101 Chapter 20 Spring 2014

Geology 101Class 20Spring 2014

Objectives –Chapter 11

• Identify the types of rock deformation on the surface of the Earth.

• Explain the relationship of stress and strain and how they explain the causes and effects of earthquakes

• Explain the connection between rock deformations and the origin of Earth resources.

Objectives –Chapter 11

• Identify the types of rock deformation on the surface of the Earth.

Folds, Faults, and other

Records of Rock Deformation

What can cause “hard” rocks to be deformed like this?The study of structural geology

Deformation of Rocks

• Folding and faulting are the most common forms of deformation in the sedimentary, igneous and metamorphic rocks that compose the Earth’s crust

• “Structural Geology” is the study of the deformation of rocks and its effects.

Orientation of Deformed RocksWe need some way to describe the geometry of

geologic structures. So we use the terms strike and dip.

Strike: compass direction of a rock layer as it intersects with a horizontal surface.

Dip: acute angle between the rock layer and the horizontal surface, measured perpendicular to strike.

Strike and Dip on a Rooftop

Strike and Dip in a Rock StructureDip and Strike in Rock Formation

Displaying Strike and Dip on a Map

35O

N

S

Direction of strike

E

Direction of down dip

W

15

FOLDS

Fold in strata in Wyoming: anticline or syncline?

Cross-section of a Syncline

18

Not always possible to tell the anticlines from synclines on surface

19

Extreme Folding

Overturned fold

• An overturned fold takes place when folding rock becomes bent or warped.

• Sometimes the folds can become so disfigured that they may even overlap each other.

• An example of overturned folding is shown in the diagram below.

Asymmetrical folds

Overturned folds

In many areas, many anticlines and synclines are plunging folds rather than horizontal folds

And Even More Fold Terminology

Dome: a sequence of folded rocks in which all the beds dip away from a central point

Basin: a sequence of folded rocks in which all the beds dip towards a central point

Objectives –Chapter 11

• Identify the types of rock deformation on the surface of the Earth.

• Explain the relationship of stress and strain and how they explain the causes and effects of earthquakes

Rock Fractures

• Joints–Cracks in rocks along which there has been no

appreciable displacement.• Faults

–Fractures in rocks created bytectonic processes(Movement of the rock on both sides of the fault)

Types of Faults

• Faults classified by direction of relative movement or “SLIP”

• Dip-slip faults –Normal–Reverse

• Strike-slip faults–Right-lateral–Left-lateral

• Oblique-slip faults

• “Hanging Wall”: Term used by miners. They could “hang” their light on this side of the fault because it was above them.

• “Footwall”: Also from the miners, this side of the wall upon which they could stand below the hanging wall.

Faults

Dip-slip Faults

• Motion of the fault blocks is parallel to the dip direction

• Two types:Normal – movement is down dipReverse – movement is up dip

Hanging wall

Foot wall

Hanging wall

Foot wall

Rift ValleyReverse Faulting in Rift zones

Thrust Fault

footwall

hanging wall

cross section

Thrust faults are low-angle reverse faults

Strike-slip Faults

Motion of the fault blocks is parallel to the strike direction

There are 2 typesRight-lateral

Left-lateral

Left-lateral

Left-lateral Strike Slip Fault

aerial (map) view

Right-lateral Strike Slip Fault

aerial (map) view

San Andreas Fault (right-lateral)

Displacement both vertically and horizontally

What determines if a rock Folds (bends)

or faults (breaks)?

• Type of force applied

• Pressure

• Temperature

• Rock (mineral) composition

Depth at Which the Deformation Occurs is a Direct Factor

• At shallow crust depths, rock has a greater probability of breaking

• At deeper crust depths, rock usually deforms• Why????

– Hotter– Higher constraining pressure

Strength• Ability of an object to resist

deformation• In lab, marble was tested

Fractured Deformed

StrainAny change in original shape or size of an object in response to stress acting on the object

Three Major Typesof Directed Stress

• Compression• Tension• Shear

Anatomy of an Earthquake

All is coolNo stress, no strain in rocks

Tectonic forcespush the farside to left and nearside toRight, stress and strainbuild in rocks

Finally the stress exceeds thestrength of rocks and they fail along the weakestplane, the fault line, releasingthe energy stored -EARTHQUAKE.

The Earth is displaced along fault line but the stresses go to zero

Rayleigh Waves

Particle motion

Particle motion consists of elliptical motions (generally retrograde elliptical) in the vertical plane and parallel to the direction of propagation. Amplitude decreases with depth. Material returns to its original shape after wave passes.

