Revealing the geophysical environment of slow slip using core-log-seismic integration
Lead Research Organisation:
Imperial College London
Department Name: Earth Science and Engineering
Abstract
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.
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.
Planned Impact
This research will have three major classes of non-academic beneficiaries:
(1) Geohazards community and local communities in New Zealand. At an international level, the results from this and the wider Hikurangi projects will improve our understanding of the slow slip process. In turn this will help us understand the fault slip process in general and related hazards (earthquake, tsunami), and the role slow slip might play in potentially leading to earthquakes or tsunami earthquakes. This will significantly impact our ability to assess geohazard potential worldwide with implications for government policy makers and authorities in areas of seismic hazard globally. Local authorities in New Zealand will benefit from improved knowledge of the seismic hazard associated with the Hikurangi subduction margin;.
(2) The general public in the UK and internationally will benefit from being informed about subduction zone and fault slip processes from research-led outreach activities aimed at a broad range of age groups and backgrounds. The international public will benefit from coverage surrounding the results of this study in the media, and the advances made in terms of earthquake and tsunami hazard at subduction zones and potential for the resources industry.
(3) The hydrocarbon and mining industry continue to be keen sponsors of the development of full-waveform inversion (FWI) methods because of the improved imaging of fine-scale structure that this technique allows. Validation of FWI models from subduction zones using drilling data, as is proposed here, will be an important test of the FWI method in regions of deep water and high structural complexity;.
We will interact with these beneficiaries by:
(1) Fully engaging with Bell's colleagues at GNS Science New Zealand, and her links with local authorities in New Zealand. In particular, new rock property information that will be recovered from drilling and integration with geophysical datasets will directly be used to update seismic and tsunami hazard models for New Zealand. Bell will work closely with hazards teams at GNS to make sure they are using the most realistic parameters in their models based on the results of this project.
(2) Bell will update her existing NZ3D FWI website to include information about expedition 375 and provide public education material related to the research. Bell is also intending to give talks at geological societies and festivals around the UK in 2019-2020. Bell will also produce an exhibition for the Imperial College Festival which attracts visitor numbers of ~ 10,000 including government policy makers, industry professionals and the general public of all backgrounds and age groups. In addition, Bell will develop materials suitable for delivery in Imperial College London outreach activities.
(3) Talks will be given at industry-focused conferences including EAGE and AAPG.
(1) Geohazards community and local communities in New Zealand. At an international level, the results from this and the wider Hikurangi projects will improve our understanding of the slow slip process. In turn this will help us understand the fault slip process in general and related hazards (earthquake, tsunami), and the role slow slip might play in potentially leading to earthquakes or tsunami earthquakes. This will significantly impact our ability to assess geohazard potential worldwide with implications for government policy makers and authorities in areas of seismic hazard globally. Local authorities in New Zealand will benefit from improved knowledge of the seismic hazard associated with the Hikurangi subduction margin;.
(2) The general public in the UK and internationally will benefit from being informed about subduction zone and fault slip processes from research-led outreach activities aimed at a broad range of age groups and backgrounds. The international public will benefit from coverage surrounding the results of this study in the media, and the advances made in terms of earthquake and tsunami hazard at subduction zones and potential for the resources industry.
(3) The hydrocarbon and mining industry continue to be keen sponsors of the development of full-waveform inversion (FWI) methods because of the improved imaging of fine-scale structure that this technique allows. Validation of FWI models from subduction zones using drilling data, as is proposed here, will be an important test of the FWI method in regions of deep water and high structural complexity;.
We will interact with these beneficiaries by:
(1) Fully engaging with Bell's colleagues at GNS Science New Zealand, and her links with local authorities in New Zealand. In particular, new rock property information that will be recovered from drilling and integration with geophysical datasets will directly be used to update seismic and tsunami hazard models for New Zealand. Bell will work closely with hazards teams at GNS to make sure they are using the most realistic parameters in their models based on the results of this project.
(2) Bell will update her existing NZ3D FWI website to include information about expedition 375 and provide public education material related to the research. Bell is also intending to give talks at geological societies and festivals around the UK in 2019-2020. Bell will also produce an exhibition for the Imperial College Festival which attracts visitor numbers of ~ 10,000 including government policy makers, industry professionals and the general public of all backgrounds and age groups. In addition, Bell will develop materials suitable for delivery in Imperial College London outreach activities.
