Paleoseismic deformation in behind-ARC lacustrine settings: Acambay, Mexico and Ana River, Oregon.

摘要

Paleoseismic techniques offer the means to study fault activity in "behind-arc" tectonic settings where rates of deformation and historic seismicity are low. This dissertation presents geologic evidence of large earthquakes in the behind-arc, and establishes this setting as one that generates large (M ;The 1912 M;Trenches and exposures across and near the Ana River Fault, Oregon reveal evidence of multiple late Pleistocene and Holocene earthquakes from a well-exposed and dated sequence of tephra-bearing lacustrine sediments of pluvial Lake Chewaucan. Near- to far-field correlation of event horizons has helped establish a long paleoseismic record for the Ana River Fault. Large earthquakes recur every 10-20,000 years on this structure, with a slip rate of ;Many of the paleoseismic events on the Huapango Plain, Mexico and at Ana River occurred underwater during Pleistocene pluvial periods. Seismically-deformed thixotropic sedimentary packages are defined by the presence of low-angle faulting, folding, slumping with section stacking, subtle bevel unconformities, addition or removal of section, liquefaction, and boudinage structures. Detailed mapping of seismites has resulted in a tectonic model for submerged normal faults, based on shaking-related failure and gravity-driven block transport on gentle slopes.