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Kenneth W. Hudnut U. S. Geological Survey


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Title: Kenneth W. Hudnut U. S. Geological Survey

Measuring Fault Slip - Why and How?
  • Kenneth W. Hudnut U. S.
    Geological Survey
  • Pasadena, California

Earthquake Hazards Seminar USGS - Menlo Park,
California May 13, 2003
Measuring fault slip - why and how?
  • Why?
  • What can details of slip variation tell us about
    earthquake source physics? (You may suggest or
    prefer other reasons … )
  • Variance and other statistical properties of slip
    distributions - physical relation to fundamental
    quantities (such as maximum slip, seismic and
    aseismic energy, stress drop, Dc )
  • Large slip variations, if real, could constrain
    rupture process models and explain high-frequency
    seismic energy radiation
  • How?
  • my bias here is that great earthquakes do
    differ from small ones
  • Attempt to observe slip pulses or other crack
    propagation phenomena
  • Real-time GPS Fault Slip Sensor - to complement
    inertial sensors
  • Variation in slip along-strike and with depth -
    quantify the errors
  • Airborne Laser Swath Mapping - to observe
    near-fault deformation

to observe these quantities, need to devise
develop new methods
earthquake scaling
  • Are stress drops constant?
  • e.g., Brune (1970, 71)
  • What about L-model scaling for large events?
  • e.g., Scholz (1982, 1994)
  • and Romanowicz (1992)
  • Bi-linear scaling model
  • Hanks and Bakun (2002)
  • Great continental strike-slip earthquakes are of
    special interest - their slip (and stress drops)
    may become larger with longer ruptures (up to 10
    x W)
  • 1857 and 1906 SAF
  • 1905 Bulnay and 1957 Gobi-Altay
  • 1920 Haiyun
  • 1939 Erzincan
  • Kunlun Denali

some questions …
  • How may friction drop co-seismically?
  • Opening? What mode of crack propagation?
  • Key observation - accurate 3D particle motions
    close to the fault --- inertial sensors are
    unable to discriminate between tilt
    acceleration GPS fault slip sensors can help to
    observe this for future large events
  • What impedes and stops rupture?
  • Roughness and variation in slip - heterogeneity
    of stress, as well as fault interaction and
    dynamic effects
  • Key observation - objective systematic
    measurements of slip along-strike at surface for
    bedrock-on-bedrock fault with large amount of
    slip ALSM for Hector Mine

GPS is now vital to earthquake monitoring (array
technology and GPS satellites were developed in
Southern California)
  • Measures buildup of strain on faults due to
    accumulating tectonic motion
  • Used to detect damage to large engineered
    structures such as dams, and effects of ground
    tilt and subsidence on water systems
  • Can be used in real-time to detect fault slip at
    surface, for early warning system

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Science Review
  • List of publications - updates on the main
    project web page at http//
  • 45 papers from 1996 through April 2002 (includes
    several on Hector Mine co-seismic) - many
    important contributions that would have been
    impossible without SCIGN.
  • BSSA Hector Mine special issue (May, 2002)
    contains 16 papers (out of a total of 36) that
    made direct or indirect use of SCIGN data. Nearly
    all 36 then also cited these 16.
  • Fall AGU 2002 abstracts contain reports on
    several new projects using SCIGN data in
    innovative ways, as well as reports of the new
    results from the ongoing and coordinated SCIGN
    Analysis Committee effort, chaired by Nancy King.
    The use of continuous GPS data for various
    geophysical and other uses is increasing
    worldwide, and SCIGN has provided data used in a
    far wider range of studies than was ever imagined
    (e.g., Varner and Cannon, 2002). The open data
    policy has been a key to success.
  • SCIGN has become an integral part of what the
    broader SCEC community does in southern
    California. These results influence peoples
    thinking well outside of our regional scope, just
    as we all learn greatly from studies of other
    regions. Others see the value inherent in having
    a state-of-the-art array like SCIGN available
    (hence the PBO part of the EarthScope
    initiative). New data products are making SCIGN
    data more easily accessible to a larger and
    broader base of earthquake and other earth

SCIGN Data Products
  • 1st Year
  • Combined time
  • series (1996-2002)
  • 3rd Year
  • Real-time earth-
  • quake response
  • 5th Year
  • Resolve rates on
  • primary LA basin
  • faults (and others)

Hector Mine (Mw7.1)
  • Earthquake response
  • rapidly assess the earthquake source

Photo by Paul Kip Otis-Diehl, USMC, 29 Palms
Pacoima Dam GPS structural health monitoring
system (with LA County since Sept. 1995)
  • Damage estimation
  • rapidly assess damage, casualties, and losses

