The kinematic characteristics of an earthquake source offer insights into its physical properties, with macroscopic parameters such as seismic moment and radiated energy serving as key indicators for describing seismic hazards. In this study, we explored the characteristics of earthquake sources in the frequency domain. Specifically, we introduced a hybrid method using teleseismic P-wave data to derive source spectra for over 200 large (MW > 7) shallow (depth < 70 km) earthquakes from 2000 to 2024. Our analysis reveals that in a simple ω-n model, the power exponent n is consistently less than 2 when the corner frequency aligns with the earthquake's total duration. To further characterize earthquake source properties, we defined the centroid frequency (fe) as the centroid of the energy spectral density which can represent the dimension of asperities on the fault plane. We also proposed the ratio between observed radiated energy and that predicted by the ω-² decay model as a metric for quantifying rupture heterogeneity (RH). Relationships of fe and RH with focal mechanism, magnitude, and centroid depth were analyzed within the conventional asperity model framework. Our source spectra dataset can also provide a robust foundation for future investigations into earthquake sources.
How to cite: Jiangcheng, Z. and Yong, Z.: Source Spectra for Global Shallow Large Earthquakes from 2000 to 2024, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2135, https://doi.org/10.5194/egusphere-egu25-2135, 2025.
The 17th of December 2024, a deadly M7.3 earthquake struck Port Vila, the capital of Vanuatu. This earthquake, located 30 km West of Port Vila, was strongly felt and damaged heavily the city economical center. This earthquake shows an unusual focal mechanism: a nearly-vertical fault with slip predominantly along-dip, and with strike perpendicular to the Vanuatu subduction. Comparing this earthquake with regional focal mechanisms for 30 years shows the uniqueness of this event. A local seismic network recorded a precursory seismic sequence (we detail this in another presentation, EGU25-16072). In this study we analyze the position time series recorded by a continuous GNSS station located in Port Vila, putting it in relation with the local and regional seismotectonic context, with a focus on the weeks preceding the mainshock and on the coseismic displacement. Finally, using Coulomb stress modeling and analyzing the spatio-temporal evolution of the seismicity in the neighboring subduction, we examine the potential impact of this earthquake on the subduction behavior.
How to cite: Durand, V., Tari, D., Aru, M., Laga, J., Gualandi, A., Patriat, M., Niroa, J., and Antfalo, L.: The 2024 M7.3 Vanuatu earthquake: an overview, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16939, https://doi.org/10.5194/egusphere-egu25-16939, 2025.
The earthquake that happened the 17th of December 2024, located 30km West of Port Vila, the Vanuatu capital, is characterized by an unusual focal mechanism: a nearly-vertical fault with slip predominantly along-dip, and with strike perpendicular to the Vanuatu subduction. In addition to numerous aftershocks, the local seismic networks of Vanuatu and New Caledonia recorded seismic events preceding the mainshock. In this study, we relocate the main event using the local networks. This allows us to better constrain its depth with respect to the available global catalogs, and to determine if it happened in the slab or in the upper plate. A relative relocation of the whole seismic sequence (preshocks and aftershocks) will also allow us to better image the geometry of the fault that activated during this event. A detailed analysis of the preshock activity will give us hints on the mechanisms that led to this large unconventional earthquake.
How to cite: Tari, D., Aru, M., Laga, J., Durand, V., Kobayashi, K., Niroa, J., and Antfalo, L.: Detailed study of the seismic activity preceding and following the 2024 M7.3 Vanuatu earthquake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16072, https://doi.org/10.5194/egusphere-egu25-16072, 2025.
SeisComP (Seismological Communication Processor) is an open-source, free seismic monitoring software that features an automated seismic data processing workflow, flexible database integration, and data interface capabilities. This study integrates SeisComP with the scanloc module, ETHZ-SED SeisComP Earthquake Early Warning (EEW) system algorithms, and SeisBench to develop three distinct seismic monitoring systems, optimizing three key tasks for the Central Weather Administration (CWA): earthquake early warning, seismic activity analysis, and global earthquake data acquisition. During the ML 7.2 Hualien earthquake on April 3, 2024, at 7:58 AM (UTC+8) CWA, in collaboration with ETHZ-SED, applied the EEW algorithms, including the Virtual Seismologist (VS) and Finite-Fault Rupture Detector (FinDer). Both algorithms, tested in parallel at the time, successfully generated complete results within 26 seconds of the earthquake’s origin. Based on these results, Public Warning System (PWS) alerts would have been issued for 17 out of 19 counties in Taiwan, thereby supporting CWA’s existing system. For the seismic activity analysis system, which integrates SeisComP, SeisBench, and the scanloc module, 3,789 automatic location results were produced within three days of the event. Compared to 604 official earthquake reports from CWA, the horizontal location error was approximately 4 km, the depth error 5 km, and the magnitude error 0.17. These results demonstrate the system’s ability to quickly assess seismic activity and estimate subsequent disaster risks. It also has the potential to automate earthquake catalog creation and reduce manual workload. In the global earthquake monitoring system, data is received from IRIS and GEOFON, currently generating results for earthquakes with magnitudes of 6.0 or larger and depths of 30 km or less in the Pacific region. In addition to providing valuable data for tsunami simulations, the system utilizes the global network to calculate Moment Magnitude Mw, which is derived from broadband P-wave amplitudes. For example, the system calculated a Mw of 7.4 for the 2024 Hualien event, which closely matched the magnitude result reported by the USGS. This helps avoid saturation issues with CWA’s ML estimation, particularly for larger earthquakes, and provides a more accurate measurement of earthquake size and dynamics, ultimately enhancing the system’s ability to monitor and assess earthquake risk. This study successfully tested the use of SeisComP in the aforementioned tasks. Although discrepancies remain between automatic results and the official catalog, ongoing testing and parameter optimization are expected to significantly enhance Taiwan’s earthquake monitoring capabilities and integrate more seismic data, ultimately improving the quality of earthquake monitoring services.
Keywords: SeisComP, earthquake early warning, earthquake monitoring
How to cite: Song, G.-Y., Chen, D.-Y., Wu, Y.-M., Böse, M., Clinton, J., and Massin, F.: Application of SeisComP at the Central Weather Administration (CWA) for Earthquake Monitoring and Early Warning: A Case Study of the 2024 ML 7.2 Hualien, Taiwan, Earthquake Sequence, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5275, https://doi.org/10.5194/egusphere-egu25-5275, 2025.
