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In this study, The ENVISAT advanced synthetic aperture radar observations from 2003 to 2010 of a descending track covering an area of 100 km × 300 km were used to map the surface velocity field in northwestern Tibet. The derived line-of-sight (LOS) velocity map revealed that interseismic deformation was mainly located on the Altyn Tagh Fault (ATF) and other four immature subsidiary faults (i.e., Tashikule Fault, Muzitage-jingyuhe Fault, Heishibeihu Fault, and Woniuhu Fault). A 2D elastic screw dislocation model was used to interpret the interferometric synthetic aperture radar (InSAR) velocity profiles, which revealed the following results. (a) The oblique movement is partitioned between left-lateral slip at a rate of 6.3 ± 1.4 mm/y on the ATF and 5.9 ± 2.8 mm/y on the subsidiary faults. The low slip rate of the ATF indicates that the ATF does not drive the northeastward extrusion of material, with most of the extrusion occurring in the eastern interior of the plateau and the four subsidiary faults localizing the oblique convergence partitioned in the west. This can reasonably explain why catastrophic earthquakes and rapid slip do not occur all over along the ATF. (b) Based on the four subsidiary faults accommodating the oblique movement and the traces amalgamation with the EKLF (delineated Bayan Har plate boundary to the northeast), we concluded guardedly that the four subsidiary faults are the evoluting plate boundary of the Bayan Har block to the northwest. (c) The Tanan top-up structure had an uplift rate of ~0.6 mm/y at the south of the Tarim Basin. [ABSTRACT FROM AUTHOR]

The density of GPS measurements is usually one of the key issues in resolving 3-D coseismic deformation field from integrating GPS and Interferometric Synthetic Aperture Radar (InSAR) measurements with pure mathematic interpolation methods An approach that combines the elastic dislocation model with the Best Quadratic Unbiased Estimator (BQUE) or a robust estimation method named IGG (Institute of Geodesy and Geophysics) is proposed to reconstruct 3-D coseismic deformation field, in which only a small amount of GPS data is needed to produce a reasonable initial 3-D coseismic deformation. Then the BQUE and IGG are used to weight the InSAR and GPS measurements to avoid computational issues caused by the negative variance problem and to decrease the impact from gross errors. The Wenchuan earthquake is used to test the proposed method. We find that the developed method makes it possible to use only a few GPSs and InSAR data to recover the 3-D coseismic deformation field, which offers extensive future usage for measuring earthquake deformation, particularly in some tectonically active regions with sparse GPS measurements. [ABSTRACT FROM AUTHOR]

Based on the working principle of satellite radars, the earthquake deformation field measured by interferometric synthetic aperture (InSAR) is the projection of ground displacement associated with the seismogenic fault in the line of sight (LOS) of the satellite. However, LOS projections are complex, and are not only related to the ascending/descending modes and incidence angles of SAR data, but also related to the strike and motion senses of the fault. Even for the same earthquake, the LOS deformation derived from different ascending/descending data can be almost identical in one case, but quite different in another case, which makes the interpretation of InSAR seismic deformation and its comparison with field observations difficult. In this study, we undertook a quantitative analysis of the relationships between LOS observation sensitivity of InSAR and fault strike, fault motion sense, and ascending/descending modes, as well as 3D deformation fields. We studied the features and differences of the LOS deformation fields in different types of earthquakes using ascending/descending modes, with a particularly detailed analysis of the relations for a strike-slip type of earthquake. We also summarized the characteristics of LOS deformation fields of faults with different strikes and optimal observational data modes. Taking the strike-slip Yushu earthquake and the normal Gaize event as examples, we used SAR data of the ascending/descending modes to verify the results of quantitative calculations. These analyses will not only provide a more reasonable interpretation of InSAR seismic deformation fields and but also help understand the differences of seismic deformation fields revealed by data with different observational modes, therefore promoting the application of InSAR technology in seismology. [ABSTRACT FROM AUTHOR]

