Corne Kreemer

The Global Strain Rate Map project II-8, initiated in 1998 by the International Lithosphere Program (ILP), provides constraints for understanding continental dynamics and for quantifying seismic hazards in general. To date, the Global Strain Rate Map (GSRM) model is a numerical velocity gradient tensor field solution (i.e.,spatial variations of horizontal strain rate tensor components and rotation rates) for the entire Earth surface [Kreemer et al., 2003].The global model consists of 25 rigid spherical plates and ˜25,000 0.6°×0.5° deformable grid areas within the diffuse plate boundary zones which lie between these plates (e.g., western North America, central Asia, the Alpine-Himalaya belt). This model provides an estimate of the horizontal strain rates, rotation rates, and velocity fields for the diffuse plate boundary zones as well as an estimate of the motions of the spherical caps.

... 741-770 doi: 10.1029/2000JB900302. CrossRef. ↵ Bennett, RA, Wernicke, BP, Niemi, NA, Friedrich, AM, and Davis, JL, 2003, Contemporary strain rates in the northern Basin and Range province from GPS data: Tectonics, v. 22 pp. 1008 doi: 10.1029/2001TC001355. ...

In this paper we present a global model (GSRM-1) of both horizontal velocities on the Earth's surface and horizontal strain rates for almost all deforming plate boundary zones. A model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field. In our model we perform a least-squares fit between model velocities and observed geodetic velocities, as well as between model strain rates and observed geological strain rates. Model velocities and strain rates are interpolated over a spherical Earth using bi-cubic Bessel splines. We include 3000 geodetic velocities from 50 different, mostly published, studies. Geological strain rates are obtained for central Asia only and they are inferred from Quaternary fault slip rates. For all areas where no geological information is included a priori constraints are placed on the style and direction (but not magnitude) of the model strain rate field. These constraints are taken from a seismic strain rate field inferred from (normalized) focal mechanisms of shallow earthquakes. We present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones. Generally, the strain rate tensor field is consistent with geological and seismological data. With the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs. We find that in general there is a good agreement between the present-day plate motions we obtain and long-term plate motions, but a few significant differences exist. The rotation rates for the Indian, Arabian and Nubian plates relative to Eurasia are 30, 13 and 50 per cent slower than the NUVEL-1A estimate, respectively, and the rotation rate for the Nazca Plate relative to South America is 17 per cent slower. On the other hand, Caribbean–North America motion is 76 per cent faster than the NUVEL-1A estimate. While crustal blocks in the India–Eurasia collision zone move significantly and self-consistently with respect to bounding plates, only a very small motion is predicted between the Nubian and Somalian plates. By integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in, for instance, redefining a no-net-rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation.

Reliable tsunami early warning requires a rapid assessment of the tsunamigenic potential of an earthquake as well as a prediction of the likely propagation pattern of the tsunami. Low-latency availability of the coseismic Earth's surface displacements can support the assessment of the tsunamigenic potential of an earthquake and improve predictions of the propagation pattern of the tsunami. We have developed a fingerprint methodology for the rapid determination of the surface displacement field from GNSS-determined displacements. The fingerprint methodology depends on a priori knowledge of the faults potentially involved in a rupture. The known faults are parametrized with standard elements and for each element so-called fingerprint functions are computed for unit strike and dip slips. After an event, the model space of all reasonable fault-element combinations is searched for the element-slip combination best fitting the observed displacements. This combination provides the best estimate of the displacement field and earthquake magnitude consistent with observations. Here we describe the fingerprint methodology and the main architectural elements of a prototype for the rapid determination of magnitude and displacement field.

A significant portion of the Earth's surface consists of zones of diffuse deformation. The interior regions of these diffuse zones of deformation move at distinctly different velocities from that of adjacent plates, and, because of their complexities, have been ignored in previous no-net-rotation (NNR) models (e.g., NNR-NUVEL1A). We have calculated a new NNR model from a continuous velocity field that incorporates both rigid plate motion and velocity gradients within plate boundary zones. The velocity field is obtained through a bi-cubic Bessel interpolation of almost 3000 geodetic velocities and strain rates inferred from Quaternary faults. The geodetic velocities are taken from about 50 different, mainly published, studies. For each study we have not adopted the original reference frame. Instead, we have solved for a rigid body rotation for each study that rotate the vectors of each study into a model reference frame in the process of satisfying a least-squares fit between model and observed velocities and model and observed strain rates. When compared with earlier NNR models we find significantly different angular velocities for many plates in our model. Differences between the NNR model presented here and earlier NNR models can be attributed to both the effect of including velocity gradients in diffuse plate boundary zones, as well as actual differences between geodetically derived, present-day, surface motions and geologic estimates. We find that for the Indian, Arabian, Nazca, Cocos, Philippine Sea, and the Caribbean plate the differences between our model and the NNR-NUVEL1A model are mainly due to differences between geodetic and geologic plate velocities. For the Eurasian plate the discrepancy that we find between our result and NNR-NUVEL1A model can not only be ascribed to the difference between geodetic and geologic velocities, but also to the significant effect of including plate boundary zones. The significantly different NNR rotation vectors that we find for the majority of plates suggests that caution is warranted when using the NNR-NUVEL1A model to change from an ITRF to a tectonic reference frame. Our new NNR results indicate that such practice may result in significant discrepancies in crustal velocities with respect to the chosen reference plate. Finally, similar to earlier NNR models, we find a significant difference between the NNR velocities and velocities with respect to hotspots.