Origin of seismic heterogeneity and attenuation in the Earth's upper mantle and transition zone

Lead Research Organisation: University College London
Department Name: Earth Sciences

Abstract

The Earth is a dynamic planet with a changing surface partly shaped by processes in its deep interior, which control earthquakes, volcanoes and the formation of mountain ranges. Flow in the Earth's uppermost mantle and transition zone (at depths of ~50-660 km beneath the surface) drives plate tectonics, one of the features distinguishing our planet from others.

However, there is much that we do not know about the Earth's mantle: What are the scales of variation in the properties of the Earth? Is variation in the structure of the mantle due to temperature and/or chemical composition? In what directions does mantle flow? Recent developments in seismology, thermodynamic modelling and rock physics have the potential to help solve these questions. Modern high performance computing is enabling the efficient analysis and modelling of freely-available large-scale sets of seismic data from around the world allowing us to generate increasingly detailed images of the Earth's interior. Progress in rock and mineral physics laboratory experiments, along with new developments in thermodynamic theory, now allow the construction of realistic models of planetary interiors that are thermodynamically self-consistent. As a result of the joint use of these different techniques, properties of the Earth that were very difficult to estimate in the past are within reach today. Intrinsic seismic attenuation (the amplitude loss of propagating seismic waves due to internal friction or anelastic processes) is particularly interesting, giving unique insight about temperature, chemical composition and the presence of fluids in the Earth's mantle when jointly interpreted using seismology, mineral/rock physics and geodynamics. However, up to now, seismic attenuation has received relatively little attention, and efforts for such integrated studies of the Earth's interior have been rare and limited. This project addresses these issues, with the aim of substantially advancing our fundamental understanding of the physical and chemical processes occurring in the Earth's interior, notably in the uppermost mantle and transition zone. We will achieve this by assembling a new massive seismic dataset, which will be modelled and used for the first time along with novel thermodynamical and rock physics information in a fully consistent way, to build new global 3-D images of attenuation and seismic speed in the Earth's mantle, and infer mantle's temperature, chemical composition and flow. This will help us deduce the scale, distribution and mechanisms responsible for variations in Earth's properties and attenuation in the upper mantle and transition zone, leading to an improved understanding of the dynamics of this key component of the deep Earth.

We have gathered a team of three UK scientists with complementary expertise in seismology, geodynamics and mineral physics, supported by international multidisciplinary partners, with the skills and knowledge to build a new framework for the 3-D seismo-thermodynamic characterization of the Earth's interior. We will build on our recent work in novel seismic data analysis and imaging strategies, and on mineralogical and dynamical mantle modelling. By the end of this 3-year research project, with help from two postdoctoral assistants, we will have new knowledge about the dynamic processes in the Earth's mantle, and new tools and frameworks for integrated deep Earth research, which will be widely disseminated beyond the project's duration. So far no studies of 3-D attenuation, seismic speed, temperature, chemical composition and flow in the Earth's upper mantle and transition zone have used such a comprehensive, interdisciplinary approach.

Planned Impact

The aim of this project is to produce a step change in our fundamental understanding of the mechanisms responsible for 3D structure in the Earth's upper mantle and transition zone, bringing new insight into the thermal, chemical and dynamic behaviour of the Earth's interior. We will provide high-level training of two PDRAs in geophysics, which is one of the specialisations listed in the UK's home office shortage occupation list. Given the fundamental nature of the project, the main non-academic beneficiaries of this work will be: (i) users working on practical applications requiring a good knowledge of the 3D structure of the Earth's interior, such as from government and non-government seismic monitoring agencies responsible for routine earthquake source characterizations and nuclear explosion monitoring; and, (ii) school children, teachers and the wider public, by motivating young people for exciting science, encouraging them to choose science subjects at school and university and thus contributing to the UK's skillbase.

