HR: 15:10h
AN: U43A-05    [Abstracts]
TI: Examining Stress Changes Due to Subducting Topography and Variable Rheology in the Middle America Trench at Nicoya Gulf, Costa Rica
AU: * Elliott, C E
EM: celliott@nmt.edu
AF: Department of Earth and Earth and Environmental Science, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, United States
AU: Bilek, S L
EM: sbilek@nmt.edy
AF: Department of Earth and Earth and Environmental Science, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, United States
AU: Lithgow-Bertelloni, C
EM: crlb@umich.edu
AF: Department of Geological Sciences, University of Michigan, 1100 North University Ave, Ann Arbor, MI 48109-1005, United States
AB: Offshore of the Nicoya Gulf at the Middle America Trench, the Cocos Plate is subducting beneath the Caribbean plate at about 84 mm per year. A line of seamounts are entering the trench in this region, causing dramatic deformation of the seafloor landward of the thrust. It has been suggested that these seamounts are being subducted, causing coastal uplift and seismicity. The March 25, 1990 Mw 7.0 Nicoya Gulf earthquake is thought to have occurred as one of these seamounts ruptured. How do these seamounts affect the rupture process? Are they behaving as patches of increased or decreased friction along the seismic interface? How does the subducting topography change the stress field after an earthquake? Can triggered events be explained by static stress changes, or does the rheology down dip from the seismogenic zone influence subsequent events in the region? Using a three dimensional model with patches of variable friction to simulate the seamounts as asperities, we compare the location of aftershocks to the stress changes associated with increased and decreased friction. We compare this to a model of Coulomb static stress change, which displays lobes of static stress increase and decrease due to slip on the fault plane, and the distribution of aftershocks within these lobes. To examine the stress changes associated with a set of delayed inland triggered events, we also vary the rheology of our model, using a linear elastic half space for the seismogenic zone, and viscous creep along the lower, aseismic portion of the fault below 40 kilometers. These models allow us to examine the spatial and temporal relationship of seismicity associated with stress changes due to variable friction and rheology. Our results indicate that stresses increase away from the fault with time if viscous creep is included in the model. These stress increases roughly correspond to inland areas of noted increase in seismicity, suggesting that creep along the down dip, aseismic portion of the interface, transmits stresses into the upper, elastic crust.
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Union [U]
MN: 2007 Joint Assembly