Coulomb Failure Stress Change Research Articles

Fault Instability and Its Relation to Static Coulomb Failure Stress Change in the 2016 Mw 6.5 Pidie Jaya Earthquake, Aceh, Indonesia

Herein, we applied the fault instability criterion and integrated it with the static Coulomb stress change (ΔCFS) to infer the mechanism of the 2016 Mw 6.5 Pidie Jaya earthquake and its aftershock distribution. Several possible causative faults have been proposed; however, the existence of a nearby occurrence, the 1967 mb 6.1 event, created obscurity. Hence, we applied the fault instability analysis to the Pidie Jaya earthquake 1) to corroborate the Pidie Jaya causative fault analysis and 2) to analyze the correlation between ΔCFS distribution imparted by the mainshock and the fault instability of the reactivated fault planes derived from the focal solution of the Pidie Jaya aftershocks. We performed the fault instability analysis for two possible source faults: the Samalanga-Sipopok Fault and the newly inferred Panteraja Fault. Although the maximum instability value of the Samalanga-Sipopok Fault is higher, the dip value of the Panteraja Fault coincides with its optimum instability. Therefore, we concluded that Panteraja was the causative fault plane. Furthermore, a link between the 1967 mb 6.1 event and the 2016 Mw 6.5 earthquake is discussed. To analyze the correlation between the fault instability and the ΔCFS, we resolved the ΔCFS of the Pidie Jaya mainshock on its aftershock planes and compared the ΔCFS results with the fault instability calculation on each aftershock plane. We discussed the possibility of conjugate failure as shown by the aftershock fault instability. Related to the ΔCFS and fault instability comparison, we found that not all the aftershocks have positive ΔCFSs, but their instability value is high. Thus, we suggest that the fault plane instability plays a role in events that do not occur in positive ΔCFS areas. Apart from these, we also showed that the off-Great Sumatran Fault (Panteraja and Samalanga-Sipopok Faults) are unstable in the Sumatra regional stress setting, thereby making it more susceptible to slip movement.

Tectonic tremors in the Northern Mexican subduction zone remotely triggered by the 2017 Mw8.2 Tehuantepec earthquake

Surface waves from the 2017 Mw8.2 Tehuantepec earthquake remotely triggered tectonic tremors in the Jalisco region, approximately 1000 km WNW in the northern Mexican subduction zone. This is the first observation of tremor triggering in this region and one of the largest known examples of a triggered tremor in the world. Although prior studies have found tectonic tremors triggered by teleseismic waves in subduction zones and plate boundaries, further investigation of tremor triggering is crucially important for understanding the causative mechanism. We calculate the stress and strain changes across the three-dimensional plate interface attributable to seismic waves from the earthquake by full wavefield simulation. The maximum magnitude of the dynamic strain tensor eigenvalues on the plate interface, where tremors likely occur, is approximately 10–6. The subducting slab geometry effectively amplifies triggering waves. The triggering Coulomb failure stress changes resolved for a thrust fault plane consistent with the geometry are estimated to be approximately 10–40 kPa. The relationship between the triggering stress and triggered tremor amplitude may indicate that the aσ of the rate–state-dependent friction law is 10–100 kPa.

Shallow slip of blind fault associated with the 2019Ms 6.0 Changning earthquake in fold-and-thrust belt in salt mines of Southeast Sichuan, China

SUMMARYAn earthquake with a magnitude of Ms 6.0 and shallow focal depth of ∼4 km struck the Changning county, Sichuan province, China on 2019 June 17. The hypocentre is located in the fold-and-thrust belt with plentiful shale gas and salt mine resources. One hypothesis is that the shallow fault could be affected by the artificial pressure water injection including the disposal of wastewater, fracking shale gas extraction and salt mining in Changning area. In this study, SAR (Synthetic Aperture Radar) images, historical earthquakes, aftershocks and seismic reflection data were collected to jointly investigate the characteristics of the 2019 Changning earthquake. The source model inferred from the InSAR coseismic deformation observation reveals that the 2019 Changning earthquake is attributed to a blind fault dipping to southwest with dominant thrust and sinistral strike slip. Moreover, a small shallow fault developing within the Changning anticline was triggered by the main shock, which contributed to the surface displacements as observed in the north of the epicentre. The estimated maximum slip of 0.49 m is located at the depth of ∼1.9 km, ∼9 km northwest of the epicentre. The Coulomb failure stress change caused by the previous two large earthquakes, which occurred in the hydraulic fracturing area, suggesting that they have little effect on the initial rupture of the 2019 Changning earthquake. Despite this, they have a positive triggering effect on the fault rupture in the northwest of the seismogenic fault. In addition, the analysis on the relation between the positive Coulomb failure stress change and the aftershocks suggests that the aftershocks may have different motion patterns from the main shock. The analysis also shows the earthquakes occurrence in the seismogenic zone may be affected by the high pore pressure due to the long-term injection of salt mining for more than three decades.

