Exam 2 Study Guide

_________________ stress is associated with reverse and thrust faults.

Compressional

____________ are upwarped circular displacements of rocks.Origins: broad upwarps in basement rock & magma intrusions (laccoliths)

Domes

Each unit of increase in Richter magnitude equates to roughly a ____-fold increase in the energy released (this makes each level 10 times stronger than the previous level).

32

____________ usually arise by upfolding, or arching, of sedimentary layers.

Anticlines

______________ are downwarped circular displacements of rocks. Origins: broad down-warps caused by large accumulations of sediment (increased weight results in subsidence & giant meteorite impacts)

Basins

Squeezes rocks, making them stronger and harder to break.

Confining pressure

_____________ is a term that refers to the changes in the shape or position of a rock body in response to differential stress.

Deformation

Most faults are locked except for brief, abrupt movements. Faults do not slip all at once. Initial slip begins at hypocenter and propagates along the fault surface. Slippage adds strain to adjacent sections, may trigger more slippage. Slippage mainly travels in one direction. What terms do these words describe?

Fault Rupture and Propagation

____________forms fault scarps; occurs in Eqs > M 6.5. Example: Wasatch Fault Zone. Also called fault displacement.

Fault rupture

________ are fractures in rocks, along which displacement has taken place. Displacement parallel to fracture.

Faults

_____________ are fractures in Earth's crust where the rocks on one side of the fault are displaced relative to the rocks on the other side.

Faults

_______________are fractures in Earth's crust where the rocks on one side of the fault are displaced relative to the rocks on the other side.

Faults

__________________ are common features of deformed sedimentary rocks that provide evidence that rocks can bend without breaking.

Folds

___________ is caused by seismic waves radiating from subsurface rupture. Ground accelerations occur near the epicenter of a large EQ can approach and sometimes, exceed the acceleration of gravity (1g) = 9.8 m/sec. Result: can throw objects into air; building collapse. Leading cause of economic damage and human casualties during EQs. Regions within 20 to 50 kilometers of the epicenter will experience about the same intensity of _____________________. However, destruction varies considerably, mainly due to the nature of the ground on which the structures are built.

Ground shaking

__________ is a measure of the amount of ground shaking at a particular location, based on observed property damage.

Intensity "Effects"

Amount of structural damage attributable to earthquake vibrations depends on

Intensity and duration of the vibrations Nature of the material upon which the structure rests Design of the structure

At deeper crustal depths, rocks deform by ______________.

ductile flow

A __________ is some natural or human-induced process that has the potential to cause loss (human or infrastructure).

hazard

Most crustal deformation occurs along___________.

plate boundaries

A form of energy that causes the material that transmits them to shake. Released by earthquakes, are huge amounts of stored-up energy in large earthquakes.

seismic waves

The records obtained from seismographs is called____________.

seismograms

Tools used to measure earthquakes.

seismographs/seisometers

The study of earthquake waves is called___________.

seismology

Differential stress can also cause _____________. This involves the movement of one part of a rock body past another.

shear stress

____________ generally causes greatest damage to structures. Triggered by ground shaking (~ M 4.0 or greater).

Landslides & ground subsidence

____________refer to the two sides of a fold.

Limbs

Richter Scale Calculation Example: What would be the difference in the measure of ground motion (magnitude) between a 7.5 and a 3.5 earthquake?

Log 4 = 10,000

A type of surface wave that's motion is essentially the same as an S wave but NO VERTICAL displacement takes place. Its horizontal shaking is also very damaging to structural foundations; is the most damaging to buildings.

Love Waves

__________ is a quantitative measurement that relies on data gleaned from seismic records to estimate the amount of energy released at an earthquake's source.

Magnitude "Size"

__ waves are "push/pull" waves; they momentarily push (compress) and pull (stretch) rocks in the direction the wave is traveling. This wave motion is similar to that generated by human vocal cords are they move air back and forth to create sound. Solids, liquids, and gases resist stresses that change their volume when compress and, therefore, elastically spring back once the stress is removed. These waves can travel through all these materials. Travel 6 at km/sec (granitic crust).

