ABSTRACT
Globally distributed broadband seismographs continuously record seismic disturbances arising from atmosphere, ocean, and solid Earth coupling. Seismic data, most notably from the Global Seismographic Network (GSN) and its precursory seismic stations, now extend back for over three decades, and are readily accessible from the Incorporated Research Institutions for Seismology Data Management System. Two intriguing areas of research utilizing these vast open data resources are: 1) Ocean wave impacts on Earth's cryosphere, and 2) Monitoring of the seismic background as a globally sensed proxy for ocean wave activity.
        Recent deployments of seismic instrumentation in Antarctica have revealed new seismic and dynamic processes affecting Earth's largest floating ice bodies, including powerful episodes of iceberg tremor that arise from highly repetitive stick-slip processes, and buoyant interactions between ice bodies and ocean swell. It has long been recognized that powerful storms generate swell that propagates efficiently as dispersed deep-water waves across transoceanic distances. Such transoceanic wave trains, as well as regionally originating waves, are detected at high fidelity by both land-sited and iceberg-sited floating seismometers in Antarctica. Ocean waves provide a seismically detectible mechanism for transporting atmospheric energy from the winter Arctic to Antarctic waters, arriving during the austral summer when large tabular icebergs and ice shelves may be largely unprotected by sea ice. One resulting hypothesis is that extreme storms many thousands of kilometers away may critically affect the behavior (including breakup) of enormous icebergs recently calved from the Ross Ice Shelf.
        The ocean-wave-generated microseism background signal, which arises primarily from coastal and near-coastal interactions between continents and ocean swell, holds a unique record of large storm activity. Daniel McNamara (USGS), Peter Bromirski (UCSD), and I have recently developed methods for comprehensively examining microseism histories using probabilistic power spectral density estimates. The record shows large power fluctuations with both seasonal and secular components, including especially strong northern Pacific microseism excitation influenced by El Nino/Southern Oscillation cycles. We have developed a robust "microseism index" method of counting extreme microseism events and applied it to more than 20 globally distributed sites. We find increasing numbers of microseism background outlier episodes that indicate an increase in extreme storm frequency over much of the planet during the past several decades.