Generalized Rydelek-Sacks test for distinguishing between periodic and random patterns in seismicity
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For distinguishing the periodicity of strong earthquakes on the time scale of decades, we generalized the Rydelek-Sacks test (Rydelek, Sacks, 1989) to explore whether a time series is modulated by a periodic process or not. The test is conducted by comparing the total phasor of seismicity with that produced by a random Brownian motion. The phase angle is defined by the origin time of earthquakes relative to a reference time scale. Using this method we tested two hypotheses in geodynamics and earthquake prediction study. One is the hypothesis of Romanowicz (1993) who proposed that the great earthquakes alternate in a predictable fashion between strike-slip and thrusting mechanisms on a 20–30 years cycle. The other hypothesis is that the strong earthquakes in and around China have an active period of about ten years. The test obtains a negative conclusion for the former hypothesis and a positive conclusion for the latter at the 95% confidence level.
Key wordsseismicity Rydelek-Sacks test periodicity earthquake prediction
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