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Background and Data Limitations

Project Purpose
Understanding LIDAR
Disclaimer
Source Data
    - Base Maps
    - Portland Area Relative Earthquake Hazards Study (DOGAMI IMS-1)
    - Oregon City Landslide Study (DOGAMI Open-File Report 06-27)
    - Other Overlays
Team
Funding

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Project Purpose

As part of its mission to assess geological hazards and natural resources to protect the life, safety and welfare of Oregonians, the Oregon Department of Geology & Mineral Industries, in partnership with the United States Geological Survey, has acquired 441.5 square miles of digital Light Detection and Ranging (LIDAR) data for portions of the Portland METRO area and the Columbia River. Other government authorities, such as the City of Oregon City, also have acquired and provided LIDAR data. There is a multi-agency plan to acquire approximately an additional 1,200 square miles of LIDAR during early 2007. To ”fly” LIDAR over a given area costs $400-$1000 per square mile. However, that cost can be significantly lowered by flying large areas at one time.

The purposes of this project are to make images of the “Bare Earth” digital elevation model (DEM) derived from these LIDAR data available and searchable on the web by street address and to be able to compare and contrast these against aerial photographs, topographic maps, and 10-m DEM derived from the topographic maps, in order to educate Oregonians as to the practical and superior utility of this form of elevation information. Where earthquake and landslide hazard data are available, these hazard layers may be turned on and off.

Comparison of the four types of imagery for the southern tip of Sauvie Island:
Orthophoto (aerial photo) "bare earth" shaded topographic
relief map derived from LIDAR 		USGS topographic map shaded topographic relief map from
10-m digital elevation model

Innovative uses of LIDAR

The Oregon Department of Geology and Mineral Industries (DOGAMI) uses LIDAR for hazard mapping, identifying earthquake faults and landslides in urban areas. DOGAMI is proposing LIDAR mapping for urban, urban growth boundaries, and developing areas in western Oregon.

Current and proposed LIDAR imaging in the Portland metro area to support landslide and earthquake research.

DOGAMI’s goals with LIDAR

DOGAMI’s goals for a statewide LIDAR program:

Costs –
$2Million over a 3-year period for LIDAR
$50k/year for data maintenance

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Understanding LIDAR

Most people are familiar with radar (Radio Detection and Ranging). Radar is a system that uses radio waves to detect, determine the direction and distance and/or speed of objects such as aircraft, ships, terrain, or rain, and map them.

LIDAR (Light Detection and Ranging) is similar to RADAR but uses rapid pulses of light energy particles (photons) instead of radio waves. During the past decade LIDAR has revolutionized mapping.

A LIDAR survey system collects tremendous quantities of three-dimensional point data where photons have been reflected off opaque objects like buildings, trees, bushes, and the ground surface. The dense amounts of spatial data provide surprisingly high-resolution, three-dimensional models of the shape of, and of what is on, the surface of the earth. LIDAR-based, three-dimensional models and images are thus far superior to the traditional maps we are familiar with.

Currently, LIDAR data are correct within a few inches of their true absolute elevation in space and to within a few feet laterally. In addition to being better data, LIDAR data collection is far faster than by other survey techniques and is inexpensive, averaging $500 per square mile for larger survey areas.

DOGAMI uses bare earth DEMs to identify existing natural hazards like earthquake faults and landslides that normally are very difficult to detect in forested terrain, as well as to construct accurate, precise, and high-resolution hazard maps and risk assessments. 

The following diagram is excerpted from the Cascadia issue "Seeing Landslides with LIDAR," which contains more on how LIDAR can be used to map geohazards.

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Disclaimer

Although the data have been processed successfully on a computer system at the Oregon Department of Geology and Mineral Industries (DOGAMI), no warranty expressed or implied is made regarding the accuracy or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and aggregate use with other data. We also urge you to pay careful attention to the contents of the metadata file associated with these data and to the compilation process and limitations described therein. The Oregon Department of Geology and Mineral Industries shall not be held liable for improper or incorrect use of the data described and/or contained herein. Data are not intended for site-specific investigations.

The LIDAR data project is a work in progress. DOGAMI reserves the right to update data on this web site without notification as new information becomes available.

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Source Data

Base maps:

Portland Area Relative Earthquake Hazards Study (IMS-1):

Data are mapped at 1:62,500 scale. The zones depicted should not be used as the sole basis for any type of restrictive or exclusionary policy. Source: Relative Earthquake Hazard Map of the Portland Metropolitan Region, Clackamas, Multnomah, and Washington Counties, Oregon, 1997, by M.A. Mabey and others (DOGAMI Interpretive Map Series publication IMS-1; Buy), Oregon Department of Geology and Mineral Industries and Metro Regional Services.

IMS-1 map DOGAMI IMS-1 map plate.

