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Rock material at plate boundaries can bend, slide, fracture and hence, generate earthquakes
PNW EQ Sources1. Subduction Zone EQ
PNW EQ Sources2. Benioff Zone EQs
Earthquakes produced by slip along the subduction thrust fault or by slip on faults within the down-going ocean crust as a result of bending and extension as the plate is pulled into the mantle.
Nisqually EQ was 52.4 km below the surface
PNW EQ Sources
3. Shallow, Crustal EQs
EQs due to volcanic activity Mt. Rainier
Mt. Rainier
seismometerseismograph
instruments used to record the motion of the ground during an EQ
seismometer is the internal part of the seismograph
seismogram
The Pacific Northwest Seismic Network
Richter Magnitude
Richter Magnitude Length Analogy 1 1 millimeter 2 1 centimeter 3 10 centimeters 4 1 meter 5 10 meters 6 100 meters 7 1 kilometer 8 10 kilometers 9 100 kilometers 10 1000 kilometers
Richter Magnitude Damage
Magnitude Under 2 "Micro Quake" - Generally not felt.
Magnitude 3 Normally not felt.
Magnitude 4 Often felt. Damage is rare.
Magnitude 5 Felt widely. Normally only slight damage.
Magnitude 6 Poorly constructed buildings are damaged.
Magnitude 7 - 7.8 Very serious damage occurs.
Magnitude 7.8+ "Great Quake" - Tremendous destruction and loss of life.
FEBRUARY 28, 2001 NISQUALLY EARTHQUAKE
The science of seismology is essential for the assessment of earthquake risk. Why?
The science of seismology is essential for the assessment of earthquake risk. Why?
• locations• depths• magnitudes• frequencies• episodic activity
Seismic monitoring allows seismologists to determine EQ
How often do earthquakes occur in the Pacific Northwest?
http://www.pnsn.org/INFO_GENERAL/faq.html#1
Over 1000 earthquakes with magnitude 1.0 or greater in Washington and Oregon occur every year. About 25 are large enough to be felt.
Most Recent EQ
In the 20th century, there were about 14 earthquakes of magnitude 5 or greater that have occurred near Puget Sound (most are Benioff):
1904 (M 5.3) 1909 (M 6.0) 1932 (M 5.2) 1939 (M 6.2) 1945 (M 5.9) 1946 (M 6.4) 1949 (M 7.0) 1965 (M 6.5)1990 (M 5.0) crustal (Deming, WA) 1995 (M 5.0) crustal1996 (M 5.3) crustal2001 (M 6.8)2001 (M 5.0)
Location Map
How often do earthquakes occur in the Pacific Northwest?
http://www.pnsn.org/INFO_GENERAL/faq.html#1
Over 1000 earthquakes with magnitude 1.0 or greater in Washington and Oregon occur every year. About 25 are large enough to be felt.
In the 20th century, there were 13 earthquakes of magnitude 5 or greater that have occurred near Puget Sound (most are Benioff):
1904 (M 5.3) 1909 (M 6.0) 1932 (M 5.2) 1939 (M 6.2) 1945 (M 5.9) 1946 (M 6.4) 1949 (M 7.0) 1965 (M 6.5) 1990 (M 5.0) crustal (Deming, WA)1995 (M 5.0) crustal1996 (M 5.3) crustal2001 (M 6.8)2001 (M 5.0)
What is the return period?
The last Cascadia subduction zone EQ occurred in 1700
Evidence suggests they occur every 400 to 500 years
The science of seismology is essential for the assessment of earthquake risk. Why?
• locations• depths• magnitudes• frequencies• episodic activity
Seismic monitoring allows seismologists to determine EQ
What other geologic research contributes to our understanding of EQs and hence contributes to risk assessment?
• Surface mapping with LiDAR• Monitoring plate movements with GPS• Sea-floor mapping• Mapping
10m DEM from 1:24K contours
Maple Falls
Kendall
LiDAR survey of Nooksack River revealed Kendall Scarp
(Haugerud et al, 2005)
What other geologic research contributes to our understanding of EQs and hence contributes to risk assessment?
• Surface mapping with LiDAR• Monitoring plate movements with GPS• Sea-floor mapping• Mapping
What other geologic research contributes to our understanding of EQs and hence contributes to risk assessment?
• Surface mapping with LiDAR• Monitoring plate movements with GPS• Sea-floor mapping• Mapping
What other geologic research contributes to our understanding of EQs and hence contributes to risk assessment?
• Surface mapping with LiDAR• Monitoring plate movements with GPS• Sea-floor mapping• Mapping
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