The present study explores the P waves and S-wave attenuation characteristics to reveal the crustal physical state of entire Colombia region. A quality data set of 190 records of local events occurred during 2017-2021 has been analyzed. The epicentral distance of the events upto 200 km with magnitude greater than 4.5. The data is provided by IRIS_DMC from Global Seismographic Network (GSN). The extended coda normalization method of Yoshimoto et al. (1993) is employed for estimation of P-wave quality factor (Qα) and S-wave quality factor (Qβ). For 5 second windows, the S, P, and coda-wave spectra are examined at nine center frequencies viz. 1, 1.5, 3, 6, 9, 12, 15, 18 and 24 Hz. With increase in frequency, both Qα and Qβ values rise. The Qα values increases from 50.88 at 1.0 HZ to 806.36 at 24 Hz and Qβ varies from 44.89 at 1.0 Hz to 1595.55 at 24 Hz. Therefore, both Qα and Qβ are reliant on frequency with frequency dependent relationships Qα = 40.152f0.8425and Qβ = 35.301f1.2479. The average Qα and Qβ results reported in this study are in good agreement with results from previous studies, with low Q0 values less than 200, which are indicative of seismically and tectonically active area. We found that Colombia region Qα and Qβ values are comparable to those of other seismically active regions throughout the world. The observed ratio of Qβ / Qα is greater than unity over the whole examined frequency range shows that the earth medium of the study region has a significant degree of heterogeneities. The obtained relations in the study will be quite useful in simulation of earthquake ground motion as well as seismic hazard assessment which will be quite helpful in minimizing the loss of life and damage to property in the area.

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: Q c = (61±8) f (1.23±0.03) (30s lapse time), Q c = (83±9) f (1.17±0.03) (40s lapse time) and Q c = (104±8) f (1.15±0.04) (50s lapse time). These estimated relationships clearly demonstrate Q c 's depth dependency, as longer lapse time windows would carry deeper depth information. Also, the increase in the value of Q 0 ( Q c 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 Q c relation is found equivalent to other similar seismically active regions.

The information about the ongoing tectonic faulting process causing earthquakes in an area having single or sparse seismological waveform data available remains a mystery for seismologists. The usual P-wave polarity inversion is unable to find the solution to the earthquake mechanism if the event is recorded with a lower azimuthal coverage network. Recently some seismologists seek towards the moment tensor solution and tried to find the focal mechanisms of earthquakes. The present work is a step in the same direction. Twelve regional earthquakes recorded by a distant seismological network in the Siang region of Arunachal Himalaya have been analyzed using ISOLA codes developed by Sokos and Zahradnik (2008). The solutions obtained by CMT Harvard by inversion of a large number of available waveform data have been considered standards. In the present study, moment tensor solutions have been estimated using the hypocentre locations given by the CMT catalog. The obtained solutions are comparable with the CMT solutions reported. High variance reduction has been obtained for the analyzed earthquakes that agree with the observations by Delouis and Legrand (1999), Kim and Kraeva (1999), Kim et al. (2000), Dragger (2003), and Maercklin et al. (2011) that moment tensor solutions can be obtained by using single station waveform data. The present study infers that the moment tensor inversion would be useful for obtaining information about the ongoing faulting process for which limited waveform data is available. For most of the Himalayan earthquakes which occur northern side of the Main Central Thrust (MCT), the seismological networks in those areas are either very sparse or not instrumented at all. The knowledge of undergone tectonics of this region was established with various faults visible on the surface by geologists and lacks the knowledge of the present situation of ongoing tectonics of the region. Hence, the moment tensor solutions obtained using available data will help in understanding the ongoing tectonic processes of the regions lacking well coverage of seismological networks.

A devastating earthquake (Mw 7.4) struck near Izmit city, northwestern Turkey, on 17 August 1999. The relatively large size of this earthquake and site amplification conditions caused severe damage in the Marmara region as well as the city of Istanbul. The disastrous outcome of this large earthquake requires careful analysis of the seismic hazard including local site effects in this region. Therefore, the present work addresses the issue of local site effects and modelling of strong ground motion for this earthquake. We have estimated the soil effects using the horizontal-to-vertical (H/V) ratio. Furthermore, high-frequency records are simulated using a modified semi-empirical technique (MSET) by including estimated site effects. This modification will provide more reliable and precise simulated strong motion records. In the present study, strong ground motions are simulated at nine seismic stations in the epicentral range of 40–99 km. These stations were selected based on their recorded data quality. To validate the technique, we have compared the synthetic records with the observed records in terms of root mean square error (RMSE). This comparison includes time records, pseudo-acceleration spectra, mean period and predominant period. This comparison shows MSET has successfully simulated the 1999 Izmit earthquake.

