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Earthquake
Movement in the Earth's crust after a sudden release of energy.
Epicenter
The point of origin of an earthquake on the surface of the Earth.
Focus / Hypocenter
The point of origin of an earthquake within the Earth's crust.
Fault Plane
A rupture in the lithosphere that contains the earthquake's focus.
Body Waves
Seismic waves that travel through the crust, mantle, and/or the core of the Earth. Primary and Secondary waves.
Surface Waves
Seismic waves that only travel through the uppermost layer of the crust. Slow but with greater amplitude (greater surface damage). Rayleigh and Love waves.
Primary Waves
The fastest body seismic wave that can travel through any kind of matter. Moves through compression and expansion like a slinky.
Secondary Waves
A fast body seismic wave that can only travel through solids. Moves in vertical waves, like water.
Rayleigh Waves
A surface seismic wave that travels in a vertical, rippling motion.
Love Waves
A surface seismic wave that travels in a side-to-side motion like a snake. The most damaging of seismic waves.
Foreshocks
Small tremors that precede an earthquake.
Aftershocks
Long-term (weeks to years) tremors that follow an earthquake.
Liquefaction
Occurs when soil loses its strength and allows water to flow through it, creating quicksand or quickclay.
Tsunamis
Massive waves resulting from sea-floor earthquakes, submarine landslides, volcanic eruptions, or fault movements. Unaffected by wind speed.
Base Isolation
A method of mitigating seismic activity by decoupling a superstructure from the substructure that rests on the ground. The substructure absorbs all of the seismic waves and the superstructure above ground remains unaffected.
Seismic Energy Dispersion
A method of mitigating seismic activity by dispersing energy across a wide range of frequencies. Achieved by buildings that taper, such as a pyramid or tower.
Mass Dampening
A method of mitigating seismic activity by absorbing resonant portions of a wave's frequency. Buildings move opposite to the resonance, reducing damage.
Can earthquakes be predicted?
Earthquakes can be predicted long-term (years) but not short term (hours to weeks).
Orogenesis
The process of mountain building consisting of the uplift of crust and the erosion (or exhumation) of peaks.
Stress
A force applied across a unit area.
Compression
Stress where an object is squeezed from two opposing directions.
Tension
Stress where an object is pulled apart from two opposing directions.
Shear
Stress where two objects slide past each other.
Pressure
Stress where an object undergoes compression from all directions.
Strain
The deformation a rock has after being stressed.
Brittle Deformation
Strain where hard, low-temperature rocks fracture and break. Fast rate of deformation.
Ductile Deformation
Strain where soft, high-temperature rocks bend and fold like plastic. Slow rate of deformation.
Where does the transition between brittle and ductile deformation occur?
10-15 km below Earth's surface.
Displacement
Deformation where a rock changes its location.
Rotation
Deformation where a rock changes its orientation or tilt.
Distortion
Deformation where a rock changes its shape.
Joint
A form of brittle deformation where parallel fractures break rock apart without any offset. Forms from tensile stress.
Vein
A form of brittle deformation where joints are filled with minerals (quartz or calcite) that push the joints apart and further break rock apart.
Fault
A form of brittle deformation where planar fractures displace mass amounts of rock.
Hanging Wall
The side of a fault that overhangs or is positioned above the foot wall. Undergoes displacement during seismic activity. Intersects the surface of the Earth at <90°.
Foot Wall
The side of a fault that is not displaced. Intersects the surface of the earth at >90°.
Normal Faults
The hanging wall moves down relative to the foot wall due to extension (tension). Creates a dip.
Reverse Faults
The hanging wall moves up relative to the foot wall due to compression. Sharp slope.
Thrust Faults
The hanging wall moves up relative to the foot wall due to compression. Gentle slope. D
Dip Slip Faults
The hanging wall moves parallel to the fault plane; up or down.
Strike Slip Fault
The hanging wall moves parallel to the fault line; left or right.
Oblique Slip Fault
The hanging wall moves in two directions; up and left, down and right, etc.
Fault Breccia
Rock fragments along a fault.
Fault Gouge
Pulverized, powdered rock.
Slickensides
Linear grooves along a fault.
Fold Hinge / Fold Axis
Where ductile deformation (folding) is at its greatest curvature. Always perpendicular to the compression forces.
Fold Limbs
Less curved sections of folded rock layers.
Anticline
Folded rock that arches upwards. A shape. Older rocks are in the center.
Syncline
Folded rock that dips downwards. U shape. Younger rocks are in the center.
Dome
Folded rock formed from anticlines from all sides. Older rocks are in the center.
Basin
Folded rock formed from synclines from all sides. Younger rocks are in the center.
Isostasy
The balance between buoyancy and erosion of continental crust. Thicker parts of the crust are uplifted higher but also plunge further into the mantle.
Principle of Uniformitarianism
The idea that geologic formations are created and repeated in uniform, predictable events. Processes seen today are the same as processes that occurred before. Developed by James Hutton.
