Tectonic Deformation

Oblique convergence and slip partitioning in the NW Hiamalaya : Implications from GPS measurements

We report GPS measurements of crustal deformations across the Kashmir Himalaya. We combined these results with published results of GPS measurements from the Karakoram Fault system and suggest that in Kashmir Himalaya, the motion between the Southern Tibet and India plate is oblique with respect to the structural trend. We estimated this almost north-south oblique motion to be 17 +/- 2 mm/yr, which is partitioned between dextral motion of 5 +/- 2 mm/yr on the Karakoram fault system and oblique motion of 13.6 +/- 1 mm/yr with an azimuth of N198°E in the northwest-southeast trending Kashmir...

Kundu et al., 2014 MORE

Oblique convergence and strain partitioning in the outer deformation front of NE Himalaya

Himalayan-Tibetan orogeny has considered as a natural black box in the context of geodynamic evolution and tectonic complexity. The eastward extrusion model of Tibetan crust contradicts with the oblique convergence model in the NE-Himalaya (Bhutan/Arunachal region), where the overall convergence rate accommodated in the Himalaya is about 20–25% less than that in the neighbouring central Himalaya and Eastern Himalayan syntaxis (EHS). We propose that instead of partitioning in the backarc, the NE-Himalaya has developed an active sliver along the Assam-Brahmaputra valley in the outer deformation front, in order to accommodate the deficiency in long-term plate convergence between Himalaya and southern Tibet. We argue that the strong eastward extrusion of ...

Panda et al., 2018 MORE

Aseismic plate boundary in the Indo-Burmese wedge, northwest Sunda Arc

Plate motion, crustal deformation, and earthquake occurrence processes in the northwest Sunda Arc, which includes the Indo-Burmese wedge (IBW) in the forearc and the Sagaing fault in the backarc, are very poorly constrained. Plate reconstruction models and geological structures in the region suggest that subduction in the IBW occurred in the geological past, but whether it is still active and how the plate motion between the India and Sunda plates is partitioned between motion in the IBW and Sagaing fault is largely unknown. Recent GPS measurements of crustal deformation and available long-term rates of motion across the Sagaing fault suggest that ∼20 ± 3 mm/yr of the relative plate motion of ∼36 mm/yr between the India and Sunda plates is accommodated at the Sagaing fault through dextral strike-slip motion. We report results from a dense GPS network in the IBW that has operated since 2004. . Our analysis of these measurements and the ...

Gahalaut et al., 2013 MORE

Volcanic Deformation

Eruption cycles of Mount Etna triggered by seasonal climatic Rainfall

The ability to mitigate and predict volcanic risk is a long-standing question in the Geosciences’ community, while the extent of volcanic activity may be regulated by a predictable and periodic external excitation induced by seasonal rainfall, hydrological loading, or Moon-Sun gravitational force. Moreover, the complex stress-triggering, hydro-mechanical coupling in response to seasonal rainfall, and associated feedback mechanism with deep magmatic process remains enigmatic and indeed deserves more attention in view of recent climate change scenario. In this letter, a compelling scenario of seasonal rainfall-triggered eruption cycles of Mount Etna (Italy) is found and presented on the eastern coast of Sicily with continuously erupting since last 200 kyr. Results show that the seasonal rainfall significantly weakened the Mount Etna edifice and initiated mechanical tensile failure in the complex magmatic plumbing system and adjacent flank surface by changing the pore pressure build-up, probably promoting dyke intrusion and eventual triggering of eruptive cycle. Further, the possibility of seasonal hydrological loading on the Mount Etna volcano and adjacent flank region, hydrological load-induced sliding along the impermeable outer ‘shell’ of the flank are discussed, and the effect of tidal stress perturbations on the eruptions cycle cannot be ruled out completely.

Sahoo et al., 2022 MORE

The 2005 volcano-tectonic earthquake swarm in the Andaman Sea: Triggered by the 2004 great Sumatra-Andaman earthquake

A 6 day duration earthquakes swarm occurred in the Andaman Sea, 31 days after the giant 2004 Sumatra-Andaman earthquake (Mw 9.2). The swarm occurred less than 100 km from the eastern edge of the 2004 earthquake rupture and is the most energetic ever recorded in the world. The earthquakes swarm appear to have occurred on en echelon fault system bounded by the two main right-lateral strike-slip faults, namely, the Seulimeum Strand of Sumatra Fault system (SEU) and the West Andaman Fault (WAF). At the beginning of the swarm, earthquakes with predominantly strike-slip focal mechanisms occurred which were followed by earthquakes with predominantly normal faulting focal mechanisms having significant deviatoric component. High b value, presence of double slope in the Gutenberg-Richter relation, presence of monogenetic submarine volcanoes in the region of the swarm and the earthquake focal mechanisms suggest that the swarm was of volcano-tectonic origin and fluid flow played an important role in its occurrence. Indeed, our modeling suggests that it was triggered by the 2004 Sumatra-Andaman earthquake through poroelastic relaxation of the coseismic stresses.

