Journal of Seismology最新文献

The Haynesville Shale in eastern Texas and western Louisiana has been one of the most productive shale gas plays in the USA. It is notable for being significantly over-pressured, a factor which has often been associated with an increased likelihood of hydraulic fracturing-induced seismicity (HF-IS) elsewhere. However, to date, only one case of HF-IS has been identified in the Haynesville play. Seismic monitoring across the play is relatively sparse, so it is possible that the absence of reported cases represents an absence of monitoring rather than an absence of cases. This study represents an investigation of HF-IS across the Haynesville play, primarily using data from the TexNet seismic monitoring array, which was installed in 2017. We use template matching to increase the population of detected earthquakes, increasing the number of detections by over 200% compared to the catalogs available from regional monitoring agencies. The resulting events can be clustered into several discrete sequences. We use an induced seismicity assessment framework to evaluate whether each sequence was induced and, if so, what industrial activity represents the most likely cause (both hydraulic fracturing and wastewater disposal operations take place within the footprint of the Haynesville play). We find three notable cases of HF-IS, straddling the region between Nacogdoches, San Augustine and Shelby Counties. Having identified these sequences, we examine whether any geological conditions may influence the occurrence of HF-IS. We identify increased formation depth, increased pore pressure gradients, and the thinning or absence of the underlying Louann Salt, which may otherwise serve as a hydraulic barrier between the Haynesville Shale and the basement, as factors that may account for the varying prevalence of HF-IS across the play.

This study analyzes the dynamic source parameters of S-wave displacement spectra for 104 seismic events (1.7 ≤ ({M}_{L})  ≤ 3.6) recorded by the Egyptian National Seismic Network (ENSN) between 2010 and 2024 in the Dahshour region, northwestern Egypt. The Generalized Inversion Technique (GIT) was employed to correct the source displacement spectra for receiver and path effects using a linear least-squares approach, assuming a reference site. Two seismic stations that belong to ENSN namely, New Bani Suef (NBNS) and New Katemiya (NKOT), were utilized as a reference site in the inversion analysis. Attenuation effects along the ray path and site-specific influences were removed to derive source spectra at each station. The averaged S-wave source spectrum deviates from the Brune ω² source model. Key spectral parameters, including long-period amplitude (Ω₀) and corner frequency (({f}_{C})), were determined, allowing for the estimation of source parameters. Corner frequency, Seismic moment, fault radius, and stress drop were calculated from the corrected displacement spectra. The S-wave displacement spectra exhibited a rapid decay at 10 Hz within the analyzed frequency range (0.8–50 Hz). For NBNS (reference site), the estimated corner frequency, seismic moment, source radius, and stress drop ranged from 2.6 to 9.6 Hz, 8.7 × 10¹⁸ to 1.2 × 10²¹ dyne-cm, 78.9 to 292.3 m, and 0.04 to 10.13 MPa, respectively. For NKOT, these values ranged from 2.8 to 9.9 Hz, 1.26 × 10¹⁹ to 1.58 × 10²¹ dyne-cm, 76.1 to 273.3 m, and 0.2 to 16.13 MPa, respectively. These results provide insights into the seismic source characteristics of the Dahshour region, contributing to a better understanding of earthquake dynamics, crucial for characterizing the energy release and rupture mechanisms of earthquakes in northwestern Egypt.

Most of the scientific literature on the Eastern Anatolian Fault Zone (EAFZ) mentions a very large earthquake occurring in 1513 or 1514, presumably in the Pazarcik segment. This earthquake could play an important role in the assessment of the EAFZ seismogenic potential, provided its parameters were reliable. However, these parameters have a flimsy historical basis: just a few words of a letter sent from Damascus to Venice in March 1514, reporting severe damage in three towns in south-eastern Anatolia, one of which is hundreds kilometres away from the other two. Despite extensive research into contemporary and later historical sources and the history of monumental buildings of the three towns, we have found no evidence of damage/restoration to monuments predating 1513/1514 in the affected sites. Nor are there mentions of earthquake effects elsewhere in Anatolia and surrounding countries. Contemporary reports—mostly concerned with the 1514/1517 wars between the Ottoman, Safavid and Mamluk empires—make no mention of this earthquake or of any hindrances which its aftermath might have caused to troops marching through the allegedly devastated region (e.g. with regard to procuring supplies and shelter, or to travel difficulties due to damage to road infrastructures, landslides and the like). At the current state of knowledge, we suggest that the only available earthquake description may be either unwittingly overestimated, or possibly a conflation of two smaller earthquakes, with different epicentral locations.

