HOW MANY M9 EARTHQUAKES ARE POSSIBLE? INTERSEISMIC COUPLING AND RUPTURE PATCH MAGNITUDES ALONG 15 OF THE WORLD’S SUBDUCTION ZONES

There have been five recorded magnitude 9 earthquakes: 1952 M9.0 (Kamchatka), 1960 M9.5 (Chile), 1964 M9.2 (Alaska), 2004 M9.1 (Sumatra), and 2011 M9.1 (Japan). Given their long recurrence intervals and sparse historical record, it is unclear how many M9 ruptures are possible globally and where they may be located. Here we examine 15 of the world’s subduction zones, estimating interseismic coupling and potential rupture patch size and magnitude. Using the first global block model, we invert a velocity field consisting of 19,664 GPS stations worldwide and simultaneously solve for spatially variable interseismic coupling along all subduction zone interfaces. Empirical scaling relationships are then used to relate the areas of regions contained within a constant coupling ratio to potential earthquake magnitude. We present results assuming coupling ratios of 80% and 30% and find a total of 4 and 14 M>9 rupture patches, respectively. These values represent the minimum number of potential M9 patches globally as not all subduction zones are sufficiently instrumented to resolve spatially variable coupling. We find that eleven of the fifteen subduction zones are capable of a M9 earthquake; however, all the plate boundaries studied have the potential to produce a M>8 event.