Measurement of coseismic deformation by satellite geodesy

http://www-gpsg.mit.edu/edocs/FEIGL_ET_AL_2001_BSSA D:\PapersToRead\Feigl_BSSA2002.pdf

Feigl, K. L., J. Gasperi, F. Sigmundsson, and A. Rigo (2000), Crustal deformation near Hengill volcano, Iceland 1993-1998: coupling between volcanism and faulting inferred from elastic modeling of satellite radar interferograms, J. Geophys. Res, 105, 26,555-525,670. We apply satellite radar interferometry to the Hengill Volcanic System, one of the most active areas in Iceland. We analyze several ERS image pairs spanning up to four years under favorable orbital and climatic conditions. To calculate the interferograms, we use the two-pass approach with the DIAPASON software developed by CNES and licensed via GDR INSAR. Images acquired during the snow-free summer months remain coherent on recent lava flows even after four years. We observe concentric fringes centered several km SW of Hrómundartindur which we interpret as a mostly vertical uplift due to a pressure increase near this volcano. The number of fringes is roughly proportional to the time interval spanned by the interferograms, suggesting that the volcanic uplift rate is relatively constant. This result confirms that the increased volcanic and seismic activity observed since July 1994 continues through at least the summer of 1997. We model this signal as the deformation of a spherical (Mogi) source buried in an elastic half-space. To the SW of this source, we observe a discontinuity in the fringe pattern. This discontinuity appears in all interferograms spanning August 1995 (July 31 through September 3), and does not appear in other interferograms outside this date. Furthermore, its magnitude (about a quarter of a 28-mm fringe) is the same in interferograms analyzed with two independent digital elevation models. These measurements help define the interplay between fluid pressure, seismicity, and faulting.

http://www-gpsg.mit.edu/edocs/FEIGL_REPRINTS/FeiglEtAlJGR2000.pdf

Fialko, Y., and M. Simons (2000), Deformation and seismicity in the Coso geothermal area, Inyo County, California: Observations and modeling using satellite radar interferometry, Journal of Geophysical Research, 105, 21781-21794. Interferometric synthetic aperture radar (InSAR) data collected in the Coso geothermal area, eastern California, during 1993-1999 indicate ground subsidence over a ~50 km 2 region that approximately coincides with the production area of the Coso geothermal plant. The maximum subsidence rate in the peak of the anomaly is ~3.5 cmyr -1, and the average volumetric rate of subsidence as of the order of 10^6 m 3 yr -1. The radar interferograms reveal a complex deformation pattern, with at least two irregular subsidence peaks in the northern part of the anomaly and a region of relative uplift on the south. We invert the InSAR displacement data for the positions, geometry, and relative strengths of the deformation sources at depth using a nonlinear least squares minimization algorithm. We use elastic solutions for a prolate uniformly pressurized spheroidal cavity in a semi-infinite body as basis functions for our inversions. Source depths inferred from our simulations range from 1 to 3 km, which corresponds to the production depths of the Coso geothermal plant. Underpressures in the geothermal reservoir inferred from the inversion are of the order of 0.1-1 MPa (except a few abnormally high underpressures that are apparently biased toward the small source dimensions). Analysis of the InSAR data covering consecutive time intervals indicates that the depths and/or horizontal extent of the deformation sources may increase with time. This increase presumably reflects increasing volumes of the subsurface reservoir affected by the geothermal exploitation. We show that clusters of microearthquakes associated with the geothermal power operation may result from perturbations in the pore fluid pressure, as well as normal and shear stresses caused by the deflation of the geothermal reservoir.

http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000JGR.10521781F&db_key=PHY&high=42fb8ddbb619944

