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Deformation of Rocks

Why study rock deformation?Why study rock deformation?11.1 What do deformed rocks look like?11.1 What do deformed rocks look like?11.2 How are resources related to geologic 11.2 How are resources related to geologic structures?structures?11.3 Why do rocks deform?11.3 Why do rocks deform?11.4 How do we know ... why some rocks break and 11.4 How do we know ... why some rocks break and others flow?others flow?11.5 How do geologic structures relate to stress, 11.5 How do geologic structures relate to stress, strain, and strength?strain, and strength?11.6 How does strength vary in the lithosphere?11.6 How does strength vary in the lithosphere?11.7 How do earthquakes relate to rock deformation?11.7 How do earthquakes relate to rock deformation?11.8 How are earthquakes measured?11.8 How are earthquakes measured?11.9 Why are earthquakes destructive?11.9 Why are earthquakes destructive?

Earthquakes represent a powerful and violent Earthquakes represent a powerful and violent forceforceEarthquakes are also integral in the formation Earthquakes are also integral in the formation of valuable economic resourcesof valuable economic resources–– Mineral deposits contain such things as gold and Mineral deposits contain such things as gold and

copper copper –– commonly form in areas of bent and commonly form in areas of bent and contorted rockcontorted rock

–– MetalMetal--rich fluids move through cracks and fractures rich fluids move through cracks and fractures as do migrating oil and natural gasas do migrating oil and natural gas

Why study rock deformation?Why study rock deformation?

Objectives: In this chapter you willObjectives: In this chapter you will–– observe and describeobserve and describe the types of deformation the types of deformation

visible at Earthvisible at Earth’’s surface.s surface.–– understand the relationship between deformation understand the relationship between deformation

and the forces that drive it.and the forces that drive it.–– learn the causes and effects of earthquakeslearn the causes and effects of earthquakes..

Why study rock deformation?Why study rock deformation?

11.1 What do deformed rocks look like?11.1 What do deformed rocks look like?

Describing the Describing the orientationorientation of rocks of rocks –– tilted or tilted or dipping bedsdipping beds–– StrikeStrike: the compass orientation of a line formed by : the compass orientation of a line formed by

the intersection of an imaginary horizontal line with the intersection of an imaginary horizontal line with the dipping bedthe dipping bed

–– Dip:Dip: the angle between the imaginary horizontal the angle between the imaginary horizontal plane and the inclined rock layerplane and the inclined rock layer

Visualizing strike and dipVisualizing strike and dip11.1 What do deformed rocks look like?11.1 What do deformed rocks look like?

Fig 11.2


Describing folded rocksDescribing folded rocks–– LimbsLimbs: the two dipping sides of a fold: the two dipping sides of a fold……–– Hinge lineHinge line: where the dipping limbs join: where the dipping limbs join……–– Plunging foldPlunging fold: when the hinge line plunges : when the hinge line plunges

downward into the grounddownward into the ground……–– AnticlineAnticline: a folded structure that arches upward in : a folded structure that arches upward in

the center (limbs dip away from hinge line)the center (limbs dip away from hinge line)……–– SynclineSyncline: a folded structure that arches down in : a folded structure that arches down in

the center (limbs dip in towards hinge line)the center (limbs dip in towards hinge line)


Fig 11.3

Visualizing folded rocksVisualizing folded rocks

Remember “A”for anticline


Fig 11.4 top

Visualizing folded rocks Visualizing folded rocks Centralia Coal Mine 2005 field trip—looking south

Steeper dip here

Less steep dip here—we are looking at part of a syncline!

More dipping beds—Beach #4 on the Olympic Coast—noteangular unconformity!

11.1 What do deformed rocks look like?11.1 What do deformed rocks look like?Visualizing folded rocksVisualizing folded rocks

Fig 11.4 mid-bottom


Fig 11.4 bottom left

Visualizing folded rocksVisualizing folded rocks


Visualizing folded rocksVisualizing folded rocks Fig 11.4 bottom right


Describing broken rocks Describing broken rocks –– faultsfaults–– FootwallFootwall: the rock below the fault plane: the rock below the fault plane–– Hanging wallHanging wall: the segment of rock above the fault : the segment of rock above the fault

planeplane……–– DipDip--slipslip: motion along a fracture that is primarily : motion along a fracture that is primarily

vertical displacement along the dipvertical displacement along the dip--plane surfaceplane surface……–– StrikeStrike--slipslip: motion along a fault that results in rock : motion along a fault that results in rock

displacement in a compass directiondisplacement in a compass direction……–– ObliqueOblique--slip faultslip fault: a combination of dip: a combination of dip-- and and

strikestrike--slip displacementsslip displacements


Visualizing broken rocksVisualizing broken rocks

Fig 11.7

The footwall and hanging wall convention is an old miner’s term referring to the rock under one’s feet, and the wall where you would hang your lamp.


