Using GPS as a reference frame for SAR images applied to a post eruptive period for Okmok Volcano, Aleutian Islands, Alaska

While high spatial coverage makes InSAR a popular tool to study active volcanoes its use can possess challenges for certain environments. Volcanoes along Alaska's Aleutian chain are difficult targets for InSAR as their seasonal snow cover causes decorrelation close to the volcanic caldera, their exposed location in the North Pacific renders them prone to severe atmospheric phase artifacts, and their location on small islands prevents the selection of suitable reference points necessary for deformation analysis. Existing GPS networks define a known reference frame in which SAR is better understood. Okmok volcano is one of the most active volcanoes in the Aleutian Island Chain and shows significant non-linear deformation behavior as it progresses through its eruption cycles. A stack of L-band imagery acquired by the SAR sensor PALSAR on board the JAXA Advanced Land Observing Satellite produced a post eruption deformation time series between August 2008 and October 2010. This data along with a merged DEM comprised of AirSAR SRTM and Worldview-1 stereo pair data, and GPS data from 3 continuous and 3 post eruption campaign sites was used for this study. In this research, a comparison and combination of InSAR and GPS time-series data will be presented aimed at the following research goals: 1) What is the accuracy and precision of InSAR-derived deformation estimates in such challenging environments; 2) How accurate can the deformation of the InSAR reference point be estimated from a joint analysis of InSAR and GPS deformation signals; 3) How non-linear volcanic deformation can be constrained by the measurements of a local GPS network and support the identification of residual atmospheric signals in InSAR-derived deformation time series. Further research into the combination of GPS and InSAR applied to the nonlinear aspect of volcanic deformation can enhance geodetic modeling of the volcano and associated eruption processes

High quality InSAR data linked to seasonal change in hydraulic head for an agricultural area in the San Luis Valley, Colorado

In the San Luis Valley (SLV), Colorado legislation passed in 2004 requires that hydraulic head levels in the confined aquifer system stay within the range experienced in the years 1978–2000. While some measurements of hydraulic head exist, greater spatial and temporal sampling would be very valuable in understanding the behavior of the system. Interferometric synthetic aperture radar (InSAR) data provide fine spatial resolution measurements of Earth surface deformation, which can be related to hydraulic head change in the confined aquifer system. However, change in cm-scale crop structure with time leads to signal decorrelation, resulting in low quality data. Here we apply small baseline subset (SBAS) analysis to InSAR data collected from 1992 to 2001. We are able to show high levels of correlation, denoting high quality data, in areas between the center pivot irrigation circles, where the lack of water results in little surface vegetation. At three well locations we see a seasonal variation in the InSAR data that mimics the hydraulic head data. We use measured values of the elastic skeletal storage coefficient to estimate hydraulic head from the InSAR data. In general the magnitude of estimated and measured head agree to within the calculated error. However, the errors are unacceptably large due to both errors in the InSAR data and uncertainty in the measured value of the elastic skeletal storage coefficient. We conclude that InSAR is capturing the seasonal head variation, but that further research is required to obtain accurate hydraulic head estimates from the InSAR deformation measurements

Some thoughts on the use of InSAR data to constrain models of surface deformation: Noise structure and data downsampling

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

Unrest at Domuyo Volcano, Argentina, detected by geophysical and geodetic data and morphometric analysis

New volcanic unrest has been detected in the Domuyo Volcanic Center (DVC), to the east of the Andes Southern Volcanic Zone in Argentina. To better understand this activity, we investigated new seismic monitoring data, gravimetric and magnetic campaign data, and interferometric synthetic aperture radar (InSAR) deformation maps, and we derived an image of the magma plumbing system and the likely source of the unrest episode. Seismic events recorded during 2017-2018 nucleate beneath the southwestern flank of the DVC. Ground deformation maps derived from InSAR processing of Sentinel-1 data exhibit an inflation area exceeding 300 km2, from 2014 to at least March 2018, which can be explained by an inflating sill model located 7 km deep. The Bouguer anomaly reveals a negative density contrast of ~35 km wavelength, which is spatially coincident with the InSAR pattern. Our 3D density modeling suggests a body approximately 4-6 km deep with a density contrast of -550 kg/m3. Therefore, the geophysical and geodetic data allow identification of the plumbing system that is subject to inflation at these shallow crustal depths. We compared the presence and dimensions of the inferred doming area to the drainage patterns of the area, which support long-established incremental uplift according to morphometric analysis. Future studies will allow us to investigate further whether the new unrest is hydrothermal or magmatic in origin.Fil: Astort, Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Walter, Thomas R. German Research Centre for Geosciences; AlemaniaFil: Ruiz, Francisco. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; ArgentinaFil: Sagripanti, Lucía. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Nacif, Andres Antonio. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; ArgentinaFil: Acosta, Gemma. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Folguera Telichevsky, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin

