Collaborative Research: Seismological Analysis of Earth's Microseism Record and Ocean Wave Climate

Observations from meteorology, climatology, and oceanography indicate that the global intensity of ocean waves has increased since the mid- to late-20th century. Increased ocean wave size and energy have fundamental role in erosion and other coastal hazards, as well as to human infrastructure, marine and coastal ecosystems, marine-terminating glaciers, and to other natural systems and human activities spanning the ocean, atmosphere, and solid Earth. The impact of ocean waves on the sea floor are measurable by the same instruments that detect earthquake activity across the globe. Seismic data thus provide a unique record of large-geographic-scale and long-duration ocean wave activity, and global seismographic networks are sufficiently widespread and long-lived so that the progressive seismic signal of ocean wave intensification has emerged. This project analyzes global seismic data extending back four decades to understand, localize, and quantify ocean wave state, incorporating related observations from other Earth science fields. A public-facing, non-specialist- accessible website will display and distribute near-real-time regional and global microseism metrics, placing the present in historical context. Global ocean wave energy intensification has recently become apparent in the long-term continuous seismic record, particularly but not exclusively as increasing primary microseism Rayleigh wave energy, which is sensitive to ocean waves in near-coastal regions between approximately 20 and 14 s period. With an international group of collaborating experts, this project estimates, interprets, and globally models the frequency- and polarization-dependent regional, seasonal, and secular spatial-temporal evolution of Earth’s microseism wavefield since the late 20th century in the context of global change. The project has three primary objectives. First, it advances our understanding of the long-term observational record of Earth’s incessant ocean gravity wave and seismic microseism field, including forward modeling of wave hindcast metrics, corroborated in the Mediterranean with in-situ MERMAID water column data. Second, it studies geophysical source processes guiding end-to-end seismic signal generation and the informed use of seismological proxies to infer ocean wave activity variations at multiple time scales. To this end, the project applies and advances state-of-the art long-period seismic modeling codes driven by wave hindcast inputs to improve understanding of microseism source regions, geographic influences, and seismic source efficiency. Project PIs, postdocs, collaborators, graduate students, and undergraduate students conduct this work in the context of ocean wave state studies emerging from the meteorological, oceanographic, and climate communities. Third, the project incorporates outreach activities that advances public awareness and appreciation for seismology and geophysics in the historical context of the long-term ocean wave evolution and the occurrence of exceptional wave events and communicates results so that they may complement other ocean-wave data products from the atmospheric, oceanographic, and climate communities. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.