Visualizing faults Visualizing faults –– a normal (dipa normal (dip--slip) fault, one where slip) fault, one where the hanging wall goes down relative to the footwallthe hanging wall goes down relative to the footwall

Fig 11.8


Visualizing faults Visualizing faults –– a reverse (dipa reverse (dip--slip)slip) fault, one where fault, one where the footwall goes down relative to the hanging wallthe footwall goes down relative to the hanging wall

Fig 11.8


Visualizing faults Visualizing faults ––thrust fault, a lowthrust fault, a low--angle (<45angle (<45oo) ) reverse (dipreverse (dip--slip)slip) faultfault

Fig 11.8


Visualizing faults Visualizing faults

strikestrike--slip faultsslip faults

&&

obliqueoblique--slip slip faultsfaults

Fig 11.8

11.3 Why do rocks deform?11.3 Why do rocks deform?

Rocks strain when stress exceeds strengthRocks strain when stress exceeds strength–– Stress:Stress: a force applied to a given area (Section 6.3)a force applied to a given area (Section 6.3)–– StrainStrain: the measurable rock deformation resulting : the measurable rock deformation resulting

from stressfrom stressThree types of stress and strainThree types of stress and strain–– Compressive stress Compressive stress –– results in shortening strainresults in shortening strain–– Tensional stress Tensional stress –– results in elongation strainresults in elongation strain–– Shear stress Shear stress –– results in shear strain results in shear strain

11.3 Why do rocks deform?11.3 Why do rocks deform?Fig 11.13

11.3 Why do rocks deform?11.3 Why do rocks deform?

Faulting, folding, and flowing are strainFaulting, folding, and flowing are strain

Fig 11.14

Here, in this experiment using layered sand, we can clearly see the strain resulting from applied stress.

11.3 Why do rocks deform?11.3 Why do rocks deform?Fig 11.15

A similar experiment using wax layers, which tend to bend before they break as a result of stress. Folded structures form as a result of stress. We also see flow and faulting under continued stress.

StressStress = magnitude of a force applied over a given = magnitude of a force applied over a given areaareaStrainStrain = measure of deformation that results from = measure of deformation that results from said stress.said stress.Rock strengthRock strength = amount of stress that a material = amount of stress that a material can endure before it strains.can endure before it strains.When When applied stress exceeds the strengthapplied stress exceeds the strength of a rock, of a rock, the rock the rock deformsdeforms by by folding, faulting, or flowingfolding, faulting, or flowing. . Compressive stressCompressive stress shortens rocks parallel to the shortens rocks parallel to the stress, whereasstress, whereas tensiontension elongates them. elongates them. Shear stressShear stress moves materials in opposite directions moves materials in opposite directions without shortening or lengthening.without shortening or lengthening.

11.3 Why do rocks deform?11.3 Why do rocks deform? 11.4 How do we know ... why some rocks break 11.4 How do we know ... why some rocks break and others flow?and others flow?

Some rock types and their strength at surface conditions

Weak materials such as Weak materials such as rock salt and glacial ice flow rock salt and glacial ice flow under less extreme under less extreme conditionsconditions

11.4 How do we know ... why some rocks 11.4 How do we know ... why some rocks break and others flow?break and others flow?

More brittleMore brittle——joints, faultsjoints, faults

More ductileMore ductile——plastic plastic deformationdeformation

Near surface (shallow)Near surface (shallow)

Deeper Deeper high pressure at depth high pressure at depth inhibits fracturing and inhibits fracturing and high temperature lowers high temperature lowers rock strengthrock strength

11.5 How do geologic structures relate 11.5 How do geologic structures relate to stress, strain, and strength?to stress, strain, and strength?