Fialko, Y., and M. Simons (2000), Deformation and seismicity in the Coso geothermal area, Inyo County, California: Observations and modeling using satellite radar interferometry, Journal of Geophysical Research, 105, 21781-21794. Interferometric synthetic aperture radar (InSAR) data collected in the Coso geothermal area, eastern California, during 1993-1999 indicate ground subsidence over a ~50 km^2 region that approximately coincides with the production area of the Coso geothermal plant. The maximum subsidence rate in the peak of the anomaly is ~3.5 cmyr^-1 , and the average volumetric rate of subsidence as of the order of 10^6 m^3 yr^-1 . The radar interferograms reveal a complex deformation pattern, with at least two irregular subsidence peaks in the northern part of the anomaly and a region of relative uplift on the south. We invert the InSAR displacement data for the positions, geometry, and relative strengths of the deformation sources at depth using a nonlinear least squares minimization algorithm. We use elastic solutions for a prolate uniformly pressurized spheroidal cavity in a semi-infinite body as basis functions for our inversions. Source depths inferred from our simulations range from 1 to 3 km, which corresponds to the production depths of the Coso geothermal plant. Underpressures in the geothermal reservoir inferred from the inversion are of the order of 0.1-1 MPa (except a few abnormally high underpressures that are apparently biased toward the small source dimensions). Analysis of the InSAR data covering consecutive time intervals indicates that the depths and/or horizontal extent of the deformation sources may increase with time. This increase presumably reflects increasing volumes of the subsurface reservoir affected by the geothermal exploitation. We show that clusters of microearthquakes associated with the geothermal power operation may result from perturbations in the pore fluid pressure, as well as normal and shear stresses caused by the deflation of the geothermal reservoir. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000JGR.10521781F&db_key=PHY&high=42fb8ddbb619944

Fialko, Y., and M. Simons (2001), Evidence for on-going inflation of the Socorro magma body, New Mexico, from Interferometric Synthetic Aperture Radar imaging, Geophysical Research Letters, 28, 3549-3552. Interferometric synthetic aperture radar (In-SAR) imaging of the central Rio Grande rift (New Mexico, USA) during 1992-1999 reveals a crustal uplift of several centimeters that spatially coincides with the seismologically determined outline of the Socorro magma body, one of the largest currently active magma intrusions in the Earth's continental crust. Modeling of interferograms shows that the observed deformation may be due to elastic opening of a sill-like intrusion at a rate of a few millimeters per year. Despite an apparent constancy of the geodetically determined uplift rate, thermodynamic arguments suggest that it is unlikely that the Socorro magma body has formed via steady state elastic inflation. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001GeoRL.28.3549F&db_key=AST&high=41f192cbba08585

Fialko, Y., D. Sandwell, D. Agnew, M. Simons, P. Shearer, and B. Minster (2002), Deformation on nearby faults induced by the 1999 Hector Mine earthquake, Science, 297, 1858-1862. Interferometric Synthetic Aperture Radar observations of surface deformation due to the 1999 Hector Mine earthquake reveal motion on several nearby faults the eastern California shear zone.We document both vertical and horizontal displacements of several millimeters to several centimeters across kilometerwide zones centered on pre-existing faults. Portions of some faults experienced retrograde (that is, opposite to their long-term geologic slip) motion during or shortly after the earthquake.The observed deformation likely represents elastic response of compliant fault zones to the permanent co-seismic stress changes. The induced fault displacements imply decreases in the effective shear modulus within the kilometer-wide fault zones, indicating that the latter are mechanically distinct from the ambient crustal rocks. PDF

Fialko, Y., D. Sandwell, D. Agnew, M. Simons, P. Shearer, and B. Minster (2002), Deformation on nearby faults induced by the 1999 Hector Mine earthquake, Science, 297, 1858-1862. Interferometric Synthetic Aperture Radar observations of surface deformation due to the 1999 Hector Mine earthquake reveal motion on several nearby faults the eastern California shear zone.We document both vertical and horizontal displacements of several millimeters to several centimeters across kilometerwide zones centered on pre-existing faults. Portions of some faults experienced retrograde (that is, opposite to their long-term geologic slip) motion during or shortly after the earthquake.The observed deformation likely represents elastic response of compliant fault zones to the permanent co-seismic stress changes. The induced fault displacements imply decreases in the effective shear modulus within the kilometer-wide fault zones, indicating that the latter are mechanically distinct from the ambient crustal rocks. PDF

Fialko, Y., M. Simons, and D. Agnew (2001a), The complete (3-D) surface displacement field in the epicentral area of the 1999 Mw 7.1 Hector Mine earthquake, California, from space geodetic observations, Geophysical Research Letters, 28, 3063-3066. We use Interferometric Synthetic Aperture Radar (InSAR) data to derive continuous maps for three orthogonal components of the co-seismic surface displacement field due to the 1999 Mw 7.1 Hector Mine earthquake in southern California. Vertical and horizontal displacements are both predominantly antisymmetric with respect to the fault plane, consistent with predictions of linear elastic models of deformation for a strike-slip fault. Some deviations from symmetry apparent in the surface displacement data may result from complexity in the fault geometry. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001GeoRL.28.3063F&db_key=AST&high=42fb8ddbb619944

