Abstract
AbstractKnowledge of the in situ stress state of the Earth's crust plays a key role in understanding geological processes including plate tectonics, earthquakes, slope failure, and igneous emplacement. In this paper, we determine the in situ stress orientation from the PTA2 borehole on the island of Hawai'i, drilled into a lava flow dominated sequence between Mauna Kea and Mauna Loa. High‐resolution acoustic images were collected from the open hole interval 886 m to 1,567 m. Based on identification of 371 borehole breakouts for a total length of 310 m, the mean orientation of the minimum horizontal principal stress is N106° and remains constant across different volcanic rock fabrics. Changes in borehole breakout shape are linked to the different strength of volcanic facies and intra‐facies. The orientation of the present‐day stress field at Mauna Kea deviates from the plate forces and regional tectonic stress field. We interpret the compressive stress regime at the PTA2 site as resulting from the competing gravitational fields of the large topographic highs of Mauna Kea and Mauna Loa. Our study reveals that the mass accumulation associated with shield volcano growth imparts significant local variations to the subsurface stress state on volcanic islands consisting of overlapping shield volcanoes. The results have significant implications for stress accumulation leading to brittle failure and flank collapse, along with potentially influencing magma accumulation and ascent pathways during volcanic island evolution. This study provides the first insights into the orientation of the present‐day stress field between the major island forming shield volcanoes of Hawai'i.
Highlights
The determination of the present‐day stress field in the Earth's crust is fundamental for investigations of the mechanical behavior of rocks, fluid flow at depth, and in revealing mechanisms that cause tectonic plates to move, fault, or rupture (Amadei & Stephansson, 1997; Engelder, 1993; Zang & Stephansson, 2010; Zoback, 2007)
Our study reveals that the mass accumulation associated with shield volcano growth imparts significant local variations to the subsurface stress state on volcanic islands consisting of overlapping shield volcanoes
Our analysis provides the first subsurface evidence to suggest that the competing gravitational loads of two large overlapping shield volcanoes form the primary control on the orientation of the present‐day stress field
Summary
The determination of the present‐day stress field in the Earth's crust is fundamental for investigations of the mechanical behavior of rocks, fluid flow at depth, and in revealing mechanisms that cause tectonic plates to move, fault, or rupture (Amadei & Stephansson, 1997; Engelder, 1993; Zang & Stephansson, 2010; Zoback, 2007). Available stress data for the island of Hawai'i are derived mainly from focal mechanism solutions of earthquakes and geological field analysis of recent faulting. These extensive data sets reveal the respective role of rift zone intrusions, PIERDOMINICI ET AL
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