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C‐band Interferometric Synthetic Aperture Radar (InSAR) data are widely used to map coseismic deformation. However, phase unwrapping errors are commonly distributed near faults owing to decorrelation and steep phase gradients from short radar wavelengths. Here, we propose an improved SNAPHU phase‐unwrapping algorithm that considers the prior information of the range offset gradients (P‐SNAPHU) to overcome the constraints imposed by the phase continuity assumption. P‐SNAPHU exploits median filtering of homogeneous pixels for initial denoising of range offset and then refines range offset gradients divisionally through saliency extraction. The derived gradients are used to estimate the expected values of the cost functions for the low‐coherence fringes. The synthetic experiments show significant improvements in the phase‐unwrapping accuracy of the P‐SNAPHU method compared with classical unwrapping methods. We apply the P‐SNAPHU method to unwrap Sentinel‐1 coseismic interferograms of three large (Mw > 6.5) strike‐slip earthquake events that the existing classical methods could not successfully unwrap. In the comparison of the unwrapped interferograms with the external global navigation satellite system (GNSS) displacements and those from the classical methods, we find that P‐SNAPHU significantly reduces the phase unwrapping errors with the mean absolute error of 7.2, 2.3, and 1.8 cm for the 2023 Kahramanmaraş earthquake doublet, the 2016 Kumamoto earthquake, and the 2019 Ridgecrest earthquakes, respectively. Based on the unwrapped results derived from P‐SNAPHU, an estimate is made regarding the shallow slip deficit of the 2023 Kahramanmaraş earthquake doublet, which is approximately 7%. Therefore, P‐SNAPHU is useful for developing and applying C‐band InSAR data for large earthquakes and volcanic activity. Plain Language Summary: Interferometric Synthetic Aperture Radar (InSAR) can obtain high‐precision, wide‐area ground deformation data and is essential for coseismic research of moderate to large earthquakes. However, phase unwrapping, a necessary step for InSAR to obtain accurate deformation, has historically posed a challenge for C‐band data because of large deformation gradients and decorrelation near fault ruptures. Traditional unwrapping methods typically assume that surface deformation is continuous and has small gradients that fail to unwrap intense deformation regions with substantial errors when the events are large. We propose an improved phase unwrapping method based on the SNAPHU method, which leverages prior gradients from range offsets to constrain the unwrapped gradients to be solved. This method involves two crucial steps before phase unwrapping in the workflow to reduce the negative effects of the range‐offset noise. We demonstrate this method using simulated data with different noise levels and real data from three large strike‐slip earthquake sequences. The GNSS data from the three real cases are in good agreement with our unwrapped results and prove that the proposed method can significantly increase the phase‐unwrapping accuracy near the fault rupture, which generates the largest coseismic deformation. This advancement is paramount for promoting seismic event studies using C‐band SAR data. Key Points: We present an improved SNAPHU phase unwrapping method for C‐band coseismic interferograms using range‐offset gradients as prior informationThe proposed method enables the effective unwrapping of low‐coherence regions near surface rupturesThe method significantly improves the phase‐unwrapping accuracy and aligns well with the global navigation satellite system data for three large earthquake events [ABSTRACT FROM AUTHOR]

Knowledge of the fault kinematics underlying the Papuan Fold Belt is important for better understanding the evolution of the orogen, but the active and long‐term tectonics of the region remain widely debated. The 2018 Mw 7.5 Papua New Guinea earthquake provides an unprecedented opportunity to probe the active fault structure deep in the Papuan Fold Belt. Here, we use Interferometric Synthetic Aperture Radar data from four ALOS‐2 acquisitions to study coseismic and postseismic ground deformation and invert for fault slip models. The results show that the oblique reverse earthquake reactivated a flat‐ramp structure and ruptured through most of the crust with the majority of coseismic slip confined between 5 and 25 km. Additionally, we found three separated postseismic slip zones with variable spatial complementarity between coseismic and postseismic slip, dip‐slip/strike‐slip ratio, and seismic/aseismic budget at three separated postseismic slip zones. Our results demonstrate that thick‐skinned tectonics dominate the current state of Papua New Guinea frontal orogen evolution. Plain Language Summary: On 25 February 2018, an Mw 7.5 earthquake struck the central Papua New Guinea Highland. We use Interferometric Synthetic Aperture Radar data (ALOS‐2) to study the surface displacements associated with the great earthquake, seismogenic fault geometry, and coseismic and postseismic slip. We find complex seismic and aseismic slip occurred on a flat‐ramp structure, which ruptured through most of the crust indicating thick‐skinned basement‐involved deformation during the earthquake. We also compare the uplift displacements and the topography and local folds, and highlight that thick‐skinned tectonics play a significant role in the current frontal orogen evolution of Papua New Guinea. Key Points: Coseismic and postseismic surface displacements of the 2018 Mw 7.5 Papua New Guinea earthquake are captured by InSARThe depth extent of coseismic and postseismic slip on a flat‐ramp fault suggests thick‐skinned deformationFault frictional heterogeneity is found based on variable seismic and aseismic slip behaviors of three separated postseismic slip zones [ABSTRACT FROM AUTHOR]