Fialko, Y., M. Simons, and D. Agnew (2001b), The complete (3-D) surface displacement field in the epicentral area of the 1999 Mw 7.1 Hector Mine earthquake, California, from space geodetic observations, Geophysical Research Letters, 28, 3063-3066. We use Interferometric Synthetic Aperture Radar (InSAR) data to derive continuous maps for three orthogonal components of the co-seismic surface displacement field due to the 1999 Mw 7.1 Hector Mine earthquake in southern California. Vertical and horizontal displacements are both predominantly antisymmetric with respect to the fault plane, consistent with predictions of linear elastic models of deformation for a strike-slip fault. Some deviations from symmetry apparent in the surface displacement data may result from complexity in the fault geometry. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001GeoRL.28.3063F&db_key=AST&high=42fb8ddbb619944

Fialko, Y., M. Simons, and D. Agnew (2001c), The complete (3-D) surface displacement field in the epicentral area of the 1999 Mw7.1 Hector Mine earthquake, California, from space geodetic observations, Geophys. Res. Lett., 28, 3063-3066.

Fialko, Y., M. Simons, and Y. Khazan (2001b), Finite source modelling of magmatic unrest in Socorro, New Mexico, and Long Valley, California, Geophysical Journal International, 146, 191-200. We investigate surface deformation associated with currently active crustal magma bodies in Socorro, New Mexico, and Long Valley, California, USA. We invert available geodetic data from these locations to constrain the overall geometry and dynamics of the inferred deformation sources at depth. Our best-fitting model for the Socorro magma body is a sill with a depth of 19km, an effective diameter of 70km and a rate of increase in the excess magma pressure of 0.6kPayr^-1 . We show that the corresponding volumetric inflation rate is ~6×10^-3 km^3 yr^-1 , which is considerably less than previously suggested. The measured inflation rate of the Socorro magma body may result from a steady influx of magma from a deep source, or a volume increase associated with melting of the magma chamber roof (i.e. crustal anatexis). In the latter case, the most recent major injection of mantle-derived melts into the middle crust beneath Socorro may have occurred within the last several tens to several hundreds of years. The Synthetic Interferometric Aperture Radar (InSAR) data collected in the area of the Long Valley caldera, CA, between June 1996 and July 1998 reveal an intracaldera uplift with a maximum amplitude of ~11cm and a volume of 3.5×10^-2 km^3 . Modelling of the InSAR data suggests that the observed deformation might be due to either a sill-like magma body at a depth of ~12km or a pluton-like magma body at a depth of ~8km beneath the resurgent dome. Assuming that the caldera fill deforms as an isotropic linear elastic solid, a joint inversion of the InSAR data and two-colour laser geodimeter data (which provide independent constraints on horizontal displacements at the surface) suggests that the inferred magma chamber is a steeply dipping prolate spheroid with a depth of 7-9km and an aspect ratio in excess of 2:1. Our results highlight the need for large radar look angles and multiple look directions in future InSAR missions.
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001GeoJI.146.191F&db_key=AST&high=42fb8ddbb619944

Fialko, Y., M. Simons, and Y. Khazan (2001d), Finite source modelling of magmatic unrest in Socorro, New Mexico, and Long Valley, California, Geophysical Journal International, 146, 191-200. We investigate surface deformation associated with currently active crustal magma bodies in Socorro, New Mexico, and Long Valley, California, USA. We invert available geodetic data from these locations to constrain the overall geometry and dynamics of the inferred deformation sources at depth. Our best-fitting model for the Socorro magma body is a sill with a depth of 19km, an effective diameter of 70km and a rate of increase in the excess magma pressure of 0.6kPayr -1. We show that the corresponding volumetric inflation rate is ~6×10^-3 km 3 yr -1, which is considerably less than previously suggested. The measured inflation rate of the Socorro magma body may result from a steady influx of magma from a deep source, or a volume increase associated with melting of the magma chamber roof (i.e. crustal anatexis). In the latter case, the most recent major injection of mantle-derived melts into the middle crust beneath Socorro may have occurred within the last several tens to several hundreds of years. The Synthetic Interferometric Aperture Radar (InSAR) data collected in the area of the Long Valley caldera, CA, between June 1996 and July 1998 reveal an intracaldera uplift with a maximum amplitude of ~11cm and a volume of 3.5×10^-2 km 3. Modelling of the InSAR data suggests that the observed deformation might be due to either a sill-like magma body at a depth of ~12km or a pluton-like magma body at a depth of ~8km beneath the resurgent dome. Assuming that the caldera fill deforms as an isotropic linear elastic solid, a joint inversion of the InSAR data and two-colour laser geodimeter data (which provide independent constraints on horizontal displacements at the surface) suggests that the inferred magma chamber is a steeply dipping prolate spheroid with a depth of 7-9km and an aspect ratio in excess of 2:1. Our results highlight the need for large radar look angles and multiple look directions in future InSAR missions. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001GeoJI.146.191F&db_key=AST&high=41f192cbba08585

