Fahad Mohammed

Experiments on Tsunamis Generated by 3D Granular Landslides

Subaerial and submarine landslides can trigger tsunamis with locally high amplitudes and runup, which can cause devastating effects in the near field region such as the 1958 Lituya bay, Alaska, 1998 Papua New Guinea and 2006 Java tsunamis. Tsunami generation by submarine and subaerial landslides were studied in the three dimensional NEES (George E. Brown, Jr. Network for Earthquake Engineering Simulation) tsunami wave basin (TWB) at Oregon State University based on the generalized Froude similarity. A novel pneumatic landslide generator was deployed to control the granular landslide geometry and kinematics. Measurement techniques such as particle image velocimetry (PIV), multiple above and underwater video cameras, multiple acoustic transducer arrays (MTA), as well as resistance wave and runup gauges were applied. The experimental data provided new insights on landslide deformation as it impacts the water surface, penetrates the water and finally deposits on the bottom of the basin. The influence of the landslide volume, shape and the impact speed on the generated tsunami waves were extensively studied. The instantaneous surface velocity fields measured using the PIV gave insight into the kinematics of the landslide and wave generation process. At high impact velocities, flow separation occurred on the slide shoulder resulting in a hydrodynamic impact crater. The measured wave profiles yielded information on the wave propagation and attenuation. The measured wave speed of the leading wave reaches the theoretical solitary wave celerity while the trailing waves are slower in nature. Attenuation functions of the leading wave crest amplitude, the wave length and the time period were obtained to study the wave behavior in the near field and far field regions. The measured wave data serves the validation and advancement of 3-dimensional numerical landslide tsunami and prediction models.

Laboratory experiments on three-dimensional deformable granular landslides on planar and conical slopes

Landslides of subaerial and submarine origin may generate tsunamis with locally extreme amplitudes and runup. While the landslides themselves are dangerous, the hazards are compounded by the generation of tsunamis along coastlines, in enclosed water bodies, and off continental shelves and islands. Tsunamis generated by three-dimensional deformable granular landslides were studied on planar and conical hill slopes in the three-dimensional NEES tsunami wave basin at Oregon State University based on the generalized Froude similarity. A unique pneumatic landslide tsunami generator (LTG) was deployed to control the kinematics and acceleration of the naturally rounded river gravel and cobble landslides to simulate broad ranges of landslide shapes and velocities along the slope. Lateral and overhead cameras are used to measure the landslide shapes and kinematics, while acoustic transducers provide the shape of the subaqueous deposits. The subaerial landslide shape is extracted from the camera images as the landslide propagates under gravity down the hill slope, and surface reconstruction of the landslide is conducted using the stereo particle image velocimetry (PIV) system on the conical hill slope. Subaerial landslide surface velocities are measured with a planar PIV system on the planar hill slope and stereo PIV system on the conical hill slope. The submarine deposits are characterized by the runout distances and the deposit thickness distributions. Larger cobbles are observed producing hummock type features near the maximum runout length. These unique laboratory landslide experiments serve to validate deformable landslide models as well as provide the source characteristics for tsunami generation.

TSUNAMI GENERATION BY 3D DEFORMABLE GRANULAR LANDSLIDES

Landslide generated tsunamis are particularly hazardous in enclosed water bodies. Topographical and bathymetric features can either dissipate or enhance the generated waves leading to potentially extensive damages. To study the effect of such features landslide generated tsunami experiments were conducted in physical scale models representing fjords, headlands and farfield hill slopes. A pneumatic landslide tsunami generator deploys unconfined deformable granular landslides on a hill slope which impact the water surface and thereby generate tsunami waves. The instrumentation setup includes multiple cameras, particle image velocimetry, acoustic transducers and an array of wave gauges. Landslide measurements are made to characterize the source properties. The wave profile recordings with and without the topographic features provide insights into their effects on the tsunami wave characteristics. A fjord setup traps and distributes the wave energy along the fjord slopes in the channel, while a headland captures only part of the energy and radiates the rest into the open basin.

Coastal Impacts by the 12 January 2010 Earthquake and Tsunamis in Haiti

On 12 January 2010 a magnitude Mw 7.0 earthquake occurred 25 km west-southwest of Haiti’s Capital of Port-au-Prince, which resulted in more than 230,000 fatalities thereby more than doubling any previous loss of life from a similar size earthquake. In addition tsunami waves triggered by the earthquake caused at least 3 fatalities at Petit Paradis. The international tsunami survey team (ITST) was deployed within days of the event and covered the greater Bay of Port-au-Prince and more than 100 km of Hispaniola’s southern coastline. Field observations are compared to numerical modeling results.