earthquake faults - uc berkeley seismology labseismo.berkeley.edu/~horst/lect3.pdf · ·...
TRANSCRIPT
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http://seismo.berkeley.edu/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
31 May 16
HH Horst Rademacher
Lect 3: Earthquake Faults
Summer Session 2016
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Class organization
Revised syllabus now on website
Most important change:
June 14 is now fixed as date
for field trip to Hayward Fault
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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)
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What is an earthquake?
Scientific answer:
When the ground breaks along a fault
Common/laymen’s answer:
When the ground shakes where I am
Both answers are correct! Two different aspects of a seismic event
Seismic waves
Seismic source
Recap from last lecture I
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Recap from last lecture II
Earthquakes around the world occur in a distinct pattern
Depth in km
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Recap from last lecture III
The cause is Plate Tectonics
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Divergent • Established mid-ocean ridge • New rift zone, new ocean
Transform • Along mid-ocean ridges • Across continents
Convergent • Ocean – continent • Ocean – ocean • Continent – continent
Three types of plate – plate interactions
Recap from last lecture IV
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EQ Faults
Suggested Reading:
Chapters 3 and 4
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http://seismo.berkeley.edu/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
HH Any
Questions?
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Plate Reconstruction II
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Stress and Strain
Comparable to growth speed of fingernails
= 4 inch/year
Largest EQ occur, where plate speed is fastest
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Stress and Strain
What happens when you constantly push or pull on an rock?
CA Hwy 14 near Palmdale
Limestone / Marble near Kings Canyon NP
It gets folded or contorted
One option:
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Stress and Strain
What happens when you constantly push or pull on an rock?
It brakes or fractures =
Earthquake
Another option:
Important: breakage not random, along preexisting stress planes =
Faults
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Faults
Focus = Hypocenter
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Faults
Faults, Earthquakes and Plate Tectonics
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
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1. Normal
2. Reverse
3. Strike-slip
4. Oblique
Dip-slip faults
Mixed Dip-slip & Strike-slip
Four Types of Faults Faults
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Assume a dipping surface along lake 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)
the dip angle is the angle between a vertical line down the face of the surface and horizontal The rake is the angle along which a fault slips: 0O in purely horizontal strike slip faults 90O in pure normal or thrust faults . 0
Faults: The Details Nomenclature of fault features:
dip, strike
and rake
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http://seismo.berkeley.edu/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
HH Any
Questions?
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Faults: The Details
movement purely along
the dip
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Hanging Wall & Footwall
Faults: The Details Nomenclature of fault features:
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Normal Faults b
efo
re
aft
er
Extensional environments
• Subsidence, basin formation
“Normal” because
hanging wall is sliding down
foot wall stable
Faults: The Details
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Normal Faults Faults: The Details
Examples:
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Reverse Faults also called Thrust Faults
be
fore
a
fte
r
Compressional environments
• Mountain building
Faults: The Details
“Reverse” because
hanging wall is sliding up
foot wall stable
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Reverse Faults Faults: The Details
Example:
1999 Chi-Chi Earthquake, Taiwan
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Faults: The Details
movement purely along
the strike
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Strike-slip Faults b
efo
re
aft
er
Translational environments
e.g San Andreas and Hayward Faults
• Right- and left-lateral
Faults: The Details
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Strike-slip Faults Faults: The Details
Direction?
Left lateral
Right lateral
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Oblique slip Faults b
efo
re
aft
er
Both strike-slip and dip-slip
Faults: The Details
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Oblique slip Faults Faults: The Details
Here: right lateral and normal
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Guatemala
What kind of faulting? Faults: The Details
Right lateral strike slip
Normal or Reverse??
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How are Faults and Plate Tectonics
connected?
Divergent Convergent Transform
Normal Reverse Strike Slip
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http://seismo.berkeley.edu/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
HH Any
Questions?
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Divergent
How are Faults and Plate Tectonics
connected?
EQ Faults:
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Spreading about 1 inch/yr
Can one see faults? EQ Faults:
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Can one see faults? EQ Faults:
Photo: Horst Rademacher
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Photo: Horst Rademacher
Can one see faults? EQ Faults:
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San- Andreas-
Fault
near
Palm Springs
Faults
Can one see faults?
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Faults Can one see faults?
San Andreas Fault in Carrizo Plain
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Can one see faults?
San Andreas Fault in Carrizo Plain
Photo: Horst Rademacher
Faults
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Faults Can one see faults?
San Andreas Fault – Wallace Creek Central California
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Wallace Creek: San Andreas Fault Faults:
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Off-set curbs in Hollister along Calaveras Fault
Faults Can one see faults?
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1971
Hayward Fault at Rose Street in Hayward
Faults Can one see faults?
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Faults Can one see faults?
Fault step overs = jumps to left or right
San Andreas Fault Along Hwy 25 S of Hollister
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http://seismo.berkeley.edu/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
HH Any
Questions?