Source Model of the 2014 Mw 6.9 Yutian Earthquake at the Southwestern End of the Altyn Tagh Fault in Tibet Estimated from Satellite Images

AbstractMultiple fault segments ruptured during the 2014 Yutian earthquake, but the detailed source parameters and the mechanism of rupture complexity remain poorly understood. Here, we use high-resolution TanDEM-X satellite data and Satellite Pour l’Observation de la Terre-6/7 images to map the coseismic ground deformation field of the event. We find that the majority of coseismic slip occurred in the upper 10 km with the maximum left-lateral fault slip of ∼2.5 m at ∼6 km depth. The fault ruptured across a large 4.5 km extensional stepover from one left-lateral fault segment to another, with some right-lateral relay faulting in between. We find that the earthquake was followed by shallow afterslip concentrating at the southwestern end of coseismic rupture, in an area of many aftershocks and positive Coulomb failure stress change. Our findings demonstrate the power of satellite remote sensing technology in constraining source geometry and slip model of complex earthquakes when ground measurements are limited.

Stress evolution on active faults in the southwestern Yunnan region, southeastern Tibetan Plateau, and implications for seismic hazard

Southwestern Yunnan is expressed as a seismically active region bordering the southeastern Tibetan Plateau. However, the recent seismicity in this region has been relatively quiet. Considering some highly-populated cities nearby and the historical record in this region, understanding the stress changes on the main active faults is crucial for seismic hazard analysis. In this study, we calculated the co- and post-seismic Coulomb failure stress change (ΔCFS) on these faults caused by historical earthquakes in and around the region. Then, by integrating the inter-seismic tectonic loading estimated using a geodynamic model and GPS data, we analyzed the total stress change on all of these faults. The results reveal that the ΔCFS patterns caused by events on different segments of the Sagaing Fault vary; the combined ΔCFS increased on the middle segment of the Longling-Lancang Fault, the Heihe Fault, and the Nantinghe Fault, among which the maximum change reached 3.5 kPa. The great 1950 Assam earthquake in the eastern Himalayan syntax increased the ΔCFS on almost all faults, and the maximum change reached 20 kPa. More importantly, the ΔCFS caused by earthquakes in the southwestern Yunnan region was significantly larger than that caused by earthquakes in the surrounding region because of the geographical proximity. The inter-seismic tectonic stress loading rate reached 2 kPa.yr−1. A significant total stress build-up occurred on five segments distributed among four faults, namely, the Nantinghe Fault, the Longling-Lancang Fault, the Heihe Fault, and the Menglian Fault, making them possible candidates for the next major earthquake in this region.

Combined approach of poroelastic and earthquake nucleation applied to the reservoir-induced seismic activity in the Val d’Agri area, Italy

In this work, an approach is developed to study the seismicity associated with the impoundment and level changes of a water reservoir (reservoir induced seismicity – RIS). The proposed methodology features a combination of a semi-analytical poroelastic model with an earthquake nucleation approach based on rate-and-state frictional law. The combined approach was applied to the case of the Pertusillo Lake, located in the Val d’Agri area (Italy), whose large seasonal water level changes are believed to induce protracted micro-seismicity (local magnitude M L < 3). Results show that the lake impoundment in 1962 could have produced up to 0.5 bar (1 bar = 100 kPa) changes in Coulomb failure stress (Δ CFS ), while the seasonal water level variation is responsible for variation up to 0.05 bar. Modeling results of the seismicity rates in 2001 − 2014 show that the observed earthquakes are well correlated with the modeled Δ CFS . Finally, the reason that the seismicity is only observed at southwest of the Pertusillo Lake is provided, which is likely attributed to different rock lithologies and depletion caused by significant hydrocarbon exploitation in the northeastern sector of the lake.

