Frequency-Dependent Tidal Triggering of Low Frequency Earthquakes Near Parkfield, California

Lian Xue, Roland Bürgmann, & David R. Shelly

Submitted August 1, 2017, SCEC Contribution #7376, 2017 SCEC Annual Meeting Poster #061

The effect of small periodic stress perturbations on earthquake generation in most cases is not clear. However, the rate of low-frequency earthquakes (LFEs) near Parkfield, California has been found to be strongly correlated with solid earth tides. Laboratory experiments and theoretical analyses show that the period of imposed forcing and source properties affect the sensitivity to triggering and the phase relation of the peak seismicity rate and the periodic stress, but frequency-dependent triggering has not been quantitatively explored in the field. Tidal forcing acts over a wide range of frequencies, therefore the sensitivity to tidal triggering of LFEs provides a good probe to the physical mechanisms affecting earthquake generation. In this study, we consider the tidal triggering of LFEs near Parkfield, California since 2001. We find the LFEs rate is correlated with tidal shear stress, normal stress rate and shear stress rate. The occurrence of LFEs can also be independently modulated by groups of tidal constituents at semi-diurnal, diurnal and fortnightly frequencies. The strength of the response of LFEs to the different tidal constituents varies among LFE families. Each LFE family has an optimal triggering frequency, which does not appear to be depth dependent or systematically related to other known properties. This suggests the period of the applied forcing plays an important role in the triggering process, and the interaction of periods of loading history and source region properties, such as friction, effective normal stress and pore fluid pressure, produces the observed frequency-dependent tidal triggering of LFEs.

Key Words
tidal triggering; LFEs;

Xue, L., Bürgmann, R., & Shelly, D. R. (2017, 08). Frequency-Dependent Tidal Triggering of Low Frequency Earthquakes Near Parkfield, California. Poster Presentation at 2017 SCEC Annual Meeting.

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