New Tsunami Maps Show Early Preparedness Crucial

 

During a presentation to the Warrenton City Commission Oregon’s Department of Geology and Mineral Industries  (DOGAMI) project operations manager, Rachel Smith, presented updated Tsunami maps that show areas for inundation. According to Smith, a local earthquake and subsequent tsunami would take 40 minutes to reach downtown Warrenton, giving people more time to get out of town on foot. However, those in Clatsop County living closer to the ocean may not have those crucial minutes.

“Our message is that residents and visitors need to expect to walk to high ground, not to drive,” Smith said. “You’ll probably reach congestion and won’t be able to drive. And in 15 to 30 minutes, will be the start of the tsunami.”

“It’s about 40 minutes for the tsunami wave to actually come up the Columbia River and make it to where it gets into downtown Warrenton,” Smith continued to warn.  “That number is a lot different than our normal — what we normally say you need to evacuate in 15 to 20 minutes because a tsunami wave is going to get here. In downtown, as bleak as the picture looks, it takes some time for that wave to get to downtown Warrenton.”

With the release of DOGAMI’s 10 new tsunami maps, seven new evacuation brochures covering population centers from Astoria to Arch Cape have been made.

“This is a new generation of tsunami maps based on the latest science, new mapping technology and lessons learned from earthquakes and tsunamis around the globe over the last 10 years,” said Vicki McConnell, State Geologist.

“Two years after the 2011 Tohoku earthquake and tsunami, Japan is still working through their recovery and we in Oregon are still preparing for our local Cascadia subduction zone earthquake and tsunami,” continued McConnell. “We at DOGAMI have created state-of-the-art tsunami inundation zone maps, work led with local community officials to design and produce effective tsunami evacuation brochures, and helped build a culture of preparedness to make Oregon safer where we work, live and play.”

The maps show tsunami evacuation zones for a local tsunami generated by an earthquake just offshore, along the Cascadia subduction zone, which would send tsunami waves at the Oregon coast 15-20 minutes later. DOGAMI warns, “If the ground shakes for an extended period of time, don’t wait for more warning; evacuate to high ground as fast as possible.

The maps also show danger zones for a distant tsunami caused by an earthquake in Alaska, with waves reaching Oregon some four hours later. Evacuation routes are shown on the maps, directing people to assemble in areas on high ground.

According to Oregon Dept of Geology during the 2011 Oregon Legislative Assembly the House of Representatives passed House Resolution 3, which acknowledged the threat posed to Oregon by great earthquakes from the Cascadia Subduction Zone. The Resolution also charged the Oregon State Seismic Safety Policy Advisory Commission (OSSPAC) to prepare a resilience plan for Oregon that would estimate current vulnerabilities to earthquake-related hazards. The Plan also recommends policies to address those vulnerabilities and increase the state’s resilience to a great earthquake. The Plan and recommendations were delivered to the Oregon Legislative Assembly on February 28, 2013.

To create the Oregon Resilience Plan, OSSPAC developed a strategy that involved the use of workgroups to analyze the vulnerability of their respective sectors to the chosen earthquake scenario, a magnitude 9.0 (M 9.0) great subduction earthquake off the coast of Oregon, accompanied by a large tsunami. The Cascadia Earthquake Scenario workgroup was charged with developing a description of the likely ground motion (strength of shaking) and ground deformation (earth movements) to be expected from the scenario event, as well as maps of the likely tsunami inundation for coastal cities.

The DOGAMI Open-File Report O-13-06, shows ground motion, ground deformation, tsunami inundation, co-seismic subsidence, and damage potential maps for the 2012 Oregon Resilience Plan for Cascadia Subduction Zone Earthquakes. The report, by Ian P. Madin and William J. Burns, contains definitive digital versions of the data and maps used by the Oregon Resilience Plan workgroups and OSSPAC as well as a description of the data sources and methods used to prepare the scenario maps. According to DOGAMI, this information will be useful to those interested in regional Cascadia ground motion and ground failure models. Note that these maps are not appropriate for site specific investigations, and investigations using site specific data are likely to produce results that vary from what is shown on these maps.

Where to find new evacuation maps
Paper copies: Brochures are available at upcoming Tsunami Readiness rallies
Web: Visit http://www.OregonTsunam.org for download, printing or for the interactive Evacuation Zone Map Viewer, which allows users to enter an address
Smart phone app: TsunamiEvac-NW is the free app for iPhone and Android users with a location-by-location interactive map format.

Upcoming Tsunami Readiness Rallies
These events are free, open to the public, and include a slide presentation by DOGAMI staff on earthquake and tsunami science, lessons from Japan’s 2011 tragedy, what the new maps tell, and how to prepare in Oregon. New, free, evacuation maps will be distributed. Some rallies will include information tables from local readiness groups like American Red Cross and CERT.
Seaside/Gearhart- Thursday, June 27, at 7PM at Broadway Middle School, 1120 Broadway St, Seaside.
Arch Cape – Saturday, June 29th at 10Am, at Arch Cape Fire Station, 79729 HWY 101.

Readiness Rallies were held in Warrenton and Astoria earlier this month.

Tsunami inundation maps (TIMs)
The free evacuation brochures are based on the more detailed and technical tsunami maps (TIMs) which contain a wealth of information, including estimated tsunami wave height time series charts and a measurement of the exposure each community has to the various tsunami scenarios: DOGMI count the number of buildings that are undated by each scenario. DOGAMI hopes that the public, planners, emergency managers and first responders, elected officials; and other local decision makers will use these detailed TIM map products to mitigate risk and to reduce the loss of life and property.