Science China Earth Sciences最新文献

Sedimentary strata typically exhibit the characteristics of transverse isotropy (VTI) with a vertical axis of symmetry. However, fractures in sedimentary strata tend to produce anisotropic closure due to horizontal in situ stress, resulting in pronounced orthorhombic anisotropy in VTI media under such stress conditions and influencing the propagation behavior of seismic waves. Previous studies have primarily focused on the elastic wave velocity anisotropy induced by applied stress in isotropic background media, neglecting the impact of VTI background media on the anisotropy induced by horizontal in situ stress and the response characteristics of seismic wave propagation. To address these gaps, we first establish the effective elastic stiffness tensor of VTI media under horizontal in situ stress using nonlinear acoustoelastic theory. Then, we derive the accurate and linearized approximate equations for P-wave seismic reflectivity of VTI media under horizontal in situ stress, based on wave equations and scattering theory, respectively. Finally, we compare and analyze the characteristics of orthorhombic anisotropic seismic response induced by horizontal in situ stress at various types of elastic reflection interfaces. Our results demonstrate that the linearized approximation of the seismic reflection response characteristics closely aligns with the accurate equations under conditions of small stress below 10 MPa, effectively capturing the azimuth-dependent orthorhombic anisotropy induced by horizontal in situ stress in VTI media. The results of this study also provide a novel theoretical approach and valuable insights into the seismic prediction of in situ stress.

The GRACE satellite mission provides a new approach for monitoring, tracking, and assessing drought conditions by detecting changes in Earth’s gravitational fields and inversing signals of terrestrial water storage anomalies. Existing studies of terrestrial water storage anomalies related droughts paid rare attention to the behind atmospheric physical mechanisms, nor quantified the risk propagation patterns between terrestrial water storage deficits and hydrological or agricultural droughts. In this study, we first extract terrestrial water storage (TWS) droughts, hydrological droughts, and agricultural droughts by using multiple variables including TWS from the GRACE/GRACE-FO satellites, runoff and soil moisture from the ERA5-Land reanalysis dataset. We then identify key atmospheric and oceanic oscillation indices affecting water deficits by employing machine learning technologies. We characterize the joint distributions between drought duration and severity by using the Copula function and quantify the risk propagation of hydrological and agricultural droughts to TWS droughts. The results show that: (1) From 2002 to 2021, there is a significant decrasing trend of TWS in China; the WPIO group atmospheric circulation indices (sea surface temperature index within the Western Pacific and Indian Ocean) contributes the most to TWS. Specifically, the sea surface temperature anomalies within the NINO 3.4 region as well as the Western Pacific Warm Pool area index show significantly positive correlation relationships with TWS in southern China; (2) The northwestern China, the Yangtze River basin, and the downstream of the Pearl River basin are the hotspots of TWS droughts. Besides, the hotspots of hydrological droughts locate in northwestern China and the hotspots of agricultural droughts locate in South China and eastern Tibetan Plateau; (3) The elastic coefficients of hydrological droughts propagating to TWS droughts are higher than those of agricultural droughts, indicating that the TWS droughts are more sensitive to hydrological droughts than to agricultural droughts.

The precise determination of earthquake location is the fundamental basis in seismological community, and is crucial for analyzing seismic activity and performing seismic tomography. First arrivals are generally used to practically determine earthquake locations. However, first-arrival traveltimes are not sensitive to focal depths. Moreover, they cannot accurately constrain focal depths. To improve the accuracy, researchers have analyzed the depth phases of earthquake locations. The traveltimes of depth phases are sensitive to focal depths, and the joint inversion of depth phases and direct phases can be implemented to potentially obtain accurate earthquake locations. Generally, researchers can determine earthquake locations in layered models. Because layered models can only represent the first-order feature of subsurface structures, the advantages of joint inversion are not fully explored if layered models are used. To resolve the issue of current joint inversions, we use the traveltimes of three seismic phases to determine earthquake locations in heterogeneous models. The three seismic phases used in this study are the first P-, sPg- and PmP-waves. We calculate the traveltimes of the three seismic phases by solving an eikonal equation with an upwind difference scheme and use the traveltimes to determine earthquake locations. To verify the accuracy of the earthquake location method by the inversion of three seismic phases, we take the 2021 M_S6.4 Yangbi, Yunnan earthquake as an example and locate this earthquake using synthetic and real seismic data. Numerical tests demonstrate that the eikonal equation-based earthquake location method, which involves the inversion of multiple phase arrivals, can effectively improve earthquake location accuracy.