Fialko, Y., Y. Khazan, and M. Simons (2001a), Deformation due to a pressurized horizontal circular crack in an elastic half-space, with applications to volcano geodesy, Geophys J Int, 146, 181-190. SUMMARY We consider deformation due to sill-like magma intrusions using a model of a horizontal circular crack in a semi-infinite elastic solid. We present exact expressions for vertical and horizontal displacements of the free surface of a half-space, and calculate surface displacements for a special case of a uniformly pressurized crack. We derive expressions for other observable geophysical parameters, such as the volume of a surface uplift/subsidence, and the corresponding volume change due to fluid injection/withdrawal at depth. We demonstrate that for essentially oblate (i.e. sill-like) source geometries the volume change at the source always equals the volume of the displaced material at the surface of a half-space. Our solutions compare favourably to a number of previously published approximate models. Surface deformation due to a 'point' crack (that is, a crack with a large depth-to-radius ratio) differs appreciably from that due to an isotropic point source ('Mogi model'). Geodetic inversions that employ only one component of deformation (either vertical or horizontal) are unlikely to resolve the overall geometry of subsurface deformation sources even in a simplest case of axisymmetric deformation. Measurements of a complete vector displacement field at the Earth's surface may help to constrain the depth and morphology of active magma reservoirs. However, our results indicate that differences in surface displacements due to various axisymmetric sources may be subtle. In particular, the sill-like and pluton-like magma chambers may give rise to differences in the ratio of maximum horizontal displacements to maximum vertical displacements (a parameter that is most indicative of the source geometry) that are less than 30 per cent. Given measurement errors in geodetic data, such differences may be hard to distinguish. http://www.blackwell-synergy.com/links/doi/10.1046/j.1365-246X.2001.00452.x/abs

Froger, J. L., O. Merle, and P. Briole (2001), Active spreading and regional extension at Mount Etna imaged by SAR interferometry, Earth and Planetary Science Letters, 187, 245-258. Electronic Article Available from Elsevier Science. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001E%26PSL.187.245F&db_key=AST&high=42fb8ddbb608794

Froger, J. L., P. Briole, O. Merle, M. Coltelli, G. Puglisi, C. Deplus, and F. Obrizzo, Large flank collapse at Mount Etna imaged by SAR interferometry, Earth Plan. Sci. Lett., submitted, 2000.

Froger, J. L., Y. Fukushima, P. Briole, T. Staudacher, T. Souriot, and N. Villeneuve (2004), The deformation field of the August 2003 eruption at Piton de la Fournaise, Reunion Island, mapped by ASAR interferometry, Geophysical Research Letters, 31, 14601. Three independent ASAR interferograms spanning the August 2003 Piton de la Fournaise eruption, reveal a 3 by 3 km asymmetric pattern of range changes centred on the Dolomieu crater northern flank. It corresponds to 30 cm of displacement towards the satellite east of the eruptive fissures and 7 cm away from the satellite west of the fissures. Displacements are caused by dyke emplacement below fissures. We model the deformation using a 3D mixed boundary element method for elastic media. This consists of a dyke defined by six geometric parameters and an overpressure gradient. A neighbourhood algorithm was applied to explore this 7 dimensional parameter space. The best-fit model is a 57° eastward dipping dyke with a base lying around 1520 m a.s.l. The model provides new evidence of the dyke intrusion - related seaward displacements of the volcano eastern flank. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004GeoRL.3114601F&db_key=AST&high=42fb8ddbb608794