(3) Talks will be given at industry-focused conferences including EAGE and AAPG.
People |
ORCID iD |
Rebecca Bell (Principal Investigator) |
Publications
Fagereng Å
(2019)
Mixed deformation styles observed on a shallow subduction thrust, Hikurangi margin, New Zealand
in Geology
Wallace L
(2019)
Hikurangi Subduction Margin Coring, Logging, and Observatories
Gray M
(2019)
Imaging the Shallow Subsurface Structure of the North Hikurangi Subduction Zone, New Zealand, Using 2-D Full-Waveform Inversion
in Journal of Geophysical Research: Solid Earth
Barnes PM
(2020)
Slow slip source characterized by lithological and geometric heterogeneity.
in Science advances
Cook A
(2020)
Physical Properties and Gas Hydrate at a Near-Seafloor Thrust Fault, Hikurangi Margin, New Zealand
in Geophysical Research Letters
Davy R
(2021)
Generating High-Fidelity Reflection Images Directly From Full-Waveform Inversion: Hikurangi Subduction Zone Case Study
in Geophysical Research Letters
Morgan J
(2022)
Seafloor overthrusting causes ductile fault deformation and fault sealing along the Northern Hikurangi Margin
in Earth and Planetary Science Letters
Gase A
(2023)
Subducting volcaniclastic-rich upper crust supplies fluids for shallow megathrust and slow slip
in Science Advances
Wang M
(2023)
Compactive deformation of incoming calcareous pelagic sediments, northern Hikurangi subduction margin, New Zealand: Implications for subduction processes
in Earth and Planetary Science Letters
Description | The research related to this work is still in progress. Progress was hampered in 2020-2021 due to the Covid 19 pandemic. I was due to present the work associated with this award in a post-cruise meeting in New Zealand in March 2021 but this was cancelled at the last minute. From Sept 2020-July 2021 I have been on maternity leave. This grant allowed me to be part of IODP Expedition 375 in March - May 2018. This expedition was extremely succesful and collected core data from 4 drilling sites and installed 2 borehole observatories. This is the first time the Hikurangi subduction zone has been drilled. We discovered that a splay fault at Hikurangi is a 18 m thick deformation zone, composed of brittle and ductile deformation (Fagereng et al. 2019). We also discovered that the incoming sedimentary section consists of a very variable lithology. Once subducted this lithology variation may be responsible for slow slip (Barnes et al. 2020, Science Advances). My post-cruise expedition work has determined how much dewatering happens to sediments when they are deformed at subduction zones. It has revealed that pelagic, carbonate sediments that are being deformed don't lose water as quickly as clastic sediments. This could play a role in controlling the stress on the subduction plate boundary fault and the type of earthquakes that occur. As a result of this drilling project the UK are leading a future IODP drilling proposal to return to the Hikurangi margin. This new IODP proposal (Fagereng 959) aims to drill the south Hikurangi margin and compare findings to the drilling in the North done as a result of this award. |
Exploitation Route | All of the drilling data that we collected will be freely avilable to all after the end of the 1 year moratorium in May 2019 |
Sectors | Communities and Social Services/Policy,Education,Energy,Environment |
URL | http://iodp.tamu.edu/scienceops/expeditions/hikurangi_subduction_margin.html |
Description | The research conducted in this project has been promoted to the public in the UK, New Zealand and internationally in a series of festivals, talks, radio broadcasts and magazine articles described in the outreach section of the submission. |
First Year Of Impact | 2019 |
Sector | Education,Other |
Impact Types | Societal |
Description | Eurofleets + SEA Programme call "Oceans" |
Amount | £414,400 (GBP) |
Organisation | EUROFLEETS |
Sector | Private |
Country | France |
Start | 04/2022 |
End | 06/2022 |
Description | Funding for experiment from GNS Science, New Zealand |
Amount | £25,000 (GBP) |
Organisation | GNS Science |
Sector | Public |
Country | New Zealand |
Start | 04/2022 |
End | 05/2022 |
Description | NERC UKIODP |
Amount | £22,960 (GBP) |
Organisation | Natural Environment Research Council |
Sector | Public |
Country | United Kingdom |
Start | 01/2021 |
End | 08/2022 |
Description | NIWA |
Organisation | National Institute of Water and Atmospheric Research (NIWA, New Zealand) |
Country | New Zealand |
Sector | Public |
PI Contribution | I am working together with scientists from NIWA to develop a stratigraphic framework, integrating seismic reflection and drilling data. |
Collaborator Contribution | I am working together with scientists from NIWA to develop a stratigraphic framework, integrating seismic reflection and drilling data. |
