Tsunami Time Travel Eric B. Grosfils Geology Department Pomona College Tsunami Travel Time

Tsunami Exercise: Goals CONTEXT CourseCourse HW after introduction to Spatial AnalystHW after introduction to Spatial Analyst LEARNING GOALS Perform, and apply results from, a raster calculationPerform, and apply results from, a raster calculation Extract and evaluate quantitative data from a rasterExtract and evaluate quantitative data from a raster Improve students’ ability to self-instruct within ArcGISImprove students’ ability to self-instruct within ArcGIS Reinforce previous learning (i.e., projection selection)Reinforce previous learning (i.e., projection selection) Assess exercise outcome by comparing with other research, to thereby increase depth of insight into tsunami behaviorAssess exercise outcome by comparing with other research, to thereby increase depth of insight into tsunami behavior Bust free of “I (or the computer) did it, so it’s the truth/junk”Bust free of “I (or the computer) did it, so it’s the truth/junk”

Tsunami Exercise: Step 0 Data & Approach DATA NOAA ETOPO1 raster (bathy/topo)NOAA ETOPO1 raster (bathy/topo) –Recast longitude to stitch together Pacific –Reproject to Pacific-centered Azimuthal Equidistant so that distance and direction are preserved Standard ESRI country and city shapefilesStandard ESRI country and city shapefiles Point file with tsunami origin (impact site)Point file with tsunami origin (impact site)APPROACH Presume impact of asteroid 2004MN4, 400 m diameterPresume impact of asteroid 2004MN4, 400 m diameter Tsunami wavelength is so long that it behaves like a shallow wave in deep oceanTsunami wavelength is so long that it behaves like a shallow wave in deep ocean Velocity = SQRT ( depth * g )

Tsunami Exercise: Step 1 OBJECTIVE Generate a tsunami velocity map (raster)Generate a tsunami velocity map (raster)PROCESS Invert raster values (make bathymetry positive)Invert raster values (make bathymetry positive) Convert depth values to velocityConvert depth values to velocity

Tsunami Exercise: Step 2 OBJECTIVE Calculate shortest path between two points (impact site & coastal city)Calculate shortest path between two points (impact site & coastal city) Obtain mean velocity along shortest pathObtain mean velocity along shortest path Calculate travel timeCalculate travel timePROCESS Generate distance raster from impact site, create graphic using Steepest path tool, convert graphic to polyline, calculate polyline lengthGenerate distance raster from impact site, create graphic using Steepest path tool, convert graphic to polyline, calculate polyline length Apply Zonal Statistics toolApply Zonal Statistics tool V = d/tV = d/t

Tsunami Exercise: Step 3 OBJECTIVE Compare results with USGS calculationCompare results with USGS calculation Assess patterns observed and research why your answers are differentAssess patterns observed and research why your answers are differentPROCESS Compare with animationCompare with animation Student times are roughly half those of USGS calculationStudent times are roughly half those of USGS calculation Reasons cited:Reasons cited: –Point to point calculation –No conservation of E, mass –No refraction etc. –Wave packet vel effect –Etc. For Seward, AK Class: ~6 hrs USGS: ~ 12.5 hrs animation clip

Other Parts of Spatial Analyst HW Viewshed problem (2003 Padua & Grand Prix fire visibility from my home)Viewshed problem (2003 Padua & Grand Prix fire visibility from my home) Cost Path Analysis (getting geophysical equipment from campsite to field area in Grabens District of Canyonlands NP)Cost Path Analysis (getting geophysical equipment from campsite to field area in Grabens District of Canyonlands NP) Analysis of independently obtained dataset (conclusion of assignment started in first week of course)Analysis of independently obtained dataset (conclusion of assignment started in first week of course)