by K.Silpa and Anil Earnest
Kinematic source process models using tele-seismic waveform inversion of three stable continental region (SCR) earthquakes from India (1993 Mw 6.2 Latur, 1997 Mw 5.8 Jabalpur and 2001 Mw 7.6 Bhuj) are presented in this paper to demonstrate the slip evolution and stress drop. These finite-fault models are methodologically unique to constrain the source dimensions, compared with assumptions and quasi-observations around blind faults. Our results show that these events do have a compact zone of singular asperity breakage within the Indian crust. Whereas the Bhuj and Jabalpur events have their rupture majorly restricted within the lower crustal regions. The Latur event ruptured a very shallow crustal asperity. The estimated rupture velocities are in the range of 2.6–3.2 km/s, Bhuj event the slowest and lengthiest. Our results do not favour an updip shallow component of asperity breakage for the Bhuj earthquake, as evident from lack of surface ruptures. Study also indicates that the 1993 Latur event occurred on a fault with high stress concentration which indicates stronger fault asperities or slip within a newer fault. Models on 1997 Jabalpur event imply higher frictional strength and very brittle nature at the lower crustal regions of the Indian slab, indicating a mechanically very strong lower crust. We conclude that an event like Latur can occur anywhere within continental interiors of Indian SCR, or elsewhere globally, and is an underestimated seismic hazard.
by Govindan Kutty, Rekha Gogoi, V Rakesh & M Pateria
This study compares the performance of hybrid ensemble transform Kalman filter – three dimensional variational data assimilation (HYBRID) system and three dimensional variational (3DVAR) data assimilation system in Weather Research and Forecasting Model (WRF) in simulating tropical cyclones (TC) formed over the Bay of Bengal. An Ensemble Transform Kalman Filter (ETKF) system updates the ensemble system that provides flow-evolving background error covariance for HYBRID data assimilation system. Results indicate that use of flow-evolving ensemble error covariance in 3DVAR system has systematically reduced the TC position and intensity errors in the analysis; however, adding more weights to the ensemble error covariance term in 3DVAR cost function has not made any significant impact. The 3DVAR analysis depicts a stronger TC vortex with a well pronounced warm core structure as compared to that in HYBRID analysis. The forecasts from HYBRID analysis outperform that from 3DVAR in reducing TC track forecast error. The relative improvement in TC landfall position is 43% and 49% for variously configured HYBRID experiments. The forecasts initiated from HYBRID analysis has higher skill in quantitative precipitation forecasts during TC landfall compared to 3DVAR, which may be attributed to improved track prediction in the HYBRID experiments.
Source: https://link.springer.com/article/10.1007/s12040-020-01497-8
by S. K. Sahoo, S. Himesh & K. C. Gouda
This study is about the simulation and observational analysis of a heavy rainfall event (HRE) and its sensitivity to land-use changes. The impact of urbanization on processes and mechanisms of rainfall including cloud processes is discussed. This study is based on high-resolution (2 km), time-ensemble simulation of one of the HREs that occurred on 27 May 2017 over the city of Bengaluru in the southern part of India. The simulations are carried out using the Weather Research and Forecasting (WRF) model, which is coupled with a single-layer urban canopy model (UCM). The high-resolution (30 s) land-use data derived from the Indian Space Research Organization (ISRO) for the year 2016–2017 is shown to be realistic in representing the current land-use scenario with a threefold increase in urbanization when compared to USGS land-use data of 1991–1992. Simulation and analysis of large-scale circulation patterns revealed that the event was triggered and sustained by the low-pressure system and cyclonic circulation over the Bay of Bengal. Simulated rainfall was found to be remarkably sensitive to land-use changes as shown by control (USGS) and test (ISRO) simulations. The rainfall intensity and spatial distribution are close to observation in test simulations with relatively less error at station scale with a correlation of 0.49 (95% significance) when compared to control simulations, indicating the importance of realistic representation of land use in the model and its impact on heavy rainfall processes. The test simulation which represents the current urbanization scenario has shown a significant increase in rainfall by over 100–200%. The surface energy fluxes and thermodynamic indices as shown by test simulations are favorable to HREs, and also consistent with the current land-use scenario with increased urbanization. This study demonstrated how a realistic representation of land-use data in the model can help to improve model skill. The main limitation of this research work is that it is based on the generic parameterization of urbanization using single-layer UCM. An in-depth study based on multi-layer UCM and city-specific parameterization of urbanization using sub-kilometer-scale land-use data including buildings would further enhance our understanding on this subject.