Fig 11.21 top

Tapestry of Time and Terrain

Tapestry—The Great Basin

Brittle faults/jointsBrittle faults/joints form form closeclose to the surface; to the surface; plasticplastic flowflow occurs at deeper levelsoccurs at deeper levels ((high pressure high pressure inhibits fracturing and high temperature lowers rock strength)inhibits fracturing and high temperature lowers rock strength)..CompressionCompression shortens & thickens crust by producing shortens & thickens crust by producing folds, reverse faults, & thrust faults in shallow rock, & folds, reverse faults, & thrust faults in shallow rock, & plastic flow in deeper rock.plastic flow in deeper rock.TensionTension elongates and thins crust by movement on elongates and thins crust by movement on normal faults in shallow rocks and taffynormal faults in shallow rocks and taffy--like stretching like stretching of plastic rocks at deeper levels.of plastic rocks at deeper levels.Folds form by Folds form by plastic flowplastic flow in deep crust but also in deep crust but also develop at and near the surface in sedimentary rocks develop at and near the surface in sedimentary rocks where bending of thin layers and slippage along where bending of thin layers and slippage along layers takes place.layers takes place.

11.5 How do geologic structures relate to 11.5 How do geologic structures relate to stress, strain, and strength?stress, strain, and strength?

The significance of composition and crust thicknessThe significance of composition and crust thickness–– Mantle rockMantle rock under oceanic crust is probably dry, under oceanic crust is probably dry,

whereas whereas continental continental lithosphericlithospheric mantlemantle contains contains water and waterwater and water--bearing minerals. bearing minerals.

–– The wetter continental crust is The wetter continental crust is very weak below ~15very weak below ~15kmkm in contrast to the same depth of dry mantle in contrast to the same depth of dry mantle under oceanic crust at that depth. Continental under oceanic crust at that depth. Continental lithosphere becomes weaker below 12lithosphere becomes weaker below 12––15 km while 15 km while oceanic lithosphere becomes stronger until about oceanic lithosphere becomes stronger until about 40 km.40 km.

11.6 How does strength vary in the 11.6 How does strength vary in the lithosphere?lithosphere?

Fig 11.27

11.7 How do earthquakes relate to rock 11.7 How do earthquakes relate to rock deformation?deformation?

Earthquakes in the field, as in lab simulations, absorb stress up to a finite limit and then release it when they break. It should be no surprise that earthquakes line up along the strike of a fault (left) as well as along the dip direction of the fault plane in cross section (right).

Fig 11.28


Motion along faults: Note the displacement in the highway (left) of a right-lateral strike-slip fault (the farther block moved to the right relative to the closer one), and the fault scarp (right) on the footwall of a normal dip-slip fault.


Fig 11.30

Fault motion without earthquakes – some faults are soweak that little energy is stored from stress. Instead the fault “creeps” through small increments of strain.

Fig 11.31

Elastic reboundalong the Hayward fault in California.

Elastic rebound is a “bend-bend, break, snap-back”perspective.

Not possible to know how much bend a given interval can take.


ForeshocksForeshocks, , mainshockmainshock, , aftershocksaftershocks–– ForeshocksForeshocks are a (or groups of) small displacement(s) that are a (or groups of) small displacement(s) that

occur prior to the main shockoccur prior to the main shock……–– MainshockMainshock is the is the ““main event,main event,”” the large release of energy the large release of energy

along the stressed systemalong the stressed system……–– AftershocksAftershocks are small displacements that occur after the are small displacements that occur after the

mainshock. Often these occur by the hundreds, which while mainshock. Often these occur by the hundreds, which while usually weak, often hamper relief effortsusually weak, often hamper relief efforts……

ForeshocksForeshocks are not useful indicators in predicting are not useful indicators in predicting earthquakes as there is no way to tell a foreshock (as earthquakes as there is no way to tell a foreshock (as a portent of impending rupture) from a lone, small a portent of impending rupture) from a lone, small earthquake.earthquake.


Fig 11.32

Plot of aftershocks along a fault system in Alaska. Aftershocks may stay in the mainshock region, or may transfer to adjoining faults as stresses change and adjust.

Podcasts

http://www.npr.org/templates/story/story.php?storyId=124210430 Walter Mooney on NPR re Chilean quake of 2/27/2010http://www.npr.org/templates/story/story.php?storyId=90694392 Walter Mooney, NPR, on aftershocks—China quake May 2008http://earthquake.usgs.gov/earthquakes/recenteqsww/index.php?old=world.html world quakes

google: PNSN Pacific Northwest seismic network

11.7 How do earthquakes relate to rock 11.7 How do earthquakes relate to rock deformation? deformation? Recap!!!Recap!!!

Earthquakes result from motion along faults.Earthquakes result from motion along faults.Earthquakes = brittle failure of rockEarthquakes = brittle failure of rock (hence occur in the (hence occur in the upper crust where temperature and pressure are relatively upper crust where temperature and pressure are relatively low)low)……Not all motion on faults produces earthquakes; rocks can Not all motion on faults produces earthquakes; rocks can creep along faults if the fault is too weak to store up the creep along faults if the fault is too weak to store up the energy of prolonged stressenergy of prolonged stress……Elastic rebound theoryElastic rebound theory explains deformation before and explains deformation before and during earthquakes as brittle failure following during earthquakes as brittle failure following accumulation of elastic strainaccumulation of elastic strain……Foreshocks and aftershocksForeshocks and aftershocks are smaller earthquakes are smaller earthquakes that occur before and after the main earthquake.that occur before and after the main earthquake.

