Browsing by Author "Amritansh Rai"

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Coulomb Stress Change of the 2012 Indian Ocean Doublet Earthquake
(Springer International Publishing, 2024) Pankhudi Thakur; Rohtash Kumar; Ranjit Das; Amritansh Rai; Raghav Singh; Ankit Singh; S.P. Maurya
The 2012 Sumatra (Mw 8.6) earthquake, which falls into the largest and rarest group of the great intraplate earthquakes, continues to awe many brilliant minds. An enormous aftershock (Mw 8.2) was felt two hours after the Indian Ocean earthquake along the triple intersection of the Indian, Australian, and Sunda plates in the northwest. Over the past 20 years, there have been numerous earthquakes in the Sumatran subduction zone, including the 2004 earthquake (Mw 9.2) of Sumatra-Andaman, the 2005 earthquake (Mw 8.6) of Nias-Simeulue, the 2007 earthquake (Mw 8.4) of Bengkulu, the 2010 earthquake (Mw 7.8) of Mentawai tsunami, and a large number of other minor to moderate-sized events. It often takes a few seconds to a few minutes for the stress brought on by an earthquake to dissipate. This massive discharge disrupts the lithosphere and asthenosphere, which causes more earthquakes to occur nearby. A comprehensive comprehension of stress variations along a fault and its neighboring faults is essential for effectiv ly predicting and mitigating seismic risks. Drawing inspiration from the earthquake finite fault model pioneered by Guangfu Shao, Xiangyu Li, and Chen Ji from UCSB, we have formulated Coulomb stress models tailored to the Sumatran subduction zone and the Sumatran fault. It was discovered that the primary shock’s related coulomb stress change exceeded the stress-triggering threshold. The aftershock struck a place where there was a lot of stress from the mainshock. Therefore, the Coulomb failure stress change brought on by the mainshock is likely what caused the Sumatra aftershock to occur. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.
Data-Driven Spatiotemporal Assessment of Seismicity in the Philippine Region
(Springer International Publishing, 2024) Amritansh Rai; Rohtash Kumar; S.P. Maurya; Ankit Singh; Pankhudi Thakur; Raghav Singh; Ranjit Das
The present study provides a retrospective analysis of the geographical and chronological fluctuations of three basic statistical characteristics of seismicity using a big dataset of events that occurred between 1940 and 2022 in the Philippine region. For determining the spatial-time changes in a-value (seismic activity), b-value (recurrence graph slope), and z-value, the contemporary expanded software package ZMAP with numerous sophisticated seismological functions for earthquake catalog analysis is employed (parameter of the relative seismic quiescence). For the various statistical interpretations, catalog data from the United States Geological Survey (USGS) occurred in spatial windows 0° N – 20° N and 118°E – 130oN are used. The overall conclusion is that unusually low b-values and high z-values, which define zones of comparatively seismic quiescence, may be a signal of the approaching release of more severe stress in areas near zones of relatively high a-values. Thus, the suggested joint interpretation of the spatial-time fluctuations of these three statistical characteristics of seismicity may be seen as a form of the predictor of the more powerful recent seismic occurrences in the region. Furthermore, the occurrence probability of a seven magnitude event is near about one with a return period of 2 years. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.
Determination and Identification of Focal Mechanism Solutions for the 2016 Kumamoto Earthquake from Waveform Inversion Using ISOLA Software
(Springer International Publishing, 2024) Amritansh Rai; Rohtash Kumar; Shatrughan Singh; Raghav Singh; Satya Prakash; Pnkhudi Thakur
On April 14, 2016, at 21:26 (JST), a shallow earthquake of magnitude MJMA 6.5 occurred at Kumamoto prefecture in Kyushu region, Japan. It was one of the foreshocks before the main shock of magnitude MJMA 7.3 28 hours later, on April 16 hits the area. They began at the Hinagu fault zone, which intersects the main shock Futagawa fault zone, creating a complex tectonic context for this earthquake sequence. Here we find out the focal mechanism solution for the MJMA 6.5 earthquake. A software package ISOLA-GUI, a user-friendly MATLAB-based interface, developed by J. Zahradnik and E. Sokos, is used to find moment tensor solutions. It uses data from the three-component seismogram from a single station. The earthquake data is taken from strong motion records of the KiK-net networks. Full-wave seismogram data are used for inversion for single or multiple-point source earthquake models. This software is useful to find the moment tensor solutions where data at all azimuths are not available. The software uses a graphical interface that helps the user easily interact with the software and makes it easier to work. The software allows the result to be mapped using GMT. The focal mechanism solution from multi-station data has been shown along with a cross-plot of source depth and correlation. The power and SNR spectrum are also shown to assess the quality of the data. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.