Since the occurrence of the 2019 Mw 6.4 and Mw 7.1 Ridgecrest earthquake sequence in the Eastern California Shear Zone, coseismic deformation following the two earthquakes has been intensively studied, and source modeling with interferometric synthetic aperture radar (InSAR), Global Positioning System (GPS) and seismological datasets has been favored. However, we recently found that the coseismic modeling of the two earthquakes constrained by the dense near‐field Planet‐Lab optical measurements can be more detailed than the previously estimated, which requires an accurate Planet‐Lab displacement. In this study, we improve the long wavelength orbital ramps correction method for obtaining a more accurate Planet‐Lab horizontal displacement field. The corrected dense near‐field Planet‐Lab data are firstly used together with the intermediate‐field GPS data to invert and distinguish the fault slip distribution for the two earthquakes. The same scheme is used to simultaneously invert the InSAR, SAR, GPS, and optical datasets, to improve the constraints on seismic source parameters. Our inversion results show that the joint‐event slip model is rougher than the two single‐event slip models, but it has a more concentrated slip pattern and larger slip amplitude in some zones. We show that adding a near‐field constraint of the Planet‐Lab data in the combined‐data inversion can reduce the slip parameter uncertainty and enhance the model resolution. The Coulomb failure stress changes on the southeastern Blackwater, the southern Owens Valley, and the central Panamint Valley faults are enhanced by about 0.4–0.8 bar by the 2019 Ridgecrest earthquake sequence. Plain Language Summary: In July 2019, an earthquake sequence, including an Mw 6.4 foreshock on 4 July at 17:33 UTC and an Mw 7.1 mainshock that occurred 34 hr later, struck the Ridgecrest, southern California. Previous studies have used the Planet‐Lab data to extract the surface displacement of the respective events but ignored the long wavelength ramps in each block of the Planet‐Lab image displacement field. We improve the correction method for long wavelength orbital ramps to obtain a more accurate Planet‐Lab horizontal displacement field. The source model of individual events during an earthquake sequence is routinely inverted from seismic waveforms and/or GPS data, which, however, have difficulty in obtaining the detailed slip distributions, due to their low spatial density. We use the corrected Planet‐Lab horizontal displacement to improve the near‐field data constraints in source modeling. This work is the first application of using the Planet‐Lab data to separate the fault slip model of the two strongest earthquakes during the Ridgecrest earthquake sequence, highlighting the importance of the high spatiotemporal resolution Planet‐Lab data in refining fault geometry and restoring detailed fault slip distribution. Key Points: Improved the correction method for long wavelength orbital ramps to obtain a more accurate Planet‐Lab horizontal displacement fieldResolved and separated the detailed slip distributions of the foreshock and mainshock using the GPS and dense Planet‐Lab optical dataImproved source modeling through the combined use of InSAR, SAR, GPS, and optical datasets [ABSTRACT FROM AUTHOR]

