Integration of InSAR time series analysis and water vapour correction for mapping postseismic deformation after the 2003 Bam (Iran) Earthquake

Atmospheric water-vapor effects represent a major limitation of interferometric synthetic aperture radar (InSAR) techniques, including InSAR time-series (TS) approaches (e.g., persistent or permanent scatterers and small-baseline subset). For the first time, this paper demonstrates the use of InSAR TS with precipitable water-vapor (InSAR TS + PWV) correction model for deformation mapping. We use MEdium Resolution Imaging Spectrometer (MERIS) near-infrafred (NIR) water-vapor data for InSAR atmospheric correction when they are available. For the dates when the NIR data are blocked by clouds, an atmospheric phase screen (APS) model has been developed to estimate atmospheric effects using partially water-vapor-corrected interferograms. Cross validation reveals that the estimated APS agreed with MERIS-derived line-of-sight path delays with a small standard deviation (0.3–0.5 cm) and a high correlation coefficient (0.84–0.98). This paper shows that a better TS of postseismic motion after the 2003 Bam (Iran) earthquake is achievable after reduction of water-vapor effects using the InSAR TS + PWV technique with coincident MERIS NIR water-vapor data

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

Deformation monitoring of high-latitude permafrost region of northeastern China with time series inSAR technique

Abstract. Permafrost distributed in northeast China is the only high-altitude permafrost in China. The deformation monitoring over this permafrost region is of great importance to local climate change and ecological environments. This study focuses on the deformation monitoring of high-latitude permafrost in northeast China with time series InSAR technique. The spatial distribution characteristics, the annual deformation rates and the temporal deformation evolutions of permafrost could be retrieved from multi-temporal InSAR processing with Sentinel-1 TOPS datasets. This work concludes that time series InSAR technique could help to retrieve a comprehensive and reliable permafrost deformation, while a long time-series of displacements facilitated to better understand permafrost kinematics.</p

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

Earth Observation for Crustal Tectonics and Earthquake Hazards

In this paper, we illustrate some of the current methods for the exploitation of data from Earth Observing satellites to measure and understand earthquakes and shallow crustal tectonics. The aim of applying such methods to Earth Observation data is to improve our knowledge of the active fault sources that generate earthquake shaking hazards. We provide examples of the use of Earth Observation, including the measurement and modelling of earthquake deformation processes and the earthquake cycle using both radar and optical imagery. We also highlight the importance of combining these orbiting satellite datasets with airborne, in situ and ground-based geophysical measurements to fully characterise the spatial and timescale of temporal scales of the triggering of earthquakes from an example of surface water loading. Finally, we conclude with an outlook on the anticipated shift from the more established method of observing earthquakes to the systematic measurement of the longer-term accumulation of crustal strain

Modelling co- and post-seismic displacements revealed by InSAR, and their implications for fault behaviour

The ultimate goal of seismology is to estimate the timing, magnitude and potential spatial extent of future seismic events along pre-existing faults. Based on the rate-state friction law, several theoretical physical earthquake models have been proposed towards this goal. Tectonic loading rate and frictional properties of faults are required in these models. Modern geodetic observations, e.g. GPS and InSAR, have provided unprecedented near-field observations following large earthquakes. In theory, according to the frictional rate and state asperity earthquake model, velocity-weakening regions holding seismic motions on faults should be separated with velocity-strengthening regions within which faults slip only aseismically. However, early afterslip following the 2011 MW 9.1 Tohoku-Oki earthquake revealed from GPS measurements was largely overlaid on the historical rupture zones, which challenged the velocity weakening asperity model. Therefore, the performance of the laboratory based friction law in the natural events needs further investigation, and the factors that may affect the estimates of slip models through geodetic modelling should also be discussed systematically. In this thesis, several moderate-strong events were investigated in order to address this important issue. The best-fit co- and post-seismic slip models following the 2009 MW 6.3 Haixi, Qinghai thrust-slip earthquake determined by InSAR deformation time-series suggest that the maximum afterslip is concentrated in the same area as the coseismic slip model, which is similar to the patterns observed in the 2011 Japan earthquake. In this case, complex geometric asperity may play a vital role in the coseismic nucleation and postseismic faulting. The major early afterslip after the 2011 MW 7.1 Van mainshock, which was revealed by one COSMO-SkyMed postseismic interferogram, is found just above the coseismic slip pattern. In this event, a postseismic modelling that did not allow slip across the coseismic asperity was also tested, suggesting that the slip model without slip in the asperities can explain the postseismic observations as well as the afterslip model without constraints on slip in the asperities. In the 2011 MW 9.1 Tohoku-Oki earthquake, a joint inversion with the GRACE coseismic gravity changes and inland coseismic GPS observations was conducted to re-investigate the coseismic slip model of the mainshock. A comparison of slip models from these different datasets suggests that significant variations of slip models can be observed, particularly the locations of the maximum slips. The joint slip model shows that the maximum slip of ~42 m appears near the seafloor surface close to the Japan Trench. Meanwhile, the accumulative afterslip patterns (slip >2 m) determined in previous studies appear in spatial correlation with the Coulomb stress changes generated using the joint slip model. As a strike-slip faulting event, the 2011 MW 6.8 Yushu earthquake was also investigated through co- and post-seismic modelling with more SAR data than was used in previous study. Best slip models suggest that the major afterslip is concentrated in shallow parts of the faults and between the two major coseismic slip patterns, suggesting that the performance of the rate and state frictional asperity model is appropriate in this event. Other postseismic physical mechanisms, pore-elastic rebound and viscoelastic relaxation have also been examined, which cannot significantly affect the estimate of the shallow afterslip model in this study. It is believed that the shallow afterslip predominantly controlled the postseismic behaviour after the mainshock in this case. In comparison to another 21 earthquakes investigated using geodetic data from other studies, complementary spatial extents between co- and post-seismic slip models can be identified. The 2009 MW 6.3 Qinghai earthquake is an exceptional case, in which the faulting behaviours might be dominated by the fault structure (e.g. fault bending). In conclusion, the major contributions from this thesis include: 1) the friction law gives a first order fit in most of natural events examined in this thesis; 2) geometric asperities may play an important role in faulting during earthquake cycles; 3) significant uncertainties in co- and post-seismic slip models can appreciably bias the estimation of fault frictional properties; 4) new insights derived from each earthquake regarding their fault structures and complex faulting behaviours have been observed in this thesis; and (5) a novel package for geodetic earthquake modelling has been developed, which can handle multiple datasets including InSAR, GPS and land/space based gravity changes

