Seismological Data Research Articles

Middle-Late Miocene to Pleistocene Post-Collisional Magmatism in the Arabia-Eurasia Collision Zone, an Example from Northwest Iran

Abstract Post-collisional volcanism contains important clues for understanding the processes that prevail in orogenic belts, including those in the mantle and the uplift and collapse of continents. Here we report new geochronological and geochemical data for a suite of post-collisional Miocene to Pleistocene volcanic rocks from northwest Iran. Four groups of volcanic rocks can be distinguished according to their geochemical and isotopic signatures, including: (1) Miocene depleted lavas with high Nd and Hf but low Pb and Sr isotopic ratios, (2) less depleted lavas with quite variable Pb isotopic composition, (3) lavas with non-radiogenic Nd and Hf isotopic values, but highly radiogenic Sr and Pb isotopic composition, and (4) Pleistocene adakitic rocks with depleted isotopic signatures. The isotopic data reveal that the Miocene rocks are derived from asthenospheric and highly heterogeneous sub-continental lithospheric mantle sources. Evidence suggests that the lithospheric mantle contains recycled upper continental material and is isotopically similar to the enriched mantle two (EMII) end-member. Analysis of Sr-Nd-Pb-Hf-O isotopes in both mineral and rock groundmass, in conjunction with energy-constrained assimilation and fractional crystallization (EC-AFC) numerical modeling, demonstrates that the incorporation of continental crust during magma fractionation via AFC had an insignificant impact on the isotopic composition of the Miocene lavas. Moreover, adakites are the youngest rocks and show a geochemical signature consistent with the partial melting of a young and mafic continental lower crust. Both seismological data and geochemical signatures on these Miocene to Pleistocene volcanic rocks indicate the initiation of asthenospheric upwelling and orogen uplift in the Arabia-Eurasia collision zone, which occurred after slab break-off, following the Neotethyan closure.

Enhanced crustal and intermediate seismicity in the Hindu Kush-Pamir region revealed by attentive deep learning model

The Hindu Kush-Pamir region (HKPR) is characterized by complex ongoing deformation, unique slab geometry, and intermediate seismic activity. The availability of extensive seismological data in recent decades has prompted the use of deep learning algorithms to extract valuable insights. In this study, we present a fully automated approach for augmenting earthquake catalogue within the HKPR. Our method leverages an attention mechanism-based deep learning architecture to simultaneously detect events, perform phase picking, and estimate magnitudes. We applied this model to a ten-month dataset (January 2013–October 2013) from 83 stations in the region. Utilizing a robust criterion to evaluate the model's probabilities, we associated phases at different stations and pinpointed earthquake locations in the region. Our results demonstrate a significant enhancement, revealing nearly four and a half times more earthquakes than previously documented in the International Seismological Center (ISC) catalogue. A notable portion of these newly detected events falls within the category of very low-magnitude earthquakes (<3), which were absent in the ISC catalogue. Notably, our spatiotemporal analysis reveals a concentration of crustal seismicity along poorly mapped neotectonic north and northeast-oriented faults in the western Pamir, as well as the Vakhsh Thrust System and the Darvaz Karakul Fault. These findings underscore potential sources of future seismic hazards. Furthermore, our expanded earthquake catalogue facilitates a deeper understanding of the interplay between crustal and intermediate seismic activity in the HKPR, shedding light on the deformation and active faulting resulting from Eurasian-Indian plate interactions.

Geodynamic Regimes in the Laptev Sea Region According to the Latest Seismological Data

Geodynamic Regimes in the Laptev Sea Region According to the Latest Seismological Data

The intra-orogenic normal Lakes Fault (Sila, Calabria, southern Italy): new insights from geodetic and seismological data

The intra-orogenic normal Lakes Fault (Sila, Calabria, southern Italy): new insights from geodetic and seismological data

Application of the Empirical Mode Decomposition Method to Noise Reduction Using Seismic Event Data Recorded at Kirkuk Seismological Station.

