Hypocenter Research Articles

Seismic scenario simulation and ANN-based ground motion model development on the North Tabriz Fault in Northwest Iran

AbstractEarthquakes pose significant seismic hazards in urban regions, often causing extensive damage to the built environment. In regions lacking robust seismic monitoring networks or sufficient data from historical events, ground motion simulations are crucial for assessing potential earthquake impacts. Yet, validating these simulations is challenging, leading to notable predictive uncertainty. This study aims to simulate four scenario earthquakes with moment magnitudes of 6.8, 7.1, 7.4, and 7.7 in Iran, specifically investigating variations in fault plane rupture and earthquake hypocenter. The North Tabriz Fault (NTF), located within the seismic gap in northwest Iran, is selected as the case study due to the lack of well-recorded ground motions from severe earthquakes, despite historical evidence of large-magnitude events. Simulations are conducted using a stochastic finite-fault ground motion simulation methodology with a dynamic corner frequency. Validation of the simulations is performed by comparing estimated peak ground motions and pseudo-spectral ordinates with existing ground motion models (GMMs), supplemented by inter-period correlation analysis. Simulation results reveal high hazard levels, especially in the northeastern area near the fault plane. Intensity maps in terms of the Modified Mercalli Intensity (MMI) scale underscore the urgency for comprehensive preparedness measures. Finally, a region-specific GMM is developed using Artificial Neural Networks (ANN) to predict peak ground motion parameters with an online platform accessible to end-users.

Triggering the 2022 eruption of Mauna Loa

Distinguishing periods of intermittent unrest from the run-up to eruption is a major challenge at volcanoes around the globe. Comparing multidisciplinary monitoring data with mineral chemistry that records the physical and spatio-temporal evolution of magmas fundamentally advances our ability to forecast eruptions. The recent eruption of Mauna Loa, Earth’s largest active volcano, provides a unique opportunity to differentiate unrest from run-up and improve forecasting of future eruptions. After decades of intermittent seismic and geodetic activity over 38 years of repose, Mauna Loa began erupting on 27 November 2022. Here we present a multidisciplinary synthesis that tracks the spatio-temporal evolution of precursory activity by integrating mineral and melt chemistry, fluid inclusion barometry, numerical modeling of mineral zoning, syn-eruptive gas plume measurements, the distribution and frequency of earthquake hypocenters, seismic velocity changes, and ground deformation. These diverse data indicate that the eruption occurred following a 2-month period of sustained magma intrusion from depths of 3–5 km up to 1–2 km beneath the summit caldera, providing a new model of the plumbing system at this very high threat volcano. Careful correlation of both the geochemistry and instrumental monitoring data improves our ability to distinguish unrest from the run-up to eruption by providing deeper understanding of the both the monitoring data and the magmatic system—an approach that could be applied at other volcanic systems worldwide.

