Reply to comment by Hampel et al. on “Stress and fault parameters affecting fault slip magnitude and activation time during a glacial cycle”

Abstract

Hampel et al. [2015, hereinafter Ha15] recently commented on our study [Steffen et al., 2014a], which investigates the effect of stress and fault parameters on fault slip magnitude and activation time during a glacial cycle using a newly developed two-dimensional glacial isostatic adjustment (GIA)-fault model [Steffen et al., 2014b]. In summary, Ha15 criticize the following parts of our study stating "(1) that Steffen et al.[2014a] describe our modeling approach in a misleading way, (2) that they do not mention the specific results (e.g., regarding the amount and timing of fault slip) of our studies anywhere in their article despite the similarity of the topic of their article, and (3) that the content and layout of Steffen et al.'s Figure 1 closely resembles two figures previously published in our studies but they do not cite the source (they, however, introduced conceptual errors concerning the glacial-interglacial stress evolution into their figure) ."We appreciate the comment by Ha15 as it gives us the opportunity to discuss and describe the differences between our model and Hampel et al.'s model in greater detail than in Steffen et al.[2014a] and earlier publications. We show that comparison between the results of both model approaches is not feasible.Due to the many issues raised by Ha15, we extract specific comments by Ha15 in conjunction to those above and also rephrase their statements so that we can address them in more detail: Before we deal specifically with these items, we briefly introduce the GIA process and its relation to fault activation as well as the two modeling approaches.The GIA process, which is the Earth's response to ice loading and unloading events during glacial cycles as well as the associated changing ocean loads on its surface, is known to affect Earth's shape, potential, rotation and stress [Steffen and Wu, 2011]. Changing stresses induced by the GIA process led to the reactivation of faults near the end of the last glaciation,~10,000 years ago, resulting in large earthquakes [Lagerbäck, 1978;Johnston, 1996;Lagerbäck, 1992;Arvidsson, 1996; Lagerbäck and Sundh, 2008;Lund, 2015]. These are found in northern Scandinavia, with the Pärvie fault being the largest [Lagerbäck and Sundh, 2008]; similar faults are also found in the British Isles [Stewart et al., 2001], Germany [Brandes et al., 2012[Brandes et al., , 2015 and North America [Fenton, 1994]. Early studies of the link between GIA and intraplate earthquakes are based on differential stress [e.g., Spada et al., 1991], which led to the conclusion that GIA induces earthquakes during glacial loading.

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