Investigating the postseismic deformation of strike-slip earthquakes on the Tibetan Plateau

InSAR is a useful technique to detect large-scale surface deformation from space. To place constraints on the rheological structure of the lithosphere in the Tibetan Plateau, two strike-slip earthquakes have been investigated. One is the Mw 7.6 Manyi earthquake, which occurred in the north-central Tibetan Plateau. The other is the Mw 6.5 Jiuzhaigou earthquake, which happened that on the eastern part of the Tibetan Plateau. My InSAR data cover 12 years following the Manyi earthquake, much longer than previous researchers’ dataset. I test three viscoelastic models (Maxwell, Standard linear solids, and Burgers body) and one afterslip model. The viscoelastic models cannot match the observed temporal–spatial deformation patterns. The distributions of deformation in the viscoelastic models extend into the far field and the residuals tend to increase, which are inconsistent with the data. The afterslip model has the lowest misfit and explains the temporal and spatial pattern of the observed deformation with decent result. A combined model that considers the effects of both afterslip and viscoelastic relaxation has also been tested. In this combined model, the viscoelastic relaxation that occurs with an elastic layer of thickness of 30 km over a half-space place, produce an estimate for viscosity of 5 × 1019 Pa s for this area. Therefore, either the afterslip model or the combined model can be used to explain the 12 years postseismic deformation of Manyi earthquake. The long time series of the Manyi earthquake enable us to distinguish between afterslip and viscoelastic relaxation. The seismogenic fault of the Jiuzhaigou earthquake was previously unidentified and no surface rupture is found after the earthquake. I first determined the fault geometry and calculated coseismic slip model. The slip model indicates a left-lateral strike-slip pattern, which is consistent with focal mechanisms were determined by different agencies. There is no visible postseismic deformation signal of the fault, which means the surface deformation generated by fault creeping is smaller than the noise of our observation method over that period. Therefore, I try to find the lower bound of the viscosity for this area. My preferred minimum possible viscosity of the underlying half-space is ∼6 × 1017 Pa s. Together with previous geodetic studies, the viscosities obtained from central Tibet show at least one order of magnitude difference with the viscosities obtained from the eastern Tibet. The heterogeneity indicates the rheology has a relatively large spatial change through the whole Plateau. The viscoelastic model always been proposed to explain long-term postseismic deformation and afterslip is used to explain the short-term deformation or localised deformation. Sometimes, the viscoelastic deformation signal is invisible in the moderate earthquakes as the stress is not large enough to generate observable deformation

Monitoring activity at the Daguangbao mega-landslide (China) using Sentinel-1 TOPS time series interferometry