The Western Foothills Belt of Taiwan, shaped by the collision between the Eurasian and Philippine Sea plates, exhibits high seismicity concentrated along its deformation front. For example, Chongpu region in southwestern, Taiwan, characterized by active thrust faulting and fold structures, represents a zone of elevated seismic hazard. The most significant historical event in the area was the 1941 Chongpu earthquake (ML 7.1). Since the 1999 Chi-Chi earthquake (Mw 7.6), however, seismicity has predominantly involved smaller earthquakes. Notably, two earthquake swarms near the 1941 epicenter in 2017 and 2018 have raised questions about their potential implications. Similar phenomena have been observed in the Noto Peninsula, Japan, where prolonged earthquake swarms preceded the 2024 Mw 7.5 Noto earthquake. Previous research highlights the highly fractured subsurface environment beneath the Chongpu region, suggesting the possibility of analogous swarm patterns. This study aims to investigate the spatiotemporal characteristics of recent earthquake cluster in the Chongpu area, examining their relationship to the 1941 event. By conducting seismic data inversion to derive subsurface imaging, integrating these results with structural analysis of fault-fold systems, and assessing stress distributions from geological surveys, this research seeks to elucidate the seismogenic processes at the deformation front. The findings are expected to enhance the understanding of earthquake clusters mechanisms, evaluate their potential as precursors to major seismic events, and contribute to improved earthquake hazard assessment and disaster mitigation in urban settings.
How to cite: Lai, C.-N., Wen, S., and Chen, Y.-N.: Tectonic features of the deformation front in western Taiwan and implications for recent earthquake clusters, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12368, https://doi.org/10.5194/egusphere-egu25-12368, 2025.
The Xiaojiang Fault Zone, situated in southeastern Tibet, is renowned for its intense seismic activity. Studies have identified areas of high slip rate and seismic gaps that could indicate future large earthquakes. In our latest research, we look at the detailed seismic structure of the northern Xiaojiang fault and its surroundings using data from 68 seismic stations of dense networks. By analyzing these data, we identify two types of fault zone head waves (FZHW) through a combination of automatic picking, manual selection, and horizontal particle motion analysis of seismic data of local events. The first type of FZHW is detected at four stations, indicating a 2%-4% P-wave velocity contrast across the fault. The second type of FZHW is recorded at eight stations from five clusters of earthquakes primarily in and around localized low-velocity zones. To bolster our findings, we employed teleseismic P-wave arrival time delays between station pairs, which confirmed the FZHW analysis with a velocity contrast ranging from 1%-5%. A joint analysis of FZHWs and teleseismic P-wave arrival times reveals a sharp transition in velocity contrast across the fault near 26.7°N.To the north of this latitude, the west side of the fault exhibits lower velocities, suggesting the preferred rupture direction for a future earthquake would be from north to south. Conversely, to the south, the east side shows lower velocities, indicating a northward rupture direction. This structural variation suggests that an earthquake may be unable to rupture the entire NXJF, placing limits on the maximum size of potential earthquakes in the region.
How to cite: Zheng, X., Zhao, C., Guo, W., and Niu, F.: Seismic Imaging of the North Xiaojiang Fault with Fault Zone Head Waves and Teleseismic P-Wave Arrivals, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2033, https://doi.org/10.5194/egusphere-egu25-2033, 2025.
The seismic activity of the Hälsingland region on the northeast coast of Sweden, about 270 km north of Stockholm, presents an intriguing case study of intraplate seismicity in a low-seismicity setting. The activity consists of an elongated earthquake cluster, about 100 km in length, stretching from inland in the southwest to off-shore in the northeast, at approximately 45 degree angle to the coast line. In contrast to most of the main earthquake clusters in Sweden, this Hälsingland earthquake cluster has not yet been associated with any distinct geological feature, such as a postglacial fault or a major deformation zone. In 2021, a network consisting of thirteen temporary broadband seismic stations was installed in the Hälsingland area, as part of a joint study between Uppsala University and the Geological Survey of Sweden, with the aim of better understanding the drivers of the Hälsingland seismicity. The addition of the temporary network has increased detectability by almost a factor six compared with the permanent seismic network operated by the Swedish National Seismic Network. With the aid of an automatic processing system and an in-house, machine learning based classification system, we have extracted and manually analyzed a catalog of about 900 earthquakes, and 50 industrial blasts in the area, with origin times between September, 2021 and December, 2024. The analyzed earthquakes have local magnitudes ranging from -0.2 to 2.9. This presentation will focus on the preliminary seismic results from the study. We derive a new, improved, one-dimensional seismic velocity model for the Hälsingland area, using data from analyzed blasts, and re-locate the analyzed earthquakes in this improved velocity model. We identify the presence of a swarm of highly similar earthquakes, closely located in space, using waveform cross-correlation of analyzed earthquakes and a subsequent cross-correlation search through the continuous waveform data. Finally, we perform relative re-locations of the analyzed earthquakes, based on differential travel times, and calculate focal mechanisms to study potentially activated fault planes.
How to cite: Eggertsson, G., Lund, B., Gudmundsson, O., and Roth, M.: A study of the intraplate Hälsingland earthquake cluster in central Sweden, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6595, https://doi.org/10.5194/egusphere-egu25-6595, 2025.
Reliable seismic source parameter estimates are essential for making effective seismic hazard assessments in earthquake prone regions. The Sea of Marmara, NW Türkiye, and its environs located on a major fault with a history of destructive earthquakes. The utilization of seismic coda waves has a long history in providing valuable insights into the source properties, energy release at the foci, and attenuation characteristics of the Earth's crust. In the study region where we have previously demonstrated efficiency of the automated coda wave analysis with robust seismic moment and energy estimates using Qopen approach that enables modeling coda wave envelopes via a non-empirical inversion procedure to provide earthquake source properties. Here we aim to extend the initial framework by integrating comparative insights with the Coda Calibration Tool (CCT), a well-established empirical coda wave technique, to further develop a local earthquake catalogue with relatively small events (Mw ≤ 2.5) following the coda calibration of events between 2018 and 2020 with magnitudes 2.5 ≤ ML ≤ 5.7. The findings of this study will provide a basis for comparison between empirical and non-empirical coda approaches, which has not been done previously in this region.
How to cite: Özkan, B., Eken, T., Mayeda, K., Barno, J., and Taymaz, T.: Source Parameter Estimates and Energy Scaling of Small-to-Moderate Earthquakes in the Marmara Sea Region, NW Türkiye: A Comparative Study Using Coda Wave Analysis with CCT, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13720, https://doi.org/10.5194/egusphere-egu25-13720, 2025.
Resilience during and after large earthquakes depends heavily on the rapid characterisation of the events and their impacts. To achieve the best response possible, it is useful to estimate the dynamic rupture characteristics. The duration of rupture can help us assess tsunamigenic potential, by detecting the special class of “tsunami earthquakes” [Newman & Okal 1998], characteristically long-rupturing events that generate larger tsunamis than expected for their magnitude [Kanamori 1972]. Energy partitioning between high and low frequencies can guide analysis of potential damage to the built environment.
To better understand the links between the dynamic energy parameters and seismic impacts of earthquakes in the southwest Pacific, I have compiled a catalogue of historic and recent events, to use as a baseline for future near-real-time estimates and bring some more insight into seismic activities in this part of the Pacific.
We apply proven algorithms [Newman & Okal 1998, Newman & Convers 2013, Boatwright et al 2002], that rely on different type of waves and distance ranges, as well as the more recent updates to such estimations [Ebeling & Okal 2012, Saloor & Okal 2018], to select the approaches and input assumptions most fitting for this region. However, the remote location with sparse instrumental data brings limitations in gaining reliable estimations of radiated energy.
