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## Kamchatka M8.8 Earthquake and Tsunamis Reach Across the Pacific to NSF’s OOI Regional Cabled Array   Deborah Kelley1, Joe Duprey1, Wendi Ruef1, and W. Chadwick2   1University of Washington, 2Oregon State University   On July 29 at 23:24:52 UTC, a powerful magnitude 8.8 earthquake struck the Kamchatka Peninsula in Russia, unleashing seismic energy and a tsunami that surged across the Pacific Ocean. This extraordinary event was captured in remarkable detail by the NSF Ocean Observatories Initiative’s (OOI) Regional Cabled Array—a seafloor observatory located offshore Oregon and Washington and one of the world’s most advanced underwater monitoring networks, with over 150 instruments transmitting real-time data to shore at the speed of light.   At 23:33:15, the seismic waves from the Kamchatka earthquake reached Axial Seamount, located nearly 300 miles west of the Oregon coast and almost a mile beneath the ocean’s surface, having crossed the entire Pacific in just nine minutes. The vibrations were so intense they rattled a seafloor instrument continuously for over four hours (a,b).   Then, at 06:03:00 UTC on July 30—6 hours and 30 minutes after the quake—the first tsunami waves arrived at Axial Seamount (c). Ultra-sensitive pressure sensor on bottom pressure tilt instruments picked up the waves with astonishing clarity. Lower-resolution sensors across the array also tracked the tsunami’s journey toward the UW west coast. Racing at speeds of 270 miles per hour, the first wave swept across the Juan de Fuca Plate and over the Cascadia Subduction Zone, eventually reaching seafloor monitoring instruments at the Oregon Shelf site just 14 miles offshore from Newport, Oregon. The OOI Regional Cabled Array instruments showed that the Pacific Ocean reverberated with smaller waves for several days after the first tsunami waves arrived—echoes of one of the most powerful seismic events ever recorded.   This event highlights not only the dynamic nature of our planet and the seismic and tsunami hazards that we have to be prepared for in the Pacific Northwest, but also the incredible capability of modern science to observe and understand these kinds of events—in real time from deep beneath the ocean’s surface, and the value of such monitoring to coastal communities.   ## Bottom Pressure and Tilt Meter Notes BOTPT LILY tiltmeter data (csvs) are curated by William Chadwick. The tilt units are microradians, or µrad.   BOTPT-MJ03F-BPR-29July-to-01Aug2025-15sec.csv Date/Time, Pressure (psi) with tides, De-tided Depth (m) - from 29 July @ 00:00 to 01 August @ 00:00, and a record every 15 seconds (from the NANO bottom pressure sensor)   BOTPT-MJ03F-LILY-tilt-data-29-30July2025-01sec.csv Date/Time, X-tilt, Y-tilt - from 29 July @ 00:00 to 30 July @ 23:13, and a record every 1 second (from the LILY tiltmeter)   ## Where to find Additional Data Additional data from the included sensors prior to and after the event, or from OOI's many co-located sensors can be obtained through the OOI data portal https://ooinet.oceanobservatories.org/ , the OOI data explorer https://dataexplorer.oceanobservatories.org/ or OOI's M2M API service https://oceanobservatories.org/m2m/.   ## Contact Information jduprey@uw.edu   This material is based upon work supported by the Ocean Observatories Initiative (OOI), a major facility fully funded by the US National Science Foundation under Cooperative Agreement No. 2244833, and the Woods Hole Oceanographic Institution OOI Program Office. 

Abstract Axial Seamount in the northeast Pacific erupted in 2015, 2011, and 1998. Although monitored by the Regional Cabled Array of the Ocean Observatory Initiative, few magnetic surveys have been conducted over the region. This study uses high‐resolution magnetic data over the seamount collected by autonomous underwater vehicleSentryduring three years (2015, 2017, and 2020). The goal is to investigate whether there are temporal changes in the near‐surface magnetic field observable over the time scale of one volcanic cycle. We compare magnetic maps from repeated tracklines from each year. We find maps of the yearly difference in magnetization show coherent patterns that are not random. The central region of the caldera has become more magnetic during recent years, suggesting cooling of the surficial lava flows since 2015.Sentrydata are more sensitive to shallow crustal structure compared to sea surface data which show longer wavelength anomalies extending deeper into the crust.