Earth Science: Earthquakes & Layers of the Earth

• Earth science or geoscience studies the physical, chemical, and biological aspects of Earth.
• The four spheres of Earth are the biosphere, hydrosphere, atmosphere, and geosphere.
• An earthquake is a sudden shaking of the ground, often along geologic faults.
• The focus, also called the hypocenter, is where an earthquake begins.
• The epicenter is the point directly above the focus where the greatest damage occurs.
• Earthquakes can result from tectonic forces related to volcanic activities.
• Earthquakes can occur in underground mines due to seismic waves from rock explosions.
• Detonation of nuclear or chemical devices can cause earthquakes.
• Earth's crust can break or move due to geological forces, resulting in earthquakes.

Layers of the Earth

• The crust is the outermost and thinnest layer of the Earth, ranging from about 5 to 70 kilometers in thickness.
• The crust is divided into continental crust and oceanic crust.
• Continental crust is thicker, approximately 35 kilometers thick on average, and is found under continents.
• Oceanic crust is thinner, approximately 7 kilometers thick on average, and is found under ocean basins.
• The mantle is the thickest layer, extending from the base of the crust to about 2,900 kilometers.
• The mantle is divided into an upper and lower layer.
• The upper mantle is relatively rigid and contains the asthenosphere, a semi-fluid layer enabling tectonic plate movement.
• The solid lower mantle contributes to convection and heat transfer within Earth's interior.
• The core is the innermost layer, beneath the mantle, divided into the outer core and the inner core.
• The outer core is a liquid layer mainly of molten iron and nickel, with a thickness of about 2,300 kilometers.
• The inner core is the solid, central part of Earth, with a radius of about 1,220 kilometers, composed of solid iron and nickel.
• Continents were once joined as "PANGAEA”.

Tectonic Plates

• The Earth's crust is divided into large pieces called tectonic plates.
• The plates float on the semi-fluid mantle below them.
• A long horseshoe-shaped seismically active belt is the "Ring of Fire”.
• The Ring of Fire fringes the Pacific basin, with earthquake epicenters, volcanoes, and tectonic plate boundaries.
• Continuous movement causes stress on Earth's crust.

Faults

• Excessive stress leads to cracks called faults in the crust.
• Faults form between two blocks of rock where compression and tension cause rock displacement.
• A fault plane is a flat surface where slipping occurs and may be vertical or sloping.
• A hanging wall is a block located above a fault plane, resting on the foot wall of the fault.
• A foot wall is a block located below a fault plane.
• A fault line is the surface of a fault fracture along which the rocks have been displaced.
• A fault scarp resembles a step on the Earth's surface caused by a slip on the fault.
• The San Andreas Fault is in California.