Seismic Activity Research Articles

Dynamic responses of large-diameter variable-section group-piles subjected to shaking-table tests with varying scour depths

Scouring leads to soil loss around piles, which, in turn, changes the ground-vibration characteristics and influences the seismic performance of bridges. In this study, the Xiang’an Bridge was used as a reference for constructing a large shaking-table test model to investigate the dynamic characteristics of the pore-pressure ratio of saturated sandy soils, accelerations, and bending moments of the piles, as well as the horizontal displacements of the pile-top at scouring depths of 10, 20, and 32 cm, with ground-vibration intensities ranging from 0.10-0.45 g. The results indicated that as the scour depth increased, the pile acceleration of the group piles increased and changed abruptly at the variable cross-section and soil-stratum interface. The peak values of the horizontal displacement of the pile-top and bending moment of the pile exhibited an increasing trend. As the ground-shaking intensity increased, the pore-pressure ratio of the saturated sandy soil, pile acceleration of the group piles, horizontal displacement of the pile-top, and bending moment of the pile body gradually increased, whereas the base frequency of the pile foundation gradually decreased. This study can serve as a reference for the seismic design and reinforcement of scour bridges in areas prone to seismic activity.

Analysis of Magnitude–Frequency Distribution of Earthquakes in the Sichuan Basin, Southwest China

Abstract The Sichuan basin is characterized by underdeveloped active geological structures and low seismic activities. In recent years, an increase in seismicity has been observed in the southern Sichuan basin, which includes small earthquakes induced by water injection during shale gas exploitation and M ≥ 5.0 earthquakes, causing unexpected damage and casualties. This necessitates a comprehensive analysis of the magnitude–frequency distribution of the current seismicity. In this study, we examined the current seismicity using instrumental earthquake records at different periods and estimated the temporal and spatial variations in b-value. We found that the b-values widely vary in the Sichuan basin and analyzed the spatial differences in b-value in seven different earthquake clusters. The results show that the intense fault movement on the western boundary of the Sichuan basin might be the main controlling factor of the increased seismicity in the southern basin instead of being induced by water injection. Furthermore, earthquakes in the Sichuan basin follow the same size distribution as the events on the boundary faults and the Sichuan–Yunnan rhombus active block. Thus, it is appropriate to consider the magnitude–frequency distribution of earthquakes for the Sichuan basin and the Sichuan–Yunnan rhombus block together rather than separately. These results may help improve the recurrence models in probabilistic seismic hazard assessment of the region.

Insights from tensile fracture properties and full-field strain evolution of deep coral reef limestone under dynamic loads

Coral reef limestone (CRL) commonly undergoes dynamic tension when underground structures of island reefs encounter impacts, explosions, or seismic activities. Given the complexity of biological pores, the dynamic tensile fracture characteristics of CRL are poorly understood. Therefore, the dynamic tensile fracture behaviors of deep CRL were systematically observed by Split Hopkinson Pressure Bar tests and digital image techniques. Comparing to traditional rocks, the macro-pores near failure band would significantly change cracking path. The failure patterns are dominated by loading rate. The strongly dependence of dynamic tensile strength and dynamic crack initiation toughness on loading rate suggests the two indices overcome the effect of CRL macro-pores under dynamic impacts. At low loading rates, tensile fractures predominantly follow intergranular cracks, whereas transgranular cracks dominate at higher rates. The fractal dimension of fracture surface decreases with increasing crack propagation velocity, loading rate, and dynamic crack initiation toughness. Due to the unique marine sedimentary environment, the mechanical heterogeneity in multiple scales distinguishes CRL from terrestrial rock materials. The insights into underlying mechanisms of dynamic tension provide support to optimization of blasting scheme and stability assessments for island underground engineering.

