The study of Geotechnical Earthquake Engineering requires an understanding of the various processes by which earthquakes occur and their effects on ground motion. The field of seismology developed from a need to understand the internal structure and behavior of the earth, particularly as they relate to earthquake phenomena. Although earthquakes are complex phenomena, advances in seismology have produced, a good understanding of the mechanisms and rates of occurrence of earthquakes in most seismically active areas of the world.
What is an Earthquake?
Earthquake: an event of ground shaking usually caused by the rupturing of a fault within the Earth. In other way the earthquake is defined as Unpredictable natural phenomenon of vibration of the ground. It becomes one of the most devastating natural hazard only if it’s considered in relation with structures.
What is Earthquake Engineering?
The earthquake has begun to become a problem for humans since they started to build structures. The deaths and the damage to buildings that they cause have several economic, social, psychological and even political effects. A general study of earthquakes involves many scienti?c disciplines that deal with the problem: Seismology ?? Engineering ?? Economy ?? Psychology
Earthquake Engineering : Branch of engineering devoted to mitigating earthquake hazards. It covers the investigation and solutions of the problems created by damaging structures.
Why Do Earthquakes Occur?
Earthquakes occur due to:
• Sudden formation of a new fault (fracture on which sliding occurs)
• Sudden slip on an existing fault
• Sudden change in the arrangement of atoms in the minerals of a rock
• Movement of magma in a volcano
• Explosion of a volcano
• Giant landslides
• Meteorite impact
• Underground nuclear bomb tests
2.1.1 Earthquake Terminology:
• Hypocenter (Focus): actual location of the earthquake at depth.
• Epicenter: location on the surface of the Earth above the hypocenter.
Figure 2.1 Origin of Earthquake
• Fault Plane – the plane along which the rock or crustal material has fractured
• Hanging Wall Block – the rock material which lies above the fault plane
• Footwall Block – the rock material which lies below the fault plane.
2.1.2 Causes of Earthquakes
There are basically three types:
Tectonic Earthquakes: Most earthquakes occur at plate margins due to tension, compression or shearing forces. Rocks at plate margins are in constant motion and are being pushed, pulled, bent, twisted and folded. Inevitably at some point they must break or crack to produce FAULTS!!
What is a Fault?
A fault is a break or fracture between two blocks of rocks in response to stress. There are three types of stresses produce in faults (1) Tension (2) Compression (3) Shear
Theory of plate tectonics generally assigns the relative movement of plates to one of the three preceding types of plate boundaries; examination on a smaller scale reveals that the movement at a particular location can be quite complicated. In some regions, plate boundaries are distinct and easy to identify, while in others they may be spread out with the edges of the plates broken to form smaller platelets or microplates trapped between the larger plates. Locally, the movement between two portions of the crust will occur on new or preexisting offsets in the geologic structure of the crust known as faults.
Faults may range in length from several meters to hundreds of kilometers and extend from the ground surface to depths of several tens of kilometers. Their presence may be obvious, as reflected in surficial topography, or they may be very difficult to detect. The presence of a fault does not necessarily mean that earthquakes can be expected; movement can occur a seismically, or the fault may be inactive.