Measurement of coseismic deformation by satellite geodesy

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Jacobs, A., D. Sandwell, Y. Fialko, and L. Sichoix (2002), The 1999 (Mw 7.1) Hector Mine, California, Earthquake: Near-Field Postseismic Deformation from ERS Interferometry, Bull. Seism. Soc. Amer., 92, 1433–1442. Interferometric synthetic aperture radar (InSAR) data over the area of the Hector Mine earthquake (Mw 7.1, 16 October 1999) reveal postseismic deformation of several centimeters over a spatial scale of 0.5 to 50 km. We analyzed seven SAR acquisitions to form interferograms over four time periods after the event. The main deformations seen in the line-of-sight (LOS) displacement maps are a region of subsidence (60 mm LOS increase) on the northern end of the fault, a region of uplift (45 mm LOS decrease) located to the northeast of the primary fault bend, and a linear trough running along the main rupture having a depth of up to 15 mm and a width of about 2 km. We correlate these features with a double left-bending, rightlateral, strike-slip fault that exhibits contraction on the restraining side and extension along the releasing side of the fault bends. The temporal variations in the near-fault postseismic deformation are consistent with a characteristic time scale of 135 42 or 25 days, which is similar to the relaxation times following the 1992 Landers earthquake. High gradients in the LOS displacements occur on the fault trace, consistent with afterslip on the earthquake rupture. We derive an afterslip model by inverting the LOS data from both the ascending and descending orbits. Our model indicates that much of the afterslip occurs at depths of less than 3 to 4 km.

Jonsson, S., H. Zebker, P. Segall, and F. Amelung (2002), Fault slip distribution of the Mw7.2 Hector Mine earthquake estimated from Satellite Radar and GPS measurements, Bull. Seism. Soc. Amer., in press.

Jonsson, S., P. Segall, R. Pedersen, and G. Bjornsson (2003), Post-earthquake ground movements correlated to pore-pressure transients, Nature, 424, 179 - 183. Large earthquakes alter the stress in the surrounding crust, leading to triggered earthquakes and aftershocks. A number of time-dependent processes, including afterslip, pore-fluid flow and viscous relaxation of the lower crust and upper mantle, further modify the stress and pore pressure near the fault, and hence the tendency for triggered earthquakes. It has proved difficult, however, to distinguish between these processes on the basis of direct field observations, despite considerable effort. Here we present a unique combination of measurements consisting of satellite radar interferograms and water-level changes in geothermal wells following two magnitude-6.5 earthquakes in the south Iceland seismic zone. The deformation recorded in the interferograms cannot be explained by either afterslip or visco-elastic relaxation, but is consistent with rebound of a porous elastic material in the first 1–2 months following the earthquakes. This interpretation is confirmed by direct measurements which show rapid (1–2-month) recovery of the earthquake-induced water-level changes. In contrast, the duration of the aftershock sequence is projected to be 3.5 years, suggesting that pore-fluid flow does not control aftershock duration. But because the surface strains are dominated by pore-pressure changes in the shallow crust, we cannot rule out a longer pore-pressure transient at the depth of the aftershocks. The aftershock duration is consistent with models of seismicity rate variations based on rate- and state-dependent friction laws. doi:10.1038/nature01776

Kontoes, C., P. Elias, O. Sykioti, P. Briole, D. Remy, M. Sachpazi, G. Veis, and I. Kotsis (2000), Displacement field and fault model for the September 7, 1999 Athens earthquake inferred from ERS2 satellite radar interferometry, Geophysical Research Letters, 27, 3989-3992. On September 7, 1999, a moderate (Mw =5.9) normal faulting earthquake occurred in the northwest of Athens (Hellas) causing heavy damages and casualties. Using interferometric combinations of ERS2 SAR images, we analyzed the coseismic deformation field. Two fringes are observed south of the Fili mountain, up to the coastline of the Elefsis gulf. They correspond to 56 mm increase in slant range. Modeling the earthquake as a dislocation in an elastic half-space, we inverted the interferometric data to assess the fault location and geometry and the amplitude of the coseismic slip. The model suggests ~300 mm slip on an 18 km long blind fault composed of two pieces. The intersection of the fault plane with the Earth surface is located in the Fili mountain with a ~N120° orientation. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000GeoRL.27.3989K&db_key=AST&high=42fb8ddbb608794

Legresy, B., E. Rignot, and I. E. Tabacco (2000), Constraining ice dynamics at Dome C, Antarctica, using remotely sensed measurements, Geophysical Research Letters, 27, 3493-3496. A first time description is given of the ice flow at Dome C, Antarctica, around the EPICA drilling site. We used satellite radar altimetry to obtain the precise ice surface topography, airborne radio echo sounding to obtain the ice thickness and satellite SAR interferometry to derive one component of the surface velocity field. The balance flux around the Dome C area is then accurately mapped and comparisons made between driving stress, surface and balance velocity to help us describe the ice flow in the region. As a byproduct of the study, we also recover anomalies in the ice flow conditions in sub-glacial lake locations. These effects result from localy invalid shallow-ice approximation. The results of this study form the basis for future investigations of the ice flow conditions at Dome C in relation to ice core interpretation. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000GeoRL.27.3493L&db_key=AST&high=42fb8ddbb623888

Lohman, R. B., and M. Simons (2005), Some thoughts on the use of InSAR data to constrain models of surface deformation: Noise structure and data downsampling, Geochemistry, Geophysics, Geosystems, 6, 01007. Repeat-pass Interferometric Synthetic Aperture Radar (InSAR) provides spatially dense maps of surface deformation with potentially tens of millions of data points. Here we estimate the actual covariance structure of noise in InSAR data. We compare the results for several independent interferograms with a large ensemble of GPS observations of tropospheric delay and discuss how the common approaches used during processing of InSAR data affects the inferred covariance structure. Motivated by computational concerns associated with numerical modeling of deformation sources, we then combine the data-covariance information with the inherent resolution of an assumed source model to develop an efficient algorithm for spatially variable data resampling (or averaging). We illustrate these technical developments with two earthquake scenarios at different ends of the earthquake magnitude spectrum. For the larger events, our goal is to invert for the coseismic fault slip distribution. For smaller events, we infer the hypocenter location and moment. We compare the results of inversions using several different resampling algorithms, and we assess the importance of using the full noise covariance matrix. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005GGG.601007L&db_key=PHY&high=42fb8ddbb619944

