3.2.1 Website Glossary epicenter Point on the earth’s surface directly above the hypocenter fault A zone of the earth’s crust within which the two sides have moved - faults may be hundreds of miles long, from one to over one hundred miles deep, and not readily apparent on the ground surface. hypocenter location where the earthquake starts (i.e., location of first dynamic rupture) intensity effect, or the strength, of an earthquake hazard at a specific location, commonly measured on qualitative scales such as MMI, MSK and JMA. liquefaction a process resulting in a soil’s loss of shear strength, due to a transient excess of pore water pressure. magnitude A unique measure of an individual earthquake’s release of strain energy, measured on a variety of scales, of which the moment magnitude MW (derived from seismic moment) is preferred Plate Tectonics The structure of the earth’s surface, consisting of relatively thin pieces or plates of crust. The motion of the edge of the Pacific Plate, relative to and in contact with the Eurasian, North American, South American, Philippine Sea and other plates, causes about 80+% of global earthquakes, and is termed the Ring of Fire. Another major zone of seismicity is the Trans-Alpide Belt, extending from the Mediterranean through the Middle East and Himalayas to the Indonesian Archipelago. retrofitting Seismic strengthening of an existing structure, equipment or other facility. risk and risk management Risk is the variability in potential loss. Managing the potential for such a loss is an integral activity of an organization’s risk manager, who works with the chief financial function. Ideally, risk managers monitor and manage all sources of risk to the organization aside from those associated with the organization’s central mission. For example, in a manufacturing company, the risk manager will deal with property, life, and health risk, but not market or foreign exchange risks or worker safety. In dealing with property risk, the risk manager will normally purchase property insurance, but will also examine alternatives to insurance, such as strengthening a building for earthquake so as to reduce the need for earthquake insurance. hazard the phenomena and/or expectation of an earthquake-related agent of damage, such as fault rupture, vibratory ground motion (i.e., shaking), inundation (e.g., tsunami, seiche, dam failure), various kinds of permanent ground failure (e.g. liquefaction), fire or hazardous materials release. seismic risk the product of the hazard and the vulnerability (i.e., the expected damage or loss, or the full probability distribution). vulnerability the expected damage given a specified value of a seismic hazard. Note that this is only one meaning of vulnerability. The term vulnerability has several meanings in natural hazards, and is sometimes used to refer to the social vulnerability of a population (rather than the physical vulnerability of a structure), and is sometimes used to refer to the overall set of characteristics of a population or community, that make them vulnerable.