The seismicity of the Carpathians in 2023

According to the results of observations at the seismic stations of the Carpathian region of Ukraine in 2023, the main parameters of 81 earthquakes in the range of energy classes KR=5.8÷13.7 were obtained. The parameters of seismometric equipment at active seismic stations are given. A catalog of earthquakes, their distribution by regions and energy classes, a map of epicenters, graphs of seismic energy release and the number of earthquakes in the region by month are presented. A brief description of the seismicity of certain seismically active areas of the Carpathian region is given. The total energy observed in the region was ΣЕ=9.06·1013 J, which is slightly higher than the last year’s level of ΣЕ=5.06·1013 J. This year, increased seismic activity was observed in three seismically active areas. Thus, 19 earthquakes of energy class KR=5.7÷13.7 were recorded in the North-Western region. Their total seismic energy was ΣЕ=5.02∙1013 J. The two strongest in this area were the earthquake that occurred on October 9 at 18:23 on the territory of Slovakia, near the town of Humenne, with KR=13.7 at a depth of h=8.8 km and intensity at the epicenter of I0=8 points and the earthquake in Transcarpathia, near the village of Dovge, on January 3 at 01:28 with magnitude MSH=3.1, KR=10.7 at a depth of h=9.6 km and intensity at the epicenter of about 5 points. In the Southern Carpathians, 29 earthquakes with KR=8.8÷13.0 were registered at a depth of 2―35 km with a total seismic energy of ΣЕ=3.72∙1013 J. This year, in terms of seismic activity after a long seismic lull, the Krishan region was the third. There were 8 earthquakes with KR=7.6÷12.3 with total seismic energy ΣЕ=2.56∙1012 J. The foci of earthquakes are located in the earth’s crust at depths h=2.0÷15.1 km. This year, compared to last year, the Vrancea district was less active. For the whole year, 19 events with KR=8.4÷11.5 were recorded, the total seismic energy of which is ΣЕ=6.41∙1011 J. In the territory of Bukovyna this year, there is also a decrease in seismic activity compared to 2022. A total of 4 earthquakes with an energy class of KR= 5.8÷7.8 had total seismic energy ΣЕ=1.05∙108 J. The foci of earthquakes were located in the earth’s crust at depths h=1.1÷5 km. Only 2 weak earthquakes were recorded in the Bacau region in 2023, and none in the Banat and Transylvania regions. The regional Carpathian hodograph was used to determine the main parameters of earthquakes in Transcarpathia, and the Jeffreys-Bullen hodograph was used for earthquakes in the Vrancea zone and other six districts.

MONITORING THE GEODYNAMICS OF NATURAL AND MAN-MADE RISKS OF ALMATY

The purpose of the article is to solve the problems of drawing up a map, its presentation, processing, analysis in order to comprehensively assess the regional system of natural and artificial threats of the Almaty region. By solving these problems, you can consider ways to easily resolve the upcoming conflicts and problems. It can be prevented by making predictions about natural and man-made problems. The root of natural and man-made catastrophic conditions of Almaty region are natural disasters characteristic of mountainous regions. We will take into account the conditions of seasonal mudslides and earthquakes. Since Almaty region is a region located in a mountainous zone, there are a lot of earthquake foci. Tectonic movements often occur. In order to prevent major natural disasters, it is necessary to carry out special monitoring work. From this point of view, the compilation of Geodynamic maps, the study of the Earth’s crust, the identification and differentiation of earthquake foci come to the rescue. With this, major disasters can be prevented. The article compiled a map of natural and man-made conditions of the Almaty region. In the process of creating a map, using GIS data, we created a map in the ArcGIS application. We received data from the GIS through a special platform, processing space surveys using a program. We received the data on the basis of SRTM space survey. By studying the dynamics of changes for each year, by comparing maps, you can make conclusive forecasts. Collecting data through free platforms helps to create rational solutions. It is possible to monitor, update,store,and edit the database of information using maps. In the article, a complete study of the region’s region was carried out, the importance was given to the rational, effective use of GIS data.

Illuminating the Hierarchical Segmentation of Faults Through an Unsupervised Learning Approach Applied to Clouds of Earthquake Hypocenters

AbstractWe propose a workflow for the recognition of the hierarchical segmentation of faults through earthquake hypocenter clustering without prior information. Our approach combines density‐based clustering algorithms (DBSCAN and OPTICS), and principal component analysis (PCA). Given a spatial distribution of earthquake hypocenters, DBSCAN identifies first‐order clusters, representing regions with the highest density of connected seismic events. Within each first‐order cluster, OPTICS further identifies nested higher‐order clusters, providing information on their number and size. PCA analysis is applied to first‐ and higher‐order clusters to evaluate eigenvalues, allowing discrimination between seismicity associated with planar features and distributed seismicity that remains uncategorized. The identified planes are then geometrically characterized in terms of their location and orientation in the space, length, and height. This automated procedure operates within two spatial scales: the largest scale corresponds to the longest pattern of approximately equally dense earthquake clouds, while the smallest scale relates to earthquake location errors. By applying PCA analysis, a planar feature outputted from a first‐order cluster can be interpreted as a fault surface while planes outputted after OPTICS can be interpreted as fault segments comprised within the fault surface. The evenness between the orientation of illuminated fault surfaces and fault segments, and that of the nodal planes of earthquake focal mechanisms calculated along the same faults, corroborates this interpretation. Our workflow has been successfully applied to earthquake hypocenter distributions from various seismically active areas (Italy, Taiwan, and California) associated with faults exhibiting diverse kinematics.