This study aims to use the Empirical Mode Decomposition for reducing the noise of passive seismic signals recorded across seismic event recorded at Kirkuk station which is one of the Iraqi Meteorological Organization and Seismology data, where human activities in Iraq's populous cities significantly impact the seismic recordings at Iraqi Meteorological Organization and Seismology stations sites. In this paper, we present an algorithm based on the Empirical Mode Decomposition. It is a data driven method used as a propelling tool for analyzing and decomposing non-stationary and non-linear data without any previous assumptions. Empirical Mode Decomposition generates a finite and often small number of Intrinsic Mode Functions. The decomposition is based on the direct extraction of the energy related to various intrinsic time scales, an important parameter of the system. Empirical Mode Decomposition technique is applied to the available seismic records to reduce the noise level in the records, which helps in the interpretation of the records.

A New Posthole Seismometer at Concordia Permanent Research Facility in the Heart of the Icy East Antarctic Plateau

Abstract In the Southern Hemisphere, the prevalence of oceans and the difficulty of access to land result in reduced coverage of seismological stations, limiting our detailed knowledge of Earth’s structures and of large earthquakes sources. This situation is exacerbated inside the antarctic continent, where only two permanent seismic stations are currently available (IU.QSPA at South Pole and G.CCD). The CCD station, built in early 2000s with state-of-the-art surface instrumentation and located at the French–Italian Concordia base (75° S, 123° E), has been providing seismological data since 2008. However, it suffers from several problems: the vault is deformed by the hydrostatic pressure of the snow, the firn waveguide traps anthropogenic noise from the base causing strong noise below 1 s, and a coupling defect limits the performance above 30 s on the horizontal channels. To ensure the continuity of CCD and to improve its overall performance, we started in 2014 to plan the installation of a borehole seismometer at the site. In this article, we describe in detail this renovation of CCD and some examples of data analysis. The new borehole sensor shows that short-period disturbances are largely attenuated (−20 dB at 0.1 s) compared to the surface installation and that the horizontal channels have a lower noise level at long periods (−8 dB at 100 s). Data for all components are below the standard noise model between 0.1 and 0.2 s, which makes this sensor one of the quietest installations in the world for this bandwidth. For periods &amp;gt;600 s we observe atmospheric pressure-related perturbations on the vertical component. Despite this problem, the new CCD borehole station is a success with better-than-expected performances at all periods &amp;lt;600 s. The data produced are now distributed in the world’s data centers as G.CCD.20 and we encourage the scientific community to use the data for all studies requiring seismograms from Antarctica.

Three-dimensional numerical modeling of ground motion in the Valley of Mexico: A case study from the Mw3.2 earthquake of July 17, 2019

In this study, a 3D physics-based numerical approach, based on the spectral element numerical code SPEED, is used to simulate seismic wave propagation due to a local earthquake in the Mexico City area. The availability of detailed geological, geophysical, geotechnical, and seismological data allowed for the creation of a large-scale (60 km × 60 km in plan, 10 km in depth) heterogeneous 3D numerical model of the Mexico City area, dimensioned to accurately propagate frequencies up to about 1.3 Hz. The results of numerical simulations are validated against the ground motion recordings of the July 17, 2019, Mw3.2 earthquake, with peak ground acceleration exceeding 0.3 g about 1 km away from the epicenter. A good agreement with records is found, quantitatively evaluated through goodness-of-fit checks. Furthermore, for the lake zone, the simulated decay trend of the peak ground velocity with epicentral distance is reasonably close to the observations, for both horizontal and vertical components. In spite of some limitations, the simulations are successful to provide a realistic picture of seismic wave propagation both in the hill and in the lake zones of Mexico City, including the onset of long-duration quasi-monochromatic ground motion in the basin, with strong amplification at low frequencies (between 0.4 and 0.7 Hz). The numerical results also suggest that surface waves, with predominant prograde particle motion at the ground surface and large ellipticities, dominate the wavefield in the lake zone. Based on these positive outcomes, we conclude that this numerical model may be useful for both a better insight into the seismic response of the Valley of Mexico and the simulation of ground motions during larger-magnitude earthquakes, to generate improved seismic damage scenarios in Mexico City.

