Revealing the geophysical environment of slow slip using core-log-seismic integration

利用岩心-测井-地震一体化揭示慢滑移的地球物理环境

• 批准号: NE/S00291X/1
• 负责人: Rebecca Bell
• 金额: $ 3.07万
• 依托单位: Imperial College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FS00291X%2F1
• 关键词: Revealing; geophysical; environment; slow; slip

Subduction zones are located where one of the Earth's tectonic plates slides beneath another - this motion is controlled by the plate boundary fault. These plate boundary faults are capable of generating the largest earthquakes and tsunami on Earth, such as the 2011 Tohuku-oki, Japan and the 2004 Sumatra-Andaman earthquakes, together responsible for ~250,000 fatalities. Although some plate boundary faults fail in catastrophic earthquakes, at some subduction margins the plates creep past each other effortlessly with no stress build-up along the fault, and therefore large earthquakes are not generated. Determining what controls whether a fault creeps or slips in large earthquakes is fundamental to assessing the seismic hazard communities living in the vicinity of plate boundary faults face and to our understanding of the earthquake process itself. In the last 15 years a completely new type of seismic phenomena has been discovered at subduction zones: silent earthquakes or slow slip events (SSEs). These are events that release as much energy as a large earthquake, but do so over several weeks or even months and there is no ground-shaking at all. SSEs may have the potential to trigger highly destructive earthquakes and tsunami, but whether this is possible and why SSEs occur at all are two of the most important questions in earthquake seismology today. We only know SSEs exist because they cause movements of the Earth that can be measured with GPS technology. Slow slip events have now been discovered at almost all subduction zones where there is a good, continuous GPS network, including Japan, Costa Rica, NW America and New Zealand. Importantly, there is recent evidence that SSEs preceded and may have triggered two of the largest earthquakes this decade, the 2011 Tohuki-oki and 2014 Iquique, Chile earthquakes. Therefore, there is an urgent societal need to better understand SSEs and their relationship to destructive earthquakes.We know little about SSEs because most of them occur at depths of 25-40 km: too deep to drill and to image clearly using seismic data, a remote method that uses high-energy sound waves to probe the Earth's crust. The Hikurangi margin of northern New Zealand is an important exception. Very shallow SSEs occur here at depths of less than 2 km below the sea bed, and they occur regularly every 1-2 years. This SSE zone is the only such zone worldwide within range of modern drilling capabilities and where we can image the fault clearly with seismic techniques - this location provides us with an opportunity to sample and image the fault zone that slowly slips. Drilling provides us with direct information about rock properties and fluid content, however the data is very one-dimensional, and only provides a "pot-shot" glimpse at the subsurface. Seismic data on the other hand images the geometry of the subsurface and allows us to deduce the speed of sound through the rocks over wider areas, however, it does not provide any direct evidence of fluid content or other rock properties. In places where drilling data and seismic data exist together relationships between seismic properties and rock properties can be developed. These relationships can then be applied throughout seismic data volumes to estimate rock properties in areas that have not been drilled. In the case of Hikurangi this would include the deeper part of the subduction plate boundary fault which undergoes slow slip.

俯冲带位于地球的一个构造板块向另一个板块下方滑动的地方--这种运动受板块边界断层的控制。这些板块边界断层能够引发地球上最大的地震和海啸，如2011年日本东北和2004年苏门答腊岛-安达曼地震，总共造成约25万人死亡。尽管一些板块边界断层在灾难性地震中失效，但在某些俯冲边缘，板块毫不费力地相互爬行而过，没有沿断层积累应力，因此不会产生大地震。在大地震中，确定是什么控制了断层的爬行或滑动，对于评估居住在板块边界断层附近的地震危险性社区，以及我们对地震过程本身的理解是至关重要的。在过去的15年里，在俯冲带发现了一种全新的地震现象：无声地震或慢滑事件(SSE)。这些事件释放的能量与大地震一样多，但在几周甚至几个月的时间里，根本没有什么惊天动地的事情。SSE可能有可能引发极具破坏性的地震和海啸，但这是否可能以及为什么会发生SSE是当今地震地震学中最重要的两个问题。我们之所以知道SSE的存在，是因为它们引起了可以用GPS技术测量的地球运动。现在，几乎所有拥有良好、连续GPS网络的俯冲带都发现了慢滑事件，包括日本、哥斯达黎加、美国西北部和新西兰。重要的是，最近有证据表明，SSE先于并可能引发了本十年来最大的两次地震--2011年的Tohuki-oki地震和2014年的智利伊基克地震。因此，社会迫切需要更好地了解SSE及其与破坏性地震的关系。我们对SSE知之甚少，因为它们大多发生在25-40公里的深度：太深，无法使用地震数据钻探和清晰成像，地震数据是一种使用高能声波探测地壳的远程方法。新西兰北部的希库兰吉边缘是一个重要的例外。非常浅的SSE出现在海床以下不到2公里的深度，每1-2年定期出现一次。这个SSE带是世界上唯一一个在现代钻探能力范围内的这样的带，我们可以在这里用地震技术清楚地成像断层-这个位置为我们提供了一个采样和成像缓慢滑动的断裂带的机会。钻探为我们提供了关于岩石性质和流体含量的直接信息，但这些数据是非常一维的，只提供了对地下的“锅底镜头”一瞥。另一方面，地震数据描绘了地下的几何形状，使我们能够在更大范围内推断声波通过岩石的速度，然而，它不能提供任何关于流体含量或其他岩石性质的直接证据。在钻井数据和地震数据同时存在的地方，可以建立地震属性和岩石属性之间的关系。然后，这些关系可以应用于整个地震数据体，以估计未钻探地区的岩石性质。在Hikurangi的情况下，这将包括俯冲板块边界断层的更深部分，该断层经历了缓慢滑动。

项目成果

Generating High-Fidelity Reflection Images Directly From Full-Waveform Inversion: Hikurangi Subduction Zone Case Study

直接从全波形反演生成高保真反射图像：Hikurangi 俯冲带案例研究

• DOI: 10.1029/2021gl094981
• 发表时间: 2021
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Davy R

Seafloor overthrusting causes ductile fault deformation and fault sealing along the Northern Hikurangi Margin

海底逆冲导致北希库朗吉边缘的延性断层变形和断层封闭

• DOI: 10.1016/j.epsl.2022.117651
• 发表时间: 2022
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Morgan J

Slow slip source characterized by lithological and geometric heterogeneity

• DOI: 10.1126/sciadv.aay3314
• 发表时间: 2020-03-01
• 期刊: SCIENCE ADVANCES
• 影响因子: 13.6
• 作者: Barnes, Philip M.;Wallace, Laura M.;LeVay, Leah J.
• 通讯作者: LeVay, Leah J.

Mixed deformation styles observed on a shallow subduction thrust, Hikurangi margin, New Zealand

• DOI: 10.1130/g46367.1
• 发表时间: 2019-09-01
• 期刊: GEOLOGY
• 影响因子: 5.8
• 作者: Fagereng, A.;Savage, H. M.;LeVay, L.
• 通讯作者: LeVay, L.

Imaging the Shallow Subsurface Structure of the North Hikurangi Subduction Zone, New Zealand, Using 2-D Full-Waveform Inversion

使用二维全波形反演对新西兰北 Hikurangi 俯冲带的浅层地下结构进行成像

• DOI: 10.1029/2019jb017793
• 发表时间: 2019
• 期刊: Solid Earth
• 影响因子: 3.4
• 作者: Gray M