Continental mantle earthquakes of the world.

Continental mantle earthquakes (CMEs) and their implications for the rheological structure of continents have fascinated geophysicists for more than half a century. Existence of these earthquakes is no longer debated, but their identification remains sparse across the globe. Comparing the Sn and Lg seismic wave amplitude ratio (Sn/Lg) of an earthquake with that of nearby earthquakes distinguishes CMEs and, unlike previous methods, can be applied globally. We present a global distribution of CMEs that extends well beyond previous individual detections and areas of speculation. CME occurrence is widespread globally yet patterned regionally, reflecting local lithospheric structure and tectonic history. Our results highlight the value of CMEs for understanding continents and global tectonics. Editor's summary: Deep earthquakes tend to cluster near subduction zones and can be explained by plate motions; however, this is not so for continental mantle earthquakes, which are hard to explain and even harder to detect. Wang and Klemperer developed a method that uses regional seismic waves and their relative amplitudes in the context of nearby recorded crustal earthquakes. Applied globally, this approach has detected more than 400 continental mantle earthquakes since 1990. These mantle earthquakes generally occur in areas that also have crustal earthquakes, but regional distributions suggest that mantle earthquakes occur under a wider range of tectonic and thermal conditions than previously thought. —Angela Hessler [ABSTRACT FROM AUTHOR]