Deformation propagates

“CIVILIZATION EXISTS BY GEOLOGICAL CONSENT”

The same geologic processes that make our planet

habitable also make it dangerous

US Most Deadly EarthquakesDate UTC Location Deaths Comments

1811 12 16 Northeast Arkansas - New Madrid, Missouri

Several 1811 12 16 thru 1812 02 07.

1906 04 18 San Francisco, California 3000 Deaths (approximate) from earthquake and fire.

1946 04 01 Aleutian Islands, Alaska 165 Tsunami: 159 Hawaii, 5 Alaska, 1 California.

1964 03 28 Prince William Sound, Alaska 128 Tsunami: 98 Alaska, 11 California, 4 Oregon. Earthquake: 15 Alaska.

1933 03 11 Long Beach, California 115  

1868 04 03 Hawaii Island, Hawaii 77 Landslides: 31, tsunami: 46.

1971 02 09 San Fernando, California 65  

1989 10 18 Santa Cruz County, California 63  World Series Quake

1960 05 22 Chile, South America 61 Tsunami in Hawaii.

1886 09 01 Charleston, South Carolina 60  

1994 01 17 Northridge, California 60  

1812 12 08 San Juan Capistrano, California 40  

1868 10 21 Hayward, California 30  

1959 08 18 Hebgen Lake, Montana 28  

http://pubs.usgs.gov/gip/dynamic/Vigil.html

The Infamous San AndrusTransverse Fault and JuanDe Fuca Subduction Zone

http://z.about.com/d/history1900s/1/7/Z/V/sf33.gif

Earthquake Damage 1971 San Fernando Quake

http://libraryphoto.cr.usgs.gov/cgi-bin/show_picture.cgi?ID=ID.%20Kachadoorian,20R.%20%20%20120c

http://earthquake.usgs.gov/regional/states/events/1989_10_18.php

Collapse of Nimitz Freeway – Oakland Loma Prieta Quake October 18, 1989

Collapse of section of Bay Bridge Loma Prieta Quake October 18, 1989

http://earthquake.usgs.gov/regional/states/events/1989_10_18.php

The Cocos plate is underthrusting the western edge of the Caribbean plate, while the eastern edge of the plate is be underthrust by the oceanic lithosphere created at the mid-Atlantic ridge. From: http://volcano.und.edu/vwdocs/volc_images/north_america/west_indies.html

Today’s earthquake occurred within subducted oceanic lithosphere that has been subducted below the Martinique region. 

Plate tectonic motion vectors.

Map view of Caribbean seismicity, January 1, 1960, - November 30, 2007. (Map created by the program SeismicEruption.)

Box with arrows shows the region selected for the cross section in

the next figure.

The westward dipping zone of seismicity occurs within the subducted lithosphere.

CHOR Helicorder record.

CHOR Seismogram filtered with a low-pass filter with corner set to

10 seconds. Sac-formatted file: 2007112919.sac.

The P and S phases are both quite clear.

Back

Magnitude 7.3 Caribbean Earthquake Martinique Region, Windward Islands Thursday, November 29, 2007 at 19:00:19 UTC(11:00:19 AM Pacific Standard Time)Epicenter: Latitude 14.921N, Longitude 61.264WDepth: approximately 145 kilometers.      

Plate tectonic motion vectors.

Caribbean Plate Movement and the January 13, 2010 Haiti Earthquake

http://images.google.com/imgres?imgurl=http://www.drgeorgepc.com/volcTsu2CaribbeanTectonics.jpg&imgrefurl=http://www.drgeorgepc.com/TsunamiVolcanicCaribbean.html&usg=__aWSWL8CI1CDlDtdpqBUwz4bcbVo=&h=254&w=380&sz=19&hl=en&start=26&um=1&tbnid=T09BUSSVF1o80M:&tbnh=82&tbnw=123&prev=/images%3Fq%3Dcaribbean%2Bplate%2Btectonics%26ndsp%3D20%26hl%3Den%26rlz%3D1R2SKPB_enUS336%26sa%3DN%26start%3D20%26um%3D1

Haiti 1-13-2010 Earthquakeepicenter

Miami

http://earthquake.usgs.gov/earthquakes/map/

SAN FRANCisco

SAN FRANCISCO

University of San Francisco

Berkeley, Home of the University ofCalifornia

Moraga,Home of St. Mary’sCollege

http://quake.usgs.gov/recenteqs/latest.htm

http://quake.usgs.gov/recenteqs/latest.htm

http://quake.wr.usgs.gov/info/faultmaps/slipage.html

Recency of California-Nevada Faults

San Andres

Last year you could contact this site and you could get your USGS Earthquake Probability map for the next 24 hours, now it has been discontinued.