![Page 46: Earthquake Faults - UC Berkeley Seismology Labseismo.berkeley.edu/~horst/Lect3.pdf · · 2016-05-31Assume a dipping surface along lake shore surface of the lake makes a horizontal](https://reader031.vdocuments.us/reader031/viewer/2022030502/5aaf16967f8b9a6b308ce5c3/html5/thumbnails/46.jpg)
Locked vs. creeping faults
CREEPING along
LOCKED until the
next earthquake…
Fault behavior
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SEISMIC
Earthquakes
Stick-Slip
ASEISMIC = Creep
Flanks constantly move
Free Slipping
Spectrum of fault behavior
Even along creeping faults, the reality is somewhere in between.
Fault behavior
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Hayward Fault Hybrid Fault
![Page 49: Earthquake Faults - UC Berkeley Seismology Labseismo.berkeley.edu/~horst/Lect3.pdf · · 2016-05-31Assume a dipping surface along lake shore surface of the lake makes a horizontal](https://reader031.vdocuments.us/reader031/viewer/2022030502/5aaf16967f8b9a6b308ce5c3/html5/thumbnails/49.jpg)
Source: Estelle Chaussard, SUNY Buffalo
Hayward Fault Hybrid Fault
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Faults
Locked faults cause Earthquake Cycles
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Calaveras Fault in Hollister
San Andreas Fault along Hwy 25
Fault behavior Creeping Faults
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Rose Street,
Hayward, CA 1971
1974
1993
2005
Steady creep
approx. 1 inch/year
No earthquakes
Fault behavior Creeping Faults
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10 mm/yr - 2.5 mm/yr? = ???
Long Term Buildup
(Plate Tectonics) Amount left for
Earthquake Steady slip - =
makes earthquakes smaller
Fault behavior Creeping Faults
Creep relieves
strain
![Page 54: Earthquake Faults - UC Berkeley Seismology Labseismo.berkeley.edu/~horst/Lect3.pdf · · 2016-05-31Assume a dipping surface along lake shore surface of the lake makes a horizontal](https://reader031.vdocuments.us/reader031/viewer/2022030502/5aaf16967f8b9a6b308ce5c3/html5/thumbnails/54.jpg)
http://seismo.berkeley.edu/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
HH Any
Questions?
![Page 55: Earthquake Faults - UC Berkeley Seismology Labseismo.berkeley.edu/~horst/Lect3.pdf · · 2016-05-31Assume a dipping surface along lake shore surface of the lake makes a horizontal](https://reader031.vdocuments.us/reader031/viewer/2022030502/5aaf16967f8b9a6b308ce5c3/html5/thumbnails/55.jpg)
Fault behavior Difference between 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
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Fault behavior
How does an Earthquake work?
LOCKED until
the next
earthquake…
1. A Fault has to be locked
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Fault behavior
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!
How does an Earthquake work?
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Harry F. Reid 1859-1944
Johns Hopkins U.
Elastic rebound
theory
Fault behavior
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Elastic Rebound also explains
Earthquake Cycles
Fault behavior
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http://seismo.berkeley.edu/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
HH Any
Questions?
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Slip
Fault behavior
How does an Earthquake work?
How large is the coseismic slip?
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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 (1906)
7.9 6.1 - 7.8
Maule (Chile) 2010 8.8 19
Tohoku (2011) 9 >50
Alaska (1964) 9.2 >30
Chile (1960) 9.5 90 ± 4.2
Fault behavior
Coseismic Slip
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Fault behavior
Coseismic Slip 1m at depth a few cm on surface
South Napa EQ 24 Aug 14, M=6.0
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Fault behavior
Tohoku EQ 11 Mar 11, M=9.0
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http://seismo.berkeley.edu/~horst/summer2016.html
http://seismo.berkeley.edu/~horst/summer2016.html
HH Any
Questions?
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1. Normal
2. Reverse
3. Strike-slip
4. Oblique
Dip-slip faults
Mixed Dip-slip & Strike-slip
Four Types of Faults Things to remember I
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One can see faults!
San Andreas Fault in Carrizo Plain
Things to remember II
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SEISMIC
Earthquakes
Stick-Slip
ASEISMIC = Creep
Flanks constantly move
Free Slipping
Spectrum of fault behavior
Even along creeping faults, the reality is somewhere in between.
Things to remember III
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10 mm/yr - 2.5 mm/yr? = ???
Long Term Buildup
(Plate Tectonics) Amount left for
Earthquake Steady slip - =
makes earthquakes smaller
Creeping Faults
Creep relieves
strain
Things to remember IV
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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
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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: http://earthquakes.berkeley.edu
For global events: http://ds.iris.edu/seismon/ http://earthquake.usgs.gov/earthquakes/map/
Any volunteers?
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X
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