The technique from Newman & Okal [1998], relying on teleseismic P-waves, performs reliable estimates of Mw5.5+ events but needs some adjustment to reduce uncertainties for intermediate magnitude earthquakes in the region, due to large azimuthal gaps. Following a later approach from the author [Convers & Newman 2011], I design a network of consistent and reliable stations within the distance range and correct them for permanent deviations. Lastly, I reproduce the scheme from Ebeling and Okal [2012] in evaluating an empirical correction of the scaled radiated energy for stations closer than 35° epicentral distance, but on a regional scale instead. This approach makes use of stations within regional distances of the epicentre for faster results.
Our application of the S-wave approach of Boatwright et al. [2002], relies heavily on the densely sampled New Zealand broad-band seismic network. I use the existing velocity and attenuation models for New Zealand [Eberhart-Phillips et al. 2020] to test both 1D and 3D attenuation corrections, in terms of reliability of the results and computing time. We also refine our estimations of higher frequencies to better evaluate their contribution to the energy estimates in various subduction zone settings.
In this talk, I will present the current state of the radiated energy catalogue for the South-West Pacific and the automated energy analysis under the New Zealand RCET (Rapid Characterisation of Earthquakes and Tsunamis) program. The teleseismic estimates are in good agreement with previous evaluations for large earthquakes. The richer dataset largely correlates with what we know about regional tectonics and highlights some variations that could indicate large transitions in subduction-zone stress fields.
How to cite: Chanony, S., Fry, B., Gorman, A., and Stirling, M.: Estimating radiated seismic energy for New Zealand and the South-West pacific, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13981, https://doi.org/10.5194/egusphere-egu25-13981, 2025.
In anticipation to substitute the existing manual and semi-automated methods for classifying three categories of seismic events (quarry blasts, earthquakes, and noise), we have developed three different convolutional neural network (CNN) models. The first CNN model is based on extracting relevant features from seismograms (waveform), second is based on spectrograms (spectrum), and the third model uses a combination of these two respectively. The CNNs were trained using a labeled seismological waveform dataset recorded at a station SUR from GSNet (Gujarat) during the years 2007-2022. Generally, a common limitation in applying any deep learning techniques is the limited labelled dataset. Therefore, we utilised SeisAug, a Data augmentation (DA) python toolkit to address this challenge to significantly mitigate overfitting by increasing the volume of training data and introducing variability, thereby improving the model's performance on unseen data. A total of 3414 x 3 waveforms were extracted from the three categories of seismic events with a uniform data length of 180 s, considering factors such as coda length, which varies with magnitude and epicentral distance. From this dataset, 15% of the data belonging to each category was split for testing and remaining data was augmented using ‘SeisAug’ toolkit and used for training. The waveform model (WF), spectrogram model (SPEC), and combined model (COM) produced accuracies of 95.32%, 93.13%, and 93.96%, respectively. The robustness of the developed models is indicated by high F1-scores (WF > 0.91, SPEC > 0.92, COM > 0.97) and high area under the curve (AUC) values (WF > 0.98, SPEC > 0.93, COM > 0.98). The high F-scores indicate that these models are very well trained and the probability/possibility of false positives or false negatives is minimum. The high AUC indicates that the model performs well across a range of thresholds and can effectively distinguish between different seismic events. Further, these models produced accuracies of >90% and 100% when tested on completely new datasets from SCEDC and Palitana region (Gujarat) respectively.
How to cite: Pragnath, D., Srijayanthi, G., Kumar, S., and Chopra, S.: Enhancing Seismic Event Classification in Gujarat Through SeisAug-DrivenData Augmentation for Deep Learning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-911, https://doi.org/10.5194/egusphere-egu25-911, 2025.
Seismic anisotropy -- the directional dependence of seismic wave speeds -- provides a unique view into the past and present deformation of Earth's interior. However, constraining Earth's anisotropic heterogeneity remains a challenge primarily due to imperfect data coverage combined with the increased number of free parameters required to describe elastic anisotropy. And yet, exploring this more complex model space is critical for the interpretation of seismic velocity anomalies which may be significantly distorted if anisotropy is neglected. In this presentation, I will review new imaging strategies, developed by myself and colleagues, for constraining 3D anisotropic structures and their application to studying subduction zone dynamics and volcanic processes. Key developments include moving beyond simplified assumptions regarding the orientation of anisotropic fabrics (i.e. from azimuthal and radial parameterisations to tilted-transversely isotropic models), the integration of multiple and complementary seismic observables (P and S body wave arrivals, shear wave splitting measurements, and surface wave constraints), and the use of probabilistic inversion algorithms that allow for rigorous exploration of model uncertainty and parameter trade-offs. I will discuss how applying these imaging approaches to subduction systems in the central Mediterranean and Western USA yields new insights into the geometry of mantle flow, the nature of seismic velocity heterogeneity, and trade-offs between isotropic and anisotropic features. At smaller scales, I will highlight how new anisotropic tomography reveals the structure of the magmatic plumbing system beneath Mt. Etna (Italy) and provides constraints on the geologic processes controlling crustal stresses.
How to cite: VanderBeek, B.: Improved Strategies for Seismically Imaging Earth's Anisotropic Interior with Applications to Subduction Zones and Volcanic Systems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17444, https://doi.org/10.5194/egusphere-egu25-17444, 2025.
Constraining upward mantle flow is essential for understanding global mantle dynamics and linking Earth's interior with surface processes. The ERC-funded UPFLOW (Upward Mantle Flow from Novel Seismic Observations) project addresses the limited understanding of mantle upwellings connecting the deep mantle to the surface by utilising advanced seismic imaging methods and conducting extensive data collection.
Between June 2021 and September 2022, UPFLOW deployed 50 and successfully recovered 49 ocean bottom seismometers (OBSs) across a ~1,000×2,000 km² area in the Azores-Madeira-Canaries region, with an average station spacing of ~150-200 km. This multinational collaboration involved institutions from Portugal (IPMA, IDL, Univ. of Lisbon, ISEL), Ireland (DIAS), the UK (UCL), Spain (ROA), and Germany (Potsdam University, GFZ, GEOMAR, AWI). The deployment utilized three OBS frame designs equipped with three-component wideband seismic sensors and hydrophones. The dataset exhibits high-quality recordings, including teleseismic, local seismic events, and non-seismic signals (e.g., whales, ships, and the Tonga eruption), with significant noise reduction observed in vertical component long-period data (T > ~30 s).
Initial tomographic results feature a preliminary P-wave model derived from ~8,000 multi-frequency (T ~2.7-30 s) body-wave travel time cross-correlation measurements and over 120 teleseismic events. Integrating UPFLOW's OBS data with global seismic datasets from temporary and permanent stations expands the dataset to approximately 600,000 multifrequency measurements. This comprehensive approach enables the construction of a global P-wave model with enhanced resolution throughout the entire mantle beneath the Azores-Madeira-Canaries region. We compare our new model with existing global tomography models and discuss its geodynamical implications in terms of mantle upwelling processes and their surface expressions.
