China Earthquake Administration

Abstract On 24 July 2024, an ML 4.6 earthquake occurred at 26.27° N, 104.74° E in Liupanshui City, Guizhou Province, China. The strongest ground shaking was felt in Fa’er Town, an area with several coal mines. To explore the seismogenic mechanism of this event, we analyzed broadband seismic waveforms from the China National Seismic Network to determine its source parameters, including its focal mechanism, centroid depth, and horizontal location. Because the earthquake was very close to the mining areas, we then constructed an elastic finite-element model to calculate the change in Coulomb failure stress (ΔCFS), aiming to evaluate the impact of mining activities on this event. The results show that the Liupanshui earthquake exhibited a thrust-slip focal mechanism with a centroid depth of ∼2 km. The relocated hypocenter was located directly beneath the coal mining area. Although the calculated ΔCFS in this region was relatively modest (∼4.5 kPa), the shallow depth and spatial correlation strongly suggest that the earthquake was likely induced by local mining activities.

Giant megathrust earthquakes typically occur above the upper-plate Moho or the 350°C isotherm in warm subduction zones. However, large earthquakes also occur within the mantle wedge corner at 35-55 km depth at cold subduction zones, such as the Kermadec, Japan Trench, and Chilean margins. Here we investigate the frictional behavior of lawsonite blueschist metagreywacke, potentially found in cold subduction channels, to better understand the control of metamorphic grade on such first-order variations in seismogenic depth. We perform velocity-step experiments on metagreywacke gouge from room temperature to 500°C and effective normal stresses from 50 MPa to 320 MPa, capturing the unstable friction regime and the brittle-to-flow transition. The constitutive behavior of metagreywacke indicates a potential seismogenic behavior at high temperatures below the Moho. Large megathrust earthquakes in the mantle wedge corner may develop in the lawsonite blueschist metasediment channel of cold subduction slabs.

The Gulang Ms 8.0 strong earthquake that occurred in 1927 claimed the lives of more than 40,000 people in the surrounding areas. Geological studies have shown that the occurrence of the Gulang earthquake did not reduce the seismic hazard of the Laohushan, Maomaoshan and Lenglongling faults, which are the westward extensions of the Haiyuan Fault. Based on the seismic moment accumulation rate, the existence of the Tianzhu Seismic Gap has been proposed. This seismic gap is potentially at risk of producing earthquakes of magnitude 7.0 or higher. Coupled with the frequent occurrence of small earthquakes in this area in recent years, it is regarded as being of considerable seismic danger. In the junction area of the Tianzhu Seismic Gap and its surrounding faults, we observed and collected dense broadband seismic array data for a period of more than 7 years. Through long-term continuous observations, the seismicity and the crustal S-wave velocity structure of the study area was obtained. The research results show that the current seismicity in the Gulang Seismic Zone distributes along the Wuwei-Tianzhu Fault with a southwestward trending feature, and does not extend to the Lenglongling Fault. This indicates that the seismogenic fault of the Gulang Earthquake may not include the Lenglongling Fault and the Jinqianghe Fault. In the Tianzhu Seismic Gap, seismicity distributes linearly along the Laohushan-Maomaoshan Fault, exhibiting obvious strike-slip fault characteristics. In terms of depth, seismic activities around the Maomaoshan Fault are concentrated in two intervals: the shallow layer above 10 km and the deep layer below 20 km, which also delineates the strong locking feature at the depth of 10–20 km beneath the Maomaoshan Fault. Obvious weak seismicity is also observed in the western segment of the Haiyuan Fault. The velocity structure results demonstrate that at the depth of the upper and middle crust, there are significant velocity differences on both sides of the Laohushan Fault, Maomaoshan Fault and Wuwei-Tianzhu Fault, and the seismic distribution is highly consistent with the boundary zones of these velocity differences. Beneath the Maomaoshan Fault and in the middle segment of the Laohushan Fault (at the upper and middle crust depth), there exist high-velocity anomalies distributed on both sides of the faults. These anomalies are inferred to be asperities that impede fault rupture, with a length of approximately 50 km and a width exceeding 20 km along the fault plane.

The occurrence of seismic events can be modulated by external periodic stress perturbations, such as daily tidal stress and annual hydrological stress. Such periodic modulations are crucial for understanding earthquake triggering, yet their underlying physical mechanisms are not fully understood. Here, we find that ordinary earthquakes (OEs) and low-frequency earthquakes (LFEs) on the Central San Andreas Fault (CSAF) are more sensitive to the long-period hydrological and the short-period tidal loadings, respectively. These different frequency-dependent modulations suggest pore fluid diffusion during the noninstantaneous earthquake nucleation and confirm different nucleation times of OEs and LFEs. We constrain the depth-varying physical properties of the CSAF and reveal that fluid content distribution and loading conditions fundamentally control slow-to-fast fault slip behaviors. Our study provides an alternative perspective to understand earthquake nucleation by using the information in periodic seismicity modulations, which can be applicable to subduction zones where similar slip behavior transitions occur.

The central Songpan-Ganze terrane is located in the central northern Tibetan Plateau. It borders the Qaidam Basin to the north, with the Kunlun fault marking their boundary. In the south, it is bounded by the Jinsha suture zone and borders the Qiangtang terrane to the south. A large number of left-lateral strike-slip faults have been mapped within the Songpan-Ganze terrane, showing that the shear strain is distributed over the entire block, and the crust shows the trend of eastward migration. Currently, it is still debated whether the mechanism of crust-mantle deformation and material migration of the Songpan-Ganze region is dominated by the vertical process of asthenosphere upwelling or the horizontal shearing process related to lateral extrusion. To further explore the deep dynamic mechanism, 192 broadband and long-period MT sites collected under the SinoProbe and INDEPTH projects are used to investigate the electrical structure of the crust and upper mantle beneath the central Songpan-Ganze terrane. By processing and analyzing the measured MT data, and using the LBFGS algorithm for three-dimensional (3-D) inversion, a reliable 3-D electrical structure model is derived. The deep electrical structure is analyzed and interpreted by integrating with other background geological and geophysical data. The following preliminary conclusions are drawn: (1) Under the Ganze-Yushu sinistral strike-slip fault within the Songpan-Ganze terrane, there are a series of low-resistivity channels extending northward in the middle and lower crust, which correspond to the "finger" shaped low-resistivity intrusions under the Kunlun fault, indicating that these "finger" shaped conductors have already been developed within the Songpan-Ganze terrane, and may be related to large-scale sinistral strike-slip deformation in the region. (2) These low-resistivity channels exhibit relatively weak lateral connectivity but demonstrate significant vertical extent, indicating that the deformation mechanisms in the vertical direction within the study area cannot be ignored. This phenomenon is likely closely related to the rheological structure of the block and suggests that the upwelling of mantle-derived thermal materials may play a crucial role in the regional tectonic evolution. (3) The low-resistivity body in the central Songpan-Ganze region gradually narrows from west to east, with its eastern portion exhibiting an upward extension into the upper crust. This may indicate that the Songpan-Ganze terrane experienced heterogeneous stress during the process of accommodating tectonic deformation between the Qiangtang terrane and the Qaidam Basin. As a result, the eastern part of the study area was subjected to greater compressive stress, leading to upward thrusting and the formation of a high-angle thrust conductor.*This research is funded by The China Magnetotelluric Array (Phase I), National Science and Technology Major Project (2024ZD1000202), Deep Earth Probe and Mineral Resources Exploration - National Science and Technology Major Project (2024ZD1000106-04) and NSFC (42074089).

Impoundment of the Baihetan Reservoir has triggered intense micro-seismicity, raising questions about the underlying hydro-mechanical drivers. While stress drop variations suggest fluid lubrication reduces effective normal stress, distinguishing fluid-saturated conduits from dry fracture networks remains challenging with traditional tomography. Standard attenuation imaging (Qt-1) inherently conflates scattering (structural heterogeneity) and intrinsic absorption (anelastic loss), obscuring the true physical state of the subsurface.To resolve this, we apply Multi-Resolution Attenuation Tomography (MuRAT) to a dense local seismic array dataset. By utilizing Radiative Transfer Theory, we independently invert for scattering (Qsc) and absorption (Qi) attenuation coefficients. Our results reveal a distinct spatial decoupling of these mechanisms. Scattering anomalies (low-Qsc) correlate strongly with the surface traces of the Zemuhe and Xiaojiang fault zones, effectively imaging the pre-existing fracture network. In contrast, intrinsic absorption anomalies (low-Qi) are concentrated at depths of 5–10 km. These high-absorption features are spatially consistent with theoretical zones of fluid infiltration. By separating structural damage from fluid presence, we provide independent geophysical constraints that support fluid-diffusion hypotheses derived from source parameter analysis.

Eclogite formation from lower crustal rocks requires high pressure at relatively low temperature in the presence of water. Due to the high temperature regime in the early Earth and the sparse observations of eclogitic rocks at the surface, it is generally expected that such rocks are rare in cratons. Our recent results show that large amounts of eclogitic lower crustal rocks are present below the seismic Moho in the Baltic Shield1. Such eclogites in various metamorphic grades may explain the high topography of the Scandes mountain range in northern Fennoscandia2. Our findings suggests that the amount of sub-Moho eclogite can be generally underestimated globally!Eclogitization may also play a major role in plateau formation in Tibet, where new addition of mafic underplate to the overthickened crust may immediately transform into eclogite, which founder each time the eclogite layer exceeds a critical thickness3. The whole continental crust in the central Lhasa Block has low seismic velocity (18,000 km of seismic profiles, we document that a mafic crustal layer is generally preserved in Proterozoic orogens but absent in Phanerozoic orogens5. This indicates a change in the global subduction style at the onset of the Phanerozoic, which caused massive eclogitization of lower crust in orogens and recycling of the eclogitic rocks into the mantle. The resulting buoyant felsic crust lifted continents above sea level, which enabled onshore life to develop, thus explaining the Neoproterozoic oxidation event and the explosion of life in the Phanerozoic.1. Buntin, S. et al. Long-lived Paleoproterozoic eclogitic lower crust. Nature Communications 12 (2021). https://doi.org/10.1038/s41467-021-26878-52. Kahraman, M. et al. Northern Scandinavian mountains supported by a low-grade eclogitic crustal keel. Nat Commun 16, 606 (2025). https://doi.org/10.1038/s41467-025-55865-33. Wang, G., Thybo, H. & Artemieva, I. M. No mafic layer in 80 km thick Tibetan crust. Nature Communications 12, 1069 (2021). https://doi.org/10.1038/s41467-021-21420-z4. Zhou, Z., Thybo, H., Artemieva, I. M., Kusky, T. & Tang, C. C. Crustal melting and continent uplift by mafic underplating at convergent boundaries. Nat Commun 15, 9039 (2024). https://doi.org/10.1038/s41467-024-53435-75. Xia, B., Artemieva, I. M. & Thybo, H. Phanerozoic emergence of global continental collision and onset of massive crustal eclogitization. Geology 53 (2025). https://doi.org/10.1130/g52647.