Kundu et al., 2012 MORE

Triggering relationships between magmatic and faulting processes in the May 2018 eruptive sequence at Kīlauea volcano, Hawaii

The May 2018 activity at Kīlauea Volcano, Hawaii involved magma transport and dike intrusion along the East Rift Zone (ERZ) and nucleation of the May 4, 2018 M6.9 earthquake along the basal décollement of Kīlauea’s mobile south flank. Combined Global Positioning Systems (GPS) and Interferometric Synthetic Aperture Radar (InSAR) measurements captured the deformation sequence associated with the dike intrusion, mainshock, and eruption episode along the ERZ. The earthquake was encouraged by static stress changes from the preceding magma reservoir inflation, ERZ expansion and fault creep on the décollement downdip of the rupture. Slip models derived from the inversion of GPS displacements indicate peak coseismic slip of 2-3 meters. Our model analyses, including of the pre-May 2018 deformation, suggest that prior to this event there was no slip on the section of the décollement that ruptured in the earthquake. The observed magma inflation, rapid fault creep on the décollement and coseismic rupture reflect complex cyclic interactions between the magmatic and faulting processes.

Kundu et al., 2020 MORE

Climate Induced Deformation

Seasonal modulation of deep slow-slip and earthquakes on the Main Himalayan Thrust

The interaction between seasonally-induced non-tectonic and tectonic deformation along the Himalayan plate boundary remains debated. Here, we propose that tectonic deformation along this plate boundary can be significantly influenced by the deformation induced by the non-tectonic hydrological loading cycles. We explore seasonal mass oscillations by continental water storage in Southeast Asia and Himalayan arc region using continuous Global Positioning System measurements and satellite data from the Gravity Recovery and Climate Experiment. We suggest that the substantially higher transient displacements above the base of the seismogenic zone indicate a role of changes in aseismic slip rate on the deep megathrust that may be controlled by seasonal hydrological loading.We invoke modulation of aseismic slip on the megathrust down-dip...

Panda et al., 2018 MORE

Influence of a meteorological cycle in mid-crustal seismicity of the Nepal Himalaya

The process of interseismic strain accumulation across the Nepal Himalaya is associated with micro seismicity (also called mid-crustal seismicity) which occurs along the mid-crustal ramp on the Main Himalayan Thrust (MHT). The seismicity shows strong annual periodicity in response to the annual stress variation of hydrological loads. We report dominance of annual periodicity in the eastern Nepal as compared to that of western Nepal, and overall annual periodicity dominance in the small magnitude earthquakes (Mw 0–3). Rainfall seismicity crosscorrelation is significantly higher in the eastern Nepal region as compared to that of western Nepal with a prominent phase lag of 5–6 months with respect to the occurrence of monsoonal rainfall. Seasonal modulation can be explained by Coulomb failure stress model and fault resonance hypothesis induced by meteorological....

Kundu et al., 2017 MORE

Human Induced Deformation

Influence of anthropogenic groundwater unloading in Indo-Gangetic plains on the 25 April 2015 Mw 7.8 Gorkha, Nepal earthquake

Groundwater usage in the Indo-Gangetic plains exceeds replenishment of aquifers, leading to substantial reduction in the mass. Such anthropogenic crustal unloading may promote long-term fault slip or may modulate seismic activity in the adjoining Himalayan region. Our simulation using Gravity Recovery and Climate Experiment data and hydrological models of such a process indicates that the thrust earthquakes on the Main Himalayan Thrust (MHT), including the recent 25 April 2015 Mw 7.8 Gorkha, Nepal earthquake, are probably influenced by the anthropogenic groundwater unloading process in the Gangetic plains. The groundwater withdrawal leading to crustal unloading in the Gangetic plains causes a significant component of horizontal compression which adds to the secular interseimic compression at the seismogenic depth (5–20 km) on the MHT beneath the Himalayan.....

Kundu et al., 2015 MORE

Influence of anthropogenic groundwater pumping on the 2017 November 12M7.3 Iran–Iraq border earthquake

Study of induced, triggered, stimulated and nuance earthquakes can provide a unique opportunity to probe into stress/frictional conditions on the subsurface fault. Although mechanism of faulting is tectonically driven phenomenon, anthropogenic crustal (un-)loading process can also drive long-term fault slip or modulate seismicity in the nearby seismogenic crust. Using Gravity Recovery and Climate Experiment data, surface subsidence rate captured by cGPS and 3-D hydrological stress models, we report that the 2017 November 12 M7.3 Iran–Iraq border earthquake in the Arabia–Eurasia collision boundary region of the Zagros fold-and-thrust belt was significantly influenced by the anthropogenic groundwater unloading in the Euphrates and Tigris River plains and western Iran, a region which is probably the most intensely irrigated region in the Middle East. We find that the anthropogenic crustal unloading contributed about one tenth of the secular interseismic stress change rate due to tectonic loading. Thus, the resulting cumulative stress accumulation was significantly influenced by the extensive groundwater pumping......

