INITIAL WAVES FROM DEFORMABLE SUBMARINE LANDSLIDES A STUDY ON THE SEPARATION TIME AND PARAMETER RELATIONSHIPS A Thesis by JUSTIN ANDREW O'SHAY Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May 2012 Major Subject: Geophysics INITIAL WAVES FROM DEFORMABLE SUBMARINE LANDSLIDES A STUDY ON THE SEPARATION TIME AND PARAMETER RELATIONSHIPS A Thesis by JUSTIN ANDREW O'SHAY Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Approved by: Chair of Committee, Robert Weiss David Sparks Committee Members, James Kaihatu Head of Department, Rick Giardino May 2012 Major Subject: Geophysics iii ABSTRACT Initial Waves from Deformable Submarine Landslides A Study on the Separation Time and Parameter Relationships. (May 2012) Justin Andrew O'Shay, B.S., Texas A&M University Chair of Advisory Committee: Dr. Robert Weiss Dr. David Sparks Earthquake and submarine mass failure are the most frequent causes of tsunami waves. While the process of the tsunami generation by earthquakes is reasonably well understood, the generation of tsunami waves during submarine mass failure is not. Estimates of the energy released during a tsunamigenic earthquake and respec- tive tsunami wave draw a clear picture of the efficiency of the tsunami-generating process. However for submarine landslides, this is not as straightforward because the generation process has never been recorded in nature making energy inferences very difficult. Hence the efficiency of submarine landslide as tsunami generators is yet to be conclusively determined. As the result of this uncertainty, different equa- tions, derived from experimental data or theory, result in leading-wave amplitude that vary over 6 orders of magnitude for the same initial slide conditions. To arrive at more robust estimates of the leading-wave characteristics and associated runup, the spatiotemporal dynamics of the coupling between the slide body and water col- umn needs to be investigated. The duration the water surface deformation is coupled with the slide motion is an essential question to shed light on the energy transfer. A parametric study is conducted with the state-of-the-art hydrocode iSALE in order to shed light on this complex geophysical event. The mass, viscosity, and depth iv of submergence are the particular slide parameters varied and their relationship to runup and decoupling time is analyzed. v TABLE OF CONTENTS Page ABSTRACT :::::::::::::::::::::::::::::::::::: iii TABLE OF CONTENTS ::::::::::::::::::::::::::::: v LIST OF TABLES ::::::::::::::::::::::::::::::::: vii LIST OF FIGURES :::::::::::::::::::::::::::::::: viii 1. INTRODUCTION ::::::::::::::::::::::::::::::: 1 1.1 Introduction to tsunamis ::::::::::::::::::::::::: 1 1.2 Introduction to landslide-generated tsunamis :::::::::::::: 3 1.3 Research objectives :::::::::::::::::::::::::::: 8 1.3.1 Objectives ::::::::::::::::::::::::::::: 9 2. BACKGROUND ::::::::::::::::::::::::::::::: 10 2.1 Analytical theories and numerical approaches ::::::::::::: 10 2.2 Laboratory modeling approaches :::::::::::::::::::: 19 2.3 Evaluation of current approaches :::::::::::::::::::: 27 2.4 Hydrocode modeling ::::::::::::::::::::::::::: 28 2.4.1 Impact modeling ::::::::::::::::::::::::: 31 2.4.2 Landslide modeling :::::::::::::::::::::::: 31 2.4.3 iSALE validation ::::::::::::::::::::::::: 32 3. NUMERICAL EXPERIMENTS ::::::::::::::::::::::: 36 3.1 Grids and geometries ::::::::::::::::::::::::::: 36 3.2 Initial conditions ::::::::::::::::::::::::::::: 37 3.3 Data analysis ::::::::::::::::::::::::::::::: 39 3.3.1 Cavity dynamics analysis ::::::::::::::::::::: 41 3.3.2 Runup analysis :::::::::::::::::::::::::: 46 3.3.3 Modeling concerns :::::::::::::::::::::::: 47 4. RESULTS ::::::::::::::::::::::::::::::::::: 50 4.1 Cavity dynamics and separation time :::::::::::::::::: 50 4.2 Runup ::::::::::::::::::::::::::::::::::: 52 5. CONCLUSION :::::::::::::::::::::::::::::::: 55 5.1 Research impact :::::::::::::::::::::::::::::: 55 vi REFERENCES ::::::::::::::::::::::::::::::::::: 58 vii LIST OF TABLES TABLE Page 2.1 Masses used in experiments conducted by Liu et al. (2005). :::::::: 24 3.1 Table of variables used in numerical experiments. ::::::::::::: 37 3.2 Table of masses used in numerical simulations. ::::::::::::::: 38 3.3 List of depths of submergence −∆ used in numerical simulations. :::: 39 4.1 Table of r2 values for linear regression conducted on data collected from initial model runs. Calculations correspond to figure 4.1. ::::::::: 51 viii LIST OF FIGURES FIGURE Page 1.1 Estimated earthquake energy, EE, compared to the earthquakes generat- ing moment, M0. The circled dots are those nicknamed \tsunami earth- quakes" and can be determined by the two orders of magnitude