Earthquakes & Structures

What are Earthquakes

Seismic events caused by the sudden release of strain energy in the Earth's crust, resulting in ground shaking.

Divergent Plates

Resulting in shallow earthquakes

Converget

Wide zone of shallow, intermediate, and deep earthquakes

Transform

Shallow to intermediate earthquakes

Elasticity

The ability for rocks to bend/stretch & return to original shape

Stress

The force per unit applied to a rock (pulling on a rubber band).

Ductile

Rocks that bend/flow like soft metal, happens deep underground.

Brittle

Rocks that break/frature; Happens near surface

Normal (Extensional)

Stress type: Tension (pulling apart)

Movement: Hanging wall moves down in relations to foot wall

Pulling apart a noodle, it goes down the more it’s pulled

Thrust/Reverse Fault (Compressional)

Stress type: Compression (pushing together)

Movement: Hanging wall moves up

Transform (Sliding)

Stress type: Shear (sliding)

Movement: Left or right laterual fault

Seisim Waves

When rocks break, energy is released as waves moving through Earth

P-Wave (Primary waves)

Compressional waves, travels the fastest through ALL physical states of media (solids, liquids, & gas)

S-Waves (Secondary)

Shear waves, travels slower, only travels through solids.

Surface Waves

Moves along the Earth’s surface, travels the slowest but causes the most damage to buildings.

Epicenter

The point on the surface above where the Earthquake starts

Hypocenter Focus

Actual underground location where the rock breaks

Stage 1: Stress building along fault

Deep inside the Earth, tectonic plates constantly move. At the plate boundaries or along faults (cracks in crust), stress builds because of rocks pushing, pulling, or sliding against each other.

Stage 2: Elastic Deformation (strain)

As stress increases, rocks start to deform, bend & stretch without breaking

Stage 3: Rupture/Earthquake

The stress becomes too great for the rocks so they break/slip a long the fault line. The stored energy is realsed as seismic waves.

Stage 4: Aftershake

Smaller quakes can happen as rocks adjust & find a stable position. Can last days, to weeks to months.

Natural Earthquake

When there is a sudden release of strain energy caused by rock rupture (faulting)

Human activities

Induced earthquakes like reservior-induced, deep waste disposal, nuclear explosions, & magnitude.

Structual Geology

The study of how the Earth’s crust is shaped & deformed. Helps understand how rocks bend, break, & move

Deformation

All changes in the original form and/or size of the rockbody. 

Where it happens: Mostly along the plate boundaries where the Earth’s plates collide, move apart, or slide past.

Strike (Trend)

The compass direction of a line made by the intersection of an inclined rock later or fault with a horizontal plane.

Dip

The highest angle of inclination of the surface from a horizontal plane. Includes both angle direction toward which rock is inclined

Anticline

Upfolded or arched rock layers; Oldest rocks in center

Syncline

Downfolded or throughs of rock layers; Youngest rocks in the center

Recumbent (Overturned)

Fold tipped on its side

Plunging

Fold dips into the ground

How is soil formed?

From parent material (the rock it came from) & changes over time due to:

• Climate - Temperature & rainfall

• Topography - Slope/elevation

• Biological activity- Plants, animals, microbes

• Time - The older = more developed

Laterite (soil type)

Warm and wet climate

Rich in aluminum & iron. Was formed in a high/wet tropical areas. High weathered soil that is nutrient poor.

Pedocal

Dry climate. Soil that forms in grassland regions. The climate is drier with less rain. When there's less rain, there's less chemical weathering, less organic material, & soil is more fertile.

Pedalfer

Cool and wet climate. Very fertile, dark brown or black soil. Rich in aluminum and iron oxides .

Flat slopes

Soil can be thicker & more developed. Rainwater moves slowly, allowing infiltration & plant growth. More organic matter builds up

Steep slopes

Soil is thin and easily eroded. Water runs off quickly, carrying away sediment. Less time for soil to form

Relative Dating

The process of determining the chronological order of events in Earth’s history w/o knowing the exact ages in years.

Law of Superposition

In an underformed sequence of sedimentary rocks, oldest rocks are on the bottom

Principle of Original Horizontality

Sediments are deposited horiontally. If layers are tilted/folded, that was after it was deposited.

Principle Lateral Continuty

Sediment layers extend in all directions until they thin out or encounter a barrier or “valley”

Principle of Cross-Cutting Relationships

If 1 geologic feature cuts across another, it’s the youngest of what is cut

Inclusions

Fragments within a rock that are older than the rock itself

Unconformities

Gaps in the rock record that represent missing time.

Angular uncomformity

Tilted rocks + flat rocks = ?

Older layers were deposited & tilted by tectonic forces. It eroded the top off and new horizontal layers deposited on top.

Disconformity

Parallel layers + erosion gap = ?

Both rocks were deposited horizontally, BUT the upper surface eroded after some time before a new sediment was deposited. There’s missing rock record (time gap!)

Line is wavy b/c of eroded surface

Nonconformity

When sedimentary layers are in contact with igneous or metamorphic rocks

Sedimentary rocks marks a huge time gap.

What are fossils?

Traces or remains of ancient life preserved in rocks, usually sedimentary.