Lohman, R. B., M. Simons, and B. Savage (2002), Location and mechanism of the Little Skull Mountain earthquake as constrained by satellite radar interferometry and seismic waveform modeling, Journal of Geophysical Research (Solid Earth), 107f. We use interferometric synthetic aperture radar (InSAR) and broadband seismic waveform data to estimate source parameters of the 29 June 1992, Ms 5.4 Little Skull Mountain (LSM) earthquake. This event occurred within a geodetic network designed to measure the strain rate across the region around Yucca Mountain. The LSM earthquake complicates interpretation of the existing GPS and trilateration data, as the earthquake magnitude is sufficiently small that seismic data do not tightly constrain the epicenter but large enough to potentially affect the geodetic observations. We model the InSAR data using a finite dislocation in a layered elastic space. We also invert regional seismic waveforms both alone and jointly with the InSAR data. Because of limitations in the existing data set, InSAR data alone cannot determine the area of the fault plane independent of magnitude of slip nor the location of the fault plane independent of the earthquake mechanism. Our seismic waveform data tightly constrain the mechanism of the earthquake but not the location. Together, the two complementary data types can be used to determine the mechanism and location but cannot distinguish between the two potential conjugate fault planes. Our preferred model has a moment of ~3.2 × 10^17 N m (Mw 5.6) and predicts a line length change between the Wahomie and Mile geodetic benchmarks of ~5 mm. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002JGRB.107f.ETG7L&db_key=PHY&high=42fb8ddbb619944

Lu, Z., and W. R. Danskin (2001), InSAR analysis of natural recharge to define structure of a ground-water basin, San Bernardino, California, Geophysical Research Letters, 28, 2661-2664. Using interferometric synthetic aperture radar (InSAR) analysis of ERS-1 and ERS-2 images, we detect several centimeters of uplift during the first half of 1993 in two areas of the San Bernardino ground-water basin of southern California. This uplift correlates with unusually high runoff from the surrounding mountains and increased ground-water levels in nearby wells. The deformation of the land surface identifies the location of faults that restrict ground-water flow, maps the location of recharge, and suggests the areal distribution of fine-grained aquifer materials. Our preliminary results demonstrate that naturally occurring runoff and resultant recharge can be used with interferometric deformation mapping to help define the structure and important hydrogeologic features of a ground-water basin. This approach may be particularly useful in investigations of remote areas with scant ground-based hydrogeologic data. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001GeoRL.28.2661L&db_key=AST&high=42fb8ddbb620762

Lu, Z., C. Wicks, D. Dzurisin, J. A. Power, S. C. Moran, and W. Thatcher (2002c), Magmatic inflation at a dormant stratovolcano: 1996-1998 activity at Mount Peulik volcano, Alaska, revealed by satellite radar interferometry, Journal of Geophysical Research (Solid Earth), 107g. A series of ERS radar interferograms that collectively span the time interval from July 1992 to August 2000 reveal that a presumed magma body located 6.6 +/- 0.5 km beneath the southwest flank of the Mount Peulik volcano inflated 0.051 +/- 0.005 km^3 between October 1996 and September 1998. Peulik has been active only twice during historical time, in 1814 and 1852, and the volcano was otherwise quiescent during the 1990s. The inflation episode spanned at least several months because separate interferograms show that the associated ground deformation was progressive. The average inflation rate of the magma body was ~0.003 km^3 /month from October 1996 to September 1997, peaked at 0.005 km^3 /month from 26 June to 9 October 1997, and dropped to ~0.001 km^3 /month from October 1997 to September 1998. An intense earthquake swarm, including three ML 4.8-5.2 events, began on 8 May 1998 near Becharof Lake, ~30 km northwest of Peulik. More than 400 earthquakes with a cumulative moment of 7.15 × 10^17 N m were recorded in the area through 19 October 1998. Although the inflation and earthquake swarm occurred at about the same time, the static stress changes that we calculated in the epicentral area due to inflation beneath Peulik appear too small to provide a causal link. The 1996-1998 inflation episode at Peulik confirms that satellite radar interferometry can be used to detect magma accumulation beneath dormant volcanoes at least several months before other signs of unrest are apparent. This application represents a first step toward understanding the eruption cycle at Peulik and other stratovolcanoes with characteristically long repose periods. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002JGRB.107g.ETG4L&db_key=PHY&high=42fb8ddbb620762

Lu, Z., C. Wicks, D. Dzurisin, W. Thatcher, J. Freymueller, S. McNutt, and D. Mann, Aseismic inflation of Westdahl volcano, Alaska revealed by satellite radar interferometry, Geophys. Res. Lett., 27, 1567-1570, 2000.

Lu, Z., D. Mann, J. T. Freymueller, and D. J. Meyer (2000a), Synthetic aperture radar interferometry of Okmok volcano, Alaska: Radar observations, Journal of Geophysical Research, 105, 10791-10806. ERS-1/ERS-2 synthetic aperture radar interferometry was used to study the 1997 eruption of Okmok volcano in Alaska. First, we derived an accurate digital elevation model (DEM) using a tandem ERS-1/ERS-2 image pair and the preexisting DEM. Second, by studying changes in interferometric coherence we found that the newly erupted lava lost radar coherence for 5-17 months after the eruption. This suggests changes in the surface backscattering characteristics and was probably related to cooling and compaction processes. Third, the atmospheric delay anomalies in the deformation interferograms were quantitatively assessed. Atmospheric delay anomalies in some of the interferograms were significant and consistently smaller than one to two fringes in magnitude. For this reason, repeat observations are important to confidently interpret small geophysical signals related to volcanic activities. Finally, using two-pass differential interferometry, we analyzed the preeruptive inflation, coeruptive deflation, and posteruptive inflation and confirmed the observations using independent image pairs. We observed more than 140 cm of subsidence associated with the 1997 eruption. This subsidence occurred between 16 months before the eruption and 5 months after the eruption, was preceded by ~18 cm of uplift between 1992 and 1995 centered in the same location, and was followed by ~10 cm of uplift between September 1997 and 1998. The best fitting model suggests the magma reservoir resided at 2.7 km depth beneath the center of the caldera, which was ~5 km from the eruptive vent. We estimated the volume of the erupted material to be 0.055 km^3 and the average thickness of the erupted lava to be ~7.4 m. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000JGR.10510791L&db_key=PHY&high=42fb8ddbb620762

