An updated digital model of plate boundaries
Peter Bird
Department of Earth and Space Sciences, University of California, Los Angeles, California 90095, USA
(pbird@ess.ucla.edu)
[1] A global set of present plate boundaries on the Earth is presented in digital form. Most come from
sources in the literature. A few boundaries are newly interpreted from topography, volcanism, and/or
seismicity, taking into account relative plate velocities from magnetic anomalies, moment tensor solutions,
and/or geodesy. In addition to the 14 large plates whose motion was described by the NUVEL-1A poles
(Africa, Antarctica, Arabia, Australia, Caribbean, Cocos, Eurasia, India, Juan de Fuca, Nazca, North
America, Pacific, Philippine Sea, South America), model PB2002 includes 38 small plates (Okhotsk,
Amur, Yangtze, Okinawa, Sunda, Burma, Molucca Sea, Banda Sea, Timor, Birds Head, Maoke, Caroline,
Mariana, North Bismarck, Manus, South Bismarck, Solomon Sea, Woodlark, New Hebrides, Conway
Reef, Balmoral Reef, Futuna, Niuafo’ou, Tonga, Kermadec, Rivera, Galapagos, Easter, Juan Fernandez,
Panama, North Andes, Altiplano, Shetland, Scotia, Sandwich, Aegean Sea, Anatolia, Somalia), for a total
of 52 plates. No attempt is made to divide the Alps-Persia-Tibet mountain belt, the Philippine Islands, the
Peruvian Andes, the Sierras Pampeanas, or the California-Nevada zone of dextral transtension into plates;
instead, they are designated as ‘‘orogens’’ in which this plate model is not expected to be accurate. The
cumulative-number/area distribution for this model follows a power law for plates with areas between
0.002 and 1 steradian. Departure from this scaling at the small-plate end suggests that future work is very
likely to define more very small plates within the orogens. The model is presented in four digital files: a set
of plate boundary segments; a set of plate outlines; a set of outlines of the orogens; and a table of
characteristics of each digitization step along plate boundaries, including estimated relative velocity vector
and classification into one of 7 types (continental convergence zone, continental transform fault,
continental rift, oceanic spreading ridge, oceanic transform fault, oceanic convergent boundary, subduction
zone). Total length, mean velocity, and total rate of area production/destruction are computed for each
class; the global rate of area production and destruction is 0.108 m
2
/s, which is higher than in previous
models because of the incorporation of back-arc spreading.
Components: 28,925 words, 19 figures, 3 tables, 4 datasets.
Keywords: Plate tectonics; Euler pole.
Index Terms: 3040 Marine Geology and Geophysics: Plate tectonics (8150, 8155, 8157, 8158); 5475 Planetology: Solid
Surface Planets: Tectonics (8149); 8150 Tectonophysics: Evolution of the Earth: Plate boundary—general (3040); 8158
Tectonophysics: Evolution of the Earth: Plate motions—present and recent (3040).
Received 12 October 2001; Revised 23 July 2002; Accepted 3 December 2002; Published 14 March 2003.
Bird, P., An updated digital model of plate boundaries, Geochem. Geophys. Geosyst., 4(3), 1027, doi:10.1029/
2001GC000252, 2003.
G
3Geochemistry
Geophysics
Geosystems
Published by AGU and the Geochemical Society
AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES
Article
Volume 4, Number 3
14 March 2003
1027, doi:10.1029/2001GC000252
ISSN: 1525-2027
Copyright 2003 by the American Geophysical Union 1 of 52

1. Definitions of Plates and Orogens
[2] An idealized plate of lithosphere is a region
which rotates (with respect to some other specified
plate) without internal deformation about an imag-
inary axis through the center of the planet [Mor-
gan, 1968]. This axis intersects the surface of the
idealized spherical planet at two points known as
Euler poles. One variant of this definition describes
plates as features of the neotectonic velocity field
(on timescales of 10
0
to 10
6
years), in which case
the rotation may be described by an Euler vector
from the center of the planet toward the Euler pole,
with magnitude measured in degrees per million
years (or other rotation-rate units). A second var-
iant describes plates as features in a finite-displace-
ment field (on timescales of 10
6
to 10
9
years) in
which case the rotation is described by an Euler
vector with magnitude in degrees or radians. This
paper concerns neotectonics, and begins from the
former definition.
[3] On the real Earth, it is understood that any plate
model is only an approximation. First, elastic strain
accumulation around temporarily-locked faults is
always discounted, although it may not always be
clear in practice which strain rates are elastic and
which are anelastic. Second, it has been conven-
tional to overlook small amounts of anelastic
deformation within one ‘‘plate’’ provided that (1)
the ‘‘plate’’ is surrounded by boundary zones in
which anelastic strain rates are an order of magni-
tude higher than they are in the interior; and (2) the
velocity anomalies with respect to the best-fitting
ideal-plate model are near, or below, the threshold
of current measurement technologies. This
approach, in which the plate model is treated as a
useful approximation rather than literal truth, is
continued here. I overlook measured or suspected
internal velocity variations of as much as 2 to 8
mm/a; the lower threshholds apply in regions of
slow relative plate motion (e.g., North America,
Atlantic Ocean, Mediterranean, Africa) and the
higher thresholds apply to regions of rapid relative
plate motion (e.g., Indian and Pacific oceans and
their margins).
[4] Even with such a relaxed definition, there are
clearly regions (such as the Alpine-Himalayan
mountain belt) in which it is very difficult to define
plates, because there is so much seismic, geologic,
and geodetic evidence for distributed anelastic
deformation [Gordon, 1995]. One approach is to
define a large number of very small plates, as in the
Bird and Rosenstock [1984] model of 22 very
small plates in southern California alone. This is
data-intensive and time-consuming, and not yet
practical on a global basis. It may also fail in the
case of true viscous deformation, which would be
so evenly distributed as to fail criterion 1 stated
above. A second reasonable approach would be to
conduct local kinematic modeling using the con-
tinuum approaches of Holt et al. [1991, 2000],
Haines and Holt [1993], Jackson et al. [1995],
Bird [1998], Lamb [2000], or Kreemer et al.
[2000]. This is also too difficult to attempt in one
global survey paper. Alternatively, certain regions
can simply be labeled as zones of unmodeled
complexity, where more data are needed (either
to define very small plates, or to rule out their
existence). In this paper, I take this easy third
approach; I will refer to these complex regions
(which may include regions of truly distributed
deformation) as ‘‘orogens’’ (i.e., regions of moun-
tain-formation, or at least topographic roughening).
Thirteen of these zones are identified in Figure 1.
Perhaps it should be emphasized that the designa-
tion of an ‘‘orogen’’ is not purely a statement about
the nature of the kinematics in that region; it is a
culturally-relative statement that the velocity field
in that region has more degrees of freedom than
present data can constrain.
[5] For some applications of a plate model, it may
be more important to have global coverage than
high precision. One such application is the spher-
ical-harmonic expansion of plate velocities to
examine torroidal versus poloidal components.
Another is use of plate velocities as a boundary
condition in modeling of mantle convection. A
third example is the computation of element and
isotope cycling by creation and subduction of
crust. To accommodate such applications, I have
treated the set of orogens as an overlay layer
(giving warning of unmodeled complexity) rather
than as a set of polygons competing with the plates
for planetary surface area. By simply ignoring the
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