This website is dedicated as educational resources for briefing prospective students on Earthquake Engineering, which is part of my final year individual project.
Earthquake Engineering is an interdisciplinary branch of engineering concerned with protecting society, the natural environment, and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels (Wikipedia, 2019).
The main objectives of Earthquake Engineering are (Wikipedia, 2019):
- Foresee the potential consequences of strong earthquakes on urban areas and civil infrastructure
- Design, construct and maintain structures to perform at earthquake exposure up to the expectations and in compliance with building codes
History and Development
Robert Mallet, an Irish civil engineer, is often cited as the first earthquake engineer and his report on the 1857 Naples earthquake is considered to be the first scientific investigation that included observations of the seismological, geological, and engineering aspects of an earthquake.
Modern research on earthquake-resistant structures, however, began in Japan in 1881, the year of the Nobi Earthquake, with the formation of an earthquake investigation committee set up by Japanese government. It was this committee who first proposed the use of a lateral force equal to the fraction of the total weight of a building to account for the forces exerted on buildings.
Similar developments in Italy after the devastating Messina earthquake in 1908 led to the appointment of a committee composed of practicing and academic engineers to study the earthquake and the formulation of practical recommendations for the seismic design of buildings. In its report, this committee recommended buildings were to be designed for horizontal forces equal to fractions of the building weight based on different story levels (Quake Centre, 2014).
The 20th Century can be divided into three very distinct periods:
First period
The first one (until 1950) is characterized by very timid attempts to develop a consistent explanation of the nature of earthquakes. During this period no records are available (with the exception of the historical record of 1940 El Centro earthquake, the first recorded one).
Second period
The second period (1950-1980), is characterized by coherent theory development, but due to a reduced number of instrumented seismic stations, there was limited information concerning the characteristics of ground motions and damage done by these earthquakes.
Third period
A dense network of instrumental seismic stations characterizes the last period of 20th Century, where the developed theory was supported by a large number of records. At the same time, the tremendous development of engineering seismology had a great influence in the developing of anti-seismic concepts.
Ever since, earthquake engineering has unfolded at a steady pace and its principles have spread all over the world. It has rapidly evolved into a science-based discipline, with a large body of knowledge and institutionalized research and educational programs.
As a result of this cumulative knowledge and experience, cities around the world and the people living in them are becoming less vulnerable to the devastating effect of earthquakes (Quake Centre, 2014).
Occurrence and Probability of Exceedance
Another unique feature of earthquake forces is the likelihood associated with their occurrence.
At any given seismic region, small earthquakes are likely to occur often, moderate earthquakes once every few years, large earthquakes every 50-100 years, and extremely large earthquakes perhaps every 1000 or 2000 years.
The table below summarizes the average frequency with which earthquakes occur every year around the world, based on the observations since 1900. As it may be seen, the earth is in a constant state of seismic activity. As expected, large earthquakes are not as frequent as small ones, but still, great and major earthquakes occur with a frequency that is worrisome. Fortunately, great and major earthquakes do not always take place in populated areas, so they are not always catastrophic (Quake Centre, 2014).
(Reproduced from the National Earthquake Information Center, U.S. Geological survey)
In a given time interval, there is a high probability that a structure will be affected by small earthquake forces and a negligibly small probability that it will be affected by extremely large earthquake forces.
Therefore, since it is not economically feasible to design every structure to resist the largest earthquake force possible, the design earthquake forces necessarily have to be those for which there is an appreciable probability of occurrence during their lifetime.
Consequently, implicitly or explicitly, the specification of earthquake forces for the design of a structure is always accompanied with an associated probability of exceedance (Quake Centre, 2014).