UCSB Earth 20 Midterm

Processes

Physical, chemical, and biological ways in which events

affect Earth's surface

Internal processes

Come from forces within Earth (plate tectonics) and result of internal energy from earth

External processes

Come from forces on Earth's surface (atmospheric effects, energy from the Sun)

Hazard

Natural process or event that is a potential threat to human life or property

Disaster

Hazardous event that occurs over a limited time in a defined area

Criteria for disaster

1) Ten or more people killed

2) 100 or more people affected

3) State of emergency is declared

4) International assistance is requested

Catastrophe

Massive disaster that requires significant amount of money or time to recover

Geologic Conditions

Govern the type, location, and intensity of natural processes

Tectonic cycle

Refers to large scale processes that deform Earth's crust and produce landforms. Driven by forces within Earth (internal energy). Involves the creation, destruction, and movement of tectonic plates

Rock cycle

Rocks are aggregates of one or more minerals. It is the recycling of earth materials and rocks are classified according to how they were formed in the rock cycle

Igneous rocks

Form from crystallization of magma

Sedimentary rocks

Rocks are weathered into sediment by wind and water and deposited sediment undergoes lithification

Metamorphic rocks

Rocks are changed through extreme heat, pressure, or chemically active fluids

Hydrologic cycle

Movement of water between atmosphere and oceans and continents driven by solar energy

Processes of hydrologic cycle

Evaporation, precipitation, surface runoff, and subsurface flow

Residence time

Estimated average that a drop of water spends in any compartment

Biogeochemical cycle

Transfer of chemical elements through a series of reservoirs (Atmosphere, lithosphere, hydrosphere, biosphere)

Forecast vs Prediction

Prediction: Specific date, time, and magnitude of event

Forecast: Range of probability for event

Risk Analysis

Risk = (probability of event) x (consequences)

Consequences

damages to people, property, economics, etc.

Acceptable risk

the amount of risk that an individual or society is willing to take

Geoid

The shape that the surface of the oceans would take under the influence of Earth's gravity and rotation alone

Outer core

Liquid, 2,000 km (1,243 mi.) in thickness • Composition similar to inner core • Density (10.7 g/cm3)

Inner core

Solid, High Temperature, Composed of iron (90 percent by weight) and other elements (sulfur, oxygen, and nickel)

Mantle

Solid, 3000km thick, Composed of iron- and magnesium-rich silicate rocks

Crust

Outer rock layer of the earth, Moho discontinuity (separates lighter crustal rocks from from more dense mantle)

Lithosphere

cool, strong outermost layer of Earth (crust and upper mantle) with crust embedded on top

Asthensophere

Below lithosphere, Hot, soft/ductile slowly flowing layer of weak rock. Higher water content and hotter

Continent crust

Less dense, thicker, and older and typically composed of granite

Oceanic crust

More dense, younger, thinner and typically composed of basalt

Convection

Earth's internal heat causes magma to heat up and become less dense.

-less dense magma rises

-cool magma falls back downward

P-waves

travels fastest, compressional waves, can travel through solids, liquids and gasses

S-waves

Secondary waves, shearing waves (vertical or horizontal) move up/down, doesn't move through liquid

Surface waves

travel along the Earth's surfaces

Plate tectonics

Large-scale geologic processes that deform Earth's lithosphere

Seafloor spreading

Explained mechanism for plate tectonics. At mid-ocean ridges new crust is added to edges of lithospheric plates

Divergent boundary

A plate boundary where two plates move away from each other during seafloor spreading

Convergent boundary

A tectonic plate boundary where two plates collide, come together, or crash into each other.

Subduction zone

The region where oceanic plates sink down into the asthenosphere.

Transform boundary

A plate boundary where two plates move past each other in opposite directions

Paleomagnetism

The study of magnetism of rocks at the time their magnetic signature is formed, dating method based on Earth's shifting magnetic pole. Iron-bearing minerals orient themselves parallel to the magnetic field at the critical temperature known as Curie Point

Magnetic stripes

Areas of "regular" and "irregular" magnetic fields and were parallel to oceanic ridges. Sequences of stripe width patterns matched the sequences established by geologists on land

Seafloor Topography and Age

Ocean floor depths increase systematically with seafloor age, moving away from mid-ocean ridges

Hot spots

Volcanic centers resulting from hot materials deep in the mantle

Ridge push

A gravitational push away from crest of mid-ocean ridges

Slab pull

Occurs when cool, dense ocean plates sink into the hotter, less dense asthenosphere

-weight of the plate pulls the plate along

Which layer of the Earth contains soft/ductile slowly flowing weak rock?

Asthenosphere

Earthquake

The sudden slip on a fault (release of elastic energy), and the resulting ground shaking and radiated seismic energy caused by the slip

Faults

Plane of weakness in Earth's crust, Semiplanar fracture or fracture system where rocks are broken and displaced.

