Noel Bartlow, Assistant Professor, Dept. of Geological Sciences, University of Missouri
Subduction zones host the largest and most destructive earthquakes in the world, including the 2011 Tohoku earthquake in Japan and 2004 Sumatra earthquake. Our ability to forecast these earthquakes is limited by our incomplete understanding of subduction zone processes. Recent discoveries reveal the presence slow earthquakes, also called slow slip events, in many subduction zones. These slow earthquakes can release energy equivalent to a magnitude 7 earthquake, without releasing damaging seismic waves. Slow slip events have also been observed to trigger earthquakes in New Zealand, Mexico, and Japan. The extremely damaging magnitude 9.1 2011 Tohoku earthquake was directly preceded by a slow earthquake which drove the foreshock sequence. Slow earthquakes therefore provides potential clues to the location and timing of future large earthquakes but the exact relationship is not yet known. In the United States, the Cascadia subduction zone experiences very large destructive earthquakes every 300-900 years, in addition to slow earthquakes every 12-22 months. This talk will overview the current state of science and monitoring of slow earthquakes in Cascadia. In addition, this talk will discuss slow earthquakes in New Zealand and a novel application of slow earthquakes to study how slip is partitioned between shallow strike-slip faults and the deep subduction interface in a region with very oblique plate convergence.
(a) Slip distribution for a slow earthquake in New Zealand. Colors indicate slip over a 2-week period. Dark red circles indicate a swarm of typical earthquakes triggered by the slow earthquake. (b) Shear stress change caused by this slow earthquake. Black vectors and error ellipses show measured displacements at GPS stations, and green vectors show model fits.