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Progress on Reducing GPS Errors - Horizontal and Vertical. Courtesy of JPL. Kenneth W. Hudnut U. S. Geological Survey Pasadena, California. Southern California Earthquake Center --- U. S. Geological Survey Workshop on Active Deformation in the Northern LA Region

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Kenneth w hudnut u s geological survey pasadena california

Progress on Reducing GPS Errors -

Horizontal and Vertical

Courtesy of JPL

Kenneth W. Hudnut U. S. Geological Survey

Pasadena, California

Southern California Earthquake Center --- U. S. Geological Survey

Workshop on Active Deformation in the Northern LA Region

Caltech; Pasadena, California --- October 26, 2005


San gabriel valley tectonics
San Gabriel Valley Tectonics

  • San Andreas system - oblique component (new understanding of this within past decade w/ GPS)

    • Thrust fault systems

    • Rigid motion of San Gabriel mountains massif perpend. to SAF

      • Observed by Savage et al., 1992

      • Confirmed by SCEC CMM3

        and SCIGN results

    • Along-strike variations

      in deep structure (LARSE)

    • Cross-faults

    • Block rotations

SCEC CFM v.2


Statement of problems
Statement of Problems

  • Must understand complex fault interactions to understand fault system behavior

  • Some questions (also addressed in SCEC Nov. 2004 workshop & AGU FM04):

    • How does the San Andreas fault interact with abutting and nearby structures?

    • How do these secondary and tertiary structures interact with the San Andreas?

    • How is the Big Bend influencing the region - has approach to frictional lock-up caused bypasses such as the Eastern California Shear Zone and San Jacinto fault?

    • How may ruptures propagate along these fault systems?

  • Is there along-strike variation in strain along the San Gabriel Mtn. front?

  • How might such variation correspond to geological or deep structural evidence?

  • High hazard due to proximity of faults to Los Angeles greater metro area


Kenneth w hudnut u s geological survey pasadena california

Differences in Geological & Geodetic Rates

  • Sierra Madre – Cucamonga fault zone

    • Geologic rate of 0.5 mm/yr

    • Geodetic rate of a

  • Raymond fault

    • Geologic rate of 1.5-4 mm/yr

    • Geodetic rate of b

  • Discuss - are these

    rates best available?

  • Geologic rates compiled

    from FAD & literature

  • Geodetic rates from

    CMM3 and SCIGN

  • a + b ~ 6-8 mm/yr

Courtesy of

B. Meade


Uplifting thoughts or condemned to repeat history
Uplifting Thoughts or ‘Condemned to Repeat’ History?

  • How fast are the mountains going up?

    • Nikolaidis et al. vertical rates from SCIGN -suggested rate changes

Courtesy of R. Nikolaidis, UCSD dissertation


How good is gps

Gyros

How good is GPS?

Reasonable to expect

0.1 mm/yr in both

horizontal and vertical

(but not there yet)

Courtesy

of John

Langbein

(USGS)


How do the data look
How do the data look?

SCEC Crustal Motion Map 3 (CMM3) and

SCIGN combined (JPL & SOPAC) merged

solutions are now readily availalable, and

can be explored using various web-based

and Matlab tools (figures shown are from

GGMatlab by Tom Herring, MIT)

- Older stations (CHIL, MTWI, TABL) have

longer running data but are noisier than

the new SCIGN standard installations

- Horizontal velocities allow sophisticated

modeling and interpretation (see Argus

et al., 2005), yet vertical rates are

still not robust at the mm/yr level

- Appears all sites going down at 2 mm/yr (?!)

AGU FM04




Summary
Summary

  • We can potentially better understand the Northern LA Basin fault system in all of its complexity, but…

    • Must pursue a similar course for a longer time, and more will continue to be learned about deep geometry, activity, and overall geodynamics of the system

    • Perseverance and patience is especially required on geodetic rates - these take time to be well observed - can eventually obtain precise vertical rates after many more years

  • We must understand the fault interactions if we are to predict aspects of future behavior within the San Andreas fault system and adjacent San Gabriel Mtns. massif and San Gabriel Valley