How to cite: Tsekhmistrenko, M., Ferreira, A., and Miranda, M.: Unveiling Deep Earth Mantle Structures Beneath the Azores-Madeira-Canaries with UPFLOW data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12389, https://doi.org/10.5194/egusphere-egu25-12389, 2025.
Large earthquakes can trigger other earthquakes at great distances, even on a global scale, through the dynamic stresses imparted by their seismic waves. However, identifying such remote triggering is not always straightforward. It may occur not only instantaneously, during the passage of the seismic waves, but also with a delayed effect—sometimes days or even weeks after the initial event. Recognizing this phenomenon in historical earthquake catalogues, which are incomplete, is particularly challenging, yet it is essential for better understanding its occurrence following rare, large earthquakes and eventually assessing its impact on global, time-dependent seismic hazard.
In this study, we report what may be the oldest documented case of global earthquake triggering, dating back to the eighteenth century. We first integrated and revised global and regional earthquake catalogues from multiple continents, spanning a period of ten years before and after the main earthquake, in order to create a more comprehensive and reliable global dataset. Just after this main event, we observed a statistically significant increase in seismic activity, even at distances greater than 2000 km from the epicentre, followed by an Omori-like decay.
We then modelled the expected global seismic wavefield for the initial earthquake to test whether it could have triggered subsequent remote earthquakes occurred across several continents. For this modelling, we considered the likely magnitude and location of the main earthquake, as well as the focal mechanism of a large, instrumental earthquake most likely caused by the same fault, according to prior research. The subsequent earthquakes occurred precisely in the regions where the calculated dynamic stresses induced by the main earthquake were largest, strongly supporting the hypothesis that they were dynamically triggered.
How to cite: González, Á., Crespo, C., Heimann, S., and Corral, Á.: The quest for the oldest case of global earthquake triggering, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10047, https://doi.org/10.5194/egusphere-egu25-10047, 2025.
Human activity induces ground motions that dominate >1 Hz seismic data recorded in semi-rural and urban areas. Whereas the seismic noise generated by industrial and traffic activities is relatively well characterized, weaker pedestrians-related noise remains less well understood. Here, I examine the spatiotemporal distribution of seismic amplitudes to uncover the effects of human crowds and derive semi-empirical attenuation relationships between seismic amplitudes and crowd sizes. I utilize recordings from the dense MesoNet seismic network, which consists of about 300 accelerometers, primarily located near schools in the Tokyo metropolitan area. These data exhibit strong temporal variations: maximum daytime amplitudes are recorded during school hours, and minimum amplitudes coincide with daily breaks in activity during lunch and afternoon teatime. Outside school hours, I observe a wide-spread amplitude peak at 3 to 5 am daily, likely due to truck traffic. The peak amplitudes correlate very well with the number of students in each school. Given that ambient traffic volumes differ substantially in the area covered by the MesoNet stations, this correlation suggests the amplitudes are primarily influenced by daytime pedestrian school activity. I supplement the MesoNet dataset with seismograms of well-recorded outdoor cultural activities with participant sizes ranging from 200 to about 100,000. After correcting for attenuation due to surface-wave geometrical spreading, the amplitudes are found to scale logarithmically with the crowd’s size. This finding indicates that seismic data can be effectively used to study trends in pedestrian mobility within urban environments.
How to cite: Inbal, A.: The People’s Magnitude: Characterizing Seismic Motions Generated by Human Crowds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14902, https://doi.org/10.5194/egusphere-egu25-14902, 2025.
Probabilistic seismic hazard assessment (PSHA) requires the definition of seismic source models (SSM) that describe the spatial variations of the seismic activity over the region of interest. They can include and combine active faults, seismotectonic area source polygons as well as zoneless, continuous descriptions of the seismicity. In this contribution, we present the different components of the source model we developed to update the probabilistic seismic hazard model for continental France that was published by Drouet et al. (2020).
Particular effort was dedicated to produce a new historical and instrumental catalogue, homogenized in moment magnitude, with location and magnitude uncertainty estimates. The three area source models used in the previous study were also revised in order to extend them up to 300 km away from the political borders so as to allow seismic hazard calculations at longer return periods. The recently published SSM of the ESHM20 was used to that end. We also explored new methodologies to build zoneless models with less arbitrary choices. Whenever possible, we involved Bayesian methodologies for the estimation of model parameters. Finally, a new feature for the updated seismic hazard map calculations is the introduction of active faults in the source model.
We present preliminary depth distributions, style of faulting, maximum magnitude and frequency magnitude estimates for the various elements of this source model. Location, but more importantly magnitude uncertainties are carefully taken into account and propagated at each stage to properly honor epistemic uncertainties in the subsequent seismic hazard calculations.
How to cite: Arroucau, P., Mazet-Roux, G., Daniel, G., Lefèvre, M., Bollinger, L., and Le Roux-Mallouf, R.: A seismic source model for continental France probabilistic seismic hazard assessment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20447, https://doi.org/10.5194/egusphere-egu25-20447, 2025.
This work summarizes the procedure for constructing a dataset of accelerometric and velocimetric recordings of earthquakes in the subduction zones of the Mediterranean Basin. The aim is to improve the ground motion characterization of this type of events by calibrating a brand-new predictive model (GMMs) for the next generation of seismic hazard models in Europe.
The database consists of three components ground-motion recordings from selected earthquakes in subduction zones, collected and processed uniformly through the ESM (Engineering Strong Motion database, https://esm-db.eu/#/home; (Luzi, et al., 2020)) infrastructure. The dataset also includes several supporting data (metadata) relative to source (magnitude estimates and focal mechanisms), path (different distance metrics), and site (VS,30 and soil classification according to the Eurocode 8). The earthquakes are located in the Calabrian Arc, Cyprus Arc, and Hellenic Arc, whose geometries are defined based on studies carried out in the framework of the European Fault-Source Model 2020 (Basili, et al., 2022). The preliminary dataset consists of 9910 records of 475 events with a magnitude range between 2.9 to 6.6. The events that occurred in the subduction zones are classified into interface and intra-slab events, according to different strategies, since their position relative to the slab can induce different near-source. A flag to identify stations in backarc or fore-arc position is also introduced since different rates, propagation characteristics, and characteristics of ground motion attenuation characterize them. The ground motion parameters will also be compared with available datasets for other worldwide subduction zones, such as the NGA-Sub database (Mazzoni, et al., 2021). The dataset will be finally disseminated through a flatfile (parametric table), formatted according to the ESM flatfile specification (Lanzano, et al., 2019).
How to cite: Shoaib, B., Lanzano, G., and Luzi, L.: Construction of a ground motion flatfile for subduction earthquakes in the Mediterranean area, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19380, https://doi.org/10.5194/egusphere-egu25-19380, 2025.