by Chiranjeevi G. Vivek, T. S. Shrungeshwara and Sridevi Jade
This study evaluates the impact of multi-GNSS (Global Navigation Satellite System) signals on the estimation of precise position with millimetre accuracy. Compared to standalone satellite systems like the Global Positioning System (GPS), multi-GNSS improves start-up time, performance, satellite visibility, accuracy, spatial geometry and reliability. However, on the flip side it increases the noise, signal interference, hardware complexity of the receiver, intersystem interference and computation complexity which may degrade its performance. Though GNSS is similar at fundamental levels, differences exist in signal structures, reference frames and timing standards. Compatibility and interoperability between the different constellations of the highest order is required to achieve the best results. At present, GPS and Glonass navigation systems are fully functional with global coverage and comparable precision. Glonass satellite constellation, signal structure is slightly different when compared to GPS, whereas major differences exist in the reference frame and epoch time. Combined GPS–Glonass solution significantly improves the accuracy in navigation applications with increased satellite signal observations and spatial distribution of visible satellites. For precise geodetic studies using static post-processing, combined solution may degrade the accuracy, if these differences are not handled carefully. Currently for geodetic studies, only GPS observations are majorly used worldwide. For the first time, daily precise position is estimated for continuous GNSS stations located in India using static postprocessing with standalone GPS, Glonass as well as combined GPS–Glonass to study the impact of multiGNSS signals for geodetic studies.
Source: https://www.currentscience.ac.in/Volumes/119/09/1503.pdf
by Sridevi Jade, Ramees R. Mir, Chiranjeevi G. Vivek, T. S. Shrungeshwara, I. A. Parvez, Rakesh Chandra, D. Suri Babu, S. Vishal Gupta, Ankit, Siva Sai Kumar Rajana & V. K. Gaur
We present GPS velocities in Kashmir valley and adjoining regions from continuous Global Positioning System (cGPS) network during 2008 to 2019. Results indicate total arc normal shortening rates of ~ 14 mm/year across this transect of Himalaya that is comparable to the rates of ~ 10 to 20 mm/year reported else-where in the 2500 km Himalaya Arc. For the first time in Himalayas, arc-parallel extension rate of ~ 7 mm/year was recorded in the Kashmir valley, pointing to oblique deformation. Inverse modeling of the contemporary deformation rates in Kashmir valley indicate oblique slip of ~ 16 mm/year along the decollement with locking depth of ~ 15 km and width of ~ 145 km. This result is consistent with the recorded micro-seismicity and low velocity layer at a depth of 12 to 16 km beneath the Kashmir valley obtained from collocated broadband seismic network. Geodetic strain rates are consistent with the dislocation model and micro-seismic activity, with high strain accumulation (~ 7e−08 maximum compression) to the north of Kashmir valley and south of Zanskar ranges. Assuming the stored energy was fully released during 1555 earthquake, high geodetic strain rate since then and observed micro-seismicity point to probable future large earthquakes of Mw ~ 7.7 in Kashmir seismic gap.
- Site Effects Investigation in Srinagar City of Kashmir Basin Using Microtremor and Its Inversion
- Future changes in rice yield over Kerala using climate change scenario from high resolution global climate model projection
- A note on stress rotations due to the 2004 Mw 9.2 Sumatra-Andaman megathrust earthquake
- Identification of vegetation responses to soil moisture, rainfall, and LULC over different meteorological subdivisions in India using remote sensing data