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The 2021 Mw 7.4 Maduo (Madoi) earthquake that struck the northern Tibetan Plateau resulted in widespread coseismic deformation features, such as surface ruptures and soil liquefaction. By utilizing the unmanned aerial vehicle (UAV) photogrammetry technology, we accurately recognize and map 39,286 liquefaction sites within a 1.5 km wide zone along the coseismic surface rupture. We then systematically analyze the coseismic liquefaction distribution characteristics and the possible influencing factors. The coseismic liquefaction density remains on a higher level within 250 m from the surface rupture and decreases in a power law with the increasing distance. The amplification of the seismic waves in the vicinity of the rupture zone enhances the liquefaction effects near it. More than 90% of coseismic liquefaction occurs in the peak ground acceleration (PGA) > 0.50 g, and the liquefaction density is significantly higher in the region with seismic intensity > VIII. Combined with the sedimentary distribution along-strike of the surface rupture, the mapped liquefaction sites indicate that the differences in the sedimentary environments could cause more intense liquefaction on the western side of the epicenter, where loose Quaternary deposits are widely spread. The stronger coseismic liquefaction sites correspond to the Eling Lake section, the Yellow River floodplain, and the Heihe River floodplain, where the soil is mostly saturated with loose fine-grained sand and the groundwater level is high. Our results show that the massive liquefaction caused by the strong ground shaking during the Maduo (Madoi) earthquake was distributed as the specific local sedimentary environment and the groundwater level changed. [ABSTRACT FROM AUTHOR]

Forest fires have become more frequent in many regions throughout the world over recent decades, principally as a result of global warming. Polycyclic aromatic hydrocarbons (PAH) have become recognized as a byproduct of wildfires and an important indicator of ancient wildfires. However, the factors controlling wildfires remain elusive. This study presents analyses of PAH compounds found in 22 surface soil samples from the snow-capped Mount Yulong (Mt. Yulong), on the southeastern Tibetan Plateau (TP; 1906 ∼ 4132 m above sea level (asl)), as well as the total organic carbon (TOC) and n -alkanes values for these soils. This area is climatically influenced by alternating Westerlies as well as the Southwest Asian Monsoon and the Southeast Asian Monsoon. PAH ratios, including the indeno[1,2,3- cd ]pyrene/(indeno[1,2,3- cd ]pyrene + benzo[ g , h , i ]perylene) and fluoranthene/ (fluoranthene + pyrene) ratios, as well as the ratios of low molecular weight (LMW) PAH to high molecular weight (HMW) PAH (LMW/HMW) and the LMW/∑PAH ratio, can reliably confirm that these PAH were primarily produced by biomass combustion. Further principal component analysis (PCA) also supported this conclusion. The highest ∑PAH concentration (Conc PAH 89.9 ng/g) from sites >3800 m asl that exhibit significant wildfire remains further confirming that PAH can be taken as a reliable indicator of the occurrence of ancient wildfires. Analysis of variance confirmed that the composition of local vegetation type has a minimal contribution to Conc PAH across the study area, but soil type played an obvious effect on Conc PAH as the result of change in absorb ability of PAH. When analyzing samples that had no wildfire remains, there was no correlation between Conc PAH and mean annual temperature and mean annual precipitation (MAP). The relatively lower prevalence of wildfire activity (indicated by a low mean Conc PAH value of 21.29 ± 9.80 ng/g) along the Mt. Yulong transect between 2200 and 3500 m asl may be due to a wetter climate (with MAP between 800 and 1800 mm in the rainy season), a climate which would in turn have reduced the combustibility of vegetation fuel and thus limited wildfire activity. Indeed, the highest standardized dimethylphenanthrene ratio (0.76 ± 1.16), Retene/3-ring (0.81 ± 0.66) and Retene (0.63 ± 1.03 ng/g) values all presented between 2200 and 3500 m asl, confirming their reliability as indicators of conifer combustion. • PAH, TOC and n -alkanes in 22 surface soil samples were quantified along the altitudinal transect in Mt. Yulong. • Ratios analysis and PCA confirm that these parent PAH were primarily produced by biomass combustion. • Conc PAH values were affected by wildfire occurrence, preservation environment, and soil types. • DMPy, Ret/3-ring and Ret (ng/g) can be used as indicators of conifer combustion. [ABSTRACT FROM AUTHOR]