Abstract: In view of various behaviours of seismic precursory complexity, this paper probes into the genesis of precursory complexity. The complexity is studied from four different angles of earthquake source, tectonic field, fracture mechanics and precursory monitoring . It is recognized that the seismic precursory complexity exists objectively. Together with its regularity , the precursor is characterized of duality. We need to study both its regularity and complexity in the research of precursors so as to better understand and know it. Meanwhile, we should try to find the regularity from the complexity to further improve the earthquake preparation theory and develop new analytic and predictive methods. The basic cause resulting in the complexity of seismic precursors is the complexity of physical dynamic process of earthquake preparation, including quite a few of complicated factors, such as geological tectonics, seismogenic environment, dynamic process, focal failure mechanism and rupture growth process; Among the precursory complexities, the one exhibit more distinctly at short-term and imminent stag e; It is difficult to find one to one correspondence between the earthquake and the precursor; The situation that “ there is an anomaly but no earthquake occurs” can not simply be thought as interference. It may result from the development of the inhomog eneous stress field. Although the view point of “ field” and “ source” is helpful to analyze the complexity of seismic precursors, it is still necessary to be further studied to distinguish them from each other. Facing the reality that the success rate of earthquake predictio n reaches only 20% or so, we should consolidate the fundamental theoretical research, and develop high-performance seismological and precursory observ ational instruments.

Key words: Precursory complexity, Seismic focus, Field and Source, Fracture mechanics, Precursor monitoring