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Realizing an effective earthquake early warning system (EEWS) in the case of extensive regions and noisy signals is challenging, particularly in East Java, Indonesia. This letter proposes the rapid detection of the p-wave arrival and determination of the earthquake's hypocenter and magnitude using deep learning. The Ncheck algorithm is used for noise handling for picking the p-arrival on a multistation waveform as a form of picking target window prediction (PTWP). Then, multitarget regression (MTR) with a hard-shared orthogonal optimization model is proposed for earthquake parameter determination. The data sets used contained data of earthquakes recorded at three stations from the Indonesian seismic network in East Java; 2009-2017 data were used for training and validation, and 2019 data were used for real-time testing. The results show that the PTWP for picking p-arrival has a mean absolute error (MAE) of 0.12 s, and the MTR for earthquake magnitude, longitude, latitude, depth, and origin time detection shows MAEs of 0.21 M, 9.44, 18.72, 27.81 km, and 2.78 s, respectively.

The accuracy of earthquake localization is of great importance for earthquake monitoring systems. Traditionally, numerical optimization methods are used to estimate the hypocenter location and the origin time of an earthquake in an iterative manner. The traditional methods usually depend on certain theoretical models, but the geological conditions in practice can be quite different from the presumed models. In this study, an attention-based hypocenter estimation (AHE) model was proposed to locate the hypocenter and origin time of the earthquake. Rather than using the raw waveforms, the phase picking times and the positions of the triggered stations are used as the input. The attention mechanism is adapted to reveal the correlations among the input sequence. An experimental model was trained using data collected from earthquakes in Taiwan in 2016 and 2017 and tested on data in 2018. From the results, AHE is capable of locating the hypocenter with a high degree of accuracy in terms of the distance, depth, and origin time of earthquakes.

The presence of seamount on the subducting interface of oceanic and continental tectonic plates has potential to alter the characteristics of ground motion due interface earthquakes. In this study, we address the influence of seamount presence on offshore wind turbine response, through a finite element simulation of earthquake and subsequently applying the recorded shaking from earthquake simulation as input to offshore wind turbines. The wind turbine response is computing by incremental dynamic analysis and fragility curves are derived for serviceability and ultimate limits of wind turbines. The effect of hypocenter being above or below the seamount, on the offshore wind turbine fragility is also addressed.

The earthquake (ML5.2) which occurred at Chushan town, Nantou on Nov.11, 2017 resulted many aftershocks around the hypocenter of the mainshock. The coulomb stress changes (∆CFSs) by the mainshock demonstrated by most of the aftershocks located within the portions with ∆CFSs greater than 0.1 bar, revealing the aftershocks may be induced by the mainshock. After investigating the ∆CFSs at different depths, the results showed most of ∆CFSs with positive values under depth 15km were transferred to the southeast and southwest regions. About ten days later, there were many earthquakes (ML5.2~3) with depth below 15km clustered exactly in the southeast region. The southwest region near the Meishan fault, caused large earthquake with ML7.0 before 110 years ago. This means the Meishan fault may be triggered by the successive earthquakes near the fault. Based on the seismic spectrum intensities, the seismic hazards by the potential Meishan earthquake are estimated. The maximum seismic intensities will occur at Chushan township and the segment of freeway 3 connecting Nantou city and Chushan township may be damaged seriously. The landslides may happen again at the junctions of Nantou and Yunlin counties, where great landslides happened when Chi-Chi earthquake (ML7.3) occurred in 1999.

Objective. The aim of the study is to develop a method for determining the coordinates of the earthquake hypocenter using various combinations of second and fourth order figures as a geo-locus of the hypocenter position points.Method. It is known that the line of intersection of figures of the second and fourth orders, in the case of coincidence of focuses, is a circle. To determine the coordinates of the earthquake source, data from seismographs are used, which are used to construct figures of the second and fourth order, the intersection point of which is the hypocenter. When using data from two seismic sensors, there are two figures, the intersection line of which is a circle. A sphere with a radius equal to the radius of the circle is constructed through the center of this circle. For the other two pairs of seismic sensors, two more spheres are also formed, The intersection point of the three spheres obtained is the sought-for hypocenter of the earthquake.Result. A method has been developed for determining the coordinates of an earthquake source using different shapes of the second and fourth orders for different pairs of seismic sensors.Conclusion. The method allows one to select one of the second or fourth order figures for different pairs of seismic sensors, which makes it possible to reduce the error in determining the source coordinates.