Environmental control of the present-day sediment export along the extratropical Andes

Understanding how the environmental factors that determine erosion operate is essential to know the past and future evolution of the Earth and adequately manage natural resources. In this work, the main controlling factors of the current sediment export in the western side of the extratropical Andes (20°-55°S) are investigated using multidecadal series of specific suspended sediment yields from 42 rivers, as well as land cover, climatic, cryospheric, topographic, seismological and geological data. Through an automatic selection of Generalized Additive Models based on predictability and complexity, it was found that the combined effects of extreme runoff, glacier cover and channel steepness explain ~90 % of the spatial variability of sediment export. The runoff effect varies from positive for hyper-arid and semi-arid settings to slightly negative for moderate and wet settings, probably because of an associated increase in vegetation coupled with a recurrence and magnitude of floods that becomes greater than the time it takes for the basins to generate sediment. Cryosphere and channel steepness influences were also observed on the average suspended sediment concentration, which is less associated with water availability and more associated with erodibility and sediment availability.

Multidisciplinary analysis of 3D seismotectonic modelling: a case study of Serre and Cittanova faults in the southern Calabrian Arc (Italy)

Active normal faulting and uplifting, consistent with a WNW-ESE-oriented regional extension, dominate the Quaternary tectonics of the southern Calabrian Arc. The main tectonic structures of this extensional domain are considered to be the source of numerous historical and recent strong earthquakes, among which the 1783 seismic sequence (M 6.5–7) was one of the most destructive earthquakes ever recorded in Southern Italy. Previous works on the seismotectonic of the Calabrian Arc indicate a disagreement on the attitude (E-dipping vs W-dipping) of the main seismogenic sources slicing across southern Calabria, whereby the seismotectonic framework is still debated. Following a multidisciplinary approach, based on morpho-structural and seismological data, the geometry at depth of the most reliable sources (i.e., Cittanova and Serre faults) was first modelled in a 3D environment to retrieve information about their seismic potential. The GNSS data from the permanent stations of RING/RDN and TopNETlive Italy networks have been processed in order to estimate the velocity field affecting this area. Then, data inversion allowed us to document a predominant WNW-ESE active extensional strain orthogonally to the modelled faults, consistent with the regional dynamics. The reliability of the model was tested using empirical relationships and fault response modelling simulation. Furthermore, slip tendency analysis revealed the propensity to slip of the modelled planes by applying a remote stress state derived from the kinematic-structural survey on fault planes.

Model of the Seismic Rupture Surface of the Chignik Earthquake (Alaska, USA) 07.29.2021 Based on SAR Interferometry and GNSS Data

The paper presents a new rupture model for the Mw = 8.2 “Chignik” earthquake, which occurred off the coast of the Alaska Peninsula on 29.07.2021. The model is based on the Earth’s surface displacement fields obtained by InSAR (Interferometric synthetic aperture radar) method using images of the ESA Sentinel-1 satellites from 17.07 to 10.08.2021 and data on horizontal displacements at nearest permanent GPS sites from 18.07 to 08.08.2021. Obtained displacement fields include both coseismic and part of postseismic displacements. When constructing a model of the seismic rupture surface, we used F. Pollitz’s solution of the problem of the displacement fields at the surface of a spherical radially stratified planet caused by displacements on a rectangular discontinuity located inside it. For the regularization of the inverse problem, we added the condition that the direction of slip on each element of the fault plane is close to the rake angle, determined from seismological data. In the constructed model, the seismic rupture area was approximated by a single plane with a length of 225 km along the strike, 126 km along the dip, divided into 48 identical rectangles. According to the constructed model, the type of displacements is almost pure thrust, and displacements, in general, occurred throughout all the source area. The maximum displacement was 5.7 m, with an average displacement over the entire plane of 2.2 m, which is close to the USGS and GCMT estimates derived from seismological data.

