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Open-File Report O-18-02, Earthquake regional impact analysis for Clackamas, Multnomah, and Washington counties, Oregon
by John M. Bauer, William J. Burns, and Ian P. Madin; 90 p. report, including 16 tabloid sized map plates, two Esri geodatabases with internal metadata, external metadata in .xml format.
OVERVIEW: This study provides information about potential impacts to Clackamas, Multnomah, and Washington counties from earthquakes, including a magnitude 9 Cascadia Subduction Zone earthquake. By using updated data, current subduction zone science and the latest mapping and modelling techniques, the study greatly improves understanding of potential earthquake impacts for the region. The study’s estimates of injuries and fatalities, building damages, and other impacts helps communities, the region, and the state better prepare for, respond to, and recover from major earthquakes.
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EXECUTIVE SUMMARY
This report was prepared for the Regional Disaster Preparedness Organization (RDPO), with funding provided by the Urban Areas Security Initiative Program. The report provides damage and casualty estimates to buildings, people, and key infrastructure sectors resulting from a major earthquake in the Portland metropolitan region by using updated local geologic information and recent advances in loss estimation methods. Damage and casualty estimates are tabulated at county, jurisdiction, and neighborhood levels, providing actionable information for further use in emergency planning, earthquake mitigation, public awareness, and post-earthquake response and recovery.
The RDPO is a bi-state partnership of local and regional government agencies, non-governmental organizations, and private-sector stakeholders representing the Portland metropolitan region that collaborate to increase the region’s resiliency to disasters. The region spans Clackamas, Columbia, Multnomah, and Washington Counties in Oregon and Clark County in Washington. In 2016 the RDPO Steering Committee identified a need for updated, region-wide, detailed loss estimates from a major earthquake and engaged the Oregon Department of Geology and Mineral Industries (DOGAMI) to conduct this study. Previously, earthquake damage estimates in large portions of the Portland metropolitan region were limited to studies conducted in the 1990s, when understanding of the Cascadia Subduction Zone (CSZ) risk was nascent. Since then, advances have occurred in several areas, including loss estimation tool capabilities, subduction zone science, and local geologic mapping in the Portland metropolitan region. The RDPO commissioned this study to harness such advances, thereby enabling local, regional, state, and federal planners and policy makers to apply the results in their efforts to mitigate risk and building seismic resilience and to prepare for response and recovery. DOGAMI and RDPO divided the project into two phases, with the first phase focused on methodology refinement and application of those methods to evaluate impact of a major earthquake in Clackamas, Multnomah, and Washington Counties (Oregon). Phase 2 will apply the same methods in Columbia County, Oregon, and Clark County, Washington.
The Portland metropolitan region is vulnerable to regional and local earthquakes. We modeled damage for two earthquake scenarios: a magnitude 9.0 CSZ earthquake, and a magnitude 6.8 Portland Hills fault earthquake, a local crustal fault situated at the foot of the Tualatin Mountains. In order to better understand the range of possible losses, our analysis quantified impacts during saturated and dry soil conditions—the former are more likely to have earthquake-induced landslides and liquefaction; the latter may have some earthquake-induced landslides, but little occurrence of liquefaction. We derived our damage estimates primarily from Hazus®, a geographic information system (GIS)-based tool and set of methods for loss estimation from natural hazards. Hazus is developed and supported by the Federal Emergency Management Agency (FEMA).
Our project consisted of several major efforts:
A GIS database containing building footprints, population density grids, detailed casualty, debris, and building loss estimates by jurisdiction and neighborhood, key infrastructure sectors with loss estimates, and updated ground motion and ground deformation data accompanies this report. A separately published report describes the geologic mapping updates for the three-county area, consisting of National Earthquake Hazards Reduction Program (NEHRP) soil types, and earthquake-induced landslide and liquefaction susceptibility.
A Cascadia Subduction Zone (CSZ) magnitude 9.0 earthquake will have a severe impact on the three-county area, with building repair costs amounting to 23.5 and 36.7 (9% and 14% of the total building replacement cost, Table 1-1). Although damage estimates vary widely throughout the study area, no community will be unharmed. Depending on the time of day an earthquake occurs, casualties may be in the thousands or low tens of thousands. The earthquake will generate several millions of tons of debris from damaged buildings. Damage and casualty estimates resulting from a magnitude 6.8 Portland Hills fault earthquake are more than twice compared to a CSZ earthquake, primarily because of the Portland Hills fault location below densely populated and heavily developed areas (Table 1-1). However, the likelihood of a Portland Hills fault earthquake is considerably less than a Cascadia Subduction Zone earthquake.
Table 1-1. Loss estimate summary for two earthquake scenarios in the Portland metropolitan area. Lower value: dry soil conditions. Upper value: saturated soil conditions.
