Incorporating independent component analysis and multi-temporal sar techniques to retrieve rapid postseismic deformation

This study investigates the ongoing postseismic deformation induced by two moderate mainshocks of Mw 6.1 and Mw 6.0, 2017 Hojedk earthquake in Southern Iran. Available Sentinel-1 TOPS C-band Synthetic Aperture Radar (SAR) images over about one year after the earthquakes are used to analyze the postseismic activities. An adaptive method incorporating Independent Component Analysis (ICA) and multi-Temporal Small BAseline Subset (SBAS) Interferometric SAR (InSAR) techniques is proposed and implemented to recover the rapid deformation. This method is applied to the series of interferograms generated in a fully constructed SBAS network to retrieve the postseismic deformation signal. ICA algorithm uses a linear transformation to decompose the input mixed signal to its source components, which are non-Gaussian and mutually independent. This analysis allows extracting the low rate postseismic deformation signal from a mixture of interferometric phase components. The independent sources recovered from the multi-Temporal InSAR dataset are then analyzed using a group clustering test aiming to identify and enhance the undescribed deformation signal. Analysis of the processed interferograms indicates a promising performance of the proposed method in determining tectonic deformation. The proposed method works well, mainly when the tectonic signal is dominated by the undesired signals, including atmosphere or orbital/unwrapping noise that counts as temporally uncorrelated components.In contrast to the standard SBAS time series method, the ICA-based time series analysis estimates the cumulative deformation with no prior assumption about elevation dependence of the interferometric phase or temporal nature of the tectonic signal. Application of the method to 433 Sentinel-1 pairs within the dataset reports two distinct deformation patches corresponding to the postseismic deformation. Besides the performance of the ICA-based analysis, the proposed method automatically detects rapid or low rate tectonic processes in unfavorable conditions. © Authors 2020. All rights reserved

Финансовое состояние предприятия: оценка и направления улучшения (на примере ОАО «Речицкий комбинат хлебопродуктов»)

We greatly appreciate the thoughtful comments by Andrew Sowter and Francesca Cigna [1] on our paper [2]. Unfortunately, we overlooked the ISBAS acronym during the revision process of the article. Therefore, we would suggest to use the acronym of ESBAS (Enhanced Small BAseline Subset) for our method presented in Vajedian et al. [2

Mechanical Behavior of Single-Flawed Cylindrical Specimens Subjected to Axial Loading: A Numerical Investigation

Discontinuities are inherent components of rock masses and can range from fissures to large faults. Single fissures, the so-called flaws, may affect the mechanical behavior of rock mass, crack initiation, and propagation. In this paper, numerical investigations have been conducted on central-flawed cylindrical specimens subjected to axial loading to investigate the effect of flaw angle (α), length (2a), and aperture (A) on their mechanical behavior and crack development. Particle Flow Code (PFC3D) was adopted to investigate the cracking process of the cylindrical specimens and maximum principal stresses at flaw tips. The numerical models are calibrated and verified using extensive experimental tests. The results show that increasing α, UCS, and E increase while increasing 2a decreases UCS and E, and A does not affect these two parameters. Moreover, numerical simulations reveal that as α rises, the three principal stresses generally fall when 2a = 13 and 26 mm. σ1 and σ3 peak at α = 45°, and σ2 reaches a maximum at α = 30° in models with 2a = 39 mm. The cracking patterns resulting from both methods are highly consistent in that tensile cracks type 1 mainly form at α = 15° to 75°, and tensile cracks type 3 are dominant at other angles. Finally, it is concluded that flaw aperture scarcely affects failure patterns

Assessing the Use of Optical Satellite Images to Detect Volcanic Impacts on Glacier Surface Morphology

