Interferometric Synthetic Aperture Radar Time Research Articles

Transition and Drivers of Elastic to Inelastic Deformation in the Abarkuh Plain From InSAR Multi‐Sensor Time Series and Hydrogeological Data

AbstractTracking the inelastic deformation of an aquifer is important to quantify the stress experienced by the aquifer system, so that the effects of the current extraction practices are put in the context of the hydrogeological settings of a region. However, transition of elastic to inelastic deformation is hard to be monitored, particularly in the Abarkuh Plain (AP) with a dry climate. In this study, we define the confined extent of aquifer system and track the spatial evolution of inelastic deformation based on the multi‐sensor Interferometric Synthetic Aperture Radar time series in the AP in central Iran from 2003 to 2020. Our results demonstrate that many locations with experiencing no significant inelastic deformation a few years ago are now deforming inelastically, leading to partially irreversible lowering of ground surface and loss of aquifer storage. Lithological data shows that total thickness of compacted clay units controls the extent and timing of observed inelastic deformation, while joint geodetic‐well data confirms that multi‐decadal dropping of head in the confined extents of aquifer system is driving the long‐term compaction. These results show that we are possibly near a tipping point between the sustainable conditions and permanent damage to underground water resources and the current decisions have the potential to permanently change the natural resources landscape.

Post‐Earthquake Fold Growth Imaged in the Qaidam Basin, China, With Interferometric Synthetic Aperture Radar

AbstractQuestions regarding the development of folds and their interactions with the seismic faults within thrust systems remain unanswered. However, estimating fault slip and earthquake hazards using surface observations and kinematic models of folding requires an understanding of how the shortening is accommodated during the different phases of the earthquake cycle. Here, we construct 16‐years of interferometric synthetic aperture radar time series across the North Qaidam thrust system (NE Tibet), where three Mw 6.3 earthquakes occurred along basement faults underlying shortened folded sediments. The analysis reveals spatio‐temporal changes of post‐earthquake surface displacement rates and patterns, which continue more than 10 years after the seismic events. The decomposition of the Sentinel‐1 ascending and descending line of sight velocities into vertical and shortening post‐earthquake components indicates that long‐term transient uplift and shortening is in agreement with the deformation that might be expected from kinematic models of folding. Long‐term uplift coincides spatially with young anticlines observed in the geomorphology, with steep gradients in the forelimbs, gentle gradients in the back‐limbs, an absence of subsidence in the footwalls, and higher gradients along interpreted bedding planes. Long‐term shortening is also different from the surface displacements expected for typical time‐varying creep on a narrow dislocation interface and shows rates higher than the average convergence across the whole region. These findings provide evidence for anelastic fold buckling during the post‐earthquake phase and highlight the contribution of distributed aseismic deformation to the growth of topography.

Assessment of land subsidence using interferometric synthetic aperture radar time series analysis and artificial neural network in a geospatial information system: case study of Rafsanjan Plain

Land subsidence resulting from groundwater extraction is a widely recurring phenomenon worldwide. To assess land subsidence, traditional methods such as numerical and finite element methods have limitations due to the complex interactions between the different constructor factors of aquifer in each area. We produced a groundwater-induced subsidence map by applying the geological and hydrogeological information of the aquifer system using an artificial neural network (ANN) combined with interferometric synthetic aperture radar (InSAR) and geospatial information system. The main problem with neural networks is providing the ground-truth dataset for training step. Therefore, the subsidence rate used as the network output was estimated using the InSAR time series analysis method. This study indicates the ANN approach is capable of knowing the mechanism of the land subsidence and can be used as a complementary of InSAR method to estimate the land subsidence with effective parameters and accessible data such as groundwater-level data especially in those areas in which measuring the subsidence was not feasible using InSAR. However, the results indicated that average groundwater depth and groundwater level decline were the most effective factors influencing subsidence in the study area using sensitivity analysis.

Reevaluating Volcanic Deformation Using Atmospheric Corrections: Implications for the Magmatic System of Agung Volcano, Indonesia

AbstractA major challenge in using satellite interferometry (interferometric synthetic aperture radar) for volcanic monitoring in the tropics is distinguishing volcano deformation from atmospheric noise. We reanalyzed interferometric synthetic aperture radar time series from 2007–2009 from Agung volcano, Indonesia, which had previously been used as evidence for unrest. Using uncorrected data, we find an apparent velocity of 5.0±2.7 cm/yr consistent with previous reports, but we show that this signal is consistent with predictions of atmospheric contributions derived from weather models (European Centre for Medium‐Range Weather Forecasts‐High‐Resolution). Following the correction, we find a velocity of 1.4±4.2 cm/yr and conclude that there was no significant deformation related to the inflation of a shallow magma source from 2007–2009. We discuss the implications for the inferred magma storage system at Agung and consider which other reported signals might have been wrongly attributed to deformation and should be reanalyzed.

