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31 May 16

Summer Session 2016

Horst RademacherHH Lect 3: Earthquake Faults

http://seismo.berkeley.edu/~http://seismo.berkeley.edu/~horst/summer2016.htmlhorst/summer2016.html

Class organization

Revised syllabus now on website

Most important change: June 14 is now fixed as date for field trip to Hayward Class organization first homework assignement mix of short essays and multiple choice will be posted on website this afternoon Due date: Thursday, 2 June

No late work will be accepted unless prior approval No electronic submissions unless prior approval

Office hours: Tuesday 3-4 pm (after class) Where: 213 McCone Hall or BSL Conference Room (2nd floor McCone)

Recap from last lecture I What is an earthquake? Common/laymen’s answer: When the ground shakes where I am Seismic waves

Scientific answer: Seismic source When the ground breaks along a fault

Both answers are correct! Two different aspects of a seismic event Recap from last lecture II Earthquakes around the world occur in a distinct pattern

Depth in km Recap from last lecture III

The cause is Plate Three types of Recap from last lecture IV plate – plate interactions

Divergent • Established mid-ocean ridge • New zone, new ocean

Transform • Along mid-ocean ridges • Across

Convergent • Ocean – • Ocean – ocean • Continent – continent EQ Faults

Suggested Reading:

Chapters 3 and 4 Any HH Questions?

http://seismo.berkeley.edu/~http://seismo.berkeley.edu/~horst/summer2016.htmlhorst/summer2016.html

Plate Reconstruction II Largest EQ occur, where and Strain plate speed is fastest

= 4 inch/year

Comparable to growth speed of fingernails Stress and Strain What happens when you constantly push or pull on an rock?

One option: It gets folded or contorted

CA Hwy 14 near Palmdale

Limestone / Marble near Kings Canyon NP Stress and Strain What happens when you constantly push or pull on an rock? Another option: It brakes or fractures =

Earthquake

Important: breakage not random, along preexisting stress planes =

Faults Faults

Focus = Hypocenter Faults Faults, Earthquakes and

Fault: Boundary Line between two plates

Accumulates mechanical stress from tectonic movement

Releases stress in Earthquake – plates slip past each other

Over thousands and millions of years: Accumulated slip same as average tectonic movement

Four Types of Faults Faults

1. Normal Dip- slip 2. Reverse faults

3. Strike-slip

Mixed 4. Oblique Dip-slip & Strike-slip Faults: The Details Nomenclature of fault features: Assume a dipping surface along shore  surface of the lake makes a horizontal line along the surface = the strike line  the angle between the strike line and north is the strike angle (measured clockwise from north) dip,  the dip angle is the angle between a vertical line down the face of the surface and horizontal strike

 The is the angle along which a fault slips: and rake 0O in purely horizontal strike slip faults 90O in pure normal or thrust faults

. 0 Any HH Questions?

http://seismo.berkeley.edu/~http://seismo.berkeley.edu/~horst/summer2016.htmlhorst/summer2016.html

Faults: The Details

movement purely along the dip Faults: The Details Nomenclature of fault features:

Hanging Wall & Footwall

Faults: The Details Normal Faults

before

after

Extensional environments • Subsidence, basin formation

“Normal” because hanging wall is sliding down foot wall stable Faults: The Details Normal Faults

Examples: Reverse Faults

Faults: The Details also called Thrust Faults

before

after

Compressional environments • building

“Reverse” because hanging wall is sliding up foot wall stable Faults: The Details Reverse Faults

Example: 1999 Chi-Chi Earthquake, Taiwan Faults: The Details

movement purely along the strike

Faults: The Details Strike-slip Faults

before

after

Translational environments e.g San Andreas and Hayward Faults • Right- and left-lateral Faults: The Details Strike-slip Faults

Direction?

Left lateral

Right lateral

Faults: The Details Oblique slip Faults

before

after

Both strike-slip and dip-slip Faults: The Details Oblique slip Faults

Here: right lateral and normal Faults: The Details What kind of faulting?

Right lateral strike slip

Normal or Reverse?? Guatemala How are Faults and Plate Tectonics connected? Divergent Convergent Transform

Normal Reverse Strike Slip Any HH Questions?

http://seismo.berkeley.edu/~http://seismo.berkeley.edu/~horst/summer2016.htmlhorst/summer2016.html

How are EQ Faults: Faults and Plate Tectonics connected? Divergent EQ Faults: Can one see faults?

Spreading about 1 inch/yr EQ Faults: Can one see faults?

Photo: Horst Rademacher EQ Faults: Can one see faults?

Photo: Horst Rademacher Faults

Can one see faults?

San- Andreas- Fault near Palm Springs Faults Can one see faults?

San Andreas Fault in Carrizo Plain Faults Can one see faults?

