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TitleSeafloor seismometers monitor northern Cascadia earthquakes
AuthorScherwath, M; Spence, G; Obana, K; Kodaira, S; Wang, K; Riedel, M; McGuire, J; Collins, J
SourceEos, Transactions of the American Geophysical Union vol. 92, no. 47, 2011 p. 421-422,
Alt SeriesEarth Sciences Sector, Contribution Series 20110269
Mediapaper; on-line; digital
File formatpdf
ProvinceWestern offshore region; British Columbia
AreaCascadia; Vancouver Island
Lat/Long WENS-130.0000 -124.5000 50.0000 47.5000
Subjectsgeophysics; marine geology; seismic arrays; seismic interpretations; seismic zones; seismographs; seismicity; seismology; strong motion seismology; seismological network; earthquakes; earthquake studies; earthquake risk
Illustrationslocation maps; profiles
ProgramTargeted Hazard Assessments in Western Canada, Public Safety Geoscience
AbstractThe Mw = 9.0 earthquake of 11 March 2011at the Japan Trench and its devastating tsunami underscore the importance of understanding seismogenic behavior of subduction faults and realistically estimating the potential size of future earthquakes and tsunamis. For the Cascadia subduction zone (Figure 1a), a critical knowledge gap is the level of microseismicity offshore, especially near the megathrust, needed to better understand the state of the locked zone. In 2010 the first detailed seafloor earthquake monitoring campaign along the northern Cascadia subduction zone recorded nearby earthquakes in the local magnitude (ML ) range from possibly around zero to 3.8 (Figures 1b and 1c) and larger earthquakes from outside this region. Preliminary analyses indicate that the network appears to have yielded a fairly complete catalog for events with ML > 1.2. Only a few tens of these events occurred beneath the continental shelf and slope (Figure 1a). The majority of the earthquakes were located along the margin-perpendicular Nootka fault zone. The relatively low seismicity away from the Nootka fault is consistent with a fully locked megathrust. Land-based GPS measurements cannot resolve the question of
whether the offshore part of the megathrust seismogenic zone is narrow and fully locked or wider and only partially locked (slowly creeping). If it were only partially locked, the seafloor seismometer data should show many more small earthquakes along the interface than were actually detected.