Search Results (25)

On 22 July 2020, an Mw 6.4 earthquake occurred in Nima County in the Qiangtang Terrane of the central Tibetan Plateau. This event, caused by normal faulting, remains controversial in terms of its rupture process and causative fault due to the complex tectonics of the region. In this study, we analyzed the coseismic and postseismic deformation using differential interferometric synthetic aperture radar (D-InSAR). The coseismic slip distribution was independently estimated through InSAR inversion and teleseismic waveform analysis, while the afterslip distribution was inferred from postseismic deformation. Coulomb stress failure analysis was conducted to assess the potential seismic hazard. Our results showed a maximum line-of-sight (LOS) coseismic deformation of about 29 cm away from the satellite, with quasi-vertical subsidence peaking at 35 cm. Four distinct deformation zones were observed in the quasi-east–west direction. Coseismic deformation and slip models based on InSAR and teleseismic data indicate that the Nima earthquake ruptured the West Yibu Chaka fault. The seismogenic fault had a strike of 26°, an eastward dip of 43°, and a rake of −87.28°, with rupture patches at depths of 3–13 km and a maximum slip of 1.1 m. Postseismic deformation showed cumulative LOS displacement of up to 0.05 m. Afterslip was concentrated in the up-dip and down-dip areas of the coseismic rupture zone, reaching a maximum of 0.11 m. Afterslip was also observed along the East Yibu Caka fault. Coulomb stress modeling indicates an increased seismic risk between the Yibu Caka fault and the Jiangai Zangbu fault, highlighting the vulnerability of the region to future seismic activity. Full article

The Mw = 7.1 Wushi earthquake is the second-largest digitally recorded earthquake in the Tianshan seismic zone and provides an opportunity to explore the structural characteristics of the Tianshan seismic zone. In this study, we calculated the early (11-month) post-seismic deformation of the Wushi earthquake using Sentine-1 ascending and descending InSAR time series data. We found that the 11-month post-seismic deformation was dominated by afterslip along the up-dip continuation of the coseismic fault. The seismic moment released by the afterslip was Mw = 6.20, with 6.5% of that released by the mainshock. Moreover, we explored four slip models for the Mw = 5.7 aftershock that occurred on 29 January and found that this event primarily ruptured a thrust fault. However, determining the thrust fault type based on the current field investigations and InSAR data remains difficult. Finally, the Coulomb stress changes indicated that both the afterslip and aftershock were promoted by the Wushi earthquake. Full article

The observed scaling properties in the three aftershock sequences of the recent strong earthquakes of magnitudes M_w 6.1, M_w 6.4 and M_w 6.7, which occurred in the Ionian island region on the 26 January 2014 (onshore Cephalonia Island), 17 November 2015 (Lefkada Island) and 25 October 2018 (offshore Zakynthos Island), respectively, are presented. In the analysis, the frequency–magnitude distributions in terms of the Gutenberg–Richter scaling relationship are studied, along with the temporal evolution of the aftershock sequences, as described by the Omori–Utsu formula. The processing of interevent times distribution, based on non-extensive statistical physics, indicates a system in an anomalous equilibrium with long-range interactions and a cross over behavior from anomalous to normal statistical mechanics for greater interevent times. A discussion of this cross over behavior is given for all aftershock sequences in terms of superstatistics. Moreover, the common value of the Tsallis entropic parameter that was obtained suggests that aftershock sequences are systems with very low degrees of freedom. Finally, a scaling of the migration of the aftershock zones as a function of the logarithm of time is discussed regarding the rate strengthening rheology that governs the evolution of the afterslip process. Our results contribute to the understanding of the spatiotemporal evolution of aftershocks using a first principles approach based on non extensive statistical physics suggesting that this view could describe the process within a universal view. Full article

