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Tectonic map of the Korean Peninsula including the study area of South Korea. The dotted line inside the Korean peninsula depicts the tectonic division of Korea. The short name of tectonic division from north to south: Pyongnam Basin (PB), Imjingang Belt (IB), Kyonggi Massif (KM), Taebaeksan Basin (TB), Okchon Basin (OB), Yongnam Massif (YM), and Yangsan Fault (YF). The numerical numbers (1 to 9) are showing the faults like this: (1) Ongwhajae Fault, (2) New-Okchun I Fault (3) New-Okchun II Fault (4) Taebk-seogchun Fault (5) Yangsan Fault (6) Ulsan Fault Zone (7) Hupo Fault (8) Uleung Fault and (9) Tsushima Fault. The fault plane solutions with different colours are showing the list of earthquakes extracted from EMSC website and listed in Table 1
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South Korea forms the Korean Peninsula and is considered to be tectonically more stable than the other regions of Eastern Asia. Global Navigation Satellite System (GNSS) sites installed in the country contribute to geoscientific studies on contemporary deformation, strain pattern and current kinematics of tectonic blocks. In the current study, we u...
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Abstract Postseismic deformations continue to occur for a long period after major earthquakes. Temporal changes in postseismic deformations can be approximated using simple functions. Since the 2011 Tohoku-Oki earthquake, operating global navigation satellite system stations have been continuously accumulating a remarkable amount of relevant data....
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... The time series obtained from GNSS have been used to investigate the hydrological loading, glacial isostatic adjustment, and pre-seismic, coseismic as well as postseismic deformation due to earthquakes in different regions of the world (Mukul et al. 2014;Ansari et al. 2017;Mukul et al. 2018;Ansari andPark 2019, 2022;Ansari and Bae 2020;Qi et al. 2023). Although a significant number of studies related to the geodynamic motion of PKB and the surrounding region have been done based on high-precision positioning, however, there is significant space for exploring the current and past neotectonics activities, which will help to understand the complicated geological structure of PKB and surrounding region in Southern Poland. ...
The dynamic geological features of the Pieniny Klippen Belt (PKB) in southern Poland are nowadays a focal point of researchers as it is recognised as an active zone of crustal discontinuity. In the present study, we employed long-term analysis of ground-based global navigation satellite system (GNSS) measurements (from 2004 to 2020) to probe the crustal deformation, strain rates, and rotational rates in the PKB unit and the surrounding region, i.e., Magura Nappe (MN) and Podhale Flysch (PF) units. Measured velocities from GNSS observables are modelled by the auto-regressive integrated moving average (ARIMA) method to comprehend the long-term tectonic deformation. Our results showed that the ARIMA-modelled velocity varied from ~0.15 mm/yr to ~8.86 mm/yr, indicating about 8.71 mm/yr difference along all units. Such differences suggest that crustal slip along the active thrusts and folds is the major factor causing regional deformation. The strain rates in PKB are also varying from the western to the eastern part. The rotational rates in PKB show a counterclockwise (CCW) pattern similar to the strain rates. These patterns suggesting that the PKB was rotated in the CCW direction with a large angle during the Miocene period. Finally, we analysed the seismicity for a period from 2004 to 2020 by using Bayesian moment tensor inversion and multivariate Bayesian inversion. The Bayesian inversion was applied based on bootstrapping chain analysis to figure out the earthquake mechanism using moment tensor inversion for the mainshock that occurred in Poland on 20 July 2018. The inversion results for the 2018 earthquake resolved a thrusting mechanism with nodal plane-1 having a strike of 346°, dip of 32° and rake of 92° and a nodal plane-2 with a strike of 163°, dip of 58° and rake of 89°. Since the seismicity in the Poland region has experienced less significant earthquakes in the last century, it is reasonable to attribute this lower seismic activity to the correspondingly low slip rates discerned through geodetic monitoring efforts.
... The TO earthquake, with a magnitude of 9.1 Mw, close to the northeastern coastal area of Honshu, Japan, struck on March 11, 2011 (Koketsu et al. 2011;Ansari and Bae 2020). The earthquake was generated due to the faulting of shallow thrust on the subduction zone boundary plate between the Pacific Plate and the North American plate. ...
The real shape of the earth is approximated closer to an ellipsoidal curvature other than a homogeneous half-space. Therefore, the use of the dislocation theory of homogeneous half-space for the farthest epicentral distance brings an error. The study investigates the far-filed effect of dislocation modeling of homogeneous half-space due to the ellipsoidal curvature of the Earth. The co-seismic displacement in South Korea is used for the dislocation modeling of the Tohoku-Oki (TO) Japan earthquake as one of the numerical examples. The obtained slip by using geodetic measurements in South Korea is compared with the measured slip of Japan's geodetic measurements. Analysis of modeled results showed that the obtained result with accuracy is lower than around 20%. Therefore, the study concludes that it can be an error in the use of the dislocation modeling theory of homogeneous half-space for the farthest epicentral distance.
