Tectonic Plates and Faults - Earthquake Engineering for Structural Design - page 171

5.4 WORLD'S MAIN PLATE BOUNDARIES
5.4.1 Plate Boundaries Affecting the Continental Earthquakes
In spite of the great efforts made by seismologists of different countries to solve
the problem of the existing faults, reliability of their locations and characteristics
are far inferior to what it should be expected in practice. This situation is mainly
due to the fact that the processes of the fault movements are until now poorly
known. Only in the last few years, due to the GPS technique, the progress can be
qualified as notable.
Figures 5.3 presents an image of all boundaries types over the world. One can
see that, for continental areas, the divergent boundaries, with the exception of
Eastern Africa, have no influence, being situated on the ocean floor. The great
majority of boundaries are convergent and generally situated at the continent
coasts, with the exception of the Arabian and Indian areas, where they cross the
Asian Continent. The transform boundaries are rare, only the Western North
American and the North Anatolian area are affected by this boundary type.
Examining the tectonic plate boundaries it can be observed that three major
belts dominate the movements of tectonic plates: the Circum-Pacific Ring, the
Alpide-Himalayan Belt and the Mid-Atlantic Ridge. In the following, these plate
boundaries, their characteristics and the earthquake types occurring along them
will be presented.
5.4.2 Circum-Pacific Ring
The Circum-Pacific Ring (Fig. 5.27) (known also as the Ring of Fire, due to the
presence of some very active volcanoes), is composed of segments with different
characteristics. In the last century, over 90% of the world's earthquake energy
release occured along this ring.
In the Eastern part, the Pacific Plate is in contact with the North American
Plate along the continental coast. The side of Central America separates two
secondary plates, the Cocos and the Caribbean Plates. The Southern part of the ring
is formed by the contact between the Nazca and the South American Plates. The
Western part of the ring is dominated by the interaction between the Pacific Plate
and a strip of the North American, Philippine, Eurasian and Indo-Australian Plates.
In the Northern part the Pacific Plate has common boundaries with the North
American Plate, while in the Southern part with the Antarctic Plate.
The following segments characterize the EasternPacific plateboundary :
Canadian segment is composed by the North part, where the contact between
Pacific and the North American Plates produces the movements, and the South
part, where the interaction of three plates, the Pacific, the Juan de Fuca and the
North American plates exists. All these movements are produced by the Pacific
plate subduction beneath the North American plate.