Role of Space GeodesyIn GEOSS

Timothy H. Dixon

University of Miami/RSMASand

Center for Southeastern Advanced Remote Sensing(CSTARS)

Contributions from:

Jean Dickey (JPL) Jeff Freymueller (University of Alaska) Kristine Larsen (University of Colorado) Falk Amelung, Shimon Wdowinski, and Noel

Gourmelen (University of Miami)

Space Geodesy: GPS, VLBI, SLR Space Geodesy: GPS, VLBI, SLR

DORIS, INSAR

Geodesy and Subduction Zone Studies

Use steady state and time-dependent surface deformation from GPS to study locking and strain accumulation on plate interface (source of destructive earthquakes)

Combine with seismic data to define plate boundary geometry, measure and interpret physical processes of strain accumulation and release

Improve understanding of earthquake and tsunami hazard

Role for tsunami warning?

Locked Slip (cm/yr)

Plate Interface Locking vs Microearthquakes

LL

Locked Slip (cm/yr)Locked Slip (cm/yr)

Present: InterseismicStrain

Accumulation andMicro-earthquakes

Past: CoseismicRupture

GPS and Seismic Data Highly

Complimentary

Role for GPS in Seismic/Tsunami Hazard?

Pre-seismic strain transients are rare or non-existent

Present strain accumulation rate can be related to size and timing of future strain release (earthquake)

Possible GPS role in tsunami warning, via accurate, rapid earthquake magnitude estimation

GPS Can Measure Magnitude… within minutes

Final Static Displacement

F. Kimata, Nagoya University

Rapid, accurate magnitude estimation is difficult for largest earthquakes

High precision GPS receivers measure displacement, very sensitive to earthquake magnitude

Can estimate magnitude from only a few sites

But need to have data from sites near the earthquake in real-time, hypocenter (from short period data) and a system for real-time analysis.

Will require a real-time subduction zone network

Other Applications of High-rate GPS

GPS is sensitive to displacement rather than acceleration.

GPS can measure dynamic response of Earth’s surface to earthquakes, landslides and volcanic eruptions

GPS does not saturate for large signals, can augment strong motion networks

Can be done in real-time

2002 November 3 Denali Earthquake

Eberhart-Phillips et al., 2003

* GPS “Seismograms”* 60 cm peak to peak in near field* Available seismometers clipped at several cm amplitude

2003 September 25 Tokachi-Oki (Hokkaido) Earthquake

GPS network

Acceleration vs. Displacement

Seismic rupture model from GPS data (Miyazaki et al., 2004)

Miyazaki et al., 2004

QuickTime™ and aGIF decompressor

are needed to see this picture.

Geodesy and Volcano Hazard Assessment

Most volcanoes undergo inflation days to months prior to eruption

Hazard Mitigation Strategy: monitor surface deformation for long term eruption precursors

Quantify Pressure build-up; is it dangerous yet? Challenges: data quality, data density (time/space),

data “latency” (how fast to the lab?) Role for near-real time GPS and INSAR

Volcano Geodesy

Vertical Component (N-S)

InSAR Challenges

Most SAR data are C-band (6 cm wavelength) which decorrelates rapidly

L-band (24 cm wavelength) is better for most terrestrial applications involving change detection via interferometry

Most SAR systems are commercial, or otherwise have restricted data availability

Most SAR systems have no or limited DDL capability, hence no or limited real time capability

Synergetic Applications Relevant to GEOSS

INSAR can be used to measure water levels in vegetated wetlands, soil moisture, and biomass

GPS can measure atmospheric water content GPS and INSAR requires terrestrial reference

frame definition and maintenance (SLR, VLBI, DORIS); this “behind the scenes” effort yields important global geophysical data

Variation in Earth’s Oblateness (J2)

1985 1990 1995 2000

-100

-75

-50

-25

0

25

Year

J 2 Observations and Sources

(a) Geodetic

(b) Ocean

(c) Glaciers

(d) Atmosphere

(e) Groundwater

Annual Averages

Earth’s dynamic oblateness (J2) is measured by SLR, and generally decreases due to post-glacial reboundBeginning in ~1997, J2 began to increase, indicating profound global mass re-distributionMost likely cause is melting of sub-polar alpine glaciers (Dickey et al., 2003)

Conclusions Space geodetic data are useful for monitoring

dynamic solid earth effects associated with climate change, earthquake and volcano processes

Space geodetic data may augment warning systems for volcanic eruption (GPS+INSAR) and tsunami (GPS) if available in real-time

For GPS, lack of dense coverage in subduction zones is a problem

For INSAR, cost and rapid availability of data is a problem (needs to be like GSN/FDSN!)