01 Earthquake source
SCENARIOScenario loaded
Published fault-patch geometry. Assumed slip and rupture timing. These scenarios explore possibilities; they do not reconstruct or predict an event.
Computing the ocean’s response
Preparing bathymetry and elastic source…
Waves along the coast
Selected station is highlighted. The cursor shows playback time; the full traces show later wave trains.
The seafloor off Newport
SCALES EXAGGERATEDWest–east slice through the selected observation. Wave displacement and depth use separate vertical scales.
Inside the model — methods, data provenance, validation & limitations
01 / Real geography
NOAA ETOPO 2022 global relief (60 arc-second product) was sampled every 2 arc-minutes across 39–52° N, 133.5–121° W. Terrain is displayed at that sampling. Fine mode computes on the 2 arc-minute terrain sampling. Fast mode averages 2 × 2 terrain samples to 4 arc-minutes. Heights are relative to EGM2008. All data are embedded for offline use.
02 / Elastic earthquake source
Twenty archived NOAA SIFT rectangular patches, acsza56–65 and acszb56–65, define the full-margin geometry. Each is 100 × 50 km. Top depth, strike, dip and rake come from the published patch metadata distributed with GeoClaw. This uses the geometry, not SIFT forecast waveforms or a NOAA forecast scenario.
Slip is scaled so that Σ μ Aᵢ Dᵢ = 10^(1.5 Mw + 9.1) N·m, using μ = 40 GPa. Tapered and shallow-emphasis scenarios preserve this moment. Slip, hypocenter, rise time and rupture speed remain assumptions. Patches begin slipping according to their along-strike distance from the chosen origin; a half-cosine rise supplies smooth moving-seafloor forcing.
Vertical deformation uses the Okada elastic half-space rectangular-fault solution, adapted from GeoClaw, with Poisson ratio 0.25. The model omits horizontal seafloor-displacement corrections and elastic layering.
03 / Two-dimensional ocean dynamics
The linear shallow-water equations evolve free-surface elevation η and depth-integrated transports on a latitude–longitude grid, using spherical distance and area factors. A staggered finite-volume update uses 2-second time steps in Fine mode and 4 seconds in Fast mode, harmonic face depths, and a checked CFL bound. Actual water-level snapshots drive the map and charts.
Cells shallower than 20 m, including land, are masked; interfaces reflect. An approximately 100 km absorbing sponge at the domain edges reduces reflections. It does not perfectly reproduce an infinite ocean. Sea level and coastlines stay fixed; there is no wetting and drying, friction, nonlinear advection, wave breaking, dispersion, tide, or Coriolis force.
04 / What the numbers mean
Virtual stations are placed in modeled ocean cells at 100–600 m depth near the named communities. Their exact coordinates and depths are displayed. Peaks cover the full three-hour run. “First 10 cm signal” is the first |η| ≥ 0.10 m in the model, including source deformation. It is not a tsunami arrival estimate at a beach. Gray coastline and depth contours are derived from ETOPO, rather than drawn by hand.
The fixed map color scale can saturate; hover for numerical values. Playback snapshots are saved every 40 seconds and quantized with a per-frame scale; full-precision updates determine peaks and threshold times. Charts use 40-second station samples. Under-resolved bays and shallow cells may exaggerate or miss local effects.
Diagnostics appear after the simulation.
05 / Evidence and reproducibility
In an initial first-hour comparison, a 4′ grid produced a peak near Seaside about 52% above the 2′ result; other station differences ranged from about 0.2% to 11.5%. Finer sampling still does not resolve a beach, harbor, or floodplain. The source package records the test conditions and updated sensitivity results.
Checks cover elastic-source agreement with GeoClaw, conserved seismic moment, still-water equilibrium, numerical wave speed, volume conservation, resolution sensitivity and stable scenarios. These are numerical checks, not validation against a measured Cascadia tsunami.
- NOAA ETOPO 2022 · Dataset and metadata
- NOAA PMEL · Forecast propagation unit sources
- GeoClaw · Earthquake source and Okada documentation
- Archived SIFT fault-patch metadata
- USGS · Pacific Northwest earthquake hazards
- Official U.S. tsunami warnings
Data retrieved September 5, 2026. Source hashes, numerical tests, reference values and build scripts are included in the source download.
GeoClaw attribution and BSD 3-Clause license
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