Database of Earthquake Focal Mechanisms for the East Arctic Region

Database of Earthquake Focal Mechanisms for the East Arctic Region

Coseismic deformation analysis of the 2017 Milin Ms 6.9 earthquake in the Namche Barwa Syntaxis: Implications for regional tectonics

The 2017 Milin earthquake occurred near Namche Barwa on the southeastern Tibetan Plateau. This research employed Sentinel-1 imagery to capture the corresponding coseismic deformation field and adopted a joint inversion approach using geodetic measurements and teleseismic waveform data to assess earthquake mechanics. The coseismic deformation indicated distinct differential movements, indicating a thrust movement of this fault with uplift in northeast side. The calculated seismic moment magnitude was Mw 6.5, with the fault striking of 305° and a dip angle of 72° The earthquake hypocenter was located at a depth of approximately 10 km, and the maximum fault slip was approximately 1.08 m. The event was attributed to the northwestern segment of the Xixingla fault. Numerical simulations indicated a peak ground velocity of approximately 0.3 m/s. The northwestern segment of the Xixingla fault was identified as the seismogenic fault of the event. Furthermore, the Coulomb stress analysis indicates that the earthquake induced stress loading on the Dongju–Milin and Jiali faults. The surface strain analysis reveals a region of high strain adjacent to the fault. The 2017 Milin earthquake occurred because the Xixingla fault underwent predominantly thrust-type sliding due to the continuous tectonic stress induced within the Tibetan Plateau. Notably, the middle segment of the Xixingla fault currently experiences relatively low seismic activity and is in a state of stress and strain accumulation. Thus, strong earthquakes may occur within the middle segment of the Xixingla fault.

Mental health of nursing students regarding the Moroccan earthquake: A cross-sectional study

ObjectiveIn addition to the economic and social impact, mental health issues are one of health needs during natural disaster such as earthquake. Thus, surveillance for mental health variables is crucial for public health planning. Nursing students as professional students may be particularly vulnerable to adverse mental health effects after an earthquake because of their potential role in emergency response and the challenges associated with providing medical care in crisis conditions. The aim of this research was to assess the mental health of students after six months of the Moroccan earthquake and associated factors. MethodA cross-sectional survey of student nurses was conducted on March 2024; six months after the Moroccan earthquake in front to 261 students using class sampling method. Three validated psychometric measures, Post-Traumatic Stress Disorder (PCL-C), Depression, Anxiety and Stress Scale (DASS-21), and The Connor-Davidson Resilience Scale (CD-RISC) were used to assess the nursing student mental health after Moroccan earthquake. ResultsAnxiety, Depression, Stress and abnormal post-traumatic stress rank was present respectively in 44.8%, 37.1%, 7.7%, 61.3% of participants. However, a minority of students obtained the high resilience score (13.8%). The results showed that the DAS scale correlated negatively with age (p = 0.034). Furthermore, the female gender, 3rd grade students (as final year for the nursing diploma) and those who had lost a family member in the natural disaster obtained higher medians with a significant difference in the DAS scale score (p < 0.05). The post-traumatic stress scale was only affected by material damage (p = 0.044). However, the high level of scores resilience obtained significantly for students living with their families. In contrast, no association between the mental health of nursing students and attending the phenomenon or living near earthquake foci. ConclusionThis study has demonstrated the crucial need to train healthcare providers in emotion management in the event of a natural disaster, and to launch a priori initiatives, particularly with regard to the mental health of students in health universities, in order to prepare them psychologically for any intervention in the case of an alert.