Impact | Barnes et al. 2020 and more papers to submit in 2021, 2022 |
Start Year | 2018 |
Description | University of Hawaii |
Organisation | University of Hawaii |
Country | United States |
Sector | Academic/University |
PI Contribution | I am working together with scientists from University of Hawaii to develop a stratigraphic framework, integrating seismic reflection and drilling data. |
Collaborator Contribution | I am working together with scientists from University of Hawaii to develop a stratigraphic framework, integrating seismic reflection and drilling data. |
Impact | Barnes et al. 2020 and papers to submit in 2021, 2022 |
Start Year | 2018 |
Description | 50 years of IODP conference invited speaker |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | Invited to give a talk on my research related to this award at the 50 years of IODP conference. This conference celebrated 50 years of ocean drilling, inviting speakers involved in some of the first drilling expeditions and brand new research. |
Year(s) Of Engagement Activity | 2018 |
Description | BBC Radio 4 show |
Form Of Engagement Activity | A broadcast e.g. TV/radio/film/podcast (other than news/press) |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Public/other audiences |
Results and Impact | Interviewed for Radio 4 broadcast and podcast "In Our Time" with Melvyn Bragg for an episode on Seismology. The show covered a discussion of the history of seismology, current understanding and future directions. This program has resulted in me receiving questions from members of the public and international scientists outside of the field of geology (e.g. archeology). Comments related to earthquake and tsunami preparedness are now being used by newspaper 'The Independent''s travel correspondent Simon Calder in an article aimed at travellers to earthquake prone countries. |
Year(s) Of Engagement Activity | 2022 |
URL | https://www.bbc.co.uk/sounds/play/m00154gh |
Description | Great Exhibition Rd Festival 2019 |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Public/other audiences |
Results and Impact | In 2019 we hosted a stand at the Great Exhibition Rd Festival, London on IODP drilling. Part of this stand focused on drilling subduction zones, including the recent drilling at Hikurangi supported by this grant. The weekend event was attended by > 10,000 people. |
Year(s) Of Engagement Activity | 2019 |
URL | https://www.greatexhibitionroadfestival.co.uk/whats-on/ |
Description | Public talk |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Public/other audiences |
Results and Impact | Invited to give a talk to the Horsham Geological Society. 40 members attended including members of the geotechnical industry who were interested in the design of our seismometer array. |
Year(s) Of Engagement Activity | 2023 |
Description | Ship-to-shore broadcast to four different schools during IODP expedition 375 |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Schools |
Results and Impact | While onboard the JOIDES Resolution during IODP Expedition 375 I was involved in 4 "zoom" meetings with schools. This involved using zoom on an ipad to show school children in New Zealand and the US around the ship and talk to them about my research. This sparked a lot of discussion and interesting questions from the pupils, and the schools reported back that the students have a new appreciated for the types of jobs avilable to them. It was reported that the girls in the class appreciated seeing that women can have jobs in science too. |
Year(s) Of Engagement Activity | 2018 |
Description | Talk at the Leicester Literary and Philosophical Society |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | Invited to give a talk on my work on the Expedition 375 data funded by this award. The core audience is made up of amateur geologists, including some retired academics and other professional geologists, plus some current members of the department (staff and students). |
Year(s) Of Engagement Activity | 2019 |
Description | Video and animations descibing my research made onboard the JOIDES Resolution |
Form Of Engagement Activity | A broadcast e.g. TV/radio/film/podcast (other than news/press) |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Public/other audiences |
Results and Impact | Video and animation made during IODP expedition 375 that describes my role onboard the JOIDES Resolution and my work on core-log-seismic integration. IODP have never made a video/animation on the use of seismic reflection data before. |
Year(s) Of Engagement Activity | 2018 |
URL | https://joidesresolution.org/exp-375-seismic-reflection-imaging/ |