|Title||Understanding Cascadia earthquake hazards - studies by land and sea|
|Author||Cassidy, J F|
|Source||5th annual meeting, IGCP 526 Risks, resources and records of the past on the continental shelf, abstracts volume; 2011 p. 1|
|Alt Series||Earth Sciences Sector, Contribution Series 20110282|
|Meeting||5th annual IGCP 526 Continental Shelves: Risks, Resources and Records of the Past; Sidney, BC; CA; September 13-16, 2011|
|Province||Western offshore region|
|Subjects||geophysics; tectonics; subduction; subduction zones; tectonic environments; tectonic interpretations; earthquakes; earthquake magnitudes; earthquake risk; earthquake studies; Cascadia Subduction Zone;
Cascadia Margin; geological hazards|
|Program||Targeted Hazard Assessments in Western Canada, Public Safety Geoscience|
|Abstract||The Cascadia subduction zone off the coast of northern California, Oregon, Washington, and southern British Columbia is an active subduction zone. Similar active subduction zones in Japan, Chile, and
Sumatra have recently produced giant, damaging M ~ 9 megathrust earthquakes, along with devastating tsunami's. Thirty years ago it was not known that megathrust earthquakes occurred along the Cascadia margin. As a result of detailed scientific
studies, by land and sea, we now know that three types of large earthquakes occur in this region: |
1) M ~ 9 subduction earthquakes along the Cascadia zone;
2) shallow crustal earthquakes (M ~ 7-7.5) onshore; and
3) deep M ~ 7 earthquakes
within the subducting ocean plate about 50-60 km beneath the Puget Sound and Georgia Strait regions.
The key to our understanding of earthquake hazards in Cascadia has been the application of modern datasets and multidisciplinary techniques. Some
examples include: Global Positioning Satellite data and leveling data that indicated the subduction fault zone is currently "locked" and storing energy for a future megathrust earthquake; structural studies and high-precision earthquake locations
that help us map the ocean plate as it subducts beneath North America; seismic studies that indicate how wave energy propogates through the region; Episodic Tremor and Slip (ETS) that provides unique new glimpses into time varying subduction zone
processes with both spatial and time-varying hazard implications; paleoseismology on land that indicates subsidence along the west coast every 250-850 years, consistent with a megathrust earthquake; high-resolution mapping of the seafloor that
indicates the presence of faults; applications of Light Detection and Ranging (LIDAR) that help reveal active faults in the onshore regions of Cascadia; offshore "sediment coring" that indicates the presence of submarine landslides triggered by
earthquakes and suggests variations in hazard level along the Cascadia margin, the recently deployed NEPTUNE seismograph and tsunami monitoring networks; and the exploration and development of real-time earthquake (and tsunami) early-warning systems.
This presentation provides an overview of some of these studies, key results, and a look forward to future developments in assessments of earthquake hazards throughout Cascadia.