The seismic body wave attenuation (Q(alpha)(-1) and Q(beta)(-1)) characteristics of crust of the Kyushu region, Japan, has been investigated using the data of KIK-Net network of Japan. The frequency dependence relationships of Q(alpha)(-1) and Q(beta)(-1) have been computed using the extended coda wave normalization approach in the frequency range of 1.0 Hz to 24 Hz. Assessed average values Q(alpha)(-1) range from 0.03395 at 1.0 Hz to 0.00218 at 24 Hz and Q(beta)(-1) range from 0.02189 at 1.0 Hz to 0.00095 at 24 Hz. The Q(alpha)(-1) and Q(beta)(-1) values found in this study are similar to those seen in other seismically active parts of the world such as the Himalayas and other parts of Japan. The frequency-dependent relations for 'P' and 'S' waves are Q(alpha)(-1) = (0.0463 +/- 0.003) f(-(0.91 +/- 0.0.01)) and Q(beta)(-1) = (0.0225 +/- 0.002)f(-(0.936 +/- 0.2)) respectively, obtained for the study region. We also found that over the full frequency range, all estimated Q(alpha)(-1)/Q(beta)(-1) ratios are greater than unity, implying that the intrinsic and scattering processes in the crust are likely to be responsible for attenuation. The intrinsic and scattering is due to the tectonic complexity, volcanic activities and heterogeneities existing in the crust of the study region.

The perturbation produced in the atmosphere/ionosphere associated with earthquake precursors during seismic activity of two major earthquakes which occurred on (1) 24 June 2019 in Indonesia (M = 7.3) and (2) on 19 August 2018 at Ndoi, Fiji (M = 8.2), are studied. Based on statistical analysis of total electron content (TEC) data, the presence of ionospheric perturbations 5 days before and after the main shock are found, which depends on the distance as well as direction of observation point from the epicentre. In general, ionospheric perturbations after the EQ at all the stations are found larger than that before the EQ. Probable mechanisms behind these perturbations associated with EQ are also being discussed. The ionospheric perturbations are observed at stations which are at larger distances from the epicentre, but not observed over other stations in different directions which are comparatively closer to the epicentre. These results suggest that seismic induced ionospheric anomaly is not isotropic in nature. Ozone data from three satellites: AIRS, OMI, and TOMS-like and MERRA-2 model are also analyzed 5 days before the EQ day and compared to the monthly average level. A strong link between anomalous variation in ionospheric TEC and atmospheric ozone data prior to both the EQs is noticed.

Seismic inversion is a geophysical technique used to estimate subsurface rock properties from seismic reflection data. Seismic data has band-limited nature and contains generally 10–80 Hz frequency hence seismic inversion combines well log information along with seismic data to extract high-resolution subsurface acoustic impedance which contains low as well as high frequencies. This rock property is used to extract qualitative as well as quantitative information of subsurface that can be analyzed to enhance geological as well as geophysical interpretation. The interpretations of extracted properties are more meaningful and provide more detailed information of the subsurface as compared to the traditional seismic data interpretation. The present study focused on the analysis of well log data as well as seismic data of the KG basin to find the prospective zone. Petrophysical parameters such as effective porosity, water saturation, hydrocarbon saturation, and several other parameters were calculated using the available well log data. Low Gamma-ray value, high resistivity, and cross-over between neutron and density logs indicated the presence of gas-bearing zones in the KG basin. Three main hydrocarbon-bearing zones are identified with an average Gamma-ray value of 50 API units at the depth range of (1918–1960 m), 58 API units (2116–2136 m), and 66 API units (2221–2245 m). The average resistivity is found to be 17 Ohm-m, 10 Ohm-m, and 12 Ohm-m and average porosity is 15%, 15%, and 14% of zone 1, zone 2, and zone 3 respectively. The analysis of petrophysical parameters and different cross-plots showed that the reservoir rock is of sandstone with shale as a seal rock. On the other hand, two types of seismic inversion namely Maximum Likelihood and Model-based seismic inversion are used to estimate subsurface acoustic impedance. The inverted section is interpreted as two anomalous zones with very low impedance ranging from 1800 m/s*g/cc to 6000 m/s*g/cc which is quite low and indicates the presence of loose formation.

