Over 12 years of continuous monitoring of Changbaishan volcano in the border region of China and North Korea by means of volcanic seismicity, ground deformation, and volcanic gas geochemistry yields new evidence for magmatic unrest of the volcano between 2002 and 2006. In this so‐called “active period,” the frequency of volcanic earthquakes increased by about 2 orders of magnitude compared to that of the background “inactive periods.” The active period was also accompanied by ground inflation, high values of CO2, He, H2, and high ratios of N2/O2 and 3He/4He in volcanic gases released from three hot springs near the caldera rim. The monitoring evidence implies pressurization of the magma chamber, possibly caused by incremental magma recharge. The ground deformation data from both GPS and precise leveling are modeled to suggest the corresponding deformation source is at 2–60 km depth beneath the volcano's summit, where earthquake swarms were detected in 2002 and 2003. Our findings suggest that the magma chamber beneath Changbaishan volcano has awakened and resumed activity after remaining dormant since AD 1903. There is an urgent need to keep close watch on this active and very hazardous volcano in northeast China.

The increased seismic activity of the last ~10 years in Changning county of Sichuan Province comprised just small (mostly ML < 5.0) injection‐induced earthquakes. The MW 5.7 earthquake on June 17, 2019, is the largest event ever reported there. Moment tensor of the mainshock was remarkably dominated by a compensated linear vector dipole. We resolve its fine structure showing it was a doublet, allowing approximation by a thrust‐ and strike‐slip subevent. The mainshock nucleated as thrust faulting, which (together with the largest aftershocks) can be linked with previously known reverse faults, favorably oriented to regional stress field. Contrarily, the strike‐slip segment of the mainshock, less favorably oriented, was probably facilitated by elevated pore pressure due to previous injections. Shallow active strike‐slip faulting, not yet mapped in the region, is a new feature, important for future hazard assessment.

The increased seismic activity of the last ~10 years in Changning county of Sichuan Province comprised just small (mostly ML &lt; 5.0) injection-induced earthquakes. The MW 5.7 earthquake of June 17, 2019 is the largest event ever reported there. Moment tensor of the mainshock was remarkably dominated by a compensated linear vector dipole. We resolve its fine structure showing it was a doublet, allowing approximation by a thrust- and strike-slip subevent. The mainshock nucleated as thrust faulting, which (together with the largest aftershocks) can be linked with previously known reverse faults, favorably oriented to regional stress field. Contrarily, the strike-slip segment of the mainshock, less favorably oriented, was probably facilitated by elevated pore pressure due to previous injections. Shallow active strike-slip faulting, not yet mapped in the region, is a new feature, important for future hazard assessment.

Details of Pacific plate subduction under the Japan Sea and associated current seismicity remain challenging. Seismic tomography reveals a continuous slab dipping at ~30° down to ~600 km, and earthquake mechanisms point to down-dip compression. Further, the slab is lying at the 660-km discontinuity, and this zone is aseismic. We suggest that this pattern results from the slab's negative thermal buoyancy, resistance of the viscous lower mantle, and buoyancy forces associated with the phase transitions at 410 km and 660 km. Our model comprises an ageing subducting plate, nonlinear rheology and major phase transitions. The model explains the observed low dip angle of the slab and predicts a detailed stress pattern related to bending down to 450 km, followed by unbending as the slab is laid flat upon the 660 km boundary. Remarkably, in the bending/unbending regions, downdip compression occurs close to the slab top/bottom, respectively. As only down-dip compression is observed, we argue that the earthquakes are mapping the top and bottom of the slab. The absence of seismicity in the flat-lying slab is explained by significantly lower stresses and higher temperatures. With this new knowledge, increasingly accurate seismic locations will considerably improve images of finite-extent slab geometry. Present knowledge of viscoelastic structure and mineralogy provides advanced models of lithospheric slabs and their subduction in the mantle 1. When modeling a specific region of the world, several competing models can be constructed. Their common features are determined by the key model assumptions and parameters, such as rheology or thermomechanical properties of mantle material. However, due to variations of (and uncertainties in) many others-such as slab age, properties of the overriding plate, and properties of the decoupling layer between the subducting and overriding plates-such models result in large variety of slab morphologies and thermal structures. In order to tailor them to specific natural subduction regions, subduction models should be constrained by independent seismic observations, e.g. tomography, seismicity, focal mechanisms, principal stress axes. We call these geodynamic-seismic models. Though there are numerous subduction modeling studies that investigate stress evolution in kinematic models with predefined subduction geometry, thermal structure and/ or velocity 2-6 , there are only a few that study stress evolution in a fully dynamic setup 7-11 and relate it to the stress derived from seismicity in a natural subduction area 12,13. Particularly interesting are physical conditions at the deepest slab 'tips' , determining interaction with the 660-km discontinuity, e.g. temporary stagnation of slabs. Searches for suitable geodynamic-seismic models are challenging because deep-focus earthquakes are rare and their physical nature is still puzzling 14. The aim of this paper is to provide a geodynamic-seismic model for the subduction of the Pacific plate beneath the Japan Sea and Eastern China. In this region, ac...

The 2017 North Korea test is analyzed together with the previous 2009-2016 tests, and a generalized source model is derived using waveform data. Data are represented by lowfrequency records of 11 broadband near-regional stations (epicentral distances 140-310 km), bandpassed from 0.03 to 0.09 Hz. The events feature a significant degree of similarity. Therefore, mean records can be calculated by averaging the five tests, using the cross-correlation shifts and amplitude scaling. The mean records are inverted for the full moment tensor in terms of its posterior probability density function. The meansource model reveals significant uncertainties and parameter tradeoffs, due to well-known resolution problems at shallow depths and long wavelengths. Nevertheless, the moment tensor is undoubtedly dominated by its nonshear parts, that is, the isotropic component, and compensated linear vector dipole (inclined ∼15°to the vertical). The source type is very close to an opening crack, consistent with existing physical models of explosive shallow sources, accompanied by material damage. The generalized source model presented here is new. It can be used as a prior, realistically constrained model, applicable in early discriminations between natural earthquakes and explosions at the test site. Users at any station (not involved in this study) could precompute template synthetics in their preferred frequency ranges and velocity models. If fitting with real data by a single-constant source scaling, a real-time indication of an explosion similar to the previous Democratic People's Republic of Korea (DPRK) tests can be obtained. Electronic Supplement: Tables and figures illustrating details of the individual 2009-2017 tests and of the mean-source model. METHOD Moment Tensor Inversion and Resolution AnalysisThis issue has been thoroughly explained in Paper 1; thus we present only a short summary herein. Seismic waveforms are inverted for full MT using ISOLA software (e.g., Sokos et al.,