San Andreas Fault in Carrizo Plain

Photo: Horst Rademacher Faults Can one see faults?

San Andreas Fault – Wallace Creek Central California Wallace Creek: San Andreas Fault Faults: Faults Can one see faults?

Off-set curbs in Hollister along Calaveras Fault Faults Can one see faults?

1971

Hayward Fault at Rose Street in Hayward Faults Can one see faults?

Fault step overs = jumps to left or right

San Andreas Fault Along Hwy 25 S of Hollister Any HH Questions?

http://seismo.berkeley.edu/~http://seismo.berkeley.edu/~horst/summer2016.htmlhorst/summer2016.html

Fault behavior Locked vs. creeping faults

LOCKED until the next earthquake…

CREEPING along Fault behavior Spectrum of fault behavior

ASEISMIC = Creep SEISMIC Flanks constantly move Earthquakes Free Slipping Stick-Slip

Even along creeping faults, the reality is somewhere in between. Hayward Fault Hybrid Fault Hayward Fault Hybrid Fault

Source: Estelle Chaussard, SUNY Buffalo Faults

Locked faults cause Earthquake Cycles Creeping Faults Fault behavior

Calaveras Fault in San Andreas Fault Hollister along Hwy 25 Creeping Faults Fault behavior

Rose1974 Street, Hayward, CA 1971

1993

2005

Steady creep approx. 1 inch/year No earthquakes Creeping Faults Fault behavior

Creep makes relieves earthquakes strain smaller

Long Term Buildup Amount left for Steady slip (Plate Tectonics) - = Earthquake

10 mm/yr - 2.5 mm/yr? = ???

Any HH Questions?

http://seismo.berkeley.edu/~http://seismo.berkeley.edu/~horst/summer2016.htmlhorst/summer2016.html

Difference between Fault behavior Creep and an Earthquake?

Aseismic Creep: Accumulated strain gets released continuously at low rate –

no or very little seismic hazard

Earthquake: Sudden release of large amount of accumulated strain –

large seismic hazard How does an Fault behavior Earthquake work?

LOCKED until 1. A Fault has to be locked the next earthquake… How does an Fault behavior Earthquake work?

2. Stress builds up as tectonic plates move past one another

3. Friction along the fault prevents slip, Instead: elastic deformation

4. Stress exceeds rupture strength, fault slips …earthquake! Fault behavior Elastic rebound theory

Harry F. Reid 1859-1944 Johns Hopkins U. Fault behavior Elastic Rebound also explains Earthquake Cycles Any HH Questions?

http://seismo.berkeley.edu/~http://seismo.berkeley.edu/~horst/summer2016.htmlhorst/summer2016.html

How does an Fault behavior Earthquake work?

Slip

How large is the coseismic slip? Coseismic Slip Fault behavior

EQ M Slip [m]

South Napa (2014) 6 1

Coalinga (1983) 6.5 0.9

Loma Prieta (1989) 7.1 1.6 ± 0.3

San Francisco 7.9 6.1 - 7.8 (1906) Maule (Chile) 2010 8.8 19

Tohoku (2011) 9 >50 Alaska (1964) 9.2 >30 Chile (1960) 9.5 90 ± 4.2 South Napa EQ Fault behavior 24 Aug 14, M=6.0 Coseismic Slip 1m at depth a few cm on surface Tohoku EQ Fault behavior 11 Mar 11, M=9.0 Any HH Questions?

http://seismo.berkeley.edu/~http://seismo.berkeley.edu/~horst/summer2016.htmlhorst/summer2016.html

Four Types of Faults Things to remember I

1. Normal Dip- slip 2. Reverse faults

3. Strike-slip

Mixed 4. Oblique Dip-slip & Strike-slip One can see faults! Things to remember II

San Andreas Fault in Carrizo Plain Things to remember III Spectrum of fault behavior

ASEISMIC = Creep SEISMIC Flanks constantly move Earthquakes Free Slipping Stick-Slip

Even along creeping faults, the reality is somewhere in between. Things to remember IV Creeping Faults

Creep makes relieves earthquakes strain smaller

Long Term Buildup Amount left for Steady slip (Plate Tectonics) - = Earthquake

10 mm/yr - 2.5 mm/yr? = ???

Class organization first homework assignement will be posted on website this afternoon Due date: Thursday, 2 June

No late work will be accepted unless prior approval No electronic submissions unless prior approval Thursday:

Earthquakes in the US Man made EQ

Seismicity report:

look at past week’s seismicity: discuss interesting events, EQ in the news, etc.

For California events: For global events: http://earthquakes.berkeley.edu http://ds.iris.edu/seismon/ http://earthquake.usgs.gov/earthquakes/map/

Any volunteers? X