Moment Magnitude Research Articles

Multiple segmentation and seismogenic evolution of the 6th February 2023 (Mw 7.8 and 7.7) consecutive earthquake ruptures and aftershock deformation in the Maras triple junction region of SE-Anatolia, Turkey

On 6th February 2023 (UTC), two consecutive and catastrophic earthquakes with moment magnitudes (Mw) 7.8 and 7.7 struck the Maras Triple Junction (MTJ) region in SE Anatolia along with dozens of aftershocks, causing numerous casualties and significant building damage, and generating the most complex and longest surface ruptures ever observed in Turkey. The main driving mechanisms of this complex double event are still unresolved and remain controversial, even though they are likely linked with conventional fault activations, recurrence intervals and seismic gaps. Here, the aim was to gain insight into the source regimes and rupture processes of both events and their relationship with resolved fault focal solutions for the observed aftershocks, and to present an interpretation that accounts for the most puzzling aspects of the fault rupture models. In line with this, the co-seismic slip distributions of these two events were examined by joint analyses of centroid moment tensor (CMT) and finite-fault source inversions using regional and teleseismic broadband observations. Inversion results indicate that both earthquakes were left-lateral strike-slip events, and the main ruptures extended mainly from close to NNE to SSW and E to W, with maximum slips of ∼6.5–10 m, mostly confined to a shallow depth range of ≤ ∼10–15 km and extending to the surface, indicating bilateral source processes with an average rupture velocity of ∼3.5–5.5 km/s. The estimated total seismic moment range was 4.94–8.22 × 1020 N m, associated with ∼352–152 km long (along strike) and ∼ 25 km wide (along dip) fault planes at focal depth of ∼10 km. Regional CMT results indicate nearly pure normal-slip and left-lateral normal oblique-slip focal mechanisms and shallow centroid depths (≤ ∼15 km) for the early aftershock distribution that are obviously complementary with the co-seismic bilateral rupture propagations. This result highlights that double pull-apart branching of focal mechanisms for aftershock occurrence implies interacting fault ruptures embedded in the MTJ area, where two sub−/supershear-rupturing faults meet, thus explaining multiple segmentation and seismogenic evolutions of two interrelated mainshocks, i.e. “triple junction earthquakes”. The results reveal that the MTJ tends to migrate to the SSW and likely drives the SSW-stepping of the left-lateral strike-slip shear (∼136 km). This accounts for the peak slips, long co-seismic fault ruptures and the associated faulting styles. Hence, the co-seismic faulting apparently distributed across the MTJ may reflect triple junction migration, and thus large extension at the core of the Anatolian-Arabian plates, leading to very high seismic hazard in similar junction regions of the country.

Earthquake source parameters in Zagros region (Iran) from the time-evolutive P-wave displacement

The rupture process of the recent moderate-to-large earthquakes in the Zagros area along the Iran plateau is investigated by analysing the strong motion data provided by the Iranian Building and Housing Research Centre (BHRC). The selected dataset includes the largest and deadliest 2017 Mw 7.3, Iran-Iraq (Ezgeleh) earthquake. The earthquake source parameters (moment magnitude, rupture duration and length, average slip, and static stress drop) are determined using a time-domain, parametric modelling technique based on the time evolution of the P-wave displacement signals. The earthquake source parameters are calculated from simulated triangular moment-rate functions assuming the circular source models for a constant rupture velocity. The anelastic attenuation effect is modelled through the independent frequency-Q parameter ranging from 50 to 200 and accounted for by a post-processing procedure that retrieves the attenuation-corrected, moment-rate triangular shape. Results show that the average static stress-drop with different {Q}_{P}, varies between <Δσ> = 0.9 (0.7–1.2) MPa and <Δσ> = 1.6 (1.2–2.0) MPa. Overall, in this research, the rupture radius/length empirically scales with the seismic moment with a self-similar, near-constant stress drop of about 1 MPa. Assuming a circular rupture model for the Ezgeleh earthquake, we estimate a moment magnitude of 6.9, rupture duration of 7 s, source radius of 16 km, average slip of about 2 m and static stress drop of 3.4 MPa.

The Influence of Large Pendent Groups on Chain Anisotropy and Electrical Energy Loss of Polyimides at High Frequency through All-Atomic Molecular Simulation.

