Earthquake energy budget and coseismic fault temperature from seismological observations

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

Abstract

How do earthquakes happen? Understanding the nature of earthquakes is a key fundamental question in Geociences that holds many implications for society. Earthquakes are typically associated with a sudden release of energy that has slowly accumulated over hundreds to thousands of years, being strongly controlled by friction in faults buried several kilometers beneath our feet under quite extreme conditions. For example, the amount of heat produced in just a few seconds is such that it can dramatically change the nature of the fault zone near the sliding surface. Moreover, there is abundant evidence of substantial frictional weakening of faults (i.e., fault strength weakens with increasing slip or slip rate) during earthquakes. However, there are still many open questions related to earthquake source processes: How similar are earthquakes in different temperature-pressure conditions? What is the earthquake's energy budget, which controls the intensity of ground motions? What are the physical mechanisms responsible for fault weakening? Recent progress in seismological imaging methods, theoretical fracture mechanics and rupture dynamics simulations can help solve these questions. Huge volumes of freely available seismic and geodetic data from around the world now allow the routine calculation of earthquake models where earthquakes are typically described as single space-time points. Time is now ripe for systematically building robust, more detailed seismic models bearing information on earthquake's physics by using recently developed sophisticated modelling tools along with high-quality images of the 3-D Earth's interior structure enabled by high performance computing facilities. Moreover, it is now possible to model ruptures theoretically in detail using both analytical fracture mechanics calculations and numerical rupture dynamics simulations, and, for example, estimate the fault temperature during the rupture process, which is the most direct way to quantify friction. However, systematic quantitative links between these calculations and seismological observations are still lacking. This project addresses these issues through a coordinated effort involving seismology and rock mechanics aiming at estimating fault temperature rise during earthquakes from new macroscopic seismic source models. We will use advanced seismic source imaging methods to build a new set of robust kinematic, static and dynamic earthquake source parameters for a large selected set of global earthquakes (e.g., average fault length, width, rupture speed and time history, stress drop, radiated and fracture energy). These solutions will then be used as input parameters to estimate fault temperature using analytical and numerical rupture dynamics calculations. This will lead to an improved understanding of how local fault processes occurring at scales from few microns to tens of centimetres translate into macroscopic seismological properties, how energy is partitioned during earthquakes and which are the mechanisms responsible for fault weakening. Ultimately this project will shed new light on many basic questions in earthquake science such as the similarity of earthquakes in different P-T conditions and the potential geological record left by ruptures (e.g., melt). More broadly, this project will benefit hazard models and any studies relying on accurate earthquake source parameters such as studies in seismic tomography, active tectonics and microseismicity (e.g., associated with hydraulic fracturing).

Planned Impact

The goal of this project is to substantially advance our fundamental understanding of how faults slip during global large magnitude earthquakes. New source models based on seismic and geodetic data will be constructed, which will be used together with rupture dynamics calculations to better constrain earthquake physics. Given the fundamental nature of this project, the main non-academic beneficiaries of this project will be:

(1) In the short-term: school children, teachers and the wider public. Earthquakes offer great potential to spark the interest of these users in Geosciences (and, more generally, in STEM subjects) and thus contribute to the UK's skillbase, notably in geophysics, an area with high industry demand and listed in the Home Office shortage occupation list (the high-level training of a PDRA in Geophysics within the project will also contribute to this).

(2) In the long-term: government agencies and private companies responsible for earthquake monitoring and for seismic hazard and risk assessment, as a key element for assessing seismic hazard is to accurately predict ground motions, which requires a good understanding of earthquake physics (see letter of support from our impact partner USGS). Moreover, the geophysics industry working on microseismicity may also benefit from this project as a clearer understanding of the relationships between macroscopic source parameters and the frictional behaviour of faults is useful for improved seismicity monitoring efforts in shale gas extraction, geological carbon dioxide sequestration, etc (see letter of support from our impact partner Pinnacle). Although this project will principally investigate global large-magnitude earthquakes, much of the learning achieved might be useful for smaller event regional studies.

A-level students and teachers will benefit from this project through the co-production of new learning materials, a short animated educational movie on the earthquake source processes investigated in the project, as well as from other activities (e.g., visits to UCL, notably to the rock mechanics laboratory, and focus group discussions). Beyond subject knowledge, they will also benefit by engaging with the scientific process, understanding how new data are gathered and interpreted, and how new ideas are proposed. More generally, the wider public will benefit from the project's participation in high-visibility popular science exhibits and shows, science cafes and debates.

