EARTHQUAKE

Tectonic earthquakes are the most common type of earthquake. They happen when tectonic plates beneath the Earth’s surface suddenly move and release energy. This usually occurs along plate boundaries where plates collide, pull apart, or slide past each other. Tectonic earthquakes are often very strong and can cause serious damage to buildings and communities. 

Volcanic earthquakes are caused by the movement of magma beneath volcanoes. As magma rises or shifts, it creates pressure that leads to ground shaking. These earthquakes often happen before or during volcanic eruptions, such as those that may occur near Mayon Volcano. They are usually localized around volcanic areas.

Human-induced earthquakes are earthquakes caused by human activities that disturb the Earth’s crust. Unlike natural earthquakes from tectonic plate movement or volcanic activity, these occur when activities such as mining, large reservoir construction, oil and gas extraction, or geothermal drilling change underground pressure and stress. 

The primary cause of earthquakes is the movement of tectonic plates. As these plates slowly shift, pressure builds up along their boundaries. When the pressure is suddenly released, it produces energy that causes the ground to shake. Many earthquakes occur in regions such as the Pacific Ring of Fire, where multiple plates meet. 

Earthquakes can also result from volcanic activity, as moving magma beneath the surface creates pressure and ground shaking. For example, small tremors are often recorded around Mayon Volcano before eruptions. 

In some cases, human activities like mining, drilling, and large dam construction can trigger minor earthquakes. 

Earthquakes often happen along fault lines, fractures in the Earth’s crust where stress builds over time; when rocks suddenly slip, energy is released, causing an earthquake. There are three main types of faults: normal faults (formed by tensional stress where the hanging wall moves downward), reverse or thrust faults (formed by compressional stress where the hanging wall moves upward), and strike-slip faults (formed by shear stress where plates move horizontally past each other).

The ground moves in upward, downward, and sideways vibrations during an earthquake. These vibrations can damage or collapse structures and may also trigger secondary hazards such as liquefaction and landslides.

Ground rupture occurs when movement along a fault during an earthquake breaks through the Earth’s surface. This happens directly above or near an active fault line.

Ground failure is the weakening or collapse of soil during or after an earthquake when it can no longer support structures.

Types include:

• Landslide – soil and rocks move downhill, burying structures.

  • • Topples - occur suddenly when a massive part of very steep slopes breaks loose and rotate forward.

    • Rock falls - involve chunks of detached rock that fall freely for some distance or bounce and roll down the steep slope.

    • Slides - involve the large blocks of bedrock that break free and slide down along a planar or curved surface.

    • Lateral spreads - are triggered by earthquake and affect gentle slopes with less than 10 degrees’ inclination.

    • Flows - involve downslope motion of the fine grained clay silt and fine sand made mobile by water saturation.

    • Complex slides - are combinations of two or moretypes of movement.

• Liquefaction – wet soil acts like a liquid, causing buildings to sink or tilt.

• Lateral spreading – sideways ground movement near water areas.

• Ground oscillation – strong back-and-forth shaking.

• Flow failure – soil flows rapidly like liquid.

• Loss of bearing strength – the ground cannot support structures.

• Settlement – gradual sinking of the ground.

These can damage buildings, roads, bridges, and utilities.

https://temblor.net/earthquake-insights/coseismic-landslides-in-sulawesi-indonesia-7874/

https://aessoil.com/guide-to-soil-liquefaction/

A tsunami, from the Japanese words “tsu” (harbor) and “nami” (wave), is a series of large ocean waves caused by underwater earthquakes or volcanic activity. As they reach shallow areas, they grow taller and can cause severe coastal flooding. The Philippines, located along the Pacific Ring of Fire, is at risk, and PHIVOLCS monitors and issues warnings.