Dr John Townend

The tectonic stress field

What forces drive plate motion, and how can these be measured? Determining the orientations and magnitudes of stresses acting within the crust is important for distinguishing between different plate tectonic driving mechanisms, as well as for addressing such diverse problems as fault stability in oil reservoirs and deglaciation-triggered seismicity. I am working with colleagues in the United States, Sweden, Canada, and New Zealand on methods of measuring and interpreting tectonic stress parameters from routine seismological observations.

Fault mechanics and lithospheric rheology

How does the lithosphere maintain its strength? I am interested in understanding the manner by which small-scale (1-100+ m) frictional interactions between faults and the ambient fluid and stress regimes contribute to the bulk rheology at much larger scales (100-1000+ km) of the lithospheric plates themselves.The Marsden Fund has recently announced support of a three-year project led by Prof Tim Stern centred on a high-resolution seismological investigation of the central Alpine fault.

Slow earthquakes and related phenomena

Recent advances in geophysical monitoring have revealed a much broader spectrum of earth deformation processes than previously recognised, including several mechanisms operating on timescales between those of traditional seismology (in which earthquake rupture occurs in seconds) and geodesy (in which strain accumulates over years to decades). These recently identified processes include slow earthquakes (identified using continuous global positioning system (GPS) measurements), low-frequency seismic tremor, and small, triggered earthquakes. With the financial support of the Marsden Fund and the Earthquake Commission Research Foundation, my colleagues and I are working to detect and interpret seismic signals associated with slow earthquakes in the Hikurangi subduction zone.

Ambient noise tomography

Just as radiographers use ultrasound to image the internal structure of a human body, so seismologists use seismic waves generated by earthquakes or artificial sources to study the earth's interior. Modern seismological networks - such as New Zealand's GeoNet system - are designed to record seismic waves generated by earthquakes, but more than 95% of the "signal" recorded by such networks is noise generated primarily by coupled oceanic and atmospheric processes. Cross-correlating long streams of noise recorded at different locations reveals a coherent signal, or Green's function, that can be used for tomographic imaging. . Dr Stephen Bannister (GNS Science) and I are leading a Marsden-funded study of ambient noise tomography in collaboration with other VUW staff and researchers at the University of Colorado at Boulder.

Current projects

Deep Fault Drilling Project (DFDP) - Alpine Fault, New Zealand: integrated characterisation of a major earthquake-producing fault at mid-crustal depths (with colleagues from throughout New Zealand and overseas).
Bayesian methods of focal mechanism estimation (with David Walsh, MSc student, and Richard Arnold, School of Mathematics, Statistics, and Computer Science)
Bayesian methods of earthquake focal mechanism and tectonic stress estimation (with Richard Arnold, School of Mathematics, Statistics, and Operations Research, Steve Sherburn, GNS Science, Stephane Mazzotti, Geological Survey of Canada, and Bjorn Lund, Uppsala University).
Geothermal seismicity in the Taupo Volcanic Zone (with Zara Rawlinson, MSc student, and Stephen Bannister, GNS Science)
Circum-Pacific stress, strain, and mountain-building (with Mark Zoback, Stanford University, and Stephane Mazzotti, Geological Survey of Canada)
Ambient noise correlation and surface wave tomography (with Michael Ritzwoller and Fan-Chi Lin, University of Colorado at Boulder, Stephen Bannister, GNS Science, Yannik Behr (PhD student, VUW), and Martha Savage, VUW)

Graduate supervision

Current students

Yannik Behr (PhD research topic: ambient noise correlation using permanent and short-term deployment data)
Jess Johnson (PhD research topic: seismotectonics and crustal anisotropy surrounding Mt Ruapehu)
Lena Schroeter (summer research project: seismic tremor detection, southern Hikurangi subduction zone)
Syuhada (MSc research topic: seismic attenuation anisotropy in the southern Taupo Volcanic Zone)
Zara Rawlinson (MSc research topic: associated with fluid injection in an active geothermal system, Taupo Volcanic Zone)

Former students

Natalie Balfour (MSc thesis title: “Stress and crustal anisotropy in Marlborough, New Zealand: evidence for low fault strength and structure-controlled anisotropy”) - now doing PhD research at the University of Victoria
Annie Douglas (MSc thesis title: “A geodetic investigation of slow slip in the Hikurangi subduction zone”) - until recently a GPS data manager at GNS Science; now in Palo Alto, CA
Emily Delahaye (MSc thesis title: “A seismological investigation of slow slip in the Hikurangi subduction zone”) - now working at the International Seismological Centre, UK
Daniel Clarke (MSc thesis title: “Velocity modelling and earthquake relocation in the Rotorua and Kawerau geothermal areas, Taupo Volcanic Zone, New Zealand) - now doing PhD research at IPGP, Paris
David Walsh (MSc thesis title: "Directional statistics, Bayesian methods of earthquake focal mechanism estimation and their application to New Zealand seismicity data")

