Coseismic DInSAR Analysis of the 2020 Petrinja Earthquake Sequence

Interferometric SAR analysis provides an excellent opportunity to perform large-scale and rapid coseismic deformation mapping. Between December 28-30, 2020, three earthquakes with magnitudes greater than 4.3 occurred during the 2020 Petrinja Earthquake Sequence near Petrinja in Croatia, resulting in significant coseismic deformation. Considering both the available ascending and descending Sentinel-1A/B images preceding and following the Petrinja Earthquake Sequence, 2.5D differential interferometric analysis was performed to determine the resulting deformation field, which have significant importance in civil engineering related countermeasures and hazard assessment. With the applied methodology, the derived horizontal and vertical deformation fields can be characterized by a maximum of ±0.43 m local East-West, a maximum of 0.15 m local subsidence and a maximum of 0.19 m local vertical uplift near Petrinja

Fusion of remotely sensed displacement measurements: current status and challenges

International audienc

Measuring Coseismic Deformation With Spaceborne Synthetic Aperture Radar: A Review

In the past 25 years, space-borne Synthetic Aperture Radar imagery has become an increasingly available data source for the study of crustal deformation associated with moderate to large earthquakes (M > 4.0). Coseismic surface deformation can be measured with several well-established techniques, the applicability of which depends on the ground displacement pattern, on several radar parameters, and on the surface properties at the time of the radar acquisitions. The state-of-the-art concerning the measurement techniques is reviewed, and their application to over 100 case-studies since the launch of the Sentinel-1a satellite is discussed, including the performance of the different methods and the data processing aspects, which still constitute topics of ongoing research

Measuring and modelling the earthquake deformation cycle at continental dip-slip faults

