The underlying purpose of mitigation countermeasures is to save lives and to minimize property damage. In order to effectively address these dual objectives it is important that communities understand and differentiate the conditions resulting in damage and in life loss. The measures responding to these different objectives differ. Mitigation of property damage relates to the physical uses in the hazard area, i.e. allowable\non allowable uses; whereas saving lives is a function of the number of people at risk and their awareness of appropriate behavior.

The Mitigation and Counter Measures session will explore issues from recent tsunamis in relation to potential mitigation and preparedness lessons learned. Specific events could include but are not limited to Okushiri, Nicaragua, and the Kuril Islands.

Suggested topics should address characteristics of vulnerability:

Vulnerability to Direct Damage to Structures

Issues:

      Use  (high  life  loss potential, impacts  on  response etc.)
      Siting (fire breaks, evacuation difficulty etc.)
      Building materials (wood vs. concrete and steel)
      Critical and essential facilities
      Potential for Interactive hazards

Issues:

      Fire
      Surface water and well contamination
      Lifeline Disruption
      Disruption  to roadways (impacts on search and  rescue) waterline
      rupture (impacts    on fire suppression,  recovery, health impacts)
      Cisterns  inaccessibly and/or under capacity  hampering fire 
      suppression                         
      Communication disruption (hampering search and rescue efforts)

Elements of a mitigation policy must be practical as well as responsive to the above conditions. An example of a practical mitigation program is given below.

State of Oregon Tsunami Hazard Mitigation Program

Responding to the recently recognized threat from locally generated tsunamis from the Cascadia subduction zone (Heaton and Kanamori, 1984; Atwater, 1987; Adams, 1990; Darienzo and Peterson, 1990; 1995; Peterson and others, 1995), the State of Oregon Department of Geology and Mineral Industries (DOGAMI) is pursuing tsunami hazard mitigation through four parallel approaches:

1. Public education
2. Inundation mapping
3. Legislation limiting construction of essential facilities in inundation zones
4. Warning systems

Important to all of these approaches is making sure that the tsunami mitigation information is nontechnical and easy to use. In this way the users have "ownership" of the mitigation program. In some cases local volunteers are utilized in gathering data or producing local brochures and newsletters. In other cases financial contributions from local government have enhanced the inundation mapping by providing more accurate bathymetric and topographic data. In all cases local government ultimately controls the final evacuation and land use planning that leads to effective reduction of the hazard.

Public Education

Public education is the most cost-effective mitigation measure. The State of Oregon is taking the following actions:

1. Installation of warning, evacuation, and educational signs.
2. Publication of articles in both popular and technical journals.
3. Coordination with educational organizations.
4. Passage of Oregon State Senate Bill 378 (SB 378) which requires schools in potential inundation zones to teach students in grades kindergarten through eight about tsunamis and evacuation.
5. Coordination between several State of Oregon departments and the Oregon Museum of Science and Industry has resulted in an outreach plan that will utilize educational service districts, Federal Emergency Management Agency, Tremor Troops, and the Internet to teach about tsunami hazards and mitigation measures.
6. Visits to radio, newspaper, and television stations.
7. Preparation of a video.
8. Publication of a general interest brochure.
9. Preparation of information for telephone companies so evacuation information can be published in telephone books.

Inundation Mapping by the State of Oregon

Inundation maps at the local and regional reconnaissance level were completed and published by the State of Oregon in 1995. Local detailed maps at both the 1:12,000 and 1:4,800 scale were completed as a pilot study in the Siletz Bay area (Priest and others, 1995; Baptista and others, 1995; Peterson and others, 1995). Companion earthquake hazard maps illustrating zones of potential liquefaction, slope instability, and amplification of shaking were also produced for Siletz Bay (Wang and Priest, 1995).

Additional detailed inundation mapping projects have been funded for the Yaquina Bay and Seaside-Gearhart areas. The entire coast was mapped at the reconnaissance scale of 1:24,000, utilizing a partnership between DOGAMI and the Oregon Graduate Institute of Science & Technology (Priest, 1995). The latter maps were produced to implement Oregon Senate Bill 379, which limits construction of certain essential and special occupancy buildings in the tsunami inundation zone.

Tsunami Hazard Mitigation by Oregon State Senate Bill 379

Senate Bill 379 (SB 379) was passed by the Oregon Legislature in 1995. It requires the State (DOGAMI) to map the zone of expected tsunami inundation as basis for limiting new construction of essential and special occupancy facilities. Examples of essential facilities prohibited from construction in the inundation zone include schools, hospitals, fire stations, police stations and emergency response facilities. The bill also requires developers of larger buildings to consider alternative mitigation strategies prior to construction, if the building must be built in the inundation zone.

