Speaker: Rick Aster, Colorado State University

It has been recognized since the dawn of global seismology that the oceans produce a continuous and seasonally varying microseism signal that is detectable everywhere on Earth.  Standardized global digital seismographic networks such as the Global Seismographic Network (GSN) and GEOSCOPE now facilitate the uniform analysis of microseism energy across nearly four decades spanning recently accelerating anthropogenic climate change. The globally observable primary microseism signal near 20–14 s period is a particularly apt proxy for global near-coastal wave energy because it is produced by propagating ocean wave seafloor tractions applied at depths of less than about 300 meters and is less sensitive to wave and bathymetric conditions than the more energetic and widely studied secondary microseism signal.

Our inferred rates of ocean wave intensification compare well with independent estimates from oceanographic and meteorological data. Time-smoothed (e.g. 2-month) primary microseism signal station histories regionally cluster to thousands of kilometers of geographic separation, demonstrating large-scale and consistent sampling of ocean wave forces.  Multi-year primary microseism signal variations also correlate well with El Niño and La Niña conditions that affect large-scale storm energy in the Pacific region, with increasing energy in the southwest Pacific under positive El Niño-Southern Oscillation (ENSO) conditions and in the southeast Pacific under negative ENSO (positive Southern Oscillation; SOI) climate index conditions.