In order for an earthquake to become a natural disaster, it needs to be significantly large, close to vulnerable populations or both. The largest earthquakes in the world occur in subduction zones, where cool, shallowly dipping fault planes enable brittle failure over a large area. However, these earthquakes often occur far away from major cities, reducing their impact. Similar, low angle fault planes can be found in continental fold and thrust belts, where sub-horizontal decollements offer large potential rupture areas. These seismic sources are often much closer to major urban centres than off-shore subduction zone sources. It is therefore essential to understand the processes that control how strain is accommodated and released in such settings. Much of our current understanding of the earthquake cycle comes from studying strike-slip faults. Can our knowledge of strike-slip faults be transferred over to dip-slip faults, and in particular, fold and thrust belts? Previous work has suggested that there may be significant differences between strike-slip and dip-slip settings, and therefore further study of the earthquake cycle in dip-slip environments is required. The recent launch of Sentinel-1, and the extensive Synthetic Aperture Radar (SAR) archive of the European Space Agency (ESA), offer an opportunity to obtain measurements of strain in dip-slip environments that can contribute to our understanding. In this thesis, I use geodetic measurements to contribute to our understanding of the earthquake cycle. Enhanced surface deformation rates following earthquakes (so called postseismic deformation) show temporal and spatial variation. Such variation can be used to investigate the material properties of faults and the surrounding medium. I collate measurements of postseismic velocity following contintental earthquakes to examine the temporal evolution of strain following an earthquake over multiple timescales. The compilation show a simple relationship, with velocity inversely proportional to time since the earthquake. This relationship holds for all fault types, with no significant difference between dip-slip and strike-slip environments. Such lack of difference implies that, at least in terms of the temporal evolution of near field postseismic deformation, both environments behave similarly. I compare these measurements with the predictions of various models that are routinely used to explain postseismic deformation. I find that the results are best explained using either rate-strengthening afterslip or power-law creep in a shear zone with high stress exponent. Such a relationship indicates that fault zone processes dominate the near-field surface deformation field from hours after an earthquake to decades later. This implies that using such measurements to determine the strength of the bulk lithosphere should only be done with caution. I then collate geodetic measurements from throughout the earthquake cycle in the Nepal Himalaya to constrain the geometry and frictional properties of the fault system. I use InSAR to measure postseismic deformation following the 2015 Mw~7.8 Gorkha earthquake and combine this with Global Navigation Satellite System (GNSS) displacements to infer the predominance of down-dip afterslip. I then combine these measurements with coseismic and interseismic geodetic data to determine fault geometries which are capable of simultaneously explaining all three data sets. Unfortunately, the geodetic data alone cannot determine the most appropriate geometry. It is therefore necessary to combine such measurements with other relevant data, along with the expertise to understand the uncertainties in each data set. Such combined measurements ought to be understood using physically consistent models. I developed a mechanically coupled coseismic-postseismic inversion, based on rate and state friction. The model simultaneously inverts the coseismic and postseismic surface deformation field to determine the range of frictional properties and coseismic slip which can explain the data within uncertainties. I applied this model to the geodetic data compilation in Nepal and obtained a range of values for the rate-and-state 'a' parameter between 0.8 - 1.6 x 10^-3, depending on the geometry used. Whilst the Nepal Himalaya is well instrumented, many continental collision zones suffer from a severe lack of data. The Sulaiman fold and thrust belt is one such region, with very sparse GNSS data, but significant seismicity. I apply InSAR to part of the Sulaiman fold and thrust belt near Sibi to examine the evolution of strain throughout the seismic cycle. I tie together observations from ERS, Envisat and Sentinel-1 to produce a time series of displacements over 25 years long which covers an earthquake which occurred in 1997. Using this time series, I investigate the contributions of different parts of the earthquake cycle to the development of topography. I find that postseismic deformation plays a clear role in the construction of short wavelength folds, and that the combination of coseismic and postseismic deformation can reproduce the topography over a variety of lengthscales. The shape of the frontal section of the fold and thrust belt, including the gradient of the topography, is roughly reproduced in a single earthquake cycle. This suggests that fold and thrust belts can maintain their taper in a single earthquake cycle, rather than through earthquakes occurring at different points throughout the belt. I find that approximately 1000 earthquakes like the 1997 event, along with associated postseismic deformation, can reproduce the topography seen today to first order. Such a result may aid our use of topography as a long-term record of earthquake cycle deformation. I finish by drawing these various findings together and commenting on common themes. Afterslip plays an important role in the earthquake cycle, contributing to the surface deformation field in multiple locations, over multiple timescales, and generating topography. This afterslip can be explained using a rate-strengthening friction law with a*sigma between 0.2 and 1.54 MPa. Combining this rate dependence with the static coefficient of friction determined from other methods, such as critical taper analysis, would enable a more complete picture of fault friction to be determined. Fault geometry in fold and thrust belts may control the size of potential ruptures, with junctions and changes in dip angle potentially arresting ruptures. In order to fully determine the role of fault geometry and friction in controlling the earthquake cycle in dip-slip settings, I suggest a more thorough exploitation of the wealth of InSAR data which is now available. These data then need to be combined with measurements from other fields, and models produced which are consistent within the uncertainties of each data set. I suggest that measurements of topography and insights from structural geology may help with understanding the long term and short term processes governing earthquake patterns in an area. As both observations and models are developed, interdisciplinary teams may be able to better constrain the key controls on earthquake hazard in continental dip-slip settings

Along-Track Displacement of Mw 7.8 and 7.6 Kahramanmaraş Earthquakes from Sentinel-1 Offset Tracking and Burst Overlap Interferometry

On 6th February, a pair of significant earthquakes with magnitudes of 7.8 and 7.6 struck Kahramanmaraş, Turkey. The Earthquake InSAR Data Provider (EIDP) promptly produced interferograms and offset tracking results within 3 hours of acquiring Sentinel-1 satellite data. However, it was challenging to unwrap the interferograms correctly due to high displacement gradient near the rupture. Hence, early displacement fields were derived from Pixel Offset Tracking (POT) method both in range and azimuth direction with low resolution depending on pixel sizes of Sentinel-1. We used the Burst Overlap Interferometry (BOI) method to extract the accurate along-track displacement and unwrapped the BOI interferogram using Azimuth Offset Tracking (AOT) data as a guide. Combining the unwrapped BOI interferogram and the AOT data, we derive a high-quality along-track displacement field that illuminates the entire earthquake rupture over 300 km and exhibits ±4 m displacement in the along-track direction

