Negentropy anomaly analysis of the borehole strain associated with the Ms 8.0 Wenchuan earthquake

Abstract. A large earthquake of 8.0 magnitude occurred on 12 May 2012, 14:28 UTC, with the epicenter in Wenchuan. To investigate the pre-earthquake anomalous strain changes, negentropy is introduced to borehole strain data at Guza station, approximated by skewness and kurtosis revealing the non-Gaussianity of recorded fluctuations. We separate the negentropy anomalies from the background by Otsu’s method and accumulate the anomaly frequency in different scales. The results show the long-scale cumulative frequency of negentropy anomalies follows a sigmoid behaviour, while the inflection point of the fitting curve is close to the occurrence of the earthquake. For the short-scale analysis before the earthquake, there are two cumulative acceleration phases corresponding to the two crustal stress releases, indicating the preparation process of the Wenchuan earthquake. We consider that negentropy exhibits potential for the analysis of earthquake precursor anomalies.

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