Genetic algorithm (GA) and Simulated Annealing (SA) are used to minimize fitness (error) function between the real seismic data and modelled synthetic trace and to estimate subsurface rock property. This study uses modified fitness function to constraints the solution and reduce the convergence time. This additional term also reduces the non-uniqueness of the solution. In this study, we have demonstrated a synthetic example and one real data example and estimated subsurface acoustic impedance. The seismic data is interface property and acoustic impedance is layer property, hence it is more meaningful and helpful in interpreting subsurface properties in detail. The inverted results show very high resolution images of the subsurface and add additional support to interpret seismic data. The analysis shows that the convergence of the algorithm becomes very fast when one adds the additional term to constraint the solution. Both algorithms (GA and SA) work satisfactorily first for synthetic data case and then for real data case. A low acoustic impedance zone is interpreted from the inverted section which collaborated well with high seismic amplitude anomaly. This anomalous zone which corresponds to 1055 to 1065 ms time interval, is characterized as sand channel.

ESOPA-GUI, a MATLAB-based graphical user interface software, is presented in this study. The ESOPA-GUI estimates the seismic spectrum source parameters using Brune’s model (1970). The software uses two high-frequency decay models to represent the high-frequency decay of an event’s acceleration and displacement spectra: fmax-model and κ-model. The BODY-Q subprogram of ESOPA-GUI estimates and corrects the recorded time history corresponding to the loss of seismic energy by the wave propagation media. The software ESOPA-GUI has been applied to the data set of some earthquake of magnitude (MJ) 4.2 to 6.2, to estimate the spectral source parameters seismic moment (M0), moment magnitude (Mw), corner frequency (fc), stress drop (Δσ), source radius (r), fmax-model, and κ-model. The BODY-Q estimated the relationships Qβ = 26.68f1.01, Qβ = 31.56f0.96, and Qβ = 18.99f1.08 for different regions for Japan corresponding the data used, for the path correction. The solutions obtained using ESOPA are in good correlation with the solutions provided by popular agencies such as USGS and NIED which shows the reliability and stability of the software.

Many rivers of the Indo-Gangetic Plain are prone to abrupt switching of channel courses causing devastating floods over some of the world’s poorest and most densely populated regions. Recent work has identified the gravel-sand transition as an avulsion node for the channels; notably the avulsion of the Kosi River in 2008 occurred in close proximity to its gravel-sand transition. The gravel-sand transition is a geomorphic feature observed within all major mountain-fed, and smaller foothill-fed Himalayan rivers ranging from 10 to 20 km downstream from the mountain front. It is characterised by an abrupt downstream reduction in grain size from gravel to sand and is often associated with a break in channel gradient, which suggests it is a relatively stable feature over the last few thousands of years. However, new subsurface data from the Kosi mega-fan in eastern Nepal reveals 10-20 Ka gravels located ~50 km downstream from the current gravel-sand transition. The implication is that this key geomorphic boundary can periodically prograde considerably further into the Ganga Plains. A greater long-term (>106 yrs) understanding of the controls on the gravel-sand transition is achieved by studying the stratigraphic record of the Miocene Siwalik Group, which is exhumed as a series of thrusted fault blocks at the Himalayan mountain front. The Siwalik succession is divided into three lithofacies units that coarsens upwards from siltstones and sandstones to coarse conglomerates. The units are termed the Lower, Middle and Upper Siwaliks respectively and reflect the current depositional environments found on the Ganga Plains. The gravel-sand transition is recorded as the contact between the Middle and Upper Siwaliks. Significant gravel pulses have been identified directly below the Middle to Upper Siwalik contact and suggests that the gravel-sand transition is indeed mobile and can episodically prograde far into the plains. Sedimentological characteristics of the gravel pulses and sediment entrainment calculations suggest that extreme events (e.g. enhanced monsoon, earthquakes and GLOFS) can force gravel far into the Ganga Plains, impacting the position the gravel-sand transition. These episodes of distant gravel progradation must represent extreme floods from which the sedimentological system must take many years to recover. Such events are beyond the historic timescales of human narrative, and hence have not been recognised as a risk to the populations of the plains.