Autonomous Extraction of Millimeter-scale Deformation in InSAR Time Series Using Deep Learning

Systematic characterization of slip behaviours on active faults is key to unraveling the physics of tectonic faulting and the interplay between slow and fast earthquakes. Interferometric Synthetic Aperture Radar (InSAR), by enabling measurement of ground deformation at a global scale every few days, may hold the key to those interactions. However, atmospheric propagation delays often exceed ground deformation of interest despite state-of-the art processing, and thus InSAR analysis requires expert interpretation and a priori knowledge of fault systems, precluding global investigations of deformation dynamics. Here we show that a deep auto-encoder architecture tailored to untangle ground deformation from noise in InSAR time series autonomously extracts deformation signals, without prior knowledge of a fault's location or slip behaviour. Applied to InSAR data over the North Anatolian Fault, our method reaches 2 mm detection, revealing a slow earthquake twice as extensive as previously recognized. We further explore the generalization of our approach to inflation/deflation-induced deformation, applying the same methodology to the geothermal field of Coso, California

Characterization of Ground Deformation Associated with Shallow Groundwater Processes Using Satellite Radar Interferometry

Shallow groundwater processes maylead to ground deformation and even geohazards. With the features of day-and-night accessibility and large-scale coverage, time-series interferometric synthetic aperture radar (InSAR) has proven a useful tool for mapping the deformation over various landscapes at cm to mm level with weekly to monthly updates. However, it has limitations such as, decorrelation,atmospheric artifacts, topographic errors, andunwrapping errors, in particular for the hilly, vegetated, and complicated deformation patterns. In this dissertation, I focus on characterizing the ground deformation over landslides, aquifer systems, and mine tailings impoundment, using the designed advanced time-series InSAR strategy, as well as theinterdisciplinary knowledge of geodesy, hydrology, geophysics, and geology. Northwestern USA has been exposed to extreme landslide hazards due to steep terrain, high precipitation, and loose root support after wildfire. I characterize the rainfall-triggered movements of Crescent Lake landslide, Washington State. The seasonal deformation at the lobe, with larger magnitudes than the downslope riverbank, suggests an amplified hydrological loading effect due to a thicker unconsolidated zone. High-temporal-resolution InSAR and GPS data reveal dynamic landslide motions. Threshold rainfall intensities and durations wet seasons have been associated with observed movement upon shearing: antecedent rainfall triggered precursory slope-normal subsidence, and the consequent increase in pore pressure at the basal surface reduces friction and instigates downslope slip over the course of less than one month. In addition, a quasi-three-dimensional deformation field is created using multiple spaceborne InSAR observations constrained by the topographical slope, and is further used to invert for the complex geometry of landslide basal surface based on mass conservation. Aquifer skeletons deform in response to hydraulic head changes with various time scales of delay and sensitivity. I investigate the spatio-temporal correlation among deformation, hydrological records and earthquake records over Salt Lake Valley, Utah State. A clear long-term and seasonal correlation exists between surface uplift/subsidence and groundwater recharge/discharge, allowing me to quantify hydrogeological properties. Long-term uplift reflects the net pore pressure increase associated with prolonged water recharge, probably decades ago. The distributions of previously and newly mapped faults suggest that the faultsdisrupt the groundwater flow andpartition hydrological units. Mine tailings gradual settle as the pore pressure dissipates and the terrain subsides, andtailings embankment failures can be extremely hazardous. I investigate the dynamics of consolidation settlement over the tailings impoundment in the vicinity of Great Salt Lake, Utah State, as well as its associated impacts to the surrounding infrastructures. Largest subsidence has been observed around the low-permeable decant pond clay at the northeast corner.The geotechnical consolidation model reveals and predicts the long-term exponentially decaying settlement process. My studies have demonstrated that InSAR methods can advance our understanding about the potential anthropogenic impacts and natural hydrological modulations on various geodynamic settings in geodetic time scale