The variation in near-surface wind speed is a key dynamic parameter in the orographic effect of precipitation over eastern China. In this study, we used the latest high-resolution outputs from six GCMs in CMIP6-HighResMIP to evaluate the performance of high-resolution models in simulating the orographic precipitation characteristics of typical mountainous areas in summer over eastern China. The orographic precipitation under warming scenarios was projected and constrained according to observational data. The results indicated that during the contemporary climate reference period (1979–2009), although the relationship between model-simulated near-surface wind speed and orographic light rain frequency was consistently stable, the sensitivity of the orographic light rain frequency to surface wind variability was generally underestimated, with a deviation approximately 24.1% lower than the observational values. The estimated orographic light rain frequency corrected based on the observed near-surface wind speed under a 1.5°C warming scenario, was 36.1% lower than that of the contemporary period; this reduction was 8.6 times that without the wind speed constraint (4.2%). The MRI-AGCM3-2-S model, with a longer dataset, demonstrated relatively stable reductions in orographic light rain frequency under different warming scenarios (1.5°C, 2°C, 3°C, and 4°C) after the application of wind speed constraints. In all cases, the reductions exceeded those for the predictions made without the wind speed constraint.

Oceanic intraplate volcanoes with linear age progressions are usually accepted to be derived from melting of an upwelling mantle plume. Several seamount groups in NW Pacific, however, show complex age-distance relationships that are difficult to explain using the classic “mantle plume hypothesis”, and thus their origins are controversial. In this study, we present ⁴⁰Ar-³⁹Ar age, geochemical, and Sr-Nd-Pb-Hf isotopic data of lavas from Hemler, Vlinder, and Il’ichev seamounts in NW Pacific, to elucidate their petrogenesis and geodynamic process. The lavas from Hemler, Vlinder, and Il’ichev seamounts are classified as alkali basalt, basanite/nephelinite, and trachyte. Lavas with MgO>8 wt.% exhibit high contents of CaO, FeO^T, and TiO₂, similar to the composition of melts formed from reaction between carbonated eclogite-derived melts and fertile peridotite. These lavas have elevated Zr/Hf ratios (40.6–45.2) and negative Zr and Hf anomalies, indicating the presence of a carbonate component in the mantle source. They are enriched in incompatible trace elements and have enriched mantle 1 (EM1)-like Sr-Nd-Pb-Hf isotopic compositions. The isotopic compositions of Vlinder, Il’ichev basanite, and Hemler lavas in this study are similar to the Rarotonga hotspot. Although occurring at the same seamount, the Il’ichev alkali basalts display more depleted Sr-Nd-Hf isotopic compositions compared to Il’ichev basanite. According to plate tectonic reconstruction results, the ages of Hemler (100.1 Ma), Vlinder pre- (100.2 Ma) and post-shield (87.5 Ma), and Il’ichev (56.4 Ma) lavas clearly deviate from the Macdonald, Arago, Rarotonga, and Samoa hotspot tracks, indicating that they cannot directly originate from mantle plumes. We propose that in the mid-Cretaceous, when the Pacific plate passed over Rarotonga hotspot, melting of Rarotonga plume formed the Vlinder (main-shield stage), Pako, and Ioah seamounts. The Rarotonga (and possibly Samoa) plume materials would have been dispersed into the surrounding asthenosphere by mantle convection. These diffuse plume materials would undergo decompression melting beneath lithosphere fractures that are widely distributed in the Magellan area, generating non-hotspot related Hemler and pre- and post-shield Vlinder lavas. The Il’ichev alkali basalts and basanite probably result from lithospheric fracture-induced melting of heterogeneous enriched components randomly distributed in the asthenosphere.

The link between climate and war has long been a topic of great scientific and social interest. In this study, we investigate the influence of climate on warfare in China’s Hexi Corridor region since 241 A.D. Using the superposed epoch analysis of tree-ring data and historical war data, we observe a notable correlation between interannual dry-wet variations and wars instigated by nomadic groups in the Hexi Corridor. However, this relationship is dynamic and influenced by the region’s relative unity. During periods in which the Hexi Corridor was ruled by multiple regimes, wars tended to follow dry climatic conditions, which may be due to the fact that unusual drought during these periods likely heightened competition for resources and land. Conversely, during times of regional unity, wars were more likely to occur when climatic conditions were wet because the expansion of rangelands and the accumulation of resources helped fuel the nomads’ outward conquest. These findings underscore the complexity of the relationship between war and climate change. To gain a more comprehensive understanding of this relationship, continuous, high-resolution historical temperature and humidity datasets with broader and more uniform coverage are needed across multiple regions. In addition, collecting and examining disaggregated historical war data for regions with distinct characteristics is essential.