This study analyzes the characteristics of the January 23 and 24, 2022, Tabriz earthquakes in northwestern Iran. These events, with magnitudes of (M_w) 4.2 and (M_w) 4.0, occurred within the Tabriz pull-apart basin and represent the largest seismic occurrences in the region over the past two centuries. Focal mechanism solutions indicate strike-slip faulting for the first event and normal faulting with a strike-slip component for the second event. Both events occurred on NW-trending faults. Based on recorded ground motion data, the first event ruptured in the NW direction, while the second event ruptured in the opposite direction (SE). Coulomb stress changes analysis suggests that stress changes imparted by the first event, estimated about 0.1 bar at the hypocenter of the second event, likely promoted its triggering. These findings highlight the active tectonics of the Tabriz Basin and the significant seismic hazards posed by its active faults, particularly for the city of Tabriz, which has a population over 2 million and is situated within the basin.

The shallow seismic response to earthquakes is important for ground motion prediction and is controlled by the major structural heterogeneities including topography. In this study, constrained inversion of microtremor horizontal-to-vertical spectral ratios (HVSRs) and Rayleigh phase velocity dispersion curves, along with well-constrained single station HVSRs inversion, produce the first 2D near-surface shear wave velocity (({V}_{s})) model of Garhwal Himalaya, India. We analyse passive source seismic data from 158 sites, along with two-sided active seismic array records from 96 locations, to evaluate the 1D ({V}_{s}) structure for different geo-tectonic units in the studied area. To explain the observed HVSR response, we calculate the HVSR curves using both theoretical (modified Haskell matrix) and numerical (modal summation) approaches. The simulated HVSR curves agree well with the observations in ~ 1.0–25.0 Hz. We examine the feasibility of the obtained 1D ({V}_{s}) profiles through extensive synthetics. The resultant 1D ({V}_{s}) profiles were then compiled to create the 2D near-surface ({V}_{s}) models for various litho-tectonic units. High ({V}_{s}) anomalies correlate well with the major tectonic features, such as the Kaliyasaur fault, North Almora thrust, and the anticline structures, while the syncline structures, Singtali thrust, and the depression fault zones exhibit low ({V}_{s}) anomalies. The 1D ({V}_{s}) profiles of ten known stratigraphic sections clearly delineate the interface boundaries between various rock strata. For the upper 30 m depth, the ({V}_{s}) 30 value ranges from 280 m/s to 600 m/s. Our velocity model demonstrates intense rock folding and faulting beneath the region, which can be used to evaluate the local site response for improved seismic hazard assessment of the region.

In this study, we investigated the Moho reflected phases and used them to estimate the spatial variation of the Moho depth in the northwestern Iran. The Moho reflected phases are secondary phases, which can be observed at the distance range between 20 and 185 km. We used 109 earthquakes whit depth shallower than 35 km occurred from 1996 to 2017 and collected the approximate travel time of 188 PmP and 140 SmS high quality phases recorded by 36 seismic stations. We used the differential travel time of direct and the Moho reflected phases to estimate the depth of Moho. The results of the reflected phases PmP and SmS are very similar in character. Although differences are also observed, especially in the northern part of the studied area where reflection points are not well distributed. The results of the inversion of P data are more reliable owing to the accuracy of the picking of P- compared to S- phases. According to the results, the average Moho depth is about 45 km in the north and south of the North Tabriz Fault, decreasing to 43.5 km towards the eastern and northwestern parts of the study area.

We analyse the background seismicity, including mainshocks and isolated events, from a distinct clustered component using the nearest-neighbour declustering method. After declustering the seismic catalog, two components were identified: background and clustered. The clustered component includes isolated networks, and for mainshock selection within each network, we applied outdegree and closeness centrality measures from network theory. This approach differs from the conventional method, which selects mainshocks from individual clusters network based on the highest magnitude. The background events dataset was obtained using the nearest-neighbour method and network analysis. This methodology was applied to the Southern California region, encompassing four significant events with magnitudes greater than 7, over the period 1981–2021. The primary objective is to assess the relationship between background seismicity and the Poisson process, as well as to identify the magnitude threshold at which it aligns with the Poisson model. To accomplish this, the background dataset was divided into specified magnitude ranges from 3 to 4.2, with intervals of 0.2. Temporal statistical tests, including the conditional chi-square test, Brown-Zhao test, and Kolmogorov–Smirnov test, were performed, while the Luen and Stark statistical test was applied for space–time analysis. For nearly all magnitude cut-offs, the temporal statistical tests reject the null hypothesis. The exception is at a magnitude of 3.4, where the temporal test is satisfied; however, the space–time statistical test still rejects the null hypothesis. However, the background dataset for the study region does not conform to the Poisson process in either the temporal or space–time tests across all magnitude thresholds. This inconsistency may be attributed to a limited number of data points at certain magnitude cutoffs, the declustering method used, or the potential need for an alternative conditional model for analysing background events.