Seismic waves attenuation models are obtained from accelerographic data and represent one of the most important inputs for seismic hazard studies, which are essential for the design of increasingly efficient seismic-resistant structures and systems. Given that the recording of new earthquakes provides extremely valuable information to update these models and studies, it is necessary that both be reviewed and reconsidered periodically. In this work, a descriptive analysis of accelerographic data recorded in stations in Costa Rica until the year 2021 is presented, as a basis for the subsequent development of attenuation models for the country. The research is motivated by the large number of accelerographic data recorded in the last 11 years, thanks to the densification of the instrument network managed by the Seismic Engineering Laboratory of the University of Costa Rica. This means that, at the present time, there is a sufficiently broad and robust accelerographic database to be able to generate ground motion prediction equations, known as GMPEs, that represent the attenuation in the three tectonic regimes present in the country: crustal, interphase subduction and intraslab subduction. In this stage of the investigation, a total of 3,192 records associated with 245 earthquakes are analyzed, obtained after applying a series of selection filters on a database initially composed of 3,981 records. The analysis has consisted of obtaining the distributions of the number of events and the number of records based on the magnitude, depth, tectonic regime and type of soil at the recording station, classifying it following the criteria of the Seismic Code of Costa Rica (CFIA , 2010). Among the main results of this research, which will condition the ranges of applicability of the models that are developed later, are (1) the identification of a scarcity of records in conditions of hard soil or rock (S1), as well as of high magnitudes at short hypocentral distances and low magnitudes at long distances.; (2) The range of hypocentral distances from the available records is (5-300 km) for crustal earthquakes, (15-300 km) for interphase subduction, and (40-400 km) for intraslab subduction. Finally, two distance measurements were estimated for extended sources, called rupture, R RUP, and Joyner and Boore, R J&B, used when the rupture cannot be considered punctual. These distances have been calculated from the distances for point sources, epicentral and hypocentral, R EPI and R HYPO respectively, following the methodology proposed by Thompson y Worden (2018). Los modelos de atenuación de las ondas sísmicas se obtienen a partir de datos aceleográficos y representan uno de los insumos más importantes para los estudios de amenaza sísmica, la cual es fundamental para el diseño de estructuras y sistemas sismorresistentes cada vez más eficientes. En vista de que el registro de nuevos sismos aporta información sumamente valiosa para actualizar dichos modelos y estudios, es necesario que ambos se revisen y se replanteen con cierta periodicidad. En este trabajo se desarrolla un análisis descriptivo de datos acelerográficos registrados en estaciones de Costa Rica hasta el año 2021, como base para el posterior desarrollo de modelos de atenuación para el país. La investigación está motivada por el gran número de datos acelerográficos registrados en los últimos 11 años, gracias a la densificación de la red de instrumentos que administra el Laboratorio de Ingeniería Sísmica de la Universidad de Costa Rica. Esto hace que, en el momento actual, se disponga de una base de datos acelerográficos suficientemente amplia y robusta, para poder generar ecuaciones de predicción del movimiento fuerte, conocidas como GMPEs (del inglés Ground motion prediction equations) que representen la atenuación en los tres regímenes tectónicos presentes en el país: cortical, subducción interfase y subducción intraplaca. En esta etapa de la investigación se analizan un total de 3192 registros asociados a 245 sismos, obtenidos después de aplicar una serie de filtros de selección sobre una base de datos compuesta inicialmente por 3981 registros. El análisis ha consistido en obtener las distribuciones del número de eventos y del número de registros en función de la magnitud, profundidad, régimen tectónico y tipo de suelo en la estación de registro, clasificando éste siguiendo los criterios del Código Sísmico de Costa Rica (CFIA, 2010). Entre los principales resultados de esta investigación, que condicionarán los rangos de aplicabilidad de los modelos que se desarrollen posteriormente, se destacan (1) la identificación de una escasez de registros en condiciones de suelo duro o roca (S1), así como de magnitudes altas a distancias hipocentrales cortas y de magnitudes bajas a distancias largas.; (2) el rango de distancias hipocentrales de los registros disponibles es (5-300 km) para sismos corticales, (15-300 km) para subducción interfase y (40-400 km) para subducción intraplaca. Finalmente, se estimaron dos medidas de distancia para fuentes extendidas, denominadas de ruptura, R RUP, y de Joyner y Boore, R J&B, empleadas cuando la ruptura no puede considerarse como puntual. Dichas distancias se han calculado a partir de las distancias para fuentes puntuales, epicentral e hipocentral, R EPI e R HYPO respectivamente, siguiendo la metodología propuesta por Thompson y Worden (2018).

