Week 4

• A tectonic plate (also called lithospheric plate) is a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.
• Tectonic plates are always moving and extremely active.
• This constant lithospheric motion results in surface fractures in the Earth’s crust, which are called faults.
• Faults are fractures in Earth's crust where rocks on either side of the crack have slid past each other. It is formed in the Earth's crust as a brittle response to stress.
• fault plane - the surface area between two rock blocks created by an earthquake
• fault trace - the visible crack in the Earth’s crust that indicates where a fault is
• fault scarp - the vertical step that rises during tectonic activity
• hanging wall - the rock block that hangs over the fault plane
• footwall - the rock block that occurs below the fault plane
• Normal faults form when the hanging wall drops down in relation to the footwall.
• This sliding downward of normal faults creates rifts, valleys, and mountains.
• Reverse faults form when the hanging wall moves up.
• The forces creating reverse faults are compressional, pushing the sides together.
• A special type of reverse fault, with a very low-angle fault plane, is known as a thrust fault.
• Thrust faults are relatively common in areas where fold-belt mountains have been created during continent-continent collision.
• Strike-slip faults have walls that move sideways, not up or down.
• In these strike-slip faults, the fault plane is usually vertical so there is no hanging wall or footwall.
• The most common cause of earthquakes is faulting.
• During faulting, energy is released as the rocks break and move.
• Active faults are structures where there is a displacement. Usually, they produce a shallow earthquake.
• Inactive faults are structures that can be identified but do not cause earthquakes.
• Geologists have identified common features of faults and earthquakes. One is the focus or hypocenter, which is the location where the movement of the source of the earthquake begins.
• Earthquake focus can occur at a range of depths down to 700 km below the surface. The other feature is the epicenter, which is the geographic location on Earth’s surface directly above the earthquake focus.
• Earthquakes vary in how much energy they produce.
• A strong earthquake releases more seismic waves and causes more shaking than a weak earthquake.
• The shaking and energy released by different earthquakes can be compared using a single standard measure known as earthquake magnitude.
• Seismograph is the instrument that detects and measures earthquake waves known as seismic waves (P-waves, S-waves and L-waves or surface waves).
• Seismographs measure the time of arrival and amplitude of seismic waves in a record we call as a seismogram.
• The strength or magnitude of earthquakes is measured according to the Richter Scale.
• Earthquakes that occur along faults in the ocean floor cause water to rise and ripple. Giant sea waves that are produced by this phenomenon are called tsunamis.
• Tsunamis can cause destruction to human lives and properties once they reach the shoreline.
• Typhoons are characterized by high winds, heavy rainfall, and storm surges along coastlines. They are composed of a dense mass of clouds surrounding a central clear “eye”.
• Typhoons begin to develop when warm, humid air rises, cools and condenses to form clouds.
• The spinning, rising air forms a cylindrical wall of strong winds, clouds, and rainfall.
• A typhoon forms when winds blow into areas of the ocean where the water is warm.
• Eye - At the center of the typhoon. An area of very low air pressure. There are generally no clouds in it and the wind is calm.
• Eye wall - Around the outside of the eye is made up of very heavy clouds. This is the most dangerous part of the typhoon and where the highest speed winds are. The winds at it can reach speeds of 155 miles per hour.
• Rainbands - Typhoons have large spiral bands of rain. These can drop huge amounts of rainfall causing flooding when the typhoon hits land.
• In North America and the Caribbean they are called hurricanes.
• In the Indian Ocean they are called cyclones.