Late Quaternary fluvial deposits along the Janauri (JA; comprises Siwalik rocks) and Bhaddi (BA; dominantly of Quaternary deposits) anticlines over independent fault segments of the Himalayan Frontal Thrust (HFT), Kangra re-entrant, were studied to deduce the timing and causes of the Beas-Satluj rivers deflections. The deposits, 4-60 m thick, were documented from the northwestern fringe of the JA (Site-1), between JA and BA (Site-2) and entire BA (Site-3), and along the present course of the Satluj River (Site-4) in the piggyback Soan Dun. They comprise quartzite-bearing gravels and multistorey sheet sand bodies with large-scale trough cross-stratification and are deposited by the Beas (Site-1) and Satluj (Sites 2-4) rivers. The deposits at Sites 1-3 are uplifted, tilted or folded, whereas, horizontally bedded at Site-4. Based on quartz Optically Stimulated Luminescence chrono-stratigraphy, the aggradation phase is bracketed between > 46.4 +/- 2.9 and 37.4 +/- 2.3 ka (Site-1), > 69.9 +/- 4.5 and 26.1 +/- 2.6 ka (Site-2) and > 55.2 +/- 1.7 and 50.3 +/- 3.5 ka (Site-3). The terrace deposits at Site-4 were formed around 26, 11 and 6 ka. The sedimentation (9.9 to 2.7 mm yr(-1) between 61.8 and 26 ka) and uplift (3.4 +/- 0.3 mm yr(-1) over a period of 44 ka) rates along HFT show that the latter exceeds the aggradation rate with time. It is envisaged that time variable tectonic movements along independent fault segments of the I-WT forced river deflection and termination of deposition at Sites 1-3, however, the absence of any forced aggradation at the Site-4 concomitant with Site-2 termination suggests it is also governed by climate.

Late Cenozoic fluvial stratigraphic records of the Himalayan foreland basin- the Siwalik Group between Rivers Ganga and Ravi were studied and reviewed to understand the responses of allogenic forcing at variable timeframe. The Siwalik succession represents an upward stratigraphic coarsening sequence which was initiated similar to 13 Ma and terminated and deformed by the Himalayan Frontal Thrust (HFT) at around 0.2 Ma. Fluvial architecture, composition and paleoflow patterns exhibits patial and temporal variations and characteristics of a large river that evolved around 10 Ma with southward propagating mountain, ront with large gravelly alluvial fans evolving after 5 Main the proximity of Main Boundary Thrust (MBT). Influx of boulder- to pebblesized clasts indicatesmajor surface uplift at around 5 Ma all along the Himalaya. This uplift is more widespread and responsible for the generation of much of the modern drainage system. The fluvial architecture reveals variation in temporal and spatial deposition style at million-year scale in response to variable hinterland topography, tectonics and climate. However, direct climatic signatures are not evident, although stable isotopic studies suggest variability at million-year scale, which was overwhelmed by tectonics.

The delta C-13 values of long chain n-alkanes from paleosol samples (n = 74) of four NW Indian Siwalik sections have been used to reconstruct the relative abundance of C-3-C-4 plants, after isotopic characterization of modern plants from the Ganges floodplain considered equivalent to the past Siwalik floodplain. The values from the Naladkhad (11.6-8.9 Ma) and Ranital (11.3-7.4 Ma) sections of the Kangra sub-basin indicate the presence of ca. 20% C-4 plants at ca. 11 Ma. The existence of C-4 plants at ca. 11 Ma indicate an early appearance of C-4 plants, compared with the published data from the Siwalik regions. The Ranital section shows a patchy occurrence of C-4 plants between 11.3 Ma and 7.4 Ma and the Jabbarkhad section shows (5.2-3.0 Ma) a gradual increase in C-4 plant abundance. The C-4 plant abundance fluctuated between 83% and 0% (5.8-1.3 Ma) in the Haripur Khol section of the Subathu sub-basin. Comparison of C-4 plant abundance from the four sections shows that each section was characterised by a distinct evolutionary pattern. The delta D values of the same n-alkanes from the Kangra and Subathu sub-basins indicate two episodes of Indian summer monsoon intensification at ca. 9 Ma and ca. 4 Ma. The correlation between delta D-C29 and delta C-13(C29) values varied in different sections. It was also observed that the C-4 plant abundance variation could be linked to the variable channel/overbank ratio of the studied sections. This observation suggests that Indian summer monsoonal rainfall, type of overbank sediments and moisture content controlled the abundance of C-4 plants in the Siwalik floodplain. (C) 2017 Elsevier Ltd. All rights reserved.