Earthquake Source Dynamics and High-Frequency Decal Characteristics of Japanese Arc Region
(Springer International Publishing, 2024) Ankit Singh; Rohtash Kumar; Amritansh Rai
The shape of the seismic frequency spectrum and its relationship to the magnitude of earthquakes have been a significant focus. This pursuit aims to extract valuable information about the nature of earthquake source mechanisms. Additionally, it serves as a valuable reference for generating accurate simulations of strong ground motion, which is crucial for engineering applications. A data set of 10 sites, each site having 20 data of surface and well of magnitude equal to 3.8 or greater than 3.8 Japan (Kik), has been used in this study. A MATLAB script was employed to calculate key spectral parameters. These parameters include the corner frequency (fc), which designates the point beyond which the spectrum’s decline follows a specific rate of 2. Furthermore, the high-cut frequency (fmax) was determined, signifying the frequency above which the spectrum’s decay occurs, along with the rate of this decay (p) for frequencies beyond fmax. Previous research conducted by Kumar et al. demonstrates that the relationship involving fmax is not influenced by factors such as focal depth, distances from the epicenter, and the conditions of recording sites. Both fmax and fc exhibited a comparable correlation with seismic moments or magnitudes, indicating that fmax is likewise influenced by the characteristics of the earthquake source process. Across various recording locations, the observed values of fmax consistently exhibit a rise in conjunction with seismic moment or magnitudes. This trend suggests that the primary influencing factor is the seismic source itself, rather than the conditions at the recording sites. Within this particular study, it has been observed that fmax is found independent of site conditions, seismic moment is directly proportional to power (−3) of cornering frequency. Also variation of fmax with epicenter and the Average value of kappa is estimated. The exploration of this field was initiated by Aki (J Geophys Res 72:1217–1231, 1967), who delved into the relationship between the seismic wave’s amplitude spectrum and the dimensions pertaining to the origin of the earthquake. He achieved this by analyzing a pair of fault displacement models for an earthquake, extending his research until 1970. Aki conceived of the origin of an earthquake as an immediate horizontal strain surge acting on a dislocation surface. Within this framework, he introduced triple autonomous factors (source dimensions, fractional stress drop, and moment) that influence the configuration of the pattern of displacement spectrum for seismic body waves in distant regions. He established a connection between the cutoff frequency of the rupture radius and the assumption the efficiency of stress equates to the typical static stress reduction (Aki, J Geophys Res 72:1217–1231, 1967). © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.
Estimation of 3D Moho topography and vertical tectonic stress in the eastern Himalayan syntaxis using gravity data
(Springer Science and Business Media Deutschland GmbH, 2025) Amritansh Rai; Vikash Chand Patel; Anand Kumar Singh; Gyan Prakash Singh
Eastern Himalayan Syntaxis (EHS) holds the unique significance and one of the least studied regions in the eastern Himalaya. In this study, Moho topographic undulation map of the study region and the vertical tectonic stress caused by isostatic adjustment are obtained by using the Bouguer gravity anomaly (BGA), topographic and isostatic anomaly data from the WGM2012 model. The source depth and cutoff wavenumber estimated from spectral analysis are found to be ≈ 46 km and 0.012 km−1, respectively. The BGA is then filtered using a low-pass filter with 83 km wavelength to obtain the regional anomaly corresponding to Moho topography. The resulting regional anomaly map is inverted using the Parker–Oldenberg method to obtain a gravity Moho. The gravity Moho is found to be varied from 36 to 56 km. The isostatic Moho depth is computed using the Airy model. The resulting gravity Moho is in good agreement with previous seismological studies in the region. Using the resulting gravity and isostatic Moho, an isostatic compensation map is derived, which shows all three states of isostatic compensation in the region. The state of isostatic compensation obtained in our study corroborates well with the isostatic anomaly map. In addition, we estimated the vertical tectonic stress caused by lithospheric load in the study region. In the Southern Tibet detachment, Namcha Barwa Antiform (NBA), and Lohit plutonic complex (LPC), the vertical stress is negative and reaches the maximum value of 80 MPa. The central zone of the study region (EHS) features tensional and compressional stresses that vary from − 20 to 20 MPa. In the southern EHS, the Assam valley shows a significant increase in vertical compressional stress. In the Assam valley, the compressional vertical stress varies up to 60 MPa. Due to under-compensation, the mountains in the NBA and LPC subside downward, causing tensional negative stress, while the Assam valley has the highest compressional stress due to topographic uplift, which accounts for the surface mass lost during fluvial erosion. © The Author(s) under exclusive licence to Institute of Geophysics, Polish Academy of Sciences 2025.
