![]() ![]() Repeated fracturing requires a stress accumulation that is achieved after complete recovery of the mechanical strength of preexisting interfaces through fracture healing. carried out fracturing experiments on dense lavas and showed that the fracture of high-temperature magma is seismogenic. Subsequently, detailed mechanisms of the RFH cycle were proposed based on geological observations on fractured magmatic rocks. proposed that repeated fracturing and healing (RFH) in silicic melts is a trigger mechanism for such seismic events. They have been attributed to various mechanisms including magma–water interaction, stick–slip motion, shear fracturing, and episodic gas loss. Repetitive seismic events are commonly observed during the emplacement of lava domes. This microscopic healing time is consistent with the period of actual seismicity and is prolonged sufficiently to permit the formation of millimeter-thick bubble-free obsidian layers along fractures in vesicular lavas through bubble resorption due to diffusive degassing. The microscopic healing time was strongly dependent on temperature and roughness of the interface and was, for the nonpolished interfaces, 67–74, 4.0–4.9, and 0.36–0.38 h at 850°, 900°, and 950☌, respectively, whereas for the polished examples it was 1–3 and 0.5–0.6 h at 850° and 900☌, respectively. We defined this closure interval as microscopic healing time and determined this by fitting the measured profiles with a diffusion model. This change was interpreted to reflect atomic-scale closure of the interface, probably by chemical bonding. The water content across the contact initially decreased toward the interface via diffusive dehydration, but later homogenized. The contact interface became coherent and finally disappeared. These were annealed in an open-system cell. Two cylindrical obsidian cores were juxtaposed on surfaces prepared by cutting the cores both with and without polishing. To estimate the healing time of magmatic fractures, we performed healing experiments on rhyolitic melts at 850°–1000☌ and 1.6–3.2 MPa for 0.5–94 h. The healing of magmatic fractures is considered essential to repetitive seismicity and the closure of degassing paths during emplacement of lavas. ![]()
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January 2023
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