The filling and emptying cycles of reservoir operations may change hydrological mass loading, leading to a flexural deformation of the crust that may compromise the infrastructure safety or trigger earthquakes. In this study, we investigate the seasonal crustal response of the Tehri reservoir in the Garhwal Himalaya, northern India, using interferometric synthetic aperture radar (InSAR), Global Positioning System, the Gravity Recovery and Climate Experiment, radar altimetry, and in‐situ water‐level measurements. Results show that the evolution of vertical ground deformation is modulated elastically by the reservoir operation, whereas the horizontal displacement measured near the reservoir exhibits a time lag of ∼65 days with respect to the vertical displacements and water‐level variations. The delayed deformation transients indicate that the reservoir loading/unloading cycles affect the near‐surface hydrology in its neighborhood. The broader distribution and higher amplitude of ground deformation during the loading periods revealed by the InSAR time series can be explained by water–rock interactions, which cause a decrease in the effective Young's modulus within the top 300‐m crustal layer. Our results demonstrate the potential of using space geodetic data to ensure a better understanding of the solid Earth response to regional hydrological changes. Plain Language Summary: The seasonal variations of water storage in the reservoir alter the stress state and hydrologic loadings in the neighboring region thereby may bring measurable crust deformation at the lakeshore. Recent studies have worked to capture the long‐term deformation signals near the reservoirs and lakes, but seldom of them has considered the localized crust behavior on a seasonal scale. To better understand crust deformation processes from this anthropogenic source, we used multiple space geodetic observations, in‐situ data, elastic and poroelastic models to study the Tehri reservoir, India. The results show that the ∼80 m water loading cycles modulate the elastic deformation close to the reservoir. An asymmetric crustal deformation with higher amplitude and broader impacted area in the loading scenario, providing a possible weakening effect in the fractured shallow crustal medium from the water‐rock interaction. While the elastic deformation in the vertical direction is well explained, more complicated horizontal motions may be connected to the local hydrologic conditions. Key Points: We investigate crustal deformation caused by Tehri reservoir operations using multi‐source geodetic observationsThe elastic crustal response to loading dominates the seasonal ground deformation surrounding the reservoirThe best‐fitting layered elastic model implies a relatively lower effective Young's modulus in the shallow crust during water loading periods [ABSTRACT FROM AUTHOR]

Erta Ale Volcano erupted on 16 January 2017 in a difficult‐to‐access terrain in the Erta Ale volcanic range in Ethiopia. Like many other rifting ridge volcanoes, little is known about the properties of the deep magma plumbing system. Here, we analyze interferometric synthetic aperture radar data from different satellites between late January 2017 and May 2019 to study the ground deformation after the start of the intrusion to infer the possible geometry and volume change of the magma reservoir that fed the eruption. We identified volcano‐wide subsidence of up to 9 cm and horizontal contraction of up to ~5 cm that extend from Erta Ale to neighboring volcanoes. The modeling results suggest that an off‐rift NE‐SW elongated mid‐crustal source is required to explain the observed volcano‐wide deformation, but the depth is poorly constrained and the shape is complex. We suggest the presence of vertical interactions between stacked mid‐crustal magma sources. Our study demonstrates that a considerable volume of melt could have been stored in mid‐crustal magma reservoirs within the slow‐spreading Erta Ale Ridge to facilitate recent volcanic activity. Key Points: We observe volcano‐wide ground deformation following the 2017 Erta Ale dike intrusion using radar interferometryWe model ground deformation after the intrusion between late January 2017 and May 2019 to study the properties of the magma plumbing systemWe find an off‐rift NE‐SW elongated mid‐crustal source beneath Erta Ale with poorly constrained depth and a complex shape [ABSTRACT FROM AUTHOR]

Interferometric synthetic aperture radar (InSAR) has become an important technique for studying earthquake cycle deformation. However, due to the limited satellite revisit time, it is often difficult to fully separate coseismic and postseismic slip from InSAR data. Nevertheless, accurately estimating spatiotemporal coseismic and postseismic fault slip distribution models is important for quantifying earthquake slip, understanding the kinematics of seismogenic faulting, and evaluating seismic hazards. Here, we develop a logarithmic model‐based method (LogSIM) for the joint inversion of coseismic and postseismic fault slip using InSAR data from multiple platforms in different orbits. This method considers the nature of early postseismic slip following logarithmic decay. The coseismic slip, the decay time constant, and the decay amplitude of the logarithmic model can be jointly estimated from unwrapped interferograms without the need for InSAR time series calculations, thereby reducing the number of unknown parameters and stabilizing the inversion. The robustness of LogSIM is first validated with synthetic experiments. We then apply LogSIM to invert for the coseismic and postseismic slip models of the 2017 Mw 7.3 Sarpol Zahāb earthquake. We find that the maximum afterslip value and postseismic moment release during the first four months reported in previous studies are underestimated by ~26% and ~31%, respectively, due to the unavailability of the first five days of postseismic deformation. The estimated afterslip distribution spatially overlaps with the aftershocks in the updip region of the fault plane. LogSIM could potentially be extended to integrate different space geodetic data in earthquake cycle deformation modeling. Key Points: LogSIM is an effective and robust tool for coseismic and postseismic fault slip model estimationLogSIM makes use of all available geodetic data to improve the temporal resolution of afterslipLogSIM enables the retrieval of the very early postseismic fault slip [ABSTRACT FROM AUTHOR]