A Review of 15 Years of Public Earthquake Forecasting in Aotearoa New Zealand

Abstract New Zealand entered a period of increased seismic activity in 2003, which, to date, has included around 20 large or damaging earthquakes. Building on decades of forecast model research and including research into formal model evaluation, GNS Science, the governmental institution tasked with providing natural hazards information, began issuing public earthquake forecasts following the 2009 Mw 7.2 Darfield earthquake. This article provides a review of the public earthquake forecasting methods and outcomes since that time. Initially the release of forecasts was motivated by the scientific team, but interest, use and understanding quickly rose in the public, government, and private sectors which led to regular refinement and additions to the type of forecast information provided. The basic tenet of forecasting has remained the same, with the forecasts being used to inform decisions requiring consideration of timeframes from days to decades. The operational models were all based on the previous 10–20 years of research in model development and testing; this included the development of methods for combining multiple models into a single hybrid model that typically provides increased statistical forecast skill. The hybrid models combine models from three classes of time horizons: (1) short-term aftershock clustering based on the epidemic-type aftershock sequence class of models, (2) medium-term clustering with time horizons of years to decades, and (3) long-term models with time horizons of decades to nominally time independent. Forecasts have been issued in response to 14 large or significant earthquakes with the forecasts and accompanying information regularly updated on the GeoNet webpages. An important component to the successful deployment and uptake of the models was the foundation laid in the previous decades in model development and testing. This provided understanding and confidence in the models’ ability to provide useful forecasts for response and recovery decisions.

Spatio-temporal deformation characteristics and triggering factors of Wangjiashan landslide

Hydrodynamic-induced landslide is a type of landslide whose stability can be reduced by rainfall, groundwater or reservoir water level fluctuations (RWLF). Based on the monitoring data of Wangjiashan landslide located in the reservoir area of Baihetan Hydropower Station, this article illustrates the deformation characteristics of Wangjiashan landslide on time and space distribution. Spearman correlation coefficients are used to make analysis of the relationship between surface deformation and different dynamic factors such as RWLF, seismic activity, and rainfall. The results indicate that RWLF is a dominant dynamic factor of Wangjiashan landslide. Besides, two variables of deformation factors are presented to find differences during various deformation periods. The results show that the displacement and its rate are both strongly correlated with the RWLF, especially during the acceleration period and the deceleration stage. It is indicated that Wangjiashan landslide is a typical hydrodynamically induced landslide. This study provides a useful reference for understanding the instability mechanism of the landslide.

Implementation of PMDL and DRM in OpenSees for Soil-Structure Interaction Analysis

It is widely acknowledged that the effects of soil-structure interaction (SSI) can have substantial implications during periods of intense seismic activity; therefore, accurate quantification of these effects is of paramount importance in the design of earthquake-resistant structures. The analysis of SSI is typically conducted using either direct or substructure methods. Both of these approaches involve the use of numerical models with truncated or reduced-order computational domains. To ensure effective truncation, it is crucial to employ boundary representations that are capable of perfectly absorbing outgoing waves and allowing for the consistent application of input motions. At present, such capabilities are not widely available to researchers and practicing engineers. In order to address this issue, this study implemented the Domain Reduction Method (DRM) and Perfectly Matched Discrete Layers (PMDLs) in OpenSees. The accuracy and stability of these implementations were verified through the use of vertical and inclined incident SV waves in a two-dimensional problem. In terms of computational efficiency, PMDLs require a shorter analysis time (e.g., with PMDLs, the analysis concluded in 35 min as compared to 250 min with extended domain method) and less computational power (one processor for PMDLs against 20 processors for the extended domain method) thus offering a balance between accuracy and efficiency. Furthermore, illustrative examples of the aforementioned implemented features are presented, namely the response analysis of single-cell and double-cell tunnels exposed to plane waves inclined at an angle.

