­Dynamic interactions between the October 28th 2012 Haida Gwaii and January 5th 2013 Craig earthquakes and other faults in Southeast Alaska

Abstract:

The M_w 7.8 (28 October 2012) Haida Gwaii earthquake and the M_w 7.5 (5 January 2013) Craig, Alaska earthquake occurred just 400 km and 68 days apart from each other. The short duration and distance between the events poses the question of whether these two events are related. We combine existing seismic data from permanent networks in Alaska and Canada, including temporary aftershock deployments (both on land and ocean-bottom sensors) installed in the Haida Gwaii islands, to search for precursory activity prior to each of the events. In order to improve the catalog completeness, we utilize a matched-filter technique to identify potential missing earthquakes before and after each mainshock. This technique utilizes existing cataloged waveforms as templates to identify repeating or nearby earthquakes with high cross-correlations. We examine the seismic activity prior to and following each event and determine whether any dynamic or delayed triggering of earthquakes or tremor occurs regionally due to these earthquakes. We find small earthquakes on the Fairweather Fault, near Glacier Bay, directly triggered in the minutes after the Haida Gwaii event. In addition, preliminary evidence suggests the Haida Gwaii earthquake triggered some seismicity in the rupture region of the Craig earthquake over the ~2 month period of time between the mainshocks. We plan to assess whether the later-occurring Craig earthquake triggered any increase in aftershock activity within the Haida Gwaii rupture region. The static and dynamic transmission of stresses from large earthquakes has important implications for transient fault zone loading in areas adjacent to those initial rupture zones. This study should shed some light on large earthquake interactions at various distance scales and future seismic risks across Alaska and western Canada.