The 2017 Mw 5.5 Pohang Earthquake, South Korea, and Poroelastic Stress Changes Associated With Fluid Injection

AbstractThe 2017 Mw 5.5 Pohang earthquake in South Korea, the first reported and largest magnitude‐induced earthquake, occurred near the enhanced geothermal power plant in Pohang on 15 November 2017. We compute the spatiotemporal changes in poroelastic stresses perturbed by injected fluid under various conditions to better understand the occurrences of the Pohang earthquake and the small‐magnitude earthquakes preceding it. Space‐time variation of the earthquakes that occurred before the Pohang earthquake correlates significantly with fluid injection history between January 2016 and September 2017. We attribute the timing in earthquake occurrence to slow fluid diffusion, making hydraulic diffusivity of bedrock the critical model parameter for representing this slow process. In this context, the delay between the injection and the Pohang earthquake requires diffusivity estimates within a range of 1 × 10−4–5 × 10−4 m2/s for damaged granodiorite at 4–5 km, corresponding to the depth range between the well and the focal depth. According to these estimates, the pore pressure and thus the Coulomb failure stress changes are further enhanced by each injection with minimum stress dissipation. We find fluid injection can result in a change of the Coulomb stress of up to 0.4–1.1 bar, exceeding those associated with the 2016 Mw 5.5 Gyeongju earthquake by 2 orders of magnitude.

Surface Deformation and Induced Seismicity Due to Fluid Injection and Oil and Gas Extraction in Western Texas

AbstractTexas is experiencing increasing seismicity, likely related to the oil and gas production process. We used satellite InSAR (Interferometric Synthetic Aperture Radar) to monitor surface deformation at three study sites in western Texas with similar geologic characteristics. The deformation data were compared to earthquake distribution, groundwater changes, volumes of produced and injected fluid, and calculated pore pressure change and Coulomb failure stress change to assess causes of deformation and seismicity. Site 1 experienced surface uplift due to fluid injection but no increase in seismicity. The average media properties were estimated based on the deformation using a poroelastic model. Site 2 experienced subtle surface subsidence and elevated seismicity. Subsidence here might reflect groundwater withdrawal. Simulated pore pressure changes using MODFLOW suggest the earthquakes are likely induced by fluid injection. Site 3 experienced significant surface subsidence and seismicity. InSAR time series, water level data, and oil/gas extraction history suggest that subsidence in the northern part of this site reflects oil/gas extraction, while subsidence in the southern part is mainly due to groundwater withdrawal. An Okada tensile model was used to derive the equivalent source strength causing the subsidence, then Coulomb failure stress changes associated with this source were calculated. We found that pore pressure change (simulated using MODFLOW) due to fluid injection is likely the main contributor to elevated seismicity at this site. Variations in oil/gas production activity, seismicity, and surface deformation between our three sites suggest the importance of local rock structure and media properties in determining susceptibility to induced seismicity.

Significance of Nonplanar Rupture of the Mainshock and Optimal Faulting in Forecasting Aftershocks of the 2015 Mw 7.8 Gorkha Earthquake

Abstract We computed the stress-change tensor around the 2015 Mw 7.8 Gorkha earthquake with two different rupture models: a simple uniformly dipping model and a complex ramp-flat-ramp-flat fault-slip model. In general, the Coulomb failure stress changes (ΔCFS) computed on the optimally orientated faults based on a ramp-flat-ramp-flat fault-slip model showed the best spatial correlation with the aftershock seismicity. This close relationship was further verified by the focal mechanism solutions of 17 intermediate-size aftershocks. The ΔCFS calculated from the known focal mechanisms of most events were close to the values computed from the optimal fault planes and slip directions using the complex slip model with a nonplanar rupture along the Main Himalaya thrust. We further computed the stress accumulation in the seismic gap regions located around the Gorkha earthquake and between the 1505 and 1934 Mw 8+ historical earthquakes. We found a significant increase of the Coulomb failure stress by 0.2–0.5 MPa caused by the three earthquakes, especially at the shallow ramp of the seismic gap, which indicates an enhanced seismic risk around the Kathmandu area.

