NEW earthquake hazard maps for Portland metropolitan area

Portland, Oregon: On Monday, January 24th, a new series of earthquake hazard maps for the Portland metropolitan area will be released at the Department of Geology and Mineral Industries (DOGAMI) Governing Board Meeting at the State Office Building in Portland. These new maps will look at a number of different possible earthquake scenarios for the three-county area including the first ever model of a rupture along the Portland Hills Fault that runs through downtown Portland. The Agency and the State of Oregon will also be honoring a group of Japanese researchers who helped confirm the Cascadia subduction zone earthquake that occurred January 26th, 1700, and the subsequent tsunami that struck the coast of Japan two days later.

The press conference and release of the earthquake scenario maps will take place at 8:30am at the State Office Building at 800 NE Oregon Street, Portland, Conference Room 140 (first floor). Many regional emergency managers and planners, geologists and other local officials will be on hand for interviews and questions.

The maps include a hypothetical situation map that shows a magnitude 6.8 earthquake on the Portland Hills Fault. This map (IMS-15) is also the first to show all major faults in the Portland metropolitan area and what you might feel and the damage that could occur if a magnitude 6.8 earthquake struck the Portland Hills Fault. Also modeled in another set of maps is the effect of a magnitude 9.0 Cascadia subduction zone earthquake on the Portland metropolitan area.

Four years in the making, these maps differ from the Portland Metropolitan Relative Earthquake Hazard Maps (IMS-1, released by Metro and DOGAMI in 1997) in that the new maps depict much more specific effects. "IMS-1 was a generalized look at the metro area," notes State Geologist John Beaulieu. "These new maps are a much more focused effort to give people an idea of the kind of damage they can expect in certain types of earthquakes."

"We hope these maps will be used by government agencies, the engineering, urban planning, emergency preparedness and response communities and the general public as part of an overall effort to reduce earthquake hazards in the Portland metropolitan area," said Beaulieu.

Background:

The Portland metropolitan area and surrounding vicinity have been the most seismically active region in Oregon in historical times. Based on the relatively brief 150-year historic record, six earthquakes of Richter magnitude (Ml) 5 or greater have occurred within the greater Portland area including the damaging 1962 Ml 5.5 Portland and 1993 Ml 5.6 Scott Mills earthquakes. In contrast, recent geophysical studies indicate the presence of at least three crustal faults beneath the Portland metropolitan area which could generate much more damaging crustal earthquakes of Ml 6.5 or larger. An evaluation of earthquake recurrence based on the historical record suggests that crustal earthquakes of Ml 6.5 and larger occur somewhere in the Portland region on average about every 1,000 years. Additionally a convincing case has now been made that indicates Cascadia subduction zone earthquakes up to moment magnitude (Mw) 9 have occurred in the prehistoric past, as recently as the year 1700, and will occur in the future. Thus, although in its 150-year existence, the Portland metropolitan area has gone relatively unscathed by damaging earthquakes, strong ground shaking generated by either a Cascadia subduction zone earthquake or a nearby crustal event, will certainly have a major future impact on the Portland area.

More maps!

On Wednesday, January 26th, the 300th anniversary of the great Cascadia subduction zone earthquake, DOGAMI will release 28 relative earthquake hazard maps for selected communities in western Oregon. These new maps will cover 48 communities, from Columbia City to Ashland. Relative earthquake hazard maps combine the effects of ground shaking amplification, liquefaction and earthquake-induced landsliding to show the earthquake hazards relative to the local geologic conditions. In October, DOGAMI released the first set of maps in this series for 9 coastal Oregon communities. The press conference and release of maps is scheduled for 11:00am at the State Capitol, Hearing Room D. Relative earthquake hazard maps will be released for the following cities:

IMS-7 - St. Helens-Columbia City-Scappoose, Sandy, Hood River, McMinnville-Dayton-Lafayette, Newberg-Dundee, Sheridan-Willamina, Dallas and Monmouth-Independence.

IMS-8 - Canby-Aurora, Lebanon, Sweet Home, Woodburn-Hubbard, Silverton-Mt. Angel and Stayton-Sublimity-Aumsville.

IMS-9 - Ashland, Cottage Grove, Grants Pass, Sutherlin-Oakland and Roseburg.

All maps can be purchased through:

Nature of the Northwest?
800 NE Oregon St. #5
Portland, OR 97232
info@naturenw.org
www.naturenw.org
(503) 872-2750

For more information on these upcoming events and the department’s current projects, contact James Roddey at 800 NE Oregon St., Portland, OR 97232, (971) 673-1555, ext. 242.