InSAR Constrained Downdip and Updip Afterslip Following the 2015 Nepal Earthquake: New Insights into Moment Budget of the Main Himalayan Thrust

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 ~80mm 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 0.3m during the first year after the earthquake. Within the 4.5 years after the mainshock, the estimated moment released by afterslip is ~1.5174 × 1020 Nm,about 21.2% of that released by the main earthquake.

Seismic Permanent Deformation Analysis for Gravel Dams in High Altitude Meizoseismal Areas

It is commonly believed that the permanent deformation is introduced by the meizoseismal impacts of embankment dams, which is impossible to be reinstated and will further endanger the safety and normal use thereof. In this study, a three-dimensional finite element model of the dam have been established with the equivalent nodal force approach to calculate the permanent deformation of the dams under seismic protection. It was indicated by the results that the acceleration response of dams was not intense in the meizoseismal areas and the vertical seismic permanent deformation mainly occurred at the top of the dams, of which the collapse rate is less than 1% with small lateral and horizontal seismic permanent deformation. Moreover, the dam profile has been indicated with inward shrinkage upon the seismic permanent deformation, which is beneficial to the stability of the dam slopes. However, seismic measures are required to improve the seismic performance of the dam area because of the large acceleration and permanent seismic deformation at the dam tops. The research results provide a decision basis for seismic hazard assessment and reinforcement solutions of similar dams.

General Geometric Model of GNSS Position Time Series for Crustal Deformation Studies – A Case Study of CORS Stations in Vietnam

In processing of position time series of crustal deformation monitoring stations by continuousGNSS station, it is very important to determine the motion model to accurately determine the displacementvelocity and other movements in the time series. This paper proposes (1) the general geometric model foranalyzing GNSS position time series, including common phenomena such as linear trend, seasonal term,jumps, and post-seismic deformation; and (2) the approach for directly estimating time decay ofpostseismic deformations from GNSS position time series, which normally is determined based on seismicmodels or the physical process seismicity, etc. This model and approach are tested by synthetic positiontime series, of which the calculation results show that the estimated parameters are equal to the givenparameters. In addition they were also used to process the real data which is GNSS position time series of4 CORS stations in Vietnam, then the estimated velocity of these stations: DANA (n, e, u = -9.5, 31.5, 1.5mm/year), HCMC (n, e, u = -9.5, 26.2, 1.9 mm/year), NADI (n, e, u = -10.6, 31.5, -13.4 mm/year), andNAVI (n, e, u = -13.9, 32.8, -1.1 mm/year) is similar to previous studies.

Geodetic investigation of triggered slip below Fiordland

<p>Secretary Island, at the head of Doubtful Sound in Fiordland, has been seismically active in past 30 years, with earthquakes larger than M w 6.5: the 1989 Doubtful Sound, 1993 Secretary Island, and 2003 Fiordland earthquakes. These events were approximately coincident with the 17° bend in the strike of the young, obliquely-converging, and steeply dipping Puysegur Subduction Zone. This section of the plate interface also has a history of triggered slip: the 1989 earthquake is inferred to have triggered the 1993 earthquake and, further north at George Sound, triggered afterslip was reported following the 2009 Dusky Sound earthquake. We have used L-band (23.6 cm-wavelength) Synthetic Aperture Radar (SAR) data from the ALOS1 and ALOS2 satellites, and C-band (5.5 cm-wavelength) SAR data from Sentinel 1A/B satellites, to test the hypothesis that triggered slip also occurred in the vicinity of Secretary Island following the 2007 George Sound, 2009 Dusky Sound and 2016 Kaikōura earthquakes. SAR images were aligned, interfered, filtered, and unwrapped using GMTSAR processing tools. Long-wavelength ionosphere noise was removed by inverting for the best-fitting linear plane, and we assumed a linear function of height to remove short-wavelength atmospheric noise. Small Baseline Subset (SBAS) timeseries analysis indicated a localised deformation signal centred on Secretary Island following the Dusky Sound earthquake. A re-analysis was undertaken of the co- and post-seismic deformation caused by the Dusky Sound earthquake so that any surface deformation centred on Secretary Island could be isolated. Campaign and continuous Global Positioning System (GPS) data were simultaneously inverted with co- and post-seismic interferograms using a statistical Bayesian modelling approach to determine the optimal Dusky Sound earthquake source parameters. Limitations arising from orbital drift, the frequency of SAR acquisitions and the observation geometry hindered our ability to constrain the timing, magnitude and location of reactivated slip from a source similar to the 2003 Secretary Island earthquake. Our findings indicate that slip was not triggered following either the 2007 George Sound earthquake or 2016 Kaikōura earthquake. However, we cannot rule out triggered slip near Secretary Island following the 2009 Dusky Sound earthquake. Any such slip likely occurred on an area of c. 350 km² (c. 15 km updip of the Secretary Island epicentre) with an average slip of 1–3 m, producing motion away from the satellite of c. 25 mm at Secretary Island.</p>