Fault Coupling on a Creeping Thrust Fault: Joint Inversion Using Geodetic Data and Repeating Earthquakes

AbstractDue to the lack of recognized creep on dip‐slip faults, the nature of fault creep and its role in the generation of large earthquakes is largely unexplored. The Chihshang fault in Taiwan serves as one of the best examples of a thrust creeping fault in the world, exhibiting a fast creep rate of 2–3 cm/year and the capability of producing magnitude six earthquakes. Land‐based geodetic measurements are less sensitive to fault slip with depth, especially for the deeper portion of the seaward dipping fault. Taking advantage of slip rates inferred from repeating earthquake sequences (RESs) at greater depths (up to 30 km), we present a method that embeds RES‐derived slip rates into the neighboring fault patch for geodetic data inversion. Using the geodetic and seismological data from 2007 to 2011, we achieve a higher resolution of inter‐seismic slip rate distribution below a depth of 10 km. The inferred low coupling ratio establishes an extensive creeping area that coincides with a location of abundant RES and earthquake swarms. The inferred high coupling ratio, on the other hand, delineates a locked area corresponding to the two co‐seismic slip zones of the 2003 Mw 6.8 Chengkung and 2022 Mw 6.7 Yuli earthquakes. The transition zone marking the gradual change from fully locked to shallow creeping areas appears to coincide with the post‐seismic slip area of the 2003 Chengkung event. Using the fault coupling model, the moment rate deficit measured in the two locked areas is capable of generating a Mw 6.8 event every 78 years to the south and a Mw 6.7 event every 28 years to the north. This moment rate deficit is decreased by 10% when the closely located Central Range fault is considered in a two‐fault model, leading to the slightly longer recurrence interval on the Chihshang fault. The two‐fault model potentially contributes to a better understanding of the regional inter‐seismic deformation, which is recommended to be adopted in the future studies of seismic hazard assessment.

Moho Inversion by Gravity Anomalies in the South China Sea: Updates and Improved Iteration of the Parker‐Oldenburg Algorithm

AbstractThe Moho is the interface between crust and mantle, and accurate location of the Moho is important for both resource exploration and deep earth condition and structural change investigations. The theory of the traditional Parker‐Oldenburg (P‐O) method is quite simple and it is widely applied in the frequency domain of Moho depth inversion. However, Moho fluctuation simulations using the P‐O method are not reliable because of the lack of field geographic data constraints during the inversion process and the excessively smoothing of data details caused by using filters to correct the source data signals. To solve those problems, we propose an improved iteration P‐O method with a variable density contrast model, the iterative process is constrained by geological data in the inversion parameters, and the variable depth of the gravity interface is iterated using an equivalent form of upward continuation in the Fourier domain, which is more stable and convergent than downward continuation term in original P‐O method. Synthetic experiments indicate that improved method has the better consistency among the simulations than original method, and our improved method has the smallest root mean square (RMS) of 0.59 km. In a real case, we employed the improved method to invert for the Moho depth of the South China Sea (SCS), and the RMS between our Moho depth model and the seismological data is the smallest value of 2.27 km. The synthetic experiments and application of the model to the SCS further prove that our method is practical and efficient.

