Part-III(B):-Continuation of article Part-III(A)
5:- Pacific plate
2011 Tōhoku earthquake and tsunami
The magnitude-9.0 earthquake struck at 2:46 PM. (The early estimate of magnitude 8.9 was later revised upward.) The epicenter was located some 80 miles (130 km) east of the city of Sendai, Miyagi prefecture, and the focus occurred at a depth of 18.6 miles (about 30 km) below the floor of the western Pacific Ocean. The earthquake was caused by the rupture of a stretch of the subduction zone associated with the Japan Trench, which separates the Eurasian Plate from the subducting Pacific Plate. The sudden horizontal and vertical thrusting of the Pacific Plate, which has been slowly advancing under the Eurasian Plate near Japan, displaced the water above and spawned a series of highly destructive tsunami waves. A wave measuring some 33 feet high inundated the coast and flooded parts of the city of Sendai
1965 Rat Islands earthquake
The Rat Islands form part of the Aleutian Islands, a chain of volcanic islands forming an island arc, that results from the subduction of the Pacific Plate beneath the North American Plate. This plate boundary, the Alaska-Aleutian megathrust, has been the location of many megathrust earthquakes. It had a magnitude of 8.7 and triggered a tsunami of over 10 m on Shemya Island.
2006 Kuril island earthquake
Kuril Islands earthquake occurred as the result of thrust faulting on the boundary between the Pacific Plate and the Okhotsk microplate (part of the broader North America plate). It had a magnitude of 8.3 and maximum Mercalli intensity of IV
6:- Eurasian plate
1737, 1923,1952 Severo-Kurilsk earthquake
Occurred where the Pacific Plate subducts under the Okhotsk Plate at the Kuril-Kamchatka Trench. The depth of the trench at the point of the earthquakes is 7,000–7,500 m. Northern Kamchatka lies at the western end of the Bering fault, between the Pacific Plate and North American Plate or the Bering plate
7:-African plate
1761 Lisbon earthquake
The Azores-Gibraltar Fault forms part of the complex and poorly defined plate boundary between the African and Eurasian plates that converge at a rate of 3.8 mm/yr. The estimated surface-wave magnitude 8.5 event was the largest in the region.
In view of the huge devastation and enormous human cost, it is obvious that the subject of earthquake engineering which deals with how to design and construct structures and buildings that are earthquake resistant is a very important discipline of research. Roorkee, it so happens that the author belongs to has an earthquake engineering department well known in Asia
Seismic Engineering is very complex and constantly evolving. Seismic structural assessment is a powerful tool in Earthquake Engineering that uses detailed modeling of the structure in conjunction with structural analysis to get a better understanding of the building’s resistance. Retrofitting older structures with enhanced designs or materials is as important as rebuilding new structures from scratch. The ultimate goal of Earthquake Civil Engineering is to save lives so that the buildings don’t collapse and allow inhabitants to escape in a timely manner.
Some of the key ideas in the design of earthquake-resistant buildings and structures are as follows:-
1- It is necessary to reduce the connections of foundations with the soil – the source of seismic effects.
2- Side faces of the foundations in contact with the soils accumulate horizontal seismic effects on the foundation, leading to its displacement. In this connection, it is advisable to leave an air gap to reduce these effects;
3- Reducing friction between the base of the foundation and the soils reduces the transmission of horizontal seismic effects on the foundation and exceeding the friction resistance contributes to the slippage of the seismic wave under the foundation.
4- Protection of the foundation by a trench is effective and depends on the depth, size, and location of the trench closer to the building, from wavelength, type of foundation.
We give below a number of ideas that are commonly used in the construction of earthquake-resistant buildings
1-Floating foundation
2-Shock absorption
3-Rocking core-wall
4-Pendulum power
5-Symmetry, diaphragms, and cross-bracing
For more details- https://www.rishabheng.com/blog/earthquake-resistance-design-techniques-for-civil-structure/
In part IV we’ll discuss major volcanoes and their underline causes.