North-East India is located in one of the most seismic prone areas of the world. India has faced several devastating earthquakes in the past. The largest of these have originated in the Himalayan plate boundary region, which has remained a region of great scientific and engineering interest. In spite of this, very little seismological information is available about North- East India, which is the focus for present study. Only few attenuation relationships are available for this region, which are most valuable in a region where too much strong motion recordings are not available. However in recent time, with the inception of 300 strong motion instruments under Indian National Strong Motion Network deployed under Mission Mode project (Government of India), a good quality of strong motion data became available. Taking the advantage of data collected by this network and earlier analogue strong motion arrays, an endeavor has been made to develop an empirical attenuation relationship for peak horizontal ground accelerations for North-East Himalayan region in India. The data set consists of 216 peak ground horizontal accelerations from 24 earthquakes (4.0≤M≤6.8) recorded by strong-motion arrays and National Strong Motion Network project in India. The present analysis uses a two-step stratified regression model. The estimated attenuation relationship for the region is\(\log(A) = -1.097 + 0.3882M - 1.19\log(X+e^{0.2876M})\)Where A is the peak ground acceleration (g), M is the magnitude, and X is the hypocentral distance from the source. The residual sum of squares is 0.1451. The obtained Empirical attenuation relationship will provide better insight for site specific studies as well as for hazard estimation for North-East Himalayan region. Attenuation relationships for expected peak ground acceleration (g) have been presented for magnitudes 5, 6, 7 and 8 for North-East Himalayan region.References Abrahamson, N.A., Litchiser, J.J., 1989. Attenuation of vertical peak accelerations. Bulletin of the Seismological Society of America, 79, 549-580. Aman, A, Singh, U.K., Singh, R.P., 1995. A new empirical relation for strong seismic ground motion for the Himalayan region. Current Science, 69(9), 772-777. Ambraseys, N.N., Douglas, J., 2003. Near-field horizontal and vertical earthquake ground motions. Soil Dynamics and Earthquake Engineering, 23, 1-18. Atkinson, G.M., Boore, D.M., 2003. Empirical ground-motion relations for subduction zone earthquakes and their application to Cascadia and other regions. Bulletin of the Seismological Society of America, 93, 1703-1729. Ben-Menahem, A., Aboudi, E., Schild, R., 1974. The source of the great Assam earthquake-an intraplate wedge motion. 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In the present study, the scattering and intrinsic attenuation are separated using the S-wave attenuation (Q(beta)) and coda-wave attenuation (Q(c)) employing the Wennerberg (1993) method, and the frequency-dependent Q(s) and Q(i) relations have been developed for the region. The Q(i) and Q(s) show the frequency-dependent character in the frequency range 1.5-24 Hz. The average scattering and intrinsic relationships are obtained for the region as Q(s) = (31 +/- 1)f(1.04 +/- 0.02), Q(s) = (48 +/- 1)f(1.05 +/- 0.02), and Q(s) = (61 +/- 1)f(1.05 +/- 0.02) and as Q(i) = (68 +/- 1)f(0.95 +/- 0.06), Q(i) = (134 +/- 1)f(1.01 +/- 0.05), and Q(i) = (167 +/- 1)f(0.96 +/- 0.03) for lapse time windows of 30, 40, and 50 s, respectively. The quality factor for the P wave (Q(alpha)) and the S wave (Q(beta)) are estimated using the extended coda-normalization method of Yoshimoto et al. (1993). The frequency dependence Q(alpha) and Q(beta) relationships are obtained as Q(alpha) = (25 +/- 1)f((1.24 +/- 0.04)) for the P wave and Q(beta) = (58 +/- 1)f((1.16 +/- 0.04)) for the S wave. The quality factor for the coda wave (Q(c)) is estimated using the single backscattering model of Aki and Chouet (1975). The comparison of Q(beta) and Q(c) with Q(i) and Q(s) shows that both Q(i) and Q(s) are lower than the Q(beta), as well as Q(c), at 30 s lapse time. As the lapse time increases, both Q(i) and Q(s) increase in such a manner that Q(c) will increase because it contains the effects of both. This agrees with the theoretical as well as the laboratory measurements. Also Q(c) is higher than Q(beta); this supports the model given by Zeng et al. (1991), which predicts that the combination of Q(i) and Q(s) should be such that Q(c) is more than Q(beta).