On September 16, 2015, a magnitude 8.3 earthquake struck west of Illapel, Chile. We analyzed Sentinel-1A/IW InSAR data on the descending track acquired before and after the Chile Mw8.3 earthquake of 16 September 2015. We found that the coseismic deformation field of this event consists of many semi circular fringes protruding to east in an approximately 300km long and 190km wide region. The maximum coseismic displacement is about 1.33m in LOS direction corresponding to subsidence or westward shift of the ground. We inverted the coseismic fault slip based on a small-dip single plane fault model in a homogeneous elastic half space. The inverted coseismic slip mainly concentrates at shallow depth above the hypocenter with a symmetry shape. The rupture length along strike is about 340 km with maximum slip of about 8.16m near the trench. The estimated moment is 3.126×1021 N.m(Mw8.27), the maximum depth of coseismic slip near zero appears to 50km. We also analyzed the postseismic deformation fields using four interferograms with different time intervals. The results show that postseismic deformation occurred in a narrow area of approximately 65km wide with maximum slip 11cm, and its predominant motion changes from uplift to subsidence with time. that is to say, at first, the postseismic deformation direction is opposite to that of coseismic deformation, then it tends to be consistent with coseismic deformation. It maybe indicates the differences and changes in the velocity between the Nazca oceanic plate and the South American continental plate. [ABSTRACT FROM AUTHOR]

Interferometric synthetic aperture radar (InSAR) data from 6 Envisat ASAR descending tracks; spanning the 2003–2010 period; was used to measure interseismic strain accumulation across the Northeastern Tibetan Plateau. Mean line-of-sight (LOS) ratemaps are computed by stacking atmospheric-corrected and orbital-corrected interferograms. The ratemaps from one track with different atmospheric-corrected results or two parallel; partially overlapping tracks; show a consistent pattern of left-lateral motion across the fault; which demonstrates the MERIS and ECMWF atmospheric correction works satisfactorily for small stain measurement of this region; even with a limited number of interferograms. By combining the measurements of InSAR and GPS; a fine crustal deformation velocity and strain rate field was estimated on discrete points with irregular density depending on the fault location; which revealed that the present-day slip rate on the Haiyuan fault system varies little from west to east. A change (2–3 mm/year) in line-of-sight (LOS) deformation rate across the fault is observed from the Jinqianghe segment to its eastern end. Inversion from the cross-fault InSAR profiles gave a shallow locking depth of 3–6 km on the main rupture of the 1920 earthquake. We therefore infer that the middle-lower part of the seismogenic layer on the 1920 rupture is not yet fully locked since the 1920 large earthquake. Benefit from high spatial resolution InSAR data; a low strain accumulation zone with high strain rates on its two ends was detected; which corresponds to the creeping segment; i.e., the Laohushan fault segment. Contrary to the previous knowledge of squeezing structure; an abnormal tension zone is disclosed from the direction map of principal stress; which is consistent with the recent geological study. The distribution of principal stress also showed that the expanding frontier of the northeastern plateau has crossed the Liupan Shan fault zone; even arrived at the northeast area of the Xiaoguan Shan. This result agrees with the deep seismic reflection profile. [ABSTRACT FROM AUTHOR]