Globally, about 250 Holocene volcanoes are either glacier-clad or have glaciers in close proximity. Interactions between volcanoes and glaciers are therefore common, and some of the most deadly (e.g., Nevado del Ruiz, 1985) and most costly (e.g., Eyjafjallajökull, 2010) eruptions of recent years were associated with glaciovolcanism. An improved understanding of volcano-glacier interactions is therefore of both global scientific and societal importance. This study investigates the potential of using optical satellite images to detect volcanic impacts on glaciers, with a view to utilise detected changes in glacier surface morphology to improve glacier-clad volcano monitoring and eruption forecasting. Roughly 1400 optical satellite images are investigated from key, well-documented eruptions around the globe during the satellite remote sensing era (i.e., 1972 to present). The most common observable volcanic impact on glacier morphology (for both thick and thin ice-masses) is the formation of ice cauldrons and openings, often associated with concentric crevassing. Other observable volcanic impacts include ice bulging and fracturing due to subglacial dome growth; localized crevassing adjacent to supraglacial lava flows; widespread glacier crevassing, presumably, due to meltwater-triggered glacier acceleration and advance. The main limitation of using optical satellite images to investigate changes in glacier morphology is the availability of cloud- and eruption-plume-free scenes of sufficient spatial- and temporal resolution. Therefore, for optimal monitoring and eruption prediction at glacier-clad volcanoes, optical satellite images are best used in combination with other sources, including SAR satellite data, aerial images, ground-based observations and satellite-derived products (e.g., DEMs)

Massive earthquake swarm driven by magmatic intrusion at the Bransfield Strait, Antarctica

An earthquake swarm affected the Bransfield Strait, Antarctica, a unique rift basin in transition from intra-arc rifting to ocean spreading. The swarm, counting ~85,000 volcanotectonic earthquakes since August 2020, is located close to the Orca submarine volcano, previously considered inactive. Simultaneously, geodetic data reported up to ~11 cm northwestward displacement over King George Island. We use a broad variety of geophysical data and methods to reveal the complex migration of seismicity, accompanying the intrusion of 0.26-0.56 km³ of magma. Strike-slip earthquakes mark the intrusion at depth, while shallower normal faulting the ~20 km long lateral growth of a dike. Seismicity abruptly decreased after a Mw 6.0 earthquake, suggesting the magmatic dike lost pressure with the slipping of a large fault. A seafloor eruption is likely, but not confirmed by sea surface temperature anomalies. The unrest documents episodic magmatic intrusion in the Bransfield Strait, providing unique insights into active continental rifting

Coseismic Deformation Field of the Mw 7.3 12 November 2017 Sarpol-e Zahab (Iran) Earthquake: A Decoupling Horizon in the Northern Zagros Mountains Inferred from InSAR Observations

The study of crustal deformation fields caused by earthquakes is important for a better understanding of seismic hazard and growth of geological structures in tectonically active areas. In this study, we present, using interferometric measurements constructed from Sentinel-1 Terrain Observation with Progressive Scan (TOPS) data and ALOS-2 ScanSAR, coseismic deformation and source model of the Mw 7.3, 12 November 2017 earthquake that hit northwest of the Zagros Mountains in the region between Iran–Iraq border. This was one of the strongest seismic events to hit this region in the past century, and it resulted in an uplift area of about 3500 km2 between the High Zagros Fault (HZF) and Mountain Front Fault (MFF) with a maximum amount of 70 cm south of Miringe fault. A subsidence over an area of 1200 km2 with a maximum amount of 35 cm occurred near Vanisar village at the hanging wall of the HZF. Bayesian inversion of interferometric synthetic aperture radar (InSAR) observations suggests a source model at a depth between 14 and 20 km that is consistent with the existence of a decoupling horizon southwest edge of the northern portion of the Zagros Mountains near the MFF. Moreover, we present evidence for a number of coseismically induced rockslides and landslides, the majority of them which occurred along or close to pre-existing faults, causing decorrelation in differential interferograms. Exploiting the offset-tracking technique, we estimated surface motion by up to 34 and 10 m in horizontal and vertical directions, respectively, due to lateral spreading on a big coseismic-induced landslide near Mela-Kabod. Field observations also revealed several zones of en echelon fractures and crack zones developed along a pre-existing fault passing through Qasr-e Shirin City, which exhibited secondary surface slip by up to 14 cm along its strike

