Multifrequential periodogram analysis of earthquake occurrence: An alternative approach to the Schuster spectrum, with two examples in central California

Pierre Dutilleul, Christopher W. Johnson, Roland Bürgmann, Yongge Wan, & Zheng-Kang Shen

Published October 10, 2015, SCEC Contribution #6160

Periodic earthquake occurrences may reflect links with semidiurnal to multiyear 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 multifrequential
periodogramanalysis (MFPA), performed on time series ofmonthly 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 2 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
~4months; for SN-ECSZ, it finds a strong ~14month 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 4months (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
semiannual components of pole tide and tide-induced stressmodel time series and fault normal-stress reduction
from seasonal hydrological unloading. For SN-ECSZ, the dominant ~14month periodicity prevents regular
annual peaking, and Model 2 provides a better fit (ΔR
2
adjusted: 2.4%). This new MFPA application resolves several
periodicities in earthquake catalogs that reveal external periodic forcing.

Citation
Dutilleul, P., Johnson, C. W., Bürgmann, R., Wan, Y., & Shen, Z. (2015). Multifrequential periodogram analysis of earthquake occurrence: An alternative approach to the Schuster spectrum, with two examples in central California. Journal of Geophysical Research, 120(12), 8494-8515. doi: 10.1002/2015JB012467.