Earthquake Terminology

Earthquake Ground shaking resulting from a release of energy when sections of the earth’s crust move in relation to one another. Aftershock: an earthquake that follows the primary earthquake. These are often damaging because buildings and infrastructure have been weakened by the primary earthquake. Fault line is not the only place where damage occurs

Magnitude M or M w Ranges from Moment magnitude scale is most commonly used now but it is still referred to as the Richter Scale. The Richter was the first scale to categorize earthquake by size. Attempts to measure the total amount of energy released. An increase of one on the scale is a tenfold increase in magnitude

Intensity Qualitative description of how strong an earthquake feels, expressed in Roman Numerals Modified Mercalli Intensity

Intensity INot felt except by a very few. II Felt only by a few persons, especially on upper floors of buildings. Suspended objects may swing. III Felt noticeably by persons indoors. Many people do not recognize it as an earthquake. Standing cars may rock slightly. Vibration similar to the passing of a truck. IV Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably. VFelt by nearly everyone ; many awakened. Some dishes, windows broken. Unstable objects overturned. VIFelt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight. VII Damage negligible in buildings of good design. Slight damage to moderate in well-built ordinary structures. Considerable damage in poorly built or badly designed structures. Some chimneys broken. VIII Considerable damage in ordinary buildings, with partial collapse. Damage great in poorly built structures. Damage slight in specially designed structures Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. IX Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations. X Some well-built wooden structures destroyed. Most masonry and frame structures destroyed with foundations. Rails bent. XI Few, if any masonry structures remain standing. Bridges destroyed. Rails bent greatly. XIIDamage total. Lines of sight and level are distorted. Objects thrown into the air. Modified from USGS. URL:

epicenter focus = hypocenter depth

Acceleration PGA: peak ground acceleration Measured in “g” (1g is the acceleration due to gravity) Duration How long the shaking lasts, usually expressed in seconds

Geo-technology Soil type is very important Generally speaking, softer soils shake more than firmer soils. Sandy and water-saturated soils can also experience liquefaction, in which the ground turns to mush during the shaking and loses its ability to support structures.

Other related terms Tsunami Liquefaction Lateral spread Landslide Rockfall

Seismic Vulnerability Rating VR NYSDOT has a procedure for rating bridges according to the risk of damage from an event such as an earthquake Region 11 has rated the bridges in NYC

Terminology in Spanish Refer to Appendix C of MCEER Technical Report APPENDIX C: English-Spanish Translation Vocabulary is provided to facilitate use of this document and facilitate communication with professional counterparts in Spanish speaking countries. It includes technical terms that are pertinent to transportation engineering, bridge inspection, geotechnical engineering.