Ken HudnutUSGSPasadena, California
CSUN
Northridge, California
April 23, 2002
… … and some and some aspects of theaspects of the
1999 Hector Mine 1999 Hector Mine earthquakeearthquake
Merging geodesy and Merging geodesy and geology: SCIGN, laser geology: SCIGN, laser topographic mapping …topographic mapping …
The major objectives of theThe major objectives of theSCIGN array are:SCIGN array are:
• To provide regional coverage for estimating earthquake potential throughout Southern California
• To identify active blind thrust faults and test models of compressional tectonics in the Los Angeles region
• To measure local variations in strain rate that might reveal the mechanical properties of earthquake faults
• In the event of an earthquake, to measure permanent crustal deformation not detectable by seismographs, as well as the response of major faults to the regional change in strain
The SCIGN 250 station array was unveiled on July 6, 2001
“SCIGN data quality is excellent – probably the bestof any network in the world…” – Tom Herring, 6/19/01
Scientific Director, UNAVCO at the 2001 SCIGN Annual
Meeting
Plate Boundary Plate Boundary Observatory (PBO)Observatory (PBO)
New sites:•Backbone and clusters:
•Alaska and Cascadia•Volcanic complexes•San Andreas fault zone
Existing sites:•PANGA, BARD, EBRY, BARGEN, LVC, SCIGN
PBO San PBO San
Andreas planAndreas plan
New sites:•Clusters along San Andreas fault, especially along transitions from creeping to locked sections
Existing sites:•BARD, SCIGN, LVC,and BARGEN
High resolution topography along surface rupture of the High resolution topography along surface rupture of the October 16, 1999 Hector Mine, California Earthquake October 16, 1999 Hector Mine, California Earthquake
(M(Mww7.1) from Airborne Laser Swath Mapping7.1) from Airborne Laser Swath Mapping
HUDNUT, K. W., U. S. Geological Survey BORSA, A., IGPP/SIO, UCSDGLENNIE, C., Aerotec LLC
MINSTER, J.-B., IGPP/SIO, UCSD
In press, Bulletin of the Seismological Society of AmericaSpecial Issue on the Hector Mine earthquake (2002)
http://pasadena.wr.usgs.gov/office/hudnut/BSSA_ALSM/
ALSM, InSAR and TM imagingALSM, InSAR and TM imagingand mapping before & afterand mapping before & after
Laser scan of landsurfaces and urbaninfrastructure – buildings & lifelines- damage assessment
Pre- and post-disaster images can be differenced to measure damage and track recovery
LANDSAT 7 – earthquake damage - Bhuj, India
ALSM – 9/11/01
NYC
Active Faults in Southern CaliforniaActive Faults in Southern California
Surface RuptureSurface Rupture
Previously mapped, but un-named
Lavic Lake fault in recognition of breaks through dry lake bed
Up to 5.25 meters of right-lateral motion
48 km overall length of surface rupture
Only ruptured once prior through ~50 ka alluvium
Hector Mine (MHector Mine (Mww7.1)7.1)
Photo by Paul ‘Kip’ Otis-Diehl,USMC, 29 Palms
ALSM (Scanning LIDAR imaging)ALSM (Scanning LIDAR imaging)
Slow, precise helicopter flight line data acquisition at 200-300 m AGL.
6888 pps near infra-red (1064 nm) laser.
Scan Width: +/- 20 degrees. Nominally, 180 meters full-width.
200 pulses across swath, ~ 80cm spacing.
Footprint Diameter: Nominally 40cm. Half-meter posting, 15cm horizontal one-sigma
absolute accuracy specified.
Integrated GPS & INS navigation and attitude determination.
Pitch Mirror Correction: maximum +3.5/-6.5 degrees (+ forward bias).
R r
v
Geolocation Vectors and Error Sources
r
Vector from CMearth to GPS phase centerMagnitude & directional errors both arestochastic, time and location variant.
R
vVector from GPS phase center to laserMagnitude error is constant if no airframe flexing. Directional error due to constant and time-varying biases in INS.
Vector from laser to ground footprintMagnitude error due to timing, instrument and atmospheric delays. Directional errorfrom constant mirror mounting offsets and time-varying biases in reporting of scanangles (both pitch and roll).
Note: additional errors due to imperfectsynchronization of GPS, INS, mirror scanand laser firing times must be modeled and removed as well.
