Scale invariance in complex seismic system and its uses in gaining precursory information before large earthquakes: Importance of methodology

Research on precursory information about the scale invariance of seismicity before large earthquakes has been an interesting topic for geophysicists in recent years. However, in some cases, it is difficult to capture this precursory information. Our study results show that seeking a pertinent selection of methodology is really needed for the purpose of gaining precursory information in the application of the analytical methods related to scale invariance. We investigated the scale invariance of the interevent time series of the seismic sequences for the Minle and Songpan regions in China by applying the methods of R/S Hurst analysis, local scaling property, correlation dimension, and generalized dimension spectrum. It is indicated that there are clearly precursory changes of local scaling property before the Minle M6.1 and Songpan M7.2 earthquakes, as well as precursory changes of the Hurst exponent and generalized dimension spectrum before the Songpan M7.2 earthquakes, while there are no clearly precursory changes of the Hurst exponent and generalized dimension spectrum before the Minle M6.1 earthquake, as well as the precursory change of the correlation dimension before the above large earthquakes, which signifies that there is a difference in the capability for capturing precursory information among the above four methods. This result suggests that the selection of an appropriate methodology is quite necessary to obtain the precursory information on the scale invariance in the use of the above four methods. If we do not select an appropriate methodology, we might not obtain any precursory information.