Accuracy of hypocenter location, in particular focal depth, is a precondition for high-resolution seismotectonic analysis of natural and induced seismicity. For instance, linking seismicity with mapped fault segments requires hypocenter accuracy at the sub-kilometer scale. In this study, we demonstrate that inaccurate velocity models and improper phase selection can bias absolute hypocenter locations and location uncertainties, resulting in errors larger than the targeted accuracy. To avoid such bias in densely instrumented seismic networks, we propose a coupled hypocenter-velocity inversion procedure restricted to direct, first-arriving, mainly upper-crustal Pg and Sg phases. On the basis of synthetic tests and selected ground-truth events we demonstrate that a sub-kilometer hypocenter accuracy can be achieved by regional-scale, three-dimensional Pg and Sg velocity models combined with dynamic phase selection and a non-linear location algorithm. The tomographic inversion uses about 60’000 Pg and 30’000 Sg quality-checked phases of local earthquakes in the Central Alps region. The derived models image the VP and VS structure of the Central Alps upper crust at unprecedented resolution, including small-scale anomalies such as those caused by Subalpine Molasse units below the Alpine front. The relocation procedure is applied to more than 18’000 earthquakes and the relocated hypocenters reveal previously unrecognized seismogenic structures, for instance in the Swiss Molasse basin south of Bern. The ML 4.6 Urnerboden earthquake of 2017 is used as an example to demonstrate how the derived 3-D velocity structure and relocated hypocenters can be jointly interpreted to constrain the lithology hosting upper-crustal seismicity in the Central Alps., Journal of Geophysical Research: Solid Earth, 126 (12), ISSN:2169-9313, ISSN:0148-0227, ISSN:2169-9356

The purpose of this paper is to discuss the lithosphere–atmosphere–ionosphere coupling (LAIC) effects with the use of multiparameter precursor observations for two successive Japanese earthquakes (EQs) (with a magnitude of around 7) in February and March 2021, respectively, considering a seemingly significant difference in seismological and geological hypocenter conditions for those EQs. The second March EQ is very similar to the famous 2011 Tohoku EQ in the sense that those EQs took place at the seabed of the subducting plate, while the first February EQ happened within the subducting plate, not at the seabed. Multiparameter observation is a powerful tool for the study of the LAIC process, and we studied the following observables over a 3-month period (January to March): (i) ULF data (lithospheric radiation and ULF depression phenomenon); (ii) ULF/ELF atmospheric electromagnetic radiation; (iii) atmospheric gravity wave (AGW) activity in the stratosphere, extracted from satellite temperature data; (iv) subionospheric VLF/LF propagation data; and (v) GPS TECs (total electron contents). In contrast to our initial expectation of different responses of anomalies to the two EQs, we found no such conspicuous differences of electromagnetic anomalies between the two EQs, but showed quite similar anomaly responses for the two EQs. It is definite that atmospheric ULF/ELF radiation and ULF depression as lower ionospheric perturbation are most likely signatures of precursors to both EQs, and most importantly, all electromagnetic anomalies are concentrated in the period of about 1 week–9 days before the EQ to the EQ day. There seems to exist a chain of LAIC process (cause-and-effect relationship) for the first EQ, while all of the observed anomalies seem to occur nearly synchronously in time for the send EQ. Even though we tried to discuss possible LAIC channels, we cannot come to any definite conclusion about which coupling channel is plausible for each EQ.