Geodetic, teleseismic, and strong motion constraints on slip from recent southern Peru subduction zone earthquakes

We use seismic and geodetic data both jointly and separately to constrain coseismic slip from the 12 November 1996 M_w 7.7 and 23 June 2001 M_w 8.5 southern Peru subduction zone earthquakes, as well as two large aftershocks following the 2001 earthquake on 26 June and 7 July 2001. We use all available data in our inversions: GPS, interferometric synthetic aperture radar (InSAR) from the ERS-1, ERS-2, JERS, and RADARSAT-1 satellites, and seismic data from teleseismic and strong motion stations. Our two-dimensional slip models derived from only teleseismic body waves from South American subduction zone earthquakes with M_w > 7.5 do not reliably predict available geodetic data. In particular, we find significant differences in the distribution of slip for the 2001 earthquake from models that use only seismic (teleseismic and two strong motion stations) or geodetic (InSAR and GPS) data. The differences might be related to postseismic deformation or, more likely, the different sensitivities of the teleseismic and geodetic data to coseismic rupture properties. The earthquakes studied here follow the pattern of earthquake directivity along the coast of western South America, north of 5°S, earthquakes rupture to the north; south of about 12°S, directivity is southerly; and in between, earthquakes are bilateral. The predicted deformation at the Arequipa GPS station from the seismic-only slip model for the 7 July 2001 aftershock is not consistent with significant preseismic motion

Mass movement susceptibility mapping using satellite optical imagery compared with InSAR monitoring: Zigui County, Three Gorges region, China

Mass movements on steep slopes are a major hazard to communities and infrastructure in the Three Gorges region, China. Developing susceptibility maps of mass movements is therefore very important in both current and future land use planning. This study employed satellite optical imagery and an ASTER GDEM (15 m) to derive various parameters (namely geology; slope gradient; proximity to drainage networks and proximity to lineaments) in order to create a GIS-based map of mass movement susceptibility. This map was then evaluated using highly accurate deformation signals processed using the Persistent Scatterer (PS) InSAR technique. Areas of high susceptibility correspond well to points of high subsidence, which provides a strong support of our susceptibility map

Constraints on fault and lithosphere rheology from the coseismic slip and postseismic afterslip of the 2006 M_w 7.0 Mozambique earthquake

The 2006 M_w 7.0 Mozambique (Machaze) normal-faulting earthquake ruptured an unusually steeply dipping fault plane (~75°). The amount of slip in the earthquake decreased from depths of ~10 km toward the surface, and this shallow slip deficit was at least partly recovered by postseismic afterslip on the shallow part of the fault plane. An adjacent normal fault segment slipped postseismically (and possibly also co-seismically) at shallow depths with a large strike-slip component, in response to the stresses generated by slip on the main earthquake fault plane. Our observations suggest that the fault zone behaves in a stick-slip manner in the crystalline basement, and that where it cuts the sedimentary layer the coseismic rupture was partially arrested and there was significant postseismic creep. We discuss the effects of such behavior on the large-scale tectonics of continental regions, and on the assessment of seismic hazard on similar fault systems. The steep dip of the fault suggests the re-activation of a preexisting structure with a coefficient of friction at least ~25–45% lower than that on optimally oriented planes, and analysis of the deformation following an aftershock indicates that the value of the parameter ‘a’ that describes the rate-dependence of fault friction lies in the range 1 × 10^(−3)–2 × 10^(−2). The lack of long-wavelength postseismic relaxation suggests viscosities in the ductile lithosphere of greater than ~2 × 10^(19) Pa s, and an examination of the tectonic geomorphology in the region identifies ways in which similar fault systems can be identified before they rupture in future earthquakes

Slip distribution of the 2017 M(w)6.6 Bodrum-Kos earthquake: resolving the ambiguity of fault geometry

