Horizontal principal stress orientation in the Costa Rica Seismogenesis Project (CRISP) transect from borehole breakouts

Abstract

The Costa Rica Seismogenesis Project (CRISP) drilled the Pacific margin of the Middle America Trench just north of where the Cocos Ridge enters the subduction zone, resulting in basal erosion of the upper plate. Here we report the orientations of the maximum horizontal principal stress (SHmax) from borehole breakouts detected by logging‐while‐drilling and wireline downhole measurements. All SHmax directions were estimated in the sediment cover of the margin, above the deeper rocks of the deformed margin wedge. We observe three overall SHmax orientations: NNE‐SSW (25° azimuth) in the deepest interval drilled at the upper slope Site U1379; ENE‐WSW (82°) in the rest of Site U1379 and in Site U1413, also drilled in the upper slope; and NNW‐SSE (157°) in the mid‐slope Site U1378. Our preferred interpretation is that the deepest interval of Site U1379 records the stress conditions in the underlying margin wedge, as SHmax is parallel to the direction of the Cocos‐Caribbean plate convergence and of the compressional axes of plate boundary fault earthquakes. The variable SHmax directions observed elsewhere are likely due to the effect of a network of normal faults that subdivide the sediment cover into a number of independently deforming blocks. In addition, the observed SHmax directions may be influenced by the subducting Cocos Ridge, which acts as an indenter causing oblique deformation, and by the transition to seismogenic subduction along the plate boundary fault.

Normal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the Costa Rica subduction zone

“…A strongly foliated interval with abundant deformation bands and veins was identified in the recovered cores between 496.37 mbsf and $2.5 m above the MSR (548.98 mbsf). This interpretation is consistent with the current stress state (maximum horizontal stress: NNE-SSW) inferred from borehole breakouts detected by logging-while-drilling and wireline downhole measurements within the deepest intervals at Site U1379 [Malinverno et al, 2016]. Shipboard fault kinematic analyses inferred a normal fault paleostress regime with r 1 oriented vertically and r 3 oriented in a northeast-southwest direction similar to the plate convergence direction [Harris et al, 2013b].…”

“…Shipboard fault kinematic analyses inferred a normal fault paleostress regime with r 1 oriented vertically and r 3 oriented in a northeast-southwest direction similar to the plate convergence direction [Harris et al, 2013b]. This interpretation is consistent with the current stress state (maximum horizontal stress: NNE-SSW) inferred from borehole breakouts detected by logging-while-drilling and wireline downhole measurements within the deepest intervals at Site U1379 [Malinverno et al, 2016]. In contrast, borehole breakouts suggest a maximum horizontal stress oriented NNW-SSE in the shallow portion at Site U1378.…”

Horizontal compressive stress regime on the northern Cascadia margin inferred from borehole breakouts

“…In particular, whereas most sites drilled in the Nankai Trough show a margin‐perpendicular S Hmax orientation, S Hmax is margin‐parallel in a Kumano fore‐arc basin site [ Chang et al ., ; Lin et al ., ]. One out of three sites along the Costa Rica subduction zone indicates margin‐parallel S Hmax from breakouts, and here the variability in S Hmax orientation has been attributed to the effects of a network of normal faults that subdivide the sediment cover into a number of independently deforming blocks [ Malinverno et al ., ].…”

Arcuate stress state in accretionary prisms from real-scale numerical sandbox experiments

“…1(a) e.g. 3 – 5 . These deviations reflect the 3D structure of the stress state rather than the 2D structure; however the 3D stress structures as well as their effects on the evolution of the accretionary prism are not clear.…”

“…2 . The thick colored lines are the SHmax orientations from ( a ) ocean drilling 5 and ( c ) numerical modelling. The yellow lines represent sampling at a greater depth than the red lines.…”