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Invastigation of Parkfield tremor source properties using an array of tripartite seismic arrays

Asaf Inbal

Submitted September 11, 2022, SCEC Contribution #12210, 2022 SCEC Annual Meeting Poster #031

Obtaining precise tremor locations and constraining tremor source properties is essential for understanding deep crustal faulting. Yet, the poor SNR and emergent nature of tremor puts this class of signals well beyond the reach of traditional seismological techniques. The main issue is that the tremor signal contains multiple phase arrivals from nearby sources that are active simultaneously. Each source is low-amplitude and high-frequency-depleted, making seismic phase picking and association very challenging. In this study, we utilize multiple tripartite arrays of permanent stations to precisely locate and characterize the sources of high-amplitude short-term tremor bursts, during a slow-slip event that occurred along the Cholame section in 2018 (Inbal et al., 2021). These bursts give rise to highly polarized ground motions, which are remarkably correlated among stations located several km apart. We use inter-station correlations of rotated horizontal seismograms to infer the slowness of S-wave phases, and then solve for locations satisfying the inferred direction-of-arrival at multiple arrays. We apply a time-domain approach to calculate the moment and source durations, assuming the ω^2 source model.

We find that the duration of coherent inter-station high-amplitude Cholame tremor is of the order of a few seconds, much shorter than the durations of inter-station tremor correlations observed in Cascadia. Presumably, this is due to strong scattering. However, if tremor is the manifestation of the seismic failure of multiple brittle asperities embedded in a ductile matrix, then our result may suggest the bursts represent the rupture of asperities that are larger then the ones giving rise to ambient non-coherent tremor. We search for evidence supporting this hypothesis in the frequency-magnitude distribution of the newly-compiled Cholame tremor catalog.

Inbal, A. (2022, 09). Invastigation of Parkfield tremor source properties using an array of tripartite seismic arrays. Poster Presentation at 2022 SCEC Annual Meeting.

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