The objective of this work is the estimation of the moment tensor, with particular attention to the analysis of the full moment tensor, to kinematically characterize the seismogenic sources in the shallow crust of Mt. Pollino area (Southern Italy). The moment tensor analysis is an indispensable tool for understanding the rupture process, determining the fault geometry, the characteristics of the medium in the seismogenic volume, and the acting stress field. In regions with a complex tectonic structure, such as the Mt. Pollino area, the double couple model may not be sufficient for characterizing seismogenic sources. The inversion of the full moment tensor is essential to analyze also the non-double couple components, which can give very important insights in case of complex sources. Furthermore, the full moment tensor solution is of fundamental importance for verifying and estimating possible volumetric variations in the focal volume.
In this study, the dataset consists of 65 earthquakes that occurred in the Pollino area between latitudes 39.70 and 40.10 and longitudes 15.80 and 16.30 from 2010 to 2024, characterized by magnitudes 2.5<M<5.0 and a maximum depth of 10 km. The inversion of the full moment tensor was performed using "Grond" (Heimann et al. 2018), a software based on the comparison between synthetic and observed signals through a Bayesian probabilistic approach. We used seismic data at local to regional distances; the data were deconvolved to remove the instrumental response and transformed into displacement. The inversion is based on the fitting of full waveforms, on the three components, in the 0.04 - 0.10 Hz frequency band. The inversion was performed under the hypothesis of point source by applying the L1 norm for the “double couple”, “deviatoric” and “full” moment tensor configurations, using three different crustal velocity models to check the stability of the results. We obtained a stable solution for 50 earthquakes, all of them characterized by normal kinematics with strike in the NW-SE direction, and a predominant positive isotropic component. Positive values up to 53% of the isotropic component indicate tensile opening processes, thus suggesting that the seismicity may be affected by fluid transfer.
How to cite: Ponte, M., Cesca, S., Büyükakpınar, P., Calderoni, G., and La Rocca, M.: Full Moment Tensor Inversion for the Characterization of Seismogenic Sources in the Pollino Area (Italy) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10416, https://doi.org/10.5194/egusphere-egu25-10416, 2025.
Geothermal energy offers great potential for supplying heat to the large district heating networks common in central Europe and is a viable substitute for the heat fed into the district heating by coal-fired power plants that will soon be decommissioned. In the Lower Rhine Embayment, efforts are ongoing to explore the region's geothermal potential. To facilitate any future drilling and testing activities, we contribute in a seismotectonic prescreening of the study area. However, because of various anthropogenic noise sources, including open pit mining, industrial activity and densely populated urban areas, the region has an elevated noise level, influencing the seismological data quality. Furthermore, soft sediments dipping towards the northeast cause local site amplification effects. The thickness of these sediments varies greatly from almost non-existent up to 600 m. Thus, noise levels and general data quality differ strongly across the region. To overcome these restrictions, we have gradually optimized and focused our seismological monitoring in the region over the last couple of years.
As an addon to existing, permanent monitoring stations from Earthquake Observatory Bensberg (FDSN-network code BQ), Royal Observatory of Belgium (BE), the Royal Netherlands Meteorological Institute (NL), and the Geological Survey of North Rhine-Westphalia (NH), we first deployed a dense network (ZB) operating from 2021 to 2022 and consisting of 48 broadband and short period stations to investigate background seismicity and the spatially resolved noise level using probabilistic power spectral densities (PPSD). The PPSDs show the correlation of the noise level with the sediment thickness and reveal high seismic noise, especially in the north-eastern region. The seismicity is moderate and concentrated in the western part.
Following the ZB network, we currently operate a research network (YV) of eight broadband stations. The station locations were optimized using the information gained from the ZB network to deploy the best quality stations with a focus on the area where most natural seismicity occurs. One broadband sensor was deployed in a 100 m deep well, about 30 meters below the softer sediments in the center of the region to remove the effect of site amplification and anthropogenic noise as much as possible.
To prepare upcoming drilling activities, additional five stations are deployed surrounding the potential drill site at the Weisweiler power plant. We interpolate I95 values to find potential station locations with a low noise level, based on the noise levels observed on the ZB network and taking into account the existing YV stations. Different network geometries resulting from the potential locations are investigated for optimum accuracy and magnitude of completeness up to the anticipated drilling depth of about 3 km.
The optimal model promises a magnitude of completeness of down to 0.5 in the target region at the Weisweiler power plant at a depth of 3 km, showing that all potential events with a magnitude > 0.5 will be detectable. We present the used workflow, show modeling results and the evolution of data quality over the last years.
How to cite: Dietl, M., Moutote, L., Kremers, S., Roth, M. P., Carrasco, S., Neugebauer, S., Fazlibašić, N., and Finger, C.: Seismic monitoring network design in the Lower Rhine Embayment using pre-existing dense deployments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10087, https://doi.org/10.5194/egusphere-egu25-10087, 2025.
To understand the ubiquitous nature of the Precambrian shield, we investigated the structure of the mantle transition zone (MTZ) beneath the Canadian, Brazilian, Baltic, African, and Australian Shields. Receiver Functions were computed from data collected from various stations sampling these regions, and the topography of the MTZ boundaries was mapped using depth-migrated RF images generated with two 3D tomographic velocity models, LLNL_G3D_JPS and GyPSuM. The depth-migrated images from both models reveal a thinner-than-usual MTZ beneath all the Precambrian shields, with an average thickness of approximately 238 ± 8 km. The upper boundary of the MTZ (the 410 km discontinuity) shows distinct topography, while the lower boundary (the 660 km discontinuity) is found at shallower depths. This suggests that the main cause of MTZ thickness variation is the shallowing of the 660 km discontinuity, pointing to a post-spinel transition occurring at higher temperatures with a negative Clapeyron slope, supporting the theory of whole-mantle convection. These results suggest that mantle plumes have appreciable influence the MTZ beneath Precambrian shields, extending to its base, which also gains support (/may also be accounted by) from the global mantle warming observations at the 660 km discontinuity. Further numerical modeling/ simulation studies are needed to test this hypotheses.
How to cite: Srinu, U. and Rao B, P. R.: Is the mantle transition zone uniform beneath Precambrian shields?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-915, https://doi.org/10.5194/egusphere-egu25-915, 2025.
In this study, we calculated the crustal thickness and Vp/Vs ratio of the Zagros
using 3 years of data recorded in 20 permanent broadband seismic stations of
the Iranian Seismological Center (IRSC). To do this end we analyzed receiver
functions by the iterative deconvolution in the time domain applying to the
teleseismic records. Our results show the crustal thickness near the Iranian
plateau and in the Arabian plate edge is about 35 - 40 km in the northern part of
Zagros. Toward NE, In the main Zagros zone, Moho depth has a higher value
(45 Km). The moho thickness was increased to a mean of 50 km in the
Sanandaj-Sirjan zone (SSZ). Due to over thrusting Iranian plateau to continental
Arabian shield and the existence of massive volcanic rocks, SSZ is the thickest
part of Zagros. In the Southern Zagros crustal thickness is about 30-40 km. We
show that the Vp/Vs ratio decreases with the increasing Moho depth.
How to cite: Shiranzaei, G., Nasrabadi, A., and Sepahvand, M. R.: Moho depth variations and Vp/Vs ratio in the Zagros (Iran), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-538, https://doi.org/10.5194/egusphere-egu25-538, 2025.