... Such kind of analysis can figure out the seismic activities from an unknown active fault to reduce and minimize the impact of loss and damage in the socio-economic and public properties. Later, a robust statistical technique can be conducted to present a unique empirical model for earthquake clustering after including the epicentral depth as a specific variable based on the nearest-neighborhood distance method (Ansari and Bae 2020). The quiescent process of seismic activities in the spatio-temporal can be assumed as the dependent activities and described by scaling relationships with slowly decaying correlations or by scale-invariant relationships (Cho 2015;Ansari et al. 2017;Hayat et al. 2019). ...
... The scaling relationships can be analyzed in the seismic statistical scope to support the understanding of seismic properties. Seismic statistical studies have been widely studied over recent decades (Vijay and Nanda 2019;Ansari and Bae 2020;Nievas et al. 2020;Pasari et al. 2021;Ansari et al. 2022). Vijay and Nanda (2019) decluttered the hypocenters using the nearest neighborhood in the homogeneous time domain. ...
... Vijay and Nanda (2019) decluttered the hypocenters using the nearest neighborhood in the homogeneous time domain. Ansari and Bae (2020) investigated the seismic activities in the southern part of Japan and figured out the earthquake cluster in the spatial-time-magnitude domain. Nievas et al. (2020) Pasari et al. (2021) analyzed the earthquake activities in Java to figure out the nowcasting earthquake condition and the current state of the earthquake's potential risk. ...
The Lombok island is a part of the Sunda Arc, tectonically controlled by the subduction system of the Indo-Australian Plate in the southern part while the Flores thrust in the northern part. A sequence of major earthquakes consisting of Mw 5.9-6.9 struck in July-August 2018 and generated massive loss and damage in the Lombok and neighboring regions. In the current study, we analyzed the seismicity clustering of this series of shallow earthquakes including the seismic data from 2009 to 2021. We applied the logarithmic transformation of the nearest-neighborhood distance (log10η) for the seismic data within the domain of space (magnitude), time (magnitude), and depth (magnitude). The combined relationship between these factors has been estimated, which showed that the seismicity in Lombok island was prominently unimodal and indicates the existence of a single type of statistically distribute earthquake. These relationships also point out a contribution of space, time, and depth around 32.410%, 54.447%, and 13.143% respectively. Later we utilized the Welch power spectrum analysis for log10η and analyzed the performance and complexity of the seismicity. The analysis clearly showed the highest peak that was corresponding to the frequency of series earthquake distribution from 25 July to 8 August 2018.
... Average relaxation completeness (%) 85.3 ± 13.1 92.7 ± 7.0 Ansari and Bae [35] showed that the angular velocities of the northern and southern blocks of South Korea were different through the analysis of the block-wise rotation for each block before and after the 2011 Tohoku-Oki earthquake. They separated the northern and southern blocks by fault lines that crossed the middle of South Korea diagonally. ...
We investigated decaying post-seismic deformation observed on the Korean Peninsula associated with the 2011 Mw 9.0 Tohoku-Oki earthquake using Global Navigation Satellite System (GNSS). The GNSS velocity vectors were estimated in five periods from 2005 to 2019. A co-seismic offset of the Korean Peninsula caused by the 2011 earthquake was inversely proportional to epicentral distances. According to the temporal variations of two components (magnitude and direction) of the GNSS velocity vector with the epicentral distance, the difference between the eastern and western regions for the two components becomes smaller over time. For approximately nine years after the 2011 event, the direction for the crustal movement in South Korea showed a recovery pattern returning to the pre-earthquake motion. In addition, the recovery patterns of the crustal movement were observed differently with the regional geologic structure (e.g., the crustal thickness) and each period. Our estimates of the decay in post-seismic deformation of the Korean Peninsula suggest that post-seismic relaxation will be complete within 5–20 years after the 2011 earthquake. The results suggest that the crustal movement on the Korean Peninsula is gradually recovering to its pre-earthquake motion.
... Average repeatability of daily solutions was around 1.5 mm in horizontal coordinate components and up to 6 mm in vertical component. Each coordinate time series (example at Figure 6) was checked for searching of jumps (usually as a result of near earthquake), co-seismic effect (which introduce exponential behavior of time seriesas in Ansari and Bae (2020) [20]) and yearly periodicities (usually as result of temperature deformation of the building where the station is located - Figure 5a). Due to using double differenced processing with good daily repeatability, we don't use the commonmode component filtering technique [21] for improving signal-to-noise ratio of the velocities. ...
... Accuracy of determined velocities from time series longer than 2 years will be better than 1 mm/y. Based on results in Henrion et al. (2020) [18] or Ansari and Bae (2020) [20], we can assume that the longer time series will allow more accurate determination of horizontal velocities as well as determination of the vertical component of velocity at individual stations. Therefore, it is believed that data from PPGNet will provide valuable information on the Aitolo-Akarnania area internal deformation and relative motions at the main faults in the area and eventually will help us understand how this deformation is linked to the major active structures in the broader area. ...