The God of Earthquakes: Several Hypotheses Related to One Dedicatory Inscription to Poseidon Asphaleios From Mesambria on Pontus

This article aims to present to the scientific community a dedicative inscription to the God Poseidon in his capacity as Asphaleios -Securer, embedded in one of the churches in Nessebar (Bulgaria)–St. Paraskeva Church. The inscription was found in 2013 during conservation-restoration works in the church. It is published for the first time here, and comments have been made on its connection with earthquakes and seaquakes in Southeastern Europe during so-called Hellenistic Period. The inscription is in the Doric dialect in four lines built in as a spolium on a recess above the altar apse on the church’s southern side in an upside-down position. Based on specific features of palaeography and orthography of the letters, the suggested dating is the second half of the 3rd and the beginning of the 2nd century BC. The epithet of the god in this inscription–Asphaleios is attested in other Dorian poleis; however, here, it cannot be connected with a temple to Poseidon. It was probably brought to Mesambria on Pontus from somewhere else; as exemplified with similar inscriptions originating from Kallatis (present-day Mangalia, Romania) and Dionysopolis (present-day Balchik, Bulgaria). The epiklesis in the mentioned inscriptions hints at the consequences of the seismic activity during the period comprising roughly the second quarter to the middle of the 3rd century BC that swept across Southeastern Europe and caused severe damage. Therefore, this inscription is another example of Poseidon being worshipped in his capacity of Securer and Earth-Stayer and being recognized as a symbol of hope for ancient people.

Possible Identification of Precursor ELF Signals on Recent EQs That Occurred Close to the Recording Station

The Lithospheric–Atmospheric–Ionospheric Coupling (LAIC) mechanism stands as the leading model for the prediction of seismic activities. It consists of a cascade of physical processes that are initiated days before a major earthquake. The onset is marked by the discharge of ionized gases, such as radon, through subterranean fissures that develop in the lead-up to the quake. This discharge augments the ionization at the lower atmospheric layers, instigating disturbances that extend from the Earth’s surface to the lower ionosphere. A critical component of the LAIC sequence involves the distinctive perturbations of Extremely Low Electromagnetic Frequencies (ELF) within the Schumann Resonances (SR) spectrum of 2 to 50 Hz, detectable days ahead of the seismic event. Our study examines 10 earthquakes that transpired over a span of 3.5 months—averaging nearly three quakes monthly—which concurrently generated 45 discernible potential precursor seismic signals. Notably, each earthquake originated in Southern Greece, within a radius of 30 to 250 km from the observatory on Mount Parnon. Our research seeks to resolve two important issues. The first concerns the association between specific ELF signals and individual earthquakes—a question of significant importance in seismogenic regions like Greece, where earthquakes occur frequently. The second inquiry concerns the parameters that determine the detectability of an earthquake by a given station, including the requisite proximity and magnitude. Initial findings suggest that SR signals can be reliably linked to a particular earthquake if the observatory is situated within the earthquake’s preparatory zone. Conversely, outside this zone, the correlation becomes indeterminate. Additionally, we observe a differentiation in SR signals based on whether the earthquake took place over land or offshore. The latter category exhibits unique signal behaviors, potentially attributable to the water layers above the epicenter acting as a barrier to the ascending gases, thereby affecting the atmospheric–ionospheric ionization process.

FINITE ELEMENT SIMULATION OF LOW-RISE SCHOOL BUILDING MODEL WITH SEISMIC LOADS INPUT

Earthquake impacts on buildings have garnered increased attention as Malaysia experiences seismic activities, notably from nearby regions like Sumatra and within areas such as Sabah. Despite this, current Malaysian design guidelines, such as BS 8110, do not fully incorporate seismic loads. This study addresses this gap by examining the structural performance of a scaled 1:8 model of a three-storey, low-rise school building under various peak ground accelerations (PGA) from 0.1g to 1.0g. Utilizing ABAQUS finite element simulation and time-history analysis, we evaluated the seismic responses, including local deformations, von Mises stress, and principal stresses. Key findings reveal a maximum structural displacement of 10.22 mm at 1.0g PGA, with significant stress concentrations observed at the column footings, highlighting critical areas for design improvement in seismic resilience.

