[1] Using the measurements of 750 GPS stations around the Tibetan Plateau for over 10 years since 1999, we derived a high-resolution 3-D velocity field for the present-day crustal movement of the plateau. The horizontal velocity field relative to stable Eurasia displays in details the crustal movement and tectonic deformation features of the India-Eurasia continental collision zone with thrust compression, lateral extrusion, and clockwise rotation. The vertical velocity field reveals that the Tibetan Plateau is continuing to rise as a whole relative to its stable north neighbor. However, in some subregions, uplift is insignificant or even negative. The main features of the vertical crustal deformation of the plateau are the following: (a) The Himalayan range is still rising at a rate of ~2 mm/yr. The uplift rate is ~6 mm/yr with respect to the south foot of the Himalayan range. (b) The middle eastern plateau has a typical uplift rate between 1 and 2 mm/yr, and some high mountain ranges in this area, like the Longmen Shan and Gongga Shan, have surprising uplift rates as large as 2–3mm/yr. (c) In the middle southern plateau, there is a basin and endorheic subregion with a series of NS striking normal faults, showing obvious sinking with the rates between 0 and -3 mm/yr. (d) The present-day rising and sinking subregions generally correspond well to the Cenozoic orogenic belts and basins, respectively. (e) At the southeastern corner of the plateau. There is an apparent trend that the uplift rate is gradually decreasing from between 0.8 and 2.3 mm/yr in the inner plateau to between -0.5 and -1.6 mm/yr outside the plateau, with the decrease of terrain height.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2013JB010503

Three‐dimensional velocity field of present‐day crustal motion of the Tibetan Plateau derived from GPS measurements

The 2008 Wenchuan earthquake occurred on imbricate, oblique, steeply dipping, slowly slipping, listric-reverse faults. Measurements of coseismic slip, the distribution of aftershocks, and fault-plane solution of the mainshock all confirm this style of deformation and indicate cascading earthquake rupture of multiple segments, each with coseismic slip occurring in the shallow crust above a depth range of 10 to 12 km. Interactions among three geological units—eastern Tibet, the Longmen Shan, and the Sichuan basin—caused slow strain accumulation in the Longmen Shan so that measurable preearthquake slip was minor. Coseismic deformation, however, took place mostly within the interseismically locked Longmen Shan fault zone. The earthquake may have initiated from slip on a fault plane dipping 30–40° northwest in a depth range from 15 to 20 km and triggered oblique slip on the high-angle faults at depths shallower than 15 km to form the great Wenchuan earthquake.

Oblique, High-Angle, Listric-Reverse Faulting and Associated Development of Strain: The Wenchuan Earthquake of May 12, 2008, Sichuan, China

The geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation, propagation and arrest of seismic ruptures. The fault system that runs from southern California into Mexico is a simple strike-slip boundary: the west side of California and Mexico moves northwards with respect to the east. However, the M_w 7.2 2010 El Mayor–Cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike-slip fault. Here we use geodetic, remote-sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake. We find that the earthquake produced a straight 120-km-long fault trace that cut through the Cucapah mountain range and across the Colorado River delta. However, at depth, the fault is made up of two different segments connected by a small extensional fault. Both segments strike N130° E, but dip in opposite directions. The earthquake was initiated on the connecting extensional fault and 15 s later ruptured the two main segments with dominantly strike-slip motion. We show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves. We conclude that the location and detailed characteristics of the earthquake could not have been anticipated on the basis of observations of surface geology alone.

Superficial simplicity of the 2010 El Mayor-Cucapah earthquake of Baja California in Mexico

In the detection applications of synthetic aperture radar (SAR) data, a crucial problem is developing precise models for clutter statistics. Generalized gamma distribution ( $\text{G}\Gamma \text{D}$ ) has been widely applied in many fields of signal processing, and it has been demonstrated to be an appropriate model for describing the statistical behaviors of SAR sea clutter, wherein parameter estimation is a key issue for determining the practical application of $\text{G}\Gamma \text{D}$ . Work that contains three major aspects is performed in this paper. First, an approximate estimator for $\text{G}\Gamma \text{D}$ parameters based on the well-known “method-of-log-cumulants” is derived; a theoretical comparison between the approximate estimator and other known estimators is also presented. Second, based on this estimator, a scheme of parameter estimation is further given by comprehensively considering estimation precision, speed, and applicable conditions. The simulation results show that the presented scheme is fast and effective. Third, we assess the fitting performance of $\text{G}\Gamma \text{D}$ and the proposed scheme using real SAR sea clutter data, and compare the model with generalized-K distribution. The experiments on single-look complex and multilook-processing L-band ALOS-PALSAR and C-band RADARSAT-2 SAR data verify the effectiveness of the proposed scheme of $\text{G}\Gamma \text{D}$ parameter estimation. Moreover, several examples of ship detection in real SAR images testify to the usefulness of the proposed scheme in practical applications.