Our new 3D Earth models will be useful for seismic monitoring efforts, such as for more accurate estimates of earthquake sources and associated ground motions, and nuclear explosion verifications. Although we will focus on the Earth's global scale, the lessons learned will also be useful for regional/local applications. We will use our network of contacts in national and international seismic monitoring agencies (e.g., Los Alamos Nat. Lab., USGS, BGS) to disseminate our project, facilitated by the fact that the project's lead PI (A. Ferreira) works on both Earth structure and earthquake source imaging. Dr H. Patton (Los Alamos Nat. Lab.), who has a lifetime experience in earthquake and nuclear explosion monitoring, will serve the project as international impact adviser (see letter of support), advising the project from the outset and participating in the project's 2-day workshop, which will involve members of the seismic monitoring community (e.g., from CTBTO, USGS, BGS). The conclusions of the workshop will be published in a media-friendly journal (e.g., Eos, Astronomy & Geophysics) accessible to members of seismic monitoring agencies. We will use our strong links with major European and international programmes (e.g., QUEST, CIG, IRIS) to distribute our project's outputs. All these programmes are highly-visible and accessed by both academics and non-academics, including members of the seismic monitoring community.

We shall build on ongoing engagement activities by the project PIs/co-Is, such as seismometer demonstrations in schools, participation in teaching training events, local and national exhibits, and leverage activities with the geophysics industry, following a more structured approach. We will build on our existing links with the Teacher Scientist Network (www.tsn.org.uk, see support letter) to work with focus groups of teachers and students. Together, we will create new 3D deep Earth visualisation teaching and engagement materials, which will help strengthening geosciences in school curricula and engage students in the scientific process. If funded, the project will be introduced at a GIFT workshop (Geoscience Information For Teachers) in the 2013 EGU meeting, to ensure its wide-user visibility and feedback from the outset. We will also apply for project exhibits using the new 3-D visualisation materials in venues such as the Royal Norfolk Show and the Royal Society's Summer Science Exhibition. The PIs/co-I and PDRAs will prepare a popular science article for publication, e.g., in New Scientist or NERC's Planet Earth magazine. Moreover, we will communicate our findings to the media, by using UEA and UCL's press office services and training courses, and will facilitate a comprehensive training of the PDRAs, including knowledge-exchange skills, attending media training courses, co-organising the project's workshop and developing effective skills in science communication to the wider public.

Publications

10 25 50
 
Description While most seismic images are built using exclusively travel-time information associated with seismic waves, in this project we have shown that higher-resolution images of the Earth's interior can be obtained from surface wave amplitude data (which are usually thought to be too noisy or complicated to interpret). We have shown in particular that dense array data (e.g. from the USArray and others) are key to extract coherent information from seismic amplitudes are we are currently building higher resolution images of the Earth's interior for elastic and anelastic structure using these data.
Exploitation Route Our findings are useful to a wide range of users such as earthquake monitoring and seismic hazard agencies and more generally to educate the public. We will communicate them widely through these end-used communities. In addition, we are currently putting together several proposals to submit to NERC and to the EU on multidisciplinary work combining seismology, geodynamics and mineral physics in an unprecedented quantitative and detailed way.
Sectors Education,Energy,Environment

 
Description So far our findings have had an impact on the education of the wide public and schools, through a number of engagement activities, discussions with teachers, the Teacher Scientist Network and the development of a new web-based tool for A-level students on seismology and geodynamics.
First Year Of Impact 2015
Sector Education,Leisure Activities, including Sports, Recreation and Tourism
Impact Types Societal

 
Description ANR - French National Research Agency
Geographic Reach Europe 
Policy Influence Type Participation in a advisory committee
 
Description ANR - French National Research Agency
Geographic Reach Europe 
Policy Influence Type Participation in a advisory committee
Impact New attributed researched funding enhanced skills in geology and geophysics, which have strong industry demand.
 
Description Member of the Irish iCRAG advisory committee
Geographic Reach Europe 
Policy Influence Type Participation in a advisory committee
 
Description Member of the scientific advisory board of RESIF (French National Geophysics Infrastructure)
Geographic Reach Asia 
Policy Influence Type Participation in advisory committee
Impact Following advice from the board (in which I'm included), the data distributed by RESIF now flow much better and are distributed in a clearer way. Moreover, our advice has helped improving the visibility of the infrastructure as well as educational applications of the data collected and distributed.
 
