Calibrated focal-mechanism uncertainty and its effect on stress estimates in California

Preliminary version (v0.1) for a seminar on 14 Oct 2026; not peer reviewed. Later versions will update the manuscript, code and data. Preprint (version 0.1, 13 Oct 2026) with analysis code. Comparing two solutions for 578,307 California earthquakes and waveform moment tensors for the 2019 Ridgecrest sequence, the median disagreement is 39 deg (California) and 22-31 deg (Ridgecrest), and reported uncertainties must be multiplied by 1.7-2.7 to cover it. Error tables by number of polarities and magnitude, their transfer between regions, and the propagation of mechanism error into stress inversions are provided, together with the computation core of an open service for calibrated (conformal) mechanism sets and stress uncertainty. Input catalogues and STRESSINVERSE are not redistributed; see README for sources.