Publication Date:
2015-11-27
Description:
Periodic earthquake occurrences may reflect links with semi-diurnal to multi-year tides, seasonal hydrological loads and ~14-month pole-tide forcing. The Schuster spectrum is a recent extension of Schuster's traditional test for periodicity analysis in seismology. We present an alternative approach: the multi-frequential periodogram analysis (MFPA), performed on time series of monthly earthquake numbers. We explore if seismicity in two central California regions, the Central San Andreas Fault near Parkfield (CSAF-PKD) and the Sierra Nevada-Eastern California Shear Zone (SN-ECSZ), exhibits periodic behavior at periods of two months to several years. Original and declustered catalogs spanning up to 26 years were analyzed with both methods. For CSAF-PKD, the MFPA resolves ~1-year periodicities, with additional statistically significant periods of ~6 and ~4 months; for SN-ECSZ, it finds a strong ~14-month periodic component. Unlike the Schuster spectrum, the MFPA has an exact modified statistic at non-Fourier frequencies. Informed by the MFPA period estimates, trigonometric models with periods of 12, 6 and 4 months ( Model-1 ) and 14.24 and 12 months ( Model-2 ) were fitted to time series of earthquake numbers. For CSAF-PKD, Model-1 shows a peak annual earthquake occurrence during August-November and a secondary peak in April. Similar peaks, or troughs, are found in annual and semi-annual components of pole-tide and tide-induced stress model time series and fault-normal stress reduction from seasonal hydrological unloading. For SN-ECSZ, the dominant ~14-month periodicity prevents regular annual peaking, and Model-2 provides a better fit ( : 2.4%). This new MFPA application resolves several periodicities in earthquake catalogs that reveal external periodic forcing.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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