Knowledge 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.
This PTA2 borehole investigation was funded by the International Continental Scientific Drilling Program (ICDP) and by VMAPP (Volcanic Margin Petroleum Prospectivity) project (VBPR/DougalEARTH/TGS) in collaboration with the Humu'ula Groundwater Research Project. D. A. J. and S. P. are partly funded through a Norwegian Research Council Centres of Excellence project (project number 223272, CEED). We thank Marco Groh for the logging operations. We thank two anonymous reviewers for the comments and suggestions. We are particularly grateful to the Associate Editor Mike Poland for his valuable comments and his critical review that greatly improved the manuscript.
- borehole breakout
- Mauna Kea
- present-day stress field