GPS can help with…
  • Earthquake response information
  • Identify fault source, extent and amount of slip
  • Model finite fault source
  • Measure and model deformation field
  • Provide all of the above to the public, to
    emergency responders, and to other scientists
  • Damage estimation
  • Provide data for use in HAZUS, etc.
  • Support of remote sensing and positioning for
    accurate and timely collection, reporting and
    control of other data that require accurate
    position and/or timing
  • Monitor large engineered structures and lifeline
  • Basic positioning infrastructure

Early Warning
The speed of light the speed of sound
Emergency Response
Seismic and GPS Stations
Transport- ation
(e.g Wu Teng, BSSA, 2002 Allen Kanamori,
Science, 2003)
Mitigative Actions
Is 30 seconds of warning enough?
  • Stop trains
  • Stop nuclear reactions
  • Stop computers
  • Secure hazardous materials
  • Stop elevators

GPS Fault Slip Sensor
  • K. Hudnut, G. Anderson, A. Aspiotes,
  • N. King, R. Moffitt, K. Stark
  • (all at USGS-SCIGN, Pasadena CA)

APEC symposium Proc. Paper, Fall AGU poster, and
paper in preparation for Bulletin of the
Seismological Society of America http//pasadena.
what we cannot do… because the physical process
is too chaotic weather turbulence earthquakes
- friction
GPS Fault Slip Sensor is proposed to augment
Earthquake Early Warning Systems
  • Recognize a precursor for a particular event
  • Differentiate readily between the beginning of a
    M3 and a M7

GPS slip sensor can help with this!
GPS fault slip sensor
Real-Time GPS Network - Enhancing SCIGN
  • On 15 November 2002, first-ever GPS fault slip
    sensor deployed across San Andreas fault at
    Gorman, Calif.
  • Upgrade SCIGN telemetry
  • DSL, frame relay
  • Radio repeaters, WiGate and dedicated links
  • Data buffering
  • Augment SCIGN real-time acquisition and
    processing system
  • Implemented sub-daily processing (4 hr) for 100
    SCIGN stations (down from 24 hr)
  • Implementing multiple real-time streaming GPS
    processors (commercial software)

Lone Juniper Ranch and Frazier Park High School
First prototype GPS fault slip sensor
Spans the San Andreas fault near Gorman,
Initial test results from commercial real-time
GPS processing software
Large data gaps are common Large and frequent
outliers Require an attentive operator Do not
output real-time results
next slide shows this portion of data
cleaned-up test results
Why is real-time GPS processing noisy and less
robust than post-processing? Ambiguity
resolution, multipath, atmosphere and clock
errors - what can be done?
precise post-processing
  • Sub-daily and daily processing runs, e.g., with
    GAMIT/GLOBK, yield absolute station position with
    sub-centimeter scatter and baseline estimation
    with few-millimeter horizontal repeatibilities
    (any size array) and sub-mm/yr velocities
  • Approaching real-time, GPS is much noisier -
    inertial sensors are far better
  • it can be made to work, RTK
  • many commercial applications
  • Fundamental limits of GPS
  • sub-mm phase measurements
  • 1-second use of precise code narrow-laning for
    ambiguity resolution
  • Sub-daily solutions need a bit more work and
    real-time streaming needs a lot of additional
    work to be reliable

Upgrading SCIGN telemetry
Low cost options such as frequent FTS dial-up,
radio nets, and DSL Development testing of near
real-time GPS precise processing, etc.
The Plate Boundary Observatory
Has been funded (30M for FY03)
  • BARD, mini-PBO SCIGN are prototype deployments
    for PBO
  • PBO will extend the GPS strain arrays
    throughout the Western U. S. A. and Alaska
  • With Canada and Mexico, we hope to cover the
    North American Pacific plate boundary

  • Mike Jackson summary
  • 170 new continuous GPS stations
  • 60 borehole and 5 laser strainmeters
  • Full time staff of six personnel located in
    Southern CA
  • 125 SCIGN stations proposed for support under NSF
    existing networks proposal
  • After 5 years SCIGN stations transition to PBO
    operations and maintenance

before moving on …
  • State-of-the-art GPS networks and technology
    development have become vital infrastructure for
    earthquake research and response
  • Static deformation field data source models
    rapid tilt and strain mapping
  • Monitoring of large engineered structures (e.g.,
    dams, buildings)
  • Understanding earthquake source physics - e.g.,
    slip pulses (near-field accurate particle motions
    and static displacement field mapping)
  • New enhancements to telemetry support wider range
    of applications
  • Real-time GPS sub-networks of SCIGN
  • Precise RTK positioning for surveying, AVL and
    GIS applications
  • InSAR, Airborne Laser Swath Mapping (ALSM) and
    digital photography
  • SCIGN provides ground control for airborne
    imaging and surveys
  • Mapping and imaging for rapid assessment of
    damage to buildings, lifeline infrastructure,
    etc. (The National Map Homeland Security)
  • Collaboration between Scientific, Surveying, GIS,
    Engineering and Transportation communities has
    mutual benefits - this is expected to help with
    funding our projects in the future

