A Physics‑Based Seismic Risk Assessment of the Qujiang Fault:From Dynamic Rupture to Disaster Estimation

This study achieved the construction of earthquake disaster scenarios based on physics-based methods-from fault dynamic rupture to seismic wave propagation-and then population and economic loss estimations.The physics-based dynamic rupture and strong ground motion simulations can fully consider the three-dimensional complexity of physical parameters such as fault geometry,stress field,rock properties,and terrain.Quantitative analysis of multiple seismic disaster scenarios along the Qujiang Fault in western Yunnan Province in southwestern China based on different nucleation locations was achieved.The results indicate that the northwestern segment of the Qujiang Fault is expected to experience significantly higher levels of damage compared to the southeastern segment.Additionally,there are significant variations in human losses,even though the economic losses are similar across different scenarios.Dali Bai Autonomous Prefecture,Chuxiong Yi Autonomous Prefecture,Yuxi City,Honghe Hani and Yi Autonomous Prefecture,and Wenshan Zhuang and Miao Autonomous Prefecture were identified as at medium to high seismic risks,with Yuxi and Honghe being particularly vulnerable.Implementing targeted earthquake prevention measures in Yuxi and Honghe will significantly mitigate the potential risks posed by the Qujiang Fault.Notably,although the fault is within Yuxi,Honghe is likely to suffer the most severe damage.These findings emphasize the importance of considering rupture directivity and its influence on ground motion distribution when assessing seismic risk.

Petrology and Metamorphic P-T Paths of Metamorphic Zones in the Huangyuan Group,Central Qilian Block,NW China

The Central Qilian Block is a Precambrian block in the Qilian Orogen,which has long drawn international attention for the study of orogeny and continental dynamics.The Huangyuan Group in the Datong area is one of the Precambrian metamorphic basement units in the Central Qilian Block and reflects metamorphism in the Barrovian garnet zone and sillimanite zone from south to north.Based on detailed fieldwork,this study presents a systematic study of petrography,mineral chemistry and phase equilibria of schists and gneisses from the two metamorphic zones.The garnet metamorphic zone is composed of micaschist,garnet-bearing micaschist and felsic leptynite,with interlayered plagioclase amphibolite.The sillimanite metamorphic zone consists of garnet-bearing biotite micaschist,sillimanite-bearing biotite-plagioclase gneiss and felsic leptynite.Garnet from the garnet metamorphic zone shows growth zoning with increasing almandine and pyrope and decreasing spessartine from core to rim.Garnet from the sillimanite metamorphic zone is almost homogeneous.Towards the outer rim,the contents of almandine and pyrope slightly decrease and grossular slightly increase.Biotite in both metamorphic zones is ferro-biotite.Plagioclase is oligoclase in garnet metamorphic zone and andesine in sillimanite metamorphic zone.Phase equilibrium modeling of a sample from garnet metamorphic zone resulted in a clockwise P-T path with a prograde stage(4.5–5.0 kbar,520–530℃),a peak P stage(9.8–10.2 kbar,560–570℃),a stage of thermal relaxation(8.0–8.5 kbar,580–590℃)and finally a retrograde stage(6.8–7.0 kbar,560–580℃).Thermodynamic modeling of a sample from the sillimanite metamorphic zone indicates a prograde stage(5.5–6.0 kbar,540–550℃)and a peak stage(7.8–8.5 kbar,660–690℃).The results indicate that the Huangyuan Group experienced medium-pressure amphibolite-facies metamorphism,which resulted from continental-continental collision between the Qaidam Block and the Central Qilian Block.

Petrology of Garnet Amphibolites from the Hualong Group: Implications for Metamorphic Evolution of the Qilian Orogen, NW China

The Qilian Orogen marks the junction of the North China, South China and Tarim cratons. The mechanism of continental growth during the formation of the orogen remains unclear. Based on detailed fieldwork, we present a systematic study of petrography, mineral chemistry and phase equilibria of garnet amphibolites from the Hualong Group, which represents the Precambrian basement in the southern accretionary belt of the Qilian Orogen. The garnet amphibolites mainly consist of amphibole, plagioclase, garnet and quartz, with minor pyroxene, biotite and ilmenite. A peak stage of upper amphibolite facies to low-temperature granulite facies metamorphism and retrograde metamorphism in the amphibolite facies affected the samples. Garnet has a homogeneous composition of Alm66-71Grs14-17Prp9_12Sps3-s, amphibole is ferro-hornblende, biotite belongs to the ferro-biotite species and pyroxene is dominated by orthopyroxene with few clinopyroxene. Pseudosection modeling of the garnet amphibolite samples indicates clockwise P-T paths. The samples witness peak metamorphism at conditions of -4.9-6.3 kbar and -755-820 ℃ in the upper amphibolite facies to low- temperature granulite facies, and retrograde cooling and decompression at conditions of-2.5-3.1 kbar and -325-545 ℃. It is inferred that peak metamorphism with high temperature and low pressure occurred at ca. 450 Ma during northward subduction of the South Qilian oceanic crust beneath the central Qilian Block. When continental collision occurred between the central Qilian and the Qaidam blocks, the Hualong Block was aecreted onto the South Qilian accretionary complex and experienced amphibolite facies retrograde metamorphism at ca. 440 Ma.