energy deficiency between the projected ratio (Newman and Okal, 1998). :::: 5 1.2 ISSMGE Technical Committee on Landslides (TC-11) classification of submarine mass movements adapted by Locat and Lee (2002). :::::: 6 1.3 (a) Causes of submarine mass movements and factor of safety formula. (b) Schematic from Locat and Lee (2002) depicting the continuum of submarine mass movement events. ::::::::::::::::::::: 7 1.4 Pre-slide initial geometries for potential wave generation (Heller, 2008) : 8 2.1 Experimental set up for Wiegel (1955). ::::::::::::::::::: 10 2.2 Murty (1979) landslide variables sketch. :::::::::::::::::: 12 2.3 Landslide generated waves variables definition sketch (Synolakis, 2003). : 17 2.4 Photograph of Hammack's wave tank and piston generator (Hammack, 1973). ::::::::::::::::::::::::::::::::::::: 19 2.5 Comparison between Heinrich's numerical and experimental wave profiles for a submarine landslide placed 1cm below still water level. Times at t = 0:5s, t = 1:0s, t = 1:5sec : : : : : : : : : : : : : : : : : : : : : : : : : 21 2.6 Watt's schematic drawing of the experimental apparatus used in his sub- marine landslide study with a) top view b)side view (Watts, 1997) :::: 22 2.7 Water level time histories from Watts (1997) for a number of different masses. a) Shows near field water level history b) shows far field water level history. ::::::::::::::::::::::::::::::::: 23 2.8 Definition sketch for Liu et al. (2005) experiments. :::::::::::: 24 ix FIGURE Page 2.9 Photograph from Liu et al. (2005) large scale laboratory experiments. Notice the positive leading wave in front of the slide and the depression following from a series b experiment. :::::::::::::::::::: 25 2.10 Liu et al. (2005) graph of nondimensionalized run-up versus nondimen- sionalized depth of submergence. :::::::::::::::::::::: 26 2.11 Scaled initial wave height predictions (ordinate) for a given landslide and two different slide geometry scalings (abscissas); different symbols corre- spond to various empirical formula Weiss et al. (2011). :::::::::: 28 2.12 Gisler and Weaver (2006) schemtaic set up of the LaPalma landslide for two dimensional model runs conducted by SAGE. ::::::::::::: 32 2.13 A - Illustration of the Gilbert Inlet in Lituya Bay showing the rockslide, per Fritz et al. (2001). B - Simplified geometry as used in the laboratory experiments and the computions Weiss et al. (2009). ::::::::::: 33 2.14 (a-f) Snapshots illustrating the water motion associated with the maxima in the time series. (e) Comparison between the experimental data from Fritz et al. (2001) and model results computed with the iSALE model Weiss et al. (2009). :::::::::::::::::::::::::::::: 35 3.1 iSALE input file with respective variables labeled. ::::::::::::: 36 3.2 Snapshots illustrating slide motion at t = 0:0s to t = 2:50s, slope is in brown, slide blue and water in black. :::::::::::::::::::: 40 3.3 Cavity definition and evolution for a submarine landslide. The abscissa represents horizontal distance, x and the ordinate η is wave height. The 355kg slide with a submergence depth of −δ =1.935m was used to create these images. ::::::::::::::::::::::::::::::::: 41 (a) Cavity example for four different times. :::::::::::::: 41 (b) Cavity evolution from 0.0s to 0.70s. :::::::::::::::: 41 (c) Cavity decoupling stages :::::::::::::::::::::: 41 x FIGURE Page 3.4 The upper graph is an example of the area calculation and the lower is an example of the calculation of S for the 355.0 kg, −∆ =0.047m slide. : 44 3.5 Diagram of how κ the energy transfer parameter changes over the time during the coupling of the slide. From A to B the slide is fully coupled to the free surface and transferring the maximum amount of energy. From B to C represents stage 1 where the slide has undergone the initial decou- pling, C to D the second stage of decoupling has begun, D to E the third stage, and E to F the slide has decoupled from the free surface and the amount amount of conversion is going to zero. C would represent stage 1 decoupling, D stage 2 decoupling and E stage three decoupling. ::::: 45 3.6 Runup measurement example. :::::::::::::::::::::::: 46 (a) Runup calculation example. :::::::::::::::::::: 46 (b) Runup calculation exampled zoomed in. ::::::::::::: 46 3.7 Snapshots illustrating wave motion at t = 0:0s and t = 1:80s, slope is in brown, and water is in black. Notice the cell filled with water for the t = 1:80s snapshot. :::::::::::::::::::::::::::::: 47 3.8 Snapshots illustrating wave motion at t = 3:15s to t = 3:30s, slope is in brown, and water is in black. Notice the that the intersection of slope and water stays in the same grid cell for all times. ::::::::::::: 48 3.9 Snapshots illustrating