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On November 25, 2016, an MW 6.6 earthquake struck Akto, a county in the Xinjiang Autonomous Region of China. This earthquake nucleated on the dextral steep-dip strike-slip segment of the Muji fault, in the western Tibetan Plateau. In this study we conducted a joint inversion using a higher number of data than in previous works (i.e., teleseismic P and SH waveform, near-field seismic waveform, and coseismic InSAR displacement data), in order to analyze the spatiotemporal rupture process of this seismic event. The results of the joint inversion showed that the event consisted in a primarily unilateral rupture toward east-southeast (along the Muji fault) and that 90% of the scalar seismic moment was released in the first 18 s. Moreover, we confirmed the occurrence of two major asperities: the first one located right next to the hypocenter, and the second one ~30–35 km east of the hypocenter. The first asperity was found at a deeper depth than the second asperity; additionally, it was larger and had a smaller slip. The results of the Coulomb stress change analysis suggested that the rupture of the first asperity triggered the rupture of the second one. The heterogeneity of the on-fault slip revealed the heterogeneity of the inherent strength and stress of the Muji fault; moreover, the clear slip deficit area, characterized by a high Coulomb stress, might indicate a high seismic risk.

We used two tracks of ALOS PALSAR images to investigate the focal mechanism and slip distribution of the 2011 March 24, M W 6.8 Burma strike-slip earthquake. Three different SAR techniques, namely conventional interferometry, SAR pixel offsets (SPO) and multiple-aperture InSAR (MAI), were employed to obtain the coseismic surface deformation fields along the ∼30 km length of the fault rupture. Along-track measurements from SPO and MAI techniques show a high correlation, and were subsequently used to precisely determine the location and extent of the surface fault trace. The best-fitting fault model geometry derived from an iterative inversion technique suggests that the rupture occurred on a near-vertical sinistral strike-slip fault west of the Nam Ma fault with a strike of 70°. A maximum slip of 4.2 m occurs at a depth of 2.5 km, with significant slip constrained only to the upper 10 km of the crust.

In this study, we present coseismic and poseismic surface displacements caused by the 2015 M W 8.3 Illapel (Chile) earthquake with Sentinel-1A (S1A) and RADARSAT-2 (RS2) SAR imagery. The Central Chile, where the earthquake occurred, is a great place to apply InSAR techniques. All RS2 and S1A pairs have good coherence including one pair with a three-year long temporal baseline. However, topographically correlated atmospheric effects significantly influence most of InSAR results, particularly those postseismic interferograms. We use Global Atmospheric Models (GAM) simulation to mitigate the effects of stratified tropospheric delays before implementing InSAR deformation time series analysis. Two global atmospheric models, ERA-Interim and MERRA are compared for their performance to reduce the atmospheric effects. The results show that MERRA data can reduce atmospheric errors from 10% to 44%, which is slightly better than those derived from ERA-Interim. Both co- and post-seismic deformation patterns have been captured by RS2 and S1A interferograms.

A new era of space-based surveillance for global changes has begun with newly launched Synthetic Aperture Radar (SAR) missions Sentinel-1A and ALOS-2 and the upcoming RADARSAT Constellation Mission (RMC) and NASAISRO (NISAR). Heavy loads of SAR data are expected to be acquired regularly in the near future. This no doubt, is good news for a wide range of research applications. However, it also remains challenging to effectively handle such large amounts of SAR data.

Assessment of seismic hazard relies on estimates of how large an area of a tectonic fault could potentially rupture in a single earthquake. Vital information for these forecasts includes which areas of a fault are locked and how the fault is segmented. Much research has focused on exploring downdip limits to fault rupture from chemical and thermal boundaries, and along-strike barriers from subducted structural features, yet we regularly see only partial rupture of fully locked fault patches that could have ruptured as a whole in a larger earthquake. Here we draw insight into this conundrum from the 25 April 2015 Mw 7.8 Gorkha (Nepal) earthquake. We invert geodetic data with a structural model of the Main Himalayan thrust in the region of Kathmandu, Nepal, showing that this event was generated by rupture of a décollement bounded on all sides by more steeply dipping ramps. The morphological bounds explain why the event ruptured only a small piece of a large fully locked seismic gap. We then use dynamic earthquake cycle modeling on the same fault geometry to reveal that such events are predicted by the physics. Depending on the earthquake history and the details of rupture dynamics, however, great earthquakes that rupture the entire seismogenic zone are also possible. These insights from Nepal should be applicable to understanding bounds on earthquake size on megathrusts worldwide. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Published version

