This work was supported by National Science Foundation Grants OCE-0841091 and 1158167 and EAR-0842137, 1140261, and 1345100 from the Margins, Tectonics, Instrumentation-Facilities, and Geophysics programs (to T.H.D.). Y.J. was supported by a NASA Earth and Space Science Fellowship.
Proceedings of the National Academy of Sciences of the United States of America
Earthquake prediction, Tsunami forecasting, Global Positioning System, Subduction zones, Earthquake hazard analysis, Earthquake magnitude
The 5 September 2012 Mw 7.6 earthquake on the Costa Rica subduction plate boundary followed a 62-y interseismic period. High-precision GPS recorded numerous slow slip events (SSEs) in the decade leading up to the earthquake, both up-dip and down-dip of seismic rupture. Deeper SSEs were larger than shallower ones and, if characteristic of the interseismic period, release most locking down-dip of the earthquake, limiting down-dip rupture and earthquake magnitude. Shallower SSEs were smaller, accounting for some but not all interseismic locking. One SSE occurred several months before the earthquake, but changes in Mohr–Coulomb failure stress were probably too small to trigger the earthquake. Because many SSEs have occurred without subsequent rupture, their individual predictive value is limited, but taken together they released a significant amount of accumulated interseismic strain before the earthquake, effectively defining the area of subsequent seismic rupture (rupture did not occur where slow slip was common). Because earthquake magnitude depends on rupture area, this has important implications for earthquake hazard assessment. Specifically, if this behavior is representative of future earthquake cycles and other subduction zones, it implies that monitoring SSEs, including shallow up-dip events that lie offshore, could lead to accurate forecasts of earthquake magnitude and tsunami potential.
Dixon, T. H., Yan, J., Malservisi, R., McCaffrey, R., Voss, N., Protti, M., & Gonzalez, V. (2014). Earthquake and tsunami forecasts: Relation of slow slip events to subsequent earthquake rupture. Proceedings Of The National Academy Of Sciences Of The United States Of America, 111(48), 17039-17044. doi:10.1073/pnas.1412299111