Polyimide is a potential material for high-performance printed circuit boards because of its chemical stability and excellent thermal and mechanical properties. Flexible printed circuit boards must have a low static dielectric constant and dielectric loss to reduce signal loss in high-speed communication devices. Engineering the molecular structure of polyimides with large pendant groups is a strategy to reduce their dielectric constant. However, there is no systematic study on how the large pendant groups influence electrical energy loss. We integrated all-atomic molecular dynamics and semi-empirical quantum mechanical calculations to examine the influence of pendant groups on polymer chain anisotropy and electrical energy loss at high frequencies. We analyzed the radius of gyration, relative shape anisotropy, dipole moment, and degree of polarization of the selected polyimides (TPAHF, TmBPHF, TpBPHF, MPDA, TriPMPDA, m-PDA, and m-TFPDA). The simulation results show that anisotropy perpendicular to chain direction and local chain rigidity correlate to electrical energy loss rather than dipole moment magnitudes. Polyimides with anisotropic pendant groups and significant local chain rigidity reduce electrical energy loss. The degree of polarization correlated well with the dielectric loss with a moderate computational cost, and difficulties in directly calculating the dielectric loss were circumvented.

Automated shear-wave splitting analysis for single- and multi- layer anisotropic media

Shear-wave velocity anisotropy is present throughout the earth. The strength and orientation of anisotropy can be observed by shear-wave splitting (birefringence) accumulated between earthquake sources and receivers. Seismic deployments are getting ever larger, increasing the number of earthquakes detected and the number of source-receiver pairs. Here, we present a new Python software package, SWSPy, that fully automates shear-wave splitting analysis, useful for large datasets. The software is written in Python, so it can be easily integrated into existing workflows. Furthermore, seismic anisotropy studies typically make a single-layer approximation, but in this work we describe a new method for measuring anisotropy for multi-layered media, which is also implemented. We demonstrate the performance of SWSPy for a range of geological settings, from glaciers to Earth's mantle. We show how the package facilitates interpretation of an extensive dataset at a volcano, and how the new multi-layer method performs on synthetic and real-world data. The automated nature of SWSPy and the discrimination of multi-layer anisotropy will improve the quantification of seismic anisotropy, especially for tomographic applications. The method is also relevant for removing anisotropic effects, important for applications including full-waveform inversion and moment magnitude analysis.

Reappraisal of the 1926, Jersey earthquake source parameters

The Cotentin peninsula is a region located on the northeastern edge of the Armorican Massif (France) that hosts several nuclear and radioactive waste facilities. A recent publication raised some issues regarding the source parameters of the 1926, Jersey earthquake, one of the key reference earthquakes for assessing the seismic hazard at the nuclear sites. In this study, we performed in-depth analyses on both the instrumental and macroseismic data to reappraise the source parameters. While the instrumental epicentral location was fairly well constrained at about mid-distance between the Jersey Island and the Cotentin peninsula, the focal depth could not be retrieved due to the resolution limits associated with a sparse seismological network and to the uncertainties on the phase picking. Different MS formulations applicable for moderate magnitude events recorded at regional distances were implemented to better account for the epistemic uncertainties, resulting in an estimation of MS equal to 5.1 ± 0.3. Regarding the moment magnitude MW, we performed a broad series of waveform modeling accounting for a broad set of source parameterizations and signal processing techniques. The magnitude MW of the Jersey earthquake is estimated to 5.4 ± 0.3 although these evaluations are strongly influenced by the period range adopted to fit the observations. We also carried out the evaluation of both MS and MW magnitudes by modeling the macroseismic field with results (MS = 5.1 ± 0.3; Mw = 5.3 ± 0.3) that are consistent with the instrumental estimates. Regarding the focal depth, the macroseismic analyses shed light on this parameter, even though the results depend on the assumption made on the presumed epicentral intensity (∼18 km for I0 = VI-VII and ∼ 12 km for I0 = VII).