Historical earthquakes in the Holy Cross Mountains, Poland, true or false? Unveiling insights through archaeoseismology

The Holy Cross Mountains are an intraplate range with a limited historical seismicity record. The only documented earthquakes include the February 6, 1837 M 4.3 event, which caused ground cracks, and swarm events from February 1932 (M ∼ 3.5), likely triggered by the Holy Cross Fault (HCF) or sub-perpendicular faults. The apparent lack of older destructive earthquakes in historical catalogs motivated us to conduct archaeoseismological research to improve seismic hazard assessment, risk mitigation, and urban planning strategies, ultimately benefiting local communities. We focused on the 12th-century Collegiate church of Saint Martin in Opatów, located near the Holly Cross Fault (HCF). We report numerous damage features, such as leaning, bulging, and twisted walls, dropped keystones in Romanesque and Gothic portals, strike-slip displacements of these portals, surplus, oversized buttresses, and walled-up portals. While some deformations may result from humid loess instability and war destructions, our data, combined with historical records, suggest two to three seismic events in the past 800 years as a cause. We argue these deformations were co-seismically triggered by either large far-field events, like the 1259 AD earthquake, or local, shallow small-magnitude events significantly amplified by site effects. This indicates potential seismic activity in the Holy Cross Mountains during Medieval times. The absence of historical records does not imply the absence of earthquakes.

Multi-experimental seismic analysis of low-rise thin reinforced concrete wall building with unconnected elastomeric isolators using real-time hybrid simulations

In response to the pressing need for housing and streamlining construction processes, the building industry has embraced innovative construction techniques. One such method, known as the Industrialized Housing Construction (IHC) system, departs from traditional framing systems by utilizing thin-reinforced concrete walls (TRCW). These TRCWs, characterized by high flowability and rapid strength gain, enable quick and efficient monolithic construction of walls and slabs. However, challenges have arisen regarding the structural behavior of these elements, potentially compromising their seismic performance. Given the significant seismic risk, there is a compelling need to develop resilient buildings by using this cost-efficient structural system. This study proposes the use of passive control systems such as base isolation to address this problem. While base isolation has proven effective in other countries, its feasibility in structures using TRCW and its performance during actual seismic events warrants further investigation. This paper presents an innovative approach using Multi-Axial Real-Time Hybrid Simulation (M-RTHS), which combines numerical and experimental components to gain deeper insights into the seismic response of low-rise TRCW buildings with base isolation using unconnected fiber-reinforced elastomeric isolators (U-FREIs). The methodology is detailed and includes the division of the structure into numerical and experimental segments and the use of transfer systems to replicate real seismic excitations, including those from El Centro (USA, 1940), Pizarro (Colombia, 2004), Chihuahua (Mexico, 2013), Loma Prieta (USA, 1989), and Kobe (Japan, 1995), with a maximum amplitude of 7.36 [Formula: see text] (0.75 g). The results highlight a remarkable reduction in upper structure floor drifts of over 57.47%, the characterization of the behavior and energy dissipation of each experimental specimen, and the optimal evaluation of M-RTHS. This research paves the way for improving the seismic resistance of buildings in regions prone to seismic activity, especially those using innovative construction methods such as TRCW.

SEISMIC VULNERABILITY ASSESSMENT OF AN HISTORICAL UNREINFORCED MASONRY BUILDING OF THE XIXTH CENTURY: EL FETH HIGH SCHOOL IN BLIDA, ALGERIA

Schools In Algeria, built in the XIXth and XXth centuries, are not only places of education and learning, but make up a rich cultural heritage of architectural techniques and traditional know-how. However, their seismic vulnerability risks the safety of their occupants. They were built of masonry before seismic regulations were put into place, which increases their sensitivity to seismic hazard. Algeria is situated in a well-known zone of high seismic activity and the risk to these buildings challenges their structural behaviour. This study focuses on an assessment of seismic vulnerability on a specimen built entirely in hollow brick which wonderfully represents this architectural heritage leading to a better understanding of the potential risks for these buildings, at a structural level. Macro element models, using the Tremuri software, are subjected to a non-linear “Pushover” analysis in order to determine the degree of vulnerability and locate the weak sections of the structure which could collapse during seismic action. This study aims to highlight the seismic risks of these types of structures and also offer appropriate guidelines and recommendations that could be of use during a possible rehabilitation or conservation program of this built heritage site.