Lu, Z., J. A. Power, and D. Dzurisin (2000b), Ground deformation associated with the March 1996 earthquake swarm at Akutan volcano, Alaska, revealed by satellite radar interferometry, Journal of Geophysical Research, 105, 21483-21496. In March 1996 an intense swarm of volcano-tectonic earthquakes (~3000 felt by local residents, Mmax =5.1, cumulative moment of 2.7×10^18 Nm) beneath Akutan Island in the Aleutian volcanic arc, Alaska, produced extensive ground cracks but no eruption of Akutan volcano. Synthetic aperture radar interferograms that span the time of the swarm reveal complex island-wide deformation: the western part of the island including Akutan volcano moved upward, while the eastern part moved downward. The axis of the deformation approximately aligns with new ground cracks on the western part of the island and with Holocene normal faults that were reactivated during the swarm on the eastern part of the island. The axis is also roughly parallel to the direction of greatest compressional stress in the region. No ground movements greater than 2.83 cm were observed outside the volcano's summit caldera for periods of 4 years before or 2 years after the swarm. We modeled the deformation primarily as the emplacement of a shallow, east-west trending, north dipping dike plus inflation of a deep, Mogi-type magma body beneath the volcano. The pattern of subsidence on the eastern part of the island is poorly constrained. It might have been produced by extensional tectonic strain that both reactivated preexisting faults on the eastern part of the island and facilitated magma movement beneath the western part. Alternatively, magma intrusion beneath the volcano might have been the cause of extension and subsidence in the eastern part of the island. We attribute localized subsidence in an area of active fumaroles within the Akutan caldera, by as much as 10 cm during 1992-1993 and 1996-1998, to fluid withdrawal or depressurization of the shallow hydrothermal system. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000JGR.10521483L&db_key=PHY&high=42fb8ddbb620762

Lu, Z., J. A. Power, V. S. McConnell, C. Wicks, and D. Dzurisin (2002b), Preeruptive inflation and surface interferometric coherence characteristics revealed by satellite radar interferometry at Makushin Volcano, Alaska: 1993-2000, Journal of Geophysical Research (Solid Earth), 107k. Pilot reports in January 1995 and geologic field observations from the summer of 1996 indicate that a relatively small explosive eruption of Makushin, one of the more frequently active volcanoes in the Aleutian arc of Alaska, occurred on 30 January 1995. Several independent radar interferograms that each span the time period from October 1993 to September 1995 show evidence of ~7 cm of uplift centered on the volcano's east flank, which we interpret as preeruptive inflation of a ~7-km-deep magma source (DeltaV = 0.022 km^3 ). Subsequent interferograms for 1995-2000, a period that included no reported eruptive activity, show no evidence of additional ground deformation. Interferometric coherence at C band is found to persist for 3 years or more on lava flow and other rocky surfaces covered with short grass and sparsely distributed tall grass and for at least 1 year on most pyroclastic deposits. On lava flow and rocky surfaces with dense tall grass and on alluvium, coherence lasts for a few months. Snow and ice surfaces lose coherence within a few days. This extended timeframe of coherence over a variety of surface materials makes C band radar interferometry an effective tool for studying volcano deformation in Alaska and other similar high-latitude regions. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002JGRB.107k.ECV1L&db_key=PHY&high=42fb8ddbb620762

Lu, Z., T. Masterlark, D. Dzurisin, R. Rykhus, and C. Wicks (2003), Magma supply dynamics at Westdahl volcano, Alaska, modeled from satellite radar interferometry, Journal of Geophysical Research (Solid Earth), 108g. A group of satellite radar interferograms that span the time period from 1991 to 2000 shows that Westdahl volcano, Alaska, deflated during its 1991-1992 eruption and is reinflating at a rate that could produce another eruption within the next several years. The rates of inflation and deflation are approximated by exponential decay functions having time constants of about 6 years and a few days, respectively. This behavior is consistent with a deep, constant-pressure magma source connected to a shallow reservoir by a magma-filled conduit. An elastic deformation model indicates that the reservoir is located about 6 km below sea level and beneath Westdahl Peak. We propose that the magma flow rate through the conduit is governed by the pressure gradient between the deep source and the reservoir. The pressure gradient, and hence the flow rate, are greatest immediately after eruptions. Pressurization of the reservoir decreases both the pressure gradient and the flow rate, but eventually the reservoir ruptures and an eruption or intrusion ensues. The eruption rate is controlled partly by the pressure gradient between the reservoir and surface, and therefore it, too, decreases with time. When the supply of eruptible magma is exhausted, the eruption stops, the reservoir begins to repressurize at a high rate, and the cycle repeats. This model might also be appropriate for other frequently active volcanoes with stable magma sources and relatively simple magma storage systems. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003JGRB.108g.ETG9L&db_key=PHY&high=42fb8ddbb620762

Lu, Z., T. Masterlark, J. Power, D. Dzurisin, and C. Wicks (2002a), Subsidence at Kiska Volcano, Western Aleutians, detected by satellite radar interferometry, Geophysical Research Letters, 29, 2-1. Sequential interferometric synthetic aperture radar images of Kiska, the westernmost historically active volcano in the Aleutian arc, show that a circular area about 3 km in diameter centered near the summit subsided by as much as 10 cm from 1995 to 2001, mostly during 1999 and 2000. An elastic Mogi-type deformation model suggests that the source is within 1 km of the surface. Based on the shallow source depth, the copious amounts of steam during recent eruptions, and recent field reports of vigorous steaming and persistent ground shaking near the summit area, we attribute the subsidence to decreased pore-fluid pressure within a shallow hydrothermal system beneath the summit area. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002GeoRL.29r.2L&db_key=AST&high=42fb8ddbb620762

Lyuboshenko, I., and H. Maître, Unwrapping circular interferograms, Applied Optics, 39, 4817-4825, 2000.

Malassingne, C., F. Lemaître, P. Briole, and O. Pascal (2001), Potential of ground based radar for the monitoring of deformation of volcanoes, Geophysical Research Letters, 28, 851-854. The ground based radar presented here is a new tool for volcano deformation monitoring. With respect to other systems it has various advantages: operational by any weather (rain, fog, aerosols), high frequency sampling capability (10 a few tens of seconds), possibility of monitoring surfaces not equipped with reflectors. It can be used to monitor unstable and dangerous parts of volcanoes (craters, lava domes.). The all weather capability and the high frequency sampling rate are crucial on volcanoes where activity can change within a few hours or less. We present the system and show an application for range measurements on corner reflectors. Then, we present the results obtained in the Pyrénées mountains (France) on a natural surface not equipped with reflectors. We analyze the evolution of the coherence of the reflected signal as a function of the nature of the terrain and elapsed time. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001GeoRL.28.851M&db_key=AST&high=42fb8ddbb608794

