Linking Ocean Storms and Earth's Hum Excitation: Seasonal Infragravity Wave Observations in the Pacific Ocean

Infragravity waves (IGWs) are long-period ocean waves that bridge the atmosphere, ocean, solid Earth and polar ice, influencing sea level measurements, coastal sediment transport, the breakup of Antarctic ice shelves and the excitation of Earth's seismic hum. We collected ocean-bottom pressure data recorded by approximately 700 pressure gauges from 15 ocean-bottom seismometer arrays deployed on the Pacific seafloor and computed cross-correlation functions between each station pair to extract coherent energy of IGWs. We conducted beamforming analysis to determine the incoming direction of IGWs and applied ray-tracing calculations to locate their sources. Our results reveal pronounced seasonal variations in the spatial extent of IGW sources. During boreal winter, coastlines of the northern and eastern Pacific Ocean are distinct sources, particularly in the northeastern segment, strongly correlating with IGW height predictions and with significant wave height triggered by eastward-moving storms. By contrast, during boreal summer (i.e., austral winter), waves predominantly originate from the western coast of South America and New Zealand coasts, as those in the prediction model. A secondary region is illuminated along the Antarctic coast, which we hypothesize originates from distant primary sources in the Southern Hemisphere, reflecting off the Antarctic coast. The reflected waves then likely propagate northward several hundred to thousands of kilometers seaward toward the Northern Hemisphere, where they are recorded by stations in the northern Pacific Ocean. The detected IGW source locations in this study support that Earth's seismic hum is triggered unevenly, with distinct seasonal patterns.