Flight PlanFlight Plan
Two overlapping swaths
200-500m mapped width
70 km long
GPS network ≥ 1 Hz
Temporary GPS stations
Cross-swath spurs Roll/Pitch/Yaw calibration maneuvers over dry lake
Flights over well-mapped Hector Mine
GPS Sites at ≥1Hz During ALSM Mission
1Hz 2Hz
BMHLOPBLOPCPRDMTSIBETROY
AGMTHCMNNBPSOPCLOPCXOPRD
Calibration maneuvers at
Hector Mine and Lavic Lake
Fly-through the along faultFly-through the along fault
Hector Mine Mobile GPS Survey Sites
Southwest Corner of Lavic Lakedry lake bed for calibrations
Helicopter videos:Helicopter videos:45 & 90 degree angles45 & 90 degree angles
New methods to explore, new synergies New methods to explore, new synergies between data types (e.g., GPS & ALSM)between data types (e.g., GPS & ALSM)
Combinations of seismic, geologic, and geodetic data in new ways– Source modelling– Hazard modelling
Cross-overs between fields– Geology and
geodesy with InSAR and ALSM
– Seismology and geodesy with high-rate GPS
1999Hector Mineearthquakesurfacerupture
ALSM-Derived Contours of Bullion Mountain Segment
(blue lines are1-foot contours)
Lidar (Bullion Fault)… ContoursLidar (Bullion Fault)… Contours
Lidar…. Raw SpotsLidar…. Raw Spots
To assess geodetic capability of To assess geodetic capability of repeat-pass ALSM:repeat-pass ALSM:
calibration requirementscalibration requirementsGeometry: mount angles, scan offsets, GPS-Laser
vector, GPS antenna phase center.Delays: electronic, optical, atmospheric.Reference point on laser platform.Timing of various components: e.g. INS vs. GPS
vs. mirror attitude sensors.Stabilization platforms (delays, accuracy).Detectors (thresholds, amplitude-range “walk”).
Lavic LakeRoll & PitchManeuvers
Explodedordnance(crater)
pitch maneuvers
15 cm vert.
10 cm vert.
Ramp probably due to roll or scan bias
End biases are real (low roll/ pitch section)
Excellent shot- to-shot varia-bility (5cm rms)
Cal/Val Maneuver StacksCal/Val Maneuver Stacks
Geological quantification and Geological quantification and questionsquestions
Tectonic interpretation of strain release in great earthquakes from their surface rupture– Basic documentation of surface rupture
e.g., Kurushin et al. (1997) study of 1957 Gobi-Altay eq.
How does slip vary along-strike?– e.g., need to assess variance and error in slip rate estimates from
paleoseismic methods e.g., Barka et al. (2002) and Rockwell et al. (2002) extensive studies of
1999 eq.’s in Turkey and similar studies of Hector Mine earthquake (in press, BSSA)
– is high-frequency energy radiated from fault?
Does slip vary from one earthquake to the next?– can detailed topographic mapping of geomorphic features along the
fault be modeled by repeats of exactly the same slip in successive earthquakes, or must slip vary in order to explain the topography?
– slip variation models for earthquake recurrence strongly influence seismic hazard analyses – assumptions made in these analyses necessarily simplify faulting processes, with societal repurcussions
Lavic Lake – compressional stepLavic Lake – compressional step
Oblique view Oblique view and photo of and photo of thrust wedgethrust wedge
Estimating slip Estimating slip on ‘max. slip’ on ‘max. slip’ segment ofsegment of
the faultthe fault
Estimating slip on Estimating slip on ‘max. slip’ segment of‘max. slip’ segment of
the faultthe fault
Conclusions - and some open questionsConclusions - and some open questions Airborne LIDAR imaging (ALSM) offers remarkable promise for
geomorphology, even over inaccessible or vegetated areas Commercial operations are reliable and affordable on well-specified
targets with carefully designed deployments (same as photogrammetry) CAL-VAL maneuvers are essential for geodetic-quality mapping of
geomorphological features Turning ALSM into a geodetic-quality tool requires careful calibration and
considerable analysis
Slip estimation:– has been initially developed demonstrated– new and improved methods are being developed– systematic measurement along the surface rupture will be done and then
compared with geologic estimates, InSAR and other methods– quantitative assessment of slip variation along-strike
dynamic faulting models – is high-frequency energy radiating from the fault?
Quantitative geomorphology– Model tectonic landform evolution
Did topographic features form as a result of exactly repeated slip distributions? Can topography be explained by only certain combinations of slip in past events?