The 28 September 2018 Mw 7.5 Palu earthquake occurred at a triple junction zone where the Philippine Sea, Australian, and Sunda plates are convergent. Here, we utilized Advanced Land Observing Satellite-2 (ALOS-2) interferometry synthetic aperture radar (InSAR) data together with broadband regional seismograms to investigate the source geometry and rupture kinematics of this earthquake. Results showed that the 2018 Palu earthquake ruptured a fault plane with a relatively steep dip angle of ~85°. The preferred rupture model demonstrated that the earthquake was a supershear event from early on, with an average rupture speed of 4.1 km/s, which is different from the common supershear events that typically show an initial subshear rupture. The rupture expanded rapidly (~4.1 km/s) from the hypocenter and propagated bilaterally towards the north and south along the strike direction during the first 8 s, and then to the south. Four visible asperities were ruptured during the slip pulse propagation, which resulted in four significant deformation lobes in the coseismic interferogram. The maximum slip of 6.5 m was observed to the south of the city of Palu, and the total seismic moment released within 40 s was 2.64 × 1020 N·m, which was equivalent to Mw 7.55. Our results shed some light on the transtensional tectonism in Sulawesi, given that the 2018 Palu earthquake was dominated by left-lateral strike slip (slip maxima is 6.2 m) and that some significant normal faulting components (slip maxima is ~3 m) were resolved as well.

A nearly 70 yr hiatus of major seismic activity in the central eastern Bayan Har block (BKB) ended on 22 May 2021, when a multislip-peak sinistral strike-slip earthquake struck western Maduo County, Qinghai. This earthquake, which ruptured the nearly 170 km long Kunlun Pass–Jiangcuo fault, is a rather unique event and offers a rare opportunity to probe the mechanical properties of the intraplate lithosphere of the central eastern BKB. Here, we inferred the fault geometry associated with the Maduo earthquake using Interferometric Synthetic Aperture Radar (InSAR), and relocated aftershocks and inverted the slip distribution through InSAR radar phases and range offsets. Our analysis revealed that the geometry of the fault varies along the strike: the southeastern end of the fault dips steeply to the northeast, whereas the northwestern end dips southwestward. Using the combined datasets to constrain a coseismic slip, we found that the 2021 Maduo event was dominated by sinistral strike-slip movement, with a slight normal-slip component at a shallow depth, rupturing the steep-dipping fault for nearly 170 km in length. Five asperities were detected along the fault strike in the shallow crust (0–12 km) with a peak slip of ∼4.2 m corresponding mostly to simple structures, namely, continuous and straight rupture segments, suggesting that the rupture propagated across geometrical barriers in a multiasperity way. Based on an analysis of the strain field and the focal mechanisms of both the 2021 Maduo earthquake and historical earthquakes that have occurred in the BKB, we propose that the fault zones within the BKB can also generate large earthquakes and have the ability to accommodate the ongoing eastward and northeastward penetration of the Indian plate into the Eurasian plate.

A non-collinear mixing technique to measure the acoustic nonlinearity parameter of an adhesive bond from one side of the sample Determination of acoustic nonlinearity parameter (β) using nonlinear resonance ultrasound spectroscopy: Theory and experiment A contact mechanics based model for partially-closed randomly distributed surface microcracks and their effect on acoustic nonlinearity in Rayleigh surface waves Experimental characterization of fatigue damage in a nickel-base superalloy using nonlinear ultrasonic waves Abstract. As a longitudinal wave propagates through a linearly elastic solid with distributed cracks, the solid is subjected to cyclic tension and compression. During the tensile cycles, a crack might be open and its faces are traction-free. During the compressive cycles, a crack might be closed and its faces are in contact. Such contact may also be frictional because of crack face roughness. Such tension and compression asymmetry causes acoustic nonlinearity. This paper develops a micromechanics model that relates the crack density to the acoustic nonlinearity parameter. The model is based on a micromechanics homogenization of the cracked solid under dynamic loading. It is shown that the acoustic nonlinearity parameter is proportional to the crack density. Furthermore, the acoustic nonlinearity parameter also depends on the frequency of the wave motion, and the coefficient of friction of the crack faces. Unlike the second harmonic generated by dislocations, the amplitude of the second harmonic due to crack face contact is proportional to the amplitude of the fundamental frequency. To validate the micromechanics model, the finite element method is used to simulate wave propagation in solid with randomly distributed microcracks. The micromechanics model predictions agree well with the finite element simulation results.

Gaussian Markov random fields (GMRFs) are used to analyze textures. GMRFs measure the interdependence of neighboring pixels within a texture to produce features. In this paper, neighboring pixels are taken into account in a priority sequence according to their distance from the center pixel, and a step-by-step least squares method is proposed to extract a novel set of GMRF texture features, named as PS-GMRF. A complete procedure is first designed to classify texture samples of QuickBird imagery. After texture feature extraction, a subset of PS-GMRF features is obtained by the sequential floating forward-selection method. Then, the maximum a posterior iterated conditional mode classification algorithm is used, involving the selected PS-GMRF texture features in combination with spectral features. The experimental results show that the performance of classifying texture samples on high spatial resolution QuickBird satellite imagery is improved when texture features and spectral features are used jointly, and PS-GMRF features have a higher discrimination power compared to the classical GMRF features, making a notable improvement in classification accuracy from 71.84% to 94.01%. On the other hand, it is found that one of the PS-GMRF texture features-the lowest order variance-is effective for residential-area detection. Some results for IKONOS and SPOT-5 images show that the integration of the lowest order variance with spectral features improves the classification accuracy compared to classification with purely spectral features.Index Terms-Classifying texture samples, Gaussian Markov random fields (GMRFs), least squares (LS) method, priority sequence, residential-area detection.