Publications

Johnson, J.H., Prejean, S., Savage, M.K., and Townend, J., 2009. Repeating earthquakes, anisotropy, and seismicity associated with the 2008 eruption of Okmok volcano, Alaska. Journal of Geophysical Research, submitted.
Behr, Y., Townend, J., Bannister, S., and Savage, M.K., 2009. Shear-velocity structure of the Northland Peninsula, New Zealand, inferred from ambient noise correlations. Journal of Geophysical Research, under review following revision.
Brooks, L., Townend, J., Gerstoft, P., Bannister, S., and Carter, L., 2009. Fundamental and higher-order Rayleigh wave characteristics of ambient seismic noise in central New Zealand. Geophysical Research Letters, under revision.
Mazzotti, S., and Townend, J., 2008. State of stress in eastern North America seismic zones. Lithosphere, in press.
Townend, J., 2009. Deformation, seismogenesis, and mineralization in an active plate-bounding continental fault zone. EOS, 90, 312.
Wallace, et al., 2009. Characterising the seismogenic zone of a major plate boundary subduction thrust: the Hikurangi margin, New Zealand. Geochemistry, Geophysics, Geosystems, 10, Q10006, doi:10.1029/2009GC002610.
Townend, J., Sutherland, R., and Toy, V., 2009. Deep Fault Drilling Project—Alpine Fault, New Zealand. Scientific Drilling, 8, 75–82, doi: 10.2204/iodp.sd.8.12.2009.
Clarke, D., Townend, J., Savage, M. K., and Bannister, S., 2008. Seismicity in the Rotorua and Kawerau geothermal systems, Taupo Volcanic Zone, New Zealand, based on improved velocity models and cross-correlation measurements. Journal of Volcanology and Geothermal Research, 180: 50–66. (PDF)
Delahaye, E., Townend, J., Reyners, M., and Rogers, G., 2008. Microseismicity but no tremor associated with slow slip in the Hikurangi subduction zone, New Zealand. Earth and Planetary Science Letters, doi:10.1016/j.epsl.2008.09.038. (PDF)
Nicholson, T., Clarke, D., and Townend, J., 2008. Regional earthquake location using empirical travel times in a region of strong lateral velocity heterogeneity. Geophysical Journal International, doi:10.1111/j.1365-246X.2008.03858.x. (PDF)
Walsh, D., Arnold, R., and Townend, J., 2008. A Bayesian approach to determining and parameterising earthquake focal mechanisms. Geophysical Journal International, doi:10.1111/j.1365-246X.2008.03979.x. (PDF)
Arnold, R., and Townend, J., 2007. A Bayesian approach to estimating tectonic stress from seismological data. Geophysical Journal International, doi:10.1111/j.1365-246X.2007.03485.x. (PDF)
Lin, F.-C., Ritzwoller, M., Townend, J., Bannister, S., and Savage, M.K., 2007. Ambient noise Rayleigh wave tomography of New Zealand. Geophysical Journal International, doi:10.1111/j.1365-246X.2007.03414.x. (PDF) (animation by Fan-Chi Lin, University of Colorado at Boulder)
Lund, B., and Townend, J., 2007. Calculating horizontal stress orientations with full or partial knowledge of the tectonic stress tensor. Geophysical Journal International, doi:10.1111/j.1365-246X.2007.03468.x. (PDF)
Sutherland et al., 2007. Do great earthquakes occur on the Alpine fault in central South Island, New Zealand? In A Continental Plate Boundary: Tectonics at South Island, New Zealand, edited by D. Okaya, et al., pp. 235–251, American Geophysical Union.
Townend, J., 2006. What do faults feel? Observational constraints on the stresses acting on seismogenic faults. In Earthquakes: Radiated Energy and the Physics of Faulting, edited by R. Abercrombie, A. McGarr, H. Kanamori, and G. Di Toro, American Geophysical Union Geophysical Monograph Series, 170, 313–327. (PDF)
Townend, J., and Zoback, M. D., 2006. Stress, strain, and mountain building in central Japan. Journal of Geophysical Research, 111, B03411, doi:10.1029/2005JB003759. (PDF)
Arnold, R., Townend, J., and Vignaux, T., 2005. Mapping tectonic stress using earthquakes. In Bayesian Inference and Maximum Entropy Methods in Science and Engineering, edited by K.K. Knuth, A.E. Abbas, R.D. Morris, J.P. Castle, CP803, American Institute of Physics, 475–482. (PDF)