On April 25, 2015, a destructive MW 7.8 earthquake struck the capital of Nepal, Kathmandu, killing more than 8800 people and destroying numerous historical structures. We analyze six coseismic interferograms from several satellites (ALOS-2, Sentinel-1 A, and RADARSAT-2), as well as three-dimensional displacements at six GPS stations to investigate fault structure and slip distribution of the Gorkha earthquake. Using a layered crustal structure, the best-fit slip model shows that the preferred dip angle of the mainshock fault is 6 ± 3.5° and the major slip is concentrated within depths of 8–15 km. The maximum slip of ~ 6.0 m occurs at a depth of 11 km, 70 km south east of the epicenter. The coseismic rupture extends ~ 150 km eastward of the epicentre with a cumulative geodetic moment of 7.8 × 1020 Nm, equivalent to an earthquake of MW 7.84. We also investigate the MW 7.2 aftershock on 12 May 2015 using another three postseismic interferograms from ALOS2, RADARSAT-2, and Sentinel-1 A. The InSAR-based best-fit slip model of the largest aftershock implies that its major slip is next to the eastern lower end of the mainshock rupture with a similar maximum slip of ~ 6 m at a depth of ~ 13 km. This study generates various coseismic geodetic measurements to determine the source parameters of the MW 7.8 Gorkha earthquake and 12 May MW 7.2 afershock, providing an additional chance to understand the local fault structure and slip extent. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore)

The moment tensor solution, source time function and spatial-temporal rupture process of the Ms6.4 earthquake, which occurred in Ning’er, Yunnan Province, are obtained by inverting the broadband waveform data of 20 global stations. The inverted result shows that the scalar seismic moment is 5.51×1018 Nm, which corresponds to a moment magnitude of MW 6.4. The correspondent best double couple solution results in two nodal planes of strike 152°/dip 54°/rake 166°, and strike 250°/dip 79°/ rake 37°, respectively. Considering the isoseismals and geological structures in the meizoseismal region, the first nodal plane (strike 152°/ dip 54°/ rake 166°) is preferred to be the seismogenic fault. Thus, the Ms6.4 earthquake occurred mainly along a right-lateral fault striking 152°. The source time function shows that the duration time of the earthquake is about 14 s. The most of the energy releases within the first 11 s and in 11–14 s the rupture is weak. The snapshots of the slip-rate indicate that the rupture process has 3 more detailed stages. In the first stage of the first 4 s after rupture initiation, the rupture propagates simultaneously toward both strike and dip directions; in the second stage of the following 3 s, the rupture extends to down-dip direction; and in the third stage, the rupture looks to be scattering on the fault. In general, this earthquake is of bilateral rupture, and the rupture mainly takes place in strike-dip direction. The major ruptured area is in the shape of a diamond with a dimension of 19 km. On the whole fault plane, the maximum slip is about 1.2 m, the average slip is about 0.1 m, the maximum slip-rate is 0.4 m/s and the average slip-rate is 0.1 m/s. The features of the co-seismic theoretical displacement field of the Ning’er earthquake fault, calculated based on the inverted fault parameters, are consistent with those of the observed isoseismals.

Focal mechanism and dynamic rupture process of the Wenchaun M s8.0 earthquake in Sichuan province on 12 May 2008 were obtained by inverting long period seismic data from the Global Seismic Network (GSN), and characteristics of the co-seismic displacement field near the fault were quantitatively ana-lyzed based on the inverted results to investigate the mechanism causing disaster. A finite fault model with given focal mechanism and vertical components of the long period P-waves from 21 stations with evenly azimuthal coverage were adopted in the inversion. From the inverted results as well as after-shock distribution, the causative fault of the great Wenchuan earthquake was confirmed to be a fault of strike 225°/dip 39°/rake 120°, indicating that the earthquake was mainly a thrust event with right-lateral strike-slip component. The released scalar seismic moment was estimated to be about 9.4×1020―2.0×1021 Nm, yielding moment magnitude of M w7.9―8.1. The great Wenchuan earthquake occurred on a fault more than 300 km long, and had a complicated rupture process of about 90 s duration time. The slip distribution was highly inhomogeneous with the average slip of about 2.4 m. Four slip-patches broke the ground surface. Two of them were underneath the regions of Wenchuan-Yingxiu and Beichuan, respectively, with the first being around the hypocenter (rupture initiation point), where the largest slip was about 7.3 m, and the second being underneath Beichuan and extending to Pingwu, where the largest slip was about 5.6 m. The other two slip-patches had smaller sizes, one having the maximum slip of 1.8 m and lying underneath the north of Kangding, and the other having the maximum slip of 0.7 m and lying underneath the northeast of Qingchuan. Average and maximum stress drops over the whole fault plane were estimated to be 18 MPa and 53 MPa, respectively. In addition, the co-seismic displacement field near the fault was analyzed. The results indicate that the features of the co-seismic displacement field were coincident with those of the intensity distribution in the meizo-seismal area, implying that the large-scale, large-amplitude and surface-broken thrust dislocation should be responsible for the serious disaster in the near fault area.

