Logarithmic and exponential transients in GNSS trajectory models as indicators of dominant processes in postseismic defo
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ORIGINAL ARTICLE
Logarithmic and exponential transients in GNSS trajectory models as indicators of dominant processes in postseismic deformation Franco S. Sobrero1 · Michael Bevis1 · Demián D. Gómez1 · Fei Wang1 Received: 1 April 2020 / Accepted: 1 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Models for postseismic transient displacements can be formulated using logarithmic and exponential decay formulas with single or multiple timescales. The logarithmic form is associated with rate and state friction theory and afterslip, while the exponential form is associated with bulk viscoelastic relaxation of coseismic stresses. It is now quite widely understood that one can model GPS/GNSS time series manifesting postseismic transient displacements almost equally well using trajectory models constructed using logarithmic or exponential transients. This is consistent with the consensus established by the late 1970s that it is difficult to use geodetic observations to distinguish between deep aseismic afterslip and more diffuse viscoelastic relaxation as the primary mechanism of postseismic deformation. In this paper, we assess the relative explanatory value of both logarithmic and exponential forms by focusing on GNSS time series measured with better than typical signal-to-noise ratios. We find that the double logarithmic transient typically provides much better fits than double exponential transient, when both models are given equal degrees of freedom. We also discuss the relative utility of the hybrid transient formulas in which the logarithmic component is assigned shorter decay timescale parameters than the exponential component. These models fit observed postseismic displacements almost as well as double logarithmic transients. Keywords GNSS trajectory models · Postseismic deformation · Logarithmic and exponential transients
1 Introduction Our understanding of the three phases of the earthquake deformation cycle, especially the coseismic phase, has significantly improved in the past few decades. The underlying mechanisms of the postseismic phase remain the least well understood. The postseismic displacements that we observe with continuous GNSS (CGNSS) networks are thought to be driven by three distinct processes: poroelastic rebound, afterslip, and viscoelastic relaxation. Afterslip and/or viscoelastic relaxation are widely regarded as the most important of these mechanisms (Scholz 2002), especially for megathrust events in subduction zones. Poroelastic rebound, which involves Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00190-020-01413-4) contains supplementary material, which is available to authorized users. * Franco S. Sobrero [email protected] 1
School of Earth Sciences, The Ohio State University, Columbus, OH 43210, USA
coseismic stresses being relieved by the flow of pore fluids, is probably more important in shallow strike-slip faults in continental crust, since the upper portions of these faults are often
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