Geodetic Model of the 2018 Mw 7.2 Pinotepa, Mexico, Earthquake Inferred from InSAR and GPS Data

ABSTRACTInvestigating the interaction between slow-slip events (SSEs) and large earthquakes provides insights into earthquake-triggering mechanisms and is crucial for earthquake hazard assessment. In this study, we used Sentinel-1 Interferometric Synthetic Aperture Radar and Global Positioning System (GPS) data to estimate the source parameters of the 2018 Mw 7.2 Pinotepa, Mexico, earthquake. The results show that the earthquake ruptured both the seismogenic zone and a long-term SSE area, with two asperities ruptured during the event. GPS time-series data indicate that an SSE was initiated approximately during March 2017 below Oaxaca; the SSE ruptured an area below the source region of the Pinotepa earthquake and intruded into the seismogenic zone. The spatiotemporal proximity may suggest that the SSE triggered the Pinotepa earthquake. We propose that the triggering mechanism may either have been Coulomb stress loading or weakening of the source area by fluid migration. Furthermore, we calculated the seismic moment deficit and Coulomb failure stress changes and conclude that the Oaxaca area still has the potential for large earthquakes.

Strong earthquake clustering around the eastern Tibetan Plateau after the 2008 MW7.9 Wenchuan earthquake

After the 2008 MW7.9 Wenchuan earthquake, the eastern Tibetan Plateau experienced a series of MW>6.0 earthquakes, including the 2013 MW6.6 Lushan, 2014 MW6.1 Kangding and 2017 MW6.5 Jiuzhaigou events. Based on available constraints, we build a three-dimensional viscoelastic finite element model to calculate Coulomb failure stress caused by these strong earthquakes. In this model, the geometry and slip vector of the initial rupture zone of each earthquake are used to better evaluate the earthquake-related stress projection. Considering reasonable ranges of viscosities for the crust and upper mantle in different tectonic units, numerical results show that after the Wenchuan earthquake, the coseismic Coulomb failure stress change at the hypocenters of the subsequent earthquakes increased to approximately +0.012–+0.040, +0.01–+0.03, and +0.008–+0.015 MPa, respectively. With viscoelastic relaxation of the lower crust and upper mantle, the Coulomb failure stress change at the hypocenters of these earthquakes accumulated to about +0.014–+0.042, +0.016–+0.036, and +0.003–+0.007 MPa just before their occurrence. This suggests that the Wenchuan earthquake indeed triggered or hastened the occurrence of the Lushan, Kangding and Jiuzhaigou events, supporting that strong earthquake clustering around the eastern Tibetan Plateau could be related to stress interaction between the seismogenic faults. Besides, ~94% and ~6% of the stress increase around (and before the occurrence of) the Kangding earthquake were contributed by the Wenchuan event and the Lushan event, respectively; the positive Coulomb failure stress change at the Jiuzhaigou earthquake hypocenter was related to coseismic slip partitioning of the Wenchuan earthquake. This means that stress interaction among the earthquakes could be controlled by the combined effect of stress of the previous events and by the complexity of earthquake ruptures. Thus, in researches on the earthquake-triggering mechanism, special attentions should be paid on both details of the rupture model and multiple factors of previous earthquakes.

Stress modulation of the seismic gap between the 2008 Ms 8.0 Wenchuan earthquake and the 2013 Ms 7.0 Lushan earthquake and implications for seismic hazard

SUMMARY Between 2008 and 2013, the Ms 8.0 Wenchuan earthquake and the Ms 7.0 Lushan earthquake occurred successively in the Longmenshan fault zone. Their aftershocks delineated a prominent seismic gap approximately 50 km long, hereafter referred to as the WLSG. The possibility of an event of Ms 7.0 or above occurring in the WLSG is a matter of great concern. In this study, we estimated the change of Coulomb failure stress (ΔCFS) along the WLSG caused by historical earthquakes in the last 300 yr. Our results revealed that 20 major earthquakes cast a stress shadow on the WLSG before 2008 (−148.7 to −7.0 kPa), hindering the rupture of the Wenchuan earthquake and the Lushan earthquake. The Wenchuan earthquake had an important influence on the stress redistribution of the WLSG, resulting in significant stress increase (14.7 to 337.5 kPa). As of 2018, although the negative ΔCFS caused by historical earthquakes (especially the Dayi earthquake) pushed the southern end of the WLSG away from failure, the positive peak ΔCFS of 323.0 kPa greatly encouraged the rupture of the northern WLSG. The small afterslip and weak microseismicity indicate that the WLSG is a stress barrier with high seismic potential, which can explain the mechanism of rupture termination of the Wenchuan earthquake and the Lushan earthquake.

