Download Motion of Bering Plate?

Motion of Bering Plate?
Jeff Freymueller
Andreanof Block Measurements
Bering Sea
Great
Sitkin
Kanaga
Pacific
Velocities are relative to North America
• 22 usable sites surveyed over a 6 to 7 year time span
• Sites with a volcanic signal are excluded
• Velocities show large along strike variations due to
changes in the subduction zone behavior
• To quantify the velocity of the Andreanof Block relative
to North America it is necessary to model the
subduction related strain
Subduction Zone Dislocation Model
Fault plane model derived
largely from relocated seismicity
of Engdahl et al. (1987)
We will estimate the slip rate
deficit for each plane
The middle and lower
fault plane boundaries
between the Adak and
Atka region are in
agreement with the
1986 earthquake
rupture area.
1996 rupture area from
Kisslinger et al. (1997)
54
28
15
7
Inversion for Arc Velocity
• Linear inversion for fault plane
coupling coefficients
• Calculation carried out over a range
of arc translation velocities
• Boundary conditions applied using
Matlab scrip least squares linear
inversion (lsqlin)
d   d  arc
m  (GT G ) 1 GT  d 
Boundary conditions
• 0 < m < 1 for all fault planes except Adak
bottom plane where (-1 < m < 1) to
accommodate postseismic affects
associated with 1986 or 1996 Andreanof
Island earthquake.
Best fit velocity of the Andreanof
Block
relative
to North
America
Trench
Parallel
= 4.8
mm/yr
Trench Normal = 3.3 mm/yr
Total Velocity = 5.8 mm/yr
Fault Plane Boundary Optimization
The offset middle plane boundary
between the Adak and Atka region
is optimized for best results and is
still in agreement with the 1986
earthquake rupture area.
54
28
15
7
Model Results and Arc Velocity
ArcN.A.
0
-18
1996
0
83
3
1986
100
3
0
• Based on model results the red vector is the velocity of the Aleutian Arc relative to
North America for Andreanof region
• Pink numbers are the percent of unit coupling for each fault plane
Alaska Peninsula/Shumagins
Bering Plate Motion
• Oblique Subduction
Location and Tectonics
• Aleutian Arc Translation
• Bering Plate Hypothesis
Bering Block ?
Pacific Plate