Relocation of Earthquakes Hypocenter Using the Double Difference Method in Bali and Its Surrounding Areas

A study on the relocation of earthquake hypocenters using the Double Difference method has been conducted in Bali and its surrounding areas. This research was carried out at the Center for Meteorology, Climatology, and Geophysics Region III Denpasar. The purpose of this study is to find out the distribution of earthquake hypocenters before and after the relocation and to know the continuity of earthquake hypocenters in the Bali region. The data used are arrival time data of 1,815 earthquake events from January 1, 2014 to December 31, 2023, and data from 26 earthquake recording stations. The relocation method applied is the Double Difference method, which is processed with ph2dt and HypoDD. The relocation that has been carried out shows a good hypocenter position which is characterized by a residual value of travel time that is close to 0. The distribution of the earthquake hypocenter in the Bali area before the relocation spread throughout the region and after the relocation, the position of the hypocenter was getting closer to the source of the earthquake, namely in the subduction zone under the Bali area as shown in the cross-section results. In addition, based on the results of the analysis of the hypocenter of the earthquake after relocation, it was found that the trend of the hypocenter continued toward the subduction subduction zone.

Continent‐Side Uplifted Mantle and Geological Imprints Along a Paleo Rift in the Western East Sea (Sea of Japan)

AbstractWe investigate the continent‐size lithospheric structures of paleo rift around the central Korean Peninsula using ambient noise tomography and earthquake‐based Eikonal tomography based on dense seismic networks. We determine Rayleigh‐wave group velocities at periods of 1–15 s from ambient noise tomography and Rayleigh‐wave phase velocities at periods of 20–80 s from earthquake‐based Eikonal tomography. We determine a 3‐D shear‐wave velocity model in the lithosphere from the Rayleigh wave velocities. The model exhibits high lateral variations ranging from ‒9% to 8%, depending on depth. The shear‐wave velocities at shallow depths (2 km) are relatively high in mountain regions and low in coastal and basin regions. Strong velocity contrasts are observed around major earthquake hypocenters at depths of 3–20 km, which may be due to the presence of seismogenic faults. Shear‐wave velocities at depths of 30–40 km are high along the east coast, suggesting uplifted mantle that is responsible for the opening of the East Sea (Sea of Japan). High velocity structures beneath Moho around the coast may suggest solidified underplated magma caused by the paleo rifting. The root of coast‐parallel high‐mountain range (Taebaek Mountain Range) is bounded by the uplifted mantle, presenting mountain range development in rift flank along paleo‐rift axis. Low shear‐wave velocities along the coast at depths km may imply elevated temperature beneath the solidified underplated magma. The continent‐side paleo rift affects the geological, thermal, and seismological properties around the continental margin at present.

Fault structure and earthquake clustering in Aswan region (Egypt) revealed by high-precision earthquake location from 35 years of recorded natural and induced seismicity

Starting from an initial catalogue of 7833 natural and reservoir-induced seismic events collected in Aswan region (south Egypt) from 1982 to 2016, we investigate the fault structure and triggering mechanisms by determining high-resolution hypocenters for 2562 earthquakes. Despite the complex network of intersecting fractures, high-precision earthquake locations reveal numerous discrete fault strands (some not mapped yet), whose kinematics have been determined from the focal mechanisms of Ml ≥ 2.5 earthquakes. Furthermore, the analysis of the space-time evolution of seismicity indicates an eastward migration of earthquakes and a progressive activation of different faults. This process could reflect fluid migration in the Wadi Kalabsha embayment likely controlled by permeability barriers at depth acting as seals, and the subsequent build-up of the pore pressure as the dominant driving mechanism of the observed seismicity in the region. A strong spatio-temporal earthquake clustering is observed in the region characterized by seismic sequences, repeated earthquakes, and long-lasting swarms. High variability of b-value in correspondence of the occurrence of mainshock-aftershock sequences also suggests the activation of faults and fractures within their respective fault zones under lower differential stress conditions due to fluids. The projection of earthquake hypocenters on an E-W vertical depth section of the study area shows a seismic gap with an approximate length of about 11 km along the Kalabsha fault, which suggests the presence of a locked fault patch that may generate a Mw 5.9 earthquake if this segment were to break in a single rupture episode.