Over the years, we have made significant updates to the Hungarian National Seismological Bulletin as velocity models, localization techniques, and station network configurations have evolved. A crucial aspect of our work involves addressing anthropogenic events since many recorded events initially classified as earthquakes are actually mining explosions, complicating geological interpretations. Since the Kövesligethy Radó Seismological Observatory has been collecting digital data since 1995, this is an ideal time for us to review the entire catalog using contemporary algorithms and velocity models.
By 2018, we had recalculated hypocenter parameters for 5,735 events (Bondár et al., 2018) using the 3D RSTT velocity model, which produced reliable results for Hungary. We have since expanded the dataset with an additional 6,578 events through December 2022, ensuring the inclusion of the highest-quality initial hypocenter parameters.
Our research has two main components: a comprehensive analysis of seismicity across the Pannonian Basin using the Bayesloc algorithm (1995-2022) and the precise relocation of specific event clusters using the double-difference method (e.g., Somogyszob, Szarvas, Móri-árok). Before conducting the Bayesloc analysis, we reviewed event types and identified hundreds as potentially anthropogenic. We also performed quality control, filtering events to retain those with favorable station geometry for accurate initial estimates.
For the Bayesloc analysis, we used GT2 events as reference points. Before finalizing results, we tested and documented the impacts of initial hypocenters, GT2 events, and a priori standard deviations on hypocenter parameters. This analysis included refining travel-time corrections, phase identification, and precision metrics to improve accuracy.
Our results showed reduced location errors and clear clustering, particularly for GT2 events, enabling more reliable geological interpretations. For local event clusters, the double-difference algorithm proved highly effective for small-scale studies, using differential times from waveform cross-correlation to achieve optimal relative positioning.
In this project, we made over 25 years of data compatible for simultaneous analysis, yielding the most reliable results for the Pannonian Basin to date and enabling improved seismic hazard assessments. Identifying and excluding anthropogenic events is crucial for accurate geological interpretation and seismic risk assessment. Our workflow also supports annual database updates and consistent processing of local event clusters.
How to cite: Czecze, B. and Bondár, I.: Review of Local and Regional Seismicity in the Carpathian Basin Using Multiple Event Location Algorithms with ground truth events, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-37, https://doi.org/10.5194/egusphere-egu25-37, 2025.
For eastern Himalayan segments the Shillong block is distinguished by clustered seismicity along the Kopili Fault Zone (KFZ) and the Dhubri-Chungthang Fault Zone (DCFZ). The foreland seismicity patterns of the KFZ and DCFZ seem to penetrate the higher Himalayan mountain belts. To understand the ability of the DCFZ in generating future great earthquakes and its role in segmentation of Himalaya which affects regional seismicity pattern, a network of 54 broadband seismic stations was installed in two phases (2018-2023, 2023-continuing) covering Sikkim and Foreland Basin along the DCFZ. Preliminary results suggest concentrated seismicity along the DCFZ. Earthquakes are of mid-crustal origin, akin to results from earlier experiments. Focal mechanisms are showing dominantly strike-slip nature of the fault zone. Crustal structure obtained using receiver functions have shown a very complex crust with prominent offsets and overlaps. The thick sedimentation in foredeep is revealed with large amplitude arrivals close to 1 s. Moho arrivals show a thick crust beneath Himalaya and its foredeep. Highly deformed middle crust show presence of dipping and anisotropic layers, evident in the backazimuthal stacks of receiver functions. The seismicity and crustal deformation with presence of dipping and anisotropic structures suggest presence of a sheared fault zone, though extent of this zone remains unclear in the preliminary results. Ongoing experiment with continuous monitoring of seismicity of DCFZ, will help to resolve critical issues, like depth extent, dominant fault mechanisms and penetration of the DCFZ within the Himalaya, its role in segmentation of the Himalayan arc and defining seismogenic boundaries and rupture zones of possible major earthquakes.
How to cite: Singh, A., Bala, S., Singh, C., Singh, P. K., Dubey, A. K., and Tiwari, A. K.: Seismogenesis of earthquakes in the Dhubri-Chungthang fault zone, India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6039, https://doi.org/10.5194/egusphere-egu25-6039, 2025.
Chile is one of the most seismically active countries in the world. In May 1960, two large earthquakes occurred along the subduction interface in southern Chile. The first took place on May 21st in Concepción, with a magnitude of Mw=8.1, and the second happened on May 22nd and corresponded to the world's most significant event recorded in instrumental history with a magnitude of Mw=9.5, popularly known as the Valdivia earthquake. Both events provoked considerable structural damage in some of the most important cities in the center and south of Chile, and the second one produced a transpacific tsunami, with casualties in Japan and Hawaii. Here, we investigate the interaction between the Concepción and Valdivia earthquakes, which occurred within a mere 33 hours of each other. According to previous studies, both earthquakes were initiated at similar locations and depths below the Arauco peninsula. We compute the Coulomb stress changes between these two seismic events to explore the increase of the regional stress produced by the Concepción earthquake into the Valdivia segment. We hypothesized that the Concepción earthquake promoted the rupture initiation of the second largest event, modifying their stress field and giving the conditions that lead to the mainshock nucleation. Our preliminary analysis indicates an interesting relationship between both earthquakes, which allows us to characterize and quantify these events' interactions at near distances and along the same subduction zone. Finally, a better understanding of the stress transference between these historical earthquakes gives us key information on the physical conditions for the nucleation of the largest earthquake ever recorded.
How to cite: Castro-Araya, F., Morales-Yañéz, C., González, J., and Ojeda, J.: Evaluation of the Coulomb stress changes between the 1960 Concepción and Valdivia earthquake in southern Chile., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-497, https://doi.org/10.5194/egusphere-egu25-497, 2025.
In 2024, the Mw 7.4 eastern Taiwan earthquake highlights Taiwan’s status as one of the most seismically active areas, driven by the complex interaction between the European Plate (EP) and Philippine Sea Plate (PSP). This dense seismicity provides a unique opportunity to investigate the earthquake rupture properties. The corner frequency, a key parameter for understanding kinematic rupture properties, is challenging to measure due to the site effect and the trade-off between corner frequency and attenuation parameter t*. Jian and Kuo (2024) proposed the Cluster Event Method 2 (CEM2), which mitigates these challenges by incorporating joint datasets of spectra and spectral ratios. This study applied CEM2 to the eastern Taiwan earthquakes recorded by local broadband stations. Site-effect patterns were first retrieved during the initial inversion stage for each station, enabling corrected corner frequency estimates in the subsequent inversion. Using the relationship of stress drop, corner frequency and seismic velocity at the source area (Madariaga, 1976), we calculate the stress drop (SD) for individual events. To prevent overestimation caused by extreme values, we calculated the average SD in log-scale. The overall average SD for earthquakes shallower than 40 km is 50 MPa. Our results reveal significant spatial variations in SD across the Taiwan collision zone. In the southern collision zone, SD in the PSP are approximately twice as high as those in the EP. To the north, where the PSP subducts beneath the EP, SD increases with longitude and depth. However, west of the Longitudinal Valley Fault (LvF), the vertical variation of SD is reversed: shallow SD (<10 km) is about twice as high as deep SD (>10 km). Considering self-similarity model of faults with constant stress drop of earthquakes, further exploration of the parameters controlling tectonic-related stress drop variability are necessary. Overall, earthquakes within the PSP exhibit higher stress drops than those in the EP. These findings provide valuable insights for different earthquake rupture properties in the tectonically complex region.