Based on GNSS observations, the co-seismic and post-seismic slip of the 2024 Noto Peninsula earthquake and the spatio-temporal pattern of afterslip are investigated in this paper. The co-seismic slip is mainly distributed in the depth range of 2 to 15 km with the maximum value of 5.94 m. Compared with the co-seismic rupture pattern, a shallow afterslip can be observed after the earthquake, and the afterslip patch is formed northeast of the epicenter. The maximum value of afterslip during the post-seismic 180 days is 1.13 m, which is situated at the longitude of 137.53°, latitude of 37.75°, and epth of 5.43 km. The spatio-temporal evolution of afterslip indicates that the fault activity has continued throughout the post-seismic 180 days, and the coverage and magnitude of afterslip have gradually increased. As time goes on, the fault activity tends to weaken, as evidenced by a decrease in slip rate. The daily images of afterslip demonstrate that the fault activity is particularly strong in the early time period following the earthquake. The maximum value of afterslip in the first week accounts for about 18% of that in the post-seismic 180 days, and the maximum slip rate reaches 0.043 m/day. In addition, the Coulomb stress analysis indicates that afterslip and most aftershocks appear in the positive Coulomb stress region, suggesting that co-seismic Coulomb stress changes may be the driving mechanism of afterslip and aftershocks. Full article

On 21 May 2021, an Mw 6.1 earthquake occurred in Yangbi County, Dali Bai Autonomous Prefecture, Yunnan Province, with the epicenter located in an unmapped blind fault approximately 7 km west of the Weixi-Qiaohou fault (WQF) on the southeastern margin of the Qinghai–Tibetan Plateau. While numerous studies have been conducted to map the coseismic slip distribution by using the Global Navigation Satellite System (GNSS), Interferometric Synthetic Aperture Radar (InSAR) and seismic data as well as their combinations, the understanding of deformation characteristics during the postseismic stage remains limited, mostly due to the long revisiting time interval and large uncertainty of most SAR satellites. In this study, we refined coseismic slip and afterslip distributions with nonlinear inversions for both fault geometry and relaxation time. First, we determined the fault geometry and coseismic slip distribution of this earthquake by joint inversion for coseismic offsets in the line-of-sight (LOS) direction of both Sentinel-1A/B ascending and descending track images and GNSS data. Then, the descending track time series of Sentinel-1 were further fitted using nonlinear least squares to extract the coseismic and postseismic deformations. Finally, we obtained the refined coseismic slip and afterslip distributions and investigated the spatiotemporal evolution of fault slip by comparing the afterslip with aftershocks. The refined coseismic moment magnitude, which was of Mw 6.05, was smaller than Mw 6.1 or larger, which was inferred from our joint inversion and previous studies, indicating a significant reduction in early postseismic deformation. In contrast, the afterslip following the mainshock lasted for about six months and was equivalent to a moment release of an Mw 5.8 earthquake. These findings not only offer a novel approach to extracting postseismic deformation from noisy InSAR time series but also provide valuable insights into fault slip mechanisms associated with the Yangbi earthquake, enhancing our understanding of seismic processes. Full article

On 22 May 2021, an earthquake (98.3° E and 34.59° N) struck Maduo town in Qinghai province, occurring along a relatively obscure secondary fault within the block. We utilized 105 archived Sentinel-1A/B acquisitions to investigate the coseismic deformation and the evolution of postseismic displacements in both the temporal and spatial domains, as well as the associated dynamic mechanisms of the 2021 Maduo earthquake. The interference fringes and coseismic deformation revealed that the primary feature of this event was the rupture along a left-lateral strike-slip fault. The released seismic moment was close to 1.88 $\times {10}^{20} \mathrm{N}·\mathrm{m}$, which is equivalent to an Mw 7.45 event. Simultaneously, the maximum coseismic slip reached approximately 4 m along the fault plane. The evolution of postseismic displacements in both the temporal and spatial domains over 450 days following the mainshock was further analyzed to explore the underlying physical mechanisms. Generally, the patterns of coseismic slip and afterslip were similar, although the postseismic displacements decayed rapidly over time. The modeled afterslip downdip of the coseismic rupture (at depths of 15–40 km) effectively explains the postseismic deformation, with a released moment estimated at 4.57 $\times {10}^{19} \mathrm{N}·\mathrm{m}$ (corresponding to Mw 7.04). Additionally, we found that regions with high coseismic slip tend to exhibit weak seismicity, and that afterslip and aftershocks are likely driven by each other. Finally, we estimated the Coulomb Failure Stress changes ($\Delta \mathrm{C}\mathrm{F}\mathrm{S}$) triggered by both coseismic rupture and aseismic slip resulting from this event. The co- and postseismic $\Delta \mathrm{C}\mathrm{F}\mathrm{S}$ show similar patterns, but the magnitude of the postseismic $\Delta \mathrm{C}\mathrm{F}\mathrm{S}$ is much lower ($\le$0.01 MPa). We found that $\Delta \mathrm{C}\mathrm{F}\mathrm{S}$ notably increased on the Yushu segment of the Garze-Yushu-Xianshuihe Fault (GYXF), as well as the Maqin–Maqu and Tuosuo Lake sections of the East Kunlun Fault (EKF). Therefore, we infer that these fault segments may have a higher potential seismic risk and should be carefully monitored in the future. Full article