Mann, D., J. Freymueller, and Z. Lu (2002), Deformation associated with the 1997 eruption of Okmok volcano, Alaska, Journal of Geophysical Research (Solid Earth), 107d. Okmok volcano, located on Umnak Island in the Aleutian chain, Alaska, is the most eruptive caldera system in North America in historic time. Its most recent eruption occurred in 1997. Synthetic aperture radar interferometry shows deflation of the caldera center of up to 140 cm during this time, preceded and followed by inflation of smaller magnitude. The main part of the observed deformation can be modeled using a pressure point source model. The inferred source is located between 2.5 and 5.0 km beneath the approximate center of the caldera and ~5 km from the eruptive vent. We interpret it as a central magma reservoir. The preeruptive period features inflation accompanied by shallow localized subsidence between the caldera center and the vent. We hypothesize that this is caused by hydrothermal activity or that magma moved away from the central chamber and toward the later vent. Since all historic eruptions at Okmok have originated from the same cone, this feature may be a precursor that indicates an upcoming eruption. The erupted magma volume is ~9 times the volume that can be accounted for by the observed preeruptive inflation. This indicates a much longer inflation interval than we were able to observe. The observation that reinflation started shortly after the eruption suggests that inflation spans the whole time interval between eruptions. Extrapolation of the average subsurface volume change rate is in good agreement with the long-term eruption frequency and eruption volumes of Okmok. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002JGRB.107d.ETG7M&db_key=PHY&high=42fb8ddbb620762

Massonnet, D. (2001), Capabilities and limitations of the interferometric cartwheel, IEEE Trans. Geoscience Rem. Sens., 39, 506-520. Quasi-simultaneous radar images can be produced by a low cost system using a set of passive receivers onboard a constellation in a special orbial configuration. The combination of thes images can improve the final resolution in range and azimuth and systematically produce across-track and along-track inteferometric data.

Massonnet, D., and F. Sigmundsson, Remote sensing of volcano deformation by radar interferometry from various satellites, in Remote sensing of active volcanism, edited by P. Mouginis-Mark, J. A. Crisp, and J. H. Fink, Geophys. Monogr. Ser., 116, 207-221, AGU, Washington, D. C., 2000.

Masterlark, T., and Z. Lu (2004), Transient volcano deformation sources imaged with interferometric synthetic aperture radar: Application to Seguam Island, Alaska, Journal of Geophysical Research (Solid Earth), 109, 01401. Thirty interferometric synthetic aperture radar (InSAR) images, spanning various intervals during 1992-2000, document coeruptive and posteruptive deformation of the 1992-1993 eruption on Seguam Island, Alaska. A procedure that combines standard damped least squares inverse methods and collective surfaces, identifies three dominant amorphous clusters of deformation point sources. Predictions generated from these three point source clusters account for both the spatial and temporal complexity of the deformation patterns of the InSAR data. Regularized time series of source strength attribute a distinctive transient behavior to each of the three source clusters. A model that combines magma influx, thermoelastic relaxation, poroelastic effects, and petrologic data accounts for the transient, interrelated behavior of the source clusters and the observed deformation. Basaltic magma pulses, which flow into a storage chamber residing in the lower crust, drive this deformational system. A portion of a magma pulse is injected into the upper crust and remains in storage during both coeruption and posteruption intervals. This injected magma degasses and the volatile products accumulate in a shallow poroelastic storage chamber. During the eruption, another portion of the magma pulse is transported directly to the surface via a conduit roughly centered beneath Pyre Peak on the west side of the island. A small amount of this magma remains in storage during the eruption, and posteruption thermoelastic contraction ensues. This model, made possible by the excellent spatial and temporal coverage of the InSAR data, reveals a relatively simple system of interrelated predictable processes driven by magma dynamics. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004JGRB.10901401M&db_key=PHY&high=42fb8ddbb620762

Mellors, R. J., H. Magistrale, P. Earle, and A. Cogbill (2004), Comparison of moderate earthquake location in Southern California using seismology and InSAR, Bull. Seism. Soc. Amer., 94, 2004 - 2014. Source parameters determined from interferometric synthetic aperture radar (InSAR) measurements and from seismic data are compared from four moderate-size (less than M 6) earthquakes in southern California. The goal is to verify approximate detection capabilities of InSAR, assess differences in the results, and test how the two results can be reconciled. First, we calculated the expected surface deformation from all earthquakes greater than magnitude 4 in areas with available InSAR data (347 events). A search for deformation from the events in the interferograms yielded four possible events with magnitudes less than 6. The search for deformation was based on a visual inspection as well as cross-correlation in two dimensions between the measured signal and the expected signal. A grid-search algorithm was then used to estimate focal mechanism and depth from the InSAR data. The results were compared with locations and focal mechanisms from published catalogs. An independent relocation using seismic data was also performed. The seismic locations fell within the area of the expected rupture zone for the three events that show clear surface deformation. Therefore, the technique shows the capability to resolve locations with high accuracy and is applicable worldwide. The depths determined by InSAR agree with well-constrained seismic locations determined in a 3D velocity model. Depth control for well-imaged shallow events using InSAR data is good, and better than the seismic constraints in some cases. A major difficulty for InSAR analysis is the poor temporal coverage of InSAR data, which may make it impossible to distinguish deformation due to different earthquakes at the same location. reviewed http://www.seismosoc.org/index.html

Michel, R., and J. P. Avouac (2002), Deformation due to the 17 August 1999 Izmit earthquake measured from SPOT images, J. Geophys. Res., 107, ETG X-1 to X-4. The geometry of the ruptured areas and the coseismic slip distribution data are key to highlighting the behavior of seismic faults. This information is generally retrieved from field investigations and geodetic measurements or synthetic aperture radar (SAR) interferometry. Here we show that SPOT images can also be used to accurately map the fault zone and to determine the slip distribution by subpixel correlation of images acquired before and after an earthquake. The measured slip includes the contribution of possible distributed shear that might not be clearly expressed in surface ruptures and smoothes out possible along-strike variability due to near-surface fault complexities. We apply the technique to the Ms = 7.4, 1999, Izmit earthquake. Our results reveal a <100-m-wide and very linear fault zone that can be traced for 70 km from Go¨lcu¨k to Akyazi, along which supershear rupture has been inferred. The obtained slip distribution compares well with the field measurements and is consistent with ground deformation measured at some distance from the fault zone using SAR images. Very little deformation was accommodated off the main fault plane. Maximum slip is observed near Sapanca lake at a small fault jog that has probably influenced rupture propagation. They no longer claim asymetric gradients across the fault. 10.1029/2000JB000102.

