RAPID: Deep Shear Wave Velocity Profiling for Seismic Characterization of Christchurch, NZ - Reliably Merging Large Active-Source and Passive-Wavefield Surface Wave Methods

RAPID：新西兰基督城地震特征的深剪切波速度剖面 - 可靠地合并大型主动源和被动波场表面波方法

• 批准号: 1303595
• 负责人: Brady Cox
• 金额: $ 19.77万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-11-15 至 2014-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1303595&HistoricalAwards=false
• 关键词: RAPID; Deep; Shear; Wave; Velocity

In 2010-2011, the city of Christchurch, New Zealand was devastated by a series of powerful earthquakes, the most destructive being the 22 February 2011 Mw6.2 Christchurch Earthquake. During this event, the seismic demands imposed on the built environment at many locations in the city were higher than engineering design levels, causing severe structural damage and collapse, especially within the central business district (CBD). Ultimately, the Christchurch Earthquake resulted in 181 casualties, thousands of injuries, and widespread soil liquefaction that caused billions of dollars in damage to buildings, homes and infrastructure. The entire CBD was cordoned-off following this event and remains closed to the public today (October 2012), while an estimated 1000 structures are being demolished. A network of 19 seismic recording stations in the greater Christchurch area captured an extensive and unique set of ground motions (GM) during the 2010-2011 earthquakes. Potentially, these GM can be used for back-analyses aimed at understanding the spatial variability of the ground shaking (particularly site and basin effects), followed by accurate forward-estimates aimed at quantifying the amplitude and frequency content of future design GM. However, detailed GM analyses cannot presently be conducted because no information exists on the shear wave velocity (Vs) structure of the greater-than-400-m deep interlayered sand and gravel deposits that underlie Christchurch. The thrust of this Rapid Response Research (RAPID) grant is to conduct deep (400 m) Vs profiling at 12-15 key sites in Christchurch, New Zealand to aid in important seismic GM response analyses. This information is needed rapidly, as plans for reconstruction of the CBD are proceeding quickly and the proposed testing will be significantly complicated (if not prohibited) once reconstruction begins in earnest in early-to-mid 2013. The only way to economically and rapidly obtain Vs estimates to these great depths is through non-intrusive surface wave testing. However, there is currently a great deal of uncertainty involved in the passive-wavefield techniques most commonly utilized for deep Vs profiling. Therefore, a unique study will be conducted to compare and merge data from large active-source and passive-wavefield surface wave methods over an extended frequency/wavelength range, which will allow robust determination of data uncertainty and relative bias. The active-source surface wave measurements will be conducted using one of the large and unique NEES@UTexas mobile, servo-hydraulic shakers and up to 48, 1-Hz geophones, while passive-wavefield data will be collected using intermediate- and large-diameter circular sensor arrays composed of 10 broadband seismometers. This research will triple the available comparisons between large active-source and passive-wavefield surface wave methods utilized for deep Vs profiling. These comparisons are needed before confidence in utilizing passive-wavefield methods independently can be achieved. Therefore, the intellectual merits of this work include: (a) the collection and interpretation of a one-of-a-kind dataset that can be used for evaluating the reliability involved with merging large active-source and passive-wavefield surface wave methods for deep Vs profiling, and (b) the advancement in accurate ground motion prediction for deep sedimentary basins made possible by these deep Vs profiles through analysis of a unique set of damaging GM records from multiple seismic events. Progress made on both of these issues will directly impact earthquake engineering studies in the US, New Zealand, and throughout the world. The broader impacts of this work are many, as these research efforts will impact Christchurch society at large through development of robust seismic design GM that will help to mitigate such extreme losses in future earthquakes. Furthermore, the additional understanding of site response in deep sediments garnered from analyzing the strong GM recorded in the Canterbury Earthquake Sequence will benefit seismically active areas of the U.S. underlain by deep sedimentary basins, such as Los Angeles and Seattle. This work will also serve to strengthen international research collaborations between the U.S. and New Zealand, and will provide U.S. graduate students with rewarding international travel experiences that will serve to balance their technical education and expose them to the globally-connected problems that still exist in earthquake engineering.

2010年至2011年，新西兰基督城市遭受了一系列强烈地震的破坏，其中最具破坏性的是2011年2月22日发生的Mw6.2基督城地震。在此事件期间，该市许多地点的建筑环境的抗震要求高于工程设计水平，造成严重的结构损坏和倒塌，特别是在中央商务区（CBD）内。最终，基督城地震造成 181 人伤亡，数千人受伤，土壤大面积液化，对建筑物、房屋和基础设施造成数十亿美元的损失。该事件发生后，整个中央商务区被封锁，至今（2012 年 10 月）仍然不对公众开放，同时估计有 1000 座建筑物正在被拆除。大基督城地区由 19 个地震记录站组成的网络在 2010 年至 2011 年地震期间捕获了一组广泛而独特的地面运动 (GM)。这些 GM 可能可用于反向分析，旨在了解地面震动的空间变化（特别是场地和盆地效应），然后进行准确的前向估计，旨在量化未来设计 GM 的振幅和频率内容。然而，目前还无法进行详细的 GM 分析，因为没有关于基督城地下超过 400 米深的夹层砂砾石沉积物的剪切波速度 (Vs) 结构的信息。 这项快速响应研究 (RAPID) 拨款的主旨是在新西兰基督城的 12-15 个关键地点进行深层 (400 m) Vs 剖面分析，以帮助进行重要的地震 GM 响应分析。由于 CBD 的重建计划正在快速推进，并且一旦 2013 年初至中期重建正式开始，拟议的测试将变得非常复杂（如果不禁止的话），因此我们很快就需要这些信息。经济且快速获得信息的唯一方法对这些深度的 Vs 估计是通过非侵入式表面波测试进行的。然而，目前最常用于深度 Vs 剖面分析的被动波场技术存在很大的不确定性。因此，将进行一项独特的研究，以在扩展的频率/波长范围内比较和合并来自大型主动源和被动波场表面波方法的数据，这将允许稳健地确定数据不确定性和相对偏差。主动源表面波测量将使用大型且独特的 NEES@UTexas 移动伺服液压振动台和高达 48、1 Hz 地震检波器之一进行，而被动波场数据将使用中型和大型地震检波器进行收集。直径圆形传感器阵列由10个宽带地震仪组成。这项研究将使用于深度 Vs 剖面的大型主动源和被动波场表面波方法之间的可用比较增加三倍。在获得独立利用无源波场方法的信心之前，需要进行这些比较。因此，这项工作的智力优点包括：（a）收集和解释一个独一无二的数据集，该数据集可用于评估合并大型主动源和被动波场表面波方法所涉及的可靠性。深 Vs 剖面，以及 (b) 通过分析来自多个地震事件的一组独特的破坏性 GM 记录，这些深 Vs 剖面使深层沉积盆地的精确地震动预测成为可能。在这两个问题上取得的进展将直接影响美国、新西兰和全世界的地震工程研究。 这项工作的更广泛影响是多方面的，因为这些研究工作将通过开发强大的抗震设计 GM 来影响整个基督城社会，这将有助于减轻未来地震中的这种极端损失。此外，通过分析坎特伯雷地震序列中记录的强 GM 获得对深层沉积物场地响应的额外了解，将有利于美国深层沉积盆地下方的地震活跃地区，例如洛杉矶和西雅图。这项工作还将有助于加强美国和新西兰之间的国际研究合作，并将为美国研究生提供有益的国际旅行经历，这将有助于平衡他们的技术教育，并使他们了解地震中仍然存在的全球相关问题工程。