Geodetic investigation of triggered slip below Fiordland

<p>Secretary Island, at the head of Doubtful Sound in Fiordland, has been seismically active in past 30 years, with earthquakes larger than M w 6.5: the 1989 Doubtful Sound, 1993 Secretary Island, and 2003 Fiordland earthquakes. These events were approximately coincident with the 17° bend in the strike of the young, obliquely-converging, and steeply dipping Puysegur Subduction Zone. This section of the plate interface also has a history of triggered slip: the 1989 earthquake is inferred to have triggered the 1993 earthquake and, further north at George Sound, triggered afterslip was reported following the 2009 Dusky Sound earthquake. We have used L-band (23.6 cm-wavelength) Synthetic Aperture Radar (SAR) data from the ALOS1 and ALOS2 satellites, and C-band (5.5 cm-wavelength) SAR data from Sentinel 1A/B satellites, to test the hypothesis that triggered slip also occurred in the vicinity of Secretary Island following the 2007 George Sound, 2009 Dusky Sound and 2016 Kaikōura earthquakes. SAR images were aligned, interfered, filtered, and unwrapped using GMTSAR processing tools. Long-wavelength ionosphere noise was removed by inverting for the best-fitting linear plane, and we assumed a linear function of height to remove short-wavelength atmospheric noise. Small Baseline Subset (SBAS) timeseries analysis indicated a localised deformation signal centred on Secretary Island following the Dusky Sound earthquake. A re-analysis was undertaken of the co- and post-seismic deformation caused by the Dusky Sound earthquake so that any surface deformation centred on Secretary Island could be isolated. Campaign and continuous Global Positioning System (GPS) data were simultaneously inverted with co- and post-seismic interferograms using a statistical Bayesian modelling approach to determine the optimal Dusky Sound earthquake source parameters. Limitations arising from orbital drift, the frequency of SAR acquisitions and the observation geometry hindered our ability to constrain the timing, magnitude and location of reactivated slip from a source similar to the 2003 Secretary Island earthquake. Our findings indicate that slip was not triggered following either the 2007 George Sound earthquake or 2016 Kaikōura earthquake. However, we cannot rule out triggered slip near Secretary Island following the 2009 Dusky Sound earthquake. Any such slip likely occurred on an area of c. 350 km² (c. 15 km updip of the Secretary Island epicentre) with an average slip of 1–3 m, producing motion away from the satellite of c. 25 mm at Secretary Island.</p>

Fault Activation in Central Mongolia during the Holocene: Results of Study of the Mogod Earthquake Ruptures

