Reply to "Comment on 'The October 2005 Georgian Bay, Canada, Earthquake Sequence: Mafic Dykes and Their Role in the Mechanical Heterogeneity of Precambrian Crust' by S. Dineva, D. Eaton, S. Ma, and R. Mereu" by G. Ranalli and M. Lamontagne

Abstract

In a recent study (Dineva et al. , 2007; hereinafter DEA), we established a spatial correlation between the earthquake sequence of 20–24 October 2005 in Georgian Bay (Ontario, Canada) and magnetic anomalies that are most likely caused by mafic dykes. The strike of both determined nodal planes of the mainshock ( m N 4.3) are consistent with the strike of the magnetic anomalies. Focal depths of the earthquake sequence are estimated to be in the range 5–12 km, mostly around 10–12 km. Assuming a highly simplified rheological model that incorporates a quartz-dominated host lithology and a plagioclase composition for the mafic dykes, we estimated the shear strength of mafic dykes to be several orders-of-magnitude greater than the felsic host rocks at 10–12 km depth. Furthermore, we proposed that creep of quartz-dominated rheology, in juxtaposition with much stronger mafic rocks, could lead to strain accumulation and episodic seismicity within this depth range. The factors that control seismicity of stable continental regions remain enigmatic, and we are pleased that our proposed model has stimulated further discussion. Ranalli and Lamontagne (2009; hereinafter RL) comment on several aspects of our hypothesis, asserting that it is critically dependent on various assumed parameters and consequently not established with any level of confidence. Their discussion and our response are organized into two parts: (1) discussion of the choice of parameters used to support our analysis, and (2) a critique of …