Finding faults with LIDAR in the Puget Lowland

Ralph Haugerud, Craig WeaverU. S. Geological Survey

Jerry HarlessPuget Sound Regional Council

and thanks to TerraPoint LLC, Houston TX

• Why LIDAR?

• What is LIDAR?

• How are we doing LIDAR?• What are we finding?

30 km

In some places, it

is easy to see where

the active faults

are.

In other places,

it is not.

30 km

Seattle

Tacoma

What are the salient differences?

SF Bay

area

Puget

Lowland

slip rate3 cm/yr

strike slip4 mm/yr

shortening

average tree height

? 10 ft ? 100 ft

age of landscape

~106 years

18,000 years

18,000 yr 1 mm/yr = 18 m106 yr 1 mm/yr = 1 km

In the Puget Lowland, to see a fault with the same slip rate as in the SF Bay area, we have to look more closely.

age slip rate = feature size

LIght Detection And Ranging• Airborne scanning laser

rangefinder• Differential GPS• Inertial Navigation System

30,000 points per second at ~15 cm accuracy

• $400–$1000/mi2, 106 points/mi2, or 0.04–0.1 cents/point

Extensive filtering to remove tree canopy (virtual defor-estation)

10-meter DEM from contours

12-ft DEM from LIDAR

Picture: Oblique view of S end Rockaway Beach

High-resolution LIDAR topography

• Fly in winter, when leaves are off

• Near-infrared laser; doesn’t penetrate clouds, rain

• Errors

Largest are in angles—up to 1 m x-y error

Ranging error = ~15 cm z error!

• 2/3 of surveyed points on trees and buildings; remove with automatic geometric filtering

• Multiple reflections from one laser pulse = better filtering

• Optimum working distance circa 1 km– Adequate reflection brightness– Keep laser eye-safe

• Spot diameter: decimeters to meters• Spot spacing: 1 to 5 meters• Multiple passes

– multiple look angles– higher point density– internal consistency check

• $400 - $1,000 / mi2

Why is LIDAR better than photogrammetry?(It’s the trees)

Suppose timber allows 1 of 3 arbitrary rays to reach ground; 1/3 of ground can be surveyed by LIDAR

Photogrammetry requires 2 separate views of a point; only 1/9 of ground will be locatable

Bainbridge Island,KPUD

1996-1997

Snoqualmie,USGS-NMD1998-2001?

Seattle

Tacoma

Puget Sound LIDAR Consortium

Participants Expertise

•Kitsap County•Kitsap PUD•City of Seattle•Puget Sound Regional Council•NASA •USGS

(exclusive of USGS) –Contracting

–Surveyor

–prior LIDAR experience

–Geologist

–GIS

Puget Sound LIDAR Consortium

• No formal structure• One agenda• One contract• Separate payments• Share data• Release all data to public domain

(www.GetItYourselfBob, to be hosted by UW library)

PSLC

Tacoma

Seattle

Tacoma

Seattle

LIDAR already flown

to be flown this

Winter ~$3.3M

~$3M

Toe Jam Hill fault scarp

Waterman Point scarp

beach uplifted during 900 AD

earthquake

15 km west of Seattle

landslides

southern Bainbridge Island

Uses for high-resolution topography

• Finding faults (earthquake frequency, kinematics)

• Geologic mapping• Landslide hazards• Flood hazards, groundwater infiltration,

runoff modelling• Fish habitat? Precision forestry? Noise propagation