Core to regional scale synthesis of fault zone properties and fluids at subduction zones: Drivers of seismogenic behaviour

Lead Research Organisation: University of Southampton
Department Name: School of Ocean and Earth Science

Abstract

Most of the world's large earthquakes happen on the plate boundary faults at subduction zones where two plates converge (e.g. Sumatra in 2004, 2005, and 2007; Chile in 2010). Because the parts of these faults that move during the earthquake lie underwater, they can also be the source of major tsunami. However, different subduction zones are subject to different sizes of earthquakes, and different patterns of earthquake rupture, so that the hazards vary significantly. In most cases rupture on the plate boundary faults is limited to a zone where the fault lies from ~30-40km up to ~5-15km beneath the seabed, but in some cases the fault rupture is thought to have been much more extensive and potentially to have reached the seabed. In other cases the faults are sometimes seen to move more gradually, without an earthquake. In other cases (e.g., Nankai margin offshore Japan), movement on the main plate boundary fault is affected by faults within the accretionary prism, that forms as sediment is scraped off the downgoing plate, and these faults may slip affecting the size of the tsunami waves generated. A final major problem with knowing these hazards at a given subduction zone is that the biggest earthquakes normally only occur every few hundred years, so that our records of the effects are very incomplete. These different fault behaviours depend on the physical properties of the faults themselves, controlled by the seabed sediments adjacent to the subduction zone, and factors such as the presence of fluids within the fault. One way to determine these properties, and presence of fluids, is to drill into the fault zone and directly take samples or measurements of the rock properties using 'logging' technology; this has been done in several places round the world, but even with the most modern technology (riser drilling), it is only possible in the shallower parts of faults, and generates a set of observations effectively at a single location. Drilling at a number of different places on subduction zones together with associated seismic experiments (that bounce sound waves off structures within the earth) show that these properties are very variable, within a single region, and between regions. This reinforces that the combination of drilling (providing local detailed information) and seismic data (providing regional information) should be the primary method for assessing fault properties and their hazard potential: the technique employed in this project. We aim to better understand the behaviour of subduction zone faults by combining seismic and drilling data from several subduction zones around the world. We have chosen regions which have contrasting thicknesses of sediments, and where known fault activity and type and size of resulting earthquakes vary. We will use the drilling data to increase our ability to interpret the properties and fluid content of the fault zones from seismic data at the same location. Then using the seismic interpretations to extend our knowledge of the fault zones over much broader regions, we will investigate variations both down and along the plate boundary fault. We will use the same methods to investigate the relationship between the main plate boundary fault and smaller faults within the accretionary prism. We will then extend our analysis to regions where seismic data have been collected, but which have not yet been drilled, including margins offshore Sumatra and New Zealand. The results generated by the project will allow drilling on these new margins (Sumatra and New Zealand) to be targeted more effectively, thus obtaining new samples and measurements from the sections of these subduction systems with greatest significance for earthquake generation. Ultimately we will relate the interpretations of the state of the plate boundary faults to the known earthquake behaviour and tsunami history, aiming to improve assessments of the hazards at other locations where the long-term behaviour is not known.

Publications

10 25 50
 
Description A methodology has been developed where comparable properties of fault zones from marine geophysical data can be generated and therefore compared from different places on one subduction zone margin and between subduction zones. This will improve understanding what controls the changes in fault properties and how this may relate to earthquake slip behaviour.
The method has been successfully applied to the Nankai subduction zone (Japan), Lesser Antilles subduction zone (Caribbean), and the Hikurangi subduction zone (New Zealand)
Exploitation Route Upon publication, the methodology developed can be applied to different seismic reflection datasets at different margins, thus generating a global database of fault properties derived from geophysical data
Sectors Environment