County |
U.S. Census Population Estimate (2010) | Number of Buildings |
Building Value ($ Billion) |
Building Repair Cost ($ Billion) |
Building Loss Ratio |
Debris (Millions of Tons) |
Long-Term Displaced Population (Thousands) | Total Casualties+ | |
| Daytime Scenario (Thousands) | Nighttime Scenario (Thousands) | ||||||||
| Cascadia Subduction Zone Magnitude 9.0 Earthquake | |||||||||
| Clackamas | 375,992 | 179,164 | 62.4 | 3.2–4.6 | 5%–7% | 1.7–2.1 | 1.9–10.1 | 2.0–2.8 | 0.5–1.1 |
| Multnomah | 735,334 | 255,577 | 114.0 | 13.3–20.5 | 12%–18% | 7.7–10.4 | 9.7–37.5 | 11.4–16.7 | 2.8–5.6 |
| Washington | 529,710 | 181,111 | 82.7 | 7.0–11.6 | 8%–14% | 3.4–4.8 | 5.2–37.7 | 4.9–7.7 | 1.1–3.7 |
| Total | 1,641,036 | 615,852 | 259.1 | 23.5–36.7 | 9%–14% | 12.8–17.3 | 16.8–85.3 | 18.3–27.2 | 4.4–10.4 |
| Portland Hills Fault Magnitude 6.8 Earthquake | |||||||||
| Clackamas | 375,992 | 179,164 | 62.4 | 12.9–16.4 | 21%–26% | 4.9–6.0 | 25.2–50.8 | 8.9–10.9 | 3.3–5.2 |
| Multnomah | 735,334 | 255,577 | 114.0 | 32.3–42.7 | 28%–37% | 15.7–19.3 | 50.8–120 | 28.9–36.3 | 9.3–15.3 |
| Washington | 529,710 | 181,111 | 82.7 | 15.4–24.3 | 19%–29% | 6.0–8.6 | 19.6–86.0 | 10.0–15.8 | 3.2–8.5 |
| Total | 1,641,036 | 615,852 | 259.1 | 60.6–83.4 | 23%–32% | 26.6–33.9 | 95.6–257 | 47.8–63.0 | 15.8–29.0 |
+ Casualty estimates include minor injuries, injuries requiring hospitalization, and fatalities.
The damage estimates are significantly higher than those given in previously published studies for the area, primarily due to usage of an updated building inventory that more accurately reflects the region’s building code history with respect to seismic resiliency, and usage of updated soils and liquefaction susceptibility data.
This study addressed a major need for consistent, updated earthquake damage estimates in the Portland metropolitan region. The data are intended not as an end in themselves, but as a platform for counties, jurisdictions, and communities to better understand their needs to prepare for, respond to, and recover from a major earthquake. We conclude our report with recommendations supported by findings in this study that can reduce the region’s vulnerability, shorten recovery time, and improve emergency operations.
GEOGRAPHIC INFORMATION SYSTEM (GIS) DATA
Geodatabase is Esri® version 10.1 format.
Metadata is embedded in the geodatabase and is also provided as separate .xml formatted files.
The GIS data included with this publication are partitioned into two ArcGIS version 10.1 file geodatabases.
Earthquake loss estimates and impact assessment data are contained in RDPO_Earthquake_Impact_Analysis_Phase1.gdb. Loss estimates for a particular earthquake scenario are contained in independent tables and can be joined to the appropriate polygon dataset to graphically represent impacts. Ground motion and ground deformation data are contained in RDPO_GroundMotion_GroundFailure_Phase1.gdb.
| RDPO_Earthquake_Impact_Analysis_Phase1.gdb: | ||
| Feature Dataset Phase1: | ||
| Building_Footprints | Outlines of buildings and other non-building structures. | .xml |
| Electrical_Transmission_Structures | Pointfile containing locations of electrical transmission poles and towers, and an estimate of permanent ground deformation at the location for all four earthquake scenarios. | .xml |
| Emergency_Transportation_Routes | Buffered and segmented version of the Metro area Emergency Transportation Routes, and a categorization, per segment, of the impact of permanent ground deformation on the segment, for all four earthquake scenarios. |
.xml |
| Jurisdictions | Cities, villages, hamlets, and unincorporated areas, and summary statistics for number of buildings, square footage, replacement cost, and population estimates. Contains Jurisdiction attribute for joining to loss estimate tables. | .xml |
| Neighborhood_Units | Neighborhood units (876 total), and summary statistics for number of buildings, square footage, replacement cost, and population estimates. Contains NUID attribute for joining to loss estimate tables. | .xml |
| Population_and_Building_Density | 20-acre hexagonal grid with summary statistics for number of buildings, number of residential buildings, and permanent residents per hexagonal cell. All cells contain at least one building. | .xml |
| Tables with building loss, casualty, and displaced population estimates for a given scenario | ||
| Loss estimates by jurisdiction | ||
| Tables can be joined to the Jurisdictions feature class using Jurisdiction attribute | ||
| Loss_Jurisdiction_CSZ_M9p0_dry | Scenario: Cascadia Subduction Zone M 9.0, “dry” soil conditions | .xml |
