Spatial, and Temporal Periodicity in the Pacific Tsunami Occurrence

Abstract

In recent years, geophysicists have devoted much attention to the search for regular spatial and temporal features in the distribution of seismic events over the Earth. At the same time, the knowledge of the lithosphere has been developed in terms of active geophysical medium with structural units capable of accumulating additional elastic energy and releasing it in the process of tectogenesis and seismic activity. The paper presents the analysis of natural symmetry patterns inherent in various geophysical processes, leading to the conclusion that the equatorial plane divides the Pacific region into northern and southern lineaments, taking into account the location of lithospheric plate boundaries. Based on the catalog of Pacific tsunamis {[}Gusiakov, 2001], events of tectonic origin with magnitudes M > 5.9 are selected for the period 1950-2001. Their total number is 141. The time distribution of these events revealed the effect of successive activation of adjacent lineaments. The set of events represented as a time series is used to construct envelope functions, and spectral power densities were calculated from their Fourier transforms in order to evaluate the energy contributions of various frequencies. Spectral peaks at periods of 20 and 6 years, as well as a weak peak at 412-437 days, are identified. These periods are close to the periods of the Chandler wobble of the Earth's geographic pole. Analysis of previously estimated contributions of external forces to the energy of the Earth's seismogenic layer suggests that disturbances in the Earth's rotation due to the polar wobble, precession, and especially tidal forces supply additional energy to the lithosphere; this energy is comparable to, and occasionally even exceeds, the yearly release of seismic energy. The 6-year period plays an important role in these processes.