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In this study, 60 crushed samples comprising four groups of particles of different sizes were used to simulate the porous and crushed conditions of a gob area in an underground mine. Size distribution, porosity range, and the ratio of wavelength to the particle size of the crushed samples were taken into account with reference to the field observations in the actual gob. The ultrasonic wave velocity and attenuation were measured at an expected porosity under a loading pressure. Meanwhile, the permeability of the samples in the same conditions as the wave measurement was measured using the steady-state method. The results showed that the P-wave velocity of the crushed material was in the range of 400–1000 m/s, which was similar to the velocity of the fractured rock in the actual gob. The model for estimating the seismic attenuation of the crushed rock was confirmed to be a function of the porosity (φ), the density of discontinuity (δ), transmission coefficient (ζ), wave frequency (f), and the scatter factor (κ) proposed in the empirical formula based on the equipment results. The estimated seismic attenuation was consistent with the measurements in the experiment as well as the actual value based on previous study. In particular, the estimation was quite accurate, while the ratio of wavelength (λ) to particle size (dm) was between 35 and 65. The estimated permeability of the crushed rock mass fell into a magnitude range of 10−12 to 10−13 m2. The permeability showed consistency with the Kozney–Carman equation but with a larger tortuosity coefficient. The field gob permeability estimated by the laboratory correlation was from 1225 to 15,866 10−12 m2, showing good agreement with the previous research. The relationship between the permeability and the seismic attenuation of the crushed rock was established based on the measurements.

Time-frequency analysis is a successfully used tool for analyzing the local features of seismic data. However, it suffers from several inevitable limitations, such as the restricted time-frequency resolution, the difficulty in selecting parameters, and the low computational efficiency. Inspired by deep learning, we suggest a deep learning-based workflow for seismic time-frequency analysis. The sparse S transform network (SSTNet) is first built to map the relationship between synthetic traces and sparse S transform spectra, which can be easily pre-trained by using synthetic traces and training labels. Next, we introduce knowledge distillation (KD) based transfer learning to re-train SSTNet by using a field data set without training labels, which is named the sparse S transform network with knowledge distillation (KD-SSTNet). In this way, we can effectively calculate the sparse time-frequency spectra of field data and avoid the use of field training labels. To test the availability of the suggested KD-SSTNet, we apply it to field data to estimate seismic attenuation for reservoir characterization and make detailed comparisons with the traditional time-frequency analysis methods.

Mars’s seismic activity and noise have been monitored since January 2019 by the seismometer of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander. At night, Mars is extremely quiet; seismic noise is about 500 times lower than Earth’s microseismic noise at periods between 4 s and 30 s. The recorded seismic noise increases during the day due to ground deformations induced by convective atmospheric vortices and ground-transferred wind-generated lander noise. Here we constrain properties of the crust beneath InSight, using signals from atmospheric vortices and from the hammering of InSight’s Heat Flow and Physical Properties (HP3) instrument, as well as the three largest Marsquakes detected as of September 2019. From receiver function analysis, we infer that the uppermost 8–11 km of the crust is highly altered and/or fractured. We measure the crustal diffusivity and intrinsic attenuation using multiscattering analysis and find that seismic attenuation is about three times larger than on the Moon, which suggests that the crust contains small amounts of volatiles.The crust beneath the InSight lander on Mars is altered or fractured to 8–11 km depth and may bear volatiles, according to an analysis of seismic noise and wave scattering recorded by InSight’s seismometer.

Despite the high detection level of the Italian seismic network and the risk associated with its fault networks, Central‐Southern Italy has no unique geophysical model of the crust able to illuminate its complex tectonics. Here, we obtain seismic attenuation and scattering tomography models of this area; both reveal high attenuation and scattering anomalies characterizing the entire Apenninic Chain and related to its East‐ and West‐dipping extensional Quaternary tectonic alignments. Fault‐associated fractured zones become preferential ways for circulating and degassing high‐attenuation CO2‐bearing fluids. A previously undetected fluid source area is a high‐attenuation volume below the Matese complex, while a similar smaller anomaly supports a fluid source near L'Aquila. The most prominent low attenuation and scattering volumes reveal a locked aseismic zone corresponding to the Fucino‐Morrone‐Porrara fault systems, representing a zone of significant seismic hazard. Plain Language Summary Geophysical methods are the most used tools for imaging the subsurface. Still, their resolution and reliability depend on the amount of good‐quality data and the sensitivity of the technique used for the target structures. Improvements in the seismic detection infrastructures of the last decade allow imaging zones characterized by sparse seismicity, like Central‐Southern Italy. Once combined with these data, new imaging techniques targeting attributes with higher sensitivity to stress and fluid saturation provide unprecedented resolution on tectonic interactions and fluid sources in this area. Here, we measured and mapped in 3D the energy lost by seismic waves during their propagation. Our results show a high‐attenuation volume elongated in the direction of the Apenninic Chain and particularly intense in Southern Italy, mapping fluid‐filled fracturing and a fluid source likely coinciding with the Matese area. The principal normal and reverse faults in the area control high‐attenuation zones. The most prominent low attenuation and scattering volume marked locked areas with low seismic energy release, suggesting them as the zones of stress accumulation. Key Points Scattering and attenuation tomography image the tectonics of the Apennine Mountain Belt Chain High‐attenuation anomalies mark crustal sources of CO2 following major structural alignments A high‐attenuation/high‐scattering volume reveals an extended fluid source beneath the Matese Mountains