Kundu et al., 2019 MORE

Atmospheric Disturbances

Atmospheric wave energy of the 2020 August 4 explosion in Beirut, Lebanon, from ionospheric disturbances

Atmospheric waves excited by strong surface explosions, both natural and anthropogenic, often disturb upper atmosphere. In this letter, we report an N-shaped pulse with period ~ 1.3 min propagating southward at ~ 0.8 km/s, observed as changes in ionospheric total electron content using continuous GNSS stations in Israel and Palestine, ~ 10 min after the August 4, 2020 chemical explosion in Beirut, Lebanon. The peak-to-peak amplitude of the disturbance reached ~ 2% of the background electrons, comparable to recently recorded volcanic explosions in the Japanese Islands. We also succeeded in reproducing the observed disturbances assuming acoustic waves propagating upward and their interaction with geomagnetic fields.

Kundu et al., 2021 MORE

The 2017 August 21 American total solar eclipse through the eyes of GPS

We explored spatio-temporal variation in total electron contents (TEC) in the ionosphere caused by the recent 2017 August 21 total solar eclipse, which was observed over the United States of America. The path of the total solar eclipse passes through the continental parts of the United States of America, starting in the northwestern state of Oregon and ending in the southeastern state of South Carolina, approximately covering 4000 km length. Across this length, EarthScope Plate Boundary Observatory (PBO) has been operating a dense Global Navigation Satellite Systems (GNSS) networks. During the course of passage of the solar eclipse, the sudden decline in solar radiation by temporarily obscuration by the Moon caused a drop of ∼6–9 × 1016 electrons m2 in the ionosphere with time-delay at the cGPS sites. The significant drop in TEC at cGPS sites captured the average migration velocity of shadow along the eclipse path......

Kundu et al., 2018 MORE

Effects of Rayleigh-Taylor instability and ionospheric plasma bubbles on the global navigation satellite System signal

Ionospheric disturbances induced by various natural (e.g., earthquakes, volcanic eruption, thunderstorms, meteorite showers, solar eclipses) or anthropogenic (e.g., nuclear explosions, launching of space shuttles) processes can be detected through change in Total Electron Content (TEC) in the F-layer. These ionospheric perturbations can be captured by worldwide expanding geodetic (GNSS) networks, mainly during the day time, when the solar radiation ionizes the air molecules. However, during post-sunset period, strong ionospheric irregularities (known as Equatorial Plasma Bubbles, EPBs) develop due to the classical configuration for the Rayleigh-Taylor (R-T) instability that diffracts navigation and communication signals. Here we use various instances of ionospheric disturbances triggered by natural processes (e.g., earthquakes and volcanic eruption), in the recent decade to investigate the spatiotemporal and seasonal effects of ionospheric irregularities on the GNSS signals. Our study suggests that in the low-latitudinal region ...

Panda et al., 2019 MORE

Miscellaneous Works

Surface gravity and crater diameter as proxies of extra-terrestrial impact

Impact cratering is a dominant geological process in the Solar system and is one of the frontier themes in planetary research. Here we explore the possible dependency of surface gravity and crater geometry in the natural and theoretical prediction from scaling factor of crater diameter using morphometric analysis. Theoretical model predicts a negative correlation between final crater diameter (Dfr) and gravitational acceleration of the target body (g). In our study, an inner solar system body reveals consistent correlation that demonstrates a fundamental relationship between Dfr and g, although such process may not be applicable if we consider outer solar system bodies. Our study indicates that impact-cratering process is primarily controlled by objects associated with asteroids belts. We also demonstrate that crater-diameter scaling can be used as the proxy for extra-terrestrial impact.

Kundu et al., 2019 MORE

Dynamics of post-slab breakoff in convergent plate margins: a “jellyfish” Model

The Earth's subduction zones are characterized by a complex architecture of the subducting slabs, including necking, tearing, detachment from the surface plate, breakoff or ultimate slab loss, in contrast to the idealized models as popularly envisaged. Here we address the fate of the subducted slab after its breakoff by employing a simple two dimensional numerical modeling. Our results agree well with the tectonic scenario and geometric evolution of slab breakoff and reveal that during the sinking of broken slab fragments, the shape of the low viscosity slab (1-1000 times more viscous than the surrounding mantle) evolves into an inverted plume, similar to the “jellyfish” model proposed in some recent studies on deep subduction slabs. Our results confirm that the penetration criteria of the jellyfish into the lower mantle are primarily governed by the viscosity contrast between the lower to upper mantle. An evaluation of the various parameters suggest that the broken slab fragments may achieve a diverse type of morphology, correlating well with a similar diversity observed from high resolution seismic tomographic studies.

Kundu et al., 2011 MORE