11.8 How are earthquakes measured?11.8 How are earthquakes measured?

IntensityIntensity –– a measure of the violence of an a measure of the violence of an earthquake. The humanearthquake. The human--realized effects such as realized effects such as damage to structures and secondary effects like damage to structures and secondary effects like landslideslandslides……Mercalli scaleMercalli scale –– made by Giuseppe Mercalli (c. 1902) made by Giuseppe Mercalli (c. 1902) and runs from a low of and runs from a low of II to a high value of to a high value of XIIXII–– Current revision is the Modified Mercalli scale Current revision is the Modified Mercalli scale –– Intensities are commonly plotted on maps with intensity Intensities are commonly plotted on maps with intensity

contourscontours–– Can be used to determine intensities of historic earthquakes Can be used to determine intensities of historic earthquakes

through newspapers, diaries, etc.through newspapers, diaries, etc.


Fig 11.33

Examples of Mercalli iso-intensity (contours of equal intensity) maps. The New Madrid earthquakes of 1811–1812 are among the largest earthquake events ever.


MagnitudeMagnitude –– a measure of earthquake size based on a measure of earthquake size based on the the energy releasedenergy released during the earthquake.during the earthquake.

Richter scale Richter scale –– the first magnitude scale (c. 1935) the first magnitude scale (c. 1935) developed by Charles Richter.developed by Charles Richter.–– Measured by the wave amplitude on a certain type of Measured by the wave amplitude on a certain type of

seismometer and the time interval between Pseismometer and the time interval between P--S waves S waves (Section 8.2).(Section 8.2).

–– Scale is logarithmic, each numeric value is 10x the Scale is logarithmic, each numeric value is 10x the amplitude of the one before.amplitude of the one before.

11.8 How are earthquakes measured?11.8 How are earthquakes measured? 11.8 How are earthquakes measured?11.8 How are earthquakes measured?----magnitudemagnitude

Fig 11.35

moment-magnitude scale -- based on physical parameters of the earthquake event. Similar to Richter scale in that each number increase ~ 10x increase in seismic moment.

Magnitude measures amplitude change -10x

Energy change ~32xSo => M7 has 100x more “seismic moment” than a M5 (10 x 10). However, the energy difference is 1024 (32 x 32).

11.8 How are earthquakes measured?11.8 How are earthquakes measured? 11.8 How are earthquakes measured?11.8 How are earthquakes measured?

Fig 11.36

Energy comparison of specific earthquake events to energy release of other “significant” events.

Some epicenters of noteworthy quakes in the Puget Lowland

gravity anomaly and Seattle faultUSGS Prof. Paper 1650, 1996

Earthquake Earthquake intensityintensity, or violence, , or violence, ---- estimated from estimated from assessments of damage and numerous eyewitness assessments of damage and numerous eyewitness accounts. accounts. Values are usually higher near the epicenter or on Values are usually higher near the epicenter or on soft soilssoft soils..EarthquakeEarthquake magnitudemagnitude relates to the energy relates to the energy released. Each whole number increase in magnitude released. Each whole number increase in magnitude is ~32is ~32--fold increase in energy released.fold increase in energy released.There is There is only one magnitude valueonly one magnitude value on any given scale on any given scale per earthquake. per earthquake. Richter ScaleRichter Scale relies more on relies more on response of seismometers to passing waves; The response of seismometers to passing waves; The momentmoment--magnitudemagnitude scale is based on the scale is based on the area of area of faultfault--plane ruptured, the displacement, and the rock plane ruptured, the displacement, and the rock strength.strength.

11.8 How are earthquakes measured?11.8 How are earthquakes measured? 11.9 Why are earthquakes destructive?11.9 Why are earthquakes destructive?

