Frequency Dependent Microseisms Sources: A Case Study in Oregon

The origin of microseisms—whether from deep-ocean sources or coastal reflections—has been debated for decades. In this study, we use Distributed Acoustic Sensing (DAS) and Ocean Bottom Seismometer data collected offshore Oregon to investigate microseisms sources across a range of frequency bands. Our results reveal a clear frequency dependence: high-frequency (0.35–1.5 Hz) microseisms primarily originates near the coastline due to wind ocean waves, with minimal contribution from the deep ocean. In short-period double frequency (SPDF, 0.2–0.35 Hz) microseisms, the source regions extend farther offshore and are increasingly influenced by deep-ocean sources. Long-period double frequency (LPDF, 0.1–0.2 Hz) microseisms are predominantly generated in the deep ocean. Furthermore, we find that microseisms generated by coastal reflections do not propagate into the deep ocean.