Long-term seismogenesis in Greece: Comparison of the evolving stress field and precursory scale increase approaches

Abstract

Recent strong (M 6.6) earthquakes in Greece are examined from the point of view of two current, but disparate, approaches to long-term seismogenesis. These are the evolving stress field (ESF) approach, in which earthquakes are considered to be triggered by accumulated stress changes from past earthquakes and tectonic loading on the major faults, and the precursory scale increase (Y) approach, in which a major earthquake is preceded in the long term by an increase in minor earthquake occurrences, with the magnitude of the precursory earthquakes, and the precursor time and area all scaling with the major earthquake magnitude. The strong earthquakes are found to be consistent with both approaches, and it is inferred that both approaches have a relevant role to play in the description of the long-term generation process of major earthquakes. A three-stage faulting model proposed previously to explain the Y phenomenon involves a major crack, which eventually fractures in the major earthquake, being formed before the onset of precursory seismicity. Hence we examine whether ESF can account for the formation of the major crack by examining the accumulated stress changes at the time of the onset of Y for each strong earthquake. In each case, the answer is in the affirmative; there is enhanced stress in the vicinity of the main shock at the time of the onset. The same is true for most, but not all, of the locations of precursory earthquakes.