Extracting the anisotropy information of crustal rocks from the seismological garbage

Abstract

Human has been eagerly expecting to know some information that can indicate a large earthquake’s impending1,2,3,4,5. Decades of efforts showed that the impending of large earthquakes was usually accompanied by a process of regional weakening manifested with multiple temporal and spatial scaled deformation, and such a deformation was often accompanied by clusters or swarms of micro-earthquakes6, which further caused observable change in anisotropy of nearby rocks7,8,9,10. Here we show that the anisotropy information of crustal rocks may be extracted from the seismological garbage, the travel-time residuals produced by dense seismic stations which record clusters or swarms of micro-earthquakes, by means of a new concept, the slowness deviation tensor expressing 3-axis slowness anisotropy. In particular, we present a real example to justify that the slowness deviation tensor with arbitrarily inclined axis may be successfully extracted from the travel-time residual data, and meanwhile to demonstrate that this anisotropy reflected by the extracted tensor mainly originated from the local stress action or deformation. Undoubtedly, this work provides a completely new methodology to link the clusters or swarms of micro-earthquakes with the weakening process which occur before large earthquakes, which essentially contributes a promising direction toward the information that human has been expecting for.