Exploring the deformation mechanism of the 2021 Mw 7.4 Maduo Earthquake is crucial for better understanding the seismic hazard of the faults with low strain rates inside the Bayan Har block. This study leverages deformation information derived from Sentient-1 A/B images and GPS data to investigate in detail the co- and postseismic deformation mechanisms using multiple methods. The main results are as follows. First, the postseismic InSAR time series robustly identified the reactivation of the Changmahe fault, indicating the impact of the Maduo event on surrounding active faults. Second, the joint inversion of Interferometric Synthetic Aperture Radar and GPS revealed that (1) there was a complementary and partially overlapping relationship between the coseismic slip and postseismic afterslip of the main rupture; and (2) the Changmahe fault exhibited thrust compression dislocation in the early stage and experienced a sustained compressive effect from afterslip in the one year after the mainshock. Third, modeling the processes of viscoelastic relaxation and poroelastic rebound revealed that the postseismic deformation was probably caused by a combination of afterslip (near-field) and viscoelastic relaxation (near and far field). Fourth, the stress changes driven by the Maduo event revealed that the seismic gaps inside the Maqin-Maqu segment and the Kunlun Pass-Jiangcuo fault will be potential seismic risks in the future. Full article

Based on subdaily kinematic GNSS solutions, the fault slip properties during the very early postseismic phase after the 2021 M 8.2 Chignik earthquake are investigated in this paper. The very early postseismic deformations captured by near-field GNSS sites can be well depicted by the power model. The comparison of afterslip determined by daily and subdaily GNSS solutions suggests that neglecting very early afterslip can result in the underestimation of postseismic slip. Compared with coseismic slip, the cumulative afterslip of the first 24 h is mainly focused in the southeast of the hypocenter, and the shallow updip afterslip appears after this earthquake. The spatio-temporal evolution of the afterslip reveals that the patch of afterslip is immediately generated after the earthquake, and then the postseismic slip gradually grows along the afterslip patch. The magnitude of the afterslip patch varies remarkably within the 24 h following the earthquake, especially in the first several hours. Meanwhile, the spatio-temporal patterns of aftershocks and afterslip exhibit strong similarity during the first 24 h, suggesting that very early afterslip may be a possible driving factor of aftershocks. Moreover, most of the afterslip patches and aftershocks occurring immediately after this earthquake are situated in the area covered by positive Coulomb Stress Change (CSC), which implies that the immediate afterslip and aftershock activities can be influenced by the coseismic CSC. The following afterslip process further releases coseismic CSC and then influences the spatio-temporal variations of aftershock activities. Thus, the afterslip may be a possible triggering mechanism of very early aftershocks for this earthquake, alongside the effects of the CSC generated by coseismic rupture. Full article

On 1 December 2016, an Mw 6.2 earthquake characterized by normal faulting occurred in the highlands of the central Andes in southern Peru, marking the region’s largest shallow event. The occurrence of the earthquake provides a significant chance to gain insight into the regional tectonic deformation and the seismogenic mechanism of the shallow normal-faulting earthquake, as well as the regional potential seismic risk. Here, we first utilize Sentinel-1A interferometric synthetic aperture radar (InSAR) data to extract the coseismic and postseismic deformation associated with this earthquake and then determine the detailed coseismic slip and postseismic afterslip distribution of this event. Coseismic modeling results indicate that the coseismic rupture is mainly characterized by normal faulting with some dextral strike-slip components. Most coseismic slip is confined to a depth range of 2–12 km, indicating an obvious slip deficit area in the shallow fault part. Further postseismic modeling reveals that the majority of afterslip is concentrated at depths of 0 to 5.4 km. The relatively shallow postseismic afterslip makes up for the coseismic slip deficit area to some extent. Through a joint analysis of the inversions, seismic data, and regional geology and geomorphology, we infer that the occurrence of this 2016 normal-faulting event is a result of regional gravitational collapse. In addition, we investigate the relationship between the 2016 earthquake and great historical earthquakes near the subduction zone of the central Andes and find that the 2016 event is likely promoted in advance by these events through our calculations of the coseismic and postseismic Coulomb stress changes. Finally, we should pay more attention to the nearby Falla Huaytacucho-Condoroma fault and the western segment of the Vilcanota Fault because of their relatively high stress loading. Full article