Quantifying the expansion rates of aftershock zones for magnitude-7 class earthquakes around the Japanese archipelago

Earthquakes (mainshocks) trigger sequences of aftershocks, the frequency of which diminishes following a power-law decay, while the spatial domain of these aftershocks extends logarithmically over time. The delineation of the aftershock zone can be modulated by variables beyond the magnitude of the mainshock, encompassing the location of the fault (whether the fault is at a plate boundary), the depth at which the event occurs, and the prevailing local stress conditions. Here, we evaluate the expansion rate of aftershock zones by analyzing earthquakes of magnitude-7 class in the vicinity of the Japanese archipelago. Prior studies have offered approximate assessments of expansion rates; however, our approach involves the utilization of a straightforward algorithm for the automated estimation of this metric, facilitating the compilation of a catalog. Across the dataset, no pronounced correlations were discerned between the expansion rate and other examined parameters. Yet, an inverse relationship is identified between the expansion rate and the b value of aftershocks for mainshocks occurring at plate boundaries. This observation suggests that the expansion rate of aftershock zones predominantly mirrors the stress field following the mainshock. Such a pattern is not detected in mainshocks occurring within the plate's interior. While the expansion rate of aftershock zones is likely influenced by various factors, aftershock zones may expand more rapidly with higher differential stress in areas surrounding hypocenters of major interplate earthquakes of magnitude 8 or 9.

Frictional Fault Strength Analysis of Palu-Koro and Matano Faults, Sulawesi, Indonesia, from Earthquake Focal Mechanism Data

ABSTRACT Sulawesi’s complex tectonic setting generates active Palu-Koro and Matano faults. Understanding earthquake mechanic is important for mitigation purpose. We performed fault strength analysis by examining its friction, through joint stress inversion and stress magnitude estimation approach, using focal mechanism data from International Seismological Centre bulletin. Friction was analyzed in four segments of the Palu-Koro Fault and two segments of the Matano Fault. Bootstrap and Jack-knife are applied to assess its uncertainty. From north to south, the friction pattern increases at the Palu-Koro Fault segments: Donggala (0.35<μs <0.56) to Palu segment (0.59<μs <0.76); then decreases sequentially: at Saluki (0.49<μs <0.55), Moa segment (0.31< μs <0.35), and further at the Matano Fault segment (Pamsoa-Ballawai) (0.26<μs <0.3). Regarding the 2018 Mw 7.5 Palu earthquake rupture, high friction at the Saluki segment coincides with and indicates its rupture termination. Seismicity records from 1977 to 2011 showed that the largest event occurred at Matano Fault has Mw less than 7.5. Low friction observed at Matano Fault correlates with small magnitude events and low fault strength.

Earthquake Focal Mechanisms of Non-Normal Type in the South Baikal Basin

Earthquake Focal Mechanisms of Non-Normal Type in the South Baikal Basin

Seismotectonics of the Philippine and Taiwan Subduction Systems and Implications for Seismic Hazards

AbstractThe seismicity of the Philippines and Taiwan provides insight into the tectonics and seismic hazards of a region characterized by subduction and collision. We summarize the seismotectonics of the Philippines and Taiwan by documenting the distribution of hypocenters for earthquakes of magnitude M ≥ 4.6 and focal mechanisms for earthquakes of magnitude M ≥ 5.0 over ∼21 years. We quantify seismicity rates (earthquake frequency) and compare seismicity distributions with proposed tectonic and faulting models. 6,187 earthquakes of magnitude M ≥ 4.6 occurred between 1 January 2000 and 31 March 2021, 79% at depths &lt;70 km and 70% having magnitudes M &lt; 5.0. Approximately 88 earthquakes of magnitude M ≥ 5.0 occur per year, with 12 events of magnitude M ≥ 7.0 occurring since January 2000. Seismic activity decreases exponentially between 50 and 210 km depth at a rate ∼10% faster than the global average. Intermediate and deep earthquakes at depths &gt;70 km trace the Wadati‐Benioff zones of subducting slabs, most of which are only seismically active to depths of ∼250 km. The distribution of earthquakes at depths &gt;70 km is likely influenced by the subduction of young lithosphere, slab tearing, and phase boundary interactions between depths of 410 and 660 km. Shallow earthquakes at depths ≤70 km are generated by megathrust, crustal, and intraslab faulting. Crustal thrust and strike‐slip faulting are the most abundant and prevalent sources of damaging earthquakes. The Philippines and Taiwan are subject to high seismic risk, similar to nearby Indonesia.