Fruneau, B., and F. Sarti (2000), Detection of ground subsidence in the city of Paris using radar interferometry: isolation of deformation from atmospheric artifacts using correlation, Geophysical Research Letters, 27, 3981-3984. This paper presents a new method for the isolation of displacement from atmospheric fringes. This novel approach is based on complex correlation of interferograms. Compared to other methods, this method has the advantage of requiring only a few interferograms (two at least). Its main limitation is the hypothesis of temporally varying atmospheric conditions between acquisitions (not the same heterogeneities on different interferograms). In the city of Paris, this method reveals 2 subsiding zones. Both have the same location as an important underground working site, which took place from 1995 to 1997. The existence of subsidence in the area was known previously from ground truth data. Their spatial extent can now be mapped by interferometry, and the temporal evolution of the subsidence is also examined here. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000GeoRL.27.3981F&db_key=AST&high=42fb8ddbb618880

Fruneau, B., E. Pathier, D. Raymond, B. Deffontaines, C. T. Lee, H. T. Wang, J. Angelier, J. P. Rudant, and C. P. Chang (2001), Uplift of Tainan Tableland (SW Taiwan) revealed by SAR interferometry, Geophysical Research Letters, 28, 3071-3074. Interferometric processing of five SAR-ERS images reveals uplift of the Tainan Tableland (SW of Taiwan) during the period 1996-1998. The maximum measured ground motion for these two years is 2.8 cm along the radar line of sight towards the satellite, indicating for the displacement vector a vertical component of 3.2 cm, and a horizontal component of 1.6 cm towards the WSW considering additional information from GPS data. The reconstructed displacement field is consistent with the geological interpretation of the Tainan Tableland as an actively growing anticline connected to the Taiwan fold-and-thrust belt. This implies that the deformation front is located farther west than usually assumed in the Tainan area. The large Tainan city is thus located in an active deformation zone. Seismic hazard assessment is however difficult because the mechanisms and kinematics are not known in detail. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001GeoRL.28.3071F&db_key=AST

Gudmundsson, S., F. Sigmundsson, and J. M. Carstensen (2002), Three-dimensional surface motion maps estimated from combined interferometric synthetic aperture radar and GPS data, Journal of Geophysical Research (Solid Earth), 107j. We provide a technique to efficiently produce high-resolution three-dimensional surface motion maps by combining information about the motion of the Earth's surface from interferometric observations of synthetic aperture radar images and repeated Global Positioning System (GPS) geodetic measurements. Unwrapped interferograms, showing pixel-wise change in range from ground to satellite, and sparse values of three-dimensional movements are required as input. The problem of finding the full three-dimensional motion field is separated into two two-dimensional problems. Initially, the vertical component of the deformation field and its horizontal component in the look direction of the satellite are found. Later, the look direction component is resolved into north and east components. Initial values for the motion fields are assigned to each pixel of interferograms from interpolation of available GPS observations. These values are then updated and optimized by comparison with the interferograms and the GPS observations. An additional constraint is an assumption of a smoothly varying motion field. Markov random field-based regularization and simulated annealing algorithm are used for the optimization. The technique is applied to create surface motion maps for the Reykjanes Peninsula, SW Iceland. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002JGRB.107jETG13G&db_key=PHY&high=42760a9e8807230

Hanssen, R., I. Weinreich, S. Lehner, and A. Stoffelen, Tropospheric wind and humidity derived from spaceborne radar intensity and phase observations, Geophys. Res. Lett., 27, 1699-1702, 2000.

Henriot, O., T. Villemin, and F. Jouanne (2001), Long period interferograms reveal 1992-1998 steady rate of deformation at Krafla volcano (North Iceland), Geophysical Research Letters, 28, 1067-1070. We formed interferograms of ERS-SAR scenes covering the area of Krafla (N. Iceland) with time span values of up to six years (1992-1998). Our data reveals a steady deformation rate at Krafla and within its fissure swarm, with values reaching +2.1 cm/y in the ground to satellite direction, at the volcano. The area affected by deformation extends 20 km both north and south of the volcano. The best fit dislocation model consists of sills, to the north and south of the volcano, and a magma chamber, located below the volcano, all of them undergoing contraction. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001GeoRL.28.1067H&db_key=AST&high=41f192cbba08585