A GLOBAL SURGE OF GREAT EARTHQUAKES FROM 2004-2014 AND IMPLICATIONS FOR CASCADIA

During the past decade from December 2004 to present 18 great (M_w ≥ 8.0) earthquakes occurred globally (~1.8 per year), compared to 71 from 1900 to mid-2004 (~0.68 per year), yielding an effective rate increase of 265%. Six events had M_w ≥ 8.5, larger than any prior event since the 1965 Rat Islands earthquake. While this overall surge of activity has not been demonstrated to be causally linked, regional spatio-temporal clustering is clearly evident for great events along the Sumatra, Kuril and Samoa subduction zones, and longer-range interactions have been established for global seismicity at lower magnitudes following some of the events. This recent decade of high great earthquake activity coincided with vastly expanded global networks of seismometers, GPS stations, tsunami gauges, and new satellite imaging capabilities such as GRACE, InSAR, and LandSAT interferometry. Individual events such as the March 11, 2011, Tohoku, Japan M_w 9.0 earthquake produced more ground motion recordings than available for all great earthquakes of the last century collectively, enabling unprecedented analyses of precursory, co-seismic and post-seismic processes around the megathrust environments where most of these events have occurred. Joint inversion and modeling of the diverse data sets exploit complementary sensitivity of the signals to different aspects of the earthquake processes. Major advances have been achieved in quantifying frictional locking and strain accumulation prior to some great events and relating it to coseismic slip heterogeneity. Many surprising aspects of these well-quantified great earthquakes have been manifested, associated with rupture dimensions, tectonic location, compound faulting, triggering interactions, aftershock complexity, and depth-varying seismic radiation characteristics. The lessons learned from quantification of recent great earthquakes hold implications for seismic hazards from great earthquakes in Cascadia that will be discussed.