The Xiaojiang Fault (XJF) Zone locates in the southeastern of Tibetan Plateau and defines the boundary between the South China and Sichuan-Yunnan blocks. Historical large earthquakes were hosted on the XJF, though its seismic hazard in the near future is under debate. In this study, we utilize portable broad-band seismic network to unravel the microseismic activities along XJF, and to further investigate the fault structures and their properties. Adopting PALM, a newly developed earthquake detection algorithm, we obtained ~13,000 relocated events. The micro-seismicity reveals widespread off-fault structures showing conjugate geometry, while the major faults present low seismicity. The fault branches conjugate to the main-fault present intensive microseismicity, which hosts repeating events and presents high b-value. Regional GPS stations reflect slips are mostly concentrated along the XJF, while the slip rate on off-fault branches correlates with seismic activities on these structures. Combining with other recent seismological and magnetotellurics evidences, we suggest a low strength on these off-fault structures, which may partially release tectonic stress loading and serve as a barrier for future big earthquakes. On the XJF, the microseismic events are clustered on the fault junctions with low b-value. A special set of clusters between 25°N to 25.5°N show an along-strike variation of depth from 10 to 25-km, imaging the boundary between creeping and locked fault portions. We revisit the seismic hazard problem of XJF, and conclude that XJF is at the late stage of inter-seismic period.

Intra-continental dip-slip earthquakes often occur in the orogen and rift zones with complex tectonics, providing rare opportunities to illuminate the deformation and evolution of continental structures. However, due to the sparse seismological and geodetic observations, such earthquakes are less studied. Here, we report the fault geometries of two dip-slip earthquakes recently occurred in Southern Tian Shan and the Mongolia-Baikal rift zone revealed by InSAR . The 2020 Mw6.0 Jiashi earthquake occurred in the Keping-tage fold-and-thrust belt in southwest Tian Shan. This region is seismically active, yet most well-recorded earthquakes occurred south of the mountain front. The lack of large earthquakes beneath the belt thus hinders our understanding of the orogenic process to the north. Combining InSAR measurements and relocated aftershocks, we found that a fault model involving a shallow thrust fault and two deeper faults can best reconcile the surface deformation and aftershock distribution. Stress analysis suggests that slips on the shallow fault reactivated the older basement structures at depth. Our results reflect the basement-involved shortening activated by a thin-skinned thrust faulting event with surface deformation, implying a southward orogenic process of the southwest Tian Shan. The 2021 Mw6.7 Lake Hövsgöl earthquake occurred in the Mongolia-Baikal rift zone (MBRZ), which is located in the northern tip of the northern Mongolia, and is bounded by the Tibet Plateau orogenic belt and the Siberian Platform. Using the Bayesian inversion method we derived a fault plane with two slip patches, one is mainly strike slip and the other is mainly normal slip component. The correlation between the observed and predicted displacements by the single fault model is 97.46%. Coulomb stress analysis shows that the 2021 event has a triggering effect on the western segment of the Tunka Fault to the north, where no large earthquakes have occurred since the 1905 M8+ earthquake, raising the potential for seismic risk in this region.

We reveal a slip-partitioning rupture on the North Hovsgol Fault during the 2021 Mw6.7 Lake Hovsgol, Mongolia earthquake. Left-lateral motions on the Mondy Fault north of the epicenter likely controlled the observed slip partitioning pattern. The earthquake highlights the non-negligible role of the bounding strike-slip fault in the formation and evolution of oblique rift.

The Keping-tage fold-thrust belt in southwest Tian Shan is seismically active, yet most well-recorded earthquakes occurred south of the mountain front, hindering our understanding of the orogenic process to the north. The 2020 Mw6.0 Jiashi earthquake is an important event with surface deformation in the nappe structure well illuminated by InSAR. Here, we employ the surface deformation and relocated aftershocks to investigate the fault slip distribution associated to this event. Further added by an analysis of Coulomb stress changes, we derive a fault model involving slips on a shallow low-angle (~10º) north-dipping thrust fault as well as on a left-lateral tear fault and a high-angle south-dipping reverse fault in mid crust. Our results reflect the basement-involved shorterning activated by a thin-skinned thrust faulting event with the surface deformation implying the basin-ward orogenic process of the southwest Tian Shan.

The geodetic measurements of accumulated strains along active faults during their interseismic periods have a strong connection with faulting dynamics and seismic hazards evaluation. InSAR has been widely applied to study the interseismic deformation along active strike-slip faults around the world. However, various limitations such as that from phase unwrapping errors and tropospheric delays are often encountered, hindering our interpretation and model inversion. Phase-gradient stacking is a method that sums up wrapped phase differences of adjacent pixels in multi-interferograms. It has been successfully conducted to reveal local deformation signals across coseismic fractures, yet lacks of application to relatively larger-scale deformation signals. Here we apply the phase-gradient stacking method, for the first time, to study the interseismic deformation along the North Anatolian Fault with Sentinel-1 SAR images acquired from 2014 to 2021. We obtain the strain rate field across the North Anatolian fault without the need of unwrapping hundreds of large interferograms. Segments with surface creep and strong coupling effects can be clearly distinguished in the phase gradient maps, allowing us to directly invert for their long-term slip rates and locking depths. Our preliminary, but promising results show that the phase-gradient stacking method has advantages in studying interseismic deformation along strike-slip faults by directly connecting strain with fault parameters.

Fault geometric complexity plays a critical role in earthquake rupture dimension. Fault bifurcations are commonly observed in earthquake geology, yet, robust kinematic rupture processes on bifurcated fault branches are largely missing, limiting our understanding of rupture dynamics and seismic hazard. Here, we holistically study the fault geometry and bilateral rupture of the 2021 Mw7.4 Maduo, China earthquake, that shows clear fault bifurcation near its eastern terminal. We integrate space geodesy imaging, back-projection of high-frequency teleseismic array waveforms, multiple point source and finite fault inversions, and constrain in detail the rupture process, in particular, through its fault bifurcation. Our models reveal a stable rupture speed of ~2.5 km/s throughout the entire rupture and a simultaneous rupture through fault branches bifurcated at 20°. The rupture on bifurcated faults radiated more high-frequency waves, especially from the stopping phases. The stopping phase on the southern branch likely stopped the rupture on the northern branch.

The rupture process of earthquakes at intermediate depth (~70-300 km) have been rarely illuminated by a joint analysis of geodetic and seismic observations, hindering our understanding on their dynamic rupture mechanisms. Here we present detailed rupture process of the 2019 Mw8.0 Peru earthquake at the depth of 122 km with a holistic approach reconciling InSAR and broadband seismological waveform data. The joint inversion of InSAR observations and teleseismic body waves results in a finite rupture model that extends ~200 km along strike, with unilateral rupture towards north that lasted for ~60 s. There are four major asperities in the finite fault model which are well corresponding to position and timing of the sources in back-projection (BP) and multiple points source (MPS) results. The largest asperity, which occurred ~40 s after the rupture initiation, was featured with longer and smoother risetime, and radiated much weaker high-frequency seismic waves compared to other smaller asperities. This distinct frequency-dependent rupture requires a strong dynamic weakening mechanism, likely thermal pressurization of pore free water rather than thermal runaway. Our frequency content analysis could be generalized to study other earthquakes including those deeper than 300 km.