Automatic Inversion of Rupture Processes of the Foreshock and Mainshock and Correlation of the Seismicity during the 2019 Ridgecrest Earthquake Sequence

Abstract The 2019 Ridgecrest, California, earthquake sequence included an Mw 6.4 foreshock on 4 July, followed by an Mw 7.1 mainshock about 32 hr later. We determined the rupture patterns of the foreshock and mainshock by applying the automatic iterative deconvolution and stacking method to strong-motion records. The foreshock was characterized by a unilateral rupture toward the southwest, and the shallow portion had a relatively large slip with the maximum value of ∼1.4 m. The mainshock presents an asymmetrical bilateral rupture with an average rupture velocity of 2.0 km/s. More than 80% of the seismic moment was released on the northwest segment of the fault, producing a maximum slip of ∼5.2 m. With the two inferred slip models, we calculated the Coulomb failure stress change (ΔCFS) to analyze the spatial–temporal correlation of the seismicity activity in this sequence. The result shows that the epicenter of the Mw 7.1 mainshock was brought 0.4 bars closer to failure by the Mw 6.4 foreshock, and the stress-increased zone has a good spatial consistence with the coseismic slip distribution of the mainshock and the aftershock distribution of the foreshock. Besides, the positive ΔCFS induced by the mainshock also enhanced its aftershock activity, especially at depths of 4–10 km where the major rupture occurred, inferring that the mainshock-induced ΔCFS may be responsible for the occurrence of aftershocks. In addition, we test the effects of different cutoff frequencies and crust velocity structures on the inversion results. The result reveals that the main source rupture characteristics are almost independent of these factors, implying a high reliability of automation inversion of strong-motion data. Overall, this work indicates that automatic inversion of strong-motion data can provide reliable and rapid rupture model, which is essential for earthquake emergency responses and tsunami early warnings.

Numerical inversion of magma chamber pressurization in volcanic areas: A case study of Changbaishan volcano

Volcanoes are commonly associated with significant topographic relief; however, most analytical models of volcanoes consider the Earth's surface as flat and use half-space solutions. Finite element method can take into account topography; we applied the equivalent body force method to the Changbaishan volcanic area to account for the influence of topographic effects on the inversion of magma chamber pressurization and to calculate the influence of the magma-induced stresses on the stability of the surrounding faults. The influence of surface topography should not be ignored when calculating the surface deformation caused by the magma chamber pressurization in a volcanic area. The shallower the burial depth, the closer the surface maximum radial displacement ur to the center of the magma chamber. When the slope reaches 30°, the maximum vertical displacement uz is no longer directly above the magma chamber. An ellipsoidal pressurization was used to satisfactorily simulate the GPS and leveling measurements at the Changbaishan volcanic area from 2002 to 2003. The superposition of the magma-induced stresses and the regional tectonic stresses likely cause the present stress directions around the Changbaishan volcano, which are dominated by the EW direction to the west of Tianchi Lake and the NW-NNW direction to the north of Tianchi Lake. The Coulomb failure stress change caused by the magma chamber is conducive to the distribution of the NW-trending earthquake swarms that mainly occur to the southwest and northeast of Changbaishan crater.

Elastic strain energy and pore-fluid pressure control of aftershocks

Aftershocks are well-known, however their triggering mechanisms remain unclear. The Coulomb failure stress change (ΔCFS) has been widely implemented to understand the spatial distribution of aftershocks. Here we propose a new metric for evaluating aftershock generation based on the energetics of shear faulting in a prestressed state. Unlike ΔCFS, the new metric depends not only on coseismic stress changes but also on background crustal stresses. The energetics-based formulation expands the ΔCFS defined on a specific plane into a generalized failure stress defined in a three-dimensional space. We examined the diagnostic ability of the new metric by applying receiver operating characteristic analysis to 12,175 aftershocks (M≥0) that followed the 1992 Landers earthquake. With a realistic background stress field inferred from thousands of earthquake focal mechanisms, the new metric was able to discriminate the triggering mechanisms of the aftershocks: two-thirds were direct responses to coseismic stress changes and one-fifth resulted from strength decreases owing to pore-fluid pressure increases.