Seismotectonic mapping and energy release analysis for Ongole city of Andhra Pradesh, India

An updated homogenised earthquake catalogue comprising 753 events from 1800 AD to 2021 AD for Ongole city andhra Pradesh, was compiled for a circular buffer zone of radius 500km with collector office (Lat 15.49880 N and Long 80.04970 E) as the centre. Dependent events were declustered using the Uhrhammer algorithm and the degree of completeness was computed using CUVI and Stepp’s methods. The analysis shows that around 11% of events were foreshocks and aftershocks. The degree of completeness for the magnitude range of 3.0 ≤ Mw &lt; 3.5, 3.5 ≤ Mw &lt; 4.0, 4.0 ≤ Mw &lt; 4.5, 4.5 ≤ Mw &lt; 5.0, 5.0 ≤ Mw &lt; 5.5 and Mw ≥ 5.5 was found to be 23, 56, 56, 63, 105 and 178 years based on CUVI method and 30, 30, 60, 60, 110 and 160 years as per Stepp’s method respectively. Values of the seismicity parameters a and b based on Gutenberg-Ritcher’s recurrence relationship for the study area were 4.02 and 0.83 respectively. Based on the current study, the maximum earthquake magnitude (Mmax) computed for the Ongole city is 7±0.27 on the moment magnitude scale and cumulative seismic energy release is 2.73x1016J. Finally, a seismotectonic map has been developed in ArcGIS 10.5.1 software comprising past seismicity, regional geology and faults details.

Spectroscopy and Photochemistry of Aluminum-Bearing Species in the Universe.

ConspectusMetal-bearing molecules impact the chemical and physical environment of many astronomical sources such as the circumstellar envelopes of large asymptotic giant branch and red supergiant stars, the interstellar medium, and planetary atmospheres (e.g., ablation of ∼20 tons per day into the Earth's upper atmosphere). In recent decades, the number of successfully detected metal-containing molecules has increased via rotational spectroscopic observations, which are driven by theoretical and experimental investigations. Following formation, the ultimate fate of each species (stabilization, dissociation, etc.) is determined by its electronic structure and electronic spectroscopic properties as it encounters the pervasive radiation fields in the vacuum of space. Studying these properties can evince the possibility of detection and predict the impact each molecule has on its surrounding environment. Aluminum, one of the most abundant elements and metals, is distributed throughout the universe as a constituent of gas-phase molecules (e.g., AlO, AlOH, AlCl, etc.) as well as condensed onto solid dust grains such as Al2O3. Free gas-phase aluminum-bearing molecules are synthesized by nonthermal equilibrium processes such as shocks and pulsations near the stellar photosphere or via the reaction of molecules on the surface of dust grains. Recent investigations in our research group utilizing quantum chemical methods, such as coupled cluster (CCSD(T) and CCSD(T)-F12) and multireference configuration interaction (MRCI) with large basis sets, have explored a wide breadth of spectroscopy and photochemistry of small (triatomic and tetratomic) aluminum-bearing molecules, including Al-H, Al-C, Al-N, Al-O, Al-Si, Al-P, and Al-S bonds, among others. The ground-state spectroscopy (rotational and vibrational) of various aluminum-bearing molecules is discussed in the context of experimental and observational detection potentials. These detection potentials depend on various factors, such as the magnitude of the permanent dipole moment (PDM) and the population of states yielding transition frequencies in detectable ranges. Many aluminum-bearing molecules possess large PDMs and may be prime candidates for astronomical and laboratory detection. Within this discussion, interesting aspects of the ground-state molecular orbital configuration of OAlNO are shown to lead to an uncommon triplet ground state. Additionally, the electronic absorption spectrum of the quasi-isoenergetic ground-state isomers of AlOSO is discussed as a sensitive method for detecting this species and differentiating between the two isomers. Finally, photochemical mechanisms key to the production of AlO and AlOH in low-density regions and the destruction of AlCO and AlOC are also discussed in order to understand the radiation-induced formation and destruction of these molecules.