Protons

Positively charged particles (found in nucleus_

Neutrons

Neutral particles (no charge, found in nucleus)

Electrons

Negatively charged particles (orbits the nucleus)

Atomic Number

Number of protons (defines the element)
Ex: Carbon = 6

Atomic Mass

Number of protons + neutrons (determines isotope type)

Isotopes

Versions of the SAME element that have the same # of protons BUT different # of neutrons

Radioactive Decay

When an unstable atom’s nucleu changes on its own (spontanous decay)

Alpha Decay

The atoms emits 2 protons + 2 neutrons

The mass decreases by 4, atomic # decreases by 2

Beta Decay

A neutron splits into an electron & proton

The electron is emitted

Atomic mass stays the same & atomic # increases by 1

Electron Capture

The electron combines with a proton to form a nucleus

Atomic mass stays the same, atomic # decreases by 1

Mass Wasting?

The downhill movement of soil, rock, and debris caused by gravity

Driving Force (gravity)

Pulls downhill, the steeper the slope, the stronger the pull

Resisting Forces (friction & strength)

Keeps materials in place & depends on:

Friction between particles

Cohesion (how well the materials stick together)

Vegetation (roots help hold still)

Angle of Response

The momentum angle at when a pile of material remains stable

Rock fall

Loose rock fragments fall straight down through air (cliffs or mountain areas)

Slide

Material moves quickly downhill along a flat or curved surface (landslides)

Slump

Loose material moves down a curved surface

Flow

A mix of soil, water, and rock moves through thick liquid (mudflows)

Creep

Very slow downslope movement, happens gradually

Hydrology

The study of water on Earth- it’s sources, cycle, & effects on land

Hydrologic Cycle

The circulation of Earth’s water supply. Constantly moes through the cycle, changing between liquid, gas, & solid states as it circulates the atmosphere, oceans & lands

Reservior

A place where water is stored (oceans, lakes, groundwater, atmosphere)

Residence Time

Reservior capacity/influx or outflux

(How long water stays in reservior)

Preciptation process

Rain, snow, sleet, hail

Evaportation process

Water changes from liquid to vapor

Infiltration process

Water soaks into the ground. It’s capacity/amount is controlled by:

Intensity/duration of rainfall, prior wetted condition of soil, soil texture (sand, clay, etc.), slope of land (steeper = more runoff), & nature of vegetation cover (plants increase this process)

Running water - Surface water

Streams that transports sediments through erosion & depositon

Dissolved Load

A river's sediment that is carried in solution, consisting of ions and small molecules from minerals and organic matter.

How it works: These materials are invisible & traveled within the water itself as a chemical solution

Suspended load

A river's sediment that is carried within the water column, consisting of larger particles like silt and clay

How it works: It remains above the ground due to turbulence

Bed load

Sediment that is transported along the bottom of a river or stream by the force of flowing water. This type of sediment transport includes larger particles, such as gravel and sand, which are moved through processes like rolling, sliding, and saltation.

Stream competence & Capacity

Streams differ in what & how they can carry depending on speed & volume

Competence

The largest particle size a stream can transport

Controlled by: Stream velocity (speed)

Ex: Fast mountain streams can carry boulders but slow rivers, only silt and clay

Capacity

The total amount (mass or volume) of sediment a stream can transport at once

Controlled by: Stream discharge

Ex: A wide, deep river has a greater ____ than small creek, even at the same velocity

Base level

The LOWEST part of erosion. This is the lowest elevation a stream can erode its channel to.

Ultimate base level

Sea level. The limit for most rivers.

Local or temporary

A lake, resistent rock layer or another river

Channel

The path in which the stream normally flows (usually V-shaped)

Floodplain

Flat area that floods when water overflows

Thalweg

Fastest flowing part of stream

Braided stream

Multi channeled

High slope/steep gradient

Usually fairly shallow & wide

High velocity

Typical of moutain regions

Meandering Stream

Single channeled

Low slope/shallow gradient

Slower flow

Found in plains

Drainage networks

Land area that contributes water to the stream is the drainage basin

Dendritic

Formed by small streams (twigs) that join together to form larger streams (branches), which ultimately converge into a single, main river (the trunk).

Most common type of drainage system

Rectangular

Type of river system where streams and tributaries bend at right angles, forming a grid-like network

Controlled by faults/fractures

Trells

Drainage pattern which develops in folded mountain belts (syncline & anticline) with alternating layers of hard and soft rock.

Radical

Formed by running water flowing down mountain peak

(Like a volcano is acne and the water is going down it)

Groundwater

Fills the pores of soils & cracks in rock beneath the surface. Largest reservior of freshwater.

Zone of saturation

Area in soil/below surface in which all pores are filled with water. Where underground water exists

Water table

Boundary between saturated/unsaturated zones. Shape usually mimics the land’s surface. Varies seasonably & it’s depth depends on rainfall, season, & soil type

Capillary Fringe

Extends upwards from the water table. Water is held by small pores by surface tension

Zone of aeration/vadose zone

Area above the water table in which the pores are not filled with water. Can’t pump water from here.

Gaining Stream

Water from groundwater seeping into streambed