ATC-20 building safety inspections (red, yellow
and green tagging)
  • Infrastructure for positioning
  • supports data collection and mapping
  • during disaster recovery efforts

imagery before after
Courtesy of Ron Eguchi
Courtesy of City of Glendale
High resolution topography along surface rupture
of the October 16, 1999 Hector Mine, California
Earthquake (Mw7.1) from Airborne Laser Swath
  • Hudnut, K. W. (USGS), A. Borsa (UCSD),
  • C. Glennie (Aerotec, LLC) and J.-B. Minster (UCSD)

Bulletin of the Seismological Society of
America Special Issue on the Hector Mine
earthquake (2002) http//
ALSM, InSAR and TM imaging and mapping before
USGS The National Map
Laser scan of land surfaces and
urban infrastructure buildings lifelines -
damage assessment
ALSM 9/11/01 NYC
LANDSAT 7 SRTM - damage in Bhuj, India
Pre- and post-disaster images can be differenced
to measure damage and track recovery
Active Faults in Southern California
Hector Mine earthquake
Surface Rupture
  • Previously mapped, but un-named
  • Lavic Lake fault in recognition of breaks through
    dry lake bed
  • Up to 5.7 meters of right-lateral motion
  • 48 km overall length of surface rupture
  • Only ruptured once prior through 50 ka alluvium
  • from Treiman et al. (BSSA 2002)

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
  • Pitch Mirror Correction maximum 3.5/-6.5
    degrees ( forward bias).

Geolocation Vectors and Error Sources
Vector from CMearth to GPS phase center Magnitude
directional errors both are stochastic, time
and location variant.
Vector from GPS phase center to laser Magnitude
error is constant if no airframe flexing.
Directional error due to constant and
time-varying biases in INS.
Vector from laser to ground footprint Magnitude
error due to timing, instrument and atmospheric
delays. Directional error from constant mirror
mounting offsets and time-varying biases in
reporting of scan angles (both pitch and roll).
Note additional errors due to imperfect synchroni
zation of GPS, INS, mirror scan and laser firing
times must be modeled and removed as well.
Flight 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
  • Flights over well-mapped
  • Hector Mine

GPS Sites at 1Hz During ALSM Mission
Calibration maneuvers at Hector Mine and Lavic
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New methods to explore, new synergies between
data types (e.g., GPS ALSM)
1999 Hector Mine earthquake surface rupture
  • 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

ALSM-Derived Contours of Bullion Mountain Segment
(blue lines are 1-foot contours)
To assess geodetic capability of repeat-pass
ALSM calibration requirements
  • Geometry 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)

Exploded ordnance (crater)
Lavic Lake Roll Pitch Maneuvers
pitch maneuvers
10 cm vert.
15 cm vert.
Geological quantification and questions
  • 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
    (BSSA 2002)
  • 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
  • slip variation models for earthquake recurrence
    strongly influence seismic hazard analyses
    assumptions made in these analyses necessarily
    simplify faulting processes, with societal

Southwest Corner of Lavic Lake dry lake bed for
Lavic Lake compressional step
New methods and data integration
Airborne platform navigation must be highly
precise and requires high-rate GPS data
  • precise topographic mapping of surface ruptures
    and active fault scarps
  • representation of actual fault ruptures recorded
    and preserved in unprecedented detail for use by
    future earthquake researchers

New methods and data integration
  • Precise topographic mapping of surface ruptures
    and active fault scarps
  • slip models for prehistoric events
  • rapid assessment of surface slip and damage
    patterns after large events
  • Requires precise integration of GPS INS for
    flight navigation

1957 Gobi-Altai earthquake surface rupture
Estimating slip on max. slip segment of the
Estimating slip on max. slip segment of the
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Is it a multiple-event offset?
Conclusions - and some open questions
  • Airborne LIDAR imaging (ALSM) offers remarkable
    promise for geomorphology and fault zone studies,
    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 geomorphic features
  • Turning ALSM into a geodetic-quality tool
    requires careful calibration and considerable
  • 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
  • quantitative assessment of slip variation
  • 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?
  • Demonstrated GPS application to augment
    earthquake early warning systems