| Loss_Jurisdiction_CSZ_M9p0_wet | Scenario: Cascadia Subduction Zone M 9.0, “wet” (saturated) soil conditions | .xml |
| Loss_Jurisdiction_PHF_M6p8_dry | Scenario: Portland Hills fault M 6.8, “dry” soil conditions | .xml |
| Loss_Jurisdiction_PHF_M6p8_wet | Scenario: Portland Hills fault M 6.8, “wet” (saturated) soil conditions | .xml |
| Loss estimates by neighborhood unit | ||
| Tables can be joined to the Neighborhood_Units feature class using the NUID attribute | ||
| Loss_Neighborhood_Unit_CSZ_M9p0_dry | Scenario: Cascadia Subduction Zone M 9.0, “dry” soil conditions | .xml |
| Loss_Neighborhood_Unit_CSZ_M9p0_wet | Scenario: Cascadia Subduction Zone M 9.0, “wet” (saturated) soil conditions | .xml |
| Loss_Neighborhood_Unit_PHF_M6p8_dry | Scenario: Portland Hills fault M 6.8, “dry” soil conditions | .xml |
| Loss_Neighborhood_Unit_PHF_M6p8_wet | Scenario: Portland Hills fault M 6.8, “wet” (saturated) soil conditions | .xml |
| RDPO_GroundMotion_GroundFailure_Phase1.gdb: | ||
| Synthetic Cascadia Subduction Zone magnitude 9.0 earthquake | ||
| Site ground motion (rasters) | ||
| CSZ_M9p0_pga_site | Site peak ground acceleration, in g (standard gravity). | .xml |
| CSZ_M9p0_pgv_site | Site peak ground velocity, in centimeters per second. | .xml |
| CSZ_M9p0_sa03_site | Site spectral acceleration at 0.3 sec, in g (standard gravity). | .xml |
| CSZ_M9p0_sa10_site | Site spectral acceleration at 1.0 sec, in g (standard gravity). | .xml |
| Permanent Ground Deformation (PGD) (rasters) | ||
| Each PGD raster is accompanied with a probability (Prob) raster | ||
| CSZ_M9p0_PGD_landslide_dry | Permanent ground deformation due to earthquake-induced landslide under dry soil conditions, in centimeters. | .xml |
| CSZ_M9p0_Prob_landslide_dry | Probability of earthquake-induced landslide under dry soil conditions. In percent. | .xml |
| CSZ_M9p0_PGD_landslide_wet | Permanent ground deformation due to earthquake-induced landslide under wet (or saturated) soil conditions, in centimeters. | .xml |
| CSZ_M9p0_Prob_landslide_wet | Probability of earthquake-induced landslide under wet (or saturated) soil conditions. In percent. | .xml |
| CSZ_M9p0_PGD_liquefaction_wet | Permanent ground deformation due to liquefaction lateral spreading. Liquefaction assumes wet (or saturated) soil conditions, in centimeters. | .xml |
| CSZ_M9p0_Prob_liquefaction_wet | Probability of liquefaction under wet (or saturated) soil conditions. In percent. | .xml |
| Synthetic Portland Hills fault magnitude 6.8 earthquake | ||
| Bedrock ground motion | ||
| PHF_M6p8_bedrock_groundmotion | Pointfile with descriptors of bedrock ground motion (pga, pgv, sa03, sa10) | .xml |
| Site ground motion (rasters) | ||
| PHF_M6p8_pga_site | Site peak ground acceleration, in g (standard gravity). | .xml |
| PHF_M6p8_pgv_site | Site peak ground velocity, in centimeters per second. | .xml |
| PHF_M6p8_sa03_site | Site spectral acceleration at 0.3 sec, in g (standard gravity). | .xml |
| PHF_M6p8_sa10_site | Site spectral acceleration at 1.0 sec, in g (standard gravity). | .xml |
| Permanent Ground Deformation (PGD) (rasters) | ||
| Each PGD raster is accompanied with a probability (Prob) raster | ||
| PHF_M6p8_PGD_landslide_dry | Permanent ground deformation due to earthquake-induced landslide under dry soil conditions, in centimeters. | .xml |
| PHF_M6p8_Prob_landslide_dry | Probability of earthquake-induced landslide under dry soil conditions. In percent. | .xml |
| PHF_M6p8_PGD_landslide_wet | Permanent ground deformation due to earthquake-induced landslide under wet (or saturated) soil conditions, in centimeters. | .xml |
| PHF_M6p8_Prob_landslide_wet | Probability of earthquake-induced landslide under wet (or saturated) soil conditions. In percent. | .xml |
| PHF_M6p8_PGD_liquefaction_wet | Permanent ground deformation due to liquefaction lateral spreading. Liquefaction assumes wet (or saturated) soil conditions, in centimeters. | .xml |
| PHF_M6p8_Prob_liquefaction_wet | Probability of liquefaction under wet (or saturated) soil conditions. In percent. | .xml |
PLATES (georeferenced PDFs, 11 x 17 inches each)
Plate 1. Population Density and Building Location – Clackamas County, Oregon
Plate 2. Population Density and Building Location – Multnomah County, Oregon
Plate 3. Population Density and Building Location – Washington County, Oregon
Plate 4. Site Peak Ground Acceleration, Simulated Cascadia Subduction Zone Magnitude 9.0 Earthquake
Plate 5. Site Peak Ground Acceleration, Simulated Portland Hills Fault Magnitude 6.8 Earthquake
