Plate Tectonics from Space

Satellite measurements of surface motions of Earth’s lithospheric plates are accumulating fast, and a spectacular image of horizontal crustal deformation is emerging, solving plate kinematics enigma here and there and raising new questions elsewhere. The objective of this map is to show the current plate tectonics framework in the light of these new satellite measurements, superimposed onto a physiographic basemap obtained also from space techniques.

Although thousands of geodetic stations are now available through local, regional and global networks, only the permanent sites used for the realization of the ITRF (International Terrestrial Reference Frame) are shown here. We use the latest available release ITRF2005. These geodetic measurements of current motions are indicated in the map by red arrows. Also shown in the background, using a grid of grey arrows, is a global plate model obtained from the combination of several regional networks.

It is worth to underline the fact that this new map was realized on a completely different basis. Actually, the kinematics models were so far established through an indirect method using magnetic anomalies of the oceanic crust no younger than some million years. A new plate kinematics was thus established, exclusively based on satellite measurements. The space-based models – now referred to as "geodetic models" – actually match the predictions of the conventional "geologic models" for a number of plates. This was quite surprising not only because of the large difference in time-scale (3 million years versus several years), but also because the geodetic models are exclusively derived from land measurements.

Apart from delivering horizontal crustal motion at places where conventional geologic models failed, geodetic models allow to reassess major plate motions (steady-state motion) and ultimately discuss the evolution of these motion through time – in particular close to plate boundaries (transient deformations such as those related to the seismic cycle).

Although they generally are, plates are not necessary bounded by localized faults and distributed (diffuse) boundaries are widespread over the continental lithosphere, either as regions of diffuse compression (e.g. Mediterranean, Andean and Himalayan orogens) or diffuse extension (e.g. Basin and Range Province, western Turkey). Although less studied, areas of diffuse compression and/or extension are also found over the oceanic lithosphere, such as e.g. the diffuse boundaries between India - Australia - Capricorn plates in the Indian Ocean, between North America and South America plates in the Central Atlantic Ocean, between Macquarie and Australia plates in the Southern Ocean.

Based on the observation of active deformation – either from field works and/or seismicity – the choice was made to characterized these regions of diffuse deformation by a specific pattern (superimposed light brown hue), with some indication on the type of deformation they may accommodate (bright yellow arrows).