How to cite: Jian, P.-R., Tseng, T.-L., and Kuo, B.-Y.: Variations in earthquake source properties across the Taiwan collision zone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5398, https://doi.org/10.5194/egusphere-egu25-5398, 2025.
Taiwan is not large in area, but it has a complex geological structure due to intense orogeny. From east to west, Taiwan can be divided into five major geological zones: the Coastal Range, the Central Range, the Hsuehshan Range, the Western Foothills, and the Coastal Plain. The southwestern region of Taiwan primarily comprises the Western Foothills and the Coastal Plain. The Western Foothills belong to the foreland of western Taiwan orogen. During the Oligocene, the rifting of the South China Sea led to the development of several east-west-oriented normal faults. Subsequently, in the late Quaternary, the northwestward compression of the Philippine Sea Plate caused a series of north-south-oriented, fold-thrust fault zones in the Western Foothills, and reactivating the normal faults formed during the extensional period. In recent years, most destructive earthquakes have occurred at the deformation front of the orogenic belt, making the study of the region's structural characteristics an important topic. This research utilizes data from a dense seismic array and employs nonlinear inversion of receiver functions and the double beamforming method to investigate the shallow subsurface structure of the Western Foothills. The goal is to provide a more detailed understanding of the structure, which can improve the precision of earthquake location and deepen our knowledge of the area's tectonics.
How to cite: Su, C.-M., Wen, S., and Wen, Y.-Y.: Investigation of Shallow Structure at the Western Front of Taiwan Orogen Applying Nonlinear Search Method, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3445, https://doi.org/10.5194/egusphere-egu25-3445, 2025.
Taiwan lies at the convergent boundary between the Eurasian Plate and the Philippine Sea Plate. In northeastern Taiwan, at the Ryukyu subduction zone, the Philippine Sea Plate subducts northward beneath the Eurasian Plate. This tectonic interaction has formed a series of geological features, including the Ryukyu Trench, the Ryukyu Arc, and the extensional Okinawa Trough. This study area is significantly influenced by both the extension of the trough and the plates subduction. As a result of these tectonic processes, this region experiences notable igneous activity, such as the formation of Kueishan Island and the Tatun Volcano Group. Additionally, extensional activities related to plate rifting are observed beneath the Ilan Plain.
In this study, we apply the Sequential Inversion method, utilizing seismic data provided by the Central Weather Bureau. The analysis applies Double-Difference Tomography to construct a three-dimensional velocity model of the study region. The initial model is based on the 3-D velocity structure proposed by Su et al. (2019). To address the limited resolution of seismic waves in the shallow subsurface, gravity data are integrated to enhance the resolution of shallow structures. A velocity-density conversion formula is used to transform the velocity model into a corresponding density model for gravity inversion. The resulting density model is subsequently converted back into a velocity model, completing the first iteration of the sequential inversion process.
Through multiple iterations of sequential inversion incorporating both gravity and seismic datasets, final velocity and density models are obtained that align well with observed travel-time and gravity data. These results demonstrate a significant improvement in the resolution of shallow structures, with residuals for both velocity and density models exhibiting stable convergence. In the shallow subsurface, low P-wave velocity (Vp) values are associated with the extensional basin of the Ilan Plain, whereas higher Vp values further south correspond to the topographic relief of the northern Central Range. Furthermore, Vp/Vs ratios are utilized to infer rock properties, providing insights into magmatic intrusions in the Ilan region and the geothermal heat source of the Chingshui area.
How to cite: Chiu, P. H., Yen, H. Y., and Lo, Y. T.: The 3-D velocity and density structure of NE Taiwan inferred from seismic and gravity data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5520, https://doi.org/10.5194/egusphere-egu25-5520, 2025.
Taiwan is situated at a complex plate boundary, and numerous velocity models have been published, providing significant insights into large-scale structural features. However, detailed shallow structures remain inadequately resolved. Gravity data, with its sensitivity to lateral variations in shallow regions, offers an excellent opportunity to address these limitations. This study aims to integrate gravity and seismic data through sequential inversion to develop a more precise structural model.
Seismic data will include travel-time records from the Central Weather Administration (CWA) seismic network and temporary stations deployed in mountainous areas by National Central University over the past decade, ensuring comprehensive station coverage. The seismic inversion will employ the tomoDD method, significantly improving structural resolution in regions with dense seismicity and enhancing earthquake location accuracy. The results will yield models of Vp, Vs, and Vp/Vs.
Gravity inversion will utilize free-air gravity data to resolve velocity and density variations within terrains characterized by topographic relief. By integrating terrestrial, marine, and airborne gravity data, the study ensures robust constraints on both shallow and deep structures. Wavelength analysis of Bouguer gravity anomalies will further distinguish shallow and deep residual gravity effects, elucidating their relationship with tectonic structures.
Finally, a relationship between seismic velocity and density will link the two distinct physical observations, enabling a sequential inversion that incorporates both gravity and seismic data. This approach will yield a subsurface model that aligns with both datasets. By adopting this innovative inversion strategy, the study aims to produce an improved three-dimensional velocity and density model for Taiwan.
How to cite: Lo, Y.-T. and Yen, H.-Y.: Enhancing 3D Density and Velocity Models of Taiwan Using Sequential Inversion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5436, https://doi.org/10.5194/egusphere-egu25-5436, 2025.
The Korean Peninsula has long been recognized as a stable intraplate region with relatively low seismic activity. However, moderate-to-large earthquakes, such as the 2016 Gyeongju earthquake and the 2017 Pohang earthquake, have highlighted the necessity for systematic studies on the seismic characteristics of the region. This study aims to understand the seismic characteristics of the Korean Peninsula by estimating key seismic source parameters (seismic moment, moment magnitude, stress drop, and corner frequency) for major earthquakes.
Using the Brune source model (Brune, 1970) as a basis, spectral analysis was conducted to determine the source parameters of the 2016 Gyeongju earthquake, and the results were validated through comparisons with previous studies. After verifying the results, the established framework was applied to automatically determine the seismic source parameters for earthquakes of magnitude 3.0 or greater that occurred in the Korean Peninsula after 2010. Regional comparisons of stress drop values were also conducted based on the determined results.
The framework developed in this study aims to automatically determine seismic source parameters for future earthquakes of magnitude 3.0 or greater in the Korean Peninsula. This advancement is expected to enhance the quantitative understanding of seismic activity in the region and provide a crucial foundation for future studies on seismic activity and region-specific seismic hazard assessments.