Deep fluid circulation likely triggered the large extensional events of the 2016–2017 Central Italy seismic sequence. Nevertheless, the connection between fault mechanisms, main crustal‐scale thrusts, and the circulation and interaction of fluids with tectonic structures controlling the sequence is still debated. Here, we show that the 3D temporal and spatial mapping of peak delays, proxy of scattering attenuation, detects thrusts and sedimentary structures and their control on fluid overpressure and release. After the mainshocks, scattering attenuation drastically increases across the hanging wall of the Monti Sibillini and Acquasanta thrusts, revealing fracturing and fluid migration. Before the sequence, low‐scattering volumes within Triassic formations highlight regions of fluid overpressure, which enhances rock compaction. Our results highlight the control of thrusts and paleogeography on the sequence and hint at the monitoring potential of the technique for the seismic hazard assessment of the Central Apennines and other tectonic regions. Plain Language Summary There is widespread evidence that the Amatrice‐Visso‐Norcia seismic sequence (2016–2017, Central Italy) was triggered by fluid circulation across the Apennine Chain. However, how, and why fluids migrated across the fault network is still under debate. Seismic attenuation describes how seismic waves lose energy during their propagation. When used as an imaging attribute, it has demonstrated the potential to recover the spatial extension and mechanisms of fracturing and fluid movement across volcanoes and faults. Here, we map scattering attenuation through the peak delay measurements in 3D before (2013–2016) and during the 2016–2017 sequence. Scattering attenuation separated fractured zones from regions of compaction, controlled, before and during the sequence by thrusts and lithological differences. High scattering (strong fracturing) increases through time due to intense fracturing, while low scattering (higher compaction of the rocks) marks areas where earthquakes will occur. Our results highlight the importance of the main thrusts, as they separate compartments of the shallow crust characterized by different scattering attenuation anomalies, the Triassic deposits in fluid accumulation, and subsequent triggering of normal faults. Key Points Scattering attenuation detects the control of thrusts and lithology on post‐seismic fracturing and fluid migration during the AVN sequence Overpressurized fluids compact low‐scattering rocks at thrusts' roots before earthquakes Detecting fluid overpressure and fracturing suggests an unexploited monitoring potential of scattering attenuation

Seismic attenuation tomography is used to map fluids and fractures beneath the Aluto volcano geothermal field of the Main Ethiopian Rift. We present 3D models of peak delay (Δlog10Tpd ${\\Delta }{\\log }_{10}\\left({T}_{pd}\\right)$) and inverse coda quality factor (Qc−1 ${Q}_{c}^{-1}$) which are proxies for seismic scattering and absorption. High Qc−1 ${Q}_{c}^{-1}$ anomalies are observed near productive geothermal wells with high‐temperature gradients and in areas of hydrothermal activity. High scattering attenuation anomalies are spatially associated with faults and fractures that serve as pathways for fluid flow. These variations correlate well with production variations in boreholes across the geothermal field. Furthermore, a prominent high‐scattering (low‐absorption) anomaly is observed at a depth of approximately 0–3 km below sea level (bsl) beneath Aluto, which is interpreted as the signature of an intrusive igneous body. Together, these methods for measuring seismic attenuation serve as valuable tools in geothermal exploration, offering constraints on fluid distribution, as well as structural and lithological variations.

