Supplementary Tables 1-5, and Supplementary Text S1 The 2015 VLFE spectra as a sum of smaller events It is possible to model the 2015 M W 3.8 VLFE as the sum of about 10 M W 3.2 earthquakes occurring over the course of about 10 seconds, following the approach Gomberg et al. (2016) used to model VLFEs as sums of much smaller LFEs. To see this, imagine the VLFE is the sum of N subevents, all of which have moment M 0s and corner frequency f cs , and source spectra

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We present a moment tensor catalog of 106 earthquakes in southern Alaska, and we perform a conceptually based uncertainty analysis for 21 of them. For each earthquake, we use both body waves and surface waves to do a grid search over double couple moment tensors and source depths in order to find the minimum of the misfit function. Our uncertainty parameter or, rather, our confidence parameter is the average value of the curve 𝒫0.3em(V), where 𝒫0.3em(V) is the posterior probability as a function of the fractional volume V of moment tensor space surrounding the minimum misfit moment tensor. As a supplemental means for characterizing and visualizing uncertainties, we generate moment tensor samples of the posterior probability. We perform a series of inversion tests to quantify the impact of certain decisions made within moment tensor inversions and to make comparisons with existing catalogs. For example, using an L1 norm in the misfit function provides more reliable solutions than an L2 norm, especially in cases when all available waveforms are used. Using body waves in addition to surface waves, as well as using more stations, leads to the most accurate moment tensor solutions.

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