Government agencies and private sector geophysics companies working on seismic hazard/risk and microseismicity will benefit from this project by actively following the project's development (see letters of support from our impact partners) and by participating in a final project workshop where the main scientific results will be presented and discussed, and where a reflection on the project's long-term impact for specific users will be undertaken. The conclusions of the workshop will be published in a journal accessible to the wide academic and non-academic community, such as the RAS journal 'Astronomy and Geophysics', the AGU Eos newspaper and/or journals of geophysics societies with wide visibility in industry (e.g., Society of Exploration Geophysicists (SEG) - The Leading Edge (TLE) or European Association of Geoscientists and Engineers (EAGE) - First Break (FB)).

Publications

10 25 50
 
Description We have developed two new techniques to image earthquakes. We found that these are more robust than previous related techniques that relied on an iterative scheme that can be very prompt to errors; this work is now under review for publication. We have also studied thoroughly a sequence of earthquakes in the Azores archipelago (mid-Atlantic ridge) and could quantify the errors associated with them. In addition, we studied the impact of using only distant versus near field data. This is very important because mid-oceanic events are often only studied with distance data. Thus, our work is an excellent opportunity to study the impact of such approach on the solutions. This work has now been published (Frietsch et al., 2018). Moreover, we are currently now applying one of the techniques that we developed to a series of deep earthquakes, whose mechanism remain poorly understood. We hope to publish this work next year. Finally, we confirmed that understanding the Earth structure where earthquakes occurr is very important and thus, as a results of a changing landscape of the research programme, we have devised a new efficient method to determine local Earth structure using ambient noise (Berbellini et al., 2019). This will be useful to better characterise in a cheap, fast way the Earth structure around active earthquake areas (amongst other applications). Another by-product of this project has also been the characterisation of water content in the deep Earth, whereby we expanded some of the earthquake source analysis tools to this exciting, hot topic (Chang et al., 2019).
Exploitation Route In the future we will apply our technique to a large number of earthquakes. The retrieved parameters may be very useful for the wide Earth sciences community, such as geologists studying active tectonics, and, more generally, any researcher that needs earthquake source parameters for their research work.
Sectors Environment

 
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 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 Impact - UCL (PhD studentship)
Amount £65,467 (GBP)
Organisation University College London 
Sector Academic/University
Country United Kingdom
Start 10/2014 
End 09/2017
 
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 New earthquake source imaging method 
Description We have developed two new methods to constrain earthquake source models. 
Type Of Material Improvements to research infrastructure 
Provided To Others? No  
Impact No impacts yet as the method has not been used in real data applications yet. 
 
Description Caltech - Prof. Hiroo Kanamori 
Organisation California Institute of Technology
Country United States 
Sector Academic/University 
PI Contribution This project is building new earthquake source models, which will be interpreted using earthquake physics, in collaboration with Prof. Hiroo Kanamori from Caltech.
Collaborator Contribution Prof. Kanamori will give crucial advice to the project based on his extensive knowledge and experience in earthquake physics.
Impact No outcomes yet, the work is in progress.
Start Year 2016
 
Description IPGP Paris - Dr Martin Vallee 
Organisation Paris Institute of Earth Physics
Country France 
Sector Academic/University 
PI Contribution We are analysing together high-frequency source time functions. My group is providing accurate spatial constraints on the earthquake source.
Collaborator Contribution Dr Vallee is contributing with his automated algorithms to estimate source time functions using a deconvolution approach.
Impact No outputs yet, the project is ongoing.
Start Year 2016
 
Description Sharing data and experience in earthquake source modelling with IPMA (Portuguese seismic monitoring agency) 
Organisation Portuguese Institute of Sea and Atmosphere (IPMA)
Country Portugal 
Sector Public 
PI Contribution My team performed seismic source inversions for earthquakes in the Azores archipelago using IPMA's data.
Collaborator Contribution The IPMA team made their data available to us and hosted one of our PhD students as well as myself in their institute to understand how they collect, process and analyse their data.
Impact A joint publication has resulted from this collaboration: Frietsch, M., Ferreira, A.M.G., Vales, D., Carrilho, F. (2018). On the robustness of seismic moment tensor inversions for mid-ocean earthquakes: the Azores archipelago. Geophysical Journal International, 215 (1), 564-584. doi:10.1093/gji/ggy294
Start Year 2016
 
Description Univ. California Riverside - Gareth Funning 
Organisation University of California, Riverside
Country United States 
Sector Academic/University 
PI Contribution We are currently analysing seismic and InSAR data jointly, whereby my team leads the seismic analysis and this collaborator contributes with his strong expertise and experience in geodesy studies.
Collaborator Contribution Contributed to the InSAR analysis.
Impact No outputs yet, the project is ongoing.
Start Year 2016
 
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