What are the stages of an earthquake?

Answer 1

What are the stages of an earthquake?

Earthquakes are divided into five stages. During each stage, a variety of changes occur in the earth. These changes are the geophysical precursors, and they can help scientists predict earthquakes. In order to understand how these precursors arise and how they help predict earthquakes, the five stages of an earthquake must be understood. These five stages arise from the Elastic Rebound Theory. This section will describe each of the five stages of an earthquake. The information in this section was taken from the books by Rikitake [1976], Meyer [1977], Eiby [1980], Bolt [1988], and Bolt [1993].

Stage I of an earthquake is the buildup of elastic strain. As the two sides of a fault move, elastic strain slowly builds up in the rocks, and the rock particles become compressed together.

Stage II is dilatancy and development of cracks. The rocks are now packed as tightly as possible, and the only way the rocks can change shape is to expand and occupy a larger volume. This increase in volume is called dilatancy. The volume increase is caused by the formation of microcracks. As microcracks form, the water that normally fills the pores and cracks in the rocks is forced out, much like when you step on wet beach sand. Air now fills the pores and cracks in the rocks. During this process, the rocks become stronger and can store more elastic strain. This process can be detected on the surface by uplift and tilting of the ground.

Stage III is the influx of water and unstable deformation in the fault zone. During this stage, water is forced back into the pores and cracks in the rocks by the surrounding water pressures, much like when water fills the footprint in the sand. As the water returns, the dilatant rock loses its increased strength. The rocks are already strained beyond their normal capacity, and the rate at which the rocks fall in strength determines the instant of failure. The inflow of water also prevents further generation of microcracks; thus, the rocks stop expanding. In addition, the water in the rocks provides lubrication for the eventual release of the built-up strain.

Stage IV is fault rupture, or the earthquake. Eventually, the rocks can no longer resist the strain. The fault suddenly ruptures, producing an earthquake. When the fault ruptures, the elastic energy stored in the rocks is released as heat and seismic waves. It is these waves that constitute an earthquake.

Stage V is the sudden drop in stress followed by aftershocks. Most of the elastic strain energy is released by the principal earthquake; however, additional smaller ruptures occur, producing aftershocks. The aftershocks release the remaining strain energy, and eventually the strain in the region decreases and stable conditions return.

Answer 2

1. The first stage is when stress builds up in the Earth's crust along a fault line.
2. Next, the stress is released suddenly, causing the rocks to break and creating seismic waves.
3. These waves radiate outwards from the fault line, causing the ground to shake, which is felt as an earthquake by people in the area.
4. Finally, the energy from the earthquake dissipates, and the seismic activity gradually decreases.