Earthquake Hazards
Liquefaction
What is it
Landslides
Cracks, offset and uplift
Tsunamis
How are they different from regular ocean waves?
BUILDINGS….
Buildings
Un-reinforced masonry vs wood framed
To withstand an earthquake you want a building
Flexible
To move a one unit
To stay on its foundation
Wood
Flexible: bends before it breaks
Framing holds building together as a complete unit
May be damaged by won’t fall down
Un-reinforced masonry/brick
VERY brittle
Fractures cause broken pieces to move as individuals
Retrofitting:
Masonry
Add steel framing
E-quake bolts
Install external buttress
Politics involved
Very expensive
Historic buildings, schools, museums
Tear down and build new is cheaper
Many cities are retrofitting
Starbucks in Seattle
1998 8.5 million on x-frame bracing
2001 Nisqualli quake
Olympia Capitol building
Finished repairing/retrofitting 2005
High rises and wave amplification
Buildings sway during earthquakes
Movement during an earthquake can be amplified with the height of the building
Each building has a natural frequency
When the buildings frequency equals the frequency of the earthquake waves motion
is amplified
Mexico City; 1985; 8.1
Earthquake wave frequency = 2 seconds
10-14 story building wave freq = 2 seconds
Loma Prieta: 1989, 7.1
Collapse of the Nimitz freeway
What can be done to help prevent collapse?
High Rise Buildings:
Base isolation structures
Rollers (ball bearings)
Shocks (spring type systems)
Rubber/steel pads
Bridges:
Many bridges have poor attachment at footing
VERY expensive to fix
2 bridges in CA à $50 million
After Loma Prieta and Northridge quake Oregon sent delegations to these regions
Began examination of bridges
Learned from CA earthquakes
Oregon Bridges:
How many bridges are there?
Current retrofit and repair
Budget?
2003 legislature
$1.3 billion was set aside for work on 365 state bridges in the next
decade.
Different “types” of quakes
Strike slip fault quakes
Remotely triggered quakes
Volcanic quakes
Subduction zone quakes
Slow Quakes
Types Of Quakes
Strike Slip Faults
Nearly vertical fault
Motion?
San Andreas Fault Zone
Runs Length of CA from Mendocino to Salton Sea
Divides N. American and Pacific Plates
Series of Right Lateral SS faults
Extension of transform fault
Motion ~2” per year
Total Displacement: ~ 350 mile in 15-20 mil years
All size earthquakes
Notable Quakes
1857 Ft. Tejon 7.8
1906 San Fran 7.7
1989 Loma Prieta 7.1
1992 Landers 7.3
1994 Northridge 6.7
1999 Hector Mine 7.1
2004 Parkfield 6.0
Why do these types of quakes cause so much damage?
Locked Fault
Parts of the San Andreas Fault are locked
Parkfield
Central CA
6.0 quakes have occurred here ~every 22 years since 1857
Last one (prior to 2004) was in 1966
What was discovered from 2004 Parkfield quake?
Previous three quakes all had foreshocks 17 minutes before major shock
2004 quake did not
Previous three quakes ruptured NW-SE
2004 quake ruptured SE-NW
2004 quake ruptured same section of fault as previous quakes
More research
Observatory being built in Parkfield
Drill into fault ~4 km
Record stress build up
Sample rocks
USGS and Stanford
Landers Quake
Why was this quake important
Question of remote triggered quakes
Can one earthquake trigger another
NO: Reason is different fault systems that aren’t connected
Ex// San Andreas quake and Nisqually quake
YES: Recent studies have show that it is possible due to stress changes
on regional faults
Landers supported the idea of remotely triggered earthquakes
June 28, 1992
Landers quake
4:58 am
Big Bear quake
8:05 am
Some segments of the fault system had stress increased by as much as 14x
what they would have accumulated in 1 year
Other Segments of the fault system had the stress relieved
1999
Hector mine quake (7.1)
Other quakes attributed to Landers
Lassen Peak
Geysers (N. California)
W. Nevada (Mag 5)
Volcanic Quakes
Small quakes associated with movement of magma
Creates harmonic tremors
Used to measure how deep magma is
Can often precede an eruption
http://www.ess.washington.edu/SEIS/PNSN/HELENS/helensep_mo.html
Quakes Triggering Volcanic Activity?
Evidence: Landers Quake triggered activity in N. CA
Lassen volcano
Long Valley caldera
Yellowstone
Denali Alaska Nov 3, 2002, Mag 7.9
Geysers (N. CA)
Long Valley caldera
Yellowstone
Mt. Rainier
How does this work
Bubbles or gas break loose move up causing quakes
Subduction Zone Earthquakes
All depths and sizes of quakes
Quakes help to define plate boundary
Benioff Zone
Flat plane defined by quakes as down-going plate interacts with overriding plate
Quakes cause by sliding or as down going plate breaks
Normal faults on surface of plate
Seismic gaps
Region where quake activity should be but isn’t
Occurs along many faults
Occurs along subduction zones
When releasedà BIG QUAKE
Subduction zones can
produce Great quakes
Great quake is any quake over magnitude 8.0
1960 Chili 9.5
1964 Alaska 9.2
2004 MacQuarie Isl. 8.1
2004 Sumatra 9.0
Slow Quakes
More recent discovery
Original research in Japan
Creep Events that last weeks at a time
Discovered using GPS
mm changes in seismic station locations
Seismic signals similar to volcanic quakes
Lower frequency and intermittent through event
Moderate to deep (15-30 miles)
Common in NW (adding strain?)
Monitoring techniques
Seismographs
Electronic Distance meter
Changes in distance between two points
Precision : ~0.5 mm
Global Positioning systems
Vertical and horizontal displacement
Precision: Vertical ~10mm, horizontal ~2-3 mm
Strain Meters
Precision: change of 1 ppb or 1” in 16,000 miles
Creep meters
Paleo-seismology