Objective Evaluation of the Source Models for Seismic Hazard Investigations Using the Logic Tree Approach: Case Study Semnan, Iran

Probabilistic seismic hazard analysis (PSHA) has become a fundamental tool in assessing seismic hazards and for estimating seismic design and seismic safety evaluation of ground motions. This report describes a study to test and verify the numerical approaches and software used in PSHA on Semnan, one of the important cities of Iran country. The geological and seismological data are integrated into a probabilistic seismic hazard model for the region. Historical and instrumental earthquake data, geology, tectonics, fault activity, and seismic source models associated with seismic events are taken into account. A probabilistic approach within a logic-tree framework is used to calculate seismic hazard for Semnan. The results were also displayed in terms of uniform hazard spectra for rock sites for return periods of 100, 475 and 2475 years, which is deemed appropriate for structural design standards in the Iran building code. As the results of this study have been displayed on the map for different return periods and different natural periods, it can provide the basis for the preparation of new seismic risk maps.

Comparing geologic structural mapping techniques in tectonically active region of Lake Van using gravity and seismological data

Comparing geologic structural mapping techniques in tectonically active region of Lake Van using gravity and seismological data

The 2020–2021 seismic sequence in the Western Gulf of Corinth: Insights on the triggering mechanisms through high resolution seismological and geodetic data analysis

The 2020–2021 seismic sequence at the Western Gulf of Corinth, Central Greece, has been thoroughly analyzed using seismological and geodetic data processing. We present a high-resolution dataset of over 4000 relocated earthquakes between June 2020 and February 2021, delineating the activated structures. We examine the evolution of various clusters that were triggered during a three-stage sequence which began on December 23, 2020, with an Mw = 4.6 event near Marathias, migrated eastwards, following an Mw = 5.0 event on January 12, 2021 near Trizonia Island, and culminated on February 17 with an Mw = 5.3 offshore event north of Psathopyrgos. Focal mechanisms for the 20 stronger events, determined by moment tensor inversion, and 36 weaker ones, obtained through first motion polarities measurements, revealed dominant normal faulting. The fault plane of the February 17, 2021 major event is modeled through the inversion of geodetic data. Results suggest a very shallow geodetic centroid at 1.5 km depth, consistent with the seismic centroid (3.5 km), but different from the relocated hypocenter (7.5 km). Spatiotemporal analysis reveals seismic migration, following a diffusion law with D values in the range 0.06–0.25 m2s−1, consistent with triggering due to pore-pressure diffusion by fluids intrusion. This enables failure on non-optimally oriented faults, which explains the significant proportion of the observed strike-slip and oblique-normal faulting. Coulomb stress transfer due to the major events shows only weak stress-loading on the fault of the January 12, 2021 earthquake and a higher level of positive stress transfer to the south-dipping than to the north-dipping nodal plane of the 17 February event. The latter could have facilitated the nucleation of the rupture at 7.5 km and its further propagation to shallower depths along a south-dipping plane, where the bulk of its seismic and geodetic moment was released.

Magmatic activity of Klyuchevskoy volcano triggering eruptions of Bezymianny volcano based on seismological and petrological data

The Frac-Digger method based on seismological data of the Kamchatka Branch Federal Research Center United Geophysical Survey Russia Academy of Sciences (KB FRC UGS RAS) was applied to reveal the 3D distribution and chronology of injections of dykes and sills from the deep and shallow magma chambers of Klyuchevskoy volcano preceding the eruptions of Bezymianny volcano during period from 2000 to 2020. The orientation of magma injections (dykes and sills) and mechanisms of volcano-tectonic earthquakes reveal radial horizontal extensional stress conditions in volcanic structures and sometimes local radial compression around magma chambers. Geochemical history of eruption samples shows the parentage of Klyuchevskoy magma for Bezymianny volcano products, tracing magma transport patterns. The result is a 3D conceptual model of the magma-feeding system of Bezymianny volcano from Klyuchevskoy volcano.

