ME-$\mu $SR MgO study: search for O[-1] earthquake-like precursors

We analyze O$^{-1}$ earthquake-like precursor effects [1,2] by studying the $\mu $SR signals of MgO using Muon-Spin Resonance and Maximum Entropy (ME) [3,4]. Due to its abundance in the earth crust, MgO is ideal for studying these features: O$^{-1}$ (or positive hole) formation results from a break in an oxygen anion pair under elevated temperature or high pressure conditions [2]. For a 3N-MgO single crystal above RT, a small percentage (\textless 1{\%}) is predicted to be in an O$^{-1}$ state, instead of typical O$^{-2}$ ions. ME analysis of transverse field (100 Oe) MgO data show asymmetrical $\mu $SR peaks at $\sim$ 1.4 MHz. [4] Small T-dependent deviations from a Lorentzian (Lor) signal could be effects of O$^{-1}$ states in MgO. We have fitted ME transforms with three Lorentzians to obtain a reasonable description of the 1.4-MHz peak. The T dependences of this 3-Lor set and their B-field dependences at 17$^{\circ}$C are reported and discussed, and their relation to precursor earthquake-like O-valency effects. Research supported by RSCA-SJSU, SETI, WiSE-SJSU and AFC San Jose. \\[4pt] [1] FT Freund, Nat Hazards Earth Sys Sci \textbf{7} (2007) 1-7.\\[0pt] [2] FT Freund \textit{et al,} Phys Chem Earth \textbf{31} (2006) 389.\\[0pt] [3] C Boekema and MC Browne, MaxEnt 2008, AIP Conf Proc {\#}1073 p260.\\[0pt] [4] S Lee \textit{et al,} HUIC Educ, Math {\&} Eng Tech Conf, Uo HI (2013).