Rapid estimation of disaster losses for the M6.8 Luding earthquake on September 5,2022

An M6.8 earthquake occurred in Luding,Sichuan Province,China,on September 5,2022.Since towns and villages in the earthquake-stricken area are densely populated,the earthquake caused severe fatalities and economic losses.Rapid estimation of earthquake intensity and disaster losses is significantly important for post-earthquake emergency rescue,scientific anti-seismic deployment,and the reduction of casualties and economic losses.Therefore,we make a preliminary rapid estimation of the earthquake intensity and disaster losses in the aftermath of the Luding earthquake.The seismic intensity represents the distribution of earthquake disasters and the degree of ground damage and can be directly converted from the peak ground velocity(PGV)map.To obtain a reliable PGV distribution map of this earthquake,we combined the finite-fault model constrained by seismic observations,with the complex three-dimensional(3D)geological environment and topographical features to perform strong ground motion simulation.Then,we compared the consistency between the simulated ground motion waveforms and observations,indicating the plausibility and reliability of simulations.In addition,we transformed the PGV simulation results into intensity and obtained a physics-based map of the intensity distribution of the Luding earthquake.The maximum simulated intensity of this earthquake is IX,which is consistent with the maximum intensity determined from the postearthquake field survey.Based on the simulated seismic intensity map of the Luding earthquake and the earthquake disaster loss estimation model,we rapidly estimated the death and economic losses caused by this earthquake.The estimated results show that the death toll caused by this earthquake is probably 50-300,with a mathematic expectation of 89.Thus the government should launch a Level II earthquake emergency response plan.The economic losses are likely to be 10-100 billion RMB,with a mathematical expectation of 23.205 billion RMB.Such seismic intensity simulations and rapid estimation of disaster losses are expected to provide a preliminary scientific reference for governments to carry out the targeted deployment of emergency rescue and post-disaster reconstruction.

Metamorphic P-T Path Differences between the Two UHP Terranes of Sulu Orogen, Eastern China: Petrologic Comparison between Eclogites from Donghai and Rongcheng

The Sulu Orogen constitutes the eastern part of the Sulu-Dabie Orogen formed by Triassic collision between the Sino-Korean and Yangtze plates. An HP Slice Ⅰ and two UHP slices Ⅱ and Ⅲ with contrasting subduction and exhumation histories within the Sulu Orogen were postulated. This study presents the metamorphic P-T paths of eclogites from the two UHP belts constructed by petrog- raphy, mineral chemistry and Perple_X P-T pseudosection modeling in the MnC（K）NFMASHO system. Eclogites from Slice Ⅲ mainly consist of omphacite, garnet and quartz, with minor rutile, ilmenite, amphibole and phengite. Eclogites from Slice Ⅱ show a porphyroblastic texture with epidote porphyroblasts and garnet, omphacite, phengite, quartz and rutile in matrix. Pseudosection modeling reveals that eclogites from Slice Ⅱ witness a peak metamorphism of eclogite-facies under conditions of 3.1-3.3 GPa and 660-690 ℃, and a retrograde cooling decompression process. The eclogites from Slice Ⅲ record a heating decompressive P-T path with a peak-P stage of 3.2 GPa and 840℃ and a peak-T stage of 2.4 GPa and 950 ℃, suggesting an apparent granulite-facies metamorphism overprint during exhumation. Both eclogites recorded clockwise P-T paths with peak P-T conditions suggesting a subduction beneath the Sino-Korean Plate to -100-105 km depth. Combined with tectonic scenarios from previous studies, it is concluded that the two UHP crustal slices in the Sulu terrane have a similar geodynamic evolution, but the UHP rocks in Slice Ⅱ exhumed after the eclogitic peak-pressure conditions earlier than that of Slice Ⅲ. The existence of Slice Ⅱ diminished the buoyancy force on Slice Ⅲ, resulting in a granulite-facies overprint on Slice Ⅲ. The Sulu orogenic belt is made up of different crustal slices that underwent different subduction and exhumation histories, rather than a single unit.