"The Grand Canyon was formed by the gradual erosion of rock over millions of years."
Principle of Catastrophism
The idea that geologic formations are created after singular major events.
"The Grand Canyon was formed by a singular massive flood."
Relative Ages
A method of dating rocks based upon the order of formation. A qualitative method that determines older vs younger relationships.
Numerical Ages
A method of dating rocks based upon the years since its formation or metamorphosis. A quantitative method that only works on igneous and metamorphic rocks.
Principle of Original Horizontality
Sediments are deposited in straight, horizontal beds under regular conditions.
Principle of Superposition
Older rock beds are found underneath younger rock beds.
Principle of Lateral Continuity
Strata (rock layers) form horizontally across the Earth's surface. Allows separated strata to be connected.
Principle of Cross-Cutting Relations
Younger features pass through older features. Faults, intrusions, erosion, etc must be younger than the material that is faulted, intruded, or eroded.
Principle of Baked Contacts
Igneous intrusions bake the rock it invades and thus must be younger than the rock it invades.
Principle of Inclusions
Rock fragments intruding another material must always be older than the material enclosing it. Older rock weathers and becomes enclosed by younger rock.
Flow
A layer of magma that covers older layers and does not contain inclusions.
Sill
An igneous intrusion that invades layers of older rock. Contains inclusions.
Species Range
All of the rock layers in which a particular species' fossil can be found.
Index Fossils
Specific species that are diagnostic to a particular time period.
Unconformity
A time gap in the rock record caused by erosion or nondeposition.
Angular Unconformity
Ancient rocks become folded, erode, and young sediments are deposited on top. Ancient sediments are no longer layered horizontally whereas the young sediments are.
Nonconformity
Ancient igneous or metamorphic rocks have eroded and sedimentary rocks have been deposited on top. All beds are parallel.
Disconformity
Ancient sedimentary rock layers are eroded or have a pause in deposition, and much younger sedimentary rock layers are deposited above. Very short time gap.
Isotopes
Elements that have varying numbers of neutrons that affect the stability of the atom.
Stable Isotopes
Isotopes that do not change over time.
Unstable Isotopes
Isotopes that spontaneously, radioactively decay over time.
Radioactive Decay
The process of a radioactive parent isotope decaying and producing a stable daughter isotope.
Half-Life
A known, fixed rate at which the parent isotope decays 50% into the daughter isotope.
Isotope for Archaeological Dating
Carbon-14
Isotopes for Geological Dating
Uranium, Potassium, Rubidium, Samarium.
Closure Temperature
The temperature at which an igneous rock has solidified or a metamorphic rock has metamorphosed, locking in its elements. Radioactive elements begin to decay after temperature is reached.
Age of the Earth
4.57 Ga / 4.57 billion years
Stratigraphic Correlation
The study and connection of different rock layers across the surface of the Earth to create a global geologic column.
How long are Eons?
Hundreds of millions to billions of years.
How long are Eras?
65 to hundreds of millions of years.
How long are Periods?
2 to 70 million years.
How long are Epochs?
Less than 22 million years.
How long was the Hadeon Eon?
4.57 - 3.8 Ga
Hadeon Eon
First Eon of Earth's history. "Hell-like", the Earth was still forming. Its mantle and core cooled and differentiated and much of the surface was covered in magma oceans.
How long was the Archean Eon?
3.85 - 2.5 Ga
Archean Eon
The second Eon of Earth's history. Earth's crust solidified and plate tectonics began to occur. Oceans filled with water. Life first developed in the form of thermophilic bacteria deep underwater.
When did life first evolve?
3.2 Ga / 3.2 billion years ago, in the Archean Eon.
Stromatolites
Alternating layers of cyanobacteria and sediments. Oldest extant (still living) life on Earth.
How long was the Proterozoic Eon?
2.5 Ga - 542 Ma.
Proterozoic Eon
The third eon of Earth's history. Supercontinents assembled and rifted and early life began to develop.
When did Eukaryotes evolve?
~2.7 Ga / in the Proterozoic Eon.
The Great Oxygenation Event
Photosynthetic organisms oxygenated Earth's atmosphere between 2.4 and 1.8 Ga / in the Proterozoic Eon.
When did multicellular life evolve?
~750 Ma / in the Proterozoic Eon.
Rodinia
A supercontinent of the Proterozoic Eon that formed ~1 Ga and rifted ~700 Ma. Precursor to Pangaea.
Snowball Earth
A major shift in Earth's climate in the late Proterozoic that covered the continents in glaciers and froze the oceans. Ended with volcanic activity.
How long is the Phanerozoic Eon?
542 Ma to Present Day
Phanerozoic Eon
The fourth eon of Earth's history. Defined by visible life and the widespread diversification of life in Earth's oceans and landmasses. Carbonate and skeletal material enhance the preservation of these organisms.
Epicontinental Sea
A shallow ocean that forms above lowland continental crust.
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