Co-seismic Coulomb stress changes on the northern Tanlu fault zone caused by the Tohoku-Oki MW9.0 earthquake*

Based on the spherical earth dislocation theory and a fault slip model of the Tohoku-Oki MW9.0 earthquake, the co-seismic Coulomb failure stress changes (ΔCFS) on the northern Tanlu fault zone at depths of 0–40 km are calculated. By comparing two sets of results from the spherical earth dislocation theory and the semi-infinite space one, the effect of earth curvature on the calculation results is analyzed quantitatively. First, we systematically summarize previous researches related to the northern Tanlu fault zone, divide the fault zone as detailed as possible, give the geometric parameters of each segment, and establish a segmented structural model of the northern Tanlu fault zone. Second, we calculate the Coulomb stress changes on the northern Tanlu fault zone by using the spherical earth dislocation theory. The result shows the Coulomb stress changes are no more than 0.003 MPa, which proves the great earthquake did not significantly change the stress state of the fault zone. Finally, we quantitatively analyze the disparities between the results of semi-infinite space dislocation theory and the spherical earth one. The average disparity between them is about 7.7% on the northern Tanlu fault zone and is 16.8% on the Fangzheng graben, the maximum disparity on this graben reaches up to 25.5%. It indicates that the effect of earth curvature can not be ignored. So it’s necessary to use the spherical earth dislocation theory instead of the semi-infinite space one to study the Coulomb stress change in the far field.

Sequential modelling of the 2016 Central Italy earthquake cluster using multisource satellite observations and quantitative assessment of Coulomb stress change

SUMMARYA sequence of earthquake events consisting of three large shocks occurred in Central Italy from August to October in 2016 with the duration of almost 2 months. The preliminary study on the seismic mechanism suggests that the sequence of events is the result from the activity of the SW dipping Mt Bove–Mt Vettore–Mt Gorzano normal fault system. For investigation and understanding of the coseismic faulting of the seismogenic fault alignment, we collect a set of comprehensive satellite observations including the Sentinel-1A, ALOS-2/PALSAR-2 and GPS data to map the coseismic surface deformation and estimate the source models in this study. The derived faulting model for the first Amatrice event is characterized by two distinct slip asperities suggesting that it is a predominantly normal dip-slip motion with slight strike-slip component. The second event, Visso earthquake is almost a purely normal rupture. The third Norcia event is dominated by the normal dip-slip rupture of the seismogenic fault, and has propagated up to the ground with significant slip. The three faulting models are then utilized to quantify the Coulomb failure stress (CFS) change over the seismic zone. First, the CFS change on the subsequent two seismogenic faults of the earthquake sequence is estimated, and the derived positive CFS change induced by the preceding earthquakes suggests that the early events have positive effects on triggering the subsequent seismicity. We then explore the response relation of the aftershocks including 961 events with magnitudes larger than M 3.0 to the CFS change over the seismic zone. It suggests that the rupture pattern of the aftershocks is similar to the major shocks with predominantly normal dip-slip. To assess the risk of the future seismic hazard, we analyse quantitatively the spatial distribution of aftershock occurrence and CFS transfer at the seismogenic depth, indicating that the ruptures of the three major shocks do partly release the accumulated strain on the associated fault alignment as well as the dense aftershock, but the CFS increase zone with few aftershocks in the southwest of the eastern Quaternary fault alignment of Central Italy poses the potential of further rupture. In particular, the distribution of aftershock migration also suggests that the north extension of the Mt Bove fault is the potential zone with rupture risk.

Interactions of Earthquakes in Central Italy over the Past 100 Yr through Coulomb Stress Changes, and Implications for Seismic Hazards

ABSTRACT Italy has a historical earthquake record that is complete for events with a magnitude above 5.8 since A.D. 1349, making it possible to study Coulomb failure stress changes (ΔCFS) over a long period. In this study, we investigated the interactions between moderate-to-large earthquakes through ΔCFS over 100 yr in central Italy. This region is characterized by intense seismicity with predominantly extensional components. Hence, earthquake hazard assessment is of great public concern. Besides, earthquake interactions on normal faults are relatively less studied compared to reverse and strike-slip faults. ΔCFS calculations in this study incorporated both coseismic stress transfer and postseismic viscoelastic relaxation, and found the epicenters of 13 out of 15 events located in positively stressed lobes induced by previous earthquakes, confirming a correlation between the ΔCFS pattern and locations of moderate-to-large earthquakes. Next, we estimated the current distribution of ΔCFS on active faults, and after a comprehensive analysis of ΔCFS accumulation, slip rates, historical seismicity, and locations of populated cities, we identified three regions of potential seismic hazards in this region.

