HR: 1330h
AN: S42A-0147    [PDF]
TI: Evidence for conjugate shear failure and time-transient strain within the Cascadia forearc
AU: * DiLeonardo, C
EM: dilonardo@foothill.edu
AF: Geology Department, Foothill College 12345 El Monte Road, Los Altos Hills, CA 94022
AB: Understanding deformation of the Cascadia forearc is key to assessing potential subduction zone earthquakes in the region. Anelastic strain, within the forearc, may limit the magnitude and/or increase the recurrence interval of such events. Strain geometries within the forearc are complex and seemingly inconsistent. Within the submarine portion of the forearc, nine left-lateral arc-oblique transcurrent faults cut the subducting Juan de Fuca plate and overlying accretionary wedge. These active faults have formed in a stress regime that is nearly perpendicular to the documented north-south compression of the onshore areas of the forearc. The relationship between the offshore and onshore mechanics of faulting and the potential temporal variability of strain within the forearc are poorly understood. An integrated study was undertaken that merged offshore geophysical mapping, onshore geology and remote sensing data to compare strain patterns across the forearc. Orientation analysis of:(1) active faults in the submarine forearc; (2) Tertiary and younger faults of the Oregon Coast Range; (3) Tertiary and younger faults of the Willamette Valley; and (4) lineaments on thermal imagery at multiple spatial resolutions; all point to a geometrically consistent record of compression across the Cascadia forearc. The strain record of the rocks is in seeming conflict with the results of GPS surveys over the past decade, borehole breakout studies and recent crustal earthquakes, which all point to north-south compression. Integration of this data, representing a recent and potentially short record, points to temporal variation of the stress field within the Cascadia forearc over relatively brief periods of geologic time.
DE: 7230 Seismicity and seismotectonics
DE: 8164 Stresses--crust and lithosphere
SC: Seismology [S]
MN: 2003 Fall Meeting