Soil–Structure Interactions in a Capped CBP Wall System Triggered by Localized Hydrogeological Drawdown in a Complex Geological Setting

Retaining walls are often used to construct basements and underground station boxes. This unique case study compares the field-measured contiguous bored pile (CBP) wall, surrounding geology, and hydrogeology or groundwater responses against the results using 2D and 3D numerical back analyses of a deep excavation project that experienced localized groundwater drawdown through the leaking ground anchor points. Site observations indicated that the ground anchor installation works had caused larger than expected through-the-wall leakages that subsequently triggered nearby ground and building settlements. In order to study the complex soil–structure interaction behavior, back analyses using a hybrid modeling technique of through-the-wall transient hydrogeological seepage and geomaterial stress-strain analyses was implemented. Through these soil-structure interaction back analyses, it was evidently revealed that the presence of the continuous capping beam was key in providing pile head restraints against the active earth pressures when the groundwater was depressed, as well as efficiently distributing the beneficial wall corner effects towards the middle CBP wall, leading to smaller bending moment magnitudes, characterized by their ‘S-shaped’ profiles. This behavior had been correctly diagnosed, as opposed to the ‘D-shaped’ bending moment profile usually only seen in a typical free-head cantilever wall in similar geology. The eventual results show that the wall and ground responses, i.e., deflection, bending moment, and settlement, were reasonably well predicted when compared against the instrumented field data, thus validating the reliability of the geotechnical modeling technique, key geological parameters, and hydrogeological fluctuations adopted in the 2D and 3D numerical models, as well as the beneficial contributions of the continuous capping beam, which tend to be overlooked during routine retaining wall design.

Molecular configuration, electronic properties, reaction activity of metal-free naphthalocyanine under the external electric field

This work presents a regulation effect of external electric fields on geometric structures, polarisability and reaction activity of metal-free naphthalocyanine (H2Nc). In particular, EEF more than 0.015 a.u.(0.77 V/Å) will bend two pairs of opposing molecular arms (naphthalene subunits) to the x-positive and x-negative directions of the planar molecule. Flipping the EEF direction flips also the bending direction of molecular arms. Furthermore, when the EEF is removed, the molecule can be restored to the planar structure. EEF can induce a significant dipole moment transformation (magnitude and direction of the dipole moment), reduce LUMO-HOMO gap of H2Nc, enhance the first hyperpolarizability from 0 to a significant amount, and change the distribution of electrophilic or nucleophilic reaction sites and enhance reactivity of H2Nc. EEF can be used to regulate the structure transformation and properties of H2Nc, which can promote the potential application of H2Nc such as molecular devices or chemical reactions.

Imaging the Sources of the March 2021 Seismic Sequence in Thessaly Basin (Central Greece) from Kinematic Slip Inversion and Backprojection of Waveform Envelopes

ABSTRACT In March 2021, a series of three moderate events with moment magnitudes Mw 6.3, 6.0, and 5.5 occurred within a span of 10 days in northern Thessaly, Greece, resulting in a stop–start pattern. The moment tensors (MTs) obtained from the events suggested normal faulting along distinct yet adjacent southeast–northwest-trending faults, indicating a sequential triggering process. We applied two methods to investigate the spatial and temporal characteristics of the source process of the triplet. This approach includes linear slip inversion of regional seismic waveforms and static Global Positioning System offsets, along with backprojection of regional waveforms using the Source-Scanning Algorithm technique. The detailed modeling suggests that three adjacent, subparallel (∼300°), and low-angle, detachment-type structures were responsible for the earthquakes. The stress axes orientation was determined by inverting a dataset of recomputed MTs combined with published solutions of the sequence. The results indicated a clockwise rotation of the local extensional axis by ∼25° compared to the regional ∼north–south extension. This rotation is consistent with the orientation of the modeled seismogenic structures. Inversions for both nodal planes and grid-searching fault geometry and orientation showed that for the first-two strongest events, the activated fault planes dipped to the northeast, whereas an antithetic (southwest dipping) fault was activated during the last weaker event. For the Mw 6.3 event, both the independent analyses indicated an overall rupture duration of ∼10 s, energy bursts above and near the hypocenter, up-dip (toward the southwest) rupture propagation in the early stages of the source process, and a bilateral rupture at later stages.

