The Multifractal Detrended Fluctuation Analysis (Mf-Dfa) and Anomalies in Geomagnetic Total Field Intensity Prior To Mw~5.5 Earthquake

193-197In the research article, we report the anomalies observed in geomagnetic total field intensity (BTotal) prior to Mw 5.5 Kokrajhar event. The multifractal analysis was scrutinized to reveal the underlying dynamics in the Geomagnetic Total field intensity time series. The multifractal spectrum on the day when the event occurred (TEvent day) and its surrogate (TSurrogate) was investigated to understand the behavior and dynamics hidden in BTotal time series. A significant variation in the multifractal spectrum was observed between TDay one (multifractal spectrum a day prior to the event) and TEvent day. It was also observed that the mulfractality of BTotal when the event occurred (TEvent day) got stronger than the multifractality of TDay one and was sourced from low values distribution. The multifractality in TDay one and TEvent day time series was not from source type long range correlation or sourced from broad probability density function. The investigation also manifests some non-linear features which probably evinces the anomalies to be seismic induced. The observations are elaborately emphasized in the article. The study scrutinizes the underlying dynamics in geomagnetic field intensity time series for earthquake precursory and forecast studies

Modelling of the Kopili Fault based on slip rate, moment rate and seismic activity in Mikir Hills Plateau of Northeastern India

The recurrence period of maximum magnitude earthquake in a seismogenically active formation along the Kopili Fault has been estimated having adequate dependence on the slip rate, moment rate and its seismicity pattern. Here, the frequency–magnitude cum fault area–maximum magnitude relations play a key role with input parameters pertinent to the Kopili Fault zone. Subsequently, where the fault slip rate estimates are not available, the seismic activity is studied from the seismic moment release. The results of this study show that the return period has a strong relation with the fault length, slip rate, strain drop and rigidity. This study ascertains the activity rate in terms of the return period as ∼50 ± 5 years with the moment release of 2.12E+23 dyne-cm from the most active 80-km fault length considering Mw 5.5 as reference magnitude under the Kopili Fault zone that may produce a maximum magnitude of Mw ∼ 7.6. Finally, we conclude that these models can be used to study the rate of seismicity of the active faults in Northeast India which will provide us prime inputs for seismic hazard analysis of the region and is especially significant for estimating expected return period for poorly known faults or blind faults that lack surface expression

Recent Seismotectonic Stress Regime of most Seismically active zones of gulf of Guinea and its Kinematic implications on the adjoining sub-Sahara west African region

The Tectonic stress regime of Gulf of Guinea region has been studied by stress tensor inversion analysis for the area bounded by lati− tude −10.0 0 S to 4.0oN and longitude −25 0 W to −11.0 0 E. A total of one hundred and four focal mechanism solutions, pertaining to the earthquake events which have occurred in this region, were used for this study. In order to decipher the stress pattern of this region, we have divided the region into four fracture zones namely Romanche, Chain−Romanche, Charcot and Ascension fracture−zones based on seismicity clustering, tectonics and available focal mechanism solutions. The seismicity pattern indicates that none of the nearby coun− tries on the border line between the west Africa region and the gulf of Guinea is devoid of seismicity. Simultaneously, the stress tensor inversion in the four subzones of investigation indicates different types of stress orientations. All of these zones are characterized by vary− ing principal axial directions. The orientation of the principal axial direction along Romanche, Chain−Romanche, Charcot and Ascen− sion fracture−zones are along NE−SW, NE−SW, ENE−WSW and ESE−WNW respectively. The stress tensor inversion results indicate that Chain−Romanche, Charcot and Ascension fracture zones are characterized by extensional stress regime while Romanche fracture zone is characterized by strike−slip stress regime respectively. These patterns imply sea floor spreading activities in and around the mid oceanic ridges and the general orientation of the extensional stress regime is found towards the continents, along the line of migration / progression of earthquakes

The Multifractal Detrended Fluctuation Analysis (Mf-Dfa) and Anomalies in Geomagnetic Total Field Intensity Prior To Mw~5.5 Earthquake

In the research article, we report the anomalies observed in geomagnetic total field intensity (BTotal) prior to Mw 5.5 Kokrajhar event. The multifractal analysis was scrutinized to reveal the underlying dynamics in the Geomagnetic Total field intensity time series. The multifractal spectrum on the day when the event occurred (TEvent day) and its surrogate (TSurrogate) was investigated to understand the behavior and dynamics hidden in BTotal time series. A significant variation in the multifractal spectrum was observed between TDay one (multifractal spectrum a day prior to the event) and TEvent day. It was also observed that the mulfractality of BTotal when the event occurred (TEvent day) got stronger than the multifractality of TDay one and was sourced from low values distribution. The multifractality in TDay one and TEvent day time series was not from source type long range correlation or sourced from broad probability density function. The investigation also manifests some non-linear features which probably evinces the anomalies to be seismic induced. The observations are elaborately emphasized in the article. The study scrutinizes the underlying dynamics in geomagnetic field intensity time series for earthquake precursory and forecast studies

