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The April 20, 2013, Ms 7.0 Lushan Earthquake was a major earthquake that followed the Ms 8.0 Wenchuan Earthquake on May 12, 2008. Frequent earthquakes have caused heavy casualties and property loss in Western Sichuan. Earthquake disasters are often closely related to the amplification effect of ground motion. Studying the ground motion characteristics of near-surface geological structures helps to understand the distribution of potential earthquake disasters. In this study, we investigated ground motion amplification in the downtown area of Lushan using numerical simulation and aftershock data from the Lushan Earthquake. Using the Lushan earthquake aftershock data from nine seismic stations distributed in the area, the amplification effect of the sites was determined using the "reference site spectral ratio" method. The results show that the frequency of the ground motion amplification in the area was in the range 5–10 Hz, and the corresponding amplification peak was from 3 to 14. Among the study sites, the amplification (14 times) at L07 was the most prominent. To study further the amplification characteristics, shear-wave velocity models for the structures under these sites were established using passive-source Rayleigh surface-wave exploration. One-dimensional (1D) and two-dimensional (2D) seismic amplification effects were simulated using horizontally propagating shear-wave modeling. Except Site L07, the 1D simulation results of each site well reflected the variation feature of the seismic amplification on the frequency band below the observed peak frequency, although the overall simulated amplification peaks were smaller than the observed results. The 2D simulation of the remarkable amplification phenomenon at L07 was in better agreement with the observation result than was the 1D simulation, indicating that the seismic amplification in the Modong area is influenced by lateral variation of the Quaternary sediments. [ABSTRACT FROM AUTHOR]

A major breakthrough in shale gas exploration and development has been made concerning the black shale of the Upper Ordovician and Lower Silurian. In recent years, significant progresses have been made regarding the exploration and development of shale gas in the black shale of the Upper Ordovician and Lower Silurian. Accordingly, we investigated the petrological and geochemical characteristics of the black shale from WF2‐LM5 graptolite biozones and performed a source analysis of quartz as well as evaluated its effect on shale gas reservoirs. The black shale mainly contains clay, carbonate, and quartz with the average TOC of 2.21%. Three quartz types, Q1, Q2, and Q3, were identified via petrological and cathodoluminescence (CL) analysis. Q1 of detrital origin as suggested by its typical morphology with monocrystal structure, large grain‐size, subrounded to angular outlines, and clear edges. This is further supported by the occurrence of medium luminescence under cathodoluminescence and medium intensity of P1 and P2 and high intensity P3 according to CL images. Q2 accounts for more than 90% of quartz and exhibits cryptocrystalline texture, an irregular shape, blurring edges, and low luminescence, and its CL images show low intensity P1, low intensity P2, and high intensity P3. Q3 have the morphologies of siliceous organisms, for example, sponge spicules, radiolaria, and foraminifera. Q2 and Q3 belong to authigenic quartz derived from siliceous organisms. Th/U and V/Cr indicate black shale from LM1–3 mainly deposited in the dysoxic‐anoxic environment while black shale from LM4–5 deposited in the oxic environment. Authigenic quartz‐rich shales from LM1–3 were speculated to be the best shale gas reservoirs characterized by high TOC content, high gas content, and with negligible amount of detrital quartz. Compared with shale from LM1–3, black shale from LM4–5 usually have relatively high detrital quartz content and low TOC content and gas content. Considering the abundant interparticle pore space, the detrital quartz‐rich shale interbedded within the black shale from LM4–5, could also become good shale gas reservoirs if sufficient gas supply is guaranteed. [ABSTRACT FROM AUTHOR]

In the Upper Ediacaran Dengying Formation of the Sichuan Basin, the presence of abundant, well-preserved microbial carbonates provides a unique opportunity to study Precambrian paleoceanography and microbial carbonate origins. Particularly, the underexplored coated grain dolostones of this formation, characterized by distinct microbially induced fabrics and intragranular dissolution, offer crucial insights for understanding late Ediacaran microbial mineralization and diagenetic sequences. Utilizing selected typical samples, we conducted detailed petrographic and geochemical analyses, revealing a dynamic interplay between microbial processes and sedimentary dynamics. We observe the coexistence of constructive micrite envelopes with microbially induced fabrics such as clots and laminations, highlighting microbial biomineralization's key role in fabric formation. The sedimentary dynamics critically determines the formation processes of the coated grains: low-energy settings foster grain agglomeration and consolidation through clot precipitation between grains, while high-energy settings favor smaller grains binding to microbial mats. Geochemically, micrite envelopes play an essential role in preserving distinct rare earth element (REE) signatures. The weak negative Ce anomalies and positive Eu anomalies within these envelopes point to a suboxic to anoxic depositional environment, directly indicative of the microenvironmental conditions conducive to microbial mineralization processes. Furthermore, our study sheds light on the structural evolution of coated grains with hollow nuclei, proposing that their internal pore formations are influenced by both mineral instability and selective dissolution by meteoric freshwater. These findings not only provide fresh insights into complex diagenetic processes in the Dengying Formation but also substantially advance our understanding of early microbial life and environmental adaptations during the Precambrian. • Revealed the relationship between micrite envelopes and microbially induced fabrics • Proposed a novel formation mechanism for coated grain dolostone in the Dengying Fm. • Investigated the diverse environmental responses of microbiolite fabrics • Established micrite envelopes as dependable records of seawater REE compositions [ABSTRACT FROM AUTHOR]