HR: 1330h
AN: T43C-02    [Abstracts]
TI: In Situ Stress Field From Borehole Measurements and Plate Tectonic Models
AU: * Grandi, S
EM: grandi@mit.edu
AF: Massachusetts Institute of Technology. Earth Resources Laboratory, 77 Massachusetts Avenue. E34., Cambridge, MA 02139 United States
AU: Toksöz, N
EM: toksoz@mit.edu
AF: Massachusetts Institute of Technology. Earth Resources Laboratory, 77 Massachusetts Avenue. E34., Cambridge, MA 02139 United States
AB: We obtain in situ stress information based on two methods. The first method consists of estimating stress directions from the orientation of breakouts in a borehole. Stress magnitudes are interpreted from elastic models of stress distribution around the borehole. The second method is applied where the borehole is not deformed and a crossover in the dispersions of polarized flexural waves is observed. Data rotation to principal axes provides stress orientation. Magnitudes are inferred from the velocity anisotropy measured at low frequencies. For a particular field dataset we observe that the greatest stress is horizontal in the NNW-SSE direction (SHmax). Both methods agree in the estimation of stress orientation and magnitude. The relative magnitudes of principal stresses are on average SHmax ~eq 1.1 Sv (Sv: vertical stress) and Shmin ~eq 0.9 Sv (Shmin: minimum horizontal stress), suggesting predominantly strike slip tectonics. The estimated stress orientation is in agreement with a regional stress field calculated from the relative motion of the Caribbean and South America plates.
DE: 0915 Downhole methods
DE: 3210 Modeling
DE: 8155 Plate motions--general
DE: 8164 Stresses--crust and lithosphere
SC: Tectonophysics [T]
MN: 2005 Joint Assembly