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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, B07404, doi:10.1029/2004JB003410, 2005

Structure and stress state of Hawaiian island basalts penetrated by the Hawaii Scientific Drilling Project deep core hole

Roger H. Morin

U.S. Geological Survey, Denver, Colorado, USA


Roy H. Wilkens

Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, Hawaii, USA


Abstract

As part of the Hawaii Scientific Drilling Project (HSDP), an exploratory hole was drilled in 1993 to a depth of 1056 meters below sea level (mbsl) and a deeper hole was drilled to 3098 mbsl in 1999. A set of geophysical well logs was obtained in the deeper hole that provides fundamental information regarding the structure and the state of stress that exist within a volcanic shield. The acoustic televiewer generates digital, magnetically oriented images of the borehole wall, and inspection of this log yields a continuous record of fracture orientation with depth and also with age to 540 ka. The data depict a clockwise rotation in fracture strike through the surficial Mauna Loa basalts that settles to a constant heading in the underlying Mauna Kea rocks. This behavior reflects the depositional slope directions of lavas and the locations of volcanic sources relative to the drill site. The deviation log delineates the trajectory of the well bore in three-dimensional space. This path closely follows changes in fracture orientation with depth as the drill bit is generally prodded perpendicular to fracture strike during the drilling process. Stress-induced breakouts observed in the televiewer log identify the orientations of the maximum and minimum horizontal principal stresses to be north-south and east-west, respectively. This stress state is attributed to the combination of a sharp break in onshore-offshore slope that reduces stress east-west and the emergence of Kilauea that increases stress north-south. Breakouts are extensive and appear over approximately 30% of the open hole.

Received 27 August 2004; accepted 16 March 2005; published 16 July 2005.

Keywords: geophysical logs; stress; borehole.

Index Terms: 8010 Structural Geology: Fractures and faults; 8015 Structural Geology: Local crustal structure; 8164 Tectonophysics: Stresses: crust and lithosphere; 8429 Volcanology: Lava rheology and morphology; 0915 Exploration Geophysics: Downhole methods.

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Citation: Morin, R. H., and R. H. Wilkens (2005), Structure and stress state of Hawaiian island basalts penetrated by the Hawaii Scientific Drilling Project deep core hole, J. Geophys. Res., 110, B07404, doi:10.1029/2004JB003410.