The three‐dimensional (3‐D) deformation field associated with the 2016 Central Tottori earthquake is retrieved from advanced land observing satellite 2 interferometric synthetic aperture radar (InSAR) observations with four different viewing geometries, that is, ascending/descending tracks and left‐/right‐looking modes. The strain model and variance component estimation (SM, VCE, SM‐VCE) method is exploited and improved to integrate the InSAR observations with different viewing geometries so that the 3‐D deformation field is not affected by the inconsistent coverage of SAR footprints or the gross errors in InSAR observations. The obtained results are consistent with GNSS observations, indicating that the improved SM‐VCE method, known as SM‐RVCE in this paper, is capable of retrieving an accurate and spatially complete 3‐D deformation field for this earthquake. In addition, the precision of the InSAR observations and the estimated 3‐D deformation are quantitatively assessed by the SM‐RVCE method. Finally, on the basis of the estimated 3‐D coseismic deformation, the source parameters of this event are inverted, revealing an asperity with a maximum strike‐parallel slip of ~1.1 m concentrated at depths between 2 and 10 km. The estimated seismic moment is 2.4 × 1018 Nm, which corresponds to a Mw 6.2 event. Key Points: We retrieve the 3‐D deformation field of the 2016 Central Tottori earthquake from left‐ and right‐looking InSAR observationsWe conduct a precision assessment for InSAR observations based on the variance component estimation (VCE) methodWe employ the robust VCE method to mitigate the effects of gross InSAR errors such as unwrapping errors on the 3‐D deformation [ABSTRACT FROM AUTHOR]

The detailed spatial variations of strain accumulation and creep on major faults in the northern San Francisco Bay Area (North Bay), which are important for seismic potential and evaluation of natural hazards, remain poorly understood. Here we combine interferometric synthetic aperture radar data from the ERS‐1/2 and Envisat satellites between 1992 and 2010 with continuous and campaign GPS data to obtain a high spatial and temporal coverage of ground deformation of the North Bay. The SAR data from both ascending and descending orbits are combined to separate horizontal and vertical components of the deformation. We jointly invert the horizontal component of the mean velocities derived from these data to infer the deep strike‐slip rates on major locked faults. We use the estimated deep rates to simulate the long‐wavelength deformation due to interseismic elastic strain accumulation along these locked faults. After removing the long‐wavelength signal from the InSAR horizontal mean velocity field, we estimate fault‐parallel surface creep rates of up to 2 mm/year along the central section of the Rodgers Creek fault and surface creep rates ranging between 2 and 4 mm/year along the Concord fault. No surface creep is geodetically resolved along the West Napa and Green Valley fault zones. We identified characteristically repeating earthquakes on the Rodgers Creek fault, the West Napa fault, the Green Valley fault, and the Concord fault. Nontectonic deformation in the Geysers geothermal field and in Late Cenozoic basins (Rohnert Park and Sonoma basins) are also observed, likely due to hydrological and sediment‐compaction processes, respectively. Key Points: Interseismic ground deformation map of the greater San Francisco Bay Area is generatedDeep strike‐slip rates on major locked faults are estimatedSurface creeping signals are observed on the Rodgers Creek fault and the Concord fault [ABSTRACT FROM AUTHOR]

Abstract: Large earthquakes often do not occur on a simple planar fault but involve rupture of multiple geometrically complex faults. The 2016 Mw 7.8 Kaikoura earthquake, New Zealand, involved the rupture of at least 21 faults, propagating from southwest to northeast for about 180 km. Here we combine space geodesy and seismology techniques to study subsurface fault geometry, slip distribution, and the kinematics of the rupture. Our finite‐fault slip model indicates that the fault motion changes from predominantly right‐lateral slip near the epicenter to transpressional slip in the northeast with a maximum coseismic surface displacement of about 10 m near the intersection between the Kekerengu and Papatea faults. Teleseismic back projection imaging shows that rupture speed was overall slow (1.4 km/s) but faster on individual fault segments (approximately 2 km/s) and that the conjugate, oblique‐reverse, north striking faults released the largest high‐frequency energy. We show that the linking Conway‐Charwell faults aided in propagation of rupture across the step over from the Humps fault zone to the Hope fault. Fault slip cascaded along the Jordan Thrust, Kekerengu, and Needles faults, causing stress perturbations that activated two major conjugate faults, the Hundalee and Papatea faults. Our results shed important light on the study of earthquakes and seismic hazard evaluation in geometrically complex fault systems. [ABSTRACT FROM AUTHOR]