Center of resistance assessment of upper lateral incisors with different dentoalveolar bone height and crown–root ratio: A finite element method study

ABSTRACT Background: In orthodontics, the type of tooth displacement is very important for determining the best way to apply force and how the teeth will move as a result. The link between a tooth’s center of resistance (CRest) and the force’s line of action is crucial for effective orthodontic tooth movement. To regulate tooth displacement patterns, translation, or tilting, the CRest has been a crucial point of reference. Changes in bone support brought on by dentoalveolar bone loss cause a shift in CRest. To provide the same movement in a tooth with bone loss as in a tooth with a healthy-supporting structure, modification to the applied force system is demanded. Aim: The study aimed to assess the CRest of upper lateral incisor with varying dentoalveolar bone heights and crown–root ratio, with a finite element method. Materials and Methods: Eight three-dimensional finite element models of upper lateral incisors of varying dentoalveolar bone height and root resorption were developed, and a force of 1N was applied labiolingually. The CRest is derived by altering the moment/force ratio to produce the translation by the following formula: moment = Force × distance. Results: The CRest changes more coronally as apical root resorption rises and more apically as bone loss progresses. Moment/force ratio required to produce bodily movement increases in association with dentoalveolar bone loss and decreases with root resorption. Conclusion: To maintain physiologically acceptable movements with the least amount of harm to the supporting tissues, applied force and moment magnitudes must be adjusted in response to dentoalveolar bone loss and altered crown–root ratio.

Exciton-induced electric dipole moment in organic ferromagnets

Based on an Anderson-like model including electron–lattice interaction and electron–electron (e–e) interactions, charge and spin properties of excitons in quasi-one-dimensional organic ferromagnets with spin radicals are investigated. The results demonstrate the appearance of an unusually large electric dipole moment in the magnetic molecule upon the formation of the exciton. The sign of the dipole moment depends on the spin of the excited electron relative to the magnetization of the spin radicals. The underlying mechanism is analysed based on the different charge distribution and lattice distortion in the two excitation modes with opposite spin. The origin is attributed to the preferred occupation on different domain walls of the exciton distortion for different spin-resolved excitonic levels. The experimental realization of the large dipole moment is discussed. Although the realization of a large dipole moment is impeded by the superposition state formed due to the degeneracy of two excitation modes, we propose an achievable route to break the symmetry and create controllable electric polarization by optical illumination. The dipole moment is robust even if the long-range e–e interaction is included. The effects of the system parameters, including the electron hopping between the main chain and the radicals and the e–e interaction, on the magnitude of the dipole moment are also discussed. This work indicates a novel way to realize organic multiferroic materials with controllable polarization, which can be induced by photon excitation.

Detection of Long‐ and Short‐Term Slow Slip Events Using a Network Inversion Filter and Dense Global Navigation Satellite System Network in Shikoku, Japan

AbstractThe study of slow slip events is essential to elucidating the slip mechanisms and frictional properties of plate interfaces. We imaged the aseismic slip at the plate interface between the subducting Philippine Sea Plate and overriding Amur Plate beneath Shikoku Island, Japan, by applying a network inversion filter to the position time series obtained from Global Navigation Satellite System data spanning January 2012 to April 2022. The results show long‐term slow slip events in the Bungo Channel, central Shikoku, and the Kii Channel, which started from 2018. We also identified 39 short‐term slow slip events associated with low‐frequency tremors. The estimated moment magnitudes of the Bungo Channel, central Shikoku, and Kii Channel slow slip events were Mw7.0, Mw6.4, and Mw6.3, respectively, with a rigidity of 30 GPa. The estimated moment magnitudes of the short‐term slow slip events ranged from Mw5.7 to Mw6.4. Most of the detected short‐term slow slip events are associated with low‐frequency tremor, and many showed propagation through the spatial domain. Events with magnitudes of ≥Mw6.30 typically consist of subevents. The slip rate of short‐term slow slip events ranges from 1 to 7 mm/day, which is considerably larger than the plate convergence rate. The short‐term slow slip events are 6 to 40 days, and follow the accepted scaling law between slip event duration and total magnitude. The short‐term slow slip event zone is consistent with a three‐segment hypothesis. The short‐term slow slip event in northwest Shikoku and long‐term slow slip event in central Shikoku may be correlated.

