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Title: The mechanics of deep earthquakes
Author: Santangeli, J. R.
ISNI:       0000 0004 7225 7251
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2017
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Deep-focus earthquakes have remained a puzzle for researchers since 1928 when they were first reliably identified by Kiyoo Wadati in Japan. At the time it was understood that earthquakes at these depths should not have been possible as ductile deformation should be dominant. It is now known that deep-focus earthquakes occur in the depth range of 300 to 700 km with two peaks in activity around 400 and 600 km, although this does vary among slabs. Investigations into the mechanism responsible for generating deep-focus earthquakes have concentrated on transformational faulting, a process whereby a metastable mineral undergoing a phase change can cause seismogenic failure via a thermally driven runaway mechanism. Various previous high-pressure high-temperature experiments have been conducted on the olivine-spinel transition in both the germanate analogue and the natural magnesium silicate systems. However there is contention over whether olivine could in fact survive metastably beyond 500 km, and there are other candidate phases that could be responsible. This thesis presents experiments involving MgGeO3 high-clinopyroxene - ilmenite transition as an analogue for MgSiO3 clinopyroxene-akimotoite transition. The P-T phase relations have been determined experimentally and from a Debeye fit to the thermal expansivity of the germanate clinopyroxene and ilmenite phases. Further experiments have demonstrated that, under a set of critical conditions, compression through the clinopyroxene-ilmenite phase boundary results in large acoustic emissions emanating from the sample volume, at pressures very close to the phase boundary. This implies that the natural transition may well be capable of being seismogenic within the Earth.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available