Collaborative Research: RAPID Geodetic Field Response to the 2018 Magnitude 7 Anchorage Earthquake

合作研究：2018 年安克雷奇 7 级地震的快速大地测量场响应

• 批准号: 1917435
• 负责人: Jeffrey Freymueller
• 金额: $ 1.5万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-03-15 至 2021-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1917435&HistoricalAwards=false
• 关键词: Collaborative; Research; RAPID; Geodetic; Field

On November 30, 2018 a magnitude 7 earthquake struck just north of Anchorage, Alaska and caused over $75 million in damage to private and public facilities. The earthquake took place in the upper part of a subducting slab where the slab may be bending downwards, and early indications suggest that the event was related to stresses caused by plate bending. In the weeks and months following a large earthquake, slip and deformation can continue to take place along a tectonic plate boundary. To better understand that nature of this deformation, this study would place five continuous GPS (global positioning system) stations near the earthquake epicenter, as well as record campaign GPS measurements at other local benchmark locations. Data from this study could be used to better understand the behavior along the Denali fault and improve constraints on local seismic hazards. This project focuses on constraining postseismic deformation due to the magnitude 7 Anchorage earthquake, a normal faulting event within the Yakutat flat slab, including how coseismic and postseismic deformation may trigger changes in slip along the subduction interface. To achieve this, five new continuous GPS sites will be installed in the near-field of the earthquake and repeat campaign surveys will be conducted at benchmarks throughout the region. These measurements will provide a dataset that will be able to more completely characterize postseismic deformation, variations in locking and creeping behavior on the subduction interface, and potential triggered slow slip events. The effect of intraslab normal-faulting earthquakes on upper plate deformation, coupling along the subduction interface, and transient events on the interface is not well understood. Coseismic displacements recorded at continuous GPS sites show a complex deformation pattern and the location of the event make it likely that viscoelastic relaxation in the asthenosphere will occur. Aftershocks recorded in the first weeks after the earthquake roughly delineate a horizontal surface, suggesting that the events may be occurring at or near the plate interface. The main shock occurred within a region that has experienced multi-year slow slip events in the past and studies in other subduction zones suggest that such regions are more prone to triggered slow-slip events after an earthquake. Along the eastern limit of the Yakutat flat slab, a postseismic study of the 2002 Denali earthquake suggested that that event may have caused long-term changes of the coupling along that section of the subduction interface. The sparseness of GPS sites within the aftershock zone makes it likely that transient changes on the underlying interface may go undetected and that postseismic deformation and changes in the coupling along the interface may not be able to be fully characterized. Data collected from the proposed new network of continuous GPS added to the data from existing continuous GPS and repeat surveys at campaign benchmarks will allow an evaluation of these signals at a more temporally and spatially dense scale than is currently possible.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.

2018 年 11 月 30 日，阿拉斯加州安克雷奇北部发生了 7 级地震，造成私人和公共设施损失超过 7,500 万美元。 地震发生在俯冲板块的上部，板块可能向下弯曲，早期迹象表明该事件与板块弯曲引起的应力有关。 在大地震发生后的几周和几个月内，沿着板块边界可能会继续发生滑动和变形。 为了更好地了解这种变形的性质，本研究将在地震震中附近放置五个连续的 GPS（全球定位系统）站，并记录其他当地基准位置的活动 GPS 测量结果。 这项研究的数据可用于更好地了解德纳利断层沿线的行为并改善对当地地震灾害的限制。 该项目的重点是限制由安克雷奇 7 级地震（雅库塔平板内的正常断层事件）引起的震后变形，包括同震和震后变形如何触发沿俯冲界面滑移的变化。为了实现这一目标，将在地震近场安装五个新的连续 GPS 站点，并将在整个地区的基准上进行重复活动调查。这些测量将提供一个数据集，能够更全面地表征震后变形、俯冲界面上锁定和蠕动行为的变化以及潜在触发的慢滑移事件。 板内正断层地震对上部板块变形、沿俯冲界面的耦合以及界面瞬变事件的影响尚不清楚。 连续 GPS 站点记录的同震位移显示出复杂的变形模式，并且事件发生的位置使得软流圈中可能会发生粘弹性松弛。 地震发生后最初几周记录的余震大致勾画出水平面，表明事件可能发生在板块界面处或附近。主震发生在过去经历过多年慢滑移事件的地区，而对其他俯冲带的研究表明，这些地区在地震后更容易引发慢滑移事件。沿着雅库塔特平板的东部边界，对 2002 年德纳利地震的震后研究表明，该事件可能导致沿俯冲界面该部分的耦合发生长期变化。余震区内 GPS 站点的稀疏性使得可能无法检测到底层界面上的瞬态变化，并且可能无法完全表征震后变形和沿界面耦合的变化。从拟议的新连续 GPS 网络收集的数据添加到现有连续 GPS 的数据中，并在活动基准上进行重复调查，这将允许在比目前可能的时间和空间更密集的范围内对这些信号进行评估。该奖项反映了 NSF 的法定使命通过使用基金会的智力优点和更广泛的影响审查标准进行评估，并被认为值得支持。