A linked-fault-element model is employed to invert for contemporary slip rates along major active faults in the Sichuan-Yunnan region (96°-108°E, 21°-35°N) using the least squares method. The model is based on known fault geometry, and constrained by a GPS-derived horizontal velocity field. Our results support a model attributing the eastward extrusion of the Tibetan Plateau driven mainly by the north-northeastward indentation of the Indian plate into Tibet and the gravitational collapse of the plateau. Resisted by a relatively stable south China block, materials of the Sichuan-Yunnan region rotate clockwise around the eastern Himalayan tectonic syntaxis. During the process the Garzê-Yushu, Xianshuihe, Anninghe, Zemuhe, Daliangshan, and Xiaojiang faults, the southwest extension of the Xiaojiang fault, and the Daluo-Jinghong and Mae Chan faults constitute the northeast and east boundaries of the eastward extrusion, with their left slip rates being 0.3-14.7, 8.9-17.1, 5.1 ± 2.5, 2.8 ± 2.3, 7.1 ± 2.1, 9.4 ± 1.2, 10.1 ± 2.0, 7.3 ± 2.6, and 4.9 ± 3.0 mm/a respectively. The southwestern boundary consists of a widely distributed dextral transpressional zone other than a single fault. Right slip rates of 4.2 ± 1.3, 4.3 ± 1.1, and 8.5 ± 1.7 mm/a are detected across the Nanhua-Chuxiong-Jianshui, Wuliangshan, and Longling-Lancang faults. Crustal deformation across the Longmenshan fault is weak, with shortening rates of 1.4 ± 1.0 and 1.6 ± 1.3 mm/a across the Baoxing-Beichuan and Beichuan-Qingchuan segments. Northwest of the Longmenshan fault lies an active deformation zone (the Longriba fault) with 5.1±1.2 mm/a right slip across. Relatively large slip rates are detected across a few faults within the Sichuan-Yunnan block: 4.4±1.3 mm/a left slip and 2.7±1.1 mm/a shortening across the Litang fault, and 2.7±2.3 mm/a right-lateral shearing and 6.7±2.3 mm/a shortening across the Yunongxi fault and its surrounding regions.In conclusion, we find that the Sichuan-Yunnan region is divided into more than a dozen active micro-blocks by a large number of faults with relatively slow slip rates. The eastward extrusion of the Tibetan Plateau is absorbed and adjusted in the region mainly by these faults, other than a small number of large strike-slip faults with fast slip rates.Sichuan-Yunnan region, GPS, linked-fault-element, slip rate

No abstract

The paper describes results of studying effects of total electron content (TEC) variations triggered by the Chelyabinsk meteoroid airburst as inferred from unique data of a dense GPS network located around the final part of the meteoroid atmospheric path. Well‐pronounced TEC disturbances with an average period of about 10 min and amplitude of 0.07–0.5 TECU (total electron content unit, 1 TECU = 1016 el m−2) were detected. These disturbances were initiated by an ionospheric source activated about 5–6 min after the airburst. The disturbance velocity damping with time and distance from the airburst was revealed using a GPS interferometric technique. Several modes of TEC disturbances with propagation velocities ranging from 250 to 660 m/s were distinguished through the distance‐time diagram analysis. The estimated position of ionospheric source of TEC disturbances is shifted 36 km southwestward from the airburst, which is most likely to be associated with the conjoint influence of TEC data errors, damping and anisotropy of TID propagation velocity.

On 22 May 2021, an Mw 7.4 earthquake struck Maduo, China, within the eastern Bayan Har block of the Tibetan plateau. The eastward-extruding Bayan Har block is marked by active seismicity along its boundary faults, including the 2008 Mw 7.9 Wenchuan earthquake, but large earthquakes within the block are relatively rare. Thus, the Maduo earthquake could provide useful information about crustal deformation of the Tibetan plateau. Early reports, shortly after the earthquake, have suggested a sinistral strike-slip fault rupture, but the fault geometry and slip distribution vary in these models due to the limited observational constraints. Here, we reconstructed a model of fault geometry and coseismic slip using Interferometric Synthetic Aperture Radar and Global Positioning System data. A nonplanar fault model was constructed based on pixel-offset images and the optimized dip angle. The along-strike variation of the dip angle is small, so a single optimized dip is used. Our results suggest that the Maduo earthquake ruptured ∼156 km on a northwest-striking major fault that dips 78°, and ∼24 km on a minor southeast-striking fault that dips 64°. Most fault slip occurred above 15 km depth, and released a moment of ∼1.65×1020  N·m. Using the resolved fault source model, we calculated the change of coulomb failure stress in the region and on the neighboring faults. The Maduo earthquake highlighted intrablock deformation in the Tibetan plateau whereas numerous lithospheric blocks extrude along major strike-slip faults.