The largest earthquake (Mw 6.4) in northwestern Croatia ruptured the faults near the city of Petrinja on 29 December 2020, at 11:19 UTC. The epicenter was located ~3 km southwest of Petrinja, ~40 km southeast of Zagreb, the capital of the Republic of Croatia. Here we investigated the geometric and kinematic properties of the 2020 Mw 6.4 Petrinja earthquake using a joint inversion of ascending and descending interferograms from three tracks of Sentinel-1 Single-Look Complex (SLC) images. The coseismic and early postseismic surface displacements associated with the Petrinja earthquake were imaged using standard DInSAR and SBAS time-series InSAR methods, respectively. The distributed slip model was inverted based on the ground surface displacements with maximum slip patch in 5 km depth. The early postseismic deformation occurred on the northwestern extent of coseismic slip, and it cannot be well modeled by the coseismic model. We thus suggested that the postseismic deformation was caused by a combined effect of the postseismic afterslips and aftershocks occurring in this area. Based on the inverted slip model, we calculated the Coulomb stress change in the region, and found a good correlation between positive Coulomb failure stress ∆CFS and the distribution of aftershocks. Based on these results, we identified which faults are more active, and then better estimated the seismic hazards in the region. Full article

Spatiotemporal distribution of early afterslip is essential for seismic hazard evaluation and determination of fault friction properties. In this study, we used early post-seismic COSMO-SkyMed (19 February 2014–08 April 2014) and long-term Sentinel-1 (16 October 2014–17 June 2020) observations from multiple platforms over different periods to create a rate decay model driven by post-seismic afterslip. The combined observations provide full coverage of the post-seismic deformation following the 2014 Yutian Mw 6.9 earthquake that occurred at the southwestern end of the Altyn Tagh Fault. The observation and modeling results showed that post-seismic deformation was characterized by left-lateral strike-slip movement with minor normal slip, which was consistent with that of co-seismic rupture. The maximum early afterslip (7–55 days) was as large as approximately 0.09 m with a depth of 7 km in the west of co-seismic rupture, and the maximum long-term afterslip was about 0.24 m. The simulated post-seismic deformation caused by poroelastic rebound and viscoelastic relaxation suggests that the afterslip mechanism controls the post-seismic deformation. The coupling pattern of the aftershock and afterslip indicates that the aftershock was mainly caused by the afterslip. The post-seismic spatiotemporal features of the 2014 Yutian earthquake have significant implications for analyzing seismic hazards at the southwestern end of the Altyn Tagh Fault. Full article

On 22 July 2020, an Mw 6.3 earthquake occurred in Nima County, central Qinghai-Tibet Plateau, China. We used the synthetic aperture radar interferometry (InSAR) technique with Sentinel-1 images to retrieve the line of sight (LOS) coseismic deformation fields which indicate that the maximum surface displacement reached ~30 cm. We then processed a series of interferograms spanning one year after the Nima earthquake with the Small Baseline Subset Interferometric SAR (SBAS-InSAR) technique. The maximum cumulative postseismic LOS surface displacement reached ~8 cm and approximately followed a logarithmic function over time. The inversion of the fault geometry and co- and afterslip distribution shows that the epicenter location was (33.18°N, 86.88°E) at a depth of 7.4 km, and the causative fault had an N29.1°E strike and 50.2° dip. The most coseismic slip was concentrated at depths between 3 to 12 km with a peak value of 2.0 m at 7.4 km, whilst most afterslips were concentrated at depths between 0 to 12 km with a peak value of 0.2 m at 5 km. The postseismic moment energy was about 5.04 × 10¹⁷ N∙m 308 days after the event, which was approximately 13.8% of the coseismic moment energy. By analyzing the contribution of afterslip and poroelastic rebound to postseismic deformation, it was concluded that afterslip was the main early postseismic deformation mechanism. Future attention should be paid to the northern segment of the West Yibug Caka fault and East Yibug Caka fault. Full article

