1. Big Bend in the San Andreas Fault
* Many faults in Southern California
other than San Andreas (SAF)
* Most are right-lateral (like SAF) but
many in So-Cal are not
(thrust, normal, blind thrust)
* Right-lateral strike slip motion common
in northern California but things are
different in LA at the “Big Bend”
* Bend in SAF causes intense compression
and formation of the transverse ranges
(San Gabriels, Santa Susanas...)
* Pressure causes rocks here to deform
and break alleviating stress and
creating non-uniform slip events.

2. Big Bend in the San Andreas Fault
North America
Plate
Pacific Plate
Right-lateral strike-slip
motion along the SAF
becomes compressional
at a bend in the fault line.

3. Northridge Earthquake, 1994
CSUN Parking Structure
- January 17, 1994, 4:30 am
- Magnitude = 6.9
- Blind thrust fault
- Difficult to find or predict
- Duration seconds

4. Earthquakes Chapter 16
1989, Loma Prieta earthquake, Mw = 7.2

5. Historic Earthquakes 1906 San Francisco (7.8)
- 280 miles of displacement
- Shaking ~1 minute
- Damaged water mains, fires spread and caused many deaths (3000).

6. Historic Earthquakes 1989 Loma Prieta, Mw = 7.2
- Shaking for 15 seconds
- Death toll 63

7. Historic Earthquakes 1964 southern Alaska (Mw = 9.2)
- Shaking for 3 minutes
- Rupture 350,000 square miles
- Death toll from quake 15 (remote area)
- Tsunami, landslides 100 more

8. Historic Earthquakes 1994 Northridge - 1.8 miles from CSUN
- Shaking 40 seconds
- Damaged all 53 CSUN buildings
- Damaged 300 other schools
- Lower story buildings collapsed
- 4 interstate hwy's closed for months
(Golden State, Santa Monica fwys)
people live in tents for days
without water, elect, gas
- Arid climate did not cause liquifaction of soils – shaking minimized
(compared to 1964 Alaska and 1989 Loma Prieta).
- Landslides in Santa Susana, Santa Monica, San Gabriel Mtns
blocked roads and traffic, damaged water lines and homes in Palisades
- Sylmar – Olive View Hospital – rebuilt from 1971 to code stayed intact.
- Aftershocks min after main shock, hrs after.

9. Historic Earthquakes 2002 inland Alaska – Denali Fault
- Propagated east 7000 miles/hr
- Offset streams, glaciers, landslides
- Trans-Alaska Oil Pipeline no
serious damaged - pre-engineered

10. Historic Earthquakes 2004 Sumatra – Andaman E.Q. - Mw = 9.3
- Second largest recorded on Earth
- Major damage in Sumatra
- Tsunami damage spread far to
Indonesia, Thailand, Sri Lanka,
India, East Africa
- Death toll 220,000 from force
of tsunami wave

11. Faults and Crater Offsets on the Moon

12. Moon Quakes
Moon quakes were recorded by a seismometer from the Apollo 16 mission

13. INSIGHT Mission to Mars
* The INSIGHT missionwill deploy one seismometer to measure Mars quakes!
* Do you think this is a good use of our research dollars ? Why or Why not ?

14. Earthquakes
An earthquake is a trembling or shaking of the ground caused by the sudden release of energy
Tectonic forces produce stresses on rocks that eventually exceed their elastic limits, resulting in brittle failure
Energy is released during earthquakes in the form of seismic waves
Elastic rebound theory - earthquakes
are a sudden release of strain stored in
rocks that bend until they finally break
and move along a fault

15. Seismic Waves
Focus (or hypocenter) - the point of initial breakage and movement along a fault, where seismic waves originate
Epicenter - point on Earth’s surface directly above the focus
Two types of seismic waves are produced during earthquakes
Body waves - travel outward from the focus in all directions through Earth’s interior
Surface waves - travel along Earth’s surface away from the epicenter

16. Body Waves
P wave - compressional body wave in which rock vibrates back and forth parallel to the direction of wave propagation
Fast (4 to 7 kms/sec) wave that is the first or primary wave to arrive at recording station following earthquake
Pass through solids and fluids
S wave – shearing body wave in which rock vibrates back and forth perpendicular to the direction of wave propagation
Slower (2 to 5 km/sec) wave that is the secondary wave to arrive at recording station following earthquake
Pass through solids only

17. Surface Waves Surface waves are slower than
body waves but have the larges
amplitude
Love waves - side-to-side motion of the ground surface
Can’t travel through fluids
Rayleigh waves - ground to moves in an elliptical path opposite the direction of wave motion
Extremely destructive to buildings

18. Measuring Earthquakes
Seismometers - used to measure seismic waves
Seismographs - recording devices used to produce a permanent record of the motion detected by seismometers

19. Measuring Earthquakes
Seismograms - permanent paper (or digital) records of the earthquake vibrations
Used to measure the earthquake strengths