http://pasadena.wr.usgs.gov/step

Richter Earthquake Scale• Magnitude Effects Estimated Number• Each Year• 2.5 or less Usually not felt, but can be 900,000• recorded by seismograph . • 2.5 to 5.4 Often felt, but only causes 30,000• minor damage• 5.5 to 6.0 Slight damage to buildings 500• and other structures • 6.1 to 6.9 May cause a lot of damage 100• in very populated areas.• 7.0 to 7.9 Major earthquake. 20• Serious damage• 8.0 or greater Great earthquake. Can totally One every 5 to 10 • destroy communities years

• The Richter scale is logarithmic scale (base 10) so the amplitude of earth movement is 10 times increased for each one point increase and 32 times more energy is released. The highest reading recorded was a 9.5 during a 1960 Chilean quake.

Moment Magnitude Scale• Richter scale measures movement 100 km from

point of failure. Good for small quakes.• Moment-magnitude used to measure total

energy released from larger quakes.• Area moved times the average displacement

times the rock shear strength = Mw

• Still log based: 4 to 5, 32 times more energy;4 to 6, 1032 times bigger

• 2004 Sumatra quake 9.3 – 1500 km rip, 7 to 20 meter displacement: Energy equal to ½ US annual consumption.

Modified Mercalli ScaleMeasures what is feltI – Not feltII – May be felt by those in tall buildingsIII - Many indoors feel somethingIV - Most people indoors feel it, Dishes Rattle, Many outdoors feel nothingV- Almost everyone feels somethingVI – Everyone feels movement – no structural damageVII – Hard to stand, considerable damage in poorly built buildingsVIII – Hard to steer car, well built building suffer slight damageIX – Well built building damagedX – Most buildings destroyed, dams collapseXI – Most buildings collapseXII – End of the world as we know it almost everything destroyed

Mercalli dependent on distance, soil conditions, intensity

Modified Mercelli ScaleReadings from the October 1989 “World Series” Quake

1800-1999 Greater than VII Mercalli index Occurrences

http://www.conservation.ca.gov/cgs/rghm/quakes/Pages/MS49.aspx

Summary Major Earthquakes

• San Fernando 1971- VII-IX 6.5• Loma Prieta 1989 – VII-IX 7.1• Northridge 1994 – VII-IX 6.8• San Francisco 1906 – XI 8.25• Chile 1960 - XII 8.6 or 9.5• Alaska 1964 X-XII 8.6• Chile 2010 – IX – 8.8• Charleston S.C. 1886 - X? - 7.3 (in the middle of a

plate)

Earthquake Hazards

• Surface faulting• Ground shaking• Ground failure (Liquefaction)• Tsunamis

Earthquake Effects - Ground Shaking

KGO-TV News ABC-7Loma Prieta, CA 1989

Earthquake Effects - Ground Shaking

Northridge, CA 1994

Repairs underway to Washington Monument, damaged in 2011 Virginia M5.8 Quake

Kobe Japan 1996

Turkey 1999

San Fernando 1971 Hydraulic dam fill failure

Niigita 1964 Liquefaction of foundation soils

What effects the damage caused?

• Strength of quake, how much energy is released.• Natural rock conditions – does it trigger

landslides which in water can cause tsunamis

• Soil conditions – does it cause liquefaction of soils (Kobe, Japan)

• How well designed and built are structures• Engineers learn more from every quake – Bridge

designs totally changed after San Fernando 1994 quake

Earthquakes over 3.0 1974-2011

Mercali readings of intensity of August 23, 2011 Virginia M5.8 Quake.

Earthquake Effects - Tsunamis

Photograph Credit: Henry Helbush. Source: National Geophysical Data Center

1957 Aleutian Tsunami

NOAA

Objectives –Chapter 11

• Identify the types of rock deformation on the surface of the Earth.

• Explain the relationship of stress and strain and how they explain the causes and effects of earthquakes

• Explain the connection between rock deformations and the origin of Earth resources.

Two Texas Basins, one from Permian Age, mostly carbonate, the Cretaceous-Tertary-Quaternary sandstones

Objectives –Chapter 11

• Identify the types of rock deformation on the surface of the Earth.

• Explain the relationship of stress and strain and how they explain the causes and effects of earthquakes

• Explain the connection between rock deformations and the origin of Earth resources.