The 2014 Mw 6.1 Ludian Earthquake: The Application of RADARSAT-2 SAR Interferometry and GPS for this Conjugated Ruptured Event

Although the Zhaotong–Ludian fault is a seismically active zone located in the boundary between the Sichuan–Yunnan block and the South China block, it has not experienced a large earthquake greater than Mw 7 since at least 1700. On 3 August, 2014, an Mw 6.1 earthquake (the Ludian earthquake) ruptured the Zhaotong active belt in Ludian County, Yunnan province, China. This earthquake was the largest earthquake recorded in the region since 2000, and it provides us with a unique opportunity to study the active tectonics in the region. The analysis of the aftershocks showed that two conjugate faults could have been involved in the event. We first used Global Positioning System (GPS) data and C-band RADARSAT-2 imagery to map the coseismic surface deformation. We then inverted the derived coseismic deformation for the slip distribution based on the constructed conjugate fault model. Finally, the coulomb failure stress due to the Ludian earthquake was estimated to investigate the potential seismic hazards in this region. Our investigations showed that the Ludian earthquake was mainly a bilateral rupture event. The major slip of the main shock was located at depths of 0–5 km, which is close but does not superpose with the aftershocks that are mostly located at depths of 5–20 km. Interestingly, the seismic moment released by the aftershocks (6.9 × 1018 N∙m) was greater than that of the main shock (2.6 × 1018 N∙m). This evidence suggests that the accumulated elastic strain at depths of 0–20 km could have been fully released by the Ludian earthquake and its subsequent aftershocks. Furthermore, our analysis of the coulomb failure stress changes due to the main shock showed that the aftershocks could be the result of dynamic triggering rather than static triggering.

Source Characteristics of the 28 September 2018 Mw 7.4 Palu, Indonesia, Earthquake Derived from the Advanced Land Observation Satellite 2 Data

On 28 September 2018, an Mw 7.4 earthquake, followed by a tsunami, struck central Sulawesi, Indonesia. It resulted in serious damage to central Sulawesi, especially in the Palu area. Two descending paths of the Advanced Land Observation Satellite 2 (ALOS-2) synthetic aperture radar (SAR) data were processed with interferometric synthetic aperture radar (InSAR) and pixel tracking techniques to image the coseismic deformation produced by the earthquake. The deformation measurement was used to determine the fault geometry and the coseismic distributed slip model with a constrained least square algorithm based on the homogeneous elastic half-space model. We divided the fault into four segments (named AS, BS, CS and DS, from the north to the south) in the inversion. The BS segment was almost parallel to the DS segment, the CS segment linked the BS and DS segments, and these three fault segments formed a fault step-over system. The Coulomb failure stress (CFS) change on the causative fault was also calculated. Results show that the maximum SAR line-of-sight (LOS) and horizontal deformation were −1.8 m and 3.6 m, respectively. The earthquake ruptured a 210-km-long fault with variable strike angles. The ruptured pattern of the causative fault is mainly a sinistral slip. Almost-pure normal characteristics could be identified along the fault segment across the Palu bay, which could be one of the factors resulting in the tsunami. The main slip area was concentrated at the depths of 0–20 km, and the maximum slip was 3.9 m. The estimated geodetic moment of the earthquake was 1.4 × 1020 Nm, equivalent to an earthquake of Mw 7.4. The CFS results demonstrate that the fault step-over of 5.3 km width did not terminate the rupture propagation of the main shock to the south. Two M&gt;6 earthquakes (the 23 January 2005 and the 18 August 2012) decreased CFS along CS segment and the middle part of DS segment of the 2018 main shock. This implies that the stress release during the previous two earthquakes may have played a vital role in controlling the coseismic slip pattern of the 2018 earthquake.