Mapping fluid accumulation in the crust is pertinent for numerous applications including volcanic hazard assessment, geothermal energy generation, and mineral exploration. Here, we use seismic attenuation tomography to map the distribution of fluids in the crust below Uturuncu volcano, Bolivia. Seismic P wave and S wave attenuation, as well as their ratio (QP/QS), constrain where the crust is partially and fully fluid‐saturated. Seismic anisotropy observations further constrain the mechanism by which the fluids accumulate, predominantly along aligned faults and fractures in this case. Furthermore, subsurface pressure‐temperature profiles and conductivity data allow us to identify the most likely fluid composition. We identify shallow regions of both dry and H2O/brine‐saturated crust, as well as a deeper supercritical H2O/brine column directly beneath Uturuncu. Our observations provide a greater understanding of Uturuncu's transcrustal hydrothermal system, and act as an example of how such methods could be applied to map crustal fluid pathways and hydrothermal/geothermal systems elsewhere. Plain Language Summary Locating where water/brines, gas, and molten rock are in the crust is important various applications, including assessing volcanic hazard, generating geothermal energy, and exploring for critical metals. Here, we map how seismic energy is absorbed (or attenuated) in Earth's crust, in order to look for fluids in the subsurface. We do this at Uturuncu volcano, Bolivia. This allows us to imagine whether the crust is partly or fully saturated with fluids. We also use seismic anisotropy to help us understand how the seismic energy is absorbed. We then use other data, including pressure, temperature, and electrical conductivity data to identify what fluids can be found where. We find that we can map where water/brines are and whether they contain carbon dioxide (i.e., are “sparkling”) or not (i.e., “still”). Key Points Seismic attenuation tomography can map crustal fluids and elucidate whether fluids are compressible, incompressible, or supercritical S wave velocity anisotropy suggests that crustal fluids at Uturuncu migrate and/or accumulate along fractures Seismic attenuation combined with temperature, pressure, and conductivity measurements can provide constraint on fluid composition

The amplitude‐dependent seismic attenuation in the crust and uppermost mantle was investigated using spectral analysis of crustal and intraslab earthquakes that occurred in two areas in northeastern Japan. P‐wave attenuation (Q−1${Q}^{-1}$ ) was found to be weakly proportional to amplitude (A$A$ ) in both areas, following the relationship, Q−1∝An${Q}^{-1}\\mathit{\\propto }{A}^{n}$ . Quantitative analysis reveals that amplitude‐dependent attenuation is more pronounced in the uppermost mantle (n ∼ 0.16) than in the crust (n ∼ 0.05). This depth‐dependent behavior of attenuation may be attributed to increasing temperature and pressure, which enhance dislocation density and mobility. Our findings challenge the common assumption of amplitude‐independent attenuation. Although we infer dislocation mechanisms as the primary cause of the amplitude‐dependent energy dissipation, further experimental studies under high temperature and pressure conditions are necessary for better understanding of the complex nature of seismic attenuation and the underlying processes. Plain Language Summary Seismic attenuation, the energy loss per one cycle as seismic waves propagate through the Earth, has traditionally been considered amplitude independent. Our research challenges this assumption, revealing a weak amplitude dependence of attenuation. We found this effect is more pronounced in the uppermost mantle than in the crust. This depth‐dependent behavior likely results from increasing temperature and pressure affecting the microstructure of rocks. These findings will improve the accuracy of seismic wave propagation models and enhance our understanding of Earth's internal structure, contributing to advancements in seismology. Key Points We revealed amplitude‐dependent attenuation in both the crust and the uppermost mantle using a spectral analysis Amplitude‐dependent attenuation is more dominant in the uppermost mantle than in the crust We quantified amplitude‐dependent attenuation with an exponent of about 0.05 for the crust and 0.16 for the uppermost mantle

We show that the spatial coherency of the ambient seismic field can be used for attenuation tomography in the western United States. We evaluate the real portion of the spatial coherency with an elastic geometric spreading term (a Bessel function) and a distance dependent decay (an attenuation coefficient). In order to invert the spatial coherency, a weight stack inversion technique is applied. We recover phase velocity and attenuation coefficient maps at periods of 8–32s, which correspond to the elastic and anelastic structure at crustal and upper mantle depths. The phase velocity maps obtained by this method are of similar resolution to more standard two‐station methods. The attenuation results provide an important complement to the information extracted from earthquake‐based tomography. Several geological features are easily identifiable in the attenuation coefficient maps, such as the highly attenuating sedimentary basins along the West Coast of the United States, and the highly attenuating Yellowstone region, and the boundaries of the Snake River Plains. Key Points Lateral variations in seismic attenuation can be obtained from ambient noise Seismic attenuation structure is illuminated beneath the western United States Empirical greens functions contain amplitude content for attenuation studies

We present a multiscale seismic attenuation tomography of a seismotectonically complex region in northern Italy hosting the well‐characterized Collalto Underground Gas Storage (UGS). Beyond its specific relevance, this site provides a natural laboratory for assessing the ability of attenuation imaging to distinguish fluid‐rich zones from highly strained, failure‐prone volumes. We integrated scattering and absorption tomography models: scattering anomalies, between the two principal thrusts, highlight localized strain near fault tips; absorption tomography images the shallow UGS and reveals a deeper fluid‐saturated volume. Seismicity concentrated around this deeper anomaly, exhibiting a pulsatory temporal pattern, suggests a fluid‐driven role in the deformation processes. These findings show that attenuation tomography, combined with multiscale and complementary geophysical models, can resolve critical subsurface features related to fluids and strain. The approach is broadly applicable to geothermal and volcanic contexts and supports seismic hazard assessment in tectonically active regions where natural and anthropogenic processes may interact.