Information on stress conditions in the oceanic crust from oval fractures in a deep borehole

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doi: 10.1029/GL017i009p01311
Author(s): Morin, Roger H.
Author Affiliation(s): Primary:
U. S. Geol. Surv., Denver, CO, United States
Volume Title: Geophysical Research Letters
Source: Geophysical Research Letters, 17(9), p.1311-1314. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0094-8276 CODEN: GPRLAJ
Note: In English. 18 refs.; illus. incl. sketch map
Summary: Oval images etched into the vail of a deep borehole were detected in DSDP (Deep Sea Drilling Project) Hole 504B, eastern equatorial Pacific Ocean, from analysis of an acoustic televiever log. Initial speculation as to the origin of these remarkable features considered the intersection of pillow basalts with the wellbore. However, a systematic inspection of these ovals has identified intriguing consistencies in appearance that cannot be explained satisfactorily by a random, coincidental distribution of pillov lavas. As an alternative hypothesis, Mohr-Coulomb failure criterion is used to account for the generation and orientation of similarly curved, stress-induced fractures. Consequently, these oval features can be interpreted as fractures and related directly to stress conditions in the oceanic crust at this site. The azimuth of the oval center corresponds to the orientation of maximum horizontal principal stress (SH), and the oval width, which spans approximately 180° of the borehole, is aligned vith the azimuth of minimum horizontal principal stress (Sh). The oval height is controlled by the fracture angle and thus is a function of the coefficient of internal friction of the rock. Copyright 1990 by the American Geophysical Union.
Year of Publication: 1990
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 16 Structural Geology; Acoustical methods; Boreholes; Brittle deformation; Crust; DSDP Site 504; Deep Sea Drilling Project; Deformation; Field studies; Fractures; Geophysical methods; Geophysical surveys; IPOD; Interpretation; Lava; Leg 111; Leg 137; Leg 140; Leg 148; Leg 69; Leg 70; Leg 83; Leg 92; Ocean Drilling Program; Oceanic crust; Pacific Ocean; Pillow lava; Shear; Stress; Surveys; Tectonophysics; Televiewer logging
Coordinates: N011338 N011338 W0834349 W0834349
Record ID: 1990053618
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.