Scheme of Parameter Estimation for Generalized Gamma Distribution and Its Application to Ship Detection in SAR Images

Geological conditions along the Karakorum Highway (KKH) promote the occurrence of frequent natural disasters, which pose a serious threat to its normal operation. Landslide susceptibility mapping (LSM) provides a basis for analyzing and evaluating the degree of landslide susceptibility of an area. However, there has been limited analysis of actual landslide activity processes in real-time. The SBAS-InSAR (Small Baseline Subsets-Interferometric Synthetic Aperture Radar) method can fully consider the current landslide susceptibility situation and, thus, it can be used to optimize the results of LSM. In this study, we compared the results of LSM using logistic regression and Random Forest models along the KKH. Both approaches produced a classification in terms of very low, low, moderate, high, and very high landslide susceptibility. The evaluation results of the two models revealed a high susceptibility of land sliding in the Gaizi Valley and the Tashkurgan Valley. The Receiver Operating Characteristic (ROC) curve and historical landslide verification points were used to compare the evaluation accuracy of the two models. The Area under Curve (AUC) value of the Random Forest model was 0.981, and 98.79% of the historical landslide points in the verification points fell within the range of high and very high landslide susceptibility degrees. The Random Forest evaluation results were found to be superior to those of the logistic regression and they were combined with the SBAS-InSAR results to conduct a new LSM. The results showed an increase in the landslide susceptibility degree for 2808 cells. We conclude that this optimized landslide susceptibility mapping can provide valuable decision support for disaster prevention and it also provides theoretical guidance for the maintenance and normal operation of KKH.

Landslide Susceptibility Mapping of Karakorum Highway Combined with the Application of SBAS-InSAR Technology.

Tectonic and Geometric Control on Fault Kinematics of the 2021 Mw7.3 Maduo (China) Earthquake Inferred From Interseismic, Coseismic, and Postseismic InSAR Observations

Coseismic deformation fields and a fault slip model for the Mw7.8 mainshock and Mw7.3 aftershock of the Gorkha-Nepal 2015 earthquake derived from Sentinel-1A SAR interferometry

Coseismic deformation derived from analyses of C and L band SAR data and fault slip inversion of the Yushu Ms7.1 earthquake, China in 2010

Locking degree and slip rate deficit distribution on MHT fault before 2015 Nepal Mw 7.9 earthquake

SAR image from sea can constantly contain ships and their ambiguities in azimuth and range directions. For maritime applications, the ambiguities are visible due to their strong intensities in a low backscattering background of sea environment. Thus, the ambiguities can be often mistaken as ships and cause false alarms. Many approaches have been proposed for reducing the azimuth ambiguities in single channel SAR image. This paper analyzed scattering mechanisms of the azimuth ambiguities for PolSAR images and proposed a method for detecting ships from PolSAR images. By using eigenvector-eigenvalue decomposition, three eigenvalues can be used to differentiate ship targets, azimuth ambiguities and sea clutter. One C-band JPL AIRSAR polarimetric data have been chosen to evaluate the method. The experimental results show that the proposed method can effectively reduce false alarms caused by the azimuth ambiguities.

/pdf/ship-detection-from-polarimetric-sar-images-3g8q47iif4.pdf

Xiaogang Song

Papers

Tectonic and Geometric Control on Fault Kinematics of the 2021 Mw7.3 Maduo (China) Earthquake Inferred From Interseismic, Coseismic, and Postseismic InSAR Observations

Coseismic deformation fields and a fault slip model for the Mw7.8 mainshock and Mw7.3 aftershock of the Gorkha-Nepal 2015 earthquake derived from Sentinel-1A SAR interferometry

Coseismic deformation derived from analyses of C and L band SAR data and fault slip inversion of the Yushu Ms7.1 earthquake, China in 2010

Locking degree and slip rate deficit distribution on MHT fault before 2015 Nepal Mw 7.9 earthquake

Ship detection from polarimetric sar images