Probabilistic Tsunami Hazard Maps and GIS

2005 ESRI International User Conference, San Diego, California, July 2005, Proceedings, http://gis.esri.com/library/userconf/index.html. Probabilistic Tsunami Hazard Maps and GIS Florence L. Wong 1, Eric L. Geist 1, and Angie J. Venturato 2 1 U.S. Geological Survey, 345 Middlefield Road, MS 999, Menlo Park, CA 94025 2 Joint Institute for the Study of the Atmosphere and Ocean (JISAO), University of Washington, Box 354235, Seattle, WA 98115 Abstract Probabilistic tsunami hazard mapping is performed at Seaside, Oregon, the site of a pilot study that is part of the Federal Emergency Management Agency's (FEMA) effort to modernize its Flood Insurance Rate Maps (FIRMs). Because of the application of the study to FIRMs, we focus on developing aggregate hazard values (e.g., inundation area, flow depth) for the 1% and 0.2% annual probability events, otherwise known as the 100-year and 500-year floods. Both far-field and local tsunami sources are considered, each with assigned probability parameters. Introduction Figure 1. Flood Insurance Rate Map (FIRM) for Seaside, Oregon (FEMA, 1981). Major FIRM zones: A, areas of 100-year flood; B, areas between 100- year flood and 500-year flood; C, areas of minimal flooding; V, areas of 100- year coastal flood with velocity (wave action). The Federal Emergency Management Agency s (FEMA) National Flood Insurance Program (NFIP) is charged with floodplain identification and mapping, floodplain management, and administration Wong, Geist, and Venturato: ESRI Paper #2000, July 2005 1

of flood insurance. One important tool of the program is the Flood Insurance Rate Map (FIRM), which presents flood risk information (FEMA, 2003; Figure 1). As part of FEMA s Flood Insurance Map Modernization Program, a Tsunami Pilot Study was carried out in the Seaside/Gearhart, Oregon, area to provide information from which tsunami mapping guidelines could be developed (Figure 2). The Study was an interagency effort by scientists from the U.S. Geological Survey, the National Oceanic and Atmospheric Administration (NOAA), the University of Southern California, and the Middle East Technical University (Ankara, Turkey). This paper describes preliminary results from the development of the 100-year and 500-year tsunami flood maps from probabilistic tsunami hazard analysis (Tsunami Pilot Study Working Group TPSWG, 2005). The 100-year and 500-year flood, as used in this report, is defined as the water elevation that has a 1% or 0.2% chance, respectively, of being equaled or exceeded in any given year (IACWD, 1982). Figure 2. Seaside and Gearhart, on the northwest Oregon coast, is the site of a pilot study that is part of FEMA s effort to modernize its Flood Insurance Rate Maps. Paleoseismic and paleotsunami evidence, the state of knowledge regarding source recurrence, the existence of historical tsunami records, the availability and quality of data needed for the development of computational grids, and programmatic factors led to the selection of this site (Gonzalez and others, 2004). In historic times, Seaside has experienced flooding from at least two major tsunamis one from a 1700 Cascadia subduction zone earthquake and another from the 1964 Alaskan earthquake (Priest, 1995). Mapping of tsunami deposits and, for the more recent event, eyewitness accounts have defined minimum extents of the tsunami runup or flooding for each event (Figure 3; Horning, 1997; Priest and others, 1997; Fiedorowicz, 1997; Jaffe and others, 2004). Wong, Geist, and Venturato: ESRI Paper #2000, July 2005 2

Figure 3. Deposits from several historic tsunamis in the Seaside area have been identified and mapped (Fiedorowicz, 1997; Jaffe and others, 2004). The locations of samples from the deposits (dot symbols) are compared in this figure with inundation limits for (1) casc1700ln, a worst case scenario of a Cascadia subduction zone (CSZ) earthquake (Priest and others, 1997); (2) ak64ln, the 1964 Alaskan earthquake tsunami (Horning, 1997); and (3) DOGAMI 95, a limit based on onedimensional modeling of the CSZ in response to 1995 Oregon Senate Bill 379 (Priest, 1995). The background map is the Flood Insurance Rate Map (FIRM) for Seaside, Oregon (FEMA, 1981). The impact of tsunamis in the Seaside area was incorporated in the existing FIRM (FEMA, 1981) from work by Houston and Garcia (1978) based on models of far-field tsunamis, tides, and local runup probabilities. They developed longitude-independent curves of tsunami heights for 100-year and 500- year scenarios; in the Seaside/Gearhart area (latitude 45 58 to 46 02 N), their runup calculations are 2.3 m and 4.9 m (mean high water), respectively. Methods Probabilistic tsunami hazard analysis (PTHA) is based on techniques developed in the related field of probabilistic seismic hazard analysis (PSHA) and attempts to model the magnitude of tsunami flooding from multiple sources for particular recurrence rates (Geist and Parsons, 2004, 2005; TPSWG, Wong, Geist, and Venturato: ESRI Paper #2000, July 2005 3