P

Which wave hits first, according to a typical seismogram?

P wave

A type of surface wave that causes the ground to move up and down, similar to the movement of Ocean waves. Move both vertically and horizontally in vertical plane in direction of wave travel. Sets up rolling/elliptical motion in ground. Motion dissipates with increasing depth beneath surface.

Rayleigh Waves

____________ occur where crustal rocks are shortened and thickened.

Reverse and thrust faults

______________ faults are associated with subduction zones and continental collisions.

Reverse and thrust faults

The _____________ is calculated by measuring the amplitude of the largest seismic wave recorded on a seismogram.

Richter Scale

___ waves "shake" the particles at right angles to their direction of travel. Temporarily change the shape of the material that transmits them. Liquids and gases will not transmit this type of wave; can only travel through solid material. ) Travel at ~ 3.6 km/sec (granitic crust). Greater amplitude (slightly) than the other type of body wave.

S

Which body wave has the greatest amplitude, as viewed on a seismogram?

S wave

_______ are the rhythmic sloshing of water in lakes, reservoirs, and enclosed basins. Caused by ground shaking from great earthquakes

Seiches

Reducing EQ Risk

Seismic hazard in a region cannot be changed No way to prevent EQs. Seismic Risk can be reduced to minimize our exposure Hazard Characterization: Seismic research projects Historic seismicity Paleoseismic studies Better understanding of both seismic hazards and associated risks Land-use policies - restrict certain types of land use over localized hazard areas Earthquake Engineering - building codes Emergency Response Real-Time Earthquake Warning (30 - 80 seconds)

_______________ are seismic ground shaking and tectonic deformation measured as MAGNITUDE and FREQUENCY at some specific location.

Seismic hazards

___________ is damage that can be expected for a specific region due to hazard occurrence. Measured: dollar loss/year. Depends on Seismic hazard Region's exposure to seismic damage (population, buildings, infrastructure). Region's fragility = vulnerability of buildings to EQ hazards.

Seismic risk

____________________ is changes in the shape or size of a rock body caused by differential stress

Strain

_____________occur where large segments of Earth's crust slip horizontally past each other.

Strike-slip faults

Which wave type appears last? These waves retain their maximum amplitude longer and as a result cause greater ground shaking and more property damage.

Surface waves

_____________are usually down-folded or troughs of sedimentary rock layers.

Syncline

________________ is the subsidence or uplift caused by faulting.

Tectonic deformation

_________________ stress is associated with normal faults.

Tensional

_________ are caused by either a vertical displacement of a slab of seafloor along a thrust fault on the ocean floor, OR a large submarine landslide triggered by an earthquake.

Tsunami

How is Seismic risk determined?

Use historic data, occurrence, intensity Evaluate related risk factors, e.g. landslide potential Risk maps used to develop regional planning and building codes

An __________________ is an imaginary surface that divides a fold symmetrically.

axial plane

Crystalline igneous rocks generally experience what type of deformation?

brittle deformation

Lower temperature rocks exhibit what type of deformation?

brittle deformation

Rocks that break into smaller pieces exhibit ___________. Stress has broken the chemical bonds that hold a material together.

brittle deformation

At shallow depths, rocks exhibit __________as a result of differential stress.

brittle fracture

Most folds result from _________________ stresses that shorten and thicken the crust.

compressional

Differential stress that squeezes a rock mass as if placed in a vise is known as ___________.

compressional stress

When stress is applied uniformly in all directions, it's called _____________.

confining pressure

When stress is applied unequally in different directions, it is termed __________.

differential stress

Faults in which movement is primarily parallel to the inclination of the fault surface are called _______________.

dip-slip faults

Shear at deeper crustal depths causes rocks to ___________, usually along the shear zones. They are changed by ____________________.

distort ductile flow

Forces applied over a long period of time generally result in what type of deformation?

ductile deformation

Higher temperature rocks exhibit what type of deformation?

ductile deformation

Sedimentary and metamorphic rocks with zones of weakness generally experience what type of deformation?