SUMMARY The 2017 July 20, Mw6.6 Bodrum–Kos earthquake occurred in the Gulf of Gökova in the SE Aegean, a region characterized by N–S extension in the backarc of the easternmost Hellenic Trench. The dip direction of the fault that ruptured during the earthquake has been a matter of controversy where both north- and south-dipping fault planes were used to model the coseismic slip in previous studies. Here, we use seismic (seismicity, main shock modelling, aftershock relocations and aftershock mechanisms using regional body and surface waves), geodetic (GPS, InSAR) and structural observations to estimate the location, and the dip direction of the fault that ruptured during the 2017 earthquake, and the relationship of this event to regional tectonics. We consider both dip directions and systematically search for the best-fitting locations for the north- and south-dipping fault planes. Comparing the best-fitting planes for both dip directions in terms of their misfit to the geodetic data, proximity to the hypocenter location and Coulomb stress changes at the aftershock locations, we conclude that the 2017 earthquake ruptured a north-dipping fault. We find that the earthquake occurred on a 20–25 km long, ∼E–W striking, 40° north-dipping, pure normal fault with slip primarily confined between 3 and 15 km depth, and the largest slip exceeding 2 m between depths of 4 and 10 km. The coseismic fault, not mapped previously, projects to the surface within the western Gulf, and partly serves both to widen the Gulf and separate Kos Island from the Bodrum Peninsula of SW Anatolia. The coseismic fault may be an extension of a mapped, north-dipping normal fault along the south side of the Gulf of Gökova. While all of the larger aftershocks are consistent with N–S extension, their spatially dispersed pattern attests to the high degree of crustal fracturing within the basin, due to rapid trenchward extension and anticlockwise rotation within the southeastern Aegean

Slip in the 2010–2011 Canterbury earthquakes, New Zealand

The 3rd September 2010 Mw 7.1 Darfield and 21st February 2011 Mw 6.3 Christchurch (New Zealand) earthquakes occurred on previously unknown faults. We use InSAR ground displacements, SAR amplitude offsets, field mapping, aerial photographs, satellite optical imagery, a LiDAR DEM and teleseismic body-wave modeling to constrain the pattern of faulting in these earthquakes. The InSAR measurements reveal slip on multiple strike-slip segments and secondary reverse faults associated with the Darfield main shock. Fault orientations are consistent with those expected from the GPS-derived strain field. The InSAR line-of-sight displacement field indicates the main fault rupture is about 45 km long, and is confined largely to the upper 10 km of the crust. Slip on the individual fault segments of up to 8 m at 4 km depth indicate stress drops of 6–10 MPa. In each event, rupture initiated on a reverse fault segment, before continuing onto a strike-slip segment. The non-double couple seismological moment tensors for each event are matched well by the sum of double couple equivalent moment tensors for fault slip determined by InSAR. The slip distributions derived from InSAR observations of both the Darfield and Christchurch events show a 15-km-long gap in fault slip south-west of Christchurch, which may present a continuing seismic hazard if a further unknown fault structure of significant size should exist there

Evidence for postseismic deformation of the lower crust following the 2004 Mw6.0 Parkfield earthquake

Previous studies have shown that postseismic relaxation following the 2004 Mw6.0 Parkfield, CA, earthquake is dominated by afterslip. However, we show that some fraction of the afterslip inferred from kinematic inversion to have occurred immediately below the seismically ruptured area may in fact be a substitute for viscous postseismic deformation of the lower crust. Using continuous GPS and synthetic aperture radar interferometry, we estimate the relative contribution of shallow afterslip (at depth less than 20km) and deeper seated deformation required to account for observed postseismic surface displacements. Exploiting the possible separation in space and time of the time series of displacements predicted from viscoelastic relaxation, we devise a linear inversion scheme that allows inverting jointly for the contribution of afterslip and viscoelastic flow as a function of time. We find that a wide range of models involving variable amounts of viscoelastic deformation can fit the observations equally well provided that they allow some fraction of deep-seated deformation (at depth larger than ∼20 km). These models require that the moment released by postseismic relaxation over 5 years following the earthquake reached nearly as much as 200% of the coseismic moment. All the models show a remarkable complementarity of coseismic and shallow afterslip distributions. Some significant deformation at lower crustal depth (20–26 km) is required to fit the geodetic data. The condition that postseismic deformation cannot exceed complete relaxation places a constraint on the amount of deep seated deformation. The analysis requires an effective viscosity of at least ~10^(18) Pa s of the lower crust (assuming a semi-infinite homogeneous viscous domain). This deep-seated deformation is consistent with the depth range of tremors which also show a transient postseismic response and could explain as much as 50% of the total postseismic geodetic moment (the remaining fraction being due to afterslip at depth shallower than 20 km). Lower crustal postseismic deformation could reflect a combination of localized ductile deformation and aseismic frictional sliding