2005). The probabilities of interest for the Flood Insurance Rate Maps are 1% and 0.2% per year or the 100-year and 500-year maps, respectively. The products described in this section were developed with a combination of numerical models and geographic information systems (GIS) tools. The first step in tsunami modeling for this area was construction of a new1/3-arc-second (10 m) digital elevation model (DEM) (Venturato, 2004). The DEM data go into the Method of Splitting Tsunami (MOST) model, a numerical model that simulates tsunami generation, transoceanic propagation and inundation on land (Titov and Synolakis, 1998; Titov and Gonzalez, 1997). This tsunami inundation model is part of the NOAA Facility for the Analysis and Comparison of Tsunami Simulations (FACTS) tool, which can run numerous simulations of tsunamigenic earthquakes from both far-field and near-field tsunami sources (Borrero and others, 2004). The MOST model requires three nested grids to properly simulate tsunami processes -- 36 arc-second pixels at the ocean-basin scale, 6 arc-second at the regional scale, and 1/3 arc-second in the study area (TPSWG, 2005). Figure 4. Far-field sources used in the tsunami models for Seaside, Oregon, are located in the Kuril- Kamchatka, Aleutian-Alaska, and southern Chile subduction zones. The main near-field source is the Cascadia subduction zone, immediately offshore of Washington, Oregon, and northern California. Numbers identify FACTS inundation model runs. Plate boundaries from Coffin and others (1998). Distant or far-field sources for the probabilistic model calculations are the Kuril-Kamchatka, Alaska-Aleutian, and southern Chile subduction zones (Figure 4). Local or near-field sources are all from the Cascadia subduction zone adjacent to the Washington-Oregon-northern California margin. Of Wong, Geist, and Venturato: ESRI Paper #2000, July 2005 4

several parameters provided by the MOST model database (Borrero and others, 2004), the maximum wave height was selected for input to the probabilistic model. The maximum wave height was determined for each of the 14 inundation models based on the far-field sources (10-meter grid interval, Figure 5) and the 13 models based on near-field sources (30-meter grid interval, Figure 6). The reference vertical datum is mean high water. Figure 5. Far-field inundation model result (one of 14) for Seaside, Oregon, based on a magnitude 9.2 earthquake from the Alaskan-Aleutian subduction zone (Titov and others, 2004). Wave height of the maximum wave ranges from 0.02 to 3.34 meters (mean 0.87 m) in the study area. Figure 6. Near-field inundation model result (one of 13) for Seaside, Oregon, based on a magnitude 9.0 earthquake from the Cascadia subduction zone (Titov and others, 2004). Wave height of the maximum wave ranges from 2.5 to 39.3 meters (mean 1.1 m) in the study area. For each grid location x-y, the inundation data have been combined with tidal data by probabilistic tsunami hazard assessment calculations to generate a hazard curve that describes the probability of recurrence at that location of a tsunami flood exceeding some wave height z (Mofjeld and Wong, Geist, and Venturato: ESRI Paper #2000, July 2005 5

others, in press). For each wave height z from 0.5 m to 10.5 at 0.5-m intervals, a grid of probabilities was generated and contoured at 0.002 (0.2%) intervals (Figure 7; TPSWG, 2005). Figure 7. Probabilities of exceedance for selected tsunami wave heights. (a) A wave height of 0.5 m is expected to be exceeded near the coast at 100-year recurrence rates and farther inland at the 500-year recurrence rate. (b) A wave height of 4.0 m is likely to be exceeded in limited areas near the coast at 100- year recurrence rates, but quite extensively at a 500-year recurrence rate. (c) A wave height of 6.5 m is not expected to be exceeded at 100-year recurrence rates. For the 500-year recurrence rate, the wave height of 6.5 m is expected to be exceeded but not as far inshore as the 4.0-m wave height. The 0.010 contour is extracted from each of the probability grids into a map of wave heights with a probability of exceedance of 1% per year (i.e., the 100-year tsunami map) (Figure 8). Similarly, the 0.002 contours are collected to generate the 500-year tsunami map. Wong, Geist, and Venturato: ESRI Paper #2000, July 2005 6