In earthquake engineering, the precise characterization of long-period ground motion in the form of surface waves (Love and Rayleigh type) is crucial for designing resilient structures, particularly in complex environments such as sedimentary basins. This study evaluates the efficacy of the Normalized Inner Product (NIP) method for estimating surface wave parameters using limited input data within seismic analyses conducted based on numerical simulations. The method is benchmarked against two established techniques–Six Degrees-of-Freedom Polarization Analysis (6C-Pol) and Multiple Signal Classification (MUSIC)–to evaluate its precision in parameter identification. As an example, the methodologies are first applied to analyze surface waves from synthetically generated signals and then from basin-induced surface waves coming from a simplified basin with known characteristics, employing the the spectral element code SEM3D for 3D wave propagation simulation. The results revealed that the NIP method efficiently estimated surface wave characteristics using minimal information, demonstrating its efficiency. Furthermore, due to its capacity to rapidly process large datasets, the NIP method effectively quantified basin-induced surface waves across the basin surface, offering a robust framework for a more comprehensive understanding of 3D basin effects.

We investigated stress change parameters during ruptures for earthquakes globally with M_w ≥ 6.0 from 1991 to 2023. Employing a formulation and alternative graphical method, we analyzed variations between initial and final stresses as compared to frictional stress during rupture. Our goal was to assess the validity of Orowan’s model (final stress equals frictional stress) across different environments, crucial for recurrent source studies. Our findings reveal significant deviations among event types: reverse-type events diverge slightly from Orowan’s model, while normal events show even larger discrepancy. Strike-slip events exhibit a blend of stress difference mechanisms, with around 30% displaying overshoot (final stress smaller than average frictional stress). The partial stress drop (final stress larger than average frictional stress) percentage for reverse and normal types indicates that approximately 21–23% of the available stress for rupture was not relieved. Our results suggest that partial stress drop is a widespread phenomenon across all event types. This observation implies higher energy at higher frequencies than expected for an ω² frequency decay in the source spectra (Brune, 1976), potentially leading to underestimation of expected damaging accelerations. Our observations underscore the complexity of stress dynamics during earthquakes, with potential implications for energy release and damaging effects.

Two earthquakes from the first half of the twentieth century in the Peloponnese region (southern Greece) are analyzed here. These earthquakes occurred 1 year apart in the summers of 1926 and 1927; epicentral locations in the literature show them close to each other (~ 50 km apart). The earthquakes are of particular importance for at least two reasons: they appear to be of intermediate depth and macroseismic data associated with them has been available until now in paper format. Intermediate depth earthquakes are associated with the subduction zone along the Hellenic arc and do not occur as frequently as crustal earthquakes, therefore making the revisiting of such events even more important. Historical European databases which hold macroseismic data, such as AHEAD ((Albini et al. Istituto Nazionale Di Geofisica e Vulcanologia (INGV), 2013), are essential for disseminating this data type and making the different studies for each seismic event in the catalogue available. However, AHEAD includes earthquakes that occurred prior to 1900. Paradoxically, it is easier to find the macroseismic field of an earthquake from the 1500s than one from the early twentieth century. Therefore, disseminating and analyzing the macroseismic data of the two Peloponnese events from this period, previously available only in paper format, is crucial. In line with this goal, newly collected eyewitness accounts with existing observations for these events are presented, while macroseismic intensities are re-assigned in EMS98. Re-estimated epicentres suggest that the 1926 earthquake occurred further offshore, while the 1927 earthquake was on land at the southernmost tip of the Peloponnese peninsula. Isoseismal maps were created for both events using the Rossi-Forel and EMS98 scales. The use of modern unified European macroseismic scale (EMS98) in the study of historical earthquakes is essential for harmonizing the present and past with future hazard and risk analyses. The use of EMS98 with additional IDPs in the construction of isoseismal maps further refines the macroseismic field of the 2 events, while suggesting a different fault rupture orientation.