Description Participation in a advisory committee - Member of the Irish iCRAG advisory committee (2016)
Geographic Reach Europe 
Policy Influence Type Participation in a advisory committee
 
Description Participation in a advisory committee - UK representative in the EU COST action TIDES (2016)
Geographic Reach Europe 
Policy Influence Type Participation in a advisory committee
 
Description Participation in a advisory committee - UK representative in the EU COST action TIDES (2017)
Geographic Reach Europe 
Policy Influence Type Participation in a advisory committee
 
Description UK representative in the EU COST action TIDES
Geographic Reach Europe 
Policy Influence Type Participation in a advisory committee
 
Description Impact - UCL (PhD studentship)
Amount £65,467 (GBP)
Organisation University College London 
Sector Academic/University
Country United Kingdom
Start 10/2014 
End 09/2017
 
Description SAN-ICE: Seismic Ambient Noise as a proxy to investigate ICE in polar regions
Amount € 183,000 (EUR)
Funding ID 747805 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 05/2018 
End 05/2018
 
Description SIGHT - SeIsmic and Geochemical constraints on the Madeira HoTspot system
Amount € 400,000 (EUR)
Funding ID SIGHT (funded by Fundacao para a Ciencia e Tecnologia - FCT, Portugal) 
Organisation University of Lisbon 
Sector Academic/University
Country Portugal
Start 06/2019 
End 05/2022
 
Title Ambient noise imaging of shallow Earth structure 
Description We developed a new tool to image the shallow structure of the Earth and demonstrated its applicability to image ice and shallow crustal structure. Our publication on this tool is currently in revision and we are also currently preparing our software to distribute it openly to the scientific community. 
Type Of Material Improvements to research infrastructure 
Year Produced 2017 
Provided To Others? No  
Impact We are currently finalizing our tool and its distribution, so there have been no notable impacts yet. 
 
Title Local amplification inversions 
Description We have developed a new method to quantify local seismic amplification and to invert it for local Earth structure (velocity and attenuation) as a function of depth. We are currently carrying out extensive tests of the new method. 
Type Of Material Improvements to research infrastructure 
Provided To Others? No  
Impact No impacts yet as it's a new tool and we are still finishing testing it. 
 
Title Database of local seismic amplification beneath N. America and S. Africa 
Description We have built a database of local seismic amplification measurements beneath N. America and S. Africa. We are still finishing testing these new measurements, but preliminary tests look very positive. 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact No impacts yet. 
 
Title Database of seismic surface wave amplitudes 
Description Massive dataset of surface wave amplitudes, which will be key to obtain improved models of attenuation in the Earth's mantle as proposed in this NERC project. We have organised the database into a user-friendly format and logged some issues identified (e.g., repeated ad inconsistent data). 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact We will present a poster at the fall AGU meeting in December 2014. Other than that, no other notable impacts have been achieved yet because the project has started recently and hence there hasn't been enough time to apply and model the data. 
 
Title Database of synthetic seismic waveforms 
Description We built a database of synthetic seismic waveforms using high-performance computing facilities which are key to image and understand the behaviour of the Earth's lowermost mantle. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
Impact This is very recent, so we do not have any clear evidence of impacts yet, but we hope that the database will have a notable impact on other deep scientists' work in the future. 
 
Title New images of crustal structure beneath Portugal 
Description We have built the first country-wide model of the crust beneath Portugal. This consists of images of shear wave speed in the region. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
Impact These images will be useful to simulate seismic wave propagation in Portugal and, more generally, in Western Iberia. Ultimately this will help better assess seismic hazard in the region. This is important because the largest historical earthquake in Europe occurred in Portugal (the 1755 M~8.5 earthquake). 
 
Title New images of crustal structure beneath northern Italy 
Description We have obtained new images of shear wave speed of the crust beneath northern Italy; these images are now published and publicly available (Berbellini et al, PEPI, 2017). 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
Impact These images are currently being used by colleagues at INGV, Italy and University of Bologna, Italy, to simulate seismic wave propagation in the region. Ultimately this will help better assess seismic hazard in Northern Italy. 
 
Title New images of seismic wave speed beneath N America 
Description We built new high-resolution images of seismic wave speed beneath N America. 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact This will help us better understand the tectonic processes beneath N America and potential associated earthquake hazard. 
 
