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Open-File Report O-19-09, Coseismic landslide susceptibility, liquefaction susceptibility, and soil amplification class maps, Clackamas, Columbia, Multnomah, and Washington Counties, Oregon: For use in Hazus: FEMA's methodology for estimating potential losses from disasters
by Christina A. Appleby, William J. Burns, Robert W. Hairston-Porter, and John M. Bauer; 50 p. report, including four tabloid sized map figures, one Esri geodatabase with internal metadata, external metadata in .xml format.

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SUMMARY

The Portland region, the most densely populated area in the state of Oregon, is vulnerable to both regional earthquakes from the Cascadia Subduction Zone and events on local faults like the Portland Hills fault. When an earthquake occurs, surficial geology at a given location will impact the local experience of ground motion and ground deformation. By leveraging the best available surficial geologic maps and lidar-based topographic maps, we created new coseismic geohazard maps to inform earthquake models. These models allow us to estimate the impact of an earthquake at a neighborhood-scale with greater accuracy.

The data can be used to help communities become more resilient to future earthquakes and coseismic hazards. The methods and results of this study are intended for Hazus-specific mapping and are not to be used in place of site-specific mapping. For example, the data produced by this study were used to estimate the impact of potential earthquakes on current buildings and infrastructure and to estimate casualties and long-term displaced population as described in DOGAMI Open-File Report O-18-02, Earthquake regional impact analysis for Clackamas, Multnomah, and Washington Counties, Oregon (Bauer and others, 2018).

This work was funded by the Regional Disaster Preparedness Organization (RDPO), an organization that aims to increase the region’s resiliency to disasters in the Portland metropolitan region.

GEOGRAPHIC INFORMATION SYSTEM (GIS) DATA
Esri® formated geodatabase.
Metadata is embedded in the geodatabase and is also provided as separate .xml formatted files.

Coseismic_Hazard_Data_Clackamas_Columbia_Multnomah_Washington_Counties.gdb:
LandslideSusceptibility_Dry Coseismic landslide susceptibility is a rating that combines a units slope angle and geologic material group. In combination with peak ground acceleration for a particular earthquake, the FEMA Hazus earthquake model then estimates permanent ground deformation with an associated probability of occurrence. This raster dataset models the dry (groundwater below level of sliding) soil condition. .xml
LandslideSusceptibility_Wet

Coseismic landslide susceptibility is a rating that combines a units slope angle and geologic material group. In combination with peak ground acceleration for a particular earthquake, the FEMA Hazus earthquake model then estimates permanent ground deformation with an associated probability of occurrence. This raster dataset models the wet (groundwater level at ground surface) soil condition.

.xml
Liquefaction_Classes Liquefaction susceptibility is a rating that represents the degree to which any given geologic map unit is susceptible to liquefaction during an earthquake, assuming full soil saturation. Liquefaction susceptibility classes were based on data from Youd and Perkins (1978) [Youd, T. L., and Perkins, D. M., 1978, Mapping of liquefaction induced ground failure potential: Journal of the Geotechnical Engineering Division, American Society of Civil Engineers, v. 104, no. 4, p. 433–446.]. Liquefaction classes range from none to very high, which range numerically from 0 - 5, respectively. We created this liquefaction dataset by compiling the best available surficial geologic maps, amending linework to align to features visible in the lidar, and assigning geologic units liquefaction susceptibility classes. The liquefaction potential of landslide geologic units is not included in this dataset. .xml
Reference_Table This table provides a list of the sources for geologic data used in this study. The REF_ID_COD field can be used to join to the Liquefaction or Soil Amplification feature classes. .xml
Soil_Amplification_Class_and_Landslide_
Geologic_Group

This dataset includes both the soil amplification classes and the landslide susceptible geologic groups. Soil amplification classification, or ground motion amplification potential, is a rating that represents the National Earthquake Hazards Reduction Program (NEHRP) class assigned to the geologic map units within the study area (FEMA 2003) [Federal Emergency Management Agency (FEMA), 2003, Hazus-MH, FEMA’s tool for estimating potential losses from natural disasters, Earthquake Technical Manual: Washington, D. C., National Institute of Building Sciences.]. These ratings are based on the NEHRP classification scheme, defined by the average speed at which a shear-wave propagates through the upper 30-meters of a geologic profile. There are 6 separate classes, hard rock (A), rock (B), very dense soil and soft rock (C), stiff soils (D), soft soils (E), and soils requiring site-specific evaluation (F). Geologic units used for assigning NEHRP classes were obtained from combining multiple published geologic maps. Linework amendments were performed in areas of high soil amplification potential, mainly areas of alluvium and unmapped landslide deposits. Areas composed of artificial fill and landslides were classified as ‘F’ given that they require site-specific analysis. The landslide susceptible geologic group data is an intermediary classification used to produce the landslide susceptibility data. Based on their geotechnical characteristics, geologic units are divided into A) Strongly Cemented Rocks, B) Weakly Cemented Rocks and Soils, and C) Argillaceous Rocks. These factors relate to the unit’s general geotechnical properties such as strength, but also to depositional setting and unit history. Group C includes existing landslides.

.xml