Identification and Application of Wave Field Characteristics of Channel Waves in Extra-Thick Coal Seams

Channel wave seismic activity often occurs with thin and medium-thick coal seams being the main target layer. To address the problem of channel wave applicability detection in extremely thick coal seams, the propagation and identification characteristics of channel waves remain the focus of research. Therefore, this paper takes the in-seam wave exploration of a 27 m extremely thick coal seam as an example and uses the staggered mesh finite difference method to construct a three-dimensional medium model for numerical simulation. An analysis of the physical parameters of coal and rock, along with the dispersion characteristics of channel waves in extra-thick coal seams, is utilized, through the Zoeppritz equation and the total reflection propagation method, to calculate the imaging. We found the following: (1) The dispersion areas and weak dispersion areas along the detection direction are extremely thick coal seams. (2) There are apparent channel waves in extra-thick coal seams, with a waveform similar to body waves; the length of the wave train is shorter than that of the conventional channel wave, and the arrival time can be estimated accurately. The amplitude of the apparent channel wave is affected by the degree of dispersion, with lower attenuation and higher resolution. The characteristic of total reflection in extremely thick coal seams is that the incident angle is equal to the critical angle, and the dispersion characteristics are weak. (3) The channel waves with weak dispersion characteristics in extra-thick coal seams are mainly Love-type waves.

Shaking-table tests and numerical simulations study of subway stations in loess region

The loess region in China, known for its high seismic activity and the extreme vulnerability of loess to earthquakes, presents a considerable threat to the seismic safety of underground structures, including subway stations. With the Xi'an Aerospace City subway station as the background, a subway station model was designed, and shaking table tests were conducted under various conditions to analyze the seismic damage and dynamic responses in this study. The study reveals the seismic vulnerable areas and dynamic response patterns of the subway station under different spectral earthquake actions. Simultaneously, a three-dimensional numerical modeling analysis accounting for soil-structure interaction, was conducted to explore the displacement response of the structure and soil. Results indicate a noticeable amplification effect on the acceleration of both the structure and the soil under seismic motion. The structure exhibits a suppressive effect on the acceleration amplification of the surrounding soil, diminishing with increasing seismic motion intensity. Different depths show varying differences in acceleration responses between the structure and adjacent soil. Structural strain responses and damage phenomena suggest that the central column is the seismic vulnerable area of the subway station. Additionally, the strain distribution of the structure exhibits a distinct spatial effect. The relative horizontal displacement between the structure and the soil follows certain patterns in the depth direction, with the structure experiencing smaller relative horizontal displacement than the soil under seismic action due to the constraining effect of surrounding soil on its displacement response. The experimental conclusions provide valuable reference points for the seismic design and analysis of subway station structures in loess regions.

Distribution and genesis of geothermal waters in the Xianshuihe fault zone, Western Sichuan plateau, China: Constraints on fracture system and regional seismic activities

The Xianshuihe fault zone (XSFZ), which is characterized by intense tectonic activities, frequent earthquakes and great number of hot springs, has significant potential for exploiting geothermal resources. Previous studies primarily focus on certain hydrothermal systems in southeastern segment of XSFZ, such as Kangding hydrothermal system, but lack the synthetical comparison and systematic analysis of geothermal waters along the XSFZ. Based on detailed geological investigation, the XSFZ hydrothermal system has divided into six geothermal activity areas: Luhuo (LH), Daofu (DF), Qianning-Bamei (QB), Yalahe-Zhonggu (YZ), Kangding (KD) and Moxi (MX). According to the 87Sr/86Sr ratios and elements behaving in water-rock interactions, the dissolution of silicate minerals is the primarily source of the hydrogeochemical compositions in geothermal waters. The δD and δ18O composition indicate that geothermal waters primarily originated from meteoric waters, but also affected by deep fluids. However, the contribution of deep fluids to the southeastern geothermal areas (YZ, KD and MX) with high concentrations of Cl- is greater than that of the northwestern (LH, DF and QB). The reservoir temperatures and chlorine-enthalpy model reveal that there are three distinct geothermal systems along the XSFZ: YZ and KD geothermal waters are originated from a common deep reservoir (R1), MX are from R3, and LH, DF, and QB are from R4. Due to the uneven thermal structural distribution along XSFZ, the southeastern segments generated stronger thermal stress and have more frequent earthquake occurrence. Thus, the study of geothermal waters along XSFZ can provide valuable insights into deep tectonic activities and geochemical indicators of earthquake monitoring in the region.

