GRADE 7 QUARTER 4 - MODULE 1 - EARTHQUAKE

An earthquake is the sudden shaking of the Earth's surface caused by the movement of tectonic plates. It occurs when stress builds up along faults or plate boundaries, leading to a sudden release of energy. Earthquakes can also be triggered by volcanic activity or human-induced factors such as mining and the construction of large reservoirs. The shaking produced by an earthquake travels in the form of seismic waves, which include Primary (P) waves, the fastest and capable of moving through both solids and liquids, Secondary (S) waves, which move slower and travel only through solids, and Surface waves, which cause the most destruction as they move along the Earth's crust. The strength of an earthquake is measured using a seismograph, with the Richter scale determining the magnitude based on energy released and the Modified Mercalli scale assessing the intensity based on observed effects. The impact of an earthquake can be devastating, leading to ground shaking, liquefaction (where soil behaves like liquid), landslides, and even tsunamis if it occurs under the ocean. To reduce risks, earthquake preparedness is essential. People should secure heavy objects, create emergency kits, and practice "Duck, Cover, and Hold" during an earthquake. After the shaking stops, it is crucial to check for injuries, avoid damaged buildings, and be aware of possible aftershocks. Understanding earthquakes and their effects can help communities stay safe and minimize damage.

1. SCIENCE 8

2. Types of Faults There are three (3) kinds of faults: the normal fault, the thrust (or reverse) fault, and the strike-slip fault. Each type is the outcome of different forces pushing or pulling on the crust causing rocks to slide down, up, or past each other.

3. 1. Compressive or compressional stress happens when two plates are pushed together . They are literally compressed towards each other. When you push a chunk of clay on both sides, it becomes thicker and shorter. In the same manner, compressional stress squeezes rocks causing rocks to fold or rupture (break). Thrust faults or reverse fault are often associated with convergent or compressional boundaries.

4. 2. Tensional stress happens when two blocks or slabs of rock are pulled apart . When we pull apart a chunk of clay, it becomes elongated and thin. When tensional stresses pull the crust apart, it breaks into blocks that slide up and drop down along normal faults. This results to alternating mountains and valleys. Normal faults are often associated with divergent (tensional) boundaries.

5. 3. Shear stress is experienced at transform boundaries where two plates are sliding past each other. Strike-slip faults are often associated with transform (sliding) boundaries.