Figure 8. 100-year and 500-year tsunami wave heights. Discussion The 100-year tsunami map describes the extent and wave heights of a tsunami that might be met or exceeded with an annual probability of 1%. Similarly, the 500-year map portrays the data with an annual probability of 0.2%. In the offshore area, both maps indicate that tsunami wave heights increase as they approach the outer coast in response to decreasing water depth. The 100-year tsunami map shows little inundation of the developed areas in the pilot study site. Although a deaggregation of results has yet to be performed, the 100-year map is primarily controlled by far-field or distant tsunami sources (Figure 5; TPSWG, 2005). In contrast, the 500-year map shows inundation of large regions of Seaside with significant wave heights. The 500-year map is greatly influenced by near-field sources -- the tsunamis originating from the Cascadia subduction zone (Figure 6; TPSWG, 2005). Wong, Geist, and Venturato: ESRI Paper #2000, July 2005 7

Figure 9. Contours of 500-year tsunami are plotted over the current Flood Insurance Rate Map (FEMA, 1981) for Seaside. casc1700ln is the worst-case limit for a tsunami generated by an earthquake from the nearby Cascadia subduction zone (Priest and others, 1997). The 100-year and 500-year inundation areas fall inside the 100-year flood zone for all flood sources defined in the existing FIRM for the Seaside area (FEMA, 1981; Figure 9) and inside the area defined by tsunami deposits from a worst-case Cascadia subduction zone tsunami (Priest and others, 1997). In addition, some regions (central unshaded zone C, Figure 9) that were not classified as being within the 100-year or 500-year flood zone on the existing FIRM, are included in the newly calculated 500-year tsunami flood map. The Tsunami Pilot Study Working Group is conducting further analysis of these new products. Acknowledgments This research is funded in part by the Federal Emergency Management Agency Map Modernization Program. This publication is partially funded by the Joint Institute for the Study of the Wong, Geist, and Venturato: ESRI Paper #2000, July 2005 8

Atmosphere and Ocean under NOAA Cooperative Agreement No. NA17RJ1232, Contribution #1138. Reviews by Pete Dartnell and Jamie Conrad improved this report. Any use of trade names is for descriptive purposes only and does not imply endorsement by the U.S. Government. TPSWG Tsunami Pilot Study Working Group: Frank González, NOAA/PMEL; Eric Geist, U.S. Geological Survey; Costas Synolakis, Univ. of Southern California; Diego Arca NOAA/PMEL; Doug Bellomo, FEMA, Dept. of Homeland Security; David Carlton, FEMA, Dept. of Homeland Security; Tom Horning, Horning Geoscience; Bruce Jaffe, U.S. Geological Survey; Jeff Johnson, Northwest Hydraulics Consultants; Utku Kanoglu, Middle East Technical University; Hal Mofjeld, NOAA/PMEL; Jean Newman NOAA/PMEL; Tom Parsons U.S. Geological Survey; Robert Peters, U.S. Geological Survey; Curt Peterson, Portland State University; George Priest, Oregon Dept. of Geology & Minerals; Vasily Titov, NOAA/PMEL; Angie Venturato, NOAA/PMEL; Joe Weber, FEMA, Dept. of Homeland Security; Florence Wong, U.S. Geological Survey; Ahmet Yalciner, Middle East Technical University. Glossary DOGAMI Oregon Department of Geology and Mineral Industries FACTS Facility for the Analysis and Comparison of Tsunami Simulations (Borrero and others, 2004) FIRM FEMA Flood Insurance Rate Map MOST Method of Splitting Tsunami (Titov and Gonzalez, 1997) NFIP National Flood Insurance Program http://www.fema.gov/fhm/ NTHMP NOAA National Tsunami Hazard Mitigation Program http://www.pmel.noaa.gov/tsunamihazard/ PSHA Probabilistic Seismic Hazard Analysis PTHA Probabilistic Tsunami Hazard Analysis TIME NOAA Center for Tsunami Inundation Mapping Efforts http://www.pmel.noaa.gov/tsunami/time/ TPSWG Tsunami Pilot Study Working Group References cited Borrero, J.C., Gonzalez, F.I., Titov, V.V., Newman, J.C., Venturato, A.J., and Legg, G., 2004, Application of FACTS as a tool for modeling, archiving and sharing tsunami simulation results: Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract OS23D-1362. Coffin, M.F., Gahagan, L.M., and Lawver, L.A., 1998, Present-day Plate Boundary Digital Data Compilation. University of Texas Institute for Geophysics Technical Report No. 174, pp. 5. FEMA Federal Emergency Management Agency, 1981, Flood insurance rate map, City of Seaside, Oregon, Clatsop County, panel 1 of 2: FEMA Community-Panel Number 410032 0001 C http://store.msc.fema.gov/webapp/wcs/stores/servlet/femawelcomeview?storeid=10001&catalogid =10001&langId=-1 FEMA Federal Emergency Management Agency, 2003, How to read a flood insurance rate map tutorial: 45 p. http://www.fema.gov/pdf/fhm/ot_frmsb.pdf Fiedorowicz, B.K. (1997): Geologic evidence of historic and prehistoric tsunami inundation at Seaside, Oregon. Unpublished M.S. thesis, Portland State University. Geist, E.L., and Parsons, T., 2004, Estimating Source Recurrence Rates for Probabilistic Tsunami Hazard Analysis (PTHA): Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract OS23D-1344. Wong, Geist, and Venturato: ESRI Paper #2000, July 2005 9