Dynamics of Mikir hills plateau and its vicinity: Inferences on Kopili and Bomdila Faults in Northeastern India through seismotectonics, gravity and magnetic anomalies

he Mikir Hills plateau is encompassed by two prominent faults – Bomdila Fault to the east and the Kopili Fault to the west characterized by strike-slip kinematics. The Kopili Fault has a dip of 75otowards NE. Simultaneously, the Bomdila Fault dips with 50-55otowards the NNE. An integrated approach based on seismotectonics, gravity and magnetic data is utilized to understand the tectonic activity of the Kopili and Bomdila Faults. The bottom of seismogenic zones is inferred to be 45+2 km and 50+2 km for the Kopili Fault and the Bomdila Fault region respectively. So far gravity anomaly is concerned; it varies between -110 to +60 mgals along the Kopili –Bomdila Fault regions from the Belt of Schuppen to the MCT. The low gravity values over the Bomdila Fault area indicate presence of thick alluvial deposits while along Kopili Fault lesser sediment thickness is observed. Simultaneously, basement being at shallower depth, lower magnetic values indicate presence of thick alluvial deposits in and around Bomdila Fault. The curvatures and closures of the gravity contours along the fault lines indicate structures involving basement and indicate influence of Bomdila Fault up to the basement. Simultaneously, it is observed that Kopili and Bomdila faults are neotectonically active. All these are the prime input to the seismic hazard assessment of the region

The September 2011 Sikkim Himalaya earthquake Mw 6.9: is it a plane of detachment earthquake?

The 18 September 2011 Sikkim Himalaya earthquake of Mw 6.9 (focal depth 50 km, NEIC report) with maximum intensity of VII on MM scale (www.usgs.gov) occurred in the Himalayan seismic belt (HSB), to the north of the main central thrust. Neither this thrust nor the plane of detachment envisaged in the HSB model, however, caused this strong devastating earthquake. The Engdahl–Hilst–Buland (EHB) relocated past earthquakes recorded during 1965–2007 and the available global centroid moment tensor) solutions are critically examined to identify the source zone and stress regime of the September 2011 earthquake. The depth section plot of these earthquakes shows that a deeper (10–50 km) vertical fault zone caused the main shock in the Sikkim Himalaya. The NW (North-West) and NE (North-East) trending transverse fault zones cutting across the eastern Himalaya are the source zones of the earthquakes. Stress inversion shows that the region is dominated by horizontal NNW-SSE (North of North-West-South of South-East) compressional stress and low angle or near horizontal ENE-WSW (East of North-East-West of South-West) tensional stress; this stress regime is conducive for strike-slip faulting earthquakes in Sikkim Himalaya and its vicinity. The Coulomb stress transfer analysis indicates positive values of Coulomb stress change for failure in the intersecting deeper fault zone that produced the four immediate felt aftershocks (M ≥ 4.0)

Influence of parameters on mechanical and micro-structural properties of tungsten inert gas (TIG) welded joint of 1 mm thin Inconel 625 plates

87-93Inconel 625 (IN625), since its invention, has been a material of choice for industries where components in service conditions are exposed to extremely high temperatures, corrosion, and oxidation environments. As per the American welding society for butt-joining such alloys in sheets, non-traditional techniques are the best means for producing permanent joints. These techniques require high-cost setup and high maintenance costs which are only economical for high-volume assembly line fabrication in mass-production facilities. Therefore, Tungsten Inert Gas (TIG) welding is highly suitable for producing defect-free autogenous weldments in high-strength alloy sheets with a thickness below 3mm. The current work focuses on the experimental investigation of the TIG welding of Inconel 1mm sheets. In this work, mechanical properties and microstructure are studied for controlled heat input of TIG welding. Current is varied from 40A to 65A and voltage from 10V to 12V. Only three combinations of parameters show sound weld visually and are analyzed by performing various testing. The main objective of the study is to find the feasible process parameters for the micro joining of IN625 sheets. From this discussion, it appears that arc energy, welding current, and voltage significantly affect the quality of the weld

Intracranial blastomycosis mimicking high-grade neoplasm on magnetic resonance imaging and spectroscopy

We describe a case of posterior fossa blastomycosis in an immunocompetent patient that mimicked high-grade neoplasm on neuroimaging. Histological analysis confirmed blastomycosis. Because the neuroimaging characteristics of intracerebral blastomycosis can be confused for neoplasm, these lesions must be confirmed histologically before initiating aggressive treatment for presumptive high-grade neoplasm. To our knowledge, it is the first description of a neoplasm mimic on MRS in the setting of intracranial blastomycosis

Large and great earthquakes in the Shillong plateau Assam valley area of northeast India region : pop-up and transverse tectonics

International audienceThe tectonic model of the Shillong plateau and Assam valley in the northeast India region, the source area for the 1897 great earthquake (Ms~8.7) and for the four (1869, 1923, 1930 and 1943) large earthquakes (M.≥7.0), is examined using the high precision data of a 20-station broadband seismic network. About 300 selected earthquakes M≥3.0 recorded during 2001-2009 are analysed to study the seismicity and fault plane solutions. The dominating thrust/reverse faulting earthquakes in the western plateau may be explained by the proposed pop-up tectonics between two active boundary faults, the Oldham-Brahmaputra fault to the north and the Dapsi-Dauki thrust to the south, though the northern boundary fault is debated. The more intense normal and strike-slip faulting earthquakes in the eastern plateau (Mikir massif) and in the Assam valley, on the other hand, are well explained by transverse tectonics at the long and deep rooted Kopili fault that cuts across the Himalaya and caused the 2009 Bhutan earthquake (Mw 6.3). It is conjectured that the complex tectonics of the Shillong plateau and transverse tectonics at the Kopili fault make the region vulnerable for impending large earthquake(s)