Drrr midterm

• Earthquakes in the Philippines are frequent occurrences since the country is lying on the Pacific Ring of Fire.
• Ground shaking - The shaking of the ground occurs as a result of seismic waves traveling through the different layers of the Earth caused by vibration or movement. A factor in determining the intensity of Earth shaking is the geologic profile of the ground. By principle, a solid tight bedrock is less prone to the impacts of shaking. The impacts also depend on other parameters such as duration, frequency, and proximity to the epicenter of an earthquake.
• Epicenter is the area on the surface of Earth where the origin of the earthquake is. These are some of the factors that can influence the disaster risk of an area.
• Ground rupture - Ground cracking or breaking occurs when geologic movement happens on a fault line and breaks through to the surface. This may happen in an instant during an earthquake. Slowly, the ground cracks and eventually breaks apart. Most of the time, ground rupture follows preexisting faults known as zones of weakness.
• Liquefaction - Liquefaction occurs when seismic shaking triggers the mixing of loose materials with groundwater or soil saturated with water. In effect, the soil behaves like a liquid that has lost its strength to hold and support objects on top of it. Eventually, the structures on the ground slowly sink.
• Earthquake-induced ground subsidence - Subsidence is the lowering of land due to various causes, one of which is earthquake on a fault line.
• Tsunamis - The word tsunami is a Japanese word that means "harbor wave," coined as such because of the destructive effects from the wavelike phenomenon experienced by the Japanese living on low-lying coastal communities. It is now generally used to mean a series of waves that are generated by a sudden displacement on the ocean floor caused by large-scale undersea landslides or earthquakes.
• Earthquake-induced landslide - Landslides may happen during or after an earthquake when weakened land falls off primarily due to gravity.
• seismograph is an instrument used to measure movements on the Earth's surface by picking up any vibrations caused by seismic waves.
• A seismic wave is a form of energy that travels through the interior of the Earth which is generated during an earthquake or volcanic eruption.
• Seismologists are experts that monitor seismic waves in areas that are recognized to be prone to Earth movement from volcanic activities or earthquakes.
• The seismic energy release usually occurs in openings like cracks and fissures called faults.
• Active faults release energy from time to time. If there is a known active fault and no earthquakes have occurred there or within the vicinity of the fault for a long time, seismologists may speculate that a release of energy is due soon and that this energy could be building up somewhere along this tectonic fault.
• Faults and fissures traverse the entire Philippine archipelago. Altogether, they form the Philippine fault system.
• According to the United States Geological Survey (USGS), faults are fractures along blocks of the earth's crust.
• a trench is a linear depression on the ocean floor caused by convergent plates where one plate slides under the other.
• A fault zone that is inactive for a long period of time may suddenly move without any warning.

  You should always remember that any opening on the Earth's crust is a possible outlet for the seismic energy in the Earth's interior.
•  Volcanoes are formed from the previous explosions where ash, molten rock, and gas would craft mountains and craters.
• Volcanic eruptions have been responsible for the dynamics of the Earth, shaping its landscape and liberating nutrients to make soil fertile.
• Volcanic hazards are volcano-related phenomena that pose potential threat and negative impact on life, property, and the environment in a given period of time.
• Lahar - The term lahar is originally an Indonesian term referring to a combination of debris or mud mixed with volcanic materials, such as gas and molten rocks, that flow down from a volcano.
• Ashfall - Ashfall is composed of bits and pieces of pulverized rock, minerals, and volcanic glass generated from a volcanic eruption.
• Volcanic ash is usually spewed out from explosive eruptions when dissolved gases in magma expand and are released violently into the atmosphere.
• Microclimate is a long-term atmospheric condition shared by a small region. Ash clouds can travel farther and cover a larger radius.
• • Pyroclastic flow - This is fast-moving fluidized mass of rock fragments and gases. When it travels down a volcano, it maintains a very high temperature, burning everything on its path.
• • In fact, in the Mt. Pinatubo eruption in 1991, some pyroclastic flow had temperatures of about 750 °C. Such high temperatures instantly burn man-made structures and vegetation.Pyroclastic flows can easily incinerate or asphyxiate humans and animals.
• • Asphyxiation, as described by Britannica (2022), is suffocation or difficulty in breathing caused by deprivation of oxygen. The gases that come with pyroclastic flow can explode and may even cause acid rain.
• • Ballistic projectile - This happens when a rock fragment is ejected from a volcano and hurled into the atmosphere during its explosive eruption. According to the USGS, volcanic projectiles can be bombs and blocks.
• • Blocks are solid rock fragments, while bombs are molten rock fragments. These projectiles pose a serious threat to humans, plants, animals, and properties.
• • Ballistic projectiles can travel as far as five kilometers or even further, depending on the magnitude of explosion.
• • Volcanic gas - This consists of sulfur dioxide and hydrogen sulfide which are hazardous to organisms. Because of their toxicity, volcanic gases can cause acid rain, corrosion in man-made objects and structures, and respiratory or health risks for people.
• • Lava flow - This is molten rock that pours down from the slopes of the volcano. Lava flow differs from pyroclastic flow in terms of density.
• • Lava is denser, and hence moves slower. As such, it gives more time for animals and humans to move away from its path, unlike pyroclastic flow that may leave no time for organisms to react. Similar to lahar and pyroclastic flow, lava flow can destroy anything that is on its path. It can even trigger forest fires.
• Those coded in red triangles indicate active volcanoes which, based on their history, have recorded frequent activity in terms of tremors, gas emissions, and heat release.
• The areas with yellow triangles are considered potentially active, which are categorized by volcanologists and geologists as those that are not currently exhibiting signs of eruption but have a high possibility of any form of seismic activity in the future.
• two of these common geologic hazards are landslides and sinkholes. They become hazards because of the topographic

  and geologic composition of land.
• Another term for landslide is landslip. Both pertain to movement of land on an inclined surface. Landslides can be triggered by environmental conditions such as rain, flood, and wind.

  Landslides also happen in eroded sloping grounds such as hills or mountains devoid of vegetation or have loose soils.
• sinkholes are large pits that result from the collapse of the surface exposing the hollow interior of the ground. It should be noted that sinkholes can only happen in areas with soils containing limestone. The chemical constituents of limestone (carbonate rock) are highly reactive to water.
• An Abney level or a laser rangefinder can be used to compute the slope of the ground, compaction of the soil, and the strength of soil layers.
• Sinkholes are validated using ground-penetrating radar or GPR (figure 4.14) to provide images of subsurface ground. These images show material composition of soils under the ground. The instrument can also detect spaces and estimate their size or coverage.