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
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
Computers
Other Regions with quakes
Basin and Range
How did the basin and range form?
100-30 mybp series of subduction zones caused compression
Nevadan, Sevier, Laramide orogenies
Types of faults?
Extension started around 15mybp
Types of faults created?
B&R is very active seismically
Major Cities in Basin and Range
Las Vegas
Salt Lake City
Reno
All are located near or on faults that are active
Faults break in segments
Ex// Wastach Fault
Recurrence 400-2000 yrs
1st recognized ~100 yrs ago. Why more of an issue now?
Central US
New Madrid MO
1811-1812
3 earthquakes occurred from Dec-Feb
Magnitudes 8.1, 7.8, 8.0
Quakes occurred on 3 faults
2 are right Lateral strike slip faults
One is a reverse fault
Still seismically active
Why do earthquakes occur here?
Possibly a fail rift zone
Summery
Earthquakes propagated from south to north
First quakes on southern RLSS fault
Second set on Northern RLSS fault
Third quake on reverse fault
Rupture of Reelsfoot thrust fault
Fault crosses river 3 times
Major disruptions of riverbed and flow patterns
Waterfall formed due fault scarp
Flow barriers formed due to fault scarps
Sandblows or blowouts very prevalent
Archeological accounts show this isn’t the first time this has happened in
this area
Charleston SC
August 1886 mag 7.0
High Mercalli intensity…Why?
Charleston built on Fill
Other Regions of seismic activity
Boston, Vermont, New York
Many faults on East coast
Most faults hidden by sediments (blind faults)
Stress builds up over time by plate motion
Isostatic rebound from glaciation
Northwest Earthquakes
What type of quakes do we get in the northwest due to the configuration of the
tectonic plates?
How do we know we get great subduction quakes in the NW if we have never
experienced them.
What do we know
Great quakes can cause
Large amounts of land offset
Tsunamis
Mag 8 àshaking for 1-1.5 min à 15’-20’ wave
Mag 9à shaking for 2-3 minà 30’-40’ wave
Landslides or Turbidite deposits
Studies done in the NW
Deposits found
Submerged marshes
tsunami deposits (here and in Japan)
Date to the same year
Drowned forests
Tree rings date to 1699 trees being alive but dead in 1700
Marine sediments among forest debris
All found from Vancouver island to N. CA
Current research on how subduction zone is behaving
Due to subduction zone, coast range is uplifting
S OR, Astoria, NW WAà uplifting 1” per 10 yr
Central OR and Greys Harbor not uplifting
Coastal areas are being tilted east
Subduction zone is locked and strain is accumulating at ~1.6” per year
In 1987 Cascadia subduction zone declared major threat
Potential to produce quake of mag 9.5 or greater
Question: How would fault break?
Two options:
Break in segments (mag 8 quake)
Leveling studies show only parts of zone collecting strain. Points of low
strain may terminate rupture
Other similar subduction zones create mag 8 quakes and not mag. 9
Second option:
Break entire length (mag 9 quake)
Tusnami Deposits in Japan indicate Mag 9 quake
Turbidity deposits found along length of subduction zone all date to same
time period.
Other NW Quakes
Benioff Zone Quakes
Deep quakes on down going plate
Nisqually Quake
Normal fault ruptured on subduction plate
1949 7.1 magnitude quake
Occurs generally in WA not OR…Why
Bend in subduction zone creates “wrinkle” in the down going plate
Adds stress and causes slab quakes
Creates faults in overlying crust and creates uplift
Olympic mountains
Magma Quakes
Found offshore at ridges
Within the Cascade volcanic center
Small and shallow
Transform Faults
Offshore at Juan de Fuca and Gorda Ridges
Can be large but low intensity
Inland Crustal Faults
Created by tectonic interactions
Seattle Fault
Blind fault
Found by seismic reflection and offset
Runs W-E under Seattle
Uplifted areas suggest M7 quakes
Considered active fault
Portland
3 major faults
Portland hills fault
Cuts through downtown
Capable of M6-7 quakes
Last ruptures 10,000 yrs ago
East Bank Fault
Oatfield Fault
Other Faults and Quakes
Mount Angel Fault
Scott Mills Quake: March 1993 (M5.6)
Klamath Mountain 1993
5.9 and 6.0
Killed one person