Estimation of Source and Spectral Decay Parameters for Local Earthquakes in Siang Region of Arunachal Himalaya and Its Implication to the Tectonics and Crustal Heterogeneity
(Birkhauser, 2024) Amritansh Rai; Himanshu Mittal; G.P. Singh
In our study, we estimated earthquake source parameters and spectral decay characteristics of 378 seismograms corresponding to 80 small earthquake events with magnitudes ranging from 1.5 to 3.5. These earthquakes occurred between July 2011 and May 2012 in the Siang region of the Arunachal Himalaya which is not well-studied. To estimate source parameters, the classical Brune model is employed and through the analysis, a scaling relationship is established between the estimated corner frequency (fc) and seismic moment (M0), which can be expressed as M0=1×1022fc-3.18. This relationship is in close agreement with previous studies conducted in the Arunachal and Himachal Himalaya regions. It provides support for deviations from self-similarity in the study area, offering valuable insights into the tectonics and structural heterogeneity beneath the Arunachal Himalaya. Our analysis revealed variations in source radius, ranging from 154.4 m to 312.6 m, and seismic moment, spanning from 2.37 × 1011 N-m to 9.32 × 1013 N-m. Interestingly, we observed an increasing trend in stress drop, ranging from 0.013 MPa to 3.26 MPa, within the same range of seismic moment. This significant variation in stress drop primarily occurs in the upper 10–15 km of the Earth’s crust, indicating shear brittle failure in this upper crustal region. Furthermore, we conducted an in-depth examination of spectral parameters, including fc high-cut frequency (fmax), and high-frequency spectral decay parameter kappa (κ). Our study highlighted the dependence of κ and fmax estimates on both source characteristics and propagation path, with the source having the most substantial influence. This observation was substantiated through statistical analyses. Additionally, we explored the effect of recording site characteristics on κ and observed a significant contribution of shallow geology at the recording site. This was evident through a negative correlation between the site component of κ (κ0) and VS30, indicating that the local geology of the recording site plays a significant role in spectral parameter estimation. Based on our comprehensive data analysis and statistical observations, we conclude that the variations in source and decay parameters for earthquakes of different magnitudes are attributed to the diverse structural heterogeneities and complex seismotectonic processes underlying the Arunachal Himalaya region. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2024.
Exploring GRACE and GPS and Absolute Gravity Data on the Relationship Between Hydrological Changes and Vertical Crustal Deformation in South India
(Springer International Publishing, 2024) Ankit Singh; Rohtash Kumar; Amritansh Rai; Raghav Singh; S.P. Singh
Rainfall during the monsoon across the Indian subcontinent leads to significant hydrological changes that alter the ground over a range of timescales. In the present study, both GPS and Grace data have been analysed to assess the impact of groundwater variability on ground deformation study region. The amplitudes seasonal vertical deformation phases estimated from Global Positioning System (GPS) and Gravity Recovery and Climate Experiment (GRACE) are reliable, demonstrating that hydrological factors are the main contributors of periodic deformation in the region. We compare the deformation computed from GRACE mass signal with that of altitude variations from non-stop GPS data from three locations, viz. Bangalore, Hyderabad and Lucknow. For the specified period of time, the patterns of the GRACE and GPS plots match well for Hyderabad and Bangalore but not so well for Lucknow. This shows that hydrological loading is mostly to blame for the crustal deformation seen by GPS in Hyderabad and Lucknow. The crustal d formation as determined by the GPS in Lucknow is consistent with that derived from GRACE data over Lucknow to some extent. This shows that GRACE may be used to adjust the deformation detected by GPS for the hydrological effect. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.
Exploring the Concept of Self-Similarity and High-Frequency Decay Kappa-Model and fmax-Model Using Strong-Motion Surface and Borehole Data of Japan: A Statistical Approach
(Springer International Publishing, 2024) Rohtash Kumar; Raghav Singh; Amritansh Rai; Sandeep; S.P. Singh; S.P. Maurya; Prashant Kumar Singh
We statistically analyzed the fmax-model, κ-model and stress drop (Δσ) using surface and borehole data of the KIK-NET Japan seismological network. The statistical tests show no contribution of source in the fmax-model and κ-model. The ‘fmax’ values obtained in the present study are 4.2–11.0 Hz and 5–11.0 Hz for surface and borehole data, respectively. The impact of local heterogeneities and wave propagation path is clearly visible on both surface and borehole fmax-models. The same is confirmed by the p-value ‘t-test’. The multivariate linear regression (MVLR) has been applied for the analysis of dependent variables ‘κ(s)’ and ‘κ(w)’ w.r.t. independent variables epicentral distance and magnitude. The p-value calculated by t-test indicates the strong dependence of κ(s) and κ(w) on near-surface geology and the physical state of the wave travelling media but almost no contribution of magnitude. The contribution of near-surface geology in kappa values is also confirmed by the ‘κ0’ (kappa at epicentral distance = 0). The relationships between the fmax-model and the κ-model have been developed for the study region. The stress drop (Δσ(s)) assessed from surface data is 44.16-65.86 bars with an average value of 53.19 bars and borehole derived stress drop (Δσ(w)) is 46.38-68.13 bars with an average value of 54.16 bars. This study discards the effect of depth; type of earthquake, i.e. normal, reverse and strike-slip; and signal to noise ratio (SNR) on stress drop as there is no huge variation in both Δσ(s) and Δσ(w) with the seismic moment and source radius. Therefore, the study supports the concept of self-similarity. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.
