Fault Slip Sensors:GPS, Gyros and DART buoys

in Earthquake EarlyWarning Systems

Ken Hudnut

USGS, Pasadena

California Institute of Technology

Session title - Looking at the Future…

High risk approachspecific to rare event

with great consequencesBayes’ Theorem applied to system design?

Instrument Simmler and Coachella Valley segments of San Andreas

faultand

Subduction zones at trench and wedge tip

Define “priors”

Expected “Big One” source rupture is expected on the San Andreas fault or mega-thrust at trench

If fault slip occurs at surface, it must be the case that a “Big One” is in progress (system depends on it)

Sensor technology

Frequency response

positiondisplacement velocity acceleration

Proper transducers for the EEW job:borehole strain, tilt, strong motion, GPS, gyros?

Courtesyof JohnLangbein(USGS)

Gyros

Langbein & Bock (2003)

GPS

Gyros

GPS/INS (RLG) inairborne imaging: GPS aircraft trajectory

relative to ground-based GPS array

INS (gyro) for aircraft attitude

Laser mirror and/or camera position and orientation very well known

New imaging capabilities (also for satellite imagery)

Sagnac Interferometer

RLG’s&

FOG’s

Designedto sleep

for decadesthen wakeup quickly

and performflawlessly for

several minutes

Gyros and MEMS with GPS• Stable gyro technology is costly but MEMS-gyro

and FOG are lower cost and approaching accuracy

Barbour & Schmidt, 1998

Lone Juniper Ranch and Frazier Park High School

First prototype GPS fault slip sensor; up to 10 Hz (Hudnut et al., 2002)

Spans the San Andreas fault near Gorman, California

GPS high-rate (1 Hz) analysis

• Larson, Billich and Choi - see Ji et al.– Sidereal filtering

(Larson, Choi)

– Stacking (Billich)

• Significant reduction in long-period drift

• Compares well now with our static GPS displacements

Doubly-integrated seismic vs. GPS for Parkfield 2004 (co-located @ PHOB)

Raw GPS solution in blueFiltered GPS in greenSeismic in red (Boore)

These show results prior tofinal GPS analysis step ofstacking, shown previously

Simplifying assumptions…

Sensor technology exists: Inertial

BB seismic, accelerometers, gyros

GPS - will keep improving

Telemetry technology exists

Price is no concern ;-) “blue sky”

San Andreas fault 35 mm/yr slip rate;

>70% of plate motion 1685, 1857 eq’s

SoCal is now well ‘wired’

Likely source of most future ‘Big Ones’

Fault physics experiment GPS/INS in near-field ALSM & DG scan ‘net’

Great place to test EEW

Build “zipper” arrays Cholame - Simmler Coachella Valley

San Andreas - place two betsboth ~120 km from Los Angeles (LA)

Coachella Valleysegment is ~60 kmto San Bernardino

NOAA DART buoys

Measure fault slip at the source!

On-land GPS are great tohave, but unfortunatelydo not resolve the shallowslip at the trench, which isvital for distinguishing a“tsunami earthquake”

Geist & Dmowska (1999)

Large bedforms

Geist (1999) has suggestedthat Kanamori’s “tsunamiearthquakes” are due to largerapid slip at the sea floor

NOAA DART buoys could be applied to real-time slipdetection application - a seafloor implementation of the Fault Slip Sensor concept

Initial test off Japan (not real-time) - could be done also for Cascadia & Alaska

NOAA - Frank Gonzalez &Vasily Titov’s ‘dream’ for teletsunami

sources and local tsunami sources

real-time pattern of seafloor displacements (esp. vertical since slopes are slight)

system works for undersea landslides or earthquake sources

sensors - IMU’s (accel. & gyro)

telemetry - seafloor cables

for Cascadia, work with NEPTUNE and on-land w/ ANSS and PBO - upgrades needed

Summary Slip sensor concept is to augment regional seismic coverage - one part of an

overall EEW system that is primarily using a very different approach

Measure slip directly - don’t need to know anything else - ‘quick & easy’

High risk deployment strategy tuned to rare pay-off in extreme events

Robust earthquake early warning system design obtain more accurate displacement observations (e.g., Pd) new instrumentation for dynamic and static displacement address

deficiencies due to double-integration of accelerometer records

RLGs, FOGs, MEMs-gyros and GPS all complement accelerometers (which alone are deficient in measuring displacement, tilt and rotation) - these sensors are dropping rapidly in cost - should be further evaluated for use in earthquake early warning

Finally - another technological advancefor EEW message delivery?

Cell phone with GPS (location!) opens possibility of SMS real-time warning to mobile users (outdoors) or mobile platforms (e.g., cars) - currently not feasible due to power requirements (if GPS on all the time)

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