Multiple seismo-anomalies associated with the M6.1 Ludian earthquake on August 3, 2014

Abstract Multiple geophysical parameters including groundwater level, water temperature, water radon, crustal deformation, electromagnetic waves and total electron contents (TEC) in the ionosphere, are examined together to investigate pre-earthquake anomalous phenomena associated with the Mw6.1 Ludian earthquake on August 3, 2014. Cross-parameter comparison eliminates anomalies that are detected in one parameter only and examine earthquake-related phenomena in various fields, simultaneously. Retrieved anomalies show that abnormal decreases of water temperature and radon concentration related to anomalous uplift of groundwater levels appeared about 1–8 days before the earthquake even without contributions from rain. Significant step-like changes are observed from data recorded by strainmeters on July 31 and are consistent with water-related anomalies in timing. No significant anomalies can be found from electromagnetic data through the preliminary observation. In contrast, TEC appeared positive anomalies 1–3 days before the Ludian earthquake. Although causal mechanisms of the TEC anomalies from stressed rocks are not fully understood, multiple-parameter examination can increase credibility of determination regarding pre-earthquake phenomena.