HR: 14:55h
AN: G13C-06    [Abstracts]
TI: Strain Partitioning During Oblique Divergence: a Key Concept in Matching Geodetic, Seismological and Geological Datasets.
AU: * De Paola, N
EM: nicola.depaola@durham.ac.uk
AF: Reactivation Research Group, Department of Earth Sciences, University of Durham, South Road, Durham, DH1 3LE United Kingdom
AU: Holdsworth, R E
EM: r.e.holdsworth@durham.ac.uk
AF: Reactivation Research Group, Department of Earth Sciences, University of Durham, South Road, Durham, DH1 3LE United Kingdom
AU: Jones, R R
EM: r.r.jones@durham.ac.uk
AF: Geospatial Research Ltd., Department of Earth Sciences, University of Durham, South Road, Durham, DH1 3LE United Kingdom
AU: Allen, M
EM: mark.allen@casp.cam.ac.uk
AF: CASP, West Building, 181A Huntingdon Road, Cambridge, CB3 0DH United Kingdom
AU: McCaffrey, K J
EM: k.j.w.mccaffrey@durham.ac.uk
AF: Reactivation Research Group, Department of Earth Sciences, University of Durham, South Road, Durham, DH1 3LE United Kingdom
AU: Barchi, M
EM: mbarchi@unipg.it
AF: Dipartimento di Scienze, Universita degli Studi di Perugia, P.zza Universita 1, Perugia, 06100 Italy
AB: A quantitative analysis of geodetic datasets shows that zones of oblique deformation are broadly diffuse either at regional or local scale. Oblique relative plate motion (i.e. transtension or transpression) inevitably leads to 3-D rotational strains, even in the simplest case of homogeneous deformation. However, many existing models of plate boundary deformation are based either on the assumption of 2-D plane strain and/or use systems of rigid rotating blocks overlying a viscous continuum at depth. In this presentation, we demonstrate that the deformation of obliquely divergent plate margins is typically heterogeneous and partitioned into fault-bounded domains. As a result, a more complex relationship exists between geodetic, seismological and geological datasets compared to orthogonal or transform margins. For example, seismicity associated with the N-S trending Dead Sea transform fault is spatially partitioned, with sinistral transcurrent events - concentrated in the centre of the basin - and oblique extensional events within the adjacent basin margins. Outcrop studies of active faults reveal a similar pattern and when integrated with the seismological data yield a NNE-oriented divergent plate motion vector oriented 10ø clockwise of the plate margin. Recent GPS data confirm that a minor component of extension occurs oblique to the margin, with velocity vectors rotating clockwise away from the plate boundary. Similarly, in the Basin and Range Province abrupt changes in the geodetically-derived velocity fields (Oldow, 2003, Geology) are consistent with the changes in the distribution and character of seismicity and patterns of exposed active faults. Deformation is partitioned with different components of displacement being accommodated in a series of fault-bounded crustal blocks that can be collectively integrated to derive the far-field plate tectonic velocity field. We conclude that obliquely divergent margins are characterized by heterogeneous patterns of bulk 3-D strain in which adjacent fault-bounded domains deform internally, accommodating differing proportions of margin-parallel and margin-normal displacement. Key controlling variables are the angular relationships between plate motion vectors, plate boundaries and pre-existing intraplate margin faults. Our findings also illustrate that the matching of geodetic, earthquake and geological data is not always a straightforward procedure, since the results may yield velocity fields that reflect local, domainal strains that are not necessarily of regional, plate-scale significance.
DE: 7221 Paleoseismology
DE: 8107 Continental neotectonics
DE: 8159 Rheology--crust and lithosphere
DE: 1206 Crustal movements--interplate (8155)
DE: 1242 Seismic deformations (7205)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting