Zhaofei Liu

Although substantial gas emissions from postearthquake rupture zones have been documented, their underlying mechanisms, sources, and fault-related migration pathways remain uncertain. Here, we present a systematic tectonogeochemical survey across the surface rupture zone of the 1975 Ms 7.3 Haicheng earthquake, northeast China. A total of 233 sampling sites were established for soil gas concentration measurements, among which nine were further selected for carbon isotope analysis. Synchronous in situ measurements of Rn, CO2, and H2 concentrations were performed at all sites to elucidate the spatial coupling between soil gas concentration anomalies, seismic activity, and fault structures. The results indicate that soil gas concentrations along the rupture zone remain higher than those in background areas 50 yr after the Haicheng earthquake. The peak concentrations of Rn, CO2, and H2 reach 376.60 kBq/m3, 9.98 vol.%, and 1292.00 ppm, respectively, implying distinct geochemical anomalies along the fault zone. The carbon isotope results reveal that the contribution of deep-derived CO2 ranges from approximately 5% to 12%, indicative of the potential upward migration of deep crustal fluids. According to the analysis of gas emission-controlling factors, fault offset, persistent small-to-moderate seismicity, and deep fluid activity are likely the primary controls on these geochemical anomalies. Furthermore, the pronounced H2 anomalies and unique geological conditions of the Haicheng area may be useful for regional geochemical screening of fault-controlled gas migration. In conclusion, this study provides a representative case for understanding decadal-scale postseismic gas migration and its primary controls along the rupture zone of a major continental earthquake.

Following the September 2021 M _S 6.0 Luxian earthquake in China's Luzhou shale-gas field, soil methane enrichment shifted between fault zones and the epicentral area. We combine 4 surveys during 2021–2026 with 2021 isotopes, seismicity, shallow geophysical structure, and mechanical calculations to examine this redistribution. Concentration–carbon-isotope covariation (ρ = 0.61; n = 14) supports a thermogenic contribution compatible with regional shale gas. Enrichment was concentrated on the anticlinal flanks in 2021, weakened in 2023, peaked centrally in 2024, and shifted northwestward in 2026. Localized buried slip and heterogeneous Coulomb stress changes favor selective adjustment of existing pathways. We interpret the sequence as rapid shallow release, episodic deeper replenishment, and a later northwestern response associated with local seismicity. Methane thus provides a geochemical tracer of evolving subsurface connectivity, guiding monitoring of fossil methane escape after strong earthquakes.

Mantle‐like helium signatures ( R _c / R _a up to 2.99) in hot spring gases from tectonic intersection zones in the capital region of China have repeatedly been interpreted as evidence for ongoing mantle‐fluid input. Here, we integrate gas geochemistry, heat‐flow data, geophysical observations, radiogenic ⁴ He ingrowth calculations, and structural geology to reassess this anomaly. Air‐corrected R _c / R _a values reach 2.04–2.99 in the intersection zones, well above those of the adjacent tectonic units, whereas their CO ₂ is isotopically light ( = −17.1‰ to −10.0‰), is uncorrelated with helium concentrations, and lacks characteristics of active magmatic degassing. The region has relatively low heat flow and reservoir temperatures; although a localized reduced‐velocity zone occurs at ∼50–60 km depth beneath the intersection zones, it cannot be uniquely attributed to present‐day thermal or magmatic activity and is compatible with lithospheric modification inherited from Mesozoic craton destruction. Radiogenic ⁴ He ingrowth calculations show that relatively U‐ and Th‐poor mafic compositions can retain mantle‐like R _c / R _a values comparable to observations over representative Early Cretaceous timescales. We therefore propose that mantle‐derived helium introduced during Mesozoic magmatism was subsequently remobilized by Cenozoic tectonic degassing: uplift and denudation lowered pressure and promoted transfer of helium dissolved in ancient pore water into a gas phase, whereas composite strike‐slip‐extensional deformation ruptured helium‐bearing microreservoirs, enhanced permeability, and focused upward migration into the hydrothermal system. These results indicate that mantle‐like helium anomalies in tectonically active nonvolcanic regions may reflect tectonic degassing of ancient crustal reservoirs without requiring substantial present‐day mantle recharge, although a minor low‐flux mantle contribution cannot be excluded.

The Tan–Lu Fault Zone (TLFZ) is a lithosphere-scale fault system in eastern Asia with pronounced along-strike heterogeneity in structure and fluid activity. Previous geochemical studies have largely focused on individual segments, sample media, or single tracers, leaving the fault-zone-scale organization of fluid geochemical signals unresolved. Here, published helium-isotope data and cross-fault soil-gas CO₂ and Rn observations are integrated within a common fault-parallel coordinate framework to compare source-sensitive proxies with those more responsive to transport and near-surface processes. The three proxy groups define contrasting spatial patterns. Mantle-derived He is strongest and spatially focused in Liaoning, intermediate but comparatively persistent in Anhui–Jiangsu, and generally subdued in the available Shandong dataset. Soil-gas CO₂ and Rn anomalies, by contrast, are most continuous in Anhui–Jiangsu, locally enhanced in Liaoning, and subdued to intermediate in the available Shandong transects. Combining the mantle-derived He state with the soil-gas response identifies four proxy-association types. The most laterally continuous Type I interval extends for approximately 200 km in the Anhui–Jiangsu segment, whereas southern Liaoning is characterized by spatially focused, adjacent Type II and Type I intervals. These contrasting associations show that the near-surface expression of deep-derived fluids depends not only on volatile availability, but also on crustal pathway connectivity, groundwater circulation, and modification during transport and release. The integrated comparison reveals where deep-source and shallow-response signals are coupled or decoupled along the TLFZ, providing a basis for evaluating fault-zone fluid segmentation.

断层带的温泉提供了对流体的重要见解 环流、断层活动和地震前兆。在地震 活跃的中央天山山脉 （CTM），我们分析 17 个温泉 （2017-2023） 揭示水文地球化学与 区域构造。主量和微量元素、氢和氧 同位素、Sr 同位素、SiO2 和气体数据揭示了流星补给 （海拔 1.3-4.1 公里），以 Na-Cl 为主的蒸发岩成分 溶出和深层流体贡献（储层温度： 17-123°C;环流深度：0.5-6.3 公里）。氦同位素 （0.02-0.05 Ra） 表示地壳起源。北部中部的斯普林斯 天山和南天山断裂带环流最深，并且 最高的地震活动，将流体化学与断层联系起来 渗透性。连续监测（2021-2023 年）捕捉到地震前 2023 Shaya MS6.1 和 2024 Wushi 之前的水文地球化学异常 MS7.1 地震：Na+、Cl- 和 SO42- 突然下降 （13.3-99.3%） 和同步同位素（δD、δ18O、δ13CDIC）偏移，可能反映了 应力驱动的微压裂和流体混合。地震后 波动表明断层愈合和水文重组。这 研究结果表明，温泉可以有效地追踪岩石水 蚀变过程和短期地震前兆，同时整合 地球化学监测为检测菌株提供了更高的分辨率 在活跃的造山带中积累。

The investigation of tectonic controls on CH₄ and CO₂ emissions was conducted by measuring the fluxes of the gases in the different tectonic units along the northwestern margin of the Ordos Block in China, a region renowned for its intricate tectonic configuration. The mean fluxes of CH₄ ranged from −1.5 to 1.1 mg m⁻² d⁻¹, while CO₂ fluxes spanned from 2.0 to 29.2 g m⁻² d⁻¹. Notably, the Minqin, Ordos, and Haiyuan blocks primarily exhibited absorption characteristics for CH₄. In contrast, within the Hetao and Yinchuan grabens, both degassing and absorption processes coexist. A striking observation was that blocks with high internal deformation exhibited significantly higher CH₄ and CO₂ fluxes compared to those in the stable blocks. Additionally, regions experiencing extensional deformation demonstrated greater gas emission than those undergoing compressional deformation. The spatial distribution of CH₄ and CO₂ fluxes at the study points exhibited a similar trend to faults in the Yinchuan Graben. Our findings revealed that CH₄ and CO₂ are mainly of biogenic origin, accompanied by abiotic emissions from underground. And the gas source, migration pathway, and tectonic stress were the primary factors influencing gas emission, with tectonic stress playing a pivotal role. This stress controlled the formation of tectonic structures, changed the degassing pathway, and served as the driving force for gas migration. The results of this study offer valuable insights into the mechanisms governing CH₄ and CO₂ emission in faulted regions. Furthermore, our results may contribute to future assessments aimed at quantifying the contribution of geological sources to greenhouse gas emissions.

During the ongoing uplift and expansion of the southeastern margin of the Tibetan Plateau, the front edge of the Sichuan‐Yunnan rhombic block (SYB) has experienced intense tectonic activity and frequent seismicity. In this study, the fluid geochemistry in the primary active faults at the front edge of the SYB was investigated, with the aim of understanding the tectonic activity and intersection relationship between the Xiaojiang fault (XJF) and the Red River fault (RRF). Thermal spring water and gases exhibit a coupled spatial distribution relationship; relatively high ion concentrations and ³He/⁴He ratios (Rc/Ra ratios of 0.21 to 0.62Ra) are observed along the RRF, Qujiang fault (QJF), and Shiping‐Jianshui fault (SJF). Multidisciplinary research results have indicated that mantle‐derived intrusion has been detected in the crust beneath the QJF and SJF. The current tectonic activity in the front edge of the SYB remains intense, with compressive stresses shifting toward the western side of the XJF and accumulating on the QJF and SJF. This has led to the development of fractures, enhancing the water–rock interaction and deep‐derived gas degassing along the faults. The unmixing characteristics of fluids at the intersection area of these two faults suggest the absence of conduits for fluid migration between the faults. Owing to the lower gas ³He/⁴He ratios, lower shear strain rates, stable reservoir temperature field, and extremely low historical seismicity in the Indo‐Chinese block, it is speculated that the current movement of the XJF may not cut through the RRF and continue southward.

Investigating the emissions of soil gas including radon, mercury and carbon dioxide (²²²Rn, Hg and CO₂) from the solid earth to the atmosphere through active fault zones is of great significance for accession of atmospheric environment. In this study, the concentrations and fluxes of ²²²Rn, Hg and CO₂ were measured at the main active fault zones at the western margin of the Ordos block, China. The concentrations of ²²²Rn, Hg and CO₂ were in the range of 0–60.1 kBq m⁻³, 3–81 ng m⁻³ and 0.04–9.23%, respectively, while the fluxes of ²²²Rn, Hg and CO₂ are in the range of 1.99–306.99 mBq m⁻² s⁻¹, 0–15.12 ng m⁻² h⁻¹ and 0–37.91 g m⁻²d⁻¹, respectively. Most of the major fault zones at the study area are CO₂ risk-free regions (CO₂ concentration in soil gas < 5%). However, the extend of ²²²Rn pollution at the fault zones of F₁, F₄, F₅ and F₉ (the fault number) and that of Hg pollution at the fault zones of F₂, F₄, F₅ and F₇ were higher than the pollution level of 1. The annual emission of Hg and CO₂ from the western margin of the Ordos block was estimated to be 2.03 kg and 0.70 Mt, respectively. Comprehensive analyses indicated that the higher emission rates of soil gases from the active fault zones were related to the seismic activities. The results suggest that the earthquake activity is a dominant factor enhancing the emission of ²²²Rn, Hg and CO₂ from the solid earth through active fault zones and, furthermore, resulting great impact on the atmospheric environment.