—In order to determine the seismotectonic activity of faults in the Holocene, we performed trench studies of the ruptures produced by the catastrophic Mogod earthquake (5 January 1967, M = 7.5–7.8, I0 = 9–10) in the junction zone of the N–S striking Hulzhin Gol fault and the NW striking Tullet fault. Paleoseismic interpretation of seismic-deformation sections and radiocarbon dating of the samples allowed determining the kinematics and obtaining, for the first time, the absolute ages of paleoevents preceding the Mogod earthquake. Analysis of the tectonic conditions for realization of earthquake sources has shed light on the complex structure of ruptures in the area of the Mogod earthquake epicenter, within which three segments differing in the displacement amplitudes and kinematics have been identified. The research data indicate the repeated activation of the Tulet and Hulzhin Gol faults in the Late Pleistocene–Holocene. The absolute age of the latest activation is 596–994 AD for the Tulet fault and 11,379–6235 BC for the Hulzhin Gol fault. The cumulative deformation from paleoearthquakes in the trench sections in the Tulet fault zone points to at least two displacements of thrust kinematics, with the latest of them having an amplitude of 2.8 m. The paleoearthquake in the Hulzhin Gol fault zone is characterized by the presence of lateral slip. The amplitudes of deformations attest to earlier earthquakes similar in energy to the 1967 Mogod event or even stronger in the fault node. The obtained data on the timing of these earthquakes and the amplitudes of the accompanying displacements made it possible to estimate slip rates along the faults: 0.2–0.3 m/kyr horizontal-slip rates on the Hulzhin Gol fault and 0.5–0.7 m/kyr vertical-slip rates on the Tulet fault.

Unified Reservoir And Seismic Simulation With Explicit Representation Of Fractures And Faults

In the context of remote sensing, the vast disparity in characteristic scales between seismic deformation (e.g. milliseconds) and transient flow (e.g. hours) allows a "two-model paradigm" for geophysics and reservoir simulation. In the context of flow-induced geohazard risk mitigation and micro-seismic data integration, this paradigm breaks down. Under micro-seismic deformation, events occur with high-frequency, and over sustained duration during which the rock-fluid coupling is significant. In risk mitigation scenarios, the onset of seismic deformation is directly tied to quasi-static coupling periods. This work develops an approach to reservoir simulation modeling that allows simultaneous resolution of transient (inertial) poromechanics and multiphase fluid flow in the presence of fracture. A mixed discretization scheme combining the extended finite element method (XFEM) and the embedded discrete fracture model (EDFM) is extended using a second-order implicit Newmark time integration scheme for the inertial mechanics. A Lagrange multiplier method is developed to model pressure-dependent contact traction in fractures. The contact constraints are adapted to accommodate fracture opening. Slip-weakening fracture friction models are incorporated. Finally, a time-step controller is proposed to combine local discretization error with contact traction and slip-rate control along the fractures. This strategy allows automatic adaptation to resolve quasi-static, inter-seismic triggering, and co-seismic spontaneous rupture periods within one model. The model is verified to simulate complete induced earthquake sequences, including inter-seismic and dynamic rupture phases. The performance of the adaptive model is illustrated for cases with various set-ups of production and injection periods in a fractured reservoir with explicit fracture representation.

Geodetic observations for constraining mantle processes in Antarctica

Geodynamic processes in Antarctica such as glacial isostatic adjustment (GIA) and post-seismic deformation are measured by geodetic observations such as GNSS and satellite gravimetry. GNSS measurements have been comprising continuous measurements as well as episodic measurements since the mid-1990s. The estimated velocities typically reach an accuracy of 1 mm/a for horizontal and 2 mm/a for vertical velocities. However, the elastic deformation due to present-day ice-load change needs to be considered accordingly.Space gravimetry derives mass changes from small variations in the inter-satellite distance of a pair of satellites, starting with the GRACE satellite mission in 2002 and continuing with the GRACE-FO mission launched in 2018. The spatial resolution of the measurements is low (about 300 km) but the measurement error is homogeneous across Antarctica. The estimated trends contain signals from ice mass change, local and global GIA signal. To combine the strengths of the individual data sets statistical combinations of GNSS, GRACE and satellite altimetry data have been developed. These combinations rely on realistic error estimates and assumptions of snow density. Nevertheless, they capture signal that is missing from geodynamic forward models such as the large uplift in the Amundsen Sea sector due to low-viscous response to century-scale ice-mass changes.