72. Bird, P., and M. M. C. Carafa [2016]: Improving
deformation models by discounting transient signals in geodetic data, 1:
Concept and synthetic examples, *J. Geophys. Res., 121*(7), 5538-5556,
doi: 10.1002/2016JB013056.

**Abstract**. GPS geodesy
provides very precise velocities of benchmarks on decadal timescales, and
geodesists often describe their uncertainties with a velocity covariance
matrix. However, those who model neotectonic deformation to estimate long-term
seismic hazard want constraints on the interseismic velocities of stable
bedrock on multi-thousand-year timescales. When the former (available data) are
used as proxies for the latter (desired constraints), it is necessary to
increase uncertainties to characterize a variety of transient and/or surficial
noise processes, including magma chamber recharge, postseismic relaxation, pore
fluid motion, extremely slow landsliding, and glacial isostatic adjustment. The
effects of transient noise on distant reference benchmarks also add to
uncertainty of the long-term velocity reference frame. We augment the reported
velocity covariance matrix with transpose products of velocity perturbation
vectors from simple models approximately describing anticipated transient and
surficial noise sources. No artifacts are introduced by this method because the
velocity-vector data are unchanged. When the inverse of the augmented
covariance matrix (the “diminished normal matrix”) is used in the objective
function of a neotectonic deformation model partially driven by GPS data, the
perturbing effects of transient and surficial signals are greatly reduced.
Improvement occurs even when the prior estimates of noise processes are rather
crude. We present two examples computed with synthetic data.