Tectonic tremor on Vancouver Island, Cascadia, modulated by the body and surface waves of the M_w 8.6 and 8.2, 2012 East Indian Ocean earthquakes

Abstract

The 2012 East Indian Ocean earthquake (Mw 8.6), so far the largest intraoceanic plate strike‐slip event ever recorded, modulated tectonic tremors in the Cascadia subduction zone. The rate of tremor activity near Vancouver Island increased by about 1.5 times from its background level during the passage of seismic waves of this earthquake. In most cases of dynamic modulation, large‐amplitude and long‐period surface waves stimulate tremors. However, in this case even the small stress change caused by body waves generated by the 2012 earthquake modulated tremor activity. The tremor modulation continued during the passage of the surface waves, subsequent to which the tremor activity returned to background rates. Similar tremor modulation is observed during the passage of the teleseismic waves from the Mw 8.2 event, which occurs about 2 h later near the Mw 8.6 event. We show that dynamic stresses from back‐to‐back large teleseismic events can strongly influence tremor sources.

Migration of Deep Low‐Frequency Tremor Triggered by Teleseismic Earthquakes in the Southwest Japan Subduction Zone

“…Migration of rapid streaking is observed only in the along‐dip direction, which is the same as our observation. There are other similar observations of the streak‐like activities of tremor modulated by a teleseismic event at the Cascadia subduction zone (Kundu et al, ). The linear tremor distribution along the dip direction is very similar to our result, although the direction of tremor streak propagation and speed was not estimated.…”

Widespread Very Low Frequency Earthquakes (VLFEs) Activity Offshore Cascadia

“…The CSZ has been generally seismically inactive along the offshore trench area in terms of regular fast earthquakes, especially between the northern Nootka Fault and the southern Blanco Fault. It is, however, a highly active place for deeper ETS events and slow earthquakes (Ghosh et al, 2009(Ghosh et al, , 2010a(Ghosh et al, , 2010b(Ghosh et al, , 2012Gomberg et al, 2012;Kundu et al, 2016) occurring downdip of the seismogenic zone.…”