Imaging faults at depth: the seismic transport properties of fault zones

Lead Research Organisation: University of Liverpool
Department Name: Earth, Ocean and Ecological Sciences

Abstract

Earthquakes and fault slip are still relatively poorly understood phenomena. One of the principal reasons for this is that fault zones, at the crustal levels where earthquakes nucleate, are very difficult to observe. Field mapping of large faults at the surface can provide valuable information, but they are often incompletely exposed and/or have suffered continued slip and hence overprinting during exhumation. As a consequence seismology is one of the key tools used to investigate fault zone structure and properties at depth. It has the potential to show fault zone structure and dimensions, slip distributions, fracture damage, stress orientations and fault fluid pressures. However the seismic data have to be inverted to decipher fault zone structure and properties and these inversions often yield non-unique answers. In this research we aim to combine field mapping, laboratory measurements and seismic experiments on an exceptionally well-exposed and characterized fault zone in southern Spain in order to understand the sensitivity of the seismic signals to the observed surface structure and physical properties of the fault rocks as determined from detailed mapping and laboratory seismic measurements. As part of a tied studentship, we will also measure the seismic properties of rocks recovered from 3km depth on the San Andreas fault in California as part of the San Andreas Fault Observatory at Depth (SAFOD) project that recently drilled a scientific borehole through the fault near Parkfield. Natural seismicity recorded on borehole instruments will provide comparison with laboratory measurements and allow us to broaden the scope of the work by detailed analysis of another major fault zone. The combination of all these data will provide a greatly improved understanding of the controls on fault zone seismology leading to a clearer picture of fault zones at depth. Specifically, we will map in detail part of the Carboneras fault in southeastern Spain; a major strike-slip fault with 40km offset that has been exhumed from 4 to 6km depth. Samples from the fault zone will have their seismic properties measured in the laboratory, including the P and S wave velocity, the attenuation of the seismic waves, and the degree of the polarization the S waves. The field and laboratory data will be combined to create a synthetic 3D model of the fault zone in which earthquake events may be 'created' and the resultant seismic signals predicted. We will additionally conduct 'active' seismic experiments on the fault zone where controlled seismic sources from explosions will excite seismic waves that we can then measure with a carefully positioned seismic network within and around the fault zone. The signals from these experiments will help characterize the subsurface structure of the fault and can be compared with predicted signals from the detailed mapping and laboratory measurement program. The project will provide information on fault zone structure from direct observation of a major fault, measurements of the physical properties of a range of fault zone materials and direct seismic measurements of the fault zone that can be directly compared with the surface structure. These data will not only provide key insights in understanding fault zone structure and properties from seismic data, but they will also be of significant interest to the hydrocarbon and mining industries, as faults control the movement of subsurface fluids, leading to problems in the recovery of oil and gas, and also distribution of hydrothermally /transported, fault hosted ore deposits.

Publications

10 25 50

 
Description We have characterized the different styles of deformation that exisit around fault zones. We have identified how these affect the seismic properties of faults.

We have constrained the geological history of the Carboneras Fault in southeastern Spain.

We have discovered that some faults may be seismically 'invisible' and to identify faults in the subsurface both reflection and trapped waves may need to be employed.
Exploitation Route They may be used as a predictive tool in order to characterize other fault zones that can only be observed at depth by means of seismology.
Sectors Construction,Education,Environment

 
Description Our scientific work has been recognized by invites to speak at major international research conferences and through citations of publications arising from the research.
First Year Of Impact 2012
Sector Construction,Energy,Environment
 
Description Parkfield attenuation 
Organisation University of California, Berkeley
Department Department of Geology
Country United States 
Sector Academic/University 
PI Contribution We processed data from the high-resolution seismic network from Parkfield California to observe sesimic attenuation changes in the crust following the 2004 earthquake.
Collaborator Contribution R. Nadeau assisted with the data processing and interpretation.
Impact Publication: C. Kelly, A. Rietbrock, D.R. Faulkner and R.M. Nadeau. 2013. Temporal changes in seismic attenuation following the 2004 M6.0 Parkfield earthquake. Journal of Geophysical Research 118, 630-645. DOI: 10.1002/jgrb.50088.
Start Year 2012
 
Description Radio interview 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Interviewed on RadioCity Talk radio concerning earthquake research.
Year(s) Of Engagement Activity 2015
 
Description School visits - seismometers for schools project 
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 Numerous visits to schools have been made as part of the 'Seismometers for Schools' project.
Year(s) Of Engagement Activity 2014,2015,2016,2017
 
Description Scientific advisor for BBC iWonder website 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact I was asked to be the scientific advisor for a BBC iWonder website on 'Predicting Earthquakes'.
Year(s) Of Engagement Activity 2015
URL http://www.bbc.co.uk/guides/zxyd2p3