 
Description The findings are relevant to understanding the properties of fault zones and comparing changes in properties at one subduction zone margin and between margins. Ultimately this is relevant to determining the earthquake potential at different subduction margins. Full impact of these results will come after publication of the methods and the results. Current, short term impact is achieved through public outreach of the methodologies during, e.g., public open days and invited talks to amateur science groups
 
Description NERC UKIODP Site Survey
Amount £243,000 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 08/2016 
End 02/2019
 
Description NanTroSEIZE Stage 3: NanTroSEIZE plate boundary deep riser 2
Amount £5,825 (GBP)
Funding ID NE/K008420/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 11/2012 
End 01/2013
 
Title Derivation of comparable seismic data properties of subduction fault zones 
Description A seismic methodology to allow comparable relative sesimic data properties to be derived from seismic reflection datasets of fault zone properties. Note: This is not an improvement to research infrastructure, but a tool for geophysical data analysis 
Type Of Material Improvements to research infrastructure 
Provided To Others? No  
Impact The methodology will be available on publication, anticipated 2015. The method can be applied to global subduction fault zones to determine fault properties and help to derive their variability, what causes these variations and what impact they may have on fault slip behaviour 
 
Description Collaborations between UK, US, New Zealand academic institutions in integrating and analysing geophysical data for subduction zone fault properties and causes 
Organisation GNS Science
Country New Zealand 
Sector Public 
PI Contribution Encouraging exchange of scientists to the host collaborators, PDRA time to analyse data leading to publication, and hosting joint meeting
Collaborator Contribution Hosting the PDRA on the project and actively contributing to the research programme. Contributing data for the use of the project in the case of GNS Science
Impact Publications in preparation for submission Conference presentation at AGU 2013
Start Year 2010
 
Description Collaborations between UK, US, New Zealand academic institutions in integrating and analysing geophysical data for subduction zone fault properties and causes 
Organisation University of Wisconsin-Madison
Country United States 
Sector Academic/University 
PI Contribution Encouraging exchange of scientists to the host collaborators, PDRA time to analyse data leading to publication, and hosting joint meeting
Collaborator Contribution Hosting the PDRA on the project and actively contributing to the research programme. Contributing data for the use of the project in the case of GNS Science
Impact Publications in preparation for submission Conference presentation at AGU 2013
Start Year 2010
 
Description A talk or presentation - Talk at UK IODP (ocean drilling) national meeting on results from subduction zone drilling and earthquake potential at the Sumatra Subduction zone 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact A talk summarising the initial results from drilling at the Sumatra subduction zone in 2016, the source of the 2004 earthquake and tsunami
Year(s) Of Engagement Activity 2016
 
Description Major National Oceanography Centre Southampton Open Day: Ocean and Earth Day, 2013 
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 Public/other audiences
Results and Impact ~3000 members of the public of all ages visit during the Open Day. Display and discussion provided about subduction zone earthquakes around the world and the different techniques used to investigate them.

No specific impacts for this part of the event but general impact of the event recorded by a questionnaire
Year(s) Of Engagement Activity 2013
 
Description Major National Oceanography Centre Southampton Open Day: Ocean and Earth Day, 2014 
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 Public/other audiences
Results and Impact ~3000 members of the public of all ages visit during the Open Day. Display and discussion provided about plate tectonics and earthquake and volcanic hazards.

No specific impacts related to this part of the event but questionnaires completed by the public for the overall event indicating specific impact
Year(s) Of Engagement Activity 2014
 
Description Talk at UK IODP (ocean drilling) national meeting on subduction zone input drilling and earthquake potential 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Presentation to broad Earth science ocean drilling community, providing information on natural hazard research applications of ocean drilling. Talk sparked questions from other scientists.

No specific impacts as yet
Year(s) Of Engagement Activity 2014
 
Description Talk to Oxford Geology Group 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Talk on subduction zone earthquakes and tsunami and the methods used to study them to local/regional amateur Geology Group (Oxford, UK). Unknown impact as yet.
Year(s) Of Engagement Activity 2016