Chapter 2 : Introduction to Dynamics Basic Quantities from Earthquake Records

Basic Quantities from Earthquake Records Earthquakes are complex, dynamic events. In order to describe and work with them, a vocabulary of terms is necessary. Terms describing the intensity or magnitude of an earthquake give the engineer a quick estimate of the degree of shaking and damage one would expect. Other values reflect the time history of the earthquake such as acceleration, velocity, displacement, power, and other values derived from the time histories. The size of an earthquake has been reported in several ways. Historically the earthquake intensity was a qualitative description of the earthquake’s ability to cause damage. The Rossi-Forel (RF) scale describing intensities with values ranging from I to X was developed in 1880’s and used for many years. the modified Mercalli intensity (MMI) scale is a better way to represent conditions in the U.S. and was adopted there in the 1930’s. The MMI scale is based on performance of familiar structures and is shown in Table 2-1. Include discussion on Richter, Surface wave, body wave, as well as energy. and Moment magnitude. Shown below is a record of earthquake acceleration versus time. Note the irregular shape of the record. However, one can differentiate portions of strong shaking from portions of weaker shaking. One can also identify, approximately, the frequency of strong motion in the record. The maximum acceleration during the event is about 0.32g or 3.1 m/sec at time = 17 seconds.