The scientific understanding of the earthquake hazard in the Portland metropolitan area has increased significantly since the late 1980's. As a result, it is now widely accepted that damaging earthquakes larger than any in the historical record are likely. To minimize losses that may occur in an earthquake, mitigation measures are necessary. Mitigation efforts, to be effective, must be based on the best possible assessment of the likely extent and distribution of earthquake damage. Damage to a structure during an earthquake will depend on the size, type, and location of the earthquake, the response of the soil and geologic materials at the site, and the characteristics of the particular structure. Earth scientists do not yet know enough about earthquake sources to assess the size, frequency, and location of future earthquakes. We can, however, evaluate the behavior of geologic units. These maps are an interpretation of the relative earthquake hazards within the Portland metropolitan area. It does not depict the absolute degree of earthquake hazard at any site, which means that in any given earthquake it is possible that damage in even the highest relative hazard category will be light. Conversely, in a severe earthquake even the lowest relative hazard category could experience severe damage. It depicts how the ground is expected to respond during an earthquake and is based on local geologic conditions. It does not take into account cultural features (e.g. types of buildings), the probability that an earthquake may occur, or the nature of an earthquake should one occur. The analysis is based on data from scattered boreholes and the best available geologic mapping and state-of-practice geotechnical analysis. This map is not a substitute for site specific data collection and analysis.

Earthquake Hazards and Effects

Three types of earthquakes threaten the metropolitan area. The few moderate earthquakes that have originated in Portland in its brief recorded history have been relatively shallow (depths of 6-10 mi) crustal earthquakes. Intraplate earthquakes are the type that severely rocked the Puget Sound area in 1949 and 1965. These earthquakes occur within the remains of ocean floor that has been shoved (subducted) beneath North America. It is now thought that intraplate earthquakes could occur directly beneath Portland at depths of 25-35 mi. Finally, great subduction zone earthquakes occur around the world in subduction zones, where continent sized pieces of the earth's crust are shoved deep into the body of the earth. These earthquakes consistently have magnitudes of 8 to 9. The Cascadia Subduction Zone has been recognized off the Oregon and Washington coasts, but it has not ruptured during our 200-year historical record. There is abundant geologic evidence that it has ruptured in the past, most recently about 300 years ago. The best evidence suggests that these great earthquakes have occurred, on average, every 300 to 600 years, and there is every reason to believe that they will continue to occur in the future.

All three types of earthquakes threaten Portland, and what is certain is that damaging earthquakes will be a part of Portland's future. These maps provide an evaluation of the influence of site geology on potential earthquake damage and are not dependant on the location or magnitude of an earthquake.

Severe damage done by an earthquake is commonly concentrated in limited areas, and results from one or more of the following phenomena:

The Relative Earthquake Hazard Map of the Portland Metropolitan Area is a composite hazard map depicting the relative hazard at any site due to the combination of all three effects. It delineates areas that likely will experience the greatest effects from any earthquake. The map predicts the tendency of a site to have greater or lesser damage than other sites in the area. The zones depicted should not be used as the sole basis for any type of restrictive or exclusionary policy.

Hazard Maps

The relative earthquake hazard map integrates three separate earthquake hazard components: ground shaking amplification, liquefaction, and earthquake-induced landsliding. Each of these phenomena is a distinct and separate hazard and in concert with others can increase the severity of the total hazard at a given locality. A brief discussion of the production of each layer follows.

Ground Shaking Amplification. The soils and soft sedimentary rocks near the surface can modify bedrock ground shaking caused by an earthquake. This modification can increase the strength of shaking (or alternatively decrease it), duration of shaking, or change the frequency of the shaking. The nature of these modifications is determined by the thickness of the geologic materials and their physical properties such as shear-wave velocity. With these parameters the effects of the local geology on ground shaking including areas where the ground shaking will be strongest can be identified.

Three amplification hazard categories were defined for the Portland metropolitan area:

Liquefaction Analysis. Liquefaction is a phenomenon in which shaking a soil causes it to rapidly change its material properties so that it begins to behave as a liquid. Liquefaction typically occurs in young, loose, granular soils (e.g. sands) that are saturated with water. Vertical and lateral displacements resulting from liquefaction can range from inches to feet. Pipelines can be ruptured, light objects such as underground storage tanks can float, and heavy objects such as buildings can sink. Soils that are prone to liquefaction can be identified, as can their thickness and influence on the severity of earthquake effects.

Four liquefaction hazard categories were defined as follows:

Landslide Analysis. Shaking resulting from an earthquake can cause existing landslides to move as well as generating forces that create new landslides. The steepness of a slope is one of the primary indicators of the stability of a slope, and this factor has been used to estimate the depicted landslide hazard.

