No abstract

[1] Microseismicity from a dike intruding the mid-crust of Iceland occurs episodically on fractures orientated parallel to the dike plane. We interpret it as caused by fragments of chilled magma being broken and pushed along the conduit by melt flow. Laboratory experiments on basalt samples under shear strains of $10 À4 show that the shear strength of a sample cooled through the glass transition initially increases to a maximum at $0.7 homologous temperature, but subsequently decreases until failure at $0.58 homologous temperature. We interpret the failure as due to the connection of microcracks. Episodicity in microseismicity on timescales of hours to days can arise from a cycle in which magma in 0.1-0.5 meter thick dikes first cools and becomes stronger, but then weakens along the dike margins with continued cooling against the country rock. Continued pressure of magma from below may then cause failure along dikeparallel fractures. Citation: White, R. S., S. A. T. Redfern, and S.-Y. Chien (2012), Episodicity of seismicity accompanying melt intrusion into the crust, Geophys. Res. Lett., 39, L08306,

The dynamic mechanical properties of quartz have been studied as a function of temperature across the α-β phase transition and in the vicinity of the incommensurate (IC) phase on cooling from the β phase. The mechanical response of the IC phase shows strong anelasticity for measurement of Young's modulus (closely related to C(11) in our geometry) with modulated stress driven at 1 Hz. The dynamic shear modulus does not show similar strong effects in its imaginary component, although a very weak anomaly is barely detectable in the real part of the modulus. Our results indicate that the incommensurate microstructures within the quartz transition interval are susceptible to dilatational stress with relaxation times around 1 s.

The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein.

No abstract