Niemi, N. A., B. P. Wernicke, A. M. Friedrich, M. Simons, R. A. Bennett, and J. L. Davis (2004), BARGEN continuous GPS data across the eastern Basin and Range province, and implications for fault system dynamics, Geophysical Journal International, 159, 842-862. We collected data from a transect of continuous Global Positioning System (GPS) sites across the eastern Basin and Range province at latitude 39°N from 1997-2000. Intersite velocities define a region ~350 km wide of broadly distributed strain accumulation at ~10 nstr yr -1. On the western margin of the region, site EGAN, ~10 km north of Ely, Nevada, moved at a rate of 3.9 +/- 0.2 mm yr -1 to the west relative to site CAST, which is on the Colorado Plateau. Velocities of most sites to the west of Ely moved at an average rate of ~3 mm yr -1 relative to CAST, defining an area across central Nevada that does not appear to be extending significantly. The late Quaternary geological velocity field, derived using seismic reflection and neotectonic data, indicates a maximum velocity of EGAN with respect to the Colorado Plateau of ~4 mm yr -1, also distributed relatively evenly across the region. The geodetic and late Quaternary geological velocity fields, therefore, are consistent, but strain release on the Sevier Desert detachment and the Wasatch fault appears to have been anomalously high in the Holocene. Previous models suggesting horizontal displacement rates in the eastern Basin and Range near 3 mm yr -1, which focused mainly along the Wasatch zone and Intermountain seismic belt, may overestimate the Holocene Wasatch rate by at least 50 per cent and the Quaternary rate by nearly an order of magnitude, while ignoring potentially major seismogenic faults further to the west. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004GeoJI.159.842N&db_key=AST

Pagli, C., R. Pedersen, F. Sigmundsson, and K. L. Feigl (2003), Triggered fault slip on June 17, 2000 on the Reykjanes Peninsula, SW-Iceland captured by radar interferometry, Geophysical Research Letters, 30, 6-1. Dynamically triggered seismicity followed shortly after a Ms 6.6 earthquake in Iceland on June 17, 2000. Smaller earthquakes occurred on the Reykjanes Peninsula up to 100 km from the mainshock rupture. Using interferometric analysis of Synthetic Aperture Radar images (InSAR), we measure crustal deformation associated with three triggered deformation events. The largest of these occurred at Lake Kleifarvatn, 85 km west of the mainshock epicenter. Modeling of the InSAR data reveals strikeslip on a north-striking fault, with a geodetic moment of 6.2 × 10^17 Nm, equivalent to magnitude Mw 5.8 earthquake. A seismological estimate of the moment is not yet available, because the seismic signature of this event is partly hidden by the mainshock waveform. The paucity of aftershocks on the triggered rupture plane suggests some aseismic slip there, compatible with a thin seismogenic crust, high heat-flow, hydrothermal alteration and the presence of fluids in the area. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003GeoRL.30f.6P&db_key=AST

Paillou, P., G. Grandjean, J. M. Malézieux, G. Ruffié, E. Heggy, D. Piponnier, P. Dubois, and J. Achache (2001), Performances of Ground Penetrating Radars in arid volcanic regions: Consequences for Mars subsurface exploration, Geophysical Research Letters, 28, 911-914. A GPR field experiment in the Republic of Djibouti provides evidence for very low radar penetration in arid volcanic materials, in the range 100-500 MHz. This phenomenon is attributed to the high iron oxide and evaporite concentration in soils, which significantly increases the conductivity, thus leading to poor subsurface imaging performances. The geologic context in Djibouti is shown to provide a good terrestrial analogue to Mars geology. Results of this study show that the future sounding radar missions to Mars may not reach the penetration depths previously anticipated. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001GeoRL.28.911P&db_key=AST&high=42fb8ddbb616940

Pedersen, R., and F. Sigmundsson (2004), InSAR based sill model links spatially offset areas of deformation and seismicity for the 1994 unrest episode at Eyjafjallajokull volcano, Iceland, Geophysical Research Letters, 31, 14610. We present InSAR observations of deformation due to an intrusion in the Eyjafjallajökull volcano, Southern Iceland, in 1994. More than 15 cm of deformation in the line of sight (LOS) direction is detected in a series of interferograms spanning a micro-earthquake swarm occurring in June 1994. The location of the seismicity is more than 6 km offset compared to the area of inferred maximum surface uplift. Through an inversion scheme we find that a horizontal sill intrusion experiencing variable opening of up to 0.36 m agrees well with the deformation data. The total intrusion volume is 0.017 km^3 . The northern periphery of the modeled intrusion fits well with the area of recorded seismicity, indicating a close connection. Several processes may be responsible. Our preferred explanation is that the earthquakes are caused by opening of a narrow magma channel from depth, feeding the sill. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004GeoRL.3114610P&db_key=AST&high=41f192cbba08585

Pedersen, R., F. Sigmundsson, K. L. Feigl, and T. Árnadóttir (2001), Coseismic interferograms of two MS=6.6 earthquakes in the South Iceland Seismic Zone, June 2000, Geophys. Res. Lett., 28, 3341-3344. We present InSAR observations of deformation due to two MS=6.6 earthquakes in the South Iceland Seismic Zone in June 2000. Coseismic deformation predominates a series of ERS interferograms. Range change, due to mainly right-lateral strike-slip on N-S striking faults, amounting to more than 15 cm is observed, although displacement is mainly perpendicular to the satellite look direction. Using elastic dislocation models in a trial-and-error scheme, we find a best-fitting model that agrees well with the aftershock locations and moment magnitudes estimated from seismograms. The June 17 model has a fault patch 16 km long, 10 km deep, striking N05°E, dipping 86°, with a slip maximum of 2.40 m. The June 21 model has a vertical patch 15 km long, 9 km deep, striking N01°W, with a slip maximum of 2.15 m.

Peltzer, G., F. Crampe, S. Hensley, and P. Rosen (2001), Transient strain accumulation and fault interaction in the Eastern California shear zone, Geology, 29, 975-978. Satellite synthetic aperture radar interferometry reveals transient strain accumulation along the Blackwater Little Lake fault system within the Eastern California shear zone. The surface strain map obtained by averaging eight years (1992 2000) of Earth Re-source Satellite (ERS) radar data shows a 120-km-long, 20-km-wide zone of concentrated shear between the southern end of the 1872 Owens Valley earthquake surface break and the northern end of the 1992 Landers earthquake surface break. The observed shear zone is continuous through the Garlock fault, which does not show any evidence of left-lateral slip during the same time period. A dislocation model of the observed shear indicates right-lateral slip at 7 +/- 3 mm/yr on a vertical fault below ~5 km depth, a rate that is two to three times greater than the geologic rates estimated on northwest-trending faults in the eastern Mojave area. This tran-sient slip rate and the absence of resolvable slip on the Garlock fault may be the manifestation of an oscillatory strain pattern between interacting, conjugate fault systems.

Pritchard, M. E., and M. Simons (2004a), An InSAR-based survey of volcanic deformation in the central Andes, Geochem. Geophys. Geosyst., 5, DOI 10.1029/2003GC000610.