Response to Sowter, A.; Cigna, F. On the Use of the ISBAS Acronym in InSAR Applications. Comment on Vajedian, S.; Motagh, M.; Nilfouroushan, F. StaMPS Improvement for Deformation Analysis in Mountainous Regions: Implications for the Damavand Volcano and Mosha Fault in Alborz. Remote Sens. 2015, 7, 8323–8347

We greatly appreciate the thoughtful comments by Andrew Sowter and Francesca Cigna [1] on our paper [2]. Unfortunately, we overlooked the ISBAS acronym during the revision process of the article. Therefore, we would suggest to use the acronym of ESBAS (Enhanced Small BAseline Subset) for our method presented in Vajedian et al. [2

Detection of subsidence in Bad Frankenhausen with time series analysis of interferometric Radar

The area of Bad Frankenhausen, a small city in Thuringia in central Germany is subject to land subsidence because of the occurrence of sinkholes. We use SAR interferometry (InSAR) time series analysis to monitor the subsidence in this area. All the available C-band Sentinel-1A data in both geometries of ascending and descending are collected in this study. We exploit Small BAseline Subset (SBAS) as a time series algorithm to derive the subsidence rate of the study area. The accuracy of the SBAS time series analysis could be affected by high rate of atmospheric artifacts especially over the humid area, therefore, selection of the appropriate method of the atmospheric correction is required. In this study, a statistical based atmospheric correction method is performed to decrease the atmospheric influence The time series analysis result in both geometries show a low rate of deformation signal along LOS directions with nearly negative sign corresponding subsidence phenomena. Availability of the InSAR time series results in both ascending and descending tracks enables us to estimate the horizontal and vertical displacement using the decomposition process.. The results show a very small rate of movement, almost zero, along with horizontal direction. Vertical displacements with a maximum subsidence rate of 1.4 mm/a$ are observed over the area. The results of the time series analysis are partially compared to GNSS and leveling data

STaMPS improvement for deformation analysis in mountainous regions : Implications for Damavand volcano and Mosha fault in Alborz

Interferometric Synthetic Aperture Radar (InSAR) capability to detect slow deformation over terrain areas is limited by temporal decorrelation, geometric decorrelation and atmospheric artefacts. Multitemporal InSAR methods such as Persistent Scatterer (PS-InSAR) and Small Baseline Subset (SBAS) have been developed to deal with various aspects of decorrelation and atmospheric problems affecting InSAR observations. Nevertheless, the applicability of both PS-InSAR and SBAS in mountainous regions is still challenging. Correct phase unwrapping in both methods is hampered due to geometric decorrelation in particular when using C-band SAR data for deformation analysis. In this paper, we build upon the SBAS method implemented in StaMPS software and improved the technique, here called ISBAS, to assess tectonic and volcanic deformation in the center of the Alborz Mountains in Iran using both Envisat and ALOS SAR data. We modify several aspects within the chain of the processing including: filtering prior to phase unwrapping, topographic correction within three-dimensional phase unwrapping, reducing the atmospheric noise with the help of additional GPS data, and removing the ramp caused by ionosphere turbulence and/or orbit errors to better estimate crustal deformation in this tectonically active region. Topographic correction is done within the three-dimensional unwrapping in order to improve the phase unwrapping process, which is in contrast to previous methods in which DEM error is estimated before/after phase unwrapping. Our experiments show that our improved SBAS approach is able to better characterize the tectonic and volcanic deformation in the center of the Alborz region than the classical SBAS. In particular, Damavand volcano shows an average uplift rate of about 3 mm/year in the year 2003–2010. The Mosha fault illustrates left-lateral motion that could be explained with a fault that is locked up to 17–18 km depths and slips with 2–4 mm/year below that depth