Intrusive mechanism of the 2018 Sierra Negra Galápagos eruption, constrained by 4D tomographic images

Understanding the mechanisms of magma intrusion underpins our ability to interpret geophysical monitoring signals at volcanoes and thus issue reliable forecasts of future activity. The basaltic caldera volcanoes of the western Galápagos Islands, Ecuador, exhibit exceptionally high rates of deformation driven by shallow magma accumulation and migration. However, the nature and evolution of magma storage at these volcanoes is poorly constrained by earthquake hypocentre locations or geodetic inversions. Here we show that transient variations in seismic velocity before, during, and after the 2018 eruption of the Sierra Negra volcano track the accumulation of magma in a shallow sill complex and the emplacement of a lateral flank intrusion. A four-dimensional tomographic technique applied to the P-wave arrivals of local earthquakes provides high spatiotemporal resolution of changes in the physical properties of the shallow volcanic system. In the month before the eruption, the expansion of a low-velocity zone above the sub-caldera sill complex coincides with caldera uplift and near-surface fracturing, driven by persistent shallow magma accumulation. A new low-velocity anomaly appeared progressively in the western flank of the volcano in the days after the onset of the eruption, coinciding with the opening of a curved sill that supplied magma to secondary eruptive fissures. The anomaly disappeared as the curved sill deflated after the initial opening, despite it remaining the conduit for magma from the caldera complex to the flank fissures. Low velocities across the shallow caldera after the end of the eruption likely result from rapid inflation due to recharge with fresh magma from depth. These results indicate a previously unknown complexity to the magmatic plumbing system at Sierra Negra and suggest velocity changes resulting from an interplay of thermal and stress perturbations.

Determination of Earthquake Depths Using Data of Cross-Sectional and Areal Deep Seismic Studies in Siberia

Abstract ––Information on the distribution of earthquake hypocenters for many seismically active zones of Siberia remains insufficient, which is associated with sparse networks of seismological observations. The paper presents the results of determining the earthquake depths in several seismogenic areas in the Altai-Sayan region, Cisbaikalia, Transbaikalia, and Yakutia using the travel time of longitudinal refracted waves from the Mohorovičič discontinuity (Pn waves) from earthquakes and the recently obtained information about the deep structure of these regions. The depth determination algorithm is tested using data from aftershocks of large earthquakes occurring in Tuva in 2011 and 2012 (ML = 6.7 and 6.8), recorded both by the regional seismological network and by a local group of seismic stations. Different methods are applied to reveal that some aftershock depths have a close match, including those for the main shocks – the Tuva-1 and Tuva-2 earthquakes. Another good match of earthquake depths is obtained using Рn waves with materials from regional and detailed studies of the Baikal branch of the Geophysical Survey of the Russian Academy of Sciences in the Muyakan activation site in the Baikal rift zone. The resulting data complement the information on the hypocenter of the main shock and confirm the change of the Muyakan activation cluster from large depths to shallow ones since the onset of activation in 2014. New information on the earthquake depths using Рn waves is obtained in Yakutia along the border of the largest Eurasian and Okhotsk tectonic plates. It is revealed that they decrease to 6–12 km as compared to higher depths of 20–30 km in adjacent areas. The resulting series of new information on the distribution of earthquake hypocenters using Рn waves is extremely important mostly because it indicates the possibility of identifying and redefining earthquake hypocenters using previous seismological observations in seismically active zones of Siberia.