Pritchard, M. E., and M. Simons (2004a), An InSAR-based survey of volcanic deformation in the central Andes, Geochemistry, Geophysics, Geosystems, 5, 2002. We extend an earlier interferometric synthetic aperture radar (InSAR) survey covering about 900 remote volcanos of the central Andes (14°-27°S) between the years 1992 and 2002. Our survey reveals broad (10s of km), roughly axisymmetric deformation at 4 volcanic centers: two stratovolcanoes are inflating (Uturuncu, Bolivia, and Hualca Hualca, Peru); another source of inflation on the border between Chile and Argentina is not obviously associated with a volcanic edifice (here called Lazufre); and a caldera (Cerro Blanco, also called Robledo) in northwest Argentina is subsiding. We explore the range of source depths and volumes allowed by our observations, using spherical, ellipsoidal and crack-like source geometries. We further examine the effects of local topography upon the deformation field and invert for a spherical point-source in both elastic half-space and layered-space crustal models. We use a global search algorithm, with gradient search methods used to further constrain best-fitting models. Inferred source depths are model-dependent, with differences in the assumed source geometry generating a larger range of accepted depths than variations in elastic structure. Source depths relative to sea level are: 8-18 km at Hualca Hualca; 12-25 km for Uturuncu; 5-13 km for Lazufre, and 5-10 km at Cerro Blanco. Deformation at all four volcanoes seems to be time-dependent, and only Uturuncu and Cerro Blanco were deforming during the entire time period of observation. Inflation at Hualca Hualca stopped in 1997, perhaps related to a large eruption of nearby Sabancaya volcano in May 1997, although there is no obvious relation between the rate of deformation and the eruptions of Sabancaya. We do not observe any deformation associated with eruptions of Lascar, Chile, at 16 other volcanoes that had recent small eruptions or fumarolic activity, or associated with a short-lived thermal anomaly at Chiliques volcano. We posit a hydrothermal system at Cerro Blanco to explain the rate of subsidence there. For the last decade, we calculate the ratio of the volume of magma intruded to extruded is between 1-10, and that the combined rate of intrusion and extrusion is within an order of magnitude of the inferred geologic rate. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004GGG.5.2002P&db_key=PHY&high=42fb8ddbb619944

Pritchard, M. E., and M. Simons (2004b), An InSAR-based survey of volcanic deformation in the central Andes, Geochemistry, Geophysics, Geosystems, 5, 2002. We extend an earlier interferometric synthetic aperture radar (InSAR) survey covering about 900 remote volcanos of the central Andes (14°-27°S) between the years 1992 and 2002. Our survey reveals broad (10s of km), roughly axisymmetric deformation at 4 volcanic centers: two stratovolcanoes are inflating (Uturuncu, Bolivia, and Hualca Hualca, Peru); another source of inflation on the border between Chile and Argentina is not obviously associated with a volcanic edifice (here called Lazufre); and a caldera (Cerro Blanco, also called Robledo) in northwest Argentina is subsiding. We explore the range of source depths and volumes allowed by our observations, using spherical, ellipsoidal and crack-like source geometries. We further examine the effects of local topography upon the deformation field and invert for a spherical point-source in both elastic half-space and layered-space crustal models. We use a global search algorithm, with gradient search methods used to further constrain best-fitting models. Inferred source depths are model-dependent, with differences in the assumed source geometry generating a larger range of accepted depths than variations in elastic structure. Source depths relative to sea level are: 8-18 km at Hualca Hualca; 12-25 km for Uturuncu; 5-13 km for Lazufre, and 5-10 km at Cerro Blanco. Deformation at all four volcanoes seems to be time-dependent, and only Uturuncu and Cerro Blanco were deforming during the entire time period of observation. Inflation at Hualca Hualca stopped in 1997, perhaps related to a large eruption of nearby Sabancaya volcano in May 1997, although there is no obvious relation between the rate of deformation and the eruptions of Sabancaya. We do not observe any deformation associated with eruptions of Lascar, Chile, at 16 other volcanoes that had recent small eruptions or fumarolic activity, or associated with a short-lived thermal anomaly at Chiliques volcano. We posit a hydrothermal system at Cerro Blanco to explain the rate of subsidence there. For the last decade, we calculate the ratio of the volume of magma intruded to extruded is between 1-10, and that the combined rate of intrusion and extrusion is within an order of magnitude of the inferred geologic rate. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004GGG.5.2002P&db_key=PHY&high=42fb8ddbb619944

Pritchard, M. E., and M. Simons (2004b), An InSAR-based survey of volcanic deformation in the southern Andes, Geophysical Research Letters, 31, 15610. We use Interferometric Synthetic Aperture Radar (InSAR) to search for surface deformation in the southern Andes (40°S-46°S and 49°S-53°S) associated with magmatic processes. Although the available data are not optimal, we can constrain the amount of volcanic deformation at about 27 Holocene volcanoes between the years 1993-1999. We detect inflation of Cerro Hudson volcano following its 1991 eruption, and use spherical and non-spherical models to constrain the source of deformation to be between 4 and 8 km below sea level. We measure the rate of deformation to be about 5 cm/year in the radar line-of-sight, and infer that the maximum deformation could exceed 10 cm/year in the center of the caldera. Within the errors of the measurements, the rate of deformation is constant from 1993-1998 (10-30 × 10^6 m^3 /year). At this rate, 100-200 years is required to accumulate the volume of material erupted in 1991. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004GeoRL.3115610P&db_key=AST&high=42fb8ddbb619944

Pritchard, M. E., and M. Simons (2004c), An InSAR-based survey of volcanic deformation in the southern Andes, Geophysical Research Letters, 31, 15610. We use Interferometric Synthetic Aperture Radar (InSAR) to search for surface deformation in the southern Andes (40°S-46°S and 49°S-53°S) associated with magmatic processes. Although the available data are not optimal, we can constrain the amount of volcanic deformation at about 27 Holocene volcanoes between the years 1993-1999. We detect inflation of Cerro Hudson volcano following its 1991 eruption, and use spherical and non-spherical models to constrain the source of deformation to be between 4 and 8 km below sea level. We measure the rate of deformation to be about 5 cm/year in the radar line-of-sight, and infer that the maximum deformation could exceed 10 cm/year in the center of the caldera. Within the errors of the measurements, the rate of deformation is constant from 1993-1998 (10-30 × 10^6 m 3 /year). At this rate, 100-200 years is required to accumulate the volume of material erupted in 1991. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004GeoRL.3115610P&db_key=AST&high=41f192cbba08585

