1. Motion of Bering Plate?
Jeff Freymueller

2. Andreanof Block Measurements
Adak
Atka
Kanaga
Velocities are relative to North America
Bering Sea
Great Sitkin
Pacific
VArc_NA
Vsubduction strain
Vmeasured
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

3. Subduction Zone Dislocation Model8 20 28 39
Dip angle
Fault plane model derived largely from relocated seismicity of Engdahl et al. (1987)
We will estimate the slip rate deficit for each plane
Aleutian Islands 54
The middle and lower fault plane boundaries between the Adak and Atka region are in agreement with the 1986 earthquake rupture area. 28
Bottom
Depth (km) 15
Lower
Middle 7
Upper
1996 rupture area from Kisslinger et al. (1997)

4. 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)
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

5. Fault Plane Boundary Optimization
Adak/Atka middle fault plane boundary
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
Bottom
Depth (km) 15
Lower
Middle 7
Upper

6. Model Results and Arc Velocity
ArcN.A.
-18 83 3
1996
1986
100 3
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

7. Alaska Peninsula/Shumagins

8. Bering Plate Motion

9. Location and Tectonics
Oblique Subduction
Aleutian Arc Translation
Bering Plate Hypothesis
Location and Tectonics
Russia
Alaska
Bering Block ?
Pacific Plate
Andreanof
Aleutian Subduction Zone