ME$\mu $SR study of MgO: Search for O$^{-1}$ Earthquake-like Precursors

While many precursory signals of earthquakes are known to exist, interpretation of these signals is inadequately understood [1-3]. Earthquake-like precursor effects are detected by studying the signals generated by positive holes in MgO using Muon-Spin Resonance ($\mu $SR) and Maximum Entropy (ME). As an abundant earth-crust compound, MgO is an ideal model for studying eartquake-like signals [3]. Positive hole formation results from a break in an oxygen anion pair under elevated temperature, or high stress conditions [2]. For a 3N-MgO single crystal at elevated temperatures, a small percentage of oxygen is predicted to be in an O$^{-1}$ state instead of normal O$^{-2}$ ions. Preliminary ME analysis of transverse field (100 Oe) $\mu $SR MgO data show asymmetrical ME peaks at $\sim$ 1.4 MHz. Small T-dependent deviations from a Lorentzian (Lor) signal seem to be effects of O$^{-1}$ states in MgO. Tentatively, we have fitted ME transforms with three Lor's to obtain a reasonable description of the 1.4-MHz peak. The T dependences of this 3-Lor set are reported and discussed. Research is 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] K Tyson et al, SJSU internal Report (2011); S Lee \textit{et al,} abstract HUIC Educ, Math {\&} Eng Tech Conf (2013).