Pritchard, M. E., M. Simons, P. A. Rosen, S. Hensley, and F. H. Webb (2002a), Co-seismic slip from the 1995 July 30 Mw= 8.1 Antofagasta, Chile, earthquake as constrained by InSAR and GPS observations, Geophysical Journal International, 150, 362-376. Summary We analyse radar interferometric and GPS observations of the displacement field from the 1995 July 30 Mw= 8.1 Antofagasta, Chile, earthquake and invert for the distribution of slip along the co-seismic fault plane. Using a fixed fault geometry, we compare the use of singular-value decomposition and constrained linear inversion to invert for the slip distribution and find that the latter approach is better resolved and more physically reasonable. Separate inversions using only GPS data, only InSAR data from descending orbits, and InSAR data from both ascending and descending orbits without the GPS data illustrate the complimentary nature of GPS and the presently available InSAR data. The GPS data resolve slip near GPS benchmarks well, while the InSAR provides greater spatial sampling. The combination of ascending and descending InSAR data contributes greatly to the ability of InSAR to resolve the slip model, thereby emphasizing the need to acquire this data for future earthquakes. The rake, distribution of slip and seismic moment of our preferred model are generally consistent with previous seismic and geodetic inversions, although significant differences do exist. GPS data projected in the radar line-of-sight (LOS) and corresponding InSAR pixels have a root mean square (rms) difference of about 3 cm. Comparison of our predictions of vertical displacement and observed uplift from corraline algae have an rms of 10 cm. Our inversion and previous results reveal that the location of slip might be influenced by the 1987 Mw= 7.5 event. Our analysis further reveals that the 1995 slip distribution was affected by a 1988 Mw= 7.2 event, and might have influenced a 1998 Mw= 7.0 earthquake that occurred downdip of the 1995 rupture. Our slip inversion reveals a potential change in mechanism in the southern portion of the rupture, consistent with seismic results. Predictions of the satellite LOS displacement from a seismic inversion and a joint seismic/GPS inversion do not compare favourably with the InSAR observations. http://www.blackwell-synergy.com/loi/gji

Pritchard, M. E., M. Simons, P. A. Rosen, S. Hensley, and F. H. Webb (2002b), Co-seismic slip from the July 30, 1995 Mw 8.1 Antofagasta, Chile, earthquake as constrained by InSAR and GPS observations, Geophysical Journal International, 150, 362. We analyse radar interferometric and GPS observations of the displacement field from the 1995 July 30 Mw= 8.1 Antofagasta, Chile, earthquake and invert for the distribution of slip along the co-seismic fault plane. Using a fixed fault geometry, we compare the use of singular-value decomposition and constrained linear inversion to invert for the slip distribution and find that the latter approach is better resolved and more physically reasonable. Separate inversions using only GPS data, only InSAR data from descending orbits, and InSAR data from both ascending and descending orbits without the GPS data illustrate the complimentary nature of GPS and the presently available InSAR data. The GPS data resolve slip near GPS benchmarks well, while the InSAR provides greater spatial sampling. The combination of ascending and descending InSAR data contributes greatly to the ability of InSAR to resolve the slip model, thereby emphasizing the need to acquire this data for future earthquakes. The rake, distribution of slip and seismic moment of our preferred model are generally consistent with previous seismic and geodetic inversions, although significant differences do exist. GPS data projected in the radar line-of-sight (LOS) and corresponding InSAR pixels have a root mean square (rms) difference of about 3 cm. Comparison of our predictions of vertical displacement and observed uplift from corraline algae have an rms of 10 cm. Our inversion and previous results reveal that the location of slip might be influenced by the 1987 Mw= 7.5 event. Our analysis further reveals that the 1995 slip distribution was affected by a 1988 Mw= 7.2 event, and might have influenced a 1998 Mw= 7.0 earthquake that occurred downdip of the 1995 rupture. Our slip inversion reveals a potential change in mechanism in the southern portion of the rupture, consistent with seismic results. Predictions of the satellite LOS displacement from a seismic inversion and a joint seismic/GPS inversion do not compare favourably with the InSAR observations.

Reilinger, R. E. et al., Coseismic and postseismic fault slip for the 17 August 1999, M=7.4, Izmit, Turkey earthquake, Science, 289, 1519-1524, 2000.

Remy, D., S. Bonvalot, P. Briole, and M. Murakami (2003), Accurate measurements of tropospheric effects in volcanic areas from SAR interferometry data: application to Sakurajima volcano (Japan), Earth and Planetary Science Letters, 213, 299-310. Electronic Article Available from Elsevier Science. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003E%26PSL.213.299R&db_key=AST&high=42fb8ddbb608794

Rigo, A., J.-B. d. Chabalier, B. Meyer, and R. Armijo (2004), The 1995 Kozani-Grevena (northern Greece) earthquake revisited: an improved faulting model from synthetic aperture radar interferometry, Geophys J Int, 157, 727-736.

Salvi, S. Stramondo S. Cocco M. Sansosti E., Hunstad I., Anzidei M., Briole P., Baldi P., Tesauro M., Lanari R., Doumaz F., Pesci A., A. Galvani, Modeling Coseismic Displacements resulting from SAR interferometry and GPS measurements during the 1997 Umbria-Marche seismic sequence, J. Seismology, in press, 2000.

Simons, F. J., and R. D. van der Hilst (2003), Seismic and mechanical anisotropy and the past and present deformation of the Australian lithosphere, Earth and Planetary Science Letters, 211, 271-286. Electronic Article Available from Elsevier Science. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003E%26PSL.211.271S&db_key=AST

Simons, M., Y. Fialko, and L. Rivera (2002), Coseismic deformation from the 1999 Mw 7.1 Hector Mine, California Earthquake as inferred from InSAR and GPS observations., Bull. Seismol. Soc. Am., 92, 1390–1402.

Stevens, N. F., G. Wadge, C. A. Williams, J. G. Morley, J.-P. Muller, J. B. Murray, and M. Upton (2001), Surface movements of emplaced lava flows measured by synthetic aperture radar interferometry, J. Geophys. Res. Lava flows continue to move after they have been emplaced by flow mechanisms. This movement is largely vertical and can be detected using differential synthetic aperture radar (SAR) interferometry. There are three main components to this motion: (1) movement of surface scatterers, resulting in radar phase decorrelation, (2) measurable subsidence of the flow surface due to thermal contraction and clast repacking, and (3) time-dependent depression of the flow substrate. These effects act in proportion to the thickness of the lava flow and decay with time, although there is a time lag before the third component becomes significant. We explore these effects using SAR data from the ERS satellites over the Etna volcano, Sicily. Phase decorrelation on young, thick a'a lava flows persists for a few years and probably results from surface block rotations during flow contraction. Maximum measured subsidence rates of the 1991-1993 lava flow over a period of 70 days are about 0.7 mm day-1, but are potentially greater in areas of data decorrelation. These rates fall to <2.7 x 10-2 mm day-1 after about 20 years in flows about 50 m thick, sooner for thinner flows. Comparison with measured subsidence rates on Kilauean lava lakes suggests that thermal contraction only accounts for about one third of the observed subsidence. The remaining motion is thought to come from surface clast repacking during cooling and from creep mechanisms in the flow substrate. Measurements of postemplacement surface movement provide new constraints on the thermomechanical properties of lava flows and have cautionary implications for the interpretation of interferometric SAR data of volcanoes.