ductile deformation

_________________ is a type of solid-state flow that produces a change in the shape of an object without fracturing; it bends. The rock returns to nearly its original size and shape when the stress is removed.

ductile deformation

Changes that result from ____________ are recoverable; the rock will snap back to nearly its original size and shape when the stress is removed.

elastic deformation

The point on Earth's surface directly above the hypocenter

epicenter

Some sections of the San Andreas Fault exhibit slow, gradual displacement known as ______________, which occurs without the accumulation of significant strain. These sections of the fault produce little seismic shaking

fault creep

The amount of displacement on the fault surface is called ________________.

fault slip

Fractures in Earth's crust

faults

Earthquake fault displacement can sever gas and electrical lines, resulting in _______. Numerous can break out at the same time.

fires

The location where slippage begins.

focus/hypocenter

A ___________ is a line drawn down the points of maximum curvature of each layer.

fold axis

Deformation involves _______________.

force

Small earthquakes that often precede major earthquakes by days, or in some cases, by several years

foreshocks

Tension at shallow depths cause rocks to ________________. These rocks exhibit ____________.

fracture and pull apart brittle fracture

What are the primary hazards of an earthquake?

ground shaking tectonic deformation fault rupture

Geologists identify the rock surface immediately above the fault as the _______________________ and the rock surface below as the _______________________.

hanging wall block footwall block

When tectonic forces cause up-warping of the crust, rocks near the surface are stretched and pulled apart, forming fractures called ___________.

joints

The intense shaking of an earthquake can cause loosely packed water-logged materials, such as sandy stream deposits or fill, to be transformed into a substance that acts like fluids. This phenomenon is known as ____________.

liquefaction

What are the secondary hazards of an earthquake?

liquefaction landslide fire tsunami seiche

Richter used a _______________ to express magnitude, in which a tenfold increase in wave amplitude corresponds to an increase of 1 on the magnitude scale.

logarithmic scale

The plate boundary between a subducting slab of oceanic lithosphere and the overlying plate is called a _________. Produce the majority of Earth's most powerful earthquakes.

megathrust fault

The _______________ measures the total energy released during an earthquake and is calculated by determining the average amount of slip on the fault, the area of the fault surface that slipped, and the strength of the faulted rock.

moment magnitude

Shear at shallow depths causes ____________ in crustal blocks along faults. These rocks exhibit ______________.

offsets brittle fracture

A ______________ is actual exposure of something of human value to a hazard. Combination of probability (hazard) and loss (lives and/or dollars) It is expressed as the probability that a certain level of loss will be achieved. Ex: 10% probability that 5000 people will be killed & over $10 billion dollars in damage will result from ground shaking.

risk

Compression at shallow depths causes ____________and rocks exhibit _____________________.

shortening brittle fracture

Compression at deeper crustal depths causes ____________ and rocks deform by ______________.

squeezing and folding ductile flow

What term is used by geologists to describe the forces that deform rocks.

stress

Tension at deeper crustal depths causes rocks to ________________. These rocks are deformed by ________________.

stretch and elongate ductile flow

Large ______________ faults may transform plate boundaries.

strike-slip

The wave type that travels in the rock layers just below Earth's surface. Cause greatest destruction.

surface waves

Differential stress that pulls apart or elongates rock bodies is known as ___________________.

tensional stress

Large strike-slip faults, like the San Andreas Fault, are called __________________ when they form plate boundaries.

transform faults

________________ stress is associated with strike-slip faults.

Shear

Each unit of Richter magnitude increase corresponds to a ______-fold increase in wave amplitude and a 32-fold energy increase.

10

The Richter Scale is logarithmic. This means it increases by a power of _______ for each step up.

10

The ____________________ was developed using California buildings as its standard. Assigns a number from 1-12 to an earthquake based on the damage done.

Modified Mercalli Intensity scale

_____________ are large, step-like folds in otherwise horizontal sedimentary strata

Monoclines

____________ faults are associated with divergent plate boundaries, mainly seafloor spreading centers, and continental rifting.

Normal

____________ occur where the crust is stretched and elongated

Normal faults