Geist, E.L., and Parsons, T., 2005 (in press), Probabilistic analysis of tsunami hazards: Natural Hazards, 38 p. Gonzalez, F.I., Geist, E.L., Synolakis, Costas, and Titov, V.V., 2004, Probabilistic Tsunami Hazard Assessment: the Seaside, Oregon Pilot Study: Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract OS22B-04 Horning, Tom, (1997, written communication), Alaska 1964 Event Line - Seaside, Oregon Houston, J.R., and Garcia, A.W., 1978, Type 16 Flood Insurance Study: Tsunami Predictions for the West Coast of the Continental United States: U.S. Army Engineer Waterways Experiment Station, Technical Report H-78-26. Interagency Advisory Committee on Water Data (IACWD), 1982, Guidelines for Determining Flood Flow Frequency: Bulletin 17B of the Hydrology Subcommittee, Department of Interior, U.S. Geological Survey, Office of Water Data Coordination, Reston, VA. Jaffe, B.E., Peterson, C.D., and Peters, R., 2004, Using Tsunami Deposits in a Probabilistic Inundation Study at Seaside, Oregon: Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract OS23D-1338. Mofjeld, H.O., González, F.I., Titov, V.V., Venturato, A.J., and Newman, J.C., (in press), Effects of tides on maximum tsunami wave heights: Probability distributions: Journal of Atmospheric and Oceanic Technology. Priest, George R., 1995, Explanation of mapping methods and use of the tsunami hazard maps of the Oregon coast: Oregon Department of Geology and Mineral Industries Open-file Report O-95-67, http://www.gis.state.or.us/data/metadata/k24/tsunami.pdf Priest, G.R., E.P. Myers III, A.M. Baptista, P. Fleuck, K. Wang, R.A. Kamphaus, and C.D. Peterson, 1997, Cascadia Subduction Zone tsunamis - Hazard mapping at Yaquina Bay, Oregon: Oregon Department of Geology and Mineral Industries Open-File Report O-97-34, 144pp. Titov, V.V., and Gonzalez, F.I., 1997, Implementation and testing of the Method Of Splitting Tsunami (MOST): NOAA Technical Memorandum ERL PMEL-112, http://www.pmel.noaa.gov/pubs/pdf/tito1927/tito1927.pdf Titov, V.V., and Synolakis, C.E., 1998, Numerical modeling of tidal wave runup: Journal of Waterway, Port, Coastal, and Ocean Engineering, v. 124, n. 4, p. 157-171. Titov, V.V., Arcas, D., Kanoglu, U., Newman, J., and Gonzalez, F.I., 2004, Inundation modeling for probabilistic tsunami hazard assessment: Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract OS23D-1340. TPSWG Tsunami Pilot Study Working Group, 2005, Seaside, Oregon Tsunami Pilot Study - Modernization of FEMA Flood Hazard Maps: U.S. Geological Survey Open-file Report 2005-xxxx, in press. Venturato, A.J., 2004, A Digital Elevation Model for Seaside, Oregon: Procedures, Data Sources, and Analysis: Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract OS23D-1342. Wong, Geist, and Venturato: ESRI Paper #2000, July 2005 10

For more information: Florence L. Wong fwong@usgs.gov 650-329-5327 Eric L. Geist egeist@usgs.gov 650-329-5457 U.S. Geological Survey 345 Middlefield Road, MS 999 Menlo Park, CA 94025 Angie J. Venturato angie.j.venturato@noaa.gov 206-526-6556 Joint Institute for the Study of the Atmosphere and Ocean (JISAO) University of Washington Box 354235 Seattle, WA 98115 http://walrus.wr.usgs.gov/tsunami/ http://www.pmel.noaa.gov/tsupilot/ Wong, Geist, and Venturato: ESRI Paper #2000, July 2005 11