Footwall

block below the fault plane, miner would stand here

Hanging wall

block above the fault plane, hang a lantern here

Faulting

Process of fault rupture,

• Similar to sliding one rough board past another

• Slow motion due to friction

• Stresses the rocks along the fault

• Rocks rupture and displaced when stress exceeds strength of rocks

Stress

Force that results from plate tectonic movements

• Tensional

• Compressional

• Shearing

Strain

Change in shape or location of the rocks due to stress

Normal dip-slip

• Vertical motion

• Hanging wall moves down relative to footwall

Reverse dip-slip

• Vertical motion

• Hanging wall moves up relative to footwall

Strike slip

Crustal moves in horizontal direction

Blind faults

not visible on satellite images; faults that do not break the Earth's surface

Types of Plate Boundaries and Stress

• Divergent = Extensional Stress >> Normal Faulting • Convergent = Compressional Stress >> Thrust or Reverse Faulting

• Transform = Shear Stress >> Strike-Slip Faulting

Elastic rebound theory

Gradual build up of stress along a fault until the strength of the rock is exceeded, resulting in a release of energy in the form of an earthquake

Epicenter

Location on surface above the rupture

Focus (hypocenter)

Point of initial breaking or rupturing.

Seismic waves

Caused by the release of energy due to earth quakes

Love wave

horizontal ground shaking

Seismic Waves and Wave Attributes

• Amplitude: height of wave

• Wavelength: distance between successive wave peaks • Period: time between wave peaks (= 1/frequency)

• Frequency: number of wave peaks in one second

Tectonic creep

Gradual movement such that earthquakes are not felt

• Can produce slow earthquakes, Also called fault creep

Ritcher scale

Local magnitude, Depends on where it is located • Specific to only one location.

-recorded with seismograph, and not even used any more

Moment magnitude scale

Absolute size of earthquake (compare multiple locations)

• Measurement of actual energy released

• Determined from area of rupture, amount of slippage, and the rigidity of the rocks

Seismic moment

• Current method of measuring earthquake size

• Relies on the amount of movement along the fault that generated the earthquake

Modified Mercalli Scale

Qualitative scale (I-XII) based on damage to structures and people's perceptions

-can vary from country to country and with same magnitude earthquakes

Shake maps

Use high-quality seismograph data to show areas of intense shaking Useful in crucial minutes after an earthquake

- Show emergency personnel where greatest damage likely occurred

- Locate areas of possible damaged gas lines and other utilities

Magnitude

is a measure for the size or energy release of an earthquake

Intensity

is a measure for the degree of shaking

Depth of focus

Depth of earthquake influences the amount of shaking

-Deeper earthquakes cause less shaking at the surface

Attenuation

loss of energy with distance from source

Direction of rupture

Direction that the rupture moves along the fault influences the shaking

Triangulation

finding the epicenter by using at least three different seismic stations

Degree of consolidation

• Seismic waves move faster through consolidated bedrock

• Move slower through unconsolidated sediment

• Move slowest through unconsolidated materials with high water content

Material amplification

Energy is transferred to the vertical motion of the surface waves

Periods of Buildings and Responses of Foundations

Buildings have natural frequencies and periods

• Periods of swaying are about 0.1 second per story

-30-story building sways at about 3 seconds per cycle

• Building materials affect building periods

- Flexible materials (wood, steel) à longer period of shaking

- Stiff materials (brick, concrete) à shorter period of shaking

Velocity of seismic waves

Depends on material through which it is moving

- Faster through hard rocks/materials

- Slower through soft rocks/materials

Intraplate Earthquakes

Earthquakes that occur within plates, often smaller M but can cause damage Bc lack of preparedness and the waves can travel greater distances through stronger continental rocks

Primary Earthquake effects

Ground shaking and surface rupture

Secondary Earthquake effects

Liquefaction of ground

• Regional changes in land elevation • Landslides

• Fire

• Tsunamis

• Disease

Ground rupture

Displacement along the fault causes in surface

Shaking

• Causes damage to buildings, bridges, dams, tunnels, pipelines, etc.

• Measured as ground acceleration

• Buildings may be damaged due to resonance

Liquification

A near-surface layer of water-saturated sand changes rapidly from a solid to a liquid

• After shaking stops, ground re-compacts and becomes

solid

Regional Changes in Land Elevation

Vertical deformation linked to some large

earthquakes

• Regional uplift

• Subsidence

Landslides

• Most closely linked natural

hazard with earthquakes

• Earthquakes are the most

common triggers in

mountainous areas

Earthquake fires

• Shaking and surface displacements

• Cause power and gas lines to break and ignite

• Knock over appliances, such as gas water heaters, and leaks ignite

Mineral Resources (Earthquakes)

Faulting may be responsible for accumulation or

exposure of economically valuable minerals

• Mineral deposits develop along fault cracks called

veins

• Can be the source of precious metals

Earthquakes Caused by Human Activity

• Loading Earth's crust, as in building a dam and

• Injecting liquid waste deep into the ground through

disposal wells

• Creating underground nuclear explosions

Which properties characterize convergent plate boundaries?

Compressional stress & Thrust or reverse faulting

Which is the most accurate way to estimate the magnitude of an earthquake?

Moment magnitude Correct

Which type of seismic waves travel the fastest?

P-waves

Which one of the following is true regarding how local geologic conditions affect earthquakes?

Seismic waves move the slowest through unconsolidated sediments with high water content

Which properties characterize normal dip-slip faults?

Vertical motion & Hanging wall moves down relative to footwall

How did geologists discover that the outer core had to be liquid?

S-waves do not propagate through liquids, and created a "shadow zone"

Tsunami

Caused by a sudden vertical displacement of ocean water

Tsunamis are triggered by

• Large earthquakes that cause uplift or subsidence of sea floor

• Underwater landslides

• Volcano Flank Collapse

• Submarine volcanic explosion

• Asteroids (mega-tsunamis)