Impact of chlorite dehydration on intermediate-depth earthquakes in subducting slabs

Abstract

Intermediate-depth earthquakes are common in the double seismic structures of many subduction zones under high pressures (~1–4 GPa). Serpentine dehydration exhibits well-established links with double seismic zone earthquakes. Additionally, dehydration of several hydrous minerals including lawsonite and chlorite underlying the upper and lower layers, respectively, may be responsible for intermediate-depth earthquakes. Here, we present experimental evidence suggesting that chlorite dehydration can trigger intermediate-depth earthquakes at the lower plane (~700 °C). We conducted deformation experiments on chlorite peridotite under high-pressure (0.5–2.5 GPa) and high-temperature (500–750 °C) using a modified Griggs apparatus. Experiments revealed the presence of faults in samples that had undergone partial chlorite dehydration with the presence of the dehydration product Ca-amphibole along these faults. Our findings confirm, together with correlation studies between seismicity and mineral stability, that a part of intermediate-depth seismicity in the lower plane of double seismic zones can be attributed to chlorite dehydration.

Anisotropic thermal conductivity of antigorite along slab subduction impacts seismicity of intermediate-depth earthquakes

“…On the other hand, the seismicity in the lower plane of a DSZ is more enigmatic and under debate. Depending on the variable temperature profile and water content, etc., in a subduction zone, the lower seismic plane could be caused by either also the dehydration of hydrous minerals 9 , 13 , or other rupture mechanisms. Another plausible trigger for intermediate-depth earthquakes is the thermal runaway 12 , 19 – 22 , a ductile deformation mechanism in shear zones, where the intense frictional heating induces weakening of rocks and causes the formation of a self-localizing slip planes.…”

“… 4 – 6 for example features of DSZs, where the separation of two seismic planes correlates with the age of a slab, i.e., with its temperature and thickness at the trench. Since its first observation in northeast Japan 7 , several mechanisms have been proposed to explain the origin of DSZs, including dehydration embrittlement 6 , 8 – 13 , fluid-related embrittlement 14 , transformation faulting 15 , plastic shear instability 16 , 17 , grain size reduction 18 , and thermal runaway 12 , 19 – 22 . Of particular importance are the dehydration embrittlement and thermal runaway, as they are considered the two major mechanisms for intermediate-depth seismicity 12 , 19 .…”