How to cite: Byun, A.-H., Jo, E., Min, K., and Park, S.-C.: Study on the determination of seismic source parameters in the Korean Peninsula, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13752, https://doi.org/10.5194/egusphere-egu25-13752, 2025.
The distribution of focal depths can enhance the understanding of seismogenic characteristics in a region. However, determining accurate focal depths is highly challenging, and the reliability of such determination is often limited, requiring careful consideration during analysis and interpretation. This study investigates the depth distribution of earthquakes in the southern Korean Peninsula to better understand regional seismicity. To minimize focal depth errors, the criteria for reliable focal depth determination were examined. For the local crustal velocity model of Kim et al. (2011), P- and S-wave travel times were computed under conditions of arbitrary seismic networks with a 150 km aperture, consisting of 1,680 seismic stations and originating from focal depths of 5 to 25 km. From these conditions, 10 seismic stations were randomly selected to determine the hypocenter of an event, which was then compared with the original focal depth. This process was repeated 100,000 times for each focal depth without noise and an additional 100,000 times with random noise ranging from -2 to 2 seconds added to the travel times. Consequently, a total of 4.2 million sets of arrival times were generated. To account for epistemic uncertainty in the crustal structure, three local velocity models, including that of Kim et al. (2011), were used for earthquake location. Various metrics were evaluated to develop selection criteria for ground truth events with well-located hypocenters. The Gradient Boosting method identified the minimum distance to a station as the most important metric. In this study, a new metric was introduced by gridding the epicentral distance within 100 km and the azimuth while considering the distribution of seismic stations within each grid. Using this metric, along with considerations of epicentral distance and azimuthal gaps, criteria were established to ensure the reliability of input data for accurately determining focal depths. Seismic events from 2018 to 2022 were located after meticulously inspecting seismic phases and selected based on the criteria proposed in this study to analyze the focal depth distribution in the southern Korean Peninsula.
How to cite: Sheen, D.-H.: Analyzing Earthquake Focal Depth Distribution in the Southern Korean Peninsula, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14240, https://doi.org/10.5194/egusphere-egu25-14240, 2025.
The Haichenghe fault zone (HFZ), renowned as the site of a successfully predicted earthquake, namely the 1975 M7.3 Haicheng earthquake, as well as the 1999 M5.4 Xiuyan earthquake, is one of the most seismically active zones in eastern China. Nevertheless, fault structures within the key areas of the HFZ remain inadequately characterized, which limits the understanding of the fault behavior and seismological mechanism of the region. Consequently, from August 2021 to September 2023, we deployed the densest array to date, consisting of 23 broadband seismic stations with an average distance interval of about 6 km. Based on the dense observation data, we constructed a high-precision catalog of the HFZ utilizing neural network-based phase picking, earthquake association, and relocation methods. Our results show that:
- The HFZ is characterized by a conjugate fault system composed of WNW-striking and NE-striking subvertical faults of different scales. The Haichenghe Fault (HF) appears as a WNW-trending en echelon fault, traversing the entire study area. The 30-kilometer-long main segment (MHF) in the northwest is responsible for the Haicheng 7.3 earthquake, while the 5-kilometer-long Xiuyan segment (XYF) in the southeast generated the Xiuyan M5.4 earthquake.
- The MHF is further segmented into eastern and western sections. A several-kilometer-wide step-over between two sections is connected by two NE/NNE trending faults. It can be deduced that the rupture of the Haicheng earthquake along the WNW direction was not continuous throughout, but terminated or transferred to these two NE/NEE trending faults at the step-over.
- At the intersection of the MHF and its main NE-trending conjugate fault, a horizontally asymmetric conjugate rupture area of the Haicheng M7.3 earthquake has been identified. Moreover, a vertically triangular seismic gap has been discovered, suggesting a strong heterogeneity of the subsurface medium in this region.
How to cite: Bai, L., Sun, Q., Jiao, M., Wang, L., Yang, S., Wang, J., Li, E., and Wu, Q.: New insights into fault structures of the Haichenghe Fault Zone through dense array observation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5539, https://doi.org/10.5194/egusphere-egu25-5539, 2025.
The quest for reliable earthquake prediction has led researchers to explore various unconventional methods, one of which involves the study of animal behaviour. Observations have shown that some animals exhibit unusual behaviours before seismic events, suggesting a potential link between animal activities and impending earthquakes. This abstract summarizes the emerging research on using animal behaviour as an indicator for earthquake prediction. Studies have documented phenomena such as increased agitation, abnormal movements, and changes in vocalizations among various species prior to seismic occurrences. These behaviours are hypothesized to be responses to subtle environmental changes, such as shifts in electromagnetic fields, ground vibrations, or gas emissions, which are imperceptible to humans. By systematically recording and analysing these behavioural changes in different animal species, researchers aim to develop predictive models that could serve as an early warning system. The integration of animal behaviour data with traditional seismological methods may enhance the accuracy of earthquake forecasts and contribute to disaster preparedness and risk reduction strategies. Despite promising preliminary findings, further research is needed to establish standardized protocols and validate the reliability of these biological indicators in various seismic contexts.
How to cite: Kumar, Y.: A Review: on the Animal abnormal behaviour during the Earthquake or Before Earthquake , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1345, https://doi.org/10.5194/egusphere-egu25-1345, 2025.
Traditional research grade 3-component seismic sensors by their very design are sensitive to both translational ground movement as well as rotational (or tilt) motion. This is most prevalent in the horizontal components of sensors which are most sensitive to tilt of the ground. The outputs of traditional seismometers represent a sum of rotation and displacement information. Most applications processing the data make the assumption that the outputs are proportional to purely displacement although this is not strictly the case in commercial devices.
New technologies are now allowing for accurate and precise discrimination between the two components which make up the vast majority of seismic records.
Stratis is the world’s first integrated seismic sensor offering simultaneous output of both rotational and displacement data in all 3 axis. Stratis offers six concurrent outputs providing Z, N and E ground displacement channels proportional to velocity (Metres/second) and rotation channels in the Z, N and E planes proportional to velocity in rotation (Radians/Second). The provision of the measurement of the six degree of freedom now permits derivation of the Elasticity Tensor from a single sensor.
The Stratis displacement output removes these rotation effects and gives a ‘pure’ displacement measurement. This is unique in the seismic sensor marketplace, providing true displacement data that is uncontaminated by rotational signals. This will therefore allow for higher fidelity seismic measurements, improving our analysis and understanding of earthquake processes.
These six parameters are measured at a single point in the geometric centre of the sensor. Use of multiple separated sensors to derive rotation can only approximate true rotation at the same point as displacement. By integrating these measurements into a single instrument, the installation process is also greatly simplified thereby enabling wider access to rotational seismic data. Naturally, the separation of rotational information from the displacement outputs also gives a pure displacement sensor – something unique for the seismological community.
How to cite: Watkiss, N., Hill, P., Calver, J., Mohr, S., Kerkenyakova, A., Restelli, F., and Lindsey, J.: Guralp Stratis - a Commercial Six Degree of Freedom Seismometer for Academic and Research Applications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16935, https://doi.org/10.5194/egusphere-egu25-16935, 2025.