The 27 September 2021 damaging mainshock (Mw6.0) close to Arkalochori village is the strongest earthquake that was recorded during the instrumental period of seismicity in Central Crete (Greece). The mainshock was preceded by a significant number of foreshocks that lasted nearly four months. Maximum ground subsidence of about 18 cm was estimated from InSAR processing. The aftershock sequence is located in an almost NE-SW direction and divided into two main clusters, the southern and the northern ones. The foreshock activity, the deformation area, and the strongest aftershocks are located within the southern cluster. Based on body-wave travel times, a 3-D velocity model was developed, while using combined space and ground-based geodetic techniques, the co-seismic ground deformation is presented. Moreover, we examined the co-seismic static stress changes with respect to the aftershocks’ spatial distribution during the major events of the foreshocks, the Mw = 6.0 main event as well as the largest aftershock. Both the foreshock and the aftershock sequences obey the scaling law for the frequency-magnitude distribution as derived from the framework of non-extensive statistical physics (NESP). The aftershock production rate decays according to the modified Omori scaling law, exhibiting various Omori regimes due to the generation of secondary aftershock sequences. The analysis of the inter-event time distribution, based on NESP, further indicates asymptotic power-law scaling and long-range correlations among the events. The spatiotemporal evolution of the aftershock sequence indicates triggering by co-seismic stress transfer, while its slow migration towards the outer edges of the area of the aftershocks, related to the logarithm of time, further indicates a possible afterslip. Full article

We use ALOS-2 and Sentinel-1 data spanning 2015–2020 to obtain the post-seismic deformation of the 2015 Mw 7.8 Nepal earthquake. ALOS-2 observations reveal that the post-seismic deformation was mainly distributed in four areas. A large-scale uplift deformation occurred in the northern subsidence area of the co-seismic deformation field, with a maximum uplift of ~80 mm within 4.5 yr after the mainshock. While in the southern coseismic uplift area, the direction of the post-seismic deformation is generally opposite to the co-seismic deformation. Additionally, two notable deformation areas are located in the region around 29° N, and near the MFT, respectively. Sentinel-1 observations reveal post-seismic uplift deformation on the north side of the co-seismic deformation field with an average rate of ~20 mm/yr in line-of-stght. The kinematic afterslip constrained by InSAR data shows that the frictional slip is distributed in both updip and downdip areas. The maximum cumulative afterslip is 0.35 m in downdip areas, and 0.2 m in the updip areas, constrained by the ALOS measurements. The stress-driven afterslip model shows that the afterslip is distributed in the downdip area with a maximum slip of 0.3 m during the first year after the earthquake. Within the 4.5 yr after the mainshock, the estimated moment released by afterslip is ~1.5174 × 10²⁰ Nm,about 21.2% of that released by the main earthquake. Full article

The 21 May 2021 Maduo earthquake was the largest event to occur on a secondary fault in the interior of the active Bayanhar block on the north-central Tibetan plateau in the last twenty years. A detailed kinematic study of the Maduo earthquake helps us to better understand the seismogenic environments of the secondary faults within the block, and its relationship with the block-bounding faults. In this study, firstly, SAR images are used to obtain the coseismic deformation fields. Secondly, we use a strain model-based method and steepest descent method (SDM) to resolve the three-dimensional displacement components and to invert the coseismic slip distribution constrained by coseismic displacement fields, respectively. The three-dimensional displacement fields reveal a dominant left-lateral strike-slip motion, local horizontal displacement variations and widely distributed near-fault subsidence/uplift deformation. We prefer a five-segment fault slip model, with well constrained fault geometry featuring different dip angles and striking, constrained by InSAR observations. The peak coseismic slip is estimated to be ~5 m near longitude 98.9°E at a depth of ~4–7 km. Overall, the distribution of the coseismic slip on the fault is highly correlated to the measured surface displacement offsets along the entire rupture. We observe the moderate shallow slip deficit and limited afterslip deformation following the Maduo earthquake, it may indicate the effects of off-fault deformation during the earthquake and stable interseismic creep on the fault. The occurrence of the Maduo earthquake on a subsidiary fault updates the importance and the traditional estimate of the seismic hazards for the Kunlun fault. Full article