In 1998 the International Lithosphere Program (ILP) initiated the Global Strain Rate Map Project. As a major component to the Global Strain Rate Map Project, Kreemer et al. [2001a] have determined a global strain rate model. The global strain rate model is the first model to describe the kinematics of the plates and the deformation zones between the plates for all of the Earth's surface. The model provides estimates of the style and magnitude of the strain rate field within plate boundary zones at a resolution of about 0.5° (Figure 1 shows the contours of the second invariant of the model strain rate tensor field, as viewed from space).
FIGURE 1: Contours of second invariant of model strain rate field (shown for most of the eastern hemisphere) obtained (mainly) through an inversion of 2933 geodetic velocities. Black regions are assumed to behave rigidly.
Because the model solves for a continous velocity gradient tensor field, velocity field estimates are obtained within plate boundary zones as well, and relative angular velocities are determined to describe the motions between the defined rigid plates. Most data that are used in the modeling consist of geodetic velocities; a total of 2933 velocities are incorporated, located on 2682 locations (Figure 2), taken from 50 (mainly) published studies. Implicit in the procedure is the assumption that a single rigid body rotation can be applied to the velocity vectors from each individual study (one rotation vector for each study) such that the model velocity field provides a 'best-fit' to the observed vectors that have been rotated into a single model frame of reference.
FIGURE 2: Locations for which geodetic velocities are incorporated in the model.
Additional data come from Quaternary fault slip rates in Asia. Furthermore, the style and direction (but not magnitude) of the model strain rate field is constrained, a priori, by seismic moment tensors of shallow events. An example of the quality and resolution of the model is shown in Figure 3 for Sulawesi. The strain rate and velocity model results are accesible online at: world-strain-map.org/, designed with help from UCAR UNAVCO's Lou Estey, Chuck Meertens, and Jim Riley. On this website users can download raw data (as used in model) as well as both files and figures of model strain rate and velocity results. Users will also have the opportunity to create custom maps of model results on a special version of the 'Jules Verne Voyager' Tool.
FIGURE 3: Principal axes of model strain rates in Sulawesi. Open vectors are extension and black vectors are compression. Model grid is outlined in red.
A detailed estimate of the strain rate field associated with ongoing lithospheric motions can be of great benefit in regional and global studies on seismotectonics, lithospheric dynamics, and seismic hazard. A global analysis of the distribution of teconic moment rates (inferred from the model strain rates), seismic moment rates, and seismicity rates (i.e., the number of shallow events above a cut-off magnitude) has already been perfomed by Kreemer et al. [2001b]. From that analysis a clear correlation between tectonic moment rates and seismicity rates was found for subduction zones and most regions of continental deformation. The global model velocity field has been taken by Kreemer and Holt  to re-determine a no-net-rotation (NNR) reference frame. Such a re-examination is timely because current NNR models use geologic instead of geodetically-derived, present-day, plate motions, and NNR models so far have excluded the velocity gradient fields within plate boundary zones. The new NNR model indicates significantly different NNR angular velocities for many plates compared with earlier results.
Kreemer C., and W.E. Holt, A non-net-rotation model of present-day surface motions, Geophys. Res. Lett., in press, 2001.
Kreemer, C. W.E. Holt, and A.J. Haines, An integrated global model of present-day plate motions and plate boundary deformation, Geophys. J. Int., in review, 2001a.
Kreemer, C. W.E. Holt, and A.J. Haines, The global moment rate distribution within plate boundary zones, in Plate Boundary Zones, AGU Monograph Series, in press, 2001b.
Last modified: Sunday, 11-May-2014 18:02:16 UTC