Low Frequency Earthquakes below Northern and Central Vancouver Island

English Abstract:

Tectonic tremor and low frequency earthquakes (LFE) in northern Washington and southern Vancouver Island (VI) have been extensively studied in recent years. However, far less attention has been directed to northern and central VI where the behavior of tremor and LFEs is less well understood. In this study, we aim to investigate the properties of slow slip events in these latter regions by assembling LFE templates using data from the POLARIS-NVI and SEAJADE II experiments. The POLARIS-NVI experiment comprised 27 broadband seismometers arranged along two mutually perpendicular arms with an aperture of ~60 km centered near station WOS (lat. 50.16, lon. -126.57). It recorded two ETS events in June 2006 and May 2007, each with duration less than a week. For these two episodes, we constructed more than 50 independent, high signal to noise ratio LFE templates representing spatially distinct asperities on the plate boundary in NVI, along with a catalogue of over fifty thousand detections. We plan to further extend the POLARIS-NVI template catalogue with data from the more recent SEAJADE II experiment. The SEAJADE II experiment included 35 OBS stations offshore west of the central VI and 9 land-based stations. It captured an unusually active and protracted ETS episode in the central and northern VI region that began in July 2014 and extended intermittently into November 2014. The combined LFE template catalog will help to delineate the detailed spatiotemporal distributions of ETS in the northernmost part of the Cascadia margin, thereby enabling comparison among the 3 different episodes and with episodes in other parts of Cascadia.