Motion of Bering Plate? Jeff Freymueller

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

Subduction Zone Dislocation Model 8 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) 1996 7.9 15 1986 8.0 Lower Middle 7 Upper 1996 rupture area from Kisslinger et al. (1997)

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

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) 1996 7.9 15 1986 8.0 Lower Middle 7 Upper

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

Alaska Peninsula/Shumagins

Bering Plate Motion

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