Rupture process of the January 8, 2022, Menyuan M 6.9 earthquake

After the occurrence of destructively strong earthquakes, rapid acquisition of the source rupture process can provide important reference information for post-earthquake disaster relief and aftershock trend determination. An M 6.9 earthquake occurred in Menyuan County, Qinghai Province on January 8, 2022. The epicenter is located in the seismic gap in the middle section of the Haiyuan fault belt. Such a typical strong earthquake was taken as an example to investigate the rupture process of strong earthquakes. Three days after the earthquake, the InSAR (Interferometric Synthetic Aperture Radar) coseismic deformation field was obtained by Sentinel radar, indicating that the surface ruptured obviously. The southern block of the earthquake faces towards the satellite about 95 ​cm along the LOS (line of sight) direction, and the northern block is away from the satellite by ​∼ ​74 ​cm, consistent with the characteristic of left-lateral strike-slip motion. In this study, InSAR coseismic deformation data and far-field waveform data were used to jointly invert the earthquake rupture process, and a four-segment finite fault model was constructed by referring to the surface deformation. The inversion results show that the focal depth of the Menyuan earthquake is about 7 ​km, and the strike of the seismogenic fault is 89.0°, 104.0°, 119.0° and 131.0° from west to east, respectively. It is a high-dip left-lateral strike-slip earthquake event lasting about 14 ​s. The rupture propagation mode is a bilateral extension. The maximum slip along the fault is about 380 ​cm, and the seismic moment magnitude is 6.7. The surface rupture length is about 24 ​km, which is consistent with that measured in the field survey. The detailed seismic source model can provide basic data for the aftershock trend determination and seismic risk analysis of the adjacent active faults.

ICOLD 2023, Gothenburg Sweden: Turkish experience of the February 2023 seismic event

This technical briefing provides a summary of the findings and assessments presented by the DSI (State Hydraulic Works, Türkiye) team during the ICOLD 2023 meeting regarding the performance of embankment dams during the seismic events that occurred in February 2023. Two powerful earthquakes with moment magnitudes (Mw) initially estimated to be between 7.5 and 7.8 struck the eastern Anatolian Fault Line, impacting several embankment dams in the region. The seismic activity resulted in significant lateral displacements, settlements and cracks in the embankment dams structures. For the first earthquake, peak acceleration recorded at the nearest station (TK4614 – Pazarcik) was 2.21g, for the second earthquake, the peak acceleration recorded at the nearest station (TK4612 – Goksun) was 0.59g. The presentation at the conference, as reported here, provided valuable insights into the performance of the embankment dams during and after earthquakes.

Geotechnical and Structural Investigations in Malatya Province after Kahramanmaraş Earthquake on February 6, 2023

Two earthquakes with moment magnitudes of 7.7 and 7.6 occured on February 6, 2023, at 04:17 a.m. (with local time, GMT+3) in Kahramanmaraş-Ekinözü Pazarcık and at 13:24 p.m. (with local time, GMT+3) in Kahramanmaraş-Elbistan, respectively, in Turkey. The earthquake was felt in a wide area within Turkey and caused structural destructions and heavy damage of buildings, especially in eleven cities including Adana, Adıyaman, Diyarbakır, Gaziantep, Hatay, Kahramanmaraş, Kilis, Malatya, Osmaniye, Şanlıurfa and Elazığ. The aim of this study was to present the detailed field investigation in Malatya province which was one of the most affected city in the region. The strong ground motion records have been analyzed and PGA distribution maps were presented. Structural defects in damaged and collapsed buildings were examined, and design and manufacturing defects were examined. The performance of soil structures was examined, and the defects demonstrated were evaluated in the context of the geological environment. The study is essential in terms of evaluating the damage and possible causes of the building stock in Malatya city center and its districts after the earthquake. In this sense, a holistic evaluation has been carried out, which can be a useful resource for Anatolian cities with typical building characteristics.

Ground Motion Duration Patterns for Vrancea (Romania) Intermediate-Depth Earthquakes

This study is focused on evaluating ground motion durations of Vrancea intermediate-depth earthquakes in Romania, in the context of future updates to the Romanian seismic design code P100-1/2013. The ground motion database compiled for this study consists of about 200 ground motions recorded during five moderate and large Vrancea intermediate-depth earthquakes that occurred in the period of 1977–2004 and had moment magnitudes of MW ≥ 6.0. Two empirical models were derived in this study for the significant ground motion duration considering two time intervals (5–75% and 5–95%) for the accumulation of the Arias Intensity IA. An analysis of the data shows that the mean ratio between D5-95 and D5-75 is about 2.8. Moreover, the regression also shows that the largest share of variability is due to the within-event component (site term). Among the regression coefficients, the hypocentral distance and the soil conditions appear to have a larger impact on the ground motion duration compared to the earthquake magnitude. It was also observed that the median ground motion durations predicted using the empirical model proposed in this study were much smaller than the ones from the proposed Eurocode 8 draft for the same magnitude range. Finally, geographic trends related to the distribution of residuals were also evaluated using the data from the three earthquakes with the largest number of available ground motion recordings.