Description Collaborative work with Prof. Carolina Lithgow-Bertelloni on mineral physics interpretation of the project 
Organisation University College London
Country United Kingdom 
Sector Academic/University 
PI Contribution Our team performed mineral physics calculations essential to the interpretation of the project's results assisted by Prof. Lithgow-Bertelloni.
Collaborator Contribution Prof. Lithgow-Bertelloni provided guidance and assistance on the mineral physics calculations and their interpretation compared to seismic data.
Impact One paper resulted from this collaborative work: Faccenda, M., Ferreira, A.M.G., Tisato, N., Lithgow-Bertelloni, C., Stixrude, L., Pennacchioni, G. (2019). Extrinsic elastic anisotropy in a compositionally heterogeneous Earth's mantle. Journal of Geophysical Research, doi:10.1029/2018JB016482
Start Year 2016
 
Description Collaborative work with Prof. Lars Stixrude on mineral physics interpretation of the project 
Organisation University College London
Country United Kingdom 
Sector Academic/University 
PI Contribution Together with Prof. Stixrude we performed mantle thermodynamics, mineral physics calculations essential for the interpretation of results from the project.
Collaborator Contribution Prof. Stixrude guided the mineral physics calculations and provided us his database of thermodynamical models.
Impact A join research paper resulted from this work: Faccenda, M., Ferreira, A.M.G., Tisato, N., Lithgow-Bertelloni, C., Stixrude, L., Pennacchioni, G. (2019). Extrinsic elastic anisotropy in a compositionally heterogeneous Earth's mantle. Journal of Geophysical Research, doi:10.1029/2018JB016482
Start Year 2016
 
Description Collaborative work with Prof. Sung-Joon Chang 
Organisation Kangwon National University
PI Contribution We have performed work together on the analysis of the robustness of seismic tomography images and on their interpretation in terms of deep mantle processes, notably on slab-plume interactions. Our group provided expertise on seismic tomography inversions and data analysis techniques.
Collaborator Contribution Local knowledge of the tectonic context in the western Pacific and on the performance of robustness tests of tomography models.
Impact Publications: Chang et al, 2014; Chang et al., 2015; Chang et al., 2016; Chang and Ferreira, 2017.
Start Year 2014
 
Description INVG - University of Bologna, Italy - Prof. Andrea Morelli 
Organisation National Institute for Geophysics and Volcanology (INGV)
Country Italy 
Sector Public 
PI Contribution Our research group has performed normal mode calculations and measurements of Rayleigh wave ellipticity in the framework of this collaboration.
Collaborator Contribution The partner has given substantial input regarding Monte Carlo inversions in the framework of this collaboration.
Impact Publications: Berbellini et al, GJI, 2016 ; Berbellini et al., PEPI, 2017; Attanayake et al., Tectonophysics, 2017
Start Year 2015
 
Description University of Michigan, USA - Prof. Jeroen Ritsema 
Organisation University of Michigan
Country United States 
Sector Academic/University 
PI Contribution My research group has performed seismic data analyses and tomographic inversions within the framework of this collaboration.
Collaborator Contribution The partner has provided substantial insight on body wave analyses within the framework of this collaboration.
Impact Publications: Chang et al., 2014, Chang et al., 2015.
Start Year 2014
 
Description University of Padova - Prof. Manuele Faccenda 
Organisation University of Padova
Department Department of Geosciences
Country Italy 
Sector Academic/University 
PI Contribution We performed all the seismological analyses carried out under the framework of this partnership.
Collaborator Contribution Our partner performed all the geodynamical simulations and analyses carried out under the framework of this partnership.
Impact Publications: Chang et al, Nature Communications, 2016. We also presented a series of conference presentations of our ongoing work, notably at AGU and EGU meetings.
Start Year 2014
 
Description Development of web-based tool for A-level students named Build your planet (ongoing activity) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact The tool is still being developed, so there are no end-products yet. However, we have discussed the tool development with teachers, which sparked an even greater interest in seismology and geodynamics and on how it can improve A-level student engagement in science.

See previous answer.
Year(s) Of Engagement Activity 2014
 
Description Meeting with school teachers facilitated by the charity Teacher Scientist Network (TSN) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact This meeting led to the design of a new web-based tool for A-level students to learn more and participate in activities in seismology and geodynamics.

After this meeting, the school asked to visit the department of Earth Sciences at UCL, which we are currently organising.
Year(s) Of Engagement Activity 2014
 
Description Meetings with teachers 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact We carry out two group discussions with teachers, also in liaison with the Teacher Scientist network in Norwich, around our "Build your planet" web-based tool for A-level students.
Year(s) Of Engagement Activity 2015
 
Description School visits to UCL - "taster" classes 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact We organised fours sets of outreach events for groups of school students and teachers (primary and secondary schools), with about 70 students attending in total. We did some demonstrations around earthquakes and seismometers, and for the more advanced students we did a demonstration using our work-in-progress "Build your planet" web-based outreach tool.
Year(s) Of Engagement Activity 2015,2016,2017,2018