Lapse-Time Dependence of Coda Quality Factor Within the Lithosphere of Northern Ecuador
(Springer International Publishing, 2024) Amritansh Rai; Rohtash Kumar; Ankit Singh; Raghav Singh; Indrajit Das; S.P. Maurya
In the current study, a frequency-dependent attenuation relationship based on coda waves is developed for the Ecuador region. The single backscattering model developed by Aki and Chouet (J Geophys Res 80:3322–3342, 1975) is used to investigate the dependence of Coda-Q on lapse time frames. The waveforms of 49 local earthquakes recorded by a one-station local seismological network are used for the analysis. The frequency-dependent Coda-Q relations estimated for the region are: Qc = (65.75) f0.6302 (10 sec lapse time), Qc = (92.48) f0.6868 (20 sec lapse time), Qc = (18.17) f1.3337 (30 sec lapse time), Qc = (30.95) f1.2303 (40 sec lapse time), Qc = (88.22) f0.9117, and Qc = (125.19) f0.9342. Given that greater areas would be sampled by longer lapse time windows, the rise in Qc values with lapse time demonstrates the depth dependency of Qc. The increase in value of Q0 (QC at 1 Hz) with time depicts that the heterogeneities decrease with depth. The observed quality factor is highly variable with the lapse time and frequency. The more significant value of n shows that the area is seismically active. The observed Qc relation is found equivalent to other similar seismically active regions. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.
Moho Mapping of Northern Chile Region Using Receiver Function Analysis and HK Stacking
(Springer International Publishing, 2024) Amritansh Rai; Rohtash Kumar; Dipankan Srivastava; Raghav Singh; Ankit Singh; S.P. Maurya
In this study, Rfpy software is utilized to compute the receiver functions to map Moho in the Northern Chile region. To obtain the teleseismic waveforms within an epicentral distance of 30° to 90°, the Package makes use of the IRIS station database. The receiver functions over stations AC04 and AC05 indicate a low-velocity layer possible area at a shallower depth. Additionally, the delay periods of the Moho Ps phase at various different back azimuths are used to infer the anisotropy or dipping Moho. With the aid of H-K Stacking the receiver functions for Poisson’s ratio and Moho depth were also inverted. Under the AC07 station, which is situated in Caldera, Atacama, a higher Moho depth of 46 km is discovered. This results in a Poisson’s ratio of 0.24. Below the CO10 station, which is in Coquimbo, an extraordinary poisson ratio is found. Accordingly, a Moho depth of 25 km is discovered. Inverting the acquired P-wave receiver functions may effectively determine the S-wave velocity structure below each station. This would aid in enhancing the region’s crustal imaging. Additionally, harmonic decompositions of the receiver functions might be performed to examine the behavior of anisotropy. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.
Understanding the physical state and tectonics of Eastern Himalaya using coda wave attenuation
(Springer, 2023) Rohtash Kumar; Amritansh Rai; Raghav Singh; S.C. Gupta; Arjun Kumar; S.P. Singh; Prashant Kumar Singh; S.P. Maurya; Vinay Kumar; G.P. Singh
Several strong to great earthquakes occurred in northeast India, indicating that the region is seismically very active. For a better understanding of the complex nature of tectonics in the Eastern Himalaya, a frequency-dependent attenuation relation based on coda waves is developed. The backscattering model of Aki and Chouet (J. Geophys. Res. 80: 3322–3342, 1975) is used to study the dependency of coda-Q on lapse time windows and frequency. Analysis of waveforms from 104 local earthquakes recorded by a five-station local seismological network provides frequency-dependent coda-Q relations: Qc = (61±8)f (1.23±0.03) (30s lapse time), Qc = (83±9)f (1.17±0.03) (40s lapse time) and Qc = (104±8)f (1.15±0.04) (50s lapse time). These estimated relationships clearly demonstrate Qc's depth dependency, as longer lapse time windows would carry deeper depth information. Also, the increase in the value of Q 0 (Qc at 1 Hz) with lapse time depicts heterogeneity decrease with depth. The observed quality factor is highly variable with the frequency and lapse time. The higher the value of ‘n,' the more seismically active the region. The observed Qc relation is found equivalent to other similar seismically active regions. © 2023, Indian Academy of Sciences.