High Frequency Tremor Below Southern Vancouver Island
Abstract
The geology of southern Vancouver Island is dominated by the Wrangellia terrane that is seismically transparent with low scattering and intrinsic attenuation. Along with low levels of anthropogenic noise, P- and S-waves from regional events recorded on seismograms consequently exhibit clean, impulsive arrivals with high signal to noise ratios. These geologic conditions also enable the study of low-amplitude, emergent tectonic tremor signals and constituent low-frequency earthquakes with higher resolution and greater fidelity than has been achieved at other locations along the Cascadia subduction zone margin. At high-quality sites, high-frequency tremor envelopes, with dominant frequencies at ≥ 10 Hz and low-pass filtered at periods of minutes, correlate strongly with those for tremor in the traditional (e.g., 1-8 Hz) band. Furthermore, the energy levels of high-frequency tremor suggest a constant particle velocity spectrum. However, when observed at shorter time scales of several seconds, waveforms of impulsive high frequency tremor are frequently offset from those of classic low frequency earthquakes, in accord with recent models that posit a stochastic, very broadband-slow-earthquake-like slip process. In anticipation of an ETS event in autumn 2019, we are deploying a suite of 12 portable 3-component seismometers, the Pacific Geoscience Center Institute of Ocean Sciences Seismic Array (PISA), near Sidney, BC. These will complement the permanent Canadian National Seismic Network (CNSN), Plate Boundary Observatory (PB) and North Saanich Marine Technology Centre (NV) stations (PGC; B009, B010, B011; NSMTC, respectively) and form a small-aperture seismic array comprised of 17 stations. The dense station distribution in combination with the ideal geologic setting of southern Vancouver Island will allow a detailed analysis of high frequency tremor, thus providing further insight into the slow-slip source process. We will present preliminary results from the predicted 2019 ETS event and previous ETS events recorded at PGC.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S13F0500L
- Keywords:
-
- 7209 Earthquake dynamics;
- SEISMOLOGY;
- 7215 Earthquake source observations;
- SEISMOLOGY;
- 7230 Seismicity and tectonics;
- SEISMOLOGY;
- 8170 Subduction zone processes;
- TECTONOPHYSICS