The Hazard U.S. (HAZUS) model estimates damage to various structure types and the human and economic impacts that may result from future earthquakes. HAZUS is used to create Geographic Information System (GIS)-based maps depicting damage to various structural types as well as reports of direct physical damage to buildings, essential facilities and lifelines, induced physical damage, and direct economic and social losses.
The earth's surface, or crust is composed of a number of large plates, or sections of crust that are continually moving. Areas where these plates meet, and either grind past each other, dive under each other, or spread apart, are called plate boundaries. Earthquakes typically occur along plate boundaries, where fault lines, or weaknesses in the earth's crust can be found. When stress in the crust exceeds the strength of the surrounding rock, the rock breaks along either a pre-existing or new fault plane. Earthquakes are the sudden release of strain in the earth's crust, and result in waves of shaking that radiate outward from the earthquake source. The point where an earthquake starts is termed the focus, or hypocenter and may be many kilometers deep within the earth. The point at the surface directly above the focus is called the earthquake epicenter.
An earthquake which occurred in Kobe, Japan in January of 1995,
caused major destruction of infrastructure - including the collapse
of the Nishinomiyako Bridge. (Photo: EQE)
Approximately 75% of the world's seismic energy is released along the edges of the Pacific Ocean, where the thinner Pacific plate is forced beneath thicker continental crust along subduction zones. This 40,000 kilometer band of seismicity also known as the "Ring of Fire," stretches up the west coasts of South and Central America and from the North American continent to the Aleutians, Japan, China, the Philippines, Indonesia, and Australasia.
Around 15% of the earth's total seismic energy is released where the Eurasian and African plates are colliding, forming a band of seismicity that stretches from Burma, westward to the Himalayas, to the Caucasus, and the Mediterranean Sea.
Scientists now have a fairly good understanding of how plates move and how such movements relate to earthquake activity. Most movement occurs along narrow zones between plates, where the results of plate-tectonic forces are most evident.
Types of Plate Boundaries
Divergent boundaries: Where new crust is generated as the plates pull away from each other.
Convergent boundaries: Where crust is destroyed as one plate dives under another.
Transform boundaries: Where crust is neither produced nor destroyed as the plates slide horizontally past each other.
Plate boundary zones: Broad belts in which boundaries are not well defined and the effects of plate interaction are unclear.
Detailed illustration of plate boundaries.