Understanding the Juan de Fuca Plate System: A 20-Minute Overview, Slides of Earth Sciences

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A brief overview of the Juan de Fuca

plate system in 20 minutes or less

Rob Porri=

UC Berkeley

EQW 2.17.

Teleseismic P waveforms (34-­‐40 degrees)

Teleseismic SV (0.02 – 0.1hz)

USGS Plate tectonics map (more of a cartoon really)

Anisotropy

Long and Becker 2010, modified from

Long and Silver, 2008

40 ˚ 42 ˚ 44 ˚ 46 ˚ 48 ˚ SN CR CV OP CB CRB WV OCR HLP BR K CCR

a

ï 126 ˚ ï 123 ˚ ï 120 ˚ 40 ˚ 42 ˚ 44 ˚ 46 ˚ 48 ˚

e

0 0 4

b

0 (^40)

c

20

d

ï 126 ˚ ï 123 ˚ ï 120 ˚

0 0 0 10

f

ï 126 ˚ ï 123 ˚ ï 120 ˚

• 0 2 2 2

g

ï 126 ˚ ï 123 ˚ ï 120 ˚ 0 0 0 2 2 4 4

h

ï 20 ï 16 ï 12 ï 8 ï 4 0 4 8 12 16 20 dVsv (%) ï 10 ï 8 ï 6 ï 4 ï 2 0 2 4 6 8 10 dVsv (%) 5km 10km 15km 35km 70km 100km

Porri= et

al., 2011

Ac^ve P

imaging

Calvert et al., 2011

Rogers and Dragert, 2003

Brudzinski and

Allen, 2007

0 20 40 60 80 100 120

Depth (km)

40 41 42 43 44 45 46 47 48 49

Latitude (°N)

-6 -

0 0 0 0 2 2 2 4

c^4

Gorda S. JdF N. JdF

0 1 2

Elevation (km)

b

0 2 4 6 8 10 12

Percentage of tremor

0 100 200 300 400 500 600 700 800 900 1000

Distance Along Subduction Interface (km)

a

10 months

Klamath

20 months

Siletzia

14 months

Wrangelia

ï 10 ï 8 ï 6 ï 4 ï 2 0 2 4 6 8 10 dVs (%) ï 126 ˚ ï 123 ˚ ï 120 ˚ 40 ˚ 42 ˚ 44 ˚ 46 ˚ 48 ˚

d

Porri= et al., 2011

Guilhem et al., 2007

Slow earthquakes (Mw ≥ Ml+0.5 –red) Repea^ng earthquakes (black)

Conclusions

• The Juan de Fuca plate system represents the

last stages of farallon subduc^on beneath the

North American Plate

• Slab fragmenta^on plays a key role in the

subduc^on system.

• Unusual forms of seismicity are more common

than the garden variety earthquakes.

• While being a black sheep of subduc^on

zones, Cascadia is very well studied due to its

poten^al hazard in the US.