Offshore Fault Geometry Revealed from Earthquake Locations Using New State-of-Art Techniques: The Case of the 2022 Adriatic Sea Earthquake Sequence

Abstract Precise hypocenter locations are critical for properly interpreting earthquake occurrence processes. However, when the coverage with seismic stations is unfavorable or sparse, locating precisely earthquake hypocenters, in particular their depth, is challenging. Here we apply a newly developed approach, which uses only two land stations, to the recently occurred 2022 Adriatic Sea offshore earthquake sequence (mainshock of magnitude Mw 5.5) and achieve location results that are comparable to the catalog locations obtained using dozens of stations. First, six events with magnitudes M ≥3.0 were relocated using a travel-time stacking method. Next, using these six earthquakes as reference events, we applied a two-station differential travel-time method to reconstruct the earthquake cluster geometry and locate the remaining events, including the mainshock. The obtained earthquake distribution shows a dipping direction that varies from south to southwest, depending on the choice of the input parameters. Our preferred result shows a cluster dipping at an angle of ∼30° toward the south-southwest. This solution was chosen because the depth of the mainshock hypocenter obtained using the differential-time procedure agrees well with the depth constrained using depth phases. Moreover, the relatively sharp earthquake cluster geometry is in general consistent with the thrust fault structures revealed by a local seismic reflection survey and focal mechanism solutions.

Magma intrusion process during pre-magmatic period (2010−2013) of Sinabung volcano as revealed by seismicity of volcano-tectonic and hybrid earthquakes

Sinabung volcano in Indonesia reactivated, with a series of phreatic eruptions, in August and September 2010. These eruptions were followed by various types of magmatic eruption at the summit, including lava dome growth, pyroclastic density currents, lava flow, and vulcanian eruptions, starting in December 2013. Prior to the magmatic eruptions, Sinabung exhibited two sequences of phreatic eruption and an increase in the seismicity of volcanic earthquakes. This study clarifies the progress of magma intrusion during the pre-magmatic period based on the hypocenter distribution, waveform similarity, seismic moment, rupture length, and stress drop for volcano-tectonic (VT) and hybrid earthquakes. It was found that the hypocenters of VT earthquakes are distributed north and northwest of the summit at a depth range of 1–10 km below sea level. Deep seismicity (4–10 km) alternated with shallow seismicity (2–4 km). The last shallow seismicity, from July to mid-December 2013, was different from previous seismicity in terms of higher intensity, as determined from the seismic moment, a temporary increase in the rupture length, and the migration of hypocenters towards the summit. The seismicity of VT earthquakes was altered by a swarm of hybrid earthquakes in mid-December. The hybrid earthquakes were smaller, in terms of seismic moment (mostly <3 × 1010 Nm), than the VT earthquakes. Their hypocenters were concentrated in the shallowest depth range (−0.5 to 1.5 km below sea level) directly below the summit, their source process was repeatable (they could be grouped into six earthquake families), their dominant peak was in a low-frequency range (2.5–4.5 Hz), and they had a relatively low stress drop (<0.15 MPa). This suggests that the swarm of hybrid earthquakes was induced by a frequent repeated fracture of fluid-filled cracks due to the intrusion of magma up to directly below the summit. The transition of the earthquake family and the change in its source parameters, namely an increase in the stress drop prior to the appearance of a lava dome and then a slight decrease, may reflect a gradual change in internal pressure in the hypocentral zone through the magma intrusion process.

Real-time earthquake magnitude estimation via a deep learning network based on waveform and text mixed modal

Rapid and accurate earthquake magnitude estimations are essential for earthquake early warning (EEW) systems. The distance information between the seismometers and the earthquake hypocenter can be important to the magnitude estimation. We designed a deep-learning, multiple-seismometer-based magnitude estimation method using three heterogeneous multimodalities: three-component acceleration seismograms, differential P-arrivals, and differential seismometer locations, with a specific transformer architecture to introduce the implicit distance information. Using a data-augmentation strategy, we trained and selected the model using 5365 and 728 earthquakes. To evaluate the magnitude estimation performance, we use the root mean square error (RMSE), mean absolute error (MAE), and standard deviation error (ϭ) between the catalog and the predicted magnitude using the 2051 earthquakes. The model could achieve RMSE, MAE, and ϭ less than 0.38, 0.29, and 0.38 when the passing time of the earliest P-arrival is 3 s and stabilize to the final values of 0.20, 0.15, and 0.20 after 14 s. The comparison between the proposed model and model ii, which is retrained without the specific architecture, indicates that the architecture contributes to the magnitude estimation. The P-arrivals picking error testing indicates the model could provide robust magnitude estimation on EEW with an absolute error of less than 0.2 s.Graphical