Four landslide hazard categories were defined as:

Relative Earthquake Hazard Map: The relative earthquake hazard map was created to show which areas will have the greatest tendency to experience damage due to any of, or a combination of, these hazards. On the individual hazard maps, areas were categorized as zones 0, 1, 2, or 3, with 3 being the greatest hazard. For every point on the map, the zone rating for each individual hazard (amplification, liquefaction, and landslide) was squared, and the resulting numbers were added together. Then the square root of this sum was calculated and rounded to the nearest whole number. A result of 4 or 5 is assigned to category A, a result of 3 is assigned to category B, a result of 2 is assigned to category C, and a result of 0 or 1 is assigned to category D.

Hazard Map Methodology

The basis for earthquake hazard assessment is a good geologic model. The geologic model for the Portland metropolitan area was produced by integrating the data from hundreds of boreholes drilled for water wells and foundation investigations with the best available geologic mapping and geophysics. This information was used to define the nature of the soil and rock column beneath any site on the map so that its effect on ground response could be assessed.

In addition to a geologic model, knowledge of the engineering characteristics of the various geologic units is required. Many of the required measurements, such as the Standard Penetration Tests (SPT), are acquired in the normal course of a foundation investigation and are available from many of the same sources as thickness information. Other data are obtained by running laboratory tests of borehole samples.

Shear-wave velocities of the geologic units are also required for the assessment technique. These were obtained from measurements at dozens of carefully selected sites by using both conventionally drilled boreholes and cone penetrometer techniques.

All of the information is combined to give a detailed computer model of what lies beneath the surface throughout the map area. With this information, the response to earthquake shaking at a specific location can be assessed.

For those interested in a detailed description of the construction of these maps, please see: Mabey, M.A., Madin, I.P., Youd, T.L., and Jones, C.F., 1993, Earthquake hazard maps of the Portland quadrangle, Multnomah and Washington counties, Oregon, and Clark County, Washington: Oregon Department of Geology and Mineral Industries Geologic Map Series GMS-79.

Relative earthquake hazard maps at scales of 1:24,000 are available from DOGAMI for the Portland, Mount Tabor, Beaverton, Lake Oswego, Gladstone, and Linnton quadrangles.

Oregon City Landslide Study (DOGAMI Open-File Report 06-27):

Potential landslide hazards in the Oregon City area are mapped at 1:15,000 scale. The data are derived from DOGAMI field mapping and from high-resolution topographic data in the form of a digital elevation model (DEM) derived from light detection and ranging (LIDAR) surveys conducted by the City of Oregon City. Source: Map of Landslide Geomorphology of Oregon City, Oregon, and Vicinity Interpreted from LIDAR Imagery and Aerial Photographs, 2006, by Ian P. Madin and William J. Burns (DOGAMI Open-File Report O-06-27; Buy), Oregon Department of Geology and Mineral Industries.

O-06-27 map DOGAMI Open-file report O-06-27 map plate.

 

Other Overlays:

See the metadata file for full reference information.

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Team

The team includes Ian P. Madin, Oregon Department of Geology and Mineral Industries (DOGAMI); Paul E. Staub and Mark Sanchez, formerly with DOGAMI; David Percy, Research Faculty, Geospatial Data Manager, Department of Geology, Portland State University; and Tim Welch, computer programmer, Academic & Research Computing Center, Portland State University. Contact.

The software used to build the map page is Map-Fu (http://sourceforge.net/projects/map-fu/), an open-source web mapping interface written in PHP/JavaScript that works with UMN MapServer (http://mapserver.gis.umn.edu/) software. The software was developed as part of the Oregon Sustainable Community Digital Library (OSCDL) by Academic & Research Computing at Portland State University.

The address locator functionality uses the free Google geocoder (http://www.google.com/apis/maps/documentation/#Geocoding_Examples), which converts addresses into geographic coordinates.

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Funding

Development of these data was partially funded as follows:

Relative Earthquake Hazard Map of the Portland Metropolitan Region, Clackamas, Multnomah, and Washington Counties, Oregon, 1997 (DOGAMI IMS-1)
This research was supported by the U.S. Geological Survey (USGS), Department of the Interior, under USGS award numbers 14-08-001-G1985, 14-08-001-G2132, 1434-93-G-2324, and 14-08-0001-A0512 and the Federal Emergency Management Agency (FEMA) under award numbers EMS-95-K-0363 and EMS-96-CA-0055. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.

Oregon City Landslide Study (DOGAMI Open-file Report O-06-27)
This research was supported in part by the U.S. Geological Survey (USGS), Department of the Interior, under USGS award number 03HQAG0013. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government. LIDAR data for hillshade base courtesy of the City of Oregon City.

LIDAR Survey Data
This LIDAR survey was flown for DOGAMI using funds provided by the National Earthquake Hazards Reduction Program.