Coseismic deformation observed with radar interferometry: Great earthquakes and atmospheric noise

Spatially dense maps of coseismic deformation derived from Interferometric Synthetic Aperture Radar (InSAR) datasets result in valuable constraints on earthquake processes. The recent increase in the quantity of observations of coseismic deformation facilitates the examination of signals in many tectonic environments associated with earthquakes of varying magnitude. Efforts to place robust constraints on the evolution of the crustal stress field following great earthquakes often rely on knowledge of the earthquake location, the fault geometry, and the distribution of slip along the fault plane. Well-characterized uncertainties and biases strengthen the quality of inferred earthquake source parameters, particularly when the associated ground displacement signals are near the detection limit. Well-preserved geomorphic records of earthquakes offer additional insight into the mechanical behavior of the shallow crust and the kinematics of plate boundary systems. Together, geodetic and geologic observations of crustal deformation offer insight into the processes that drive seismic cycle deformation over a range of timescales. In this thesis, I examine several challenges associated with the inversion of earthquake source parameters from SAR data. Variations in atmospheric humidity, temperature, and pressure at the timing of SAR acquisitions result in spatially correlated phase delays that are challenging to distinguish from signals of real ground deformation. I characterize the impact of atmospheric noise on inferred earthquake source parameters following elevation-dependent atmospheric corrections. I analyze the spatial and temporal variations in the statistics of atmospheric noise from both reanalysis weather models and InSAR data itself. Using statistics that reflect the spatial heterogeneity of atmospheric characteristics, I examine parameter errors for several synthetic cases of fault slip on a basin-bounding normal fault. I show a decrease in uncertainty in fault geometry and kinematics following the application of atmospheric corrections to an event spanned by real InSAR data, the 1992 M5.6 Little Skull Mountain, Nevada, earthquake. Finally, I discuss how the derived workflow could be applied to other tectonic problems, such as solving for interseismic strain accumulation rates in a subduction zone environment. I also study the evolution of the crustal stress field in the South American plate following two recent great earthquakes along the Nazca- South America subduction zone. I show that the 2010 Mw 8.8 Maule, Chile, earthquake very likely triggered several moderate magnitude earthquakes in the Andean volcanic arc and backarc. This suggests that great earthquakes modulate the crustal stress field outside of the immediate aftershock zone and that far-field faults may pose a heightened hazard following large subduction earthquakes. The 2014 Mw 8.1 Pisagua, Chile, earthquake reopened ancient surface cracks that have been preserved in the hyperarid forearc setting of northern Chile for thousands of earthquake cycles. The orientation of cracks reopened in this event reflects the static and likely dynamic stresses generated by the recent earthquake. Coseismic cracks serve as a reliable marker of permanent earthquake deformation and plate boundary behavior persistent over the million-year timescale. This work on great earthquakes suggests that InSAR observations can play a crucial role in furthering our understanding of the crustal mechanics that drive seismic cycle processes in subduction zones

Improved surface displacement estimation through stacking cross-correlation spectra from multi-channel imagery

Studying sporadic and complex geophysical surface flows, like earthquakes or sea surface circulation, are challenging cases. If a satellite is able to image an event, it becomes essential to pull out as much information as possible. In this contribution we demonstrate a method to increase the coverage and signal-to-noise ratio for displacement estimation, making such surface flow estimates more complete. We leverage upon the redundant offset information acquired by multi-channel push-broom imagery. The individual cross-correlation spectra (cross power spectral density; Fourier transform of the cross-correlation function) of different spectral bands are averaged in the frequency domain before sub-pixel offset-estimation by phase-plane fitting. The method is demonstrated near Kaikōura, where in 2016 a surface rupture occurred. RapidEye data from two different dates were used to reconstruct the displacement. In addition, the circulation along the coast is estimated from data from a single date where multiple spectral bands were acquired within seconds which made stacking of cross-correlation spectra possible. The demonstrated methodology is applied to data from the already decommissioned RapidEye constellation, but can be adopted to other pushbroom systems, such as the Landsat legacy or Sentinel-2