Regional, local and current forecast of the impact hazard of coal seam sites based on seismic monitoring

Relevance. Insufficient validity of the quantitative criteria of the regional, local and current forecast of the impact hazard of the coal seams being developed, the absence of algorithms linking the use of geophysical and direct geomechanical methods in forecasting. Aim. To develop a comprehensive method of geodynamic forecasting, including determining the extent of an impact-prone area identified by the results of a regional forecast based on the registration data of the GITS seismic monitoring system, for conducting local and current forecasts of impact hazard by regulatory methods. Object. An array of rocks of the excavation column 4-1-5-7 of the Osinnikovskaya mine during mining operations in the zone of a group of tectonic disturbances and the intersection of advanced workings. Methods. Regional geomechanical forecast by the geophysical method of seismic activity registration (GITS system), local (current) forecast by natural electromagnetic radiation methods (Angel-M equipment) and the output of drilling fines. Results. The paper introduces the results of complex studies in the excavation column 4 1-5-7 of the Osinnikovskaya mine to establish a correlation between seismic activity and the parameters of the stress-strain state of the array. The authors have introduced the concept of integral indicators of the considered parameters IF and Ikσ. They take into account the area of the zone for the i-th range according to the complex parameter of seismic activity F and the coefficient of vertical stresses in the roof of the formation Kσ. It is established that the informative value of the integral indicators is almost twice as high as the informative value of the initial parameters. Experimental nomograms и are presented to determine the category "DANGEROUS/NON-DANGEROUS" for the regional forecast of impact hazard according to the GITS seismic monitoring system. The authors developed a general algorithm for predicting the impact hazard during clean-up operations. This algorithm uses an integrated approach that includes a regional forecast for recording seismic activity within the mine field and local forecasting methods, both geophysical and direct, to clarify the boundaries of seismic energy release zones and confirm the category of impact hazard. Thу paper introduces the example of determining the width of the zone of increased seismic energy release in the mine closest to the seismically active zone. The dynamics of the occurrence, development and decrease of the seismic energy release zone in the considered areas in the mine workings is shown. The authors give the examples of the implementation of a local forecast of impact hazard in previously established potentially dangerous areas by methods of recording natural electromagnetic radiation of rocks and by the output of drilling fines.

Using RSQSim to Determine Seismic Sequence in Eastern Taiwan Fault System

Abstract Understanding the spatial and temporal patterns of seismic activity, along with fault interactions in Taiwan, is essential for earthquake hazard assessment and advancing knowledge of regional tectonics. This study employs the Rate and State Earthquake Simulator (RSQSim) to simulate the eastern Taiwan fault system, integrating fault geometry from the multidisciplinary Taiwan Earthquake Model. We applied long-term simulations spanning 400,000 yr to conduct earthquake sequences and recurrence intervals on five distinct faults in eastern Taiwan: Milun fault, Longitudinal Valley fault, Central Range structure, Luyeh fault, and Taimali Coastline structure. The simulated earthquake catalogs are compared against the historical record in terms of seismicity, frequency–magnitude statistics, and recurrence patterns. The model reasonably reproduces key observational constraints, including spatial patterns, magnitude probabilities fitting a gamma distribution, and periods of quiescence resulting from fault interactions. Overall, the results demonstrate RSQSim’s potential for physics-based seismic hazard modeling and provide insights into regional seismotectonic processes in eastern Taiwan for constructing sustainable cities and communities.