During the lithospheric buildup to an earthquake, complex physical changes occur within the earthquake hypocenter. Data pertaining to the changes in the ionosphere may be obtained by satellites, and the analysis of data anomalies can help identify earthquake precursors. In this paper, we present a deep-learning model, SeqNetQuake, that uses data from the first China Seismo-Electromagnetic Satellite (CSES) to identify ionospheric perturbations prior to earthquakes. SeqNetQuake achieves the best performance [F-measure (F1) = 0.6792 and Matthews correlation coefficient (MCC) = 0.427] when directly trained on the CSES dataset with a spatial window centered on the earthquake epicenter with the Dobrovolsky radius and an input sequence length of 20 consecutive observations during night time. We further explore a transferring learning approach, which initially trains the model with the larger Electro-Magnetic Emissions Transmitted from the Earthquake Regions (DEMETER) dataset, and then tunes the model with the CSES dataset. The transfer-learning performance is substantially higher than that of direct learning, yielding a 12% improvement in the F1 score and a 29% improvement in the MCC value. Moreover, we compare the proposed model SeqNetQuake with other five benchmarking classifiers on an independent test set, which shows that SeqNetQuake demonstrates a 64.2% improvement in MCC and approximately a 24.5% improvement in the F1 score over the second-best convolutional neural network model. SeqNetSquake achieves significant improvement in identifying pre-earthquake ionospheric perturbation and improves the performance of earthquake prediction using the CSES data. Published version This work is funded by the National Key Research and Development of China under Grant No. 2018YFC1503505. This work is also supported by the LIMADOU-Science under Grant No. 2020-31-HH.0, a project funded by the Italian Space Agency (ASI), and INGV Further and MiUR Pianeta Dinamico-Working Earth Project.

We apply a template matching detection to report a swarm-like foreshock sequence concentrated near the northern edge of the strike-slip fault rupture of the 25 September 2019 MW 6.5 Ambon earthquake in Seram, Indonesia. The template matching helps to identify small earthquakes that the routine earthquake catalog has not listed. The magnitude of completeness decreases from 3.1 (Badan Meteorologi Klimatologi dan Geofisika – BMKG catalog) to 1.7 in the improved catalog. We detect 3201 foreshocks which are tens fold the number of foreshocks in the routine earthquake catalog. We did not find a significant temporal variation in the b-value of the frequency–magnitude distribution (FMD) of the foreshock seismicity prior to initiating the dynamic rupture of the mainshock. The foreshocks around the mainshock hypocenter start to be busy since the beginning of July 2019 and continuously accelerates, with a minor variation in the seismicity rates and b-values. Although possible, we did not suggest that the stochastic cascade effect plays a role in the mainshock nucleation process. We discuss and highlight the possibility of fluid triggering to explain the high b-values of foreshock seismicity.

An unusual earthquake doublet ruptured the high-risk middle segment of the Xianshuihe fault in November 2014, exhibiting significant variations in the rupture and aftershock characteristics. By conducting rupture kinematic inversions jointly with local broadband seismic data, strong-motion data, and coseismic InSAR data, we find diverse rupture processes of this earthquake doublet. The first event ruptured upward along the dip and bilaterally along the strike with the duration of 8.0 s, whereas the second event ruptured mainly around the hypocenter with the duration of 3.5 s. The estimated moment magnitudes of the first and second events of this earthquake doublet were MW 6.0 and MW 5.7, respectively. The further analysis of rupture model-based static and dynamic stress change suggests that the first event is likely responsible for triggering the second event. Based on the comprehensive analysis of aftershock migration features, we find complex and diverse driving mechanisms of aftershocks. Aftershocks of the first event of the earthquake doublet were likely driven by afterslip. Early aftershocks of the second event were also likely driven by afterslip; however, later aftershocks were likely driven by fluid diffusion. The revealed diverse rupture characteristics of the 2014 Kanding earthquake doublet sequence suggest the inherent strength and/or stress heterogeneities on the seismogenic faults.

