Current Reference Frame Treatment and Future Needs Regional

North America plate frame realization for southwestern US Choose RF rotation rate so as

Southwestern US North America plate frame statistics SITE ----ALGO NLIB DRAO STJO MDO 1

Some southwestern US North America plate frame caveats 1) Data used to define the

Example 1 Estimate relative motions of faultbounded blocks accounting for elastic strain associated with

Example 1 continued One solution is to define local no-net translation reference frame: Residual

Example 2 Determine the relative motions between the Colorado Plateau (CP), central Great Basin

Example 2 continued SNGV-CGB Bennett et al. , 2003 SNGV-CP

Motion of a deforming body in space Deformation term depends on reference frame selection.

Motion Cont… Simple 2 D Cartesian deformation analysis problem: Choose coordinate axes such that:

Summary • BARGEN North America plate frame determined by minimizing velocities at 11 NA

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Current Reference Frame Treatment and Future Needs: Regional Arrays …from the southwestern US perspective Rick Bennett Harvard-Smithsonian Cf. A SNARF Workshop 27 January 2004

North America plate frame realization for southwestern US Choose RF rotation rate so as to minimize velocities at sites in North America interior: I used ALGO, DRAO, NLIB, STJO, MDO 1, PIE 1, HEBE, PRDS, CAST, FRED, FERN

Southwestern US North America plate frame statistics SITE ----ALGO NLIB DRAO STJO MDO 1 PIE 1 HEBE PRDS CAST FRED FERN R. R. -----1. 1 0. 4 2. 8 3. 3 0. 8 0. 4 2. 5 0. 4 0. 8 1. 0 Sigma (all values in mm/yr) -------0. 03 0. 04 R. R. = rate residual 0. 03 to realization of 0. 04 the plate frame. 0. 03 0. 04 0. 03 0. 07 Number of sites = 11 Number sites with R. R. < 1 mm/yr = 6 Percentage with < 1 mm/yr = 55 The rate NRMS is 48 The rate WRMS is 1. 6 mm/yr The component NRMS is 34 The component WRMS is 1. 1 mm/yr

Some southwestern US North America plate frame caveats 1) Data used to define the frame is evolving • New NA stations • Changing equipment • Always more data 2) Inconvenient to compute geophysical models in the geodetically determined frame.

Example 1 Estimate relative motions of faultbounded blocks accounting for elastic strain associated with locked faults. Observed velocities Half-space fault models do not accurately represent far-field plate rates.

Example 1 continued One solution is to define local no-net translation reference frame: Residual velocities

Example 2 Determine the relative motions between the Colorado Plateau (CP), central Great Basin (CGB), and Sierra Nevada-Great Valley (SNGV) regions.

Example 2 continued SNGV-CGB Bennett et al. , 2003 SNGV-CP

Motion of a deforming body in space Deformation term depends on reference frame selection.

Motion Cont… Simple 2 D Cartesian deformation analysis problem: Choose coordinate axes such that: Then the information matrix looks like this: Note the trade-off depending on network and/or model geometry.

Summary • BARGEN North America plate frame determined by minimizing velocities at 11 NA interior sites. • Should distinguish between geodetic and geophysical reference frame issues – Geodesist • Frame definition • Frame realization – Geophysicist • Account for differences between model and data frames, regardless of errors.