Ground shakingGround shaking……–– Surface wavesSurface waves radiating outward from the radiating outward from the

epicenter cause ground motion: epicenter cause ground motion: up/downup/down and and side side to sideto side. The stress damages buildings, bridges, . The stress damages buildings, bridges, dams, etcdams, etc……

–– Disrupts infrastructureDisrupts infrastructure (water, gas, power, and (water, gas, power, and roads), starting fires and limiting ability to respond roads), starting fires and limiting ability to respond and often damaging more property than ground and often damaging more property than ground shaking itselfshaking itself……

–– Ground shakingGround shaking also triggers also triggers mass movementmass movement(landslides). (landslides).

11.9 Why are earthquakes destructive?11.9 Why are earthquakes destructive?Damage from ground shaking

Fig 11.37

landslide

11.9 Why are earthquakes destructive?11.9 Why are earthquakes destructive?Damage from ground shaking

Fig 11.37

11.9 Why are earthquakes destructive?11.9 Why are earthquakes destructive?

Underlying material Underlying material greatly affects greatly affects susceptibility of an susceptibility of an area to ground area to ground shaking damage.shaking damage.Saturated sedimentsSaturated sedimentsundergo liquefaction undergo liquefaction (become fluidal) (become fluidal) during strong ground during strong ground motion.motion.

Fig 11.38

Liquefaction

11.9 Why are earthquakes 11.9 Why are earthquakes destructive?destructive?

Fig 11.39 top

Generation of a seismic sea wave, aka tsunami, erroneously called “tidal wave” by some.

tsunami

Tsunami simulation

http://staff.aist.go.jp/kenji.satake/animation.gif

11.9 Why are earthquakes destructive?11.9 Why are earthquakes destructive?Tsunami imagery in Sri Lanka from the Dec. 2004 Sumatra earthquake.

Fig 11.39

11.9 Why are earthquakes destructive?11.9 Why are earthquakes destructive?Tsunami imagery in Sri Lanka from the Dec. 2004 Sumatra earthquake.

Fig 11.39

Where? Along the interface between the Juan de Where? Along the interface between the Juan de Fuca and North American PlatesFuca and North American Plates

Subduction zone earthquakes

megathrust quake

WhyWhy?? Locked fault fails and slips!Locked fault fails and slips!

Locking and Bulging GPS: ½ in/year

Tahoma

uplift subsidence

What can happen when the subduction zone What can happen when the subduction zone breaks? Tsunami!!!breaks? Tsunami!!!

Rebound

upliftsubsidence

Sand volcano caused by the 2/28/01 Nisqually quake at Nisqually Wildlife Refuge.

The sand is full of pumice and charred wood that had been deposited here by lahar-derived floods from Mount Rainier!

Photo by Pat Pringle

2001 Nisqually eq damage at Tolmie State Park

2/29/01 by Pat Pringle; view is to North.

Nisqually earthquake, 2/28/01. Damaged road at University Place. Photo by Pat Pringle on 2/29/01

2/28/01 Nisqually quake: ground cracks and liquefaction at Timberline High School baseball field. Fill over peat.

Ground cracks and lateral spreading Nisqually quake 2001. Photo by Michael Polenz.

Nisqually quake 2001: damage to road around Capital Lake

Magnitude 5.8

Magnitude 6.8

Landslide into home at Salmon Beach near Tacoma.

chimney is damaged beneath flashing!

SEATAC control tower after 2001 Nisqually quake!

Historic Examples:Historic Examples:

Alaska, 1964 M 9.2 Chile, 1960 M 9.5

Top: forest killed by Top: forest killed by inundation of seainundation of sea--water after water after tectonic subsidence during tectonic subsidence during 1964 Alaska earthquake1964 Alaska earthquake

Bottom: forest killed by Bottom: forest killed by inundation of seainundation of sea--water after water after tectonic subsidence 300 years tectonic subsidence 300 years ago on the Copalis river SW ago on the Copalis river SW Washington coast!!Washington coast!!