Local repulsion of planar Gaussian critical points

We study the local repulsion between critical points of a stationary isotropic smooth planar Gaussian field. We show that the critical points can experience a soft repulsion which is maximal in the case of the random planar wave model, or a soft attraction of arbitrary high order. If the type of critical points is specified (extremum, saddle point), the points experience a hard local repulsion, that we quantify with the precise magnitude of the second factorial moment of the number of points in a small ball.

Thermal Infrared Anomalies Associated with Recent Crustal Earthquakes in Gorj County in Romania

Cumulative stress-energy in tectonic active regions associated with ongoing deformation (co-seismic stress) along the main active geologic faults manifests various earthquakes’ precursors. Macro-fracturing processes are preceded by micro-fracturing phenomena which amplify strain field, and geophysical fields’ disturbances like space-time anomalies of Earth’s fracto-emission signals (Thermal; Ionospheric; Electric Field; Acoustic; Radon in air, underground water, and soil; Neutron, etc.) registered months to days before the occurrence of earthquakes. Multispectral and multisensor time series satellite data and space-based geodetic (GPS and GNSS) measurements in synergy with ground-based geophysical/geochemical measurements bring a significant contribution to survey pre-earthquake signals in the tectonic active areas. This study aims to assess the role of seismo-induced thermal infrared (TIR) anomalies characterized by the ground-level air-AT and land surface temperature-LST changes as significant precursors of crustal moderate and strong earthquakes recorded in Gorj County, Oltenia region in Romania. North-West Targu Jiu area is an active tectonic area characterized by two strike-slip faults systems of North-West- South West and East-West orientation, where on 13 February 2023 was recorded a shallow strong earthquake of moment magnitude Mw= 5.2 and 17 km focal depth, followed by 14 February 2023 stronger earthquake of Mw = 5.7 and 6 km focal depth. Several months beyond have been recorded more than 1000 aftershocks of Mw ≤ 4.9. Based on MODIS Terra/Aqua and NOAA AVHRR time series data, some days to weeks before the seismic sequence has detected LST and AT anomalies.

Revisiting the 2015Mw = 8.3 Illapel earthquake: unveiling complex fault slip properties using Bayesian inversion

SUMMARYThe 2015 moment magnitude Mw = 8.3 Illapel earthquake is the largest mega-thrust earthquake that has been recorded along the Chilean subduction zone since the 2010 Mw = 8.8 Maule earthquake. Previous studies indicate a rupture propagation from the hypocentre to shallower parts of the fault, with a maximum slip varying from 10 to 16 m. The amount of shallow slip differs dramatically between rupture models with some results showing almost no slip at the trench and other models with significant slip at shallow depth. In this work, we revisit this event by combining a comprehensive data set including continuous and survey GNSS data corrected for post-seismic and aftershock signals, ascending and descending InSAR images of the Sentinel-1A satellite, tsunami data along with high-rate GPS, and doubly integrated strong-motion waveforms. We follow a Bayesian approach, in which the solution is an ensemble of models. The kinematic inversion is done using the cascading capability of the AlTar algorithm, allowing us to first get a static solution before integrating seismic data in a joint model. In addition, we explore a new approach to account for forward problem uncertainties using a second-order perturbation approach. Results show a rupture with two main slip patches, with significant slip at shallow depth. During the rupture propagation, we observe two regions that are encircled by the rupture, with no significant slip, westward of the hypocentre. These encircling effects have been previously suggested by back-projection results but have not been observed in finite-fault slip models. We propose that the encircled regions correspond to zones where the yield stress largely exceeds the initial stress or where fracture energy is too large to be ruptured during the Illapel earthquake. These asperities may potentially break in the future and probably already broke in the past.