Aitolo-Akarnania prefecture, western Greece, is an area with strong earthquakes and large active fault systems. The most prominent are the Katouna sinistral strike slip fault and the Trichonis Lake normal fault system. Their proximity to large cities, and the lack of detailed information on their seismogenic potential, calls for multiparametric research. Since 2013, the area’s crustal deformation has been monitored by a dense GNSS Network (PPGNet), consisting of five stations, equipped with Leica and Septentrio receivers. The objective of this network is to define the rate of deformation across these two main fault systems. Data is recorded using two sampling frequencies, 1 Hz and 10Hz, producing hourly and daily files. Daily data is processed using Bernese GNSS Processing Software using final orbits of International GNSS Service. Double-difference solution is computed using phase measurements from the PPGNet network complemented by four stations from Athens’ National Observatory GNSS network and six stations from METRICA network. First results show a NNE movement at PVOG station of 12 mm/y and a similar movement at RETS station of about 9 mm/y. This means that the Trichonis Lake normal fault system, located between these two stations, depicts a slip rate of 3 mm/y. KTCH and RGNI stations move eastwards at a velocity of about 5 mm/y due to the Katouna-Stamna fault system. Data from PPGNet has provided important results on crustal deformation in the area, i.e. slip rates have been attributed to specific fault systems. The comparison and links of these data with broader geodynamic models is now possible and we expect, in a later phase that will provide a more detailed image of the associated seismic hazard for Aitolo-Akarnania. Doi: 10.28991/cej-2021-03091633 Full Text: PDF
Distributions of the density contrast and velocity of seismic waves into the crust and upper mantle in the Yellow Sea region are considered. The rheological section of the tectonosphere of the Yellow Sea consists of two rigid (crystal crust and lower layer of the lithosphere) and two viscous (subcrustal and asthenospheric) layers. The crust of the Yellow Sea is shattered and decreased in density. Processes of stretching and shifting are depicted as crustal shift duplexes as a result of which the Liaodong and Korean peninsulas were torn off from the continent and moved, respectively, in the northeast and east directions. In the central region of the Yellow Sea, manifestations of a central type mantle structure, screened by the lower layer of a lithosphere, have been revealed. This structure was disturbed by the neotectonic rifting processes.
A magnitude Mw 7.8 earthquake occurred on 25 April 2015 (referred as Gorkha earthquake). We have analyzed the spatial variation of b-value and two-dimensional strain () within Nepal Himalaya before and after the Gorkha earthquake. We have used continuous Global Navigation Satellite System (GNSS) data from 30 stations in the Nepal region for geodetic strain estimation and earthquake data for b-value estimation. The GNSS data were processed using double differencing technique for the accurate position of each station. The precise velocity vectors show a general azimuth of north east for all the stations and have been used to derive two-dimensional strain. Between epicenters of Gorkha (25 April 2015) and Dolakha earthquakes (12 May 2015), we observed high co-seismic horizontal displacements (0.2m to 2m). In the Pre-seismic deformation study, maximum strain accumulation (56.40×10-9) and low b-value (0.79 to 0.89) was observed in and around the Western Nepal region, which may be responsible for the 2015 Gorkha earthquake. The potential seismic zones were identified by GIS based integration of geodetic strain and b-value map and superimposition using weighted overlay method. The Maximum strain and low b-value are now observed in the eastern part of Nepal. Hence, the spatial disposition of elastic energy has changed after the two major earthquakes and continuous seismic hazard assessment is required in the eastern Nepal.
This article reviews geometric model parameters (length, width, depth, dip angle, and strike) of the Main Himalayan Thrust (MHT) in Eastern, Western, Central, and other portions of the Himalaya. It is expected that when a fieldworker works on the Main Frontal Thrust (MFT), these compiled data will be useful in generating models involving subsurface and surface data sets.
This analysis is an extension of the studies based on the space-time-magnitude (STM) domain nearest-neighborhood distances (ƞ) obtained from two successive earthquakes. We included epicentral depth as a parameter, and established a new analytical solution for seismicity clustering in the space-time-depth-magnitude (STDM) domain. The proposed technique was applied to SW Japan seismic observation data for 2011–2018, and revealed that the temporal, spatial, and epicentral (T, R, E) components of the joint distribution for ƞ were prominently bimodal, indicating the presence of two, statistically distinct, earthquake populations. We used the Lomb–Scargle periodogram (LSP) to generate a power spectrum preceding the Kumamoto earthquake, and detected the periodic component of unequally spaced points for log 10 ƞ (logarithmic scale of ƞ). The LSP showed a dominant peak corresponding to the time period between foreshocks and aftershocks, due to the highest number of recorded ƞ observations. The technique presented in this paper can be applied globally for any time-period and any seismotectonic zone preceding large earthquakes of interest.
