Transpressional Rupture Cascade of the 2016 M_w 7.8 Kaikoura Earthquake, New Zealand

Large earthquakes often do not occur on a simple planar fault but involve rupture of multiple geometrically complex faults. The 2016 M_w 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

Transpressional Rupture Cascade of the 2016 Mw 7.8 Kaikoura Earthquake, New Zealand

Large earthquakes often do not occur on a simple planar fault but involve rupture of multiple geometrically complex faults. The 2016 M 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.

Efficient SAR MTI simulator of marine scenes

Tècniques de detecció de moviment amb radars d'apertura sintètica multicanals sobre escenaris marítims.[ANGLÈS] Multichannel spaceborne and airborne synthetic aperture radars (SAR) offer the opportunity to monitor maritime traffic through specially designed instruments and applying a suitable signal processing in order to reject sea surface clutter. These processing techniques are known as Moving Target Indication techniques (MTI) and the choice of the most adequate method depends on the radar system and operating environment. In maritime scenes the seas presents a complicated clutter whose temporal/spatial coherence models and background reflectivity depends on a large number of factors and are still subject of research. Moreover the targets kinematics are influenced by the sea conditions, producing in some situations high alterations in the imaged target. These aspects make difficult the detectability analysis of vessels in maritime scenarios, requiring both theoretical models and numerical simulations. This thesis looks into the few available MTI techniques and deals experimentally with them in a developed simulator for maritime SAR images. The results are also presented in a image format, giving the sequence for one trial simulation and the asymptotic probability of detection for the simulated conditions.[CASTELLÀ] Los radares de apertura sintética (SAR) multicanal a bordo de satélites o plataformas aerotransportadas ofrecen la oportunidad de monitorizar el tráfico marítimo a través de instrumentos especialmente diseñados y procesando los datos recibidos de forma adecuada para rechazar la señal provocada por la reflexión del mar. A estas técnicas se las conoce como Moving Target Indication techniques (MTI) y la elección de la más adecuada depende del sistema y del entorno de aplicación. En escenarios marinos, el mar presenta un clutter complicado de modelar, cuya coherencia espacio-temporal y reflectividad radar dependen de un gran número de factores que hoy en día todavía siguen siendo investigados. Por otra parte los parámetros dinámicos del target estan influenciados por las condiciones del mar, produciendo en algunas situaciones graves alteraciones en la formación de la imagen. Estos aspectos dificultan el análisis de la detección de las embarcaciones, requiriendo modelos teóricos y simulaciones numéricas. Este Proyecto Final de Carrera investiga las técnicas MTI disponibles, aplicándolas sobre las imágenes marítimas generadas por un simulador SAR. Los resultados son la generación de los productos MTI en formato imagen y el cálculo de la probabilidad de detección para cada target.[CATALÀ] Els radars d'obertura sintètica (SAR) multicanal embarcats en satèl·lits o plataformes aerotransportades ofereixen l'oportunitat de monitoritzar el tràfic marítim a través d'instruments especialment dissenyats i processant les dades rebudes de forma adequada per rebutjar la senyal provocada per la reflexió del mar. A aquestes tècniques se les coneix com Moving Target indication techniques (MTI) i l'elecció de la més adequada depèn del sistema i de l'entorn d'aplicació. En escenaris marins, el mar presenta un clutter complicat de modelar, la coherència espai-temporal i reflectivitat radar depenen d'un gran nombre de factors que avui dia encara segueixen sent investigats. D'altra banda els paràmetres dinàmics del target estan influenciats per les condicions de la mar, produint en algunes situacions greus alteracions en la formació de la imatge. Aquests aspectes dificulten l'anàlisi de la detecció de les embarcacions, requerint models teòrics i simulacions numèriques. Aquest Projecte Final de Carrera investiga les tècniques MTI disponibles, aplicant-les sobre les imatges marítimes generades per un simulador SAR. Els resultats són la generació dels productes MTI en format imatge i el càlcul de la probabilitat asimptòtica de detecció per a cada target

Radar Imaging in Challenging Scenarios from Smart and Flexible Platforms

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Anti-jamming techniques for multichannel SAR imaging

© The Institution of Engineering and Technology 2006 IEE Proceedings online no. 20045090An airborne broadband jammer present in the mainbeam of a synthetic aperture radar (SAR) can potentially destroy a large region of the SAR image. In addition to this, multipath reflections from the ground, known as hot-clutter or terrain scattered interference will add a non-stationary interference component to the image. The goal of interference suppression for SAR is to successfully suppress these interferences while not significantly effecting the image quality by blurring, reducing the resolution or raising the sidelobe level. The paper provides an analysis of the degradation from hot-clutter, the limited restoration that multichannel imaging and slow-time space time adaptive processing (STAP) can provide and how fast-time STAP can improve the final image quality.L. Rosenberg and D. Gra

Compressive sensing for 3D microwave imaging systems

Compressed sensing (CS) image reconstruction techniques are developed and experimentally implemented for wideband microwave synthetic aperture radar (SAR) imaging systems with applications to nondestructive testing and evaluation. These techniques significantly reduce the number of spatial measurement points and, consequently, the acquisition time by sampling at a level lower than the Nyquist-Shannon rate. Benefiting from a reduced number of samples, this work successfully implemented two scanning procedures: the nonuniform raster and the optimum path. Three CS reconstruction approaches are also proposed for the wideband microwave SAR-based imaging systems. The first approach reconstructs a full-set of raw data from undersampled measurements via L1-norm optimization and consequently applies 3D forward SAR on the reconstructed raw data. The second proposed approach employs forward SAR and reverse SAR (R-SAR) transforms in each L1-norm optimization iteration reconstructing images directly. This dissertation proposes a simple, elegant truncation repair method to combat the truncation error which is a critical obstacle to the convergence of the CS iterative algorithm. The third proposed CS reconstruction algorithm is the adaptive basis selection (ABS) compressed sensing. Rather than a fixed sparsifying basis, the proposed ABS method adaptively selects the best basis from a set of bases in each iteration of the L1-norm optimization according to a proposed decision metric that is derived from the sparsity of the image and the coherence between the measurement and sparsifying matrices. The results of several experiments indicate that the proposed algorithms recover 2D and 3D SAR images with only 20% of the spatial points and reduce the acquisition time by up to 66% of that of conventional methods while maintaining or improving the quality of the SAR images --Abstract, page iv

Impact of scene decorrelation on geosynchronous SAR data focusing

We discuss the effects of the clutter on geosynchronous SAR systems exploiting long integration times (from minutes to hours) to counteract for two-way propagation losses and increase azimuth resolution. Only stable targets will be correctly focused whereas unstable targets will spread their energy along azimuth direction. We derive here a generic model for the spreading of the clutter energy based on the power spectral density of the clutter itself. We then assume the Billingsley Intrinsic Clutter Motion model, representing the clutter power spectrum as an exponential decay, and derive the expected GEOSAR signal-to-clutter ratio. We also provide some results from a Ground Based RADAR experiment aimed at assessing the long-term clutter statistics for different scenarios to complement the Internal Clutter Motion model, mainly derived for windblown trees. Finally, we discuss the expected performances of two GEOSAR systems with different acquisition geometries.Peer ReviewedPostprint (published version