Continuation of Events Detection with Global Long-Period Seismic Data: An Analysis from 2010 to 2022

Abstract We develop an algorithm to detect and locate sources of long-period (25–100 s) seismic signals. Our method is based on the analysis of seismological data recorded at global networks, plus all available stations at latitude larger (smaller) than 60° (−60°). We use a delay and stack method to identify coherent Rayleigh waves generated at the free surface of the Earth. The application of our approach to 13 yr of continuous data permitted us to detect more than 36,000 events. After a precise analysis to classify known events and to remove spurious detections, we report more than 1700 previously unidentified source of long-period seismic signals. Each source is characterized by its location (with associated uncertainty) and moment magnitude. This new catalog mainly reveals sources in the polar regions likely associated with glaciers dynamics but also volcanic activity, landslides, and regular earthquakes located in remote areas of the planet. Our study reveals the importance of maintaining global seismic networks and exploring the recorded data, beyond providing new observations that can be the basis to future studies to better characterize physical processes occurring at the free surface of our planet.

Active Collapse in the Central Betic Cordillera: Development of the Extensional System of the Granada Basin

The Betic Cordillera was formed by the collision between the Alboran Domain and the South Iberian paleomargin in the frame of the NW–SE convergent Eurasia–Nubia plate boundary. The central region is undergoing a heterogeneous extension that has not been adequately analysed. This comprehensive study addressed it by collecting structural geologic, seismologic, and geodetic data. The region west of the Sierra Nevada is deformed by the extensional system of the Granada Basin, which facilitates E–W to NE–SW extension. Moreover, the southern boundary of Sierra Nevada is affected by a remarkable N–S extension related to E–W normal to normal–dextral faults affecting the shallow crust. However, geologic and geodetic data suggest that the western and southwestern Granada Basin boundary constitutes a compressional front. These data lead to the proposal of an active extensional collapse from the uplifted Sierra Nevada region to the W–SW–S, over an extensional detachment. The collapse is determined by the uplift of the central Betics and the subsidence in the Alboran Basin due to an active subduction with rollback. Our results indicate that the central Betic Cordillera is a good example of ongoing extensional collapse in the general context of plate convergence, where crustal thickening and thinning simultaneously occur.

Tectonic Framework of Central Sinai (Egypt) Using Geophysical and Seismological Data

Tectonic Framework of Central Sinai (Egypt) Using Geophysical and Seismological Data

Tracking aftershock sequences using empirical matched field processing

SUMMARY Extensive aftershock sequences present a significant problem to seismological data centres attempting to produce near real-time comprehensive seismic event bulletins. An elevated number of events to process and poorer performance of automatic phase association algorithms can lead to large delays in processing and a greatly increased human workload. Global monitoring is often performed using seismic array stations at considerable distances from the events involved. Empirical matched field processing (EMFP) is a narrow-frequency band array signal processing technique that recognizes the inter-sensor phase and amplitude relations associated with wavefronts approaching a sensor array from a given direction. We demonstrate that EMFP, using a template obtained from the first P arrival from the main shock alone, can efficiently detect and identify P arrivals on that array from subsequent events in the aftershock zone with exceptionally few false alarms (signals from other sources). The empirical wavefield template encodes all the narrow-band phase and amplitude relations observed for the main shock signal. These relations are also often robust and repeatable characteristics of signals from nearby events. The EMFP detection statistic compares the phase and amplitude relations at a given time in the incoming data stream with those for the template and is sensitive to very short-duration signals with the required characteristics. Significant deviations from the plane wavefront model that typically degrade the performance of standard beamforming techniques can enhance signal characterization using EMFP. Waveform correlation techniques typically perform poorly for aftershocks from large earthquakes due to the distances between hypocentres and the wide range of event magnitudes and source mechanisms. EMFP on remote seismic arrays mitigates these difficulties; the narrow-band nature of the procedure makes arrival identification less sensitive to the signals’ temporal form and spectral content. The empirical steering vectors derived for the main shock P arrival can reduce the frequency dependency of the slowness vector estimates. This property helps us to automatically screen out arrivals from outside of the aftershock zone. Standard array processing pipelines could be enhanced by including both plane-wave and empirical matched field steering vectors. This would maintain present capability for the plane-wave steering vectors and provide increased sensitivity and resolution for those sources for which we have empirical calibrations.