Seismic Performance of Reinforced Concrete Frames on Sloped Ground Using Non-Linear Static Pushover Analysis

Nepal, renowned for its majestic Himalayan Ranges, is also highly vulnerable to seismic activity. Buildings on hill slopes often endure more significant damage during earthquakes than those on flat terrain. Traditional seismic analyses of buildings typically employ linear-static and dynamic methods, which might not fully represent the building's behavior under actual seismic conditions. This research addresses this gap by assessing the seismic performance of buildings on hill slopes using non-linear static analysis techniques. Specifically, the study evaluates the seismic response of 5-story buildings with stepback and stepback-setback configurations on slopes of 15°, 30°, and 45°. This evaluation is conducted through non-linear static analysis, also known as Pushover Analysis, using ETABSv20 software. Key performance metrics analyzed include the building's period, topstorey displacement, and base shear. The findings reveal that buildings with stepbacksetback configurations demonstrate superior seismic performance on the sloping ground compared to those with stepback configurations. This study underscores the importance of employing non-linear analysis methods to better understand and improve seismic resilience in hilly terrains.

Separation of Intrinsic and Scattering Seismic Wave Attenuation in the Crust of Central and South-Central Alaska

ABSTRACT Seismic hazard analysis is essential for evaluating the potential consequences and dangers linked to earthquakes, particularly in areas with regular seismic activity such as central and south-central Alaska. A detailed study of attenuation can help in better defining the wave behavior and so refine the ground-motion prediction. Here, we examined the scattering (Qs−1), intrinsic (Qi−1), and coda-wave (Qc−1) attenuation in central and south-central Alaska. To do so, we performed the multiple lapse time-window analysis (MLTWA) techniques and estimated the coda energy decay. We considered earthquakes that occurred between December 2014 and December 2020, with magnitudes between 2.0 and 6.5. We observed significant spatial variations in scattering loss (Qs−1) up to 3 Hz, which diminish at 6 and 12 Hz. The Wrangell block exhibits the most significant scattering loss at a frequency of 1.5 Hz. Another area of marked scattering loss was identified north of the Alaska Range (AR), where it was pronounced up to 6 Hz. The area around Anchorage registered the lowest intrinsic absorption across all the central frequencies, whereas the highest values were detected north of the AR, particularly at 3 and 6 Hz. The seismic albedo (B0) in central and south-central Alaska varies spatially and is mainly dominated by scattering loss up to 3 Hz. Both the Chugach mountains and Yakutat block (YB) area exhibit lower B0 values at all central frequencies showing the dominance of intrinsic absorption. Low values of Qc (high attenuation) are focused almost on all the frequencies along the Denali fault and YB, showing a strong influence of these structures on the attenuation. The results yield a comprehensive understanding of the unique attenuation characteristics of each region, underscoring the significance of investigating the behavior of seismic wave attenuation for seismic risk purposes.

Twenty Years of Thermal Infrared Observations (2004–2024) at Campi Flegrei Caldera (Italy) by the Permanent Surveillance Ground Network of INGV-Osservatorio Vesuviano

Thermal infrared (TIR) time series images acquired by ground, proximal TIR stations provide valuable data to study evolution of surface temperature fields of diffuse degassing volcanic areas. This paper presents data processing results related to TIR images acquired since 2004 by six ground stations in the permanent thermal infrared surveillance network at Campi Flegrei (TIRNet) set up by INGV-Osservatorio Vesuviano. These results are reported as surface temperature and heat flux time series. The processing methodologies, also discussed in this paper, allow for presentation of the raw TIR image data in a more comprehensible form, suitable for comparisons with other geophysical parameters. A preliminary comparison between different trends in the surface temperature and heat flux values recorded by the TIRNet stations provides evidence of peculiar changes corresponding to periods of intense seismicity at the Campi Flegrei caldera. During periods characterized by modest seismicity, no remarkable evidence of common temperature variations was recorded by the different TIRNet stations. Conversely, almost all the TIRNet stations exhibited common temperature variations, even on a small scale, during periods of significant seismic activity. The comparison between the seismicity and the variations in the surface temperature and heat flux trends suggests an increase in efficiency of heat transfer between the magmatic system and the surface when an increase in seismic activity was registered. This evidence recommends a deeper, multidisciplinary study of this correlation to improve understanding of the volcanic processes affecting the Campi Flegrei caldera.