The Daguangbao mega-landslide (China), induced by the 2008 Wenchuan earthquake (Mw = 7.9), with an area of approximately 8 km2, is one of the largest landslides in the world. Experts predicted that the potential risk and instability of the landslide might remain for many decades, or even longer. Monitoring the activity of such a large landslide is hence critical. Terrain Observation by Progressive Scans (TOPS) mode from the Sentinel-1 satellite provides us with up-to-date high-quality Synthetic Aperture Radar (SAR) images over a wide ground coverage (250 × 250 km), enabling full exploitation of various InSAR applications. However, the TOPS mode introduces azimuth-dependent Doppler variations to radar signals, which requires an additional processing step especially for SAR interferometry. Sentinel-1 TOPS data have been widely applied to earthquakes, but the performance of TOPS data-based time series analysis requires further exploitation. In this study, Sentinel-1 TOPS data were employed to investigate landslide post-seismic activities for the first time. To deal with the azimuth-dependent Doppler variations, a processing chain of TOPS time series interferometry approach was developed. Since the Daguangbao landslide is as a result of the collapse of a whole mountain caused by the 2008 Mw 7.9 Wenchuan earthquake, the existing Digital Elevation Models (DEMs, e.g. SRTM and ASTER) exhibit height differences of up to approximately 500 m. Tandem-X images acquired after the earthquake were used to generate a high resolution post-seismic DEM. The high gradient topographic errors of the SRTM DEM (i.e. the differences between the pre-seismic SRTM and the actual post-seismic elevation), together with low coherence in mountainous areas make it difficult to derive a precise DEM using the traditional InSAR processing procedure. A re-flattening iterative method was hence developed to generate a precise TanDEM-X DEM in this study. The volume of the coseismic Daguangbao landslide was estimated to be of 1.189 ± 0.110 × 109 m3 by comparing the postseismic Tandem-X DEM with the preseismic SRTM DEM, which is consistent with the engineering geological survey result. The time-series results from Sentinel-1 show that some sectors of the Daguangbao landslide are still active (and displaying four sliding zones) and exhibiting a maximum displacement rate of 8 cm/year, even eight years after the Wenchuan earthquake. The good performance of TOPS in this time series analysis indicates that up-to-date high-quality TOPS data with spatiotemporal baselines offer significant potential in terms of future InSAR applications.This work was supported by the National Natural Science Foundation of China under Grant No. 41474003. The research stay of Dr. Tomás at Newcastle University was funded by the Ministry of Education, Culture and Sport within the framework of Project PRX14/00100. Additional funding was obtained from the Spanish Government under projects TIN2014-55413-C2-2-P and ESP2013-47780-C2-2-R. Part of this work is also supported by the UK Natural Environmental Research Council (NERC) through the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET, ref.: come30001) and the LICS and CEDRRiC projects (ref. NE/K010794/1 and NE/N012151/1, respectively), the ESA-MOST DRAGON-3 projects (ref. 10607 and 10665), the ESA-MOST DRAGON-4 project (ref. 32244) and the Open Fund from the Key Laboratory of Earth Fissures Geological Disaster, Ministry of Land and Resources (ref.: gla2013001)

Advanced InSAR atmospheric correction: MERIS/MODIS combination and stacked water vapour models

A major source of error for repeat-pass Interferometric Synthetic Aperture Radar (InSAR) is the phase delay in radio signal propagation through the atmosphere (especially the part due to tropospheric water vapour). Based on experience with the Global Positioning System (GPS)/Moderate Resolution Imaging Spectroradiometer (MODIS) integrated model and the Medium Resolution Imaging Spectrometer (MERIS) correction model, two new advanced InSAR water vapour correction models are demonstrated using both MERIS and MODIS data: (1) the MERIS/MODIS combination correction model (MMCC); and (2) the MERIS/MODIS stacked correction model (MMSC). The applications of both the MMCC and MMSC models to ENVISAT Advanced Synthetic Aperture Radar (ASAR) data over the Southern California Integrated GPS Network (SCIGN) region showed a significant reduction in water vapour effects on ASAR interferograms, with the root mean square (RMS) differences between GPS- and InSAR-derived range changes in the line-of-sight (LOS) direction decreasing from ,10mm before correction to ,5mm after correction, which is similar to the GPS/MODIS integrated and MERIS correction models. It is expected that these two advanced water vapour correction models can expand the application of MERIS and MODIS data for InSAR atmospheric correction. A simple but effective approach has been developed to destripe Terra MODIS images contaminated by radiometric calibration errors. Another two limiting factors on the MMCC and MMSC models have also been investigated in this paper: (1) the impact of the time difference between MODIS and SAR data; and (2) the frequency of cloud-free conditions at the global scale

Statistical comparison of InSAR tropospheric correction techniques

Correcting for tropospheric delays is one of the largest challenges facing the interferometric synthetic aperture radar (InSAR) community. Spatial and temporal variations in temperature, pressure, and relative humidity create tropospheric signals in InSAR data, masking smaller surface displacements due to tectonic or volcanic deformation. Correction methods using weather model data, GNSS and/or spectrometer data have been applied in the past, but are often limited by the spatial and temporal resolution of the auxiliary data. Alternatively a correction can be estimated from the interferometric phase by assuming a linear or a power-law relationship between the phase and topography. Typically the challenge lies in separating deformation from tropospheric phase signals. In this study we performed a statistical comparison of the state-of-the-art tropospheric corrections estimated from the MERIS and MODIS spectrometers, a low and high spatial-resolution weather model (ERA-I and WRF), and both the conventional linear and new power-law empirical methods. Our test-regions include Southern Mexico, Italy, and El Hierro. We find spectrometers give the largest reduction in tropospheric signal, but are limited to cloud-free and daylight acquisitions. We find a ~ 10–20% RMSE increase with increasing cloud cover consistent across methods. None of the other tropospheric correction methods consistently reduced tropospheric signals over different regions and times. We have released a new software package called TRAIN (Toolbox for Reducing Atmospheric InSAR Noise), which includes all these state-of-the-art correction methods. We recommend future developments should aim towards combining the different correction methods in an optimal manner