Impact craters are formed due to the high-speed collisions between small to medium-sized celestial bodies. Impact is the most significant driving force in the evolution of celestial bodies, and the impact craters provide crucial insights into the formation, evolution, and impact history of celestial bodies. In this paper, we present a detailed review of the characteristics of impact craters, impact crater remote sensing data, recognition algorithms, and applications related to impact craters. We first provide a detailed description of the geometric texture, illumination, and morphology characteristics observed in remote sensing data of craters. Then we summarize the remote sensing data and cataloging databases for the four terrestrial planets (i.e., the Moon, Mars, Mercury, and Venus), as well as the impact craters on Ceres. Subsequently, we study the advancement achieved in the traditional methods, machine learning methods, and deep learning methods applied to the classification, segmentation, and recognition of impact craters. Furthermore, based on the analysis results, we discuss the existing challenges in impact crater recognition and suggest some solutions. Finally, we explore the implementation of impact crater detection algorithms and provide a forward-looking perspective.

The extraordinarily high temperatures experienced during the summer of 2022 on the Tibetan Plateau (TP) demand attention when compared with its typical climatic conditions. The absence of precipitation alongside the elevated temperatures resulted in 2022 being the hottest and driest summer on record on the TP since at least 1961. Recognizing the susceptibility of the TP to climate change, this study employed large-ensemble simulations from the HadGEM3-A-N216 attribution system, together with a copula-based joint probability distribution, to investigate the influence of anthropogenic forcing, primarily global greenhouse gas emissions, on this unprecedented compound hot and dry event (CHDE). Findings revealed that the return period for the 2022 CHDE on the TP exceeds 4000 years, as determined from the fitted joint distributions derived using observational data spanning 1961–2022. This CHDE was directly linked to large-scale circulation anomalies, including the control of equivalent-barotropic high-pressure anomalies and the northward displacement of the subtropical westerly jet stream. Moreover, anthropogenic forcing has, to some extent, promoted the surface warming and increased variability in precipitation on the TP in summer, establishing conditions conducive for the 2022 CHDE from a long-term climate change perspective. The return period for a 2022-like CHDE on the TP was estimated to be approximately 283 years (142–613 years) by the large ensemble forced by both anthropogenic activities and natural factors. Contrastingly, ensemble simulations driven solely by natural forcing indicated that the likelihood of occurrence of a 2022-like CHDE was almost negligible. These outcomes underscore that the contribution of anthropogenic forcing to the probability of a 2022-like CHDE was 100%, implying that without anthropogenically induced global warming, a comparable CHDE akin to that observed in 2022 on the TP would not be possible.

High temperature warning indicators play a pivotal role in meteorological departments, serving as crucial criteria for issuing warnings that guide both social production and daily life. Despite their importance, limited studies have explored the relationship between different global warming levels and changes in high temperature warning indicators. In this study, we analyze data from 2,419 meteorological stations over China and utilize the Coupled Model Intercomparison Project Phase 6 (CMIP6) models to examine historical changes in high temperature warning indicators used by the China Meteorological Administration. We evaluate model performance and estimate future changes in these indicators using an annual cycle bias correction method. The results indicate that since 1961, the number of high temperature days (TX35d and TX40d) and length of season (TX40d and TX40l) with daily maximum temperature reaching or exceeding 35°C and 40°C have increased over China. The intensity of high temperatures (TXx) has strengthened and the geographical extent affected by high temperatures has expanded. In 2022, the occurrence of 40°C high temperatures surges, with Eastern China experiencing a two-day increase in TX40d and an extended seasonal length in TX40l by over five days. While CMIP6 models have underestimated the high temperature indictors associated with 35°C during historical periods, notable difference is not observed between the models and observations for TX40d and TX40l, given their rare occurrence. However, future projections, after bias correction, indicate that the increasing trends for 35°C and 40°C high temperature days and length of season become more pronounced than the raw projection, suggesting a more severe increase than that anticipated originally. As global warming intensifies, the high temperature days and length of season are projected to increase non-linearly, while the intensity of high temperatures is expected to increase linearly. For every 1°C increase in global temperature, the intensity is projected to rise by approximately 1.4°C. The impact of high temperatures is expanding, with the major hotspot for China located in the eastern and northwestern regions. Under 5°C global warming, certain regions in China may experience prolonged extreme high temperatures. For instance, 40°C high temperature days in areas like North China and the Yangtze River Basin could increase by about 32 d, and the length of season could extend by approximately 100 d.