SGER: Collaborative Research: A Rapid Geophysical Response to the Great 2006 Tonga EQ

SGER：协作研究：对 2006 年汤加 EQ 的快速地球物理响应

• 批准号: 0637229
• 负责人: Michael Bevis
• 金额: --
• 依托单位: Ohio State University Research Foundation -DO NOT USE
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-08-01 至 2007-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0637229&HistoricalAwards=false
• 关键词: SGER; Collaborative; Research; Rapid; Geophysical

For more than 20 years geophysicists and geologists have tended to classify the world's subduction zones in terms of their degree of coupling, or more specifically 'seismic coupling'. The Marianas slab is often seen as 'pulling back' from the island arc, thereby giving rise to active backarc spreading. Marianas-type subduction zones are very unlikely to generate great underthrusting (megathrust) earthquakes. After GPS measurements established that the Tonga island arc has by far the greatest rates of backarc spreading as well as plate convergence. Most geophysicists have concluded that Tonga, rather than the Marianas, is actually the least seismically-coupled subduction zone in the world. On 3 May 2006 a great (Mw = 7.9) shallow earthquake occurred near the Ha'apai island group in southern Tonga. The focal mechanism for its centroid moment tensor (CMT) almost exactly matches that expected for intraplate convergence along the shallow interplate thrust zone, i.e., a megathrust. If this interpretation is correct, this would be one of the most surprising earthquakes of the last twenty years, and it would require major rethinking on the mechanics of subduction as well as seismogenesis. However, all focal mechanisms are ambiguous, and the alternative explanation is that this event had a high angle fault plane, in which case it would constitute a great plate-tearing event. Shallow plate tearing events are rare, especially in slabs experiencing downdip compression, and no such event has been subject to careful study using GPS and broadband seismic array. It is vital to make near-field measurements quickly, while postseismic deformation remains vigorous. This small grant for exploratory research will allow a rapid survey of the rupture zone and its immediate surroundings, deployment of a broadband seismic array to study the aftershocks, survey GPS measurements to establish the sense of coseismic movements at previously established stations, and a combination of survey and continuous GPS measurements to monitor the postseismic deformation field produced by all great earthquakes. Also included is a rapid geomorphological survey of the region's coastlines to help constrain coseismic and postseismic vertical movements. No one has ever observed postseismic transients and aftershocks of a great and shallow plate tearing earthquake using modern seismic and GPS instruments. This project is a collaboration between three US institutions as well as partners in Tonga and the Pacific Rim countries. The work also could have significant implications for earthquake and tsunami hazards along Tonga.

20多年来，地球物理学家和地质学家一直倾向于根据它们的耦合程度，或者更具体地说，“地震耦合”来对世界上的俯冲带进行分类。马里亚纳板块通常被认为是从岛弧“拉回”，从而引起活跃的弧后扩张。马里亚纳型俯冲带不太可能产生巨大的逆冲断层地震。在GPS测量确定汤加岛弧具有迄今为止最大的弧后扩张速率以及板块会聚之后。大多数地震学家得出结论，汤加，而不是马里亚纳群岛，实际上是世界上地震耦合最小的俯冲带。2006年5月3日，在汤加南部的Ha'apai岛群附近发生了一次大地震（Mw = 7.9）。其质心矩张量（CMT）的震源机制几乎完全符合预期的板内会聚沿着浅板间逆冲带，即，巨型逆冲断层如果这种解释是正确的，这将是过去20年来最令人惊讶的地震之一，这将需要对俯冲机制和地震成因进行重大反思。然而，所有的震源机制都是模糊的，另一种解释是，该事件有一个高角度的断层面，在这种情况下，它将构成一个大的板块撕裂事件。浅层板块撕裂事件是罕见的，特别是在板块经历下倾压缩，没有这样的事件已受到仔细研究，使用全球定位系统和宽带地震阵列。在震后变形仍然剧烈的情况下，快速进行近场测量至关重要。这笔用于探索性研究的小额赠款将用于对断裂带及其周围环境进行快速调查，部署宽带地震阵列以研究余震，进行全球定位系统测量以确定先前建立的台站的同震运动，并将调查和连续全球定位系统测量相结合，以监测所有大地震产生的震后变形场。还包括对该地区海岸线的快速地貌调查，以帮助限制同震和震后的垂直运动。还没有人用现代地震和GPS仪器观测到一个大而浅的板块撕裂地震的震后瞬变和余震。该项目是三个美国机构以及汤加和太平洋沿岸国家合作伙伴之间的合作。这项工作还可能对沿着汤加的地震和海啸灾害产生重大影响。