Talebian, M., E. J. Fielding, G. J. Funning, M. Ghorashi, J. Jackson, H. Nazari, B. Parsons, K. Priestley, P. A. Rosen, R. Walker, and T. J. Wright (2004), The 2003 Bam (Iran) earthquake: Rupture of a blind strike-slip fault, Geophysical Research Letters, 31, 11611. An Mw 6.5 earthquake devastated the town of Bam in southeast Iran on 26 December 2003. Surface displacements and decorrelation effects, mapped using Envisat radar data, reveal that over 2 m of slip occurred at depth on a fault that had not previously been identified. It is common for earthquakes to occur on blind faults which, despite their name, usually produce long-term surface effects by which their existence may be recognised. However, in this case there is a complete absence of morphological features associated with the seismogenic fault that destroyed Bam. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004GeoRL.3111611T&db_key=AST

Van Puymbroeck, N., R. Michel, R. Binet, J. P. Avouac, and J. Taboury, Measuring earthquakes from optical satellite images, Applied Optics, 39, 2000. [Cover]

Wicks, C. W., D. Dzurisin, S. Ingebritsen, W. Thatcher, Z. Lu, and J. Iverson (2002), Magmatic activity beneath the quiescent Three Sisters volcanic center, central Oregon Cascade Range, USA, Geophysical Research Letters, 29, 26-21. Images from satellite interferometric synthetic aperture radar (InSAR) reveal uplift of a broad ~10 km by 20 km area in the Three Sisters volcanic center of the central Oregon Cascade Range, ~130 km south of Mt. St. Helens. The last eruption in the volcanic center occurred ~1500 years ago. Multiple satellite images from 1992 through 2000 indicate that most if not all of ~100 mm of observed uplift occurred between September 1998 and October 2000. Geochemical (water chemistry) anomalies, first noted during 1990, coincide with the area of uplift and suggest the existence of a crustal magma reservoir prior to the uplift. We interpret the uplift as inflation caused by an ongoing episode of magma intrusion at a depth of ~6.5 km. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002GeoRL.29g.26W&db_key=AST&high=42fb8ddbb620762

Wright, T. J. (2002), Remote monitoring of the earthquake cycle using satellite radar interferometry, Phil. Trans. R. Soc. Lond. A, 360, 2873-2888.

Wright, T. J., B. E. Parsons, and Z. Lu (2004b), Toward mapping surface deformation in three dimensions using InSAR, Geophysical Research Letters, 31, 01607. One of the limitations of deformation measurements made with interferometric synthetic aperture radar (InSAR) is that an interferogram only measures one component of the surface deformation - in the satellite's line of sight. We investigate strategies for mapping surface deformation in three dimensions by using multiple interferograms, with different imaging geometries. Geometries for both current and future missions are evaluated, and their abilities to resolve the displacement vector are compared. The north component is always the most difficult to determine using data from near-polar orbiting satellites. However, a satellite with an inclination of about 60°/120° would enable all three components to be well resolved. We attempt to resolve the 3D displacements for the 23 October 2002 Nenana Mountain (Alaska) Earthquake. The north component's error is much larger than the signal, but proxies for eastward and vertical motion can be determined if the north component is assumed negligible. Inversions of hypothetical coseismic interferograms demonstrate that earthquake model parameters can be well recovered from two interferograms, acquired on ascending and descending tracks. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004GeoRL.3101607W&db_key=AST

Wright, T. J., B. Parsons, P. C. England, and E. J. Fielding (2004), InSAR Observations of Low Slip Rates on the Major Faults of Western Tibet, Science, 305, 236-239. Two contrasting views of the active deformation of Asia dominate the debate about how continents deform: (i) The deformation is primarily localized on major faults separating crustal blocks or (ii) deformation is distributed throughout the continental lithosphere. In the ﬁrst model, western Tibet is being extruded eastward between the major faults bounding the region. Surface displacement measurements across the western Tibetan plateau using satellite radar interferometry (InSAR) indicate that slip rates on the Karakoram and Altyn Tagh faults are lower than would be expected for the extrusion model and suggest a signiﬁcant amount of internal deformation in Tibet.

Wright, T. J., E. J. Fielding, B. E. Parsons, and P. C. England, Triggered slip: observations of the 17 August 1999 Izmit (Turkey) earthquake using radar interferometry, Geophys. Res. Lett., in press, 2000.

Wright, T. J., Z. Lu, and C. Wicks (2003), Source model for the Mw 6.7, 23 October 2002, Nenana Mountain Earthquake (Alaska) from InSAR, Geophysical Research Letters, 30. The 23 October 2002 Nenana Mountain Earthquake (Mw ~ 6.7) occurred on the Denali Fault (Alaska), to the west of the Mw ~ 7.9 Denali Earthquake that ruptured the same fault 11 days later. We used 6 interferograms, constructed using radar images from the Canadian Radarsat-1 and European ERS-2 satellites, to determine the coseismic surface deformation and a source model. Data were acquired on ascending and descending satellite passes, with incidence angles between 23 and 45 degrees, and time intervals of 72 days or less. Modeling the event as dislocations in an elastic half space suggests that there was nearly 0.9 m of right-lateral strike-slip motion at depth, on a near-vertical fault, and that the maximum slip in the top 4 km of crust was less than 0.2 m. The Nenana Mountain Earthquake increased the Coulomb stress at the future hypocenter of the 3 November 2002, Denali Earthquake by 30-60 kPa. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003GeoRL.30SDE12W&db_key=AST&high=41f192cbba08585

Wright, T., B. Parsons, and E. Fielding (2001a), Measurement of interseismic strain accumulation across the North Anatolian Fault by satellite radar interferometry, Geophys. Res. Lett., 28, 2117-2120.

Zebker, H. A., F. Amelung, and S. Jonsson, Remote sensing of volcano surface and internal processes using radar interferometry, in Remote Sensing of Active Volcanos, edited by P. Mouginis-Mark, 116, pp. 179-205, Amer. Geophys. Union, Washington, D.C., 179-205, 2000.

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