20. Locating Earthquakes P- and S-waves leave E.Q. focus at the same time
P-wave gets farther and farther ahead of the S-wave with distance and time from the earthquake
Travel-time curve - used to determine distance to focus
based on time between first P- and S- wave arrivals

21. Locating Earthquakes
One station gives distance to E.Q. but not direction
Plotting distances from 3 stations on a map, as circles with radii equaling the distance from the quake. Point where 3 circles overlap locates the earthquake epicenter
Depth of focus beneath Earth’s surface can also be determined
Shallow focus km deep
Intermediate focus km deep
Deep focus km deep

22. Measuring the Sumatra – Andaman Earthquake
A Global Seismic Network (GSN)
is maintained around the Earth
to monitor earthquake activity
as well as nuclear testing.
Earthquake locations and depth
can be determined within minutes
of an earthquake using this
GSN network.

23. Measuring the “Size” of Earthquakes
Earthquake “size” measured two ways - intensity and magnitude
Intensity - a measure of the effects an earthquake produces (on both structures and people)
Modified Mercalli scale

24. Measuring the “Size” of Earthquakes
Magnitude is a measure
of the amount of energy
released by an earthquake
Richter scale
Body waves
Surface waves
Moment magnitude - more objective measure of energy released by a major earthquake Mo = m* U * A
Uses rock strength, surface area, fault rupture distance
Smaller earthquakes are more common than large ones

25. Earthquake Magnitudes
“How Big is Big ? ”
Earthquake magnitudes are logarithmic
M = 10 R
(M = ground movement, R = Richter scale)
If R = 1, then M = 10
If R = 2, then M = 100
So this means that a magnitude 7 earthquake will have 10 times
as much ground movement as a magnitude 6 earthquake.
Change by 1
Change by 10

26. Location and Size of Earthquakes
in the U.S.
Earthquakes occur throughout the U.S., but are much more common in the western states and Alaska
Largest seismic risks or hazards exist near the plate boundary along the U.S. Pacific coast (e.g., San Andreas fault), and around New Madrid, Missouri
Seismic risk determined based on the assumption that large future earthquakes will occur where they have occurred in the past
Earthquake locations since 1977

27. Effects of Earthquakes
Earthquakes produce several types of effects, all of which can cause loss of property and human life
Ground motion is the familiar trembling and shaking of the land during an earthquake
Can topple buildings and bridges
Fire is a problem just after earthquakes because of broken gas and water mains and fallen electrical wires
Landslides can be triggered by ground shaking, particularly in larger quakes
Liquefaction occurs when water-saturated soil or sediment sloshes like a liquid during a quake
Permanent displacement of the land surface can also occur, leaving fractures and scarps

28. World Earthquake Distribution
Most earthquakes occur in narrow geographic belts - plate boundaries
Most important concentrations in circum-Pacific and Mediterranean- Himalayan belts
Shallow-focus earthquakes occur at mid-oceanic ridges

29. World Earthquake Distribution
Nearly all intermediate- and deep-focus earthquakes occur
in Benioff zones
- inclined seismic activity associated with descending oceanic plate at subduction
E.Q.'s are caused by plate interactions along tectonic plate boundaries
Plate boundaries are identified and defined by earthquakes

30. Earthquakes Tectonics
Earthquakes occur at each of the three types of plate boundaries:
-At divergent boundaries, tensional forces - shallow-focus quakes on normal faults
-At transform boundaries, shear forces - shallow-focus quakes along strike-slip faults
-At convergent boundaries, compressional forces produce shallow- to deep-focus
quakes along reverse faults

31. First Motion of Ground Motion Observed on a Seismogram
Compression (thrust faults)
Extension (normal faults)

32. Activity

33. Building Codes for Earthquakes
Best materials are:
-Strong
-Flexible
-Light
Good examples:
Steel
Wood
Reinforced concrete
(rebar steel core)
Poor examples:
Simple concrete
Brick – chimneys often fall
(in moderate E.Q.'s)
Heavy roofs (Tile)
Strong liquefaction can supersede
all these precautions...
1999, Izmit Turkey
1964 Niigata, Japan - liquifaction

34. Buildings and Bridges... 1995 Kobe, Japan
Elevated highway knocked over by
strong horizontal jolt.
Damage to bridge and 88,000 buildings
costs exceeded $400 billion

35. Tsunami Waves Created by Earthquakes
Tsunami waves are generated
by submarine earthakes
Long low waves are formed
above displaced seafloor
that travel for miles along the
base of the seafloor.
Displacement of seawater
surface can be as little as
a few centimeters in the middle
of the ocean.
Displacements increase
dramatically as they approach
a continental shelf

36. Tsunami Travel time in the Pacific Ocean
Earthquake in Alaska may form a tsunami in the Pacific

37. Monitoring Tsunami Waves

38. Tsunami in Sumatra, 2004