The Daguangbao landslide was the most catastrophic mass movement triggered by the 2008 Wenchuan earthquake with a magnitude scale of Ms. 8.0. The landslide, which was 4.6 km long and 3.7 km wide, had a volume of approximately 1.2 × 109 m3. Since its occurrence, many assumptions regarding its initiation and movement mechanisms have been made; however, the mechanisms remain unclear. Our recent field evidence suggested that the Daguangbao landslide occurred along a saturated fault parallel to the bedding in the Paleozoic carbonate strata. We therefore examined whether the shear behavior of the fault material could have favored the initiation and movement of the Daguangbao landslide. First, we performed monotonic and cyclic loading tests on samples taken from the bedding fault breccia using ring-shear apparatus. We then conducted Newmark displacement analysis to examine the initiation and motion of the landslide. The laboratory results showed that the carbonate fault breccia on the sliding layer of the landslide has a high liquefaction potential and the friction coefficient at its steady-state under undrained condition could be as small as 0.04. We also found that with increase of shear displacement, the friction coefficients can at first exponentially increase to the peak-failure value and then exponentially decrease to the steady-state value. These relationships between the friction and shear displacements were incorporated in the Newmark analysis of landslide initiation and motion. The numerical calculation results showed that the landslide occurred 36 s after the 2008 Wenchuan earthquake origin time (at its hypocenter), and the landslide mass, with a speed of 94 m/s, collided with a riverbank in the 76th second. We infer that, in addition to the strong seismic force, pore-water pressure built up within the bedding fault during the seismic shaking, enhancing the instability of the Daguangbao slope, and a further increase of pore-water pressure with progress of sliding elevated the mobility of the landslide.

On 22 July 2020, the Mw 7.8 Simeonof megathrust earthquake struck offshore of the Alaska Peninsula. This was the largest event since 1917 in the enigmatic area known as the Shumagin seismic gap, a region of transitional plate interface coupling from highly coupled to the east to creeping to the west. Hence, this event provides a rare chance to understand rupture mechanics on such heterogeneously coupled faults. In this study, we examine the rupture process of the 2020 Simeonof earthquake with a combination of static GNSS displacements, InSAR displacements, high-rate GNSS waveforms and tele-seismic waveforms. Due to the discontinuous nature of the deformation field, we use InSAR data for individual islands and tie the displacement field either to GNSS observations or keep these “floating”, i.e. we estimate an ambiguity parameter during the inversion. Our results demonstrated that the rupture process of this event is unidirectional, initiating at the hypocenter and propagating westward for about 130 s with an average rupture velocity of ∼1.9 km/s. The highest slip was centered below the Koniuji Islands and occurred between 20 s to 50 s after the rupture initiation. We find that InSAR observations, especially “floating” data on near-field islands, provide essential constraints for the slip inversion, building confidence in the slipping of the less coupled region. Comparison with an existing and an alternative plate coupling model demonstrated that the remaining slip budget is unlikely to be able to generate a large event at depths from 30 to 40 km, as the Shumagin seismic gap has been mostly filled by the 2020 Simeonof earthquake at those depths. However, both coupling models suggest a substantial slip deficit in shallow near trench regions, suggesting that a significant earthquake can still occur. Seafloor geodetic observations are required to further constrain the near-trench plate coupling.

The Dead Sea pull-apart basin (DSB), which is located within the Dead Sea Transform fault system, displays tectonic asymmetry between its eastern and western longitudinal zones. We investigate the seismological and mechanical signature of this asymmetry by the analyzing the hypocenter distribution and focal-mechanisms of 114 Mw = 1.5–5.2 earthquakes recorded from 1985 till 2012. The analysis indicates that the seismicity along the western longitudinal zone is deeper than the eastern one. Focal mechanism analysis indicates that about 50% of solutions are strike-slip, compatible with the plate motions along the Dead Sea transform. Comparison between the two longitudinal zones of the basin shows that the focal mechanisms in the eastern DSB are dominated by strike-slip faulting shallower than 12 km depth, whereas those in the western DSB are dominated by oblique faulting below 12 km depth. The b value of the Gutenberg-Richter magnitude distributions also show difference between the two zones with ~0.9 in the west and ~0.7 in the east zone. We develop stress-inversion analysis to identify the fault planes of the focal mechanisms by using friction-dependent selection process. The horizontal maximum compression (σHmax) trends NNW-SSE, with increasing value of the vertical stress component along the western part of the basin, corresponds to the oblique faulting in this zone. The optimal friction coefficient determined by the stress-inversion for the fault planes is μ ~ 0.5. Our analysis emphasizes the significant contribution of frictional dependent stress-inversion as an effective tool in seismotectonic analysis.