Subsided peat Subsided peat 1/26/17001/26/1700

1100 yr B.P. subsidence

1600 yr B.P. subsided stump

Subsidence “footprints” of Cascadia earthquakesJohns River, Washington, 1988; photo by Pat Pringle

1997, Yamaguchi; Atwater; Bunker; Benson; Reid, Nature

Jacoby; Bunker; Benson, Geology

Dating of Cascadia

Earthquakes

Subsidence

A.D. 1700 Ground surface

1,100 year old ground surface

Photo by Tim Walsh

How frequent? 13 major events in 7,600 yrs

1681 +-160yr BP

Neskowin, OR

Snavely’s daterecalculated

Subsidence

Locations of subfossil trees (dots) with respect to faults (lavender), volcanic hazard zones (brown), and landslides (green)

Graphic by Pat Pringle

Lake Washington (landslide)

West Point (tsunami)

Lake WA = solid

1992, Gordon Jacoby, Pat Williams, Brendan Buckley

Cross correlated trees from Lake WA and West Point

Use of tree rings to correlate geologic events (with or without calendric ages) to study the Seattle fault

Brian Atwater high precision 14C age ~AD 900-930

Woodland Creek & Henderson Inlet in southern Puget Sound

~1240 yr BP

Subsidence

~2300 yr BP

Cross section of Benioff zone (subduction zone as defined by the trend of earthquakes)

A “shake map“ shows intensities of the 2001 quake after post quake recalibration of local seismic models.


Risk assessment tools:Risk assessment tools:–– Earthquake research saves lives and propertyEarthquake research saves lives and property……–– Seismic hazard mapping (Fig. 11.40) rates areas Seismic hazard mapping (Fig. 11.40) rates areas

on probability of groundon probability of ground--shaking hazards, shaking hazards, liquefaction, and likelihood of seismic event liquefaction, and likelihood of seismic event occurringoccurring……

–– Such risk maps commonly used by municipal Such risk maps commonly used by municipal planners, insurance companies, engineers, etc. to planners, insurance companies, engineers, etc. to guide construction and building codes to withstand guide construction and building codes to withstand such forces.such forces.

Liquefaction hazards for the Olympia area by Palmer, Walsh, & Gerstel

Subsided peat 1/26/1700Subsided peat 1/26/17001100 yr B.P. subsidence

1600 yr B.P. subsided stump

Subsidence “footprints” of Cascadia earthquakesJohns River, Washington

1997, Yamaguchi; Atwater; Bunker; Benson; Reid, Nature

Jacoby; Bunker; Benson, GeologyDating of Cascadia

Earthquake to AD 1700

C:\Documents and ettings\ppringle\My D

Sand dikes and sand volcano deposit in AK from 1964 quake. Pic by Tim Walsh.

AD 1700 tsunami deposit near coastal WA + intertidal muds on top (evidence of coseismic subsidence)

Some evidence for possible fault structures is inferred from gravity and magnetism of rocks.

landslideslandslides

southern Bainbridge Island

Young fault in Middle Fork Satsop River discovered by Tim Walsh and Josh Logan. Note ladder for scale!

landslide deposit

Spider Lake, SE Olympic Mountains

Glacier Lake, SW WA Cascade Range—oblique-aerial view.

scarpDots show buried or submerged trees; fuscialines are faults or inferredfaults; brown volcnichazards


Fig 11.40


Earthquake predictionEarthquake prediction–– Can they be predicted?Can they be predicted?

At present, seismologists At present, seismologists cannot reliably predictcannot reliably predict the the specific time, place, or magnitude of an earthquake.specific time, place, or magnitude of an earthquake.What they can offer is general probabilities (What they can offer is general probabilities (forecastsforecasts) ) that areas may undergo some size of seismic activity that areas may undergo some size of seismic activity within a time span (very much like a weather forecast, within a time span (very much like a weather forecast, but not quite so certain) such as a 67% chance that San but not quite so certain) such as a 67% chance that San Francisco Bay will see a M6.7 in the next 30 years. Francisco Bay will see a M6.7 in the next 30 years.

Earthquakes cause damage by fault rupture, ground Earthquakes cause damage by fault rupture, ground shaking, landslides, and tsunami.shaking, landslides, and tsunami.Seismic surface waves cause ground shaking. The Seismic surface waves cause ground shaking. The amplitude of the waves and hence the damage resulting amplitude of the waves and hence the damage resulting varies with earthquake intensity and the nature of the varies with earthquake intensity and the nature of the geologic material the waves traverse.geologic material the waves traverse.Earthquake rupture of the seafloor generates tsunami that Earthquake rupture of the seafloor generates tsunami that cause destruction both close to the epicenter and as far cause destruction both close to the epicenter and as far as thousands of kilometers away.as thousands of kilometers away.Predictions for specific earthquakes are still not possible, Predictions for specific earthquakes are still not possible, but risk maps identify hazards for consideration in landbut risk maps identify hazards for consideration in land--use planning, building codes, and engineering designs use planning, building codes, and engineering designs that diminish the destructive effects of earthquakes.that diminish the destructive effects of earthquakes.
