Role of Space Geodesy In GEOSS Timothy H. Dixon University of Miami/RSMAS and 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 DORIS, INSAR

Geodesy and Subduction Zone Studies l Use steady state and time-dependent surface deformation from GPS to study locking and strain accumulation on plate interface (source of destructive earthquakes) l Combine with seismic data to define plate boundary geometry, measure and interpret physical processes of strain accumulation and release l Improve understanding of earthquake and tsunami hazard l Role for tsunami warning?

Locked Slip (cm/yr)

Plate Interface Locking vs Microearthquakes

L Locked Slip (cm/yr) Present: Interseismic Strain Accumulation and Micro-earthquakes Past: Coseismic Rupture 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 l GPS is sensitive to displacement rather than acceleration. l GPS can measure dynamic response of Earth’s surface to earthquakes, landslides and volcanic eruptions l GPS does not saturate for large signals, can augment strong motion networks l 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

Geodesy and Volcano Hazard Assessment l Most volcanoes undergo inflation days to months prior to eruption l Hazard Mitigation Strategy: monitor surface deformation for long term eruption precursors l Quantify Pressure build-up; is it dangerous yet? l Challenges: data quality, data density (time/space), data “latency” (how fast to the lab?) l 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) Earth’s dynamic oblateness (J2) is measured by SLR, and generally decreases due to post-glacial rebound Beginning in ~1997, J2 began to increase, indicating profound global mass re- distribution Most likely cause is melting of sub-polar alpine glaciers (Dickey et al., 2003)

Conclusions l Space geodetic data are useful for monitoring dynamic solid earth effects associated with climate change, earthquake and volcano processes l Space geodetic data may augment warning systems for volcanic eruption (GPS+INSAR) and tsunami (GPS) if available in real-time l 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!)