We installed 10 continuous Global Positioning System (GPS) stations on the northeast margin of the Tibetan Plateau at the end of 2012, in order to qualitatively investigate strain accumulation across the Liupanshan Fault (LPSF). We integrated our newly built stations with 48 other existing GPS stations to provide new insights into three-dimensional tectonic deformation. We employed white plus flicker noise model as a statistical model to obtain realistic velocities and corresponding uncertainties in the ITRF2014 and Ordos-fixed reference frame. The total velocity decrease from northwest to southeast in the Longxi Block (LXB) was 5.3 mm/yr within the range of 200 km west of the LPSF on the horizontal component. The first-order characteristic of the vertical crustal deformation was uplift for the northeastern margin of the Tibetan Plateau. The uplift rates in the LXB and the Ordos Block (ORB) were 1.0 and 2.0 mm/yr, respectively. We adopted an improved spherical wavelet algorithm to invert for multiscale strain rates and rotation rates. Multiscale strain rates showed a complex crustal deformation pattern. A significant clockwise rotation of about 30 nradians/yr (10−9 radians/year) was identified around the Dingxi. Localized strain accumulation was determined around the intersectional region between the Haiyuan Fault (HYF) and the LPSF. The deformation pattern across the LFPS was similar to that of the Longmengshan Fault (LMSF) before the 2008 Wenchuan MS 8.0 earthquake. Furthermore, according to the distributed second invariant of strain rates at different spatial scale, strain partitioning has already spatially localized along the Xiaokou–Liupanshan–Longxian–Baoji fault belt (XLLBF). The tectonic deformation and localized strain buildup together with seismicity imply a high probability for a potential earthquake in this zone.

Global positioning system (GPS) Total electron content (TEC) Wenchuan earthquake Global ionospheric map (GIM) COSMIC f 0 F2 Crustal Movement Observation Network of China (CMONOC) a b s t r a c t Possible ionospheric disturbances relating to the May 12, 2008, Ms8.0 Wenchuan earthquake were identified by Global Positioning System (GPS)-derived total electron content (TEC), ionosonde observations, the global ionospheric map (GIM), and electron density profiles detected by the Constellation Observation System for Meteorology Ionosphere and Climate (COSMIC).We applied a statistical test to detect anomalous TEC signals and found that a unique enhancement in TEC, recorded at 16 GPS stations, appeared on May 9, 2008. The critical frequency at F2 peak (f 0 F2), observed by the Chinese ionosondes, and maximal plasma frequency, derived from COSMIC data, revealed a characteristic similar to GPS TEC variations. The GIM showed that the anomalous variations of May 9 were located southeast of the epicenter. Using GPS data from 13 stations near the epicenter, we analyzed the TEC variations of satellite orbit traces during 04:00e11:00 UT. We found that TEC decreased to the east and increased to the southeast of the epicenter during this period. Results showed that the abnormal disturbance on May 9 was probably an ionospheric precursor of the Wenchuan earthquake of May 12, 2008.

No abstract

[1] We have established 65 GPS stations and derive a detailed horizontal deformation distribution in western Sichuan region, in conjunction with previous measurements at additional 90 stations. The resulting velocity field shows that strike-slip fault system here plays a significant role in adjusting crustal movements (in direction and magnitude) along the eastern borderland of the Tibetan Plateau. We find Xianshuihe fault is essentially creeping in its southeasternmost portion with left-lateral slip rate of 8.4 ± 2.8 mm/a. We report $5.6 mm/a left-lateral slip rate across Anninghe and Daliangshan fault. Mabian fault slips left-laterally at the rate of 2.5 ± 1.4 mm/a with nearly null fault-normal motion. Deformation across Litang and Yunongxi fault appear insignificant at present time. Our results reveal recently ruptured Longmenshan fault has both right-lateral slip rate and compressional rate close to 2.0 ± 1.0 mm/a, implying that the Longmenshan fault indeed absorbs some northeastern motion of Tibetan Plateau and likely causes strain accumulation there, which leads to the breakout of the 12 May 2008 M s 8.0 earthquake. We also find several domains with markedly localized strain rates, which are associated with individual structures.