SUMMARY A new technique is presented to jointly invert the teleseismic and Interferometric Synthetic Aperture Radar (InSAR) data by simultaneously searching for the hypocentre and the relative weight of InSAR data. In this technique, the parameters of causative fault is determined by using InSAR data first, and then the hypocentre is searched for by jointly inverting teleseismic and InSAR data with the assumption that each subfault on the fault is a potential hypocentre. With this technique, we investigated the source rupture process of the 2009 April 6 L’Aquila MW 6.3 earthquake without the use of the existing hypocentre locations. Our estimated hypocentre is 42.366°N, 13.385°E, depth 6.9 km, with an uncertainty of 1∼2 km, similar to the hypocentre (42.348°N, 13.380°E, depth 9.5 km) determined by National Institute of Geophysics and Volcanology (INGV) using arrival time data within the epicentral distance of 50 km. Our joint inversion suggests a scalar moment of 3.5 × 1018 Nm, equivalent to a moment magnitude of MW 6.3. The source process consists of two subevents with a total duration of 7.7 s. The first event (0∼3 s) corresponds to the slip patch near the hypocentre and the second (in the next 4.7 s) ruptured the other slip patch at 4∼16 km along the strike direction. These unilateral rupture characteristics of the L’Aquila earthquake are confirmed by the apparent source time functions (ASTFs) analysis. In addition, two resolution tests are performed to check the reliability of this work, clarifying the differences between the inversion results with teleseismic data only, InSAR data only and joint inversion, indicating that a higher resolution can be achieved through the joint inversion.

By combining observations from satellite radar, body wave seismology and optical imagery, we have determined the fault segmentation and sequence of ruptures for the 2010 Mw 6.8 Yushu (China) earthquake. We have mapped the fault trace using displacements from SAR image matching, interferometric phase and coherence, and 2.5 m SPOT-5 satellite images. Modeling the event as an elastic dislocation with three segments fitted to the fault trace suggests that the southeast and northwest segments are near vertical, with the central segment dipping 70° to the southwest; slip occurs mainly in the upper 10 km, with a maximum slip of 1.5 m at a depth of 4 km on the southeastern segment. The maximum slip in the top 1 km (i.e., near surface) is up to 1.2 m, and inferred locations of significant surface rupture are consistent with displacements from SAR image matching and field observations. The radar interferograms show rupture over a distance of almost 80 km, much larger than initial seismological and field estimates of the length of the fault. Part of this difference can be attributed to slip on the northwestern segment of the fault being due to an Mw 6.1 aftershock two hours after the main event. The remaining difference can be explained by a non-uniform slip distribution with much of the moment release occurring at depths of less than 10 km. The rupture on the central and southeastern segments of the fault in the main shock propagated at a speed of 2.5 km/s southeastward toward the town of Yushu located at the end of this segment, accounting for the considerable building damage. Strain accumulation since the last earthquake on the fault segment beyond Yushu is equivalent to an Mw 6.5 earthquake. © 2011 by the American Geophysical Union.

[1] The 1998 Mw 5.7 Zhangbei-Shangyi (China) earthquake is the largest to have occurred in northern China since the large 1976 Ms 7.8 Tangshan earthquake. Due to its proximity to Beijing, the capital of China, it has therefore gained a lot of attention. A great number of studies have been conducted using seismic and geodetic data, but few are able to identify conclusively the orientation of the primary fault plane for this earthquake. In this paper, two independent ERS synthetic aperture radar interferograms are used to determine precisely the location and magnitude of coseismic surface displacements (∼11 cm in the radar line of sight). Modeling the event as dislocation in an elastic half-space suggests that the earthquake is associated with a buried shallow NNE-SSW oriented thrust fault with a limited amount of lateral displacement, which is consistent with seismic intensity distribution and aftershock locations.

In this paper, we discussed the techniques of accessing and analyzing remotely sensed data stored in Internet/intranet servers from client browsers. First, the existing approaches for Web-based image sharing are compared. Then, to overcome the limitations of present methods, we introduce a new architecture which integrates ION (IDL on Net) and ARCIMS in developing geographic data servers - processing the image data stored in database and/or in files. Some operations, such as online enhancement, classification and filtering, which cannot be implemented before, can now be easily achieved, although this is somewhat time-consuming in some cases. Finally, we set up our national Landsat-7 ETM Plus imagery database by integrating ION with ARCIMS, and desirable results were obtained.

Remote sensing image has such characteristics as macroscopical, real and clear structure trace, so it is an efficient method to apply remote sensing image to interpreting works, in order to study seismic geology. In this paper, we attempt to apply remote sensing image visual interpretation results to study the active structure characteristics in Turpan-Hami basin, and discuss the earthquake activity rules in this region. On the one hand, after geometric correction and mosaic we merge 4, 7, 1 bands with the 8th band of ETM+ images, gaining a color image with 15-metre resolution. Then we do some processing such as enhancement and feature extraction, in order to make the linear feature clearer. On the other hand, we analyze the image with DEM, producing 3D effect. Both them are very useful for us to study the geological structure and active faults. In our works, we primarily analyze and study the linear structure zone in Turpan-Hami basin with texture analysis and DEM, extracts the linear structure character of this region. Then we have a new understanding for double bow-backed structure, and do some study about the correlation of this special structure and the earthquake activity rule in this region

In this paper we studied the Honghe fault zone in the view of large scale extent and the relation of the association of Honghe fault and Xiaojiang fault. In our study we put emphasis upon the methodology research about the application of Digital Elevation Model (DEM) and CIS data. By utilizing DEM we perform the slope angle analysis, which gains valuable results. In addition directional filtering is also proved to be effective