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SUMMARY Tsunami generation by offshore earthquakes is a problem of scientific interest and practical relevance, and one that requires numerical modelling for data interpretation and hazard assessment. Most numerical models utilize two-step methods with one-way coupling between separate earthquake and tsunami models, based on approximations that might limit the applicability and accuracy of the resulting solution. In particular, standard methods focus exclusively on tsunami wave modelling, neglecting larger amplitude ocean acoustic and seismic waves that are superimposed on tsunami waves in the source region. In this study, we compare four earthquake-tsunami modelling methods. We identify dimensionless parameters to quantitatively approximate dominant wave modes in the earthquake-tsunami source region, highlighting how the method assumptions affect the results and discuss which methods are appropriate for various applications such as interpretation of data from offshore instruments in the source region. Most methods couple a 3-D solid earth model, which provides the seismic wavefield or at least the static elastic displacements, with a 2-D depth-averaged shallow water tsunami model. Assuming the ocean is incompressible and tsunami propagation is negligible over the earthquake duration leads to the instantaneous source method, which equates the static earthquake seafloor uplift with the initial tsunami sea surface height. For longer duration earthquakes, it is appropriate to follow the time-dependent source method, which uses time-dependent earthquake seafloor velocity as a forcing term in the tsunami mass balance. Neither method captures ocean acoustic or seismic waves, motivating more advanced methods that capture the full wavefield. The superposition method of Saito et al. solves the 3-D elastic and acoustic equations to model the seismic wavefield and response of a compressible ocean without gravity. Then, changes in sea surface height from the zero-gravity solution are used as a forcing term in a separate tsunami simulation, typically run with a shallow water solver. A superposition of the earthquake and tsunami solutions provides an approximation to the complete wavefield. This method is algorithmically a two-step method. The complete wavefield is captured in the fully coupled method, which utilizes a coupled solid Earth and compressible ocean model with gravity. The fully coupled method, recently incorporated into the 3-D open-source code SeisSol, simultaneously solves earthquake rupture, seismic waves and ocean response (including gravity). We show that the superposition method emerges as an approximation to the fully coupled method subject to often well-justified assumptions. Furthermore, using the fully coupled method, we examine how the source spectrum and ocean depth influence the expression of oceanic Rayleigh waves. Understanding the range of validity of each method, as well as its computational expense, facilitates the selection of modelling methods for the accurate assessment of earthquake and tsunami hazards and the interpretation of data from offshore instruments.
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Kamchatka M8.8 Earthquake and Tsunamis Reach Across the Pacific to NSF's OOI Regional Cabled Array
## 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.
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- Award ID(s):
- 2244833
- PAR ID:
- 10627788
- Publisher / Repository:
- Zenodo
- Date Published:
- Format(s):
- Medium: X
- Right(s):
- Creative Commons Attribution 4.0 International
- Sponsoring Org:
- National Science Foundation
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