Harm Van Avendonk Research Scientist PhD., 1998, Scripps B.S., 1993, Geophysics, Utrecht University, the Netherlands Telephone 512-471-0429 email: harm   Harm's CV

Research Interests
Harm's main scientific interest is the deep crustal structure of the Earth’s crust, particularly near the plate boundaries. Wide-angle seismic refraction data can provide good constraints on the geometry and composition of the deep crust. He uses imaging methods such as seismic tomography and wide-angle migration to interpret seismic refraction data sets.

Newfoundland rifted margin:
In the fall of 2000 a group of American, Danish and Canadian scientists collected coincident seismic reflection and refraction data along three transects across the rifted margins of the Grand Banks and the Flemish Cap, offshore Newfoundland, Canada. The apparent absence of volcanism during continental break-up and the relatively small sediment cover have created a good environment to study the mode of lithospheric extension by seismic profiling. Moreover, the transects are conjugate to existing geophysical profiles on the Iberian margin, and ODP Leg 210 will drill in the sediment and basement in the ocean-continent transition zone in July and August 2003. Two proposed end-member models for continental are uniform or pure shear extension and simple shear extension, the latter usually accompanied by crustal-scale detachment faults. Pure shear deformation is often preferred on theoretical grounds, but a weak zone in the thinning lithosphere could develop into a fault zone and result in a significant component of simple shear prior to break-up. My tomographic images show lower crust thinning but not pinching out until the continent-ocean transition. The transitional crust is ~4 km thin and characterized by an average seismic velocity of ~5.5 km/s, consistent with the onset of ultra-slow spreading.

Aleutian arc:
A large component of the material flux between mantle and crust occurs at the subduction zones that rim oceanic plates. Island arcs, the volcanic edifices that overlie subduction zones, may represent a large fraction of the crustal mass that has been added to the Earth’s continents over time. However, seismic refraction studies of island arcs to date show that the composition of island arcs is much more mafic than the average composition of continental crust. To explain this apparent paradox, differentiation and reworking of arc crust upon accretion to continents has been proposed. To understand the magmatic processes that shape island arcs, their stratification, and their mechanical state before accretion, Harm has conducted an analysis of seismic refraction data that were collected in the eastern Aleutian arc. This seismic data set that was collected in 1994 is relatively sparse, but provides good constraints on seismic velocity structure averaged over larger distances. The crust appears ~35 k thick with compressional seismic velocities from 6.5 to 7.8 km/s in much of the middle and lower crust. Presumably, a large portion of island arc crust is recycled in the mantle in the event of an arc-continent collision.

Student Involvement

Current Research Projects
TICOCAVA

ST. Elias Erosion/tectonics Project (STEEP)

Integrated Investigation of the Geodynamics of the Taiwan Orogeny [TAIGER].

Integrated geophysical and geologic investigation of the crustal structure of western Canada Basin, Chukchi Borderland and Mendeleev Ridge, Arctic Ocean.

Seismic measurements of magma flux, arc composition, and lower-plate serpentinization in the Central American subduction factory

Recent Publications
Hornbach, M.J., D.M. Saffer, W.S. Holbrook, H.J.A. Van Avendonk,, A.R. Gorman, 2007, 3D seismic imaging of the Blake Ridge methane hydrate province: evidence for large concentrated zones of gas hydrate and morphologically-driven advection, to be submitted to J. Geophys. Res. in September 2007.

Van Avendonk, H.J.A., L.L. Lavier, D.J. Shillington, and G. Manatschal, 2007, Extension of continental crust at the margin of the eastern Grand Banks, Newfoundland, submitted to Tectonophysics.

Fuis, G.S., M.D. Kohler, M. Scherwath, U. ten Brink, H.J.A. Van Avendonk, and J.M. Murphy, A comparison between the transpressional plate boundaries of the South Island, New Zealand, and Southern California, USA: The Alpine and San Andreas Fault Systems, in AGU Geophysical Monograph edited by F. Davey, in press.

Davey, F.J., D. Eberhart-Phillips, M. Kohler, S. Bannister, G. Caldwell, S. Henrys, M. Scherwath, T. Stern and H. Van Avendonk, 3-D structure of the Southern Alps orogen, South Island, New Zealand, in AGU Geophysical Monograph edited by F. Davey, in press.

Van Avendonk, H.J.A., W.S. Holbrook, G.T. Nunes, D.J. Shillington, B.E. Tucholke, K.E. Louden, H.C. Larsen, J.R. Hopper, 2006, Seismic velocity structure of the rifted margin of the eastern Grand Banks of Newfoundland, Canada, J. Geophys. Res., 111, B11404, doi:10.1029/2005JB004156.

Shillington, D.J., W.S. Holbrook, H.J.A. Van Avendonk, B.E. Tucholke, J.R. Hopper, K.E. Louden, H.C. Larsen, and G.T. Nunes, 2006, Evidence for asymmetric nonvolcanic rifting and slow incipient oceanic spreading from seismic reflection data on the Newfoundland margin, J. Geophys. Res., 111, B09402, doi:10.1029/2005JB003981.

Harm's UTIG Contributions (Publications)