The new law provides a review process for granting exceptions to the prohibition in situations that require an essential facility to be located in the inundation zone. DOGAMI is responsible for reviewing requests for exceptions and providing review and consultation for mitigation plans. SB 379 is expected to result in improved public safety as new buildings are constructed in coastal towns, many of which are experiencing rapid population growth.

Passage of this bill was facilitated by a preliminary inventory of critical and essential facilities vulnerable to earth quake or tsunami hazards on the Oregon coast (Charland and Priest, 1995).

Federal Legislation

The United States Congress is considering legislation to develop a national system of insurance for natural hazards, including earthquakes, hurricanes, volcanic eruptions and tsunamis. This 1995 legislation (Senate 1043 and House of Representatives 1856) includes tsunami mitigation measures that could lead to improved preparation in Oregon and other states on the Pacific coast.

Warning System

The existing international tsunami warning system is not designed to be effective in the short interval between a near shore or subduction zone earthquake and arrival of the first tsunami wave. The State of Oregon is working with a coalition of federal and state government agencies to improve tsunami warning for local Cascadia earthquakes. In the interim, some coastal towns are developing their own warning systems. The leading example is the City of Cannon Beach on the northern Oregon coast.

REFERENCES

Atwater, B.F.(1987), Evidence for great Holocene earthquakes along the outer coast of Washington State: Science, v. 236, p.942-944.

Adams, J. (1990), Paleoseismicity of the Cascadia subduction zone turbidites off the Oregon-Washington margin: Tectonics, v. 9, p. 569-583.

Baptista, A.M., Qi, Ming, and Myers, E.P., III (1995), Siletz Bay: A pilot investigation of coastal inundation by Cascadia subduction zone tsunamis, in Priest, G.R., ed., Explanation of mapping methods and use of the tsunami hazard map of the Siletz Bay area, Lincoln County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Report O-95-5, p. 21- 44

Charland, J.W., and Priest, G.R. (1995), Inventory of critical and essential facilities vulnerable to earthquake or tsunami hazards on the Oregon coast, Oregon Department of Geology and Mineral Industries, Open-File Report O-95-2, 52 p.

Darienzo, M.E., and Peterson, C.D. (1990), Episodic tectonic subsidence of late Holocene salt marshes, northern Oregon central Cascadia margin, Tectonics, 9, No. 1, p. 1-22.

Darienzo, M.E., and Peterson, C.D. (1995), Magnitude and frequency of subduction-zone earthquakes along the northern Oregon coast in the past 3,000 years, Oregon Geology, 57, No. 1, p. 3-12.

Heaton, T.H., and Kanamori, H. (1984), Seismic potential associated with subduction in the northwestern United States: Bulletin of the Seismological Society of America, 74, No. 3, p. 933-941.

Peterson, C.D., Darienzo, M.E., Doyle, D., and Barnett, E. (1995), Evidence for coseismic subsidence and tsunami inundation during the past 3,000 years at Siletz Bay, Oregon, in Priest, G.R., ed., Explanation of mapping methods and use of the tsunami hazard map of the Siletz Bay area, Lincoln County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Report O-95-5, p. 45-69.

Preuss, J. (1995), Lessons Learned From October 4, 1994 Tsunami Warning: Information Transmission and Land Use Implications for U. S. National Science Foundation.

Preuss, J., and Hebenstreit, G. (1990), Integrated Hazard Assessment for a Coastal Community: Grays Harbor, Washington; U.S. Geol. Survey Open File Report 91-0441-M.

Priest, G.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, 95 p.

Priest, G.R., Baptista, A.M. Qi, M., Peterson, C.D., and Darienzo, M.E. (1995), Simplified explanation of the tsunami hazard map of the Siletz Bay area, Lincoln County, Oregon, in

Priest, G.R., ed., Explanation of mapping methods and use of the tsunami hazard map of the Siletz Bay area, Lincoln County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Report O-95-5, p. 1-20.

Urban Regional Research (1982), Planning for Risk: Comprehensive Planning for Tsunami Hazard Zones, for U.S. National Science Foundation.

Urban Regional Research (1988), Planning for Risk: Comprehensive Planning for Tsunami Hazard Areas, for U.S. National Science Foundation.

Wang, Y., and Priest, G.R. (1995), Relative earthquake hazard maps of the Siletz Bay area, coastal Lincoln County, Oregon: Oregon Department of Geology and Mineral Industries GMS-93, 3 1:12,000 scale maps and text.