
An earthquake occurs due to the rupture of a fault in the Earth’s interior. Sometimes this fault can reach the Earth’s surface. In this case, the relative movement of the ground on either side of the fault becomes continuous, and over time, with subsequent earthquakes, leads to the formation of new landforms.
Constant movement along the fault is characteristic of strong earthquakes, and the strength of seismic tremors (magnitude) is directly related to the size of the rupture. The fault often reaches the surface when the magnitude is greater than 6.0. Landscape changes can be particularly noticeable during strong earthquakes with vertical displacement of tectonic plates. The 2016 earthquake in central Italy with a magnitude of 6.5 caused a subsidence of rock layers by 2 meters, exposing a surface rupture. And after the 2010 earthquake in Chile with a magnitude of 8.8, marine sediments were uplifted and exposed on the surface.
Surface ruptures caused by earthquakes can change the geometry of watercourses, topography and sedimentary deposits. These changes are often evident and can be used as indicators of seismic activity of faults. Thus, by studying ruptures, it is possible to identify past faults that have displaced surface geological layers. Analysis of the displacement makes it possible to evaluate such characteristics of past earthquakes as their time and strength.
Landscape changes after an earthquake
Seismic activity leads to changes not only in the geological structure of the mountain strata, but also in the topography of the Earth’s surface. Some of these changes last for thousands or even millions of years, while others occur during a single seismic event.
Mountain formation
According to the theory of plate tectonics, the Earth’s crust is made of large, rigid plates, ranging in thickness from 50 to 150 km, that are constantly moving. Where tectonic plates collide, their boundaries are deformed, creating a subduction zone. The denser plate subducts beneath the less dense plate. The upper plate is compressed and uplifted, gradually forming mountain ranges.
Formation of rifts
While new faults often form in areas of seismic activity, most earthquakes occur within areas where rifts have existed for a long time. Faults can be divided into three main types:
- normal – one plate moves vertically relative to the other;
- reverse – the plate descends relative to the other along the fault boundary;
- strike-slip – both plates move horizontally.
The stretching of Earth’s crust in zones where tectonic plates diverge leads to the formation of new rifts. Magma intrudes into these rifts, forming new mountain ranges.
Tsunamis
Tsunamis caused by earthquakes can change not only the shape and size of coastlines, but also the seafloor relief. Giant waves swept away layers of soil, destroy rock formations, and bring marine sediments to the coast. In shallow waters, high waves destroy coral reefs and atolls, wash away the soil and reshape the landscape. This makes navigation difficult in the disaster area and requires new mapping of the seabed. Tidal waves generated by earthquakes also affect the formation of continental shelves, accelerating the processes that shape their profile and structure.
Soil gravity movements
Another effect caused by the earthquake is the displacement of mountain ranges. These processes occur in the form of:
- landslides, when entire sections of rock slide horizontally over sediment, while vegetation remains vertical;
- vertical collapses of rock blocks, creating massive rockfalls. Such rockfalls can block river channels, destroy infrastructure in valleys, and damage buildings.
If landslides and avalanches occur near the sea coast, they can trigger local but powerful tsunamis.
Soil liquefaction
Liquefaction occurs in poorly cohesive soils (usually in sand) that are saturated with water. Pressure drops during seismic waves cause the water to move. The grains of the sand layer lose contact, which significantly reduces the shear resistance of the soil. The soil undergoes liquefaction, losing its ability to support the weight of the layers above. The more solid lower layers fracture, allowing groundwater to rise to the surface. These processes result in the formation of sand volcanoes, which can cause large areas of the landscape to literally sink into the ground.
It should be noted that earthquakes affect not only the upper layer of the Earth’s crust, but also structures built on the surface. The damage to buildings depends on the strength of the earthquake, the distance from the epicenter, the characteristics of the object, and the type of soil, which can change the intensity of seismic vibrations.