Abstract The Mw6.9 Yushu earthquake occurred on 14 April 2010, in Qinghai, China; the largest aftershock, a Mw5.8 event, occurred west of the mainshock on 29 May 2010 (˜40 days later). The aftershock had a different focal mechanism from the mainshock. Furthermore, seismicity after 29 May showed different spatial characteristics in terms of focal depth and distribution direction. To better understand the faulting and the relationship between these two events, we derived the whole displacement field caused by the Yushu mainshock and the Mw5.8 aftershock based on multi-perspective Interferometric Synthetic Aperture Radar (InSAR) data. We then conducted a robust inversion of the slip distribution jointly constrained by InSAR and GPS data. The results indicate that the Mw5.8 aftershock produced a separated deformation field with significant displacement changes of up to ˜4–6 cm, which indicates another intersecting ruptured fault at the west end of the Yushu fault. The slip distribution shows a 75-km NW rupture with a maximum slip of ˜2.1 m at a depth of ˜0–10 km on the main Yushu fault, and a 20 km NE rupture with peak slip of ˜0.4 m at a depth of ˜5–15 km on a vertical hidden fault. Both events showed a dominant left-lateral component. The total rupture length associated with the 2010 Yushu earthquake sequence reached ˜95 km. By calculating Coulomb stress changes, we confirmed that the mainshock triggered the Mw5.8 aftershock. Our results imply that the increased stress at the western end of the Yushu fault caused by the mainshock rupture may have played an important role in transferring the rupture plane from the Yushu fault to the NE hidden fault. [ABSTRACT FROM AUTHOR]

Coseismic deformation fields caused by the moment magnitude (Mw)7.8 mainshock and Mw7.3 aftershock of the 2015 Gorkha-Nepal earthquake are obtained by analyzing Sentinel-1A/IW ascending and descending interferometry data. Results show that the deformation field associated with the Mw7.8 mainshock roughly resembles a prolate ellipse, extending from the epicenter about 20° east by south. The main region of deformation is about 160 km by 110 km, comprising a large southern area of uplift, and a small northern area of subsidence. Assuming that rupture occurred in a homogeneous elastic half-space, the coseismic fault slip models of the mainshock and aftershock are inverted based on a shallow dip fault constrained by the three data sets, Sentinel-1A/IW descending data, ascending data, and ALOS-2 descending data, separately or in combination. Mainshock slip distributions generated from all three data sets are similar, and inversion constrained by all three in combination reveal a comprehensive fault slip model. Indeed, coseismic slip is mainly distributed within a narrow 40 km zone to the north of the Main Frontal Trust (MFT), and at 6–15 km subsurface depth. In addition, the maximum slip in this event was about 5.1 m, the Mw7.8 mainshock ruptured the deep part of the seismogenic zone, while the region between the southern boundary of the rupture area and the MFT remained locked. Therefore, a considerable earthquake risk remains to the south of Kathmandu. The inverted coseismic slip of the Mw7.3 aftershock was concentrated in a small area, close to, and southeast of the epicenter, with maximum displacement of about 3 m. Finally, because there is no overlap between the two slip areas of the mainshock and aftershock, the gap between them, about 15 km in length, has additional potential to generate future earthquakes. [ABSTRACT FROM AUTHOR]

Abstract: We obtained the coseismic deformation field of the Ms7.1 earthquake in Yushu, Qinghai, China on 14 April 2010 using L band and C band SAR images. The results show that the deformation fields derived from L and C bands separately are consistent in general. They are all characterized by concentric elliptic interference fringes surrounding a NW trending fault with two local intensively deformed regions. Meanwhile they have small differences in area coverage of the deformation field, magnitude of LOS displacements and other details of deformation nearby the fault. The deformation from C band and L band covers 89∗59km square and 77∗43km square, with maximum displacements of about 45cm and 65cm in the radar line of sight, respectively. Using these two kinds of InSAR measurements separately and jointly, we constructed a three-segment fault model and inverted the coseismic fault slip of the Yushu event. The inversion results show that the slip distributions constrained by the two kinds of inSAR data are in agreement on the whole. They all indicate two concentration regions of slip distribution, one is located near the Jiegu town on the southeastern segment of the Yushu fault with a large area and the maximum slip of 2.4m, and the other is at the epicenter on the northwestern segment of the fault with a relatively small area. There are also discrepancies between the two kinds of slip distribution models. In general, the scale, magnitude, and depth of slip distribution constrained by C band ASAR data are larger than that by L band PALSAR data. The slip distribution from a joint inversion of the two kinds of SAR data is considered to be the most robust model compared to the results of that constrained by L band SAR data or C band SAR data alone. [Copyright &y& Elsevier]