Balfour, N., Savage, M. K., and Townend, J., 2005. Stress and crustal anisotropy in Marlborough, New Zealand: evidence for low fault strength and structure-controlled anisotropy. Geophysical Journal International, doi:10.1111/j.1365-246X.2005.02783.x. (PDF)
Douglas, A., Beavan, J., Wallace, L., and Townend, J., 2005. Slow slip on the northern Hikurangi subduction interface, New Zealand. Geophysical Research Letters, 32, L16305, doi:10.1029/2005GL023607. (PDF)
Townend, J., Langridge, R., and Jones, A., eds., 2005. The 1855 Wairarapa Earthquake Symposium: 150 years of thinking about magnitude 8+ earthquakes and seismic hazard in New Zealand. Proceedings volume, Greater Wellington Regional Council, GW/RINV-T-05/205, 227 p. (PDF)
Townend, J., and Zoback, M. D., 2004. Regional tectonic stress near the San Andreas fault in central and southern California. Geophysical Research Letters, 31, L15S11, doi:10.1029/2003GL018918. (PDF)
Zoback, M. D., Townend, J., and Grollimund, B., 2003. Steady-state failure equilibrium and deformation of intraplate lithosphere. In The George A. Thompson Volume: The Lithosphere of Western North America and Its Geophysical Characterization, edited by S. L. Klemperer and W. G. Ernst, Geological Society of America, International Book Series, 7, 50–70.
Zoback, M. D., Townend, J., and Grollimund, B., 2002. Steady-state failure equilibrium and deformation of intraplate lithosphere. International Geological Review, 44, 383–401. (PDF)
Zoback, M. D., and Townend, J., 2001. Implications of hydrostatic pore pressures and high crustal strength for the deformation of intraplate lithosphere. Tectonophysics, 336, 19–30. (PDF)
Townend, J., and Zoback, M. D., 2001. Implications of earthquake focal mechanisms for the frictional strength of the San Andreas fault system. In The Nature and Tectonic Significance of Fault Zone Weakening, edited by R.E. Holdsworth, R. A. Strachan, J. Macloughlin, and R. J. Knipe, Special Publication of the Geological Society of London, 186, 13–21. (PDF)
Townend, J., and Zoback, M. D., 2001. How faulting keeps the crust strong: Reply. Geology, 29, 190. (PDF)
Townend, J., and Zoback, M. D., 2001. Focal mechanism stress inversions in southern California and the strength of the San Andreas fault. In Proceedings of the Conference on Tectonic Problems of the San Andreas Fault System, Stanford University Publication, Geological Sciences, 30, 268–276.
Townend, J., and Zoback, M. D., 2000. How faulting keeps the crust strong. Geology, 28, 399–402. (PDF)
Townend, J., 1999. Heat flow through the West Coast, South Island, New Zealand. New Zealand Journal of Geology and Geophysics, 42, 21–31. (PDF)
Herzer, R. H., Sykes, R.. Killops, S. D., Funnell, R. H., Burggraf, D. R., Townend, J., Raine, J. I., Wilson, G. J., 1999. Cretaceous carbonaceous rocks from the Norfolk Ridge system, SW Pacific: implications for regional petroleum potential. New Zealand Journal of Geology and Geophysics, 42, 57–73. (PDF)
Townend, J., 1997. Estimates of conductive heat flow through bottom-simulating reflectors on the Hikurangi and southwest Fiordland continental margins, New Zealand. Marine Geology, 141, 209–220. (PDF)
Townend, J., 1997. Subducting a sponge; minimum estimates of the fluid budget of the Hikurangi Margin accretionary prism. Geological Society of New Zealand Newsletter, 112, 14–16.

Professional and University Service

Management Committee member, , New Zealand Society for Earthquake Engineering
President, New Zealand Geophysical Society
Co-convener, SGEES Research Committee

Current Teaching

ESCI/GEOG 111 (The Earth System: an introduction to physical geography and earth sciences) - seismic hazards
ESCI 203 (Earth structure and deformation) - an introduction to structural geology and solid earth geophysics
ESCI 302 (Structural geology and tectonics) - introductory fault mechanics and slope stability analysis
ESCE 407 (Tectonics) - fault mechanics and kinematics, and crustal deformation
GPHS 411 (Geophysical Exploration) - ambient noise correlation and seismology using non-traditional sources