Shallow Creep Along the 1999 Izmit Earthquake Rupture (Turkey) From GPS and High Temporal Resolution Interferometric Synthetic Aperture Radar Data (2011–2017)

AbstractCharacterizing the spatiotemporal evolution of creep is essential to constrain fault slip budget and understand creep mechanism. Studies based on interferometric synthetic aperture radar and Global Positioning System (GPS) satellite observations until 2012 have shown that the central segment of the 17 August 1999 Mw 7.4 Izmit earthquake on the North Anatolian Fault began slipping aseismically following the event. In the present study, we combine new interferometric synthetic aperture radar time series, based on TerraSAR‐X and Sentinel 1A/B radar images acquired over the period 2011–2017, with near‐field GPS measurement campaigns performed every 6 months from 2014 to 2016. The mean velocity fields reveal that creep on the central segment of the 1999 Izmit fault rupture continues to decay, more than 19 years after the earthquake, in overall agreement with models of postseismic afterslip decaying logarithmically with time for a long period of time. Along the fault section that experienced supershear velocity rupture during the Izmit earthquake creep continues with a rate up to ~ 8 mm/year. A significant transient accelerating creep is detected in December 2016 on the Sentinel‐1 time series, near the maximum creep rate location, associated with a total surface slip of 10 mm released in 1 month only. Additional analyses of the vertical velocity fields show a persistent subsidence on the hanging wall block of the Golcuk normal fault that also ruptured during the Izmit earthquake. Our results demonstrate that afterslip processes along the North Anatolian Fault east‐southeast of Istanbul are more complex than previously proposed as they vary spatiotemporally along the fault.

Viscous Accretionary Prisms: Viscoelastic Relaxation of the Makran Accretionary Prism Following the 2013 Baluchistan, Pakistan Earthquake

AbstractGeodetic observations of postseismic transients following earthquakes commonly help to inform the rheology of the lower crust and mantle, frictional properties of faults, and the kinematics of deformation across the earthquake cycle. Here we use interferometric synthetic aperture radar time series observations of postseismic deformation following the 2013 Mw 7.7 Baluchistan, Pakistan earthquake to investigate the viscoelastic rheology of the Makran accretionary prism. Using observations that began 15 months after the earthquake and a suite of potential fault geometries, we show that the ongoing deformation transient in the vicinity of the earthquake cannot be explained by afterslip alone. Instead, the gross spatial and temporal characteristics of the transient can be explained by viscoelastic relaxation of a shallow (>6 km) weak zone bounded by the Baluchistan earthquake and the underthrusting Arabian oceanic plate. Our first‐order results show that the viscoelastic lower accretionary prism has a thickness of 8–12 km and exhibits power law (n = 3.5) behavior with viscosities of 1017–1018 Pa·s. These estimated viscosities may be higher if afterslip occurred during the initial period of postseismic deformation not constrained by our observations. The power law rheology suggests that creep processes common at lower crustal and mantle temperatures may be active at comparatively lower temperatures in the Makran. We hypothesize that the weak nature of the Makran accretionary prism is driven by high pore fluid pressures introduced by underplated sediments and/or hydrocarbon development, and we show a mechanically weak accretionary prism may lead to overestimates of plate coupling when linear elasticity is assumed.

Observations of Aseismic Slip Driven by Fluid Pressure Following the 2016 Kaikōura, New Zealand, Earthquake

AbstractIn this paper we examine a short‐lived aseismic slip episode which began immediately following the 2016 Kaikōura earthquake in the South Island of New Zealand. Using synthetic aperture radar data, we form an interferometric synthetic aperture radar time series over the epicentral region of the Kaikōura mainshock. Immediately following the earthquake, we observe 150 mm of localized uplift over an ∼25‐km2 region which is best explained by an increase in pore pressure within a shallow fluid trap as a result of a coseismic permeability change. After the initial uplift stops, deformation becomes focused along a NE‐SW trending discontinuity which cuts through the uplifted region. The fault lies within a large (∼−4 MPa) stress shadow induced by the coseismic stress change suggesting that failure should be inhibited. However, a reduction in the effective normal stress caused by the local pore pressure increase was sufficient to induce a short‐lived aseismic slip episode.

Surface Creep Rate and Moment Accumulation Rate Along the Aceh Segment of the Sumatran Fault From L‐band ALOS‐1/PALSAR‐1 Observations

AbstractWe analyzed the interferometric synthetic aperture radar data from the ALOS‐1/PALSAR‐1 satellite to image the interseismic deformation along the Sumatran fault. The interferometric synthetic aperture radar time series analysis reveals up to ~20 mm/year of aseismic creep on the Aceh segment along the Northern Sumatran fault. This is a large fraction of the total slip rate across this fault. The spatial extent of the aseismic creep extends for ~100 km. The along‐strike variation of the aseismic creep has an inverse “U” shape. An analysis of the moment accumulation rate shows that the central part of the creeping section accumulates moment at approximately 50% of the rate of the surrounding locked segments. An initial analysis of temporal variations suggests that the creep rate may be decelerating with time, suggesting that the creep rate is adjusting to a stress perturbation from nearby seismic activity. Our study has implications to the earthquake hazard along the northern Sumatran fault.

Temporal changes in rock uplift rates of folds in the foreland of the Tian Shan and the Pamir from geodetic and geologic data

AbstractUnderstanding the evolution of continental deformation zones relies on quantifying spatial and temporal changes in deformation rates of tectonic structures. Along the eastern boundary of the Pamir‐Tian Shan collision zone, we constrain secular variations of rock uplift rates for a series of five Quaternary detachment‐ and fault‐related folds from their initiation to the modern day. When combined with GPS data, decomposition of interferometric synthetic aperture radar time series constrains the spatial pattern of surface and rock uplift on the folds deforming at decadal rates of 1–5 mm/yr. These data confirm the previously proposed basinward propagation of structures during the Quaternary. By fitting our geodetic rates and previously published geologic uplift rates with piecewise linear functions, we find that gradual rate changes over >100 kyr can explain the interferometric synthetic aperture radar observations where changes in average uplift rates are greater than ~1 mm/yr among different time intervals (~101, 104–5, and 105–6 years).

Tectonic and Anthropogenic Deformation at the Cerro Prieto Geothermal Step-Over Revealed by Sentinel-1A InSAR

The Cerro Prieto geothermal field (CPGF) lies at the step-over between the imperial and the Cerro Prieto faults in northern Baja California, Mexico. While tectonically this is the most active section of the southern San Andreas Fault system, the spatial and temporal deformation in the area is poorly resolved by the sparse global positioning system (GPS) network coverage. Moreover, interferograms from satellite observations spanning more than a few months are decorrelated due to the extensive agricultural activity in this region. Here we investigate the use of frequent, short temporal baseline interferograms offered by the new Sentinel-1A satellite to recover two components of deformation time series across these faults. Following previous studies, we developed a purely geometric approach for image alignment that achieves better than 1/200 pixel alignment needed for accurate phase recovery. We construct interferometric synthetic aperture radar time series using a coherence-based small baseline subset method with atmospheric corrections by means of common-point stacking. We did not apply enhanced spectral diversity because the burst discontinuities are generally small (<1.4 mm) and can be effectively captured during the atmospheric corrections. With these algorithms, the subsidence at CPGF is clearly resolved. The maximum subsidence rate of 160 mm/yr, due to extraction of geothermal fluids and heat, dominates the ~40 mm/yr deformation across the proximal ends of the imperial, the Cerro Prieto, and the indiviso faults.

Time‐dependent volcano source monitoring using interferometric synthetic aperture radar time series: A combined genetic algorithm and Kalman filter approach

Modern geodetic methods allow continuous monitoring of deformation fields of volcanoes. The acquired data contribute significantly to the study of the dynamics of magmatic sources prior to, during and after eruptions and intrusions. In addition to advancing the monitoring techniques, it is important to develop suitable approaches to deal with deformation time series. Here, we present, test and apply a new approach for time‐dependent, nonlinear inversion using a combination of a genetic algorithm (GA) and a Kalman filter (KF). The GA is used in the form presented by Shirzaei and Walter (2009), and the KF implementation now allows for the treatment of monitoring data as a full time series rather than as single time steps. This approach provides a flexible tool for assessing unevenly sampled and heterogeneous time series data and explains the deformation field using time‐consistent dislocation sources. Following synthetic tests, we demonstrate the merits of time‐consistent source modeling for interferometric synthetic aperture radar (InSAR) data available between 1992 and 2008 from the Campi Flegrei volcano in Italy. We obtained multiple episodes of linear velocity for the reservoir pressure change associated with a parabolic surface deformation on the volcano. These data may be interpreted via differential equations as a linear flux to the shallow reservoir that provides new insight into how both the shallow and deep reservoirs communicate beneath Campi Flegrei. The synthetic test and case study demonstrate the robustness of our approach and the ability to track and monitor the source of systems with complex dynamics. It is applicable to time‐dependent optimization problems in volcanic and tectonic environments in other tectonic environments in other areas and allows understanding of the spatiotemporal extent of a physical process in quantitative manner.

Inverting geodetic time series with a principal component analysis‐based inversion method

The Global Positioning System (GPS) system now makes it possible to monitor deformation of the Earth's surface along plate boundaries with unprecedented accuracy. In theory, the spatiotemporal evolution of slip on the plate boundary at depth, associated with either seismic or aseismic slip, can be inferred from these measurements through some inversion procedure based on the theory of dislocations in an elastic half‐space. We describe and test a principal component analysis‐based inversion method (PCAIM), an inversion strategy that relies on principal component analysis of the surface displacement time series. We prove that the fault slip history can be recovered from the inversion of each principal component. Because PCAIM does not require externally imposed temporal filtering, it can deal with any kind of time variation of fault slip. We test the approach by applying the technique to synthetic geodetic time series to show that a complicated slip history combining coseismic, postseismic, and nonstationary interseismic slip can be retrieved from this approach. PCAIM produces slip models comparable to those obtained from standard inversion techniques with less computational complexity. We also compare an afterslip model derived from the PCAIM inversion of postseismic displacements following the 2005 8.6 Nias earthquake with another solution obtained from the extended network inversion filter (ENIF). We introduce several extensions of the algorithm to allow statistically rigorous integration of multiple data sources (e.g., both GPS and interferometric synthetic aperture radar time series) over multiple timescales. PCAIM can be generalized to any linear inversion algorithm.