Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. Geotechnical engineering is important in civil engineering, but also has applications in military, mining, petroleum and other engineering disciplines that are concerned with construction occurring on the surface or within the ground. Geotechnical engineering uses principles of soil mechanics and rock mechanics to investigate subsurface conditions and materials; determine the relevant physical/mechanical and chemical properties of these materials; evaluate stability of natural slopes and man-made soil deposits; assess risks posed by site conditions; design earthworks and structure foundations; and monitor site conditions, earthwork and foundation construction.
Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake environmental effects such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes such as explosions. A related field that uses geology to infer information regarding past earthquakes is paleoseismology. A recording of earth motion as a function of time is called a seismogram. A seismologist is a scientist who does research in seismology.
Soil liquefaction occurs when a saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in which material that is ordinarily a solid behaves like a liquid.
Peak ground acceleration (PGA) is equal to the maximum ground acceleration that occurred during earthquake shaking at a location. PGA is equal to the amplitude of the largest absolute acceleration recorded on an accelerogram at a site during a particular earthquake. Earthquake shaking generally occurs in all three directions. Therefore, PGA is often split into the horizontal and vertical components. Horizontal PGAs are generally larger than those in the vertical direction but this is not always true, especially close to large earthquakes. PGA is an important parameter for earthquake engineering, The design basis earthquake ground motion (DBEGM) is often defined in terms of PGA.
Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with our recent experiences with large earthquakes near urban centers, the need of seismic retrofitting is well acknowledged. Prior to the introduction of modern seismic codes in the late 1960s for developed countries and late 1970s for many other parts of the world, many structures were designed without adequate detailing and reinforcement for seismic protection. In view of the imminent problem, various research work has been carried out. State-of-the-art technical guidelines for seismic assessment, retrofit and rehabilitation have been published around the world – such as the ASCE-SEI 41 and the New Zealand Society for Earthquake Engineering (NZSEE)'s guidelines. These codes must be regularly updated; the 1994 Northridge earthquake brought to light the brittleness of welded steel frames, for example.
Exploration geophysics is an applied branch of geophysics, which uses physical methods, such as seismic, gravitational, magnetic, electrical and electromagnetic at the surface of the Earth to measure the physical properties of the subsurface, along with the anomalies in those properties. It is most often used to detect or infer the presence and position of economically useful geological deposits, such as ore minerals; fossil fuels and other hydrocarbons; geothermal reservoirs; and groundwater reservoirs.
Seismic magnitude scales are used to describe the overall strength or "size" of an earthquake. These are distinguished from seismic intensity scales that categorize the intensity or severity of ground shaking (quaking) caused by an earthquake at a given location. Magnitudes are usually determined from measurements of an earthquake's seismic waves as recorded on a seismogram. Magnitude scales vary on what aspect of the seismic waves are measured and how they are measured. Different magnitude scales are necessary because of differences in earthquakes, the information available, and the purposes for which the magnitudes are used.
Mitigation of seismic motion is an important factor in earthquake engineering and construction in earthquake-prone areas. The destabilizing action of an earthquake on constructions may be direct or indirect.
The George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) was created by the National Science Foundation (NSF) to improve infrastructure design and construction practices to prevent or minimize damage during an earthquake or tsunami. Its headquarters were at Purdue University in West Lafayette, Indiana as part of cooperative agreement #CMMI-0927178, and it ran from 2009 till 2014. The mission of NEES is to accelerate improvements in seismic design and performance by serving as a collaboratory for discovery and innovation.
National Center for Research on Earthquake Engineering is an organisation found in Taipei, Taiwan. Since Taiwan is located on the ridge of the Eurasian and Philippine tectonic plates, it is highly seismic. The biggest earthquake in Taiwan in more than a century was 21 September 1999, also known as the Chi-Chi earthquake which measured 7.3 on the Richter scale.
Earthquake-resistant structures are structures designed to protect buildings from earthquakes. While no structure can be entirely immune to damage from earthquakes, the goal of earthquake-resistant construction is to erect structures that fare better during seismic activity than their conventional counterparts. According to building codes, earthquake-resistant structures are intended to withstand the largest earthquake of a certain probability that is likely to occur at their location.This means the loss of life should be minimized by preventing collapse of the buildings for rare earthquakes while the loss of the functionality should be limited for more frequent ones.
In geology and other related disciplines, seismic noise is a generic name for a relatively persistent vibration of the ground, due to a multitude of causes, that is a non-interpretable or unwanted component of signals recorded by seismometers.
The 1992 Cape Mendocino earthquakes occurred along the Lost Coast of Northern California on April 25 and 26. The three largest events were the M7.2 thrust mainshock that struck near the unincorporated community of Petrolia midday on April 25 and two primary strike-slip aftershocks measuring 6.5 and 6.6 that followed early the next morning. The sequence encompassed both interplate and intraplate activity that was associated with the Mendocino Triple Junction, a complex system of three major faults that converge near Cape Mendocino. The total number of aftershocks that followed the events exceeded 2,000.
Offshore geotechnical engineering is a sub-field of geotechnical engineering. It is concerned with foundation design, construction, maintenance and decommissioning for human-made structures in the sea. Oil platforms, artificial islands and submarine pipelines are examples of such structures. The seabed has to be able to withstand the weight of these structures and the applied loads. Geohazards must also be taken into account. The need for offshore developments stems from a gradual depletion of hydrocarbon reserves onshore or near the coastlines, as new fields are being developed at greater distances offshore and in deeper water, with a corresponding adaptation of the offshore site investigations. Today, there are more than 7,000 offshore platforms operating at a water depth up to and exceeding 2000 m. A typical field development extends over tens of square kilometers, and may comprise several fixed structures, infield flowlines with an export pipeline either to the shoreline or connected to a regional trunkline.
Nicholas Neocles Ambraseys FICE FREng was a Greek engineering seismologist. He was emeritus professor of Engineering Seismology and Senior Research Fellow at Imperial College London. For many years Ambraseys was considered as the leading figure and absolute authority in earthquake engineering and seismology in Europe.
Seismic site effects are related to the amplification of seismic waves in surficial geological layers. The surface ground motion may be strongly amplified if the geological conditions are unfavourable. Therefore, the study of local site effects is an important part of the assessment of strong ground motions, seismic hazard and engineering seismology in general. Damage due to an earthquake may thus be aggravated as in the case of the 1985 Mexico City earthquake. For alluvial basins, we may shake a bowl of jelly to model the phenomenon at a small scale.
Earthquake rotational loading indicates the excitation of structures due to the torsional and rocking components of seismic actions. Nathan M. Newmark was the first researcher who showed that this type of loading may result in unexpected failure of structures, and its influence should be considered in design codes. There are different phenomena that may lead to the earthquake rotational loading of structures, such as propagation of body wave, surface wave, special rotational wave, block rotation, topographic effect, and soil structure interaction.
Rotational components of strong ground motions refer to changes of the natural slope of the ground surface due to the propagation of seismic waves. Earthquakes induce three translational and three rotational motions on the ground surface. To study the nature of strong ground motions, seismologists and earthquake engineers deploy accelerometers and seismometers near active faults on the ground surface in order to record the translational motions of ground shaking. The corresponding rotational motions are, then, estimated in terms of the gradient of the recorded translational ground motions. Different methods may be adopted for the indirect estimation of the earthquake rotational components, such as time derivation